Science.gov

Sample records for airframe noise sources

  1. Investigation of Volumetric Sources in Airframe Noise Simulations

    NASA Technical Reports Server (NTRS)

    Casper, Jay H.; Lockard, David P.; Khorrami, Mehdi R.; Streett, Craig L.

    2004-01-01

    Hybrid methods for the prediction of airframe noise involve a simulation of the near field flow that is used as input to an acoustic propagation formula. The acoustic formulations discussed herein are those based on the Ffowcs Williams and Hawkings equation. Some questions have arisen in the published literature in regard to an apparently significant dependence of radiated noise predictions on the location of the integration surface used in the solution of the Ffowcs Williams and Hawkings equation. These differences in radiated noise levels are most pronounced between solid-body surface integrals and off-body, permeable surface integrals. Such differences suggest that either a non-negligible volumetric source is contributing to the total radiation or the input flow simulation is suspect. The focus of the current work is the issue of internal consistency of the flow calculations that are currently used as input to airframe noise predictions. The case study for this research is a computer simulation for a three-element, high-lift wing profile during landing conditions. The noise radiated from this flow is predicted by a two-dimensional, frequency-domain formulation of the Ffowcs Williams and Hawkings equation. Radiated sound from volumetric sources is assessed by comparison of a permeable surface integration with the sum of a solid-body surface integral and a volume integral. The separate noise predictions are found in good agreement.

  2. Airframe noise prediction evaluation

    NASA Technical Reports Server (NTRS)

    Yamamoto, Kingo J.; Donelson, Michael J.; Huang, Shumei C.; Joshi, Mahendra C.

    1995-01-01

    The objective of this study is to evaluate the accuracy and adequacy of current airframe noise prediction methods using available airframe noise measurements from tests of a narrow body transport (DC-9) and a wide body transport (DC-10) in addition to scale model test data. General features of the airframe noise from these aircraft and models are outlined. The results of the assessment of two airframe prediction methods, Fink's and Munson's methods, against flight test data of these aircraft and scale model wind tunnel test data are presented. These methods were extensively evaluated against measured data from several configurations including clean, slat deployed, landing gear-deployed, flap deployed, and landing configurations of both DC-9 and DC-10. They were also assessed against a limited number of configurations of scale models. The evaluation was conducted in terms of overall sound pressure level (OASPL), tone corrected perceived noise level (PNLT), and one-third-octave band sound pressure level (SPL).

  3. Airframe noise: A design and operating problem

    NASA Technical Reports Server (NTRS)

    Hardin, J. C.

    1976-01-01

    A critical assessment of the state of the art in airframe noise is presented. Full-scale data on the intensity, spectra, and directivity of this noise source are evaluated in light of the comprehensive theory developed by Ffowcs Williams and Hawkings. Vibration of panels on the aircraft is identified as a possible additional source of airframe noise. The present understanding and methods for prediction of other component sources - airfoils, struts, and cavities - are discussed. Operating problems associated with airframe noise as well as potential design methods for airframe noise reduction are identified.

  4. The Airframe Noise Reduction Challenge

    NASA Technical Reports Server (NTRS)

    Lockhard, David P.; Lilley, Geoffrey M.

    2004-01-01

    The NASA goal of reducing external aircraft noise by 10 dB in the near-term presents the acoustics community with an enormous challenge. This report identifies technologies with the greatest potential to reduce airframe noise. Acoustic and aerodynamic effects will be discussed, along with the likelihood of industry accepting and implementing the different technologies. We investigate the lower bound, defined as noise generated by an aircraft modified with a virtual retrofit capable of eliminating all noise associated with the high lift system and landing gear. However, the airframe noise of an aircraft in this 'clean' configuration would only be about 8 dB quieter on approach than current civil transports. To achieve the NASA goal of 10 dB noise reduction will require that additional noise sources be addressed. Research shows that energy in the turbulent boundary layer of a wing is scattered as it crosses trailing edge. Noise generated by scattering is the dominant noise mechanism on an aircraft flying in the clean configuration. Eliminating scattering would require changes to much of the aircraft, and practical reduction devices have yet to receive serious attention. Evidence suggests that to meet NASA goals in civil aviation noise reduction, we need to employ emerging technologies and improve landing procedures; modified landing patterns and zoning restrictions could help alleviate aircraft noise in communities close to airports.

  5. Fundamental Investigations of Airframe Noise

    NASA Technical Reports Server (NTRS)

    Macaraeg, M. G.

    2004-01-01

    An extensive numerical and experimental study of airframe noise mechanisms associated with a subsonic high-lift system has been performed at NASA Langley Research Center (LaRC). Investigations involving both steady and unsteady computations and experiments on a small-scale, part-span flap model are presented. Both surface (steady and unsteady pressure measurements, hot films, oil flows, pressure sensitive paint) and off surface (5 hole-probe, particle-imaged velocimetry, laser velocimetry, laser light sheet measurements) were taken in the LaRC Quiet Flow Facility (QFF) and several hard-wall tunnels up to flight Reynolds number. Successful microphone array measurements were also taken providing both acoustic source maps on the model, and quantitative spectra. Critical directivity measurements were obtained in the QFF. NASA Langley unstructured and structured Reynolds- Averaged Navier-Stokes codes modeled the flap geometries excellent comparisons with surface and offsurface experimental data were obtained. Subsequently, these meanflow calculations were utilized in both linear stability and direct numerical simulations of the flap-edge flow field to calculate unsteady surface pressures and farfield acoustic spectra. Accurate calculations were critical in obtaining not only noise source characteristics, but shear layer correction data as well. Techniques utilized in these investigations as well as brief overviews of results will be given.

  6. Airframe Noise Reduction Studies and Clean-Airframe Noise Investigation

    NASA Technical Reports Server (NTRS)

    Fink, M. R.; Bailey, D. A.

    1980-01-01

    Acoustic wind tunnel tests were conducted of a wing model with modified leading edge slat and trailing edge flap. The modifications were intended to reduce the surface pressure response to convected turbulence and thereby reduce the airframe noise without changing the lift at constant incidence. Tests were conducted at 70.7 and 100 m/sec airspeeds, with Reynolds numbers 1.5 x 10 to the 6th power and 2.1 x 10 to the 6th power. Considerable reduction of noise radiation from the side edges of a 40 deflection single slotted flap was achieved by modification to the side edge regions or the leading edge region of the flap panel. Total far field noise was reduced 2 to 3 dB over several octaves of frequency. When these panels were installed as the aft panel of a 40 deg deflection double slotted flap, 2 dB noise reduction was achieved.

  7. Airframe Noise Studies: Review and Future Direction

    NASA Technical Reports Server (NTRS)

    Rackl, Robert G.; Miller, Gregory; Guo, Yueping; Yamamoto, Kingo

    2005-01-01

    This report contains the following information: 1) a review of airframe noise research performed under NASA's Advanced Subsonic Transport (AST) program up to the year 2000, 2) a comparison of the year 1992 airframe noise predictions with those using a year 2000 baseline, 3) an assessment of various airframe noise reduction concepts as applied to the year 2000 baseline predictions, and 4) prioritized recommendations for future airframe noise reduction work. NASA's Aircraft Noise Prediction Program was the software used for all noise predictions and assessments. For future work, the recommendations for the immediate future focus on the development of design tools sensitive to airframe noise treatment effects and on improving the basic understanding of noise generation by the landing gear as well as on its reduction.

  8. Airframe-Jet Engine Integration Noise

    NASA Technical Reports Server (NTRS)

    Tam, Christopher; Antcliff, Richard R. (Technical Monitor)

    2003-01-01

    It has been found experimentally that the noise radiated by a jet mounted under the wing of an aircraft exceeds that of the same jet in a stand-alone environment. The increase in noise is referred to as jet engine airframe integration noise. The objectives of the present investigation are, (1) To obtain a better understanding of the physical mechanisms responsible for jet engine airframe integration noise or installation noise. (2) To develop a prediction model for jet engine airframe integration noise. It is known that jet mixing noise consists of two principal components. They are the noise from the large turbulence structures of the jet flow and the noise from the fine scale turbulence. In this investigation, only the effect of jet engine airframe interaction on the fine scale turbulence noise of a jet is studied. The fine scale turbulence noise is the dominant noise component in the sideline direction. Thus we limit out consideration primarily to the sideline.

  9. Landing approach airframe noise measurements and analysis

    NASA Technical Reports Server (NTRS)

    Lasagna, P. L.; Mackall, K. G.; Burcham, F. W., Jr.; Putnam, T. W.

    1980-01-01

    Flyover measurements of the airframe noise produced by the AeroCommander, JetStar, CV-990, and B-747 airplanes are presented for various landing approach configurations. Empirical and semiempirical techniques are presented to correlate the measured airframe noise with airplane design and aerodynamic parameters. Airframe noise for the jet-powered airplanes in the clean configuration (flaps and gear retracted) was found to be adequately represented by a function of airplane weight and the fifth power of airspeed. Results show the airframe noise for all four aircraft in the landing configuration (flaps extended and gear down) also varied with the fifth power of airspeed, but this noise level could not be represented by the addition of a constant to the equation for clean-configuration airframe noise.

  10. Airframe Noise Prediction Using the Sngr Method

    NASA Astrophysics Data System (ADS)

    Chen, Rongqian; Wu, Yizhao; Xia, Jian

    In this paper, the Stochastic Noise Generation and Radiation method (SNGR) is used to predict airframe noise. The SNGR method combines a stochastic model with Computational Fluid Dynamics (CFD), and it can give acceptable noise results while the computation cost is relatively low. In the method, the time-averaged mean flow field is firstly obtained by solving Reynolds Averaged Navier-Stokes equations (RANS), and a stochastic velocity is generated based on the obtained information. Then the turbulent field is used to generate the source for the Acoustic Perturbation Equations (APEs) that simulate the noise propagation. For numerical methods, timeaveraged RANS equations are solved by finite volume method, and the turbulent model is K - ɛ model; APEs are solved by finite difference method, and the numerical scheme is the Dispersion-Relation-Preserving (DRP) scheme, with explicit optimized 5-stage Rung-Kutta scheme time step. In order to test the APE solver, propagation of a Gaussian pulse in a uniform mean flow is firstly simulated and compared with the analytical solution. Then, using the method, the trailing edge noise of NACA0012 airfoil is calculated. The results are compared with reference data, and good agreements are demonstrated.

  11. Advanced subsonic transport approach noise: The relative contribution of airframe noise

    NASA Technical Reports Server (NTRS)

    Willshire, William L., Jr.; Garber, Donald P.

    1992-01-01

    With current engine technology, airframe noise is a contributing source for large commercial aircraft on approach, but not the major contributor. With the promise of much quieter jet engines with the planned new generation of high-by-pass turbofan engines, airframe noise has become a topic of interest in the advanced subsonic transport research program. The objective of this paper is to assess the contribution of airframe noise relative to the other aircraft noise sources on approach. The assessment will be made for a current technology large commercial transport aircraft and for an envisioned advanced technology aircraft. NASA's Aircraft Noise Prediction Program (ANOPP) will be used to make total aircraft noise predictions for these two aircraft types. Predicted noise levels and areas of noise contours will be used to determine the relative importance of the contributing approach noise sources. The actual set-up decks used to make the ANOPP runs for the two aircraft types are included in appendixes.

  12. Airframe Noise Prediction by Acoustic Analogy: Revisited

    NASA Technical Reports Server (NTRS)

    Farassat, F.; Casper, Jay H.; Tinetti, A.; Dunn, M. H.

    2006-01-01

    The present work follows a recent survey of airframe noise prediction methodologies. In that survey, Lighthill s acoustic analogy was identified as the most prominent analytical basis for current approaches to airframe noise research. Within this approach, a problem is typically modeled with the Ffowcs Williams and Hawkings (FW-H) equation, for which a geometry-independent solution is obtained by means of the use of the free-space Green function (FSGF). Nonetheless, the aeroacoustic literature would suggest some interest in the use of tailored or exact Green s function (EGF) for aerodynamic noise problems involving solid boundaries, in particular, for trailing edge (TE) noise. A study of possible applications of EGF for prediction of broadband noise from turbulent flow over an airfoil surface and the TE is, therefore, the primary topic of the present work. Typically, the applications of EGF in the literature have been limited to TE noise prediction at low Mach numbers assuming that the normal derivative of the pressure vanishes on the airfoil surface. To extend the application of EGF to higher Mach numbers, the uniqueness of the solution of the wave equation when either the Dirichlet or the Neumann boundary condition (BC) is specified on a deformable surface in motion. The solution of Lighthill s equation with either the Dirichlet or the Neumann BC is given for such a surface using EGFs. These solutions involve both surface and volume integrals just like the solution of FW-H equation using FSGF. Insight drawn from this analysis is evoked to discuss the potential application of EGF to broadband noise prediction. It appears that the use of a EGF offers distinct advantages for predicting TE noise of an airfoil when the normal pressure gradient vanishes on the airfoil surface. It is argued that such an approach may also apply to an airfoil in motion. However, for the prediction of broadband noise not directly associated with a trailing edge, the use of EGF does not

  13. Airframe Noise from a Hybrid Wing Body Aircraft Configuration

    NASA Technical Reports Server (NTRS)

    Hutcheson, Florence V.; Spalt, Taylor B.; Brooks, Thomas F.; Plassman, Gerald E.

    2016-01-01

    A high fidelity aeroacoustic test was conducted in the NASA Langley 14- by 22-Foot Subsonic Tunnel to establish a detailed database of component noise for a 5.8% scale HWB aircraft configuration. The model has a modular design, which includes a drooped and a stowed wing leading edge, deflectable elevons, twin verticals, and a landing gear system with geometrically scaled wheel-wells. The model is mounted inverted in the test section and noise measurements are acquired at different streamwise stations from an overhead microphone phased array and from overhead and sideline microphones. Noise source distribution maps and component noise spectra are presented for airframe configurations representing two different approach flight conditions. Array measurements performed along the aircraft flyover line show the main landing gear to be the dominant contributor to the total airframe noise, followed by the nose gear, the inboard side-edges of the LE droop, the wing tip/LE droop outboard side-edges, and the side-edges of deployed elevons. Velocity dependence and flyover directivity are presented for the main noise components. Decorrelation effects from turbulence scattering on spectral levels measured with the microphone phased array are discussed. Finally, noise directivity maps obtained from the overhead and sideline microphone measurements for the landing gear system are provided for a broad range of observer locations.

  14. Prediction of jet exhaust noise on airframe surfaces during flight

    NASA Technical Reports Server (NTRS)

    Butzel, L. M.

    1981-01-01

    The behavior of pressure fluctuations measured on the airframe of a prototype high lift jet transport (YC-14) is presented. The data are characterized in terms of a particular jet exhaust flow field idealization, jet mixing noise, and exhaust shock noise. Generalized spectrum shapes and scaling relations for peak level and frequency of peak level are developed, and the frequency is found to depend on jet exhaust velocity and aircraft velocity. Comparisons are made with near-field engine exhaust noise of a conventional jet, and results suggest that the same two exhaust noises are important for both aircraft types. Surface fluctuating pressure data are assessed, and results suggest that the jet mixing and exhaust shock noise source characterizations for the YC-14 have useful applicability to conventionally configured jets.

  15. Preliminary Analysis of Acoustic Measurements from the NASA-Gulfstream Airframe Noise Flight Test

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R.; Lockhard, David D.; Humphreys, Willliam M.; Choudhari, Meelan M.; Van De Ven, Thomas

    2008-01-01

    The NASA-Gulfstream joint Airframe Noise Flight Test program was conducted at the NASA Wallops Flight Facility during October, 2006. The primary objective of the AFN flight test was to acquire baseline airframe noise data on a regional jet class of transport in order to determine noise source strengths and distributions for model validation. To accomplish this task, two measuring systems were used: a ground-based microphone array and individual microphones. Acoustic data for a Gulfstream G550 aircraft were acquired over the course of ten days. Over twenty-four test conditions were flown. The test matrix was designed to provide an acoustic characterization of both the full aircraft and individual airframe components and included cruise to landing configurations. Noise sources were isolated by selectively deploying individual components (flaps, main landing gear, nose gear, spoilers, etc.) and altering the airspeed, glide path, and engine settings. The AFN flight test program confirmed that the airframe is a major contributor to the noise from regional jets during landing operations. Sound pressure levels from the individual microphones on the ground revealed the flap system to be the dominant airframe noise source for the G550 aircraft. The corresponding array beamform maps showed that most of the radiated sound from the flaps originates from the side edges. Using velocity to the sixth power and Strouhal scaling of the sound pressure spectra obtained at different speeds failed to collapse the data into a single spectrum. The best data collapse was obtained when the frequencies were left unscaled.

  16. Small Engine Technology (SET). Task 33: Airframe, Integration, and Community Noise Study

    NASA Technical Reports Server (NTRS)

    Lieber, Lys S.; Elkins, Daniel; Golub, Robert A. (Technical Monitor)

    2002-01-01

    Task Order 33 had four primary objectives as follows: (1) Identify and prioritize the airframe noise reduction technologies needed to accomplish the NASA Pillar goals for business and regional aircraft. (2) Develop a model to estimate the effect of jet shear layer refraction and attenuation of internally generated source noise of a turbofan engine on the aircraft system noise. (3) Determine the effect on community noise of source noise changes of a generic turbofan engine operating from sea level to 15,000 feet. (4) Support lateral attenuation experiments conducted by NASA Langley at Wallops Island, VA, by coordinating opportunities for Contractor Aircraft to participate as a noise source during the noise measurements. Noise data and noise prediction tools, including airframe noise codes, from the NASA Advanced Subsonic Technology (AST) program were applied to assess the current status of noise reduction technologies relative to the NASA pillar goals for regional and small business jet aircraft. In addition, the noise prediction tools were applied to evaluate the effectiveness of airframe-related noise reduction concepts developed in the AST program on reducing the aircraft system noise. The AST noise data and acoustic prediction tools used in this study were furnished by NASA.

  17. Airframe Noise Results from the QTD II Flight Test Program

    NASA Technical Reports Server (NTRS)

    Elkoby, Ronen; Brusniak, Leon; Stoker, Robert W.; Khorrami, Mehdi R.; Abeysinghe, Amal; Moe, Jefferey W.

    2007-01-01

    With continued growth in air travel, sensitivity to community noise intensifies and materializes in the form of increased monitoring, regulations, and restrictions. Accordingly, realization of quieter aircraft is imperative, albeit only achievable with reduction of both engine and airframe components of total aircraft noise. Model-scale airframe noise testing has aided in this pursuit; however, the results are somewhat limited due to lack of fidelity of model hardware, particularly in simulating full-scale landing gear. Moreover, simulation of true in-flight conditions is non-trivial if not infeasible. This paper reports on an investigation of full-scale landing gear noise measured as part of the 2005 Quiet Technology Demonstrator 2 (QTD2) flight test program. Conventional Boeing 777-300ER main landing gear were tested, along with two noise reduction concepts, namely a toboggan fairing and gear alignment with the local flow, both of which were down-selected from various other noise reduction devices evaluated in model-scale testing at Virginia Tech. The full-scale toboggan fairings were designed by Goodrich Aerostructures as add-on devices allowing for complete retraction of the main gear. The baseline-conventional gear, faired gear, and aligned gear were all evaluated with the high-lift system in the retracted position and deployed at various flap settings, all at engine idle power setting. Measurements were taken with flyover community noise microphones and a large aperture acoustic phased array, yielding far-field spectra, and localized sources (beamform maps). The results were utilized to evaluate qualitatively and quantitatively the merit of each noise reduction concept. Complete similarity between model-scale and full-scale noise reduction levels was not found and requires further investigation. Far-field spectra exhibited no noise reduction for both concepts across all angles and frequencies. Phased array beamform maps show inconclusive evidence of noise

  18. Airframe noise measurements by acoustic imaging

    NASA Technical Reports Server (NTRS)

    Kendall, J. M.

    1977-01-01

    Studies of the noise produced by flow past wind tunnel models are presented. The central objective of these is to find the specific locations within a flow which are noisy, and to identify the fluid dynamic processes responsible, with the expectation that noise reduction principles will be discovered. The models tested are mostly simple shapes which result in types of flow that are similar to those occurring on, for example, aircraft landing gear and wheel cavities. A model landing gear and a flap were also tested. Turbulence has been intentionally induced as appropriate in order to simulate full-scale effects more closely. The principal technique involves use of a highly directional microphone system which is scanned about the flow field to be analyzed. The data so acquired are presented as a pictorial image of the noise source distribution. An important finding is that the noise production is highly variable within a flow field and that sources can be attributed to various fluid dynamic features of the flow. Flow separation was not noisy, but separation closure usually was.

  19. Towards Full Aircraft Airframe Noise Prediction: Lattice Boltzmann Simulations

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R.; Fares, Ehab; Casalino, Damiano

    2014-01-01

    Computational results for an 18%-scale, semi-span Gulfstream aircraft model are presented. Exa Corporation's lattice Boltzmann PowerFLOW(trademark) solver was used to perform time-dependent simulations of the flow field associated with this high-fidelity aircraft model. The simulations were obtained for free-air at a Mach number of 0.2 with the flap deflected at 39 deg (landing configuration). We focused on accurately predicting the prominent noise sources at the flap tips and main landing gear for the two baseline configurations, namely, landing flap setting without and with gear deployed. Capitalizing on the inherently transient nature of the lattice Boltzmann formulation, the complex time-dependent flow features associated with the flap were resolved very accurately and efficiently. To properly simulate the noise sources over a broad frequency range, the tailored grid was very dense near the flap inboard and outboard tips. Extensive comparison of the computed time-averaged and unsteady surface pressures with wind tunnel measurements showed excellent agreement for the global aerodynamic characteristics and the local flow field at the flap inboard and outboard tips and the main landing gear. In particular, the computed fluctuating surface pressure field for the flap agreed well with the measurements in both amplitude and frequency content, indicating that the prominent airframe noise sources at the tips were captured successfully. Gear-flap interaction effects were remarkably well predicted and were shown to affect only the inboard flap tip, altering the steady and unsteady pressure fields in that region. The simulated farfield noise spectra for both baseline configurations, obtained using a Ffowcs-Williams and Hawkings acoustic analogy approach, were shown to be in close agreement with measured values.

  20. Simulations & Measurements of Airframe Noise: A BANC Workshops Perspective

    NASA Technical Reports Server (NTRS)

    Choudhari, Meelan; Lockard, David

    2016-01-01

    Airframe noise corresponds to the acoustic radiation due to turbulent flow in the vicinity of airframe components such as high-lift devices and landing gears. Since 2010, the American Institute of Aeronautics and Astronautics has organized an ongoing series of workshops devoted to Benchmark Problems for Airframe Noise Computations (BANC). The BANC workshops are aimed at enabling a systematic progress in the understanding and high-fidelity predictions of airframe noise via collaborative investigations that integrate computational fluid dynamics, computational aeroacoustics, and in depth measurements targeting a selected set of canonical yet realistic configurations that advance the current state-of-the-art in multiple respects. Unique features of the BANC Workshops include: intrinsically multi-disciplinary focus involving both fluid dynamics and aeroacoustics, holistic rather than predictive emphasis, concurrent, long term evolution of experiments and simulations with a powerful interplay between the two, and strongly integrative nature by virtue of multi-team, multi-facility, multiple-entry measurements. This paper illustrates these features in the context of the BANC problem categories and outlines some of the challenges involved and how they were addressed. A brief summary of the BANC effort, including its technical objectives, strategy, and selective outcomes thus far is also included.

  1. In Search of the Physics: NASA's Approach to Airframe Noise

    NASA Technical Reports Server (NTRS)

    Macaraeg, Michele G.; Lockard, David P.; Streett, Craig L.

    1999-01-01

    An extensive numerical and experimental study of airframe noise mechanisms associated with a subsonic high-lift system has been performed at NASA Langley Research Center (LaRC). Investigations involving both steady and unsteady computations and experiments on small-scale models with part-span flaps and full-span flaps are presented. Both surface (steady and unsteady pressure measurements, hot films, oil flows, pressure sensitive paint) and off-surface (5 holeprobe, particle-imaged velocimetry, laser velocimetry, laser light sheet measurements) were taken in the LaRC Quiet Flow Facility (QFF) and several hard-wall tunnels. Experiments in the Low Turbulence Pressure Tunnel (LTPT) included Reynolds number variations up to flight conditions. Successful microphone array measurements were also taken providing both acoustic source maps on the model, and quantitative spectra. Critical directivity measurements were obtained in the QFF. NASA Langley unstructured and structured Reynolds-Averaged Navier-Stokes codes modeled the steady aspects of the flows. Excellent comparisons with surface and off-surface experimental data were obtained. Subsequently, these meanflow calculations were utilized in both linear stability and direct numerical simulations of the flow fields to calculate unsteady surface pressures and farfield acoustic spectra. Accurate calculations were critical in obtaining not only noise source characteristics, but shear layer correction data as well. Techniques utilized in these investigations as well as brief overviews of the results are given.

  2. Numerical investigation of tandem-cylinder aerodynamic noise and its control with application to airframe noise

    NASA Astrophysics Data System (ADS)

    Eltaweel, Ahmed

    Prediction and reduction of airframe noise are critically important to the development of quieter civil transport aircraft. The key to noise reduction is a full understanding of the underlying noise source mechanisms. In this study, tandem cylinders in cross-flow as an idealization of a complex aircraft landing gear configuration are considered to investigate the noise generation and its reduction by flow control using single dielectric barrier discharge plasma actuators. The flow over tandem cylinders at ReD = 22, 000 with and without plasma actuation is computed using large-eddy simulation. The plasma effect is modeled as a body force obtained from a semi-empirical model. The flow statistics and surface pressure frequency spectra show excellent agreement with previous experimental measurements. For acoustic calculations, a boundary-element method is implemented to solve the convected Lighthill equation. The solution method is validated in a number of benchmark problems including flows over a cylinder, a rod-airfoil configuration, and a sphere. With validated flow field and acoustic solver, acoustic analysis is performed for the tandem-cylinder configuration to extend the experimental results and understand the mechanisms of noise generation and its control. Without flow control, the acoustic field is dominated by the interaction between the downstream cylinder and the upstream wake. Through suppression of vortex shedding from the upstream cylinder, the interaction noise is reduced drastically by the plasma flow control, and the vortex-shedding noise from the downstream cylinder becomes equally important. At a free-stream Mach number of 0.2, the peak sound pressure level is reduced by approximately 16 dB. This suggests the viability of plasma actuation for active control of airframe noise. The numerical investigation is extended to the noise from a realistic landing gear experimental model. Coarse-mesh computations are performed, and preliminary results are

  3. Clean wing airframe noise modeling for multidisciplinary design and optimization

    NASA Astrophysics Data System (ADS)

    Hosder, Serhat

    A new noise metric has been developed that may be used for optimization problems involving aerodynamic noise from a clean wing. The modeling approach uses a classical trailing edge noise theory as the starting point. The final form of the noise metric includes characteristic velocity and length scales that are obtained from three-dimensional, steady, RANS simulations with a two equation k-o turbulence model. The noise metric is not the absolute value of the noise intensity, but an accurate relative noise measure as shown in the validation studies. One of the unique features of the new noise metric is the modeling of the length scale, which is directly related to the turbulent structure of the flow at the trailing edge. The proposed noise metric model has been formulated so that it can capture the effect of different design variables on the clean wing airframe noise such as the aircraft speed, lift coefficient, and wing geometry. It can also capture three dimensional effects which become important at high lift coefficients, since the characteristic velocity and the length scales are allowed to vary along the span of the wing. Noise metric validation was performed with seven test cases that were selected from a two-dimensional NACA 0012 experimental database. The agreement between the experiment and the predictions obtained with the new noise metric was very good at various speeds, angles of attack, and Reynolds Number, which showed that the noise metric is capable of capturing the variations in the trailing edge noise as a relative noise measure when different flow conditions and parameters are changed. Parametric studies were performed to investigate the effect of different design variables on the noise metric. Two-dimensional parametric studies were done using two symmetric NACA four-digit airfoils (NACA 0012 and NACA 0009) and two supercritical (SC(2)-0710 and SC(2)-0714) airfoils. The three-dimensional studies were performed with two versions of a conventional

  4. Unstructured CFD and Noise Prediction Methods for Propulsion Airframe Aeroacoustics

    NASA Technical Reports Server (NTRS)

    Pao, S. Paul; Abdol-Hamid, Khaled S.; Campbell, Richard L.; Hunter, Craig A.; Massey, Steven J.; Elmiligui, Alaa A.

    2006-01-01

    Using unstructured mesh CFD methods for Propulsion Airframe Aeroacoustics (PAA) analysis has the distinct advantage of precise and fast computational mesh generation for complex propulsion and airframe integration arrangements that include engine inlet, exhaust nozzles, pylon, wing, flaps, and flap deployment mechanical parts. However, accurate solution values of shear layer velocity, temperature and turbulence are extremely important for evaluating the usually small noise differentials of potential applications to commercial transport aircraft propulsion integration. This paper describes a set of calibration computations for an isolated separate flow bypass ratio five engine nozzle model and the same nozzle system with a pylon. These configurations have measured data along with prior CFD solutions and noise predictions using a proven structured mesh method, which can be used for comparison to the unstructured mesh solutions obtained in this investigation. This numerical investigation utilized the TetrUSS system that includes a Navier-Stokes solver, the associated unstructured mesh generation tools, post-processing utilities, plus some recently added enhancements to the system. New features necessary for this study include the addition of two equation turbulence models to the USM3D code, an h-refinement utility to enhance mesh density in the shear mixing region, and a flow adaptive mesh redistribution method. In addition, a computational procedure was developed to optimize both solution accuracy and mesh economy. Noise predictions were completed using an unstructured mesh version of the JeT3D code.

  5. Investigation of airframe noise for a large-scale wing model with high-lift devices

    NASA Astrophysics Data System (ADS)

    Kopiev, V. F.; Zaytsev, M. Yu.; Belyaev, I. V.

    2016-01-01

    The acoustic characteristics of a large-scale model of a wing with high-lift devices in the landing configuration have been studied in the DNW-NWB wind tunnel with an anechoic test section. For the first time in domestic practice, data on airframe noise at high Reynolds numbers (1.1-1.8 × 106) have been obtained, which can be used for assessment of wing noise levels in aircraft certification tests. The scaling factor for recalculating the measurement results to natural conditions has been determined from the condition of collapsing the dimensionless noise spectra obtained at various flow velocities. The beamforming technique has been used to obtain localization of noise sources and provide their ranking with respect to intensity. For flap side-edge noise, which is an important noise component, a noise reduction method has been proposed. The efficiency of this method has been confirmed in DNW-NWB experiments.

  6. In Search of the Physics: The Interplay of Experiment and Computation in Airframe Noise Research: Flap-Edge Noise

    NASA Technical Reports Server (NTRS)

    Streett, C. L.; Lockard, D. P.; Singer, B. A.; Khorrami, M. R.; Choudhari, M. M.

    2003-01-01

    The LaRC investigative process for airframe noise has proven to be a useful guide for elucidation of the physics of flow-induced noise generation over the last five years. This process, relying on a close interplay between experiment and computation, is described and demonstrated here on the archetypal problem of flap-edge noise. Some detailed results from both experiment and computation are shown to illustrate the process, and a description of the multi-source physics seen in this problem is conjectured.

  7. Integrating CFD, CAA, and Experiments Towards Benchmark Datasets for Airframe Noise Problems

    NASA Technical Reports Server (NTRS)

    Choudhari, Meelan M.; Yamamoto, Kazuomi

    2012-01-01

    Airframe noise corresponds to the acoustic radiation due to turbulent flow in the vicinity of airframe components such as high-lift devices and landing gears. The combination of geometric complexity, high Reynolds number turbulence, multiple regions of separation, and a strong coupling with adjacent physical components makes the problem of airframe noise highly challenging. Since 2010, the American Institute of Aeronautics and Astronautics has organized an ongoing series of workshops devoted to Benchmark Problems for Airframe Noise Computations (BANC). The BANC workshops are aimed at enabling a systematic progress in the understanding and high-fidelity predictions of airframe noise via collaborative investigations that integrate state of the art computational fluid dynamics, computational aeroacoustics, and in depth, holistic, and multifacility measurements targeting a selected set of canonical yet realistic configurations. This paper provides a brief summary of the BANC effort, including its technical objectives, strategy, and selective outcomes thus far.

  8. The Prediction and Analysis of Jet Flows and Scattered Turbulent Mixing Noise about Flight Vehicle Airframes

    NASA Technical Reports Server (NTRS)

    Miller, Steven A. E.

    2014-01-01

    Jet flows interacting with nearby surfaces exhibit a complex behavior in which acoustic and aerodynamic characteristics are altered. The physical understanding and prediction of these characteristics are essential to designing future low noise aircraft. A new approach is created for predicting scattered jet mixing noise that utilizes an acoustic analogy and steady Reynolds-averaged Navier-Stokes solutions. A tailored Green's function accounts for the propagation of mixing noise about the airframe and is calculated numerically using a newly developed ray tracing method. The steady aerodynamic statistics, associated unsteady sound source, and acoustic intensity are examined as jet conditions are varied about a large flat plate. A non-dimensional number is proposed to estimate the effect of the aerodynamic noise source relative to jet operating condition and airframe position.The steady Reynolds-averaged Navier-Stokes solutions, acoustic analogy, tailored Green's function, non-dimensional number, and predicted noise are validated with a wide variety of measurements. The combination of the developed theory, ray tracing method, and careful implementation in a stand-alone computer program result in an approach that is more first principles oriented than alternatives, computationally efficient, and captures the relevant physics of fluid-structure interaction.

  9. The Prediction and Analysis of Jet Flows and Scattered Turbulent Mixing Noise About Flight Vehicle Airframes

    NASA Technical Reports Server (NTRS)

    Miller, Steven A.

    2014-01-01

    Jet flows interacting with nearby surfaces exhibit a complex behavior in which acoustic and aerodynamic characteristics are altered. The physical understanding and prediction of these characteristics are essential to designing future low noise aircraft. A new approach is created for predicting scattered jet mixing noise that utilizes an acoustic analogy and steady Reynolds-averaged Navier-Stokes solutions. A tailored Green's function accounts for the propagation of mixing noise about the air-frame and is calculated numerically using a newly developed ray tracing method. The steady aerodynamic statistics, associated unsteady sound source, and acoustic intensity are examined as jet conditions are varied about a large at plate. A non-dimensional number is proposed to estimate the effect of the aerodynamic noise source relative to jet operating condition and airframe position. The steady Reynolds-averaged Navier-Stokes solutions, acoustic analogy, tailored Green's function, non- dimensional number, and predicted noise are validated with a wide variety of measurements. The combination of the developed theory, ray tracing method, and careful implementation in a stand-alone computer program result in an approach that is more first principles oriented than alternatives, computationally efficient, and captures the relevant physics of fluid-structure interaction.

  10. Hybrid Wing Body Aircraft System Noise Assessment with Propulsion Airframe Aeroacoustic Experiments

    NASA Technical Reports Server (NTRS)

    Thomas, Russell H.; Burley, Casey L.; Olson, Erik D.

    2010-01-01

    A system noise assessment of a hybrid wing body configuration was performed using NASA s best available aircraft models, engine model, and system noise assessment method. A propulsion airframe aeroacoustic effects experimental database for key noise sources and interaction effects was used to provide data directly in the noise assessment where prediction methods are inadequate. NASA engine and aircraft system models were created to define the hybrid wing body aircraft concept as a twin engine aircraft with a 7500 nautical mile mission. The engines were modeled as existing technology high bypass ratio turbofans. The baseline hybrid wing body aircraft was assessed at 22 dB cumulative below the FAA Stage 4 certification level. To determine the potential for noise reduction with relatively near term technologies, seven other configurations were assessed beginning with moving the engines two fan nozzle diameters upstream of the trailing edge and then adding technologies for reduction of the highest noise sources. Aft radiated noise was expected to be the most challenging to reduce and, therefore, the experimental database focused on jet nozzle and pylon configurations that could reduce jet noise through a combination of source reduction and shielding effectiveness. The best configuration for reduction of jet noise used state-of-the-art technology chevrons with a pylon above the engine in the crown position. This configuration resulted in jet source noise reduction, favorable azimuthal directivity, and noise source relocation upstream where it is more effectively shielded by the limited airframe surface, and additional fan noise attenuation from acoustic liner on the crown pylon internal surfaces. Vertical and elevon surfaces were also assessed to add shielding area. The elevon deflection above the trailing edge showed some small additional noise reduction whereas vertical surfaces resulted in a slight noise increase. With the effects of the configurations from the

  11. Flap Side Edge Liners for Airframe Noise Reduction

    NASA Technical Reports Server (NTRS)

    Jones, Michael G. (Inventor); Khorrami, Mehdi R. (Inventor); Choudhari, Meelan M. (Inventor); Howerton, Brian M. (Inventor)

    2014-01-01

    One or more acoustic liners comprising internal chambers or passageways that absorb energy from a noise source on the aircraft are disclosed. The acoustic liners may be positioned at the ends of flaps of an aircraft wing to provide broadband noise absorption and/or dampen the noise producing unsteady flow features, and to reduce the amount of noise generated due to unsteady flow at the inboard and/or outboard end edges of a flap.

  12. Tip Fence for Reduction of Lift-Generated Airframe Noise

    NASA Technical Reports Server (NTRS)

    Ross, James C. (Inventor); Storms, Bruce L. (Inventor)

    1998-01-01

    The present invention is directed toward a unique lift-generated noise reduction apparatus. This apparatus includes a plurality of tip fences that are secured to the trailing and leading assemblies of the high-lift system, as close as possible to the discontinuities where the vortices are most likely to form. In one embodiment, these tip fences are secured to some or all of the outboard and inboard tips of the wing slats and flaps. The tip fence includes a generally flat, or an aerodynamically shaped plate or device that could be formed of almost any rigid material, such as metal, wood, plastic, fiber glass, aluminum, etc. In a preferred embodiment, the tip fences extend below and perpendicularly to flaps and the slats to which they are attached, such that these tip fences are aligned with the nominal free stream velocity of the aircraft. In addition to reducing airframe noise, the tip fence tends to decrease drag and to increase lift, thus improving the overall aerodynamic performance of the aircraft. Another advantage presented by the tip fence lies in the simplicity of its design, its elegance, and its ready ability to fit on the wing components, such as the flaps and the slats. Furthermore, it does not require non-standard materials or fabrication techniques, and it can be readily, easily and inexpensively retrofited on most of the existing aircraft, with minimal design changes.

  13. Characterization of Flap Edge Noise Radiation from a High-Fidelity Airframe Model

    NASA Technical Reports Server (NTRS)

    Humphreys, William M., Jr.; Khorrami, Mehdi R.; Lockhard, David P.; Neuhart, Dan H.; Bahr, Christopher J.

    2015-01-01

    The results of an experimental study of the noise generated by a baseline high-fidelity airframe model are presented. The test campaign was conducted in the open-jet test section of the NASA Langley 14- by 22-foot Subsonic Tunnel on an 18%-scale, semi-span Gulfstream airframe model incorporating a trailing edge flap and main landing gear. Unsteady surface pressure measurements were obtained from a series of sensors positioned along the two flap edges, and far field acoustic measurements were obtained using a 97-microphone phased array that viewed the pressure side of the airframe. The DAMAS array deconvolution method was employed to determine the locations and strengths of relevant noise sources in the vicinity of the flap edges and the landing gear. A Coherent Output Power (COP) spectral method was used to couple the unsteady surface pressures measured along the flap edges with the phased array output. The results indicate that outboard flap edge noise is dominated by the flap bulb seal cavity with very strong COP coherence over an approximate model-scale frequency range of 1 to 5 kHz observed between the array output and those unsteady pressure sensors nearest the aft end of the cavity. An examination of experimental COP spectra for the inboard flap proved inconclusive, most likely due to a combination of coherence loss caused by decorrelation of acoustic waves propagating through the thick wind tunnel shear layer and contamination of the spectra by tunnel background noise at lower frequencies. Directivity measurements obtained from integration of DAMAS pressure-squared values over defined geometric zones around the model show that the baseline flap and landing gear are only moderately directional as a function of polar emission angle.

  14. Development of a SMA-Based, Slat-Gap Filler for Airframe Noise Reduction

    NASA Technical Reports Server (NTRS)

    Turner, Travis L.; Long, David L.

    2015-01-01

    Noise produced by unsteady flow around aircraft structures, termed airframe noise, is an important source of aircraft noise during the approach and landing phases of flight. Conventional leading-edge-slat devices for high lift on typical transport aircraft are a prominent source of airframe noise. Many concepts for slat noise reduction have been investigated. Slat-cove fillers have emerged as an attractive solution, but they maintain the gap flow, leaving some noise production mechanisms unabated, and thus represent a nonoptimal solution. Drooped-leading-edge (DLE) concepts have been proposed as "optimal" because the gap flow is eliminated. The deployed leading edge device is not distinct and separate from the main wing in DLE concepts and the high-lift performance suffers at high angles of attack (alpha) as a consequence. Elusive high-alpha performance and excessive weight penalty have stymied DLE development. The fact that high-lift performance of DLE systems is only affected at high alpha suggests another concept that simultaneously achieves the high-lift of the baseline airfoil and the noise reduction of DLE concepts. The concept involves utilizing a conventional leading-edge slat device and a deformable structure that is deployed from the leading edge of the main wing and closes the gap between the slat and main wing, termed a slat-gap filler (SGF). The deployable structure consists of a portion of the skin of the main wing and it is driven in conjunction with the slat during deployment and retraction. Benchtop models have been developed to assess the feasibility and to study important parameters. Computational models have assisted in the bench-top model design and provided valuable insight in the parameter space as well as the feasibility.

  15. Application of Circulation Control Technology to Airframe Noise Reduction

    NASA Technical Reports Server (NTRS)

    Ahuja, K. K.; Sankar, L. N.; Englar, R. J.; Munro, Scott E.; Li, Yi; Gaeta, R. J.

    2003-01-01

    This report is a summary of the work performed by Georgia Tech Research Institute (GTRI) under NASA Langley Grant NAG-1-2146, which was awarded as a part of NASA's Breakthrough Innovative Technologies (BIT) initiative. This was a three-year program, with a one-year no-cost extension. Each year's study has been an integrated effort consisting of computational fluid dynamics, experimental aerodynamics, and detailed noise and flow measurements. Year I effort examined the feasibility of reducing airframe noise by replacing the conventional wing systems with a Circulation Control Wing (CCW), where steady blowing was used through the trailing edge of the wing over a Coanda surface. It was shown that the wing lift increases with CCW blowing and indeed for the same lift, a CCW wing was shown to produce less noise. Year 2 effort dealt with a similar study on the role of pulsed blowing on airframe noise. The main objective of this portion of the study was to assess whether pulse blowing from the trailing edge of a CCW resulted in more, less, or the same amount of radiated noise to the farfield. Results show that a reduction in farfield noise of up to 5 dB is measured when pulse flow is compared with steady flow for an equivalent lift configuration. This reduction is in the spectral region associated with the trailing edge jet noise. This result is due to the unique advantage that pulsed flow has over steady flow. For a range of frequencies, more lift is experienced with the same mass flow as the steady case. Thus, for an equivalent lift and slot height, the pulsed system can operate at lower jet velocities, and hence lower jet noise. The computational analysis showed that for a given time-averaged mass flow rate, pulsed jets give a higher value of C(sub l) and a higher L/D than equivalent steady jets. This benefit is attributable to higher instantaneous jet velocities, and higher instantaneous C(sub mu) values for the pulsed jet. Pulsed jet benefits increase at higher

  16. Towards an Airframe Noise Prediction Methodology: Survey of Current Approaches

    NASA Technical Reports Server (NTRS)

    Farassat, Fereidoun; Casper, Jay H.

    2006-01-01

    In this paper, we present a critical survey of the current airframe noise (AFN) prediction methodologies. Four methodologies are recognized. These are the fully analytic method, CFD combined with the acoustic analogy, the semi-empirical method and fully numerical method. It is argued that for the immediate need of the aircraft industry, the semi-empirical method based on recent high quality acoustic database is the best available method. The method based on CFD and the Ffowcs William- Hawkings (FW-H) equation with penetrable data surface (FW-Hpds ) has advanced considerably and much experience has been gained in its use. However, more research is needed in the near future particularly in the area of turbulence simulation. The fully numerical method will take longer to reach maturity. Based on the current trends, it is predicted that this method will eventually develop into the method of choice. Both the turbulence simulation and propagation methods need to develop more for this method to become useful. Nonetheless, the authors propose that the method based on a combination of numerical and analytical techniques, e.g., CFD combined with FW-H equation, should also be worked on. In this effort, the current symbolic algebra software will allow more analytical approaches to be incorporated into AFN prediction methods.

  17. A Comparison of Ffowcs Williams-Hawkings Solvers for Airframe Noise Applications

    NASA Technical Reports Server (NTRS)

    Lockard, David P.

    2002-01-01

    This paper presents a comparison between two implementations of the Ffowcs Williams and Hawkings equation for airframe noise applications. Airframe systems are generally moving at constant speed and not rotating, so these conditions are used in the current investigation. Efficient and easily implemented forms of the equations applicable to subsonic, rectilinear motion of all acoustic sources are used. The assumptions allow the derivation of a simple form of the equations in the frequency-domain, and the time-domain method uses the restrictions on the motion to reduce the work required to find the emission time. The comparison between the frequency domain method and the retarded time formulation reveals some of the advantages of the different approaches. Both methods are still capable of predicting the far-field noise from nonlinear near-field flow quantities. Because of the large input data sets and potentially large numbers of observer positions of interest in three-dimensional problems, both codes utilize the message passing interface to divide the problem among different processors. Example problems are used to demonstrate the usefulness and efficiency of the two schemes.

  18. Computational Evaluation of Airframe Noise Reduction Concepts at Full Scale

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R.; Duda, Benjamin; Hazir, Andreas; Fares, Ehab

    2016-01-01

    High-fidelity simulations focused on full-scale evaluation of new technologies for mitigating flap and landing gear noise are presented. These noise reduction concepts were selected because of their superior acoustic performance, as demonstrated during NASA wind tunnel tests of an 18%-scale, semi-span model of a Gulfstream aircraft. The full-scale, full-aircraft, time-accurate simulations were performed with the lattice Boltzmann PowerFLOW(Registered Trademark) solver for free air at a Mach number of 0.2. Three aircraft configurations (flaps deflected at 39? without and with main gear deployed, and 0? flaps with main gear extended) were used to determine the aero-acoustic performance of the concepts on component-level (individually) and system-level (concurrent applica-tion) bases. Farfield noise spectra were obtained using a Ffowcs-Williams and Hawkings acoustic analogy approach. Comparison of the predicted spectra without (baseline) and with the noise treatments applied showed that noise reduction benefits between 2-3 dB for the flap and 1.3-1.7 dB for the main landing gear are obtained. It was also found that the full extent of the benefits is being masked by the noise generated from the flap brackets and main gear cavities, which act as prominent secondary sources.

  19. Effect of Directional Array Size on the Measurement of Airframe Noise Components

    NASA Technical Reports Server (NTRS)

    Brooks, Thomas F.; Humphreys, William M., Jr.

    1999-01-01

    A study was conducted to examine the effects of overall size of directional (or phased) arrays on the measurement of aeroacoustic components. An airframe model was mounted in the potential core of an open-jet windtunnel, with the directional arrays located outside the flow in an anechoic environment. Two array systems were used; one with a solid measurement angle that encompasses 31.6 deg.of source directivity and a smaller one that encompasses 7.2 deg. The arrays, and sub-arrays of various sizes, measured noise from a calibrator source and flap edge model setups. In these cases, noise was emitted from relatively small, but finite size source regions, with intense levels compared to other sources. Although the larger arrays revealed much more source region detail, the measured source levels were substantially reduced due to finer resolution compared to that of the smaller arrays. To better understand the measurements quantitatively, an analytical model was used to define the basic relationships between array to source region sizes and measured output level. Also, the effect of noise scattering by shear layer turbulence was examined using the present data and those of previous studies. Taken together, the two effects were sufficient to explain spectral level differences between arrays of different sizes. An important result of this study is that total (integrated) noise source levels are retrievable and the levels are independent of the array size as long as certain experimental and processing criteria are met. The criteria for both open and closed tunnels are discussed. The success of special purpose diagonal-removal processing in obtaining integrated results is apparently dependent in part on source distribution. Also discussed is the fact that extended sources are subject to substantial measurement error, especially for large arrays.

  20. Flight Test Results for Uniquely Tailored Propulsion-Airframe Aeroacoustic Chevrons: Shockcell Noise

    NASA Technical Reports Server (NTRS)

    Mengle, Vinod G.; Ganz, Ulrich W.; Nesbitt, Eric; Bultemeier, Eric J.; Thomas, Russell H.; Nesbitt, Eric

    2006-01-01

    Azimuthally varying chevrons (AVC) which have been uniquely tailored to account for the asymmetric propulsion-airframe aeroacoustic interactions have recently shown significant reductions in jet-related community noise at low-speed take-off conditions in scale model tests of coaxial nozzles with high bypass ratio. There were indications that such AVCs may also provide shockcell noise reductions at high cruise speeds. This paper describes the flight test results when one such AVC concept, namely, the T-fan chevrons with enhanced mixing near the pylon, was tested at full-scale on a modern large twin-jet aircraft (777-300ER) with focus on shockcell noise at mid-cruise conditions. Shockcell noise is part of the interior cabin noise at cruise conditions and its reduction is useful from the viewpoint of passenger comfort. Noise reduction at the source, in the exhaust jet, especially, at low frequencies, is beneficial from the perspective of reduced fuselage sidewall acoustic lining. Results are shown in terms of unsteady pressure spectra both on the exterior surface of the fuselage at several axial stations and also microphone arrays placed inside the fuselage aft of the engine. The benefits of T-fan chevrons, with and without conventional chevrons on the core nozzle, are shown for several engine operating conditions at cruise involving supersonic fan stream and subsonic or supersonic core stream. The T-fan AVC alone provides up to 5 dB low-frequency noise reduction on the fuselage exterior skin and up to 2 dB reduction inside the cabin. Addition of core chevrons appears to increase the higher frequency noise. This flight test result with the previous model test observation that the T-fan AVCs have hardly any cruise thrust coefficient loss (< 0.05%) make them viable candidates for reducing interior cabin noise in high bypass ratio engines.

  1. Application of MEMS Microphone Array Technology to Airframe Noise Measurements

    NASA Technical Reports Server (NTRS)

    Humphreys, William M., Jr.; Shams, Qamar A.; Graves, Sharon S.; Sealey, Bradley S.; Bartram, Scott M.; Comeaux, Toby

    2005-01-01

    Current generation microphone directional array instrumentation is capable of extracting accurate noise source location and directivity data on a variety of aircraft components, resulting in significant gains in test productivity. However, with this gain in productivity has come the desire to install larger and more complex arrays in a variety of ground test facilities, creating new challenges for the designers of array systems. To overcome these challenges, a research study was initiated to identify and develop hardware and fabrication technologies which could be used to construct an array system exhibiting acceptable measurement performance but at much lower cost and with much simpler installation requirements. This paper describes an effort to fabricate a 128-sensor array using commercially available Micro-Electro-Mechanical System (MEMS) microphones. The MEMS array was used to acquire noise data for an isolated 26%-scale high-fidelity Boeing 777 landing gear in the Virginia Polytechnic Institute and State University Stability Tunnel across a range of Mach numbers. The overall performance of the array was excellent, and major noise sources were successfully identified from the measurements.

  2. Towards Full Aircraft Airframe Noise Prediction: Detached Eddy Simulations

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R.; Mineck, Raymond E.

    2014-01-01

    Results from a computational study on the aeroacoustic characteristics of an 18%-scale, semi-span Gulf-stream aircraft model are presented in this paper. NASA's FUN3D unstructured compressible Navier-Stokes solver was used to perform steady and unsteady simulations of the flow field associated with this high-fidelity aircraft model. Solutions were obtained for free-air at a Mach number of 0.2 with the flap deflected at 39 deg, with the main gear off and on (the two baseline configurations). Initially, the study focused on accurately predicting the prominent noise sources at both flap tips for the baseline configuration with deployed flap only. Building upon the experience gained from this initial effort, subsequent work involved the full landing configuration with both flap and main landing gear deployed. For the unsteady computations, we capitalized on the Detached Eddy Simulation capability of FUN3D to capture the complex time-dependent flow features associated with the flap and main gear. To resolve the noise sources over a broad frequency range, the tailored grid was very dense near the flap inboard and outboard tips and the region surrounding the gear. Extensive comparison of the computed steady and unsteady surface pressures with wind tunnel measurements showed good agreement for the global aerodynamic characteristics and the local flow field at the flap inboard tip. However, the computed pressure coefficients indicated that a zone of separated flow that forms in the vicinity of the outboard tip is larger in extent along the flap span and chord than measurements suggest. Computed farfield acoustic characteristics from a FW-H integral approach that used the simulated pressures on the model solid surface were in excellent agreement with corresponding measurements.

  3. Low-frequency noise reduction of lightweight airframe structures

    NASA Technical Reports Server (NTRS)

    Getline, G. L.

    1976-01-01

    The results of an experimental study to determine the noise attenuation characteristics of aircraft type fuselage structural panels were presented. Of particular interest was noise attenuation at low frequencies, below the fundamental resonances of the panels. All panels were flightweight structures for transport type aircraft in the 34,050 to 45,400 kg (75,000 to 100,000 pounds) gross weight range. Test data include the results of vibration and acoustic transmission loss tests on seven types of isotropic and orthotropically stiffened, flat and curved panels. The results show that stiffness controlled acoustically integrated structures can provide very high noise reductions at low frequencies without significantly affecting their high frequency noise reduction capabilities.

  4. Landing Gear Door Liners for Airframe Noise Reduction

    NASA Technical Reports Server (NTRS)

    Jones, Michael G. (Inventor); Howerton, Brian M. (Inventor); Van De Ven, Thomas (Inventor)

    2014-01-01

    A landing gear door for retractable landing gear of aircraft includes an acoustic liner. The acoustic liner includes one or more internal cavities or chambers having one or more openings that inhibit the generation of sound at the surface and/or absorb sound generated during operation of the aircraft. The landing gear door may include a plurality of internal chambers having different geometries to thereby absorb broadband noise.

  5. Unsteady Flowfield Around Tandem Cylinders as Prototype for Component Interaction in Airframe Noise

    NASA Technical Reports Server (NTRS)

    Khorrami, Meldi R.; Choudhari, Meelan M.; Jenkins, Luther N.; McGinley, Catherine B.

    2005-01-01

    Synergistic application of experiments and numerical simulations is crucial to understanding the underlying physics of airframe noise sources. The current effort is aimed at characterizing the details of the flow interaction between two cylinders in a tandem configuration. This setup is viewed to be representative of several component-level flow interactions that occur when air flows over the main landing gear of large civil transports. Interactions of this type are likely to have a significant impact on the noise radiation associated with the aircraft undercarriage. The paper is focused on two-dimensional, time-accurate flow simulations for the tandem cylinder configuration. Results of the unsteady Reynolds Averaged Navier-Stokes (URANS) computations with a two-equation turbulence model, at a Reynolds number of 0.166 million and a Mach number of 0.166, are presented. The experimental measurements of the same flow field are discussed in a separate paper by Jenkins, Khorrami, Choudhari, and McGinley (2005). Two distinct flow regimes of interest, associated with short and intermediate separation distances between the two cylinders, are considered. Emphasis is placed on understanding both time averaged and unsteady flow features between the two cylinders and in the wake of the rear cylinder. Predicted mean flow quantities and vortex shedding frequencies show reasonable agreement with the measured data for both cylinder spacings. Computations for short separation distance indicate decay of flow unsteadiness with time, which is not unphysical; however, the predicted sensitivity of mean lift coefficient to small angles of attack explains the asymmetric flowfield observed during the experiments.

  6. An aeroacoustic study of micro-tab on airframe noise reduction

    NASA Astrophysics Data System (ADS)

    Kuo, Chiawei B.

    Aircraft high-lift devices such as leading-edge slats and trailing-edge flaps generate noise when extended, causing significant contributions to overall aircraft sound pressure levels, in particular in approach to land phase. It is shown by previous research efforts that noise generated by the high-lift devices increases with their deployment angles. Hence it is possible to mitigate such high-lift noise by using reduced settings without sacrificing the aerodynamic performance, particularly lift. In this dissertation research, micro-tab device attached at the pressure side of the flap surface near its trailing-edge is envisioned as the way to compensate the lift loss due to reduced high-lift device settings. Hybrid numerical method, which combines computational fluid dynamics and acoustics analogy, was adopted to predict the farfield noise spectrum. It is the goal of this research project to illustrate that noise level increase due to micro-tab deployment is smaller than that from the prescribed slat and flap setting increases, so that an overall airframe noise reduction can be achieved. Two-dimensional computational simulations and three-dimensional computational simulations were performed progressively. Results indicated that the proposed reduced high-lift settings with micro-tab application achieved noise reduction, particularly in the mid-frequency range where human hearing is most sensitive to. Parametric studies involving geometry and size effects of the micro-tab configurations were conducted using two-dimensional and three-dimensional models. Results showed that considerable noise reduction was obtained if slit micro-tab was used. An airworthiness study regarding applying micro-tab device onto existing commercial airliners as retrofit to lower noise emission in approach was also investigated and compliance strategy was provided. In the last part of this research, a different approach from aviation policy was taken as the airport noise compatibility planning

  7. Flight Test Results for Uniquely Tailored Propulsion-Airframe Aeroacoustic Chevrons: Community Noise

    NASA Technical Reports Server (NTRS)

    Nesbitt, Eric; Mengle, Vinod; Czech, Michael; Callendar, Bryan; Thomas, Russ

    2006-01-01

    The flow/acoustic environment around the jet exhaust of an engine when installed on an airplane, say, under the wing, is highly asymmetric due to the pylon, the wing and the high-lift devices. Recent scale model tests have shown that such Propulsion Airframe Aeroacoustic (PAA) interactions and the jet mixing noise can be reduced more than with conventional azimuthally uniform chevrons by uniquely tailoring the chevrons to produce enhanced mixing near the pylon. This paper describes the community noise results from a flight test on a large twin-engine airplane using this concept of azimuthally varying chevrons for engines installed under the wing. Results for two different nozzle configurations are described: azimuthally varying "PAA T-fan" chevrons on the fan nozzle with a baseline no-chevron core nozzle and a second with PAA T-fan chevrons with conventional azimuthally uniform chevrons on the core nozzle. We analyze these test results in comparison to the baseline no-chevron nozzle on both spectral and integrated power level bases. The study focuses on the peak jet noise reduction and the effects at high frequencies for typical take-off power settings. The noise reduction and the absolute noise levels are then compared to model scale results. The flight test results verify that the PAA T-fan nozzles in combination with standard core chevron nozzles can, indeed, give a reasonable amount of noise reduction at low frequencies without high-frequency lift during take-off conditions and hardly any impact on the cruise thrust coefficient.

  8. Toward Establishing a Realistic Benchmark for Airframe Noise Research: Issues and Challenges

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R.

    2010-01-01

    The availability of realistic benchmark configurations is essential to enable the validation of current Computational Aeroacoustic (CAA) methodologies and to further the development of new ideas and concepts that will foster the technologies of the next generation of CAA tools. The selection of a real-world configuration, the subsequent design and fabrication of an appropriate model for testing, and the acquisition of the necessarily comprehensive aeroacoustic data base are critical steps that demand great care and attention. In this paper, a brief account of the nose landing-gear configuration, being proposed jointly by NASA and the Gulfstream Aerospace Company as an airframe noise benchmark, is provided. The underlying thought processes and the resulting building block steps that were taken during the development of this benchmark case are given. Resolution of critical, yet conflicting issues is discussed - the desire to maintain geometric fidelity versus model modifications required to accommodate instrumentation; balancing model scale size versus Reynolds number effects; and time, cost, and facility availability versus important parameters like surface finish and installation effects. The decisions taken during the experimental phase of a study can significantly affect the ability of a CAA calculation to reproduce the prevalent flow conditions and associated measurements. For the nose landing gear, the most critical of such issues are highlighted and the compromises made to resolve them are discussed. The results of these compromises will be summarized by examining the positive attributes and shortcomings of this particular benchmark case.

  9. Development and Calibration of a Field-Deployable Microphone Phased Array for Propulsion and Airframe Noise Flyover Measurements

    NASA Technical Reports Server (NTRS)

    Humphreys, William M., Jr.; Lockard, David P.; Khorrami, Mehdi R.; Culliton, William G.; McSwain, Robert G.; Ravetta, Patricio A.; Johns, Zachary

    2016-01-01

    A new aeroacoustic measurement capability has been developed consisting of a large channelcount, field-deployable microphone phased array suitable for airframe noise flyover measurements for a range of aircraft types and scales. The array incorporates up to 185 hardened, weather-resistant sensors suitable for outdoor use. A custom 4-mA current loop receiver circuit with temperature compensation was developed to power the sensors over extended cable lengths with minimal degradation of the signal to noise ratio and frequency response. Extensive laboratory calibrations and environmental testing of the sensors were conducted to verify the design's performance specifications. A compact data system combining sensor power, signal conditioning, and digitization was assembled for use with the array. Complementing the data system is a robust analysis system capable of near real-time presentation of beamformed and deconvolved contour plots and integrated spectra obtained from array data acquired during flyover passes. Additional instrumentation systems needed to process the array data were also assembled. These include a commercial weather station and a video monitoring / recording system. A detailed mock-up of the instrumentation suite (phased array, weather station, and data processor) was performed in the NASA Langley Acoustic Development Laboratory to vet the system performance. The first deployment of the system occurred at Finnegan Airfield at Fort A.P. Hill where the array was utilized to measure the vehicle noise from a number of sUAS (small Unmanned Aerial System) aircraft. A unique in-situ calibration method for the array microphones using a hovering aerial sound source was attempted for the first time during the deployment.

  10. Results from an exploratory study of airframe noise on a small-scale model of a supersonic transport concept

    NASA Technical Reports Server (NTRS)

    Preisser, J. S.

    1977-01-01

    An exploratory study of airframe noise on a small-scale model of a supersonic transport concept was made. The model was a 0.015 scale version without landing gear of Langley's Advanced Supersonic Technology configuration concept, AST-110. Noise measurements were made at positions corresponding to directly beneath the model and at 30 deg - sideline, for both cruise and the approch flaps configurations, at velocities up to 34 m/s. In general, results showed the cruise noise to be about 3dB above the background flow noise and the approach noise to be about 11 dB above. Overall sound pressure levels and spectral shapes agreed with state of the art predictive techniques.

  11. Community noise sources and noise control issues

    NASA Technical Reports Server (NTRS)

    Nihart, Gene L.

    1992-01-01

    The topics covered include the following: community noise sources and noise control issues; noise components for turbine bypass turbojet engine (TBE) turbojet; engine cycle selection and noise; nozzle development schedule; NACA nozzle design; NACA nozzle test results; nearly fully mixed (NFM) nozzle design; noise versus aspiration rate; peak noise test results; nozzle test in the Low Speed Aeroacoustic Facility (LSAF); and Schlieren pictures of NACA nozzle.

  12. Summary of the Tandem Cylinder Solutions from the Benchmark Problems for Airframe Noise Computations-I Workshop

    NASA Technical Reports Server (NTRS)

    Lockard, David P.

    2011-01-01

    Fifteen submissions in the tandem cylinders category of the First Workshop on Benchmark problems for Airframe Noise Computations are summarized. Although the geometry is relatively simple, the problem involves complex physics. Researchers employed various block-structured, overset, unstructured and embedded Cartesian grid techniques and considerable computational resources to simulate the flow. The solutions are compared against each other and experimental data from 2 facilities. Overall, the simulations captured the gross features of the flow, but resolving all the details which would be necessary to compute the noise remains challenging. In particular, how to best simulate the effects of the experimental transition strip, and the associated high Reynolds number effects, was unclear. Furthermore, capturing the spanwise variation proved difficult.

  13. Simulation-Based Airframe Noise Prediction of a Full-Scale, Full Aircraft

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R.; Fares, Ehab

    2016-01-01

    A previously validated computational approach applied to an 18%-scale, semi-span Gulfstream aircraft model was extended to the full-scale, full-span aircraft in the present investigation. The full-scale flap and main landing gear geometries used in the simulations are nearly identical to those flown on the actual aircraft. The lattice Boltzmann solver PowerFLOW® was used to perform time-accurate predictions of the flow field associated with this aircraft. The simulations were performed at a Mach number of 0.2 with the flap deflected 39 deg. and main landing gear deployed (landing configuration). Special attention was paid to the accurate prediction of major sources of flap tip and main landing gear noise. Computed farfield noise spectra for three selected baseline configurations (flap deflected 39 deg. with and without main gear extended, and flap deflected 0 deg. with gear deployed) are presented. The flap brackets are shown to be important contributors to the farfield noise spectra in the mid- to high-frequency range. Simulated farfield noise spectra for the baseline configurations, obtained using a Ffowcs Williams and Hawkings acoustic analogy approach, were found to be in close agreement with acoustic measurements acquired during the 2006 NASA-Gulfstream joint flight test of the same aircraft.

  14. Evaluation of approximate methods for the prediction of noise shielding by airframe components

    NASA Technical Reports Server (NTRS)

    Ahtye, W. F.; Mcculley, G.

    1980-01-01

    An evaluation of some approximate methods for the prediction of shielding of monochromatic sound and broadband noise by aircraft components is reported. Anechoic-chamber measurements of the shielding of a point source by various simple geometric shapes were made and the measured values compared with those calculated by the superposition of asymptotic closed-form solutions for the shielding by a semi-infinite plane barrier. The shields used in the measurements consisted of rectangular plates, a circular cylinder, and a rectangular plate attached to the cylinder to simulate a wing-body combination. The normalized frequency, defined as a product of the acoustic wave number and either the plate width or cylinder diameter, ranged from 4.6 to 114. Microphone traverses in front of the rectangular plates and cylinders generally showed a series of diffraction bands that matched those predicted by the approximate methods, except for differences in the magnitudes of the attenuation minima which can be attributed to experimental inaccuracies. The shielding of wing-body combinations was predicted by modifications of the approximations used for rectangular and cylindrical shielding. Although the approximations failed to predict diffraction patterns in certain regions, they did predict the average level of wing-body shielding with an average deviation of less than 3 dB.

  15. Evaluation of Airframe Noise Reduction Concepts via Simulations Using a Lattice Boltzmann Approach

    NASA Technical Reports Server (NTRS)

    Fares, Ehab; Casalino, Damiano; Khorrami, Mehdi R.

    2015-01-01

    Unsteady computations are presented for a high-fidelity, 18% scale, semi-span Gulfstream aircraft model in landing configuration, i.e. flap deflected at 39 degree and main landing gear deployed. The simulations employ the lattice Boltzmann solver PowerFLOW® to simultaneously capture the flow physics and acoustics in the near field. Sound propagation to the far field is obtained using a Ffowcs Williams and Hawkings acoustic analogy approach. In addition to the baseline geometry, which was presented previously, various noise reduction concepts for the flap and main landing gear are simulated. In particular, care is taken to fully resolve the complex geometrical details associated with these concepts in order to capture the resulting intricate local flow field thus enabling accurate prediction of their acoustic behavior. To determine aeroacoustic performance, the farfield noise predicted with the concepts applied is compared to high-fidelity simulations of the untreated baseline configurations. To assess the accuracy of the computed results, the aerodynamic and aeroacoustic impact of the noise reduction concepts is evaluated numerically and compared to experimental results for the same model. The trends and effectiveness of the simulated noise reduction concepts compare well with measured values and demonstrate that the computational approach is capable of capturing the primary effects of the acoustic treatment on a full aircraft model.

  16. Characterization of Unsteady Flow Structures Around Tandem Cylinders for Component Interaction Studies in Airframe Noise

    NASA Technical Reports Server (NTRS)

    Jenkins, Luther N.; Khorrami, Mehdi R.; Choudhari, Meelan M.; McGinley, Catherine B.

    2005-01-01

    A joint computational and experimental study has been performed at NASA Langley Research Center to investigate the unsteady flow generated by the components of an aircraft landing gear system. Because the flow field surrounding a full landing gear is so complex, the study was conducted on a simplified geometry consisting of two cylinders in tandem arrangement to isolate and characterize the pertinent flow phenomena. This paper focuses on the experimental effort where surface pressures, 2-D Particle Image Velocimetry, and hot-wire anemometry were used to document the flow interaction around the two cylinders at a Reynolds Number of 1.66 x 10(exp 5), based on cylinder diameter, and cylinder spacing-todiameter ratios, L/D, of 1.435 and 3.70. Transition strips were applied to the forward cylinder to produce a turbulent boundary layer upstream of the flow separation. For these flow conditions and L/D ratios, surface pressures on both the forward and rear cylinders show the effects of L/D on flow symmetry, base pressure, and the location of flow separation and attachment. Mean velocities and instantaneous vorticity obtained from the PIV data are used to examine the flow structure between and aft of the cylinders. Shedding frequencies and spectra obtained using hot-wire anemometry are presented. These results are compared with unsteady, Reynolds-Averaged Navier-Stokes (URANS) computations for the same configuration in a companion paper by Khorrami, Choudhari, Jenkins, and McGinley (2005). The experimental dataset produced in this study provides information to better understand the mechanisms associated with component interaction noise, develop and validate time-accurate computer methods used to calculate the unsteady flow field, and assist in modeling of the radiated noise from landing gears.

  17. Evaluation of Novel Liner Concepts for Fan and Airframe Noise Reduction

    NASA Technical Reports Server (NTRS)

    Jones, M. G.; Howerton, B. M.

    2016-01-01

    This paper presents a review of four novel liner concepts: soft vanes, over-the-rotor liners, external liners, and flap side-edge liners. A number of similarities in the design and evaluation of these concepts emerged during these investigations. Since these were the first attempts to study these particular liner concepts, there was limited information to guide the design process. In all cases, the target frequencies (or frequency range) were known, but the optimum acoustic impedance and optimum liner placement were typically not known. For these cases, the maximum available surface was used and a c-impedance was targeted based on the assumption the sound field impinges on the surface at normal incidence. This choice proved fruitful for every application. An impedance prediction model was used to design variable-depth liner configurations, and a graphical design code (ILIAD) was developed to aid in this process. The ability to build increasingly complex liner configurations via additive manufacturing was key, such that multiple designs could quickly be tested in a normal incidence impedance tube. The Two-Thickness Method was used to evaluate available bulk materials, such that bulk liners could also be considered for each application. These novel liner concepts provide sufficient noise reduction to warrant further investigations.

  18. Aircraft noise prediction program theoretical manual, part 2

    NASA Technical Reports Server (NTRS)

    Zorumski, W. E.

    1982-01-01

    Detailed prediction methods for specific aircraft noise sources are given. These sources are airframe noise, combustion noise, fan noise, single and dual stream jet noise, and turbine noise. Modifications to the NASA methods which comply with the International Civil Aviation Organization standard method for aircraft noise prediction are given.

  19. Noise Hazard Evaluation Sound Level Data on Noise Sources

    DTIC Science & Technology

    1975-01-01

    AD-A021 465 NOISE HAZARD EfALUATION SOUND LEVEL DATA ON NOISE SOURCES Jeffrey Goldstein Army Environmental Hygiene Agency Prepared for: Army Health ...A. Noise Hazard Evaluation. B. Engineering Noise Control. C. Health Education. D. Audiometry. E. Hearing Protection. This technical guide concerns the...SOUND LEVEL DATA OF NOISE SOURCES Approved for public release, distribution unlimited. jGI4A C4C SENTINEL HEALTH I 5 US ARMY ENVIROIN.MENTAL HYGIENE

  20. En route noise: NASA propfan test aircraft (calculated source noise

    NASA Technical Reports Server (NTRS)

    Rickley, E. J.

    1990-01-01

    The second phase of a joint National Aeronautics and Space Administration (NASA) and Federal Aviation Administration (FAA) program to study the high-altitude, low-frequency acoustic noise propagation characteristics of the Advanced Turboprop (propfan) Aircraft was conducted on April 3-13, 1989 at the White Sands Missile Range (WSMR), New Mexico. The first phase was conducted on October 26-31, 1987 in Huntsville, Alabama. NASA (Lewis) measured the source noise of the test aircraft during both phases while NASA (Langley) measured surface noise only during the second phase. FAA/NASA designed a program to obtain noise level data from the propfan test bed aircraft, both in the near field and at ground level, during simulated en route flights (35,000 and 20,000 feet ASL), and to test low frequency atmospheric absorption algorithms and prediction technology to provide insight into the necessity for regulatory measures. The curves of calculated source noise versus emission angle are based on a second order best-fit curve of the peak envelope of the adjusted ground data. Centerline and sideline derived source noise levels are shown to be in good agreement. A comparison of the Alabama chase plane source data and the calculated source noise at centerline for both the Alabama and New Mexico data shows good agreement for the 35,000 and the 20,000 feet (ASL) overflights. With the availability of the New Mexico in-flight data, further in depth comparisons will be made.

  1. Limitations of Phased Array Beamforming in Open Rotor Noise Source Imaging

    NASA Technical Reports Server (NTRS)

    Horvath, Csaba; Envia, Edmane; Podboy, Gary G.

    2013-01-01

    Phased array beamforming results of the F31/A31 historical baseline counter-rotating open rotor blade set were investigated for measurement data taken on the NASA Counter-Rotating Open Rotor Propulsion Rig in the 9- by 15-Foot Low-Speed Wind Tunnel of NASA Glenn Research Center as well as data produced using the LINPROP open rotor tone noise code. The planar microphone array was positioned broadside and parallel to the axis of the open rotor, roughly 2.3 rotor diameters away. The results provide insight as to why the apparent noise sources of the blade passing frequency tones and interaction tones appear at their nominal Mach radii instead of at the actual noise sources, even if those locations are not on the blades. Contour maps corresponding to the sound fields produced by the radiating sound waves, taken from the simulations, are used to illustrate how the interaction patterns of circumferential spinning modes of rotating coherent noise sources interact with the phased array, often giving misleading results, as the apparent sources do not always show where the actual noise sources are located. This suggests that a more sophisticated source model would be required to accurately locate the sources of each tone. The results of this study also have implications with regard to the shielding of open rotor sources by airframe empennages.

  2. Investigation of hydraulic transmission noise sources

    NASA Astrophysics Data System (ADS)

    Klop, Richard J.

    Advanced hydrostatic transmissions and hydraulic hybrids show potential in new market segments such as commercial vehicles and passenger cars. Such new applications regard low noise generation as a high priority, thus, demanding new quiet hydrostatic transmission designs. In this thesis, the aim is to investigate noise sources of hydrostatic transmissions to discover strategies for designing compact and quiet solutions. A model has been developed to capture the interaction of a pump and motor working in a hydrostatic transmission and to predict overall noise sources. This model allows a designer to compare noise sources for various configurations and to design compact and inherently quiet solutions. The model describes dynamics of the system by coupling lumped parameter pump and motor models with a one-dimensional unsteady compressible transmission line model. The model has been verified with dynamic pressure measurements in the line over a wide operating range for several system structures. Simulation studies were performed illustrating sensitivities of several design variables and the potential of the model to design transmissions with minimal noise sources. A semi-anechoic chamber has been designed and constructed suitable for sound intensity measurements that can be used to derive sound power. Measurements proved the potential to reduce audible noise by predicting and reducing both noise sources. Sound power measurements were conducted on a series hybrid transmission test bench to validate the model and compare predicted noise sources with sound power.

  3. Airframe Noise Prediction of a Full Aircraft in Model and Full Scale Using a Lattice Boltzmann Approach

    NASA Technical Reports Server (NTRS)

    Fares, Ehab; Duda, Benjamin; Khorrami, Mehdi R.

    2016-01-01

    Unsteady flow computations are presented for a Gulfstream aircraft model in landing configuration, i.e., flap deflected 39deg and main landing gear deployed. The simulations employ the lattice Boltzmann solver PowerFLOW(Trademark) to simultaneously capture the flow physics and acoustics in the near field. Sound propagation to the far field is obtained using a Ffowcs Williams and Hawkings acoustic analogy approach. Two geometry representations of the same aircraft are analyzed: an 18% scale, high-fidelity, semi-span model at wind tunnel Reynolds number and a full-scale, full-span model at half-flight Reynolds number. Previously published and newly generated model-scale results are presented; all full-scale data are disclosed here for the first time. Reynolds number and geometrical fidelity effects are carefully examined to discern aerodynamic and aeroacoustic trends with a special focus on the scaling of surface pressure fluctuations and farfield noise. An additional study of the effects of geometrical detail on farfield noise is also documented. The present investigation reveals that, overall, the model-scale and full-scale aeroacoustic results compare rather well. Nevertheless, the study also highlights that finer geometrical details that are typically not captured at model scales can have a non-negligible contribution to the farfield noise signature.

  4. Duct Liner Optimization for Turbomachinery Noise Sources

    DTIC Science & Technology

    1975-11-01

    AD-A279 441lIIIflhIh* NASA TECHNICAL NASA TMA X-72789 MEMORANDUM oo £ 00 r-:. DUCT LINER OPTIMIZATION FOR TURBOMACHINERY w NOISE SOURCES By Harold C...Recipient’s r.atalog No. NASA TM X-72789! 4 Title diid Subtitle 5. Rewrt Date Duct Liner Optimization for Turbomachinery Noise Sources November 1975...profiles is combined wit., a numerical minimization algorithm to predict optimal liner configurations having one, two, and three sections. Source models

  5. Status of ERA Airframe Technology Demonstrators

    NASA Technical Reports Server (NTRS)

    Davis, Pamela; Jegley, Dawn; Rigney, Tom

    2015-01-01

    NASA has created the Environmentally Responsible Aviation (ERA) Project to explore and document the feasibility, benefits and technical risk of advanced vehicle configurations and enabling technologies that will reduce the impact of aviation on the environment. A critical aspect of this pursuit is the development of a lighter, more robust airframe that will enable the introduction of unconventional aircraft configurations that have higher lift-to-drag ratios, reduced drag, and lower community noise. The Airframe Technology subproject contains two elements. Under the Damage Arresting Composite Demonstration an advanced material system is being explored which will lead to lighter airframes that are more structural efficient than the composites used in aircraft today. Under the Adaptive Compliant Trailing Edge Flight Experiment a new concept of a flexible wing trailing edge is being evaluated which will reduce weight and improve aerodynamic performance. This presentation will describe the development these two airframe technologies.

  6. Active Control of Aerodynamic Noise Sources

    NASA Technical Reports Server (NTRS)

    Reynolds, Gregory A.

    2001-01-01

    Aerodynamic noise sources become important when propulsion noise is relatively low, as during aircraft landing. Under these conditions, aerodynamic noise from high-lift systems can be significant. The research program and accomplishments described here are directed toward reduction of this aerodynamic noise. Progress toward this objective include correction of flow quality in the Low Turbulence Water Channel flow facility, development of a test model and traversing mechanism, and improvement of the data acquisition and flow visualization capabilities in the Aero. & Fluid Dynamics Laboratory. These developments are described in this report.

  7. A LOW NOISE RF SOURCE FOR RHIC.

    SciTech Connect

    HAYES,T.

    2004-07-05

    The Relativistic Heavy Ion Collider (RHIC) requires a low noise rf source to ensure that beam lifetime during a store is not limited by the rf system. The beam is particularly sensitive to noise from power line harmonics. Additionally, the rf source must be flexible enough to handle the frequency jump required for rebucketing (transferring bunches from the acceleration to the storage rf systems). This paper will describe the design of a Direct Digital Synthesizer (DDS) based system that provides both the noise performance and the flexibility required.

  8. Fuel Efficiencies Through Airframe Improvements

    NASA Technical Reports Server (NTRS)

    Bezos-O'Connor, Gaudy M.; Mangelsdorf, Mark F.; Maliska, Heather A.; Washburn, Anthony E.; Wahls, Richard A.

    2011-01-01

    The factors of continuing strong growth in air traffic volume, the vital role of the air transport system on the economy, and concerns about the environmental impact of aviation have added focus to the National Aeronautics Research Policy. To address these concerns in the context of the National Policy, NASA has set aggressive goals in noise reduction, emissions, and energy consumption. With respect to the goal of reducing energy consumption in the fleet, the development of promising airframe technologies is required to realize the significant improvements that are desired. Furthermore, the combination of advances in materials and structures with aerodynamic technologies may lead to a paradigm shift in terms of potential configurations for the future. Some of these promising airframe technologies targeted at improved efficiency are highlighted.

  9. Temporal Characterization of Aircraft Noise Sources

    NASA Technical Reports Server (NTRS)

    Grosveld, Ferdinand W.; Sullivan, Brenda M.; Rizzi, Stephen A.

    2004-01-01

    Current aircraft source noise prediction tools yield time-independent frequency spectra as functions of directivity angle. Realistic evaluation and human assessment of aircraft fly-over noise require the temporal characteristics of the noise signature. The purpose of the current study is to analyze empirical data from broadband jet and tonal fan noise sources and to provide the temporal information required for prediction-based synthesis. Noise sources included a one-tenth-scale engine exhaust nozzle and a one-fifth scale scale turbofan engine. A methodology was developed to characterize the low frequency fluctuations employing the Short Time Fourier Transform in a MATLAB computing environment. It was shown that a trade-off is necessary between frequency and time resolution in the acoustic spectrogram. The procedure requires careful evaluation and selection of the data analysis parameters, including the data sampling frequency, Fourier Transform window size, associated time period and frequency resolution, and time period window overlap. Low frequency fluctuations were applied to the synthesis of broadband noise with the resulting records sounding virtually indistinguishable from the measured data in initial subjective evaluations. Amplitude fluctuations of blade passage frequency (BPF) harmonics were successfully characterized for conditions equivalent to take-off and approach. Data demonstrated that the fifth harmonic of the BPF varied more in frequency than the BPF itself and exhibited larger amplitude fluctuations over the duration of the time record. Frequency fluctuations were found to be not perceptible in the current characterization of tonal components.

  10. Aeroacoustics of Flight Vehicles: Theory and Practice. Volume 1: Noise Sources

    NASA Technical Reports Server (NTRS)

    Hubbard, Harvey H. (Editor)

    1991-01-01

    Methodology recommended to evaluate aeroacoustic related problems is provided, and approaches to their solutions are suggested without extensive tables, nomographs, and derivations. Orientation is toward flight vehicles and emphasis is on underlying physical concepts. Theoretical, experimental, and applied aspects are covered, including the main formulations and comparisons of theory and experiment. The topics covered include: propeller and propfan noise, rotor noise, turbomachinery noise, jet noise classical theory and experiments, noise from turbulent shear flows, jet noise generated by large-scale coherent motion, airframe noise, propulsive lift noise, combustion and core noise, and sonic booms.

  11. Computational Analysis of a Chevron Nozzle Uniquely Tailored for Propulsion Airframe Aeroacoustics

    NASA Technical Reports Server (NTRS)

    Massey, Steven J.; Elmiligui, Alaa A.; Hunter, Craig A.; Thomas, Russell H.; Pao, S. Paul; Mengle, Vinod G.

    2006-01-01

    A computational flow field and predicted jet noise source analysis is presented for asymmetrical fan chevrons on a modern separate flow nozzle at take off conditions. The propulsion airframe aeroacoustic asymmetric fan nozzle is designed with an azimuthally varying chevron pattern with longer chevrons close to the pylon. A baseline round nozzle without chevrons and a reference nozzle with azimuthally uniform chevrons are also studied. The intent of the asymmetric fan chevron nozzle was to improve the noise reduction potential by creating a favorable propulsion airframe aeroacoustic interaction effect between the pylon and chevron nozzle. This favorable interaction and improved noise reduction was observed in model scale tests and flight test data and has been reported in other studies. The goal of this study was to identify the fundamental flow and noise source mechanisms. The flow simulation uses the asymptotically steady, compressible Reynolds averaged Navier-Stokes equations on a structured grid. Flow computations are performed using the parallel, multi-block, structured grid code PAB3D. Local noise sources were mapped and integrated computationally using the Jet3D code based upon the Lighthill Acoustic Analogy with anisotropic Reynolds stress modeling. In this study, trends of noise reduction were correctly predicted. Jet3D was also utilized to produce noise source maps that were then correlated to local flow features. The flow studies show that asymmetry of the longer fan chevrons near the pylon work to reduce the strength of the secondary flow induced by the pylon itself, such that the asymmetric merging of the fan and core shear layers is significantly delayed. The effect is to reduce the peak turbulence kinetic energy and shift it downstream, reducing overall noise production. This combined flow and noise prediction approach has yielded considerable understanding of the physics of a fan chevron nozzle designed to include propulsion airframe aeroacoustic

  12. Non-propulsive aerodynamic noise

    NASA Astrophysics Data System (ADS)

    Willshire, William L., Jr.; Tracy, Maureen B.

    1992-04-01

    In the first part of the paper, the contribution of airframe noise to total aircraft noise on approach is assessed for a large current technology transport and for the same airframe powered with bypass ratio 10 engines with an additional 5 dB noise suppression applied to the fan and turbine noise sources. The airframe noise of the envisioned advanced subsonic transport is 2 EPNdB less than the largest contributor to the total aircraft noise, the fan inlet. The noise impact of the airframe noise, as measured by noise contour area, is 1/4 that of fan noise. Further fan noise reduction efforts should not view airframe noise as an absolute noise floor. In the second part of the paper, the results from one recent cavity noise wind tunnel experiment is reported. A cavity of dimensions 11.25 in. (28.58 cm) long, 2.5 in. (6.35 cm) wide, and variable depth was tested in the Mach number range of .20 through .90. Reynolds number varied from 5 to 100 million per foot (16 to 328 million per meter). The 1/d ratio was varied from 4.4 to 20.0. The model was tested at yaw angles from 0 to 15 degrees. In general, the deeper the cavity, the greater the amplitude of the acoustic tones. Reynolds number appeared to have little effect on acoustic tone amplitudes. Tone amplitude and bandwidth changed with Mach number. The effect of yaw on acoustic tones varied with Reynolds number, Mach number, 1/h, and mode number. At Mach number 0.90, increased yaw shifted the tone frequencies of the higher modal frequencies to lower frequencies. As cavity depth decreased, the effect of yaw decreased.

  13. Aeroacoustic sources of motorcycle helmet noise.

    PubMed

    Kennedy, J; Adetifa, O; Carley, M; Holt, N; Walker, I

    2011-09-01

    The prevalence of noise in the riding of motorcycles has been a source of concern to both riders and researchers in recent times. Detailed flow field information will allow insight into the flow mechanisms responsible for the production of sound within motorcycle helmets. Flow field surveys of this nature are not found in the available literature which has tended to focus on sound pressure levels at ear as these are of interest for noise exposure legislation. A detailed flow survey of a commercial motorcycle helmet has been carried out in combination with surface pressure measurements and at ear acoustics. Three potential noise source regions are investigated, namely, the helmet wake, the surface boundary layer and the cavity under the helmet at the chin bar. Extensive information is provided on the structure of the helmet wake including its frequency content. While the wake and boundary layer flows showed negligible contributions to at-ear sound the cavity region around the chin bar was identified as a key noise source. The contribution of the cavity region was investigated as a function of flow speed and helmet angle both of which are shown to be key factors governing the sound produced by this region.

  14. Aeroacoustics of Propulsion Airframe Integration: Overview of NASA's Research

    NASA Technical Reports Server (NTRS)

    Thomas, Russell H.

    2003-01-01

    The integration of propulsion and airframe is fundamental to the design of an aircraft system. Many considerations influence the integration, such as structural, aerodynamic, and maintenance factors. In regard to the acoustics of an aircraft, the integration can have significant effects on the net radiated noise. Whether an engine is mounted above a wing or below can have a significant effect on noise that reaches communities below because of shielding or reflection of engine noise. This is an obvious example of the acoustic effects of propulsion airframe installation. Another example could be the effect of the pylon on the development of the exhaust plume and on the resulting jet noise. In addition, for effective system noise reduction the impact that installation has on noise reduction devices developed on isolated components must be understood. In the future, a focus on the aerodynamic and acoustic interaction effects of installation, propulsion airframe aeroacoustics, will become more important as noise reduction targets become more difficult to achieve. In addition to continued fundamental component reduction efforts, a system level approach that includes propulsion airframe aeroacoustics will be required in order to achieve the 20 dB of perceived noise reduction envisioned by the long-range NASA goals. This emphasis on the aeroacoustics of propulsion airframe integration is a new part of NASA s noise research. The following paper will review current efforts and highlight technical challenges and approaches.

  15. Landing gear and cavity noise prediction

    NASA Technical Reports Server (NTRS)

    Bliss, D. B.; Hayden, R. E.

    1976-01-01

    Prediction of airframe noise radiation from the landing gear and wheel wells of commercial aircraft is examined. Measurements of these components on typical aircraft are presented and potential noise sources identified. Semiempirical expressions for the sound generation by these sources are developed from available experimental data and theoretical analyses. These expressions are employed to estimate the noise radiation from the landing gear and wheel wells for a typical aircraft and to rank order the component sources.

  16. Jet engine noise source and noise footprint computer programs

    NASA Technical Reports Server (NTRS)

    Dunn, D. G.; Peart, N. A.; Miller, D. L.; Crowley, K. C.

    1972-01-01

    Calculation procedures are presented for predicting maximum passby noise levels and contours (footprints) of conventional jet aircraft with or without noise suppression devices. The procedures have been computerized and a user's guide is presented for the computer programs to be used in predicting the noise characteristics during aircraft takeoffs, fly-over, and/or landing operations.

  17. Prewhitening of Colored Noise Fields for Detection of Threshold Sources

    DTIC Science & Technology

    1993-11-07

    determines the noise covariance matrix, prewhitening techniques allow detection of threshold sources. The multiple signal classification ( MUSIC ...SUBJECT TERMS 1S. NUMBER OF PAGES AR Model, Colored Noise Field, Mixed Spectra Model, MUSIC , Noise Field, 52 Prewhitening, SNR, Standardized Test...EXAMPLE 2: COMPLEX AR COEFFICIENT .............................................. 5 EXAMPLE 3: MUSIC IN A COLORED BACKGROUND NOISE ...................... 6

  18. Sources of noise in magneto-optical readout

    NASA Technical Reports Server (NTRS)

    Mansuripur, M.

    1991-01-01

    The various sources of noise which are often encountered in magneto-optical readout systems are analyzed. Although the focus is on magneto-optics, most sources of noise are common among the various optical recording systems and one can easily adapt the results to other media and systems. A description of the magneto-optical readout system under consideration is given, and the standard methods and the relevant terminology of signal and noise measurement are described. The characteristics of thermal noise, which originates in the electronic circuitry of the readout system, are described. The most fundamental of all sources of noise, the shot noise, is considered, and a detailed account of its statistical properties is given. Shot noise, which is due to random fluctuations in photon arrival times, is an ever-present noise in optical detection. Since the performance of magneto-optical recording devices in use today is approaching the limit imposed by the shot noise, it is important that the reader have a good grasp of this particular source of noise. A model for the laser noise is described, and measurement results which yield numerical values for the strength of the laser power fluctuations are presented. Spatial variations of the disk reflectivity and random depolarization phenomena also contribute to the overall level of noise in readout; these and related issues are treated. Numerical simulation results describing some of the more frequently encountered sources of noise which accompany the recorded waveform itself, namely, jitter noise and signal-amplitude fluctuation noise are presented.

  19. Noise reduction experience at Hughes Helicopter, Inc.

    NASA Technical Reports Server (NTRS)

    Janakiram, D. S.

    1982-01-01

    Noise reduction is mostly limited to light helicopters whose noise signature is dominated by their tail rotors. It is primarily hardware oriented. Well known noise reduction techniques such as reduction of rotor speeds with an accompanying increase in solidity to maintain performance, engine noise reduction with the use of exhaust mufflers, and acoustic blanketing of transmission and engine compartment are used. The concept of blade phasing as a means of reducing tail rotor noise is also used. Engine noise (exhaust noise), power train noise and airframe noise becomes important at low rotor tip speeds and means must be found to reduce these noise sources if further noise reductions are desired. The use of a special test rig aids in isolating the various noise sources and arriving at the penalties (performance or payload) involved in quieting them. Significant noise reduction are achieved for the light helicopter with minimum performance or weight penalties because of the dominance of a single noise source (the tail rotor).

  20. Assessing noise sources at synchrotron infrared ports

    PubMed Central

    Lerch, Ph.; Dumas, P.; Schilcher, T.; Nadji, A.; Luedeke, A.; Hubert, N.; Cassinari, L.; Boege, M.; Denard, J.-C.; Stingelin, L.; Nadolski, L.; Garvey, T.; Albert, S.; Gough, Ch.; Quack, M.; Wambach, J.; Dehler, M.; Filhol, J.-M.

    2012-01-01

    Today, the vast majority of electron storage rings delivering synchrotron radiation for general user operation offer a dedicated infrared port. There is growing interest expressed by various scientific communities to exploit the mid-IR emission in microspectroscopy, as well as the far infrared (also called THz) range for spectroscopy. Compared with a thermal (laboratory-based source), IR synchrotron radiation sources offer enhanced brilliance of about two to three orders of magnitude in the mid-IR energy range, and enhanced flux and brilliance in the far-IR energy range. Synchrotron radiation also has a unique combination of a broad wavelength band together with a well defined time structure. Thermal sources (globar, mercury filament) have excellent stability. Because the sampling rate of a typical IR Fourier-transform spectroscopy experiment is in the kHz range (depending on the bandwidth of the detector), instabilities of various origins present in synchrotron radiation sources play a crucial role. Noise recordings at two different IR ports located at the Swiss Light Source and SOLEIL (France), under conditions relevant to real experiments, are discussed. The lowest electron beam fluctuations detectable in IR spectra have been quantified and are shown to be much smaller than what is routinely recorded by beam-position monitors. PMID:22186638

  1. Three-Dimensional Application of DAMAS Methodology for Aeroacoustic Noise Source Definition

    NASA Technical Reports Server (NTRS)

    Brooks, Thomas F.; Humphreys, William M., Jr.

    2005-01-01

    At the 2004 AIAA/CEAS Aeroacoustic Conference, a breakthrough in acoustic microphone array technology was reported by the authors. A Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) was developed which decouples the array design and processing influence from the noise being measured, using a simple and robust algorithm. For several prior airframe noise studies, it was shown to permit an unambiguous and accurate determination of acoustic source position and strength. As a follow-on effort, this paper examines the technique for three-dimensional (3D) applications. First, the beamforming ability for arrays, of different size and design, to focus longitudinally and laterally is examined for a range of source positions and frequency. Advantage is found for larger array designs with higher density microphone distributions towards the center. After defining a 3D grid generalized with respect to the array s beamforming characteristics, DAMAS is employed in simulated and experimental noise test cases. It is found that spatial resolution is much less sharp in the longitudinal direction in front of the array compared to side-to-side lateral resolution. 3D DAMAS becomes useful for sufficiently large arrays at sufficiently high frequency. But, such can be a challenge to computational capabilities, with regard to the required expanse and number of grid points. Also, larger arrays can strain basic physical modeling assumptions that DAMAS and all traditional array methodologies use. An important experimental result is that turbulent shear layers can negatively impact attainable beamforming resolution. Still, the usefulness of 3D DAMAS is demonstrated by the measurement of landing gear noise source distributions in a difficult hard-wall wind tunnel environment.

  2. A Robust Waveguide Millimeter-Wave Noise Source

    NASA Technical Reports Server (NTRS)

    Ehsan, Negar; Piepmeier, Jeffrey R.; Solly, Michael; Macmurphy, Shawn; Lucey, Jared; Wollack, Edward

    2015-01-01

    This paper presents the design, fabrication, and characterization of a millimeter-wave noise source for the 160- 210 GHz frequency range. The noise source has been implemented in an E-split-block waveguide package and the internal circuitry was developed on a quartz substrate. The measured excess noise ratio at 200 GHz is 9.6 dB.

  3. Propulsion Airframe Aeroacoustic Integration Effects for a Hybrid Wing Body Aircraft Configuration

    NASA Technical Reports Server (NTRS)

    Czech, Michael J.; Thomas, Russell H; Elkoby, Ronen

    2012-01-01

    An extensive experimental investigation was performed to study the propulsion airframe aeroacoustic effects of a high bypass ratio engine for a hybrid wing body aircraft configuration where the engine is installed above the wing. The objective was to provide an understanding of the jet noise shielding effectiveness as a function of engine gas condition and location as well as nozzle configuration. A 4.7% scale nozzle of a bypass ratio seven engine was run at characteristic cycle points under static and forward flight conditions. The effect of the pylon and its orientation on jet noise was also studied as a function of bypass ratio and cycle condition. The addition of a pylon yielded significant spectral changes lowering jet noise by up to 4 dB at high polar angles and increasing it by 2 to 3 dB at forward angles. In order to assess jet noise shielding, a planform representation of the airframe model, also at 4.7% scale was traversed such that the jet nozzle was positioned from downstream of to several diameters upstream of the airframe model trailing edge. Installations at two fan diameters upstream of the wing trailing edge provided only limited shielding in the forward arc at high frequencies for both the axisymmetric and a conventional round nozzle with pylon. This was consistent with phased array measurements suggesting that the high frequency sources are predominantly located near the nozzle exit and, consequently, are amenable to shielding. The mid to low frequency sources were observed further downstream and shielding was insignificant. Chevrons were designed and used to impact the distribution of sources with the more aggressive design showing a significant upstream migration of the sources in the mid frequency range. Furthermore, the chevrons reduced the low frequency source levels and the typical high frequency increase due to the application of chevron nozzles was successfully shielded. The pylon was further modified with a technology that injects air

  4. Interaction of power plant with airframe of new generation aircraft

    NASA Astrophysics Data System (ADS)

    Baklanov, V.

    2013-03-01

    Strategic development of new generation airplanes goes in the direction of further noise decreasing and increasing fuel efficiency, where the determining role belongs to superhigh bypass ratio engines, especially with application gearbox scheme. Fan shaft components will determine the spectrum of power plant dynamic effect transferred via mounting assembly (engine attachments) on airframe structure. This spectrum is reradiated into the cabin in the form of structural noise. Long-term researches of engines (with different bypass ratio) and airframe have allowed (i) to calculate expected structural noise on the new generation aircraft; and (ii) to offer the concept of new vibration isolation mounting.

  5. Procedure for Separating Noise Sources in Measurements of Turbofan Engine Core Noise

    NASA Technical Reports Server (NTRS)

    Miles, Jeffrey Hilton

    2006-01-01

    The study of core noise from turbofan engines has become more important as noise from other sources like the fan and jet have been reduced. A multiple microphone and acoustic source modeling method to separate correlated and uncorrelated sources has been developed. The auto and cross spectrum in the frequency range below 1000 Hz is fitted with a noise propagation model based on a source couplet consisting of a single incoherent source with a single coherent source or a source triplet consisting of a single incoherent source with two coherent point sources. Examples are presented using data from a Pratt & Whitney PW4098 turbofan engine. The method works well.

  6. Teaching Doppler Effect with a passing noise source

    NASA Astrophysics Data System (ADS)

    Costa, Ivan F.; Mocellin, Alexandra

    2010-07-01

    The noise pitch variation of a passing noise source allows a low cost experimental approach to calculate speed and, for the first time, distance. We adjusted the recorded noise pitch variation to the Doppler shift equation for sound. We did this by taking into account the frequency delay due to the sound source displacement and performing a Fast Fourier Transform (FFT) of the noise signal using free software. This experimental method was successfully applied to aircraft and automobiles.

  7. Duct liner optimization for turbomachinery noise sources. [aircraft noise/engine noise - numerical analysis

    NASA Technical Reports Server (NTRS)

    Lester, H. C.; Posey, J. W.

    1975-01-01

    An acoustical field theory for axisymmetric, multisectioned lined ducts with uniform flow profiles was combined with a numerical minimization algorithm to predict optimal liner configurations having one, two, and three sections. Source models studied include a point source located on the axis of the duct and rotor/outlet-stator viscous wake interaction effects for a typical research compressor operating at an axial flow Mach number of about 0.4. For this latter source, optimal liners for equipartition-of energy, zero-phase, and least-attenuated-mode source variations were also calculated and compared with exact results. It is found that the potential benefits of liner segmentation for the attenuation of turbomachinery noise is greater than would be predicted from point source results. Furthermore, effective liner design requires precise knowledge of the circumferential and radial modal distributions.

  8. Identification of Noise Sources and Design of Noise Reduction Measures for a Pneumatic Nail Gun.

    PubMed

    Jayakumar, Vignesh; Kim, Jay; Zechmann, Edward

    An experimental-analytical procedure was implemented to reduce the operating noise level of a nail gun, a commonly found power tool in a construction site. The procedure is comprised of preliminary measurements, identification and ranking of major noise sources and application of noise controls. Preliminary measurements show that the impact noise transmitted through the structure and the exhaust related noise were found to be the first and second major contributors. Applying a noise absorbing foam on the outside of the nail gun body was found to be an effective noise reduction technique. One and two-volume small mufflers were designed and applied to the exhaust side of the nail gun which reduced not only the exhaust noise but also the impact noise. It was shown that the overall noise level could be reduced by as much as 3.5 dB, suggesting that significant noise reduction is possible in construction power tools without any significant increase of the cost.

  9. Aircraft noise source and contour estimation

    NASA Technical Reports Server (NTRS)

    Dunn, D. G.; Peart, N. A.

    1973-01-01

    Calculation procedures are presented for predicting the noise-time histories and noise contours (footprints) of five basic types of aircraft; turbojet, turofan, turboprop, V/STOL, and helicopter. The procedures have been computerized to facilitate prediction of the noise characteristics during takeoffs, flyovers, and/or landing operations.

  10. Advances in automated noise data acquisition and noise source modeling for power reactors

    SciTech Connect

    Clapp, N.E. Jr.; Kryter, R.C.; Sweeney, F.J.; Renier, J.A.

    1981-01-01

    A newly expanded program, directed toward achieving a better appreciation of both the strengths and limitations of on-line, noise-based, long-term surveillance programs for nuclear reactors, is described. Initial results in the complementary experimental (acquisition and automated screening of noise signatures) and theoretical (stochastic modeling of likely noise sources) areas of investigation are given.

  11. Noise optimization of the source follower of a CMOS pixel using BSIM3 noise model

    NASA Astrophysics Data System (ADS)

    Mahato, Swaraj; Meynants, Guy; Raskin, Gert; De Ridder, J.; Van Winckel, H.

    2016-07-01

    CMOS imagers are becoming increasingly popular in astronomy. A very low noise level is required to observe extremely faint targets and to get high-precision flux measurements. Although CMOS technology offers many advantages over CCDs, a major bottleneck is still the read noise. To move from an industrial CMOS sensor to one suitable for scientific applications, an improved design that optimizes the noise level is essential. Here, we study the 1/f and thermal noise performance of the source follower (SF) of a CMOS pixel in detail. We identify the relevant design parameters, and analytically study their impact on the noise level using the BSIM3v3 noise model with an enhanced model of gate capacitance. Our detailed analysis shows that the dependence of the 1/f noise on the geometrical size of the source follower is not limited to minimum channel length, compared to the classical approach to achieve the minimum 1/f noise. We derive the optimal gate dimensions (the width and the length) of the source follower that minimize the 1/f noise, and validate our results using numerical simulations. By considering the thermal noise or white noise along with 1/f noise, the total input noise of the source follower depends on the capacitor ratio CG/CFD and the drain current (Id). Here, CG is the total gate capacitance of the source follower and CFD is the total floating diffusion capacitor at the input of the source follower. We demonstrate that the optimum gate capacitance (CG) depends on the chosen bias current but ranges from CFD/3 to CFD to achieve the minimum total noise of the source follower. Numerical calculation and circuit simulation with 180nm CMOS technology are performed to validate our results.

  12. Review of Subcritical Source-Driven Noise Analysis Measurements

    SciTech Connect

    Valentine, T.E.

    1999-11-01

    Subcritical source-driven noise measurements are simultaneous Rossia and randomly pulsed neutron measurements that provide measured quantities that can be related to the subcritical neutron multiplication factor. In fact, subcritical source-driven noise measurements should be performed in lieu of Rossia measurements because of the additional information that is obtained from noise measurements such as the spectral ratio and the coherence functions. The basic understanding of source-driven noise analysis measurements can be developed from a point reactor kinetics model to demonstrate how the measured quantities relate to the subcritical neutron multiplication factor.

  13. Sources of noise in Brillouin optical time-domain analyzers

    NASA Astrophysics Data System (ADS)

    Urricelqui, Javier; Soto, Marcelo A.; Thévenaz, Luc

    2015-09-01

    This paper presents a thorough study of the different sources of noise affecting Brillouin optical time-domain analyzers (BOTDA), providing a deep insight into the understanding of the fundamental limitations of this kind of sensors. Analytical and experimental results indicate that the noise source ultimately fixing the sensor performance depends basically on the fiber length and the input pump-probe powers. Thus, while the phase-to-intensity noise conversion induced by stimulated Brillouin scattering can have a dominating effect at short distances, a combination of sources determines the noise in longrange sensing, basically dominated by probe double Rayleigh scattering.

  14. Continuous-variable quantum key distribution with Gaussian source noise

    SciTech Connect

    Shen Yujie; Peng Xiang; Yang Jian; Guo Hong

    2011-05-15

    Source noise affects the security of continuous-variable quantum key distribution (CV QKD) and is difficult to analyze. We propose a model to characterize Gaussian source noise through introducing a neutral party (Fred) who induces the noise with a general unitary transformation. Without knowing Fred's exact state, we derive the security bounds for both reverse and direct reconciliations and show that the bound for reverse reconciliation is tight.

  15. Noise Characterization of Supercontinuum Sources for Low Coherence Interferometry Applications

    PubMed Central

    Brown, William J.; Kim, Sanghoon; Wax, Adam

    2015-01-01

    We examine the noise properties of supercontinuum light sources when used in low coherence interferometry applications. The first application is a multiple-scattering low-coherence interferometry (ms2/LCI) system where high power and long image acquisition times are required to image deep into tissue. For this system we compare the noise characteristics of two supercontinuum sources from different suppliers. Both sources have long term drift that limits the amount of time over which signal averaging is advantageous for reducing noise. The second application is a high resolution optical coherence tomography system where broadband light is needed for high axial resolution. For this system we compare the noise performance of the two supercontinuum sources and a light source based on four superluminescent diodes (SLDs) using imaging contrast as a comparative metric. We find that the NKT SuperK has superior noise performance compared to the Fianium SC-450-4 but neither meets the performance of the SLDs. PMID:25606759

  16. Analysis and Synthesis of Tonal Aircraft Noise Sources

    NASA Technical Reports Server (NTRS)

    Allen, Matthew P.; Rizzi, Stephen A.; Burdisso, Ricardo; Okcu, Selen

    2012-01-01

    Fixed and rotary wing aircraft operations can have a significant impact on communities in proximity to airports. Simulation of predicted aircraft flyover noise, paired with listening tests, is useful to noise reduction efforts since it allows direct annoyance evaluation of aircraft or operations currently in the design phase. This paper describes efforts to improve the realism of synthesized source noise by including short term fluctuations, specifically for inlet-radiated tones resulting from the fan stage of turbomachinery. It details analysis performed on an existing set of recorded turbofan data to isolate inlet-radiated tonal fan noise, then extract and model short term tonal fluctuations using the analytic signal. Methodologies for synthesizing time-variant tonal and broadband turbofan noise sources using measured fluctuations are also described. Finally, subjective listening test results are discussed which indicate that time-variant synthesized source noise is perceived to be very similar to recordings.

  17. Noise sources in laser radar systems.

    PubMed

    Letalick, D; Renhorn, I; Steinvall, O; Shapiro, J H

    1989-07-01

    To understand the fundamental limit of performance with a given laser radar system, the phase noise of a testbed laser radar has been investigated. Apart from the phase noise in the transmitter laser and the local oscillator laser, additional phase noise was introduced by vibrations caused by fans in power supplies and cooling systems. The stability of the mechanical structure of the platform was also found to be of great importance. Furthermore, a model for the signal variations from diffuse targets has been developed. This model takes into account the stray light, the speckle decorrelation, and Doppler shift due to moving targets.

  18. Inverting seismic noise cross-correlations for noise source distribution: A step towards reducing source-induced bias in seismic noise interferometry

    NASA Astrophysics Data System (ADS)

    Ermert, Laura; Afanasiev, Michael; Sager, Korbinian; Gokhberg, Alexey; Fichtner, Andreas

    2016-04-01

    We report on the ongoing development of a new inversion method for the space- and time-dependent power spectral density distribution of ambient seismic noise sources. The method, once complete, will mainly serve two purposes: First, it will allow us to construct more realistic forward models for noise cross-correlation waveforms, thereby opening new possibilities for waveform imaging by ambient noise tomography. Second, it may provide new insights about the properties of ambient noise sources, complementing studies based on beamforming or numerical modeling of noise based on oceanographic observations. To invert for noise sources, we consider surface wave signal energy measurements on the 'causal' (station A to B) and on the 'acausal' (station B to A) correlation branch, and the ratio between them. These and similar measurements have proven useful for locating noise sources using cross-correlations in several past studies. The inversion procedure is the following: We construct correlation forward models based on Green's functions from a spectral element wave propagation code. To construct these models efficiently, we use source-receiver reciprocity and assume spatial uncorrelation of noise sources. In such a setting, correlations can be calculated from a pre-computed set of Green's functions between the seismic receivers and sources located at the Earth's surface. We then calculate spatial sensitivity kernels for the noise source distribution with respect to the correlation signal energy measurements. These in turn allow us to construct a misfit gradient and optimize the source distribution model to fit our observed cross-correlation signal energies or energy ratios. We will present the workflow for calculation of the forward model and sensitivity kernels, as well as results for both forward modeling and kernels for an example data set of long-period noise or 'hum' at a global scale. We will also provide an outlook on the noise source inversion considering the

  19. Investigation of Acoustical Shielding by a Wedge-Shaped Airframe

    NASA Technical Reports Server (NTRS)

    Gerhold, Carl H.; Clark, Lorenzo R.; Dunn, Mark H.; Tweed, John

    2006-01-01

    Experiments on a scale model of an advanced unconventional subsonic transport concept, the Blended Wing Body (BWB), have demonstrated significant shielding of inlet-radiated noise. A computational model of the shielding mechanism has been developed using a combination of boundary integral equation method (BIEM) and equivalent source method (ESM). The computation models the incident sound from a point source in a nacelle and determines the scattered sound field. In this way the sound fields with and without the airfoil can be estimated for comparison to experiment. An experimental test bed using a simplified wedge-shape airfoil and a broadband point noise source in a simulated nacelle has been developed for the purposes of verifying the analytical model and also to study the effect of engine nacelle placement on shielding. The experimental study is conducted in the Anechoic Noise Research Facility at NASA Langley Research Center. The analytic and experimental results are compared at 6300 and 8000 Hz. These frequencies correspond to approximately 150 Hz on the full scale aircraft. Comparison between the experimental and analytic results is quite good, not only for the noise scattering by the airframe, but also for the total sound pressure in the far field. Many of the details of the sound field that the analytic model predicts are seen or indicated in the experiment, within the spatial resolution limitations of the experiment. Changing nacelle location produces comparable changes in noise shielding contours evaluated analytically and experimentally. Future work in the project will be enhancement of the analytic model to extend the analysis to higher frequencies corresponding to the blade passage frequency of the high bypass ratio ducted fan engines that are expected to power the BWB.

  20. Investigation of Acoustical Shielding by a Wedge-Shaped Airframe

    NASA Technical Reports Server (NTRS)

    Gerhold, Carl H.; Clark, Lorenzo R.; Dunn, Mark H.; Tweed, John

    2004-01-01

    Experiments on a scale model of an advanced unconventional subsonic transport concept, the Blended Wing Body (BWB), have demonstrated significant shielding of inlet-radiated noise. A computational model of the shielding mechanism has been developed using a combination of boundary integral equation method (BIEM) and equivalent source method (ESM). The computation models the incident sound from a point source in a nacelle and determines the scattered sound field. In this way the sound fields with and without the airfoil can be estimated for comparison to experiment. An experimental test bed using a simplified wedge-shape airfoil and a broadband point noise source in a simulated nacelle has been developed for the purposes of verifying the analytical model and also to study the effect of engine nacelle placement on shielding. The experimental study is conducted in the Anechoic Noise Research Facility at NASA Langley Research Center. The analytic and experimental results are compared at 6300 and 8000 Hz. These frequencies correspond to approximately 150 Hz on the full scale aircraft. Comparison between the experimental and analytic results is quite good, not only for the noise scattering by the airframe, but also for the total sound pressure in the far field. Many of the details of the sound field that the analytic model predicts are seen or indicated in the experiment, within the spatial resolution limitations of the experiment. Changing nacelle location produces comparable changes in noise shielding contours evaluated analytically and experimentally. Future work in the project will be enhancement of the analytic model to extend the analysis to higher frequencies corresponding to the blade passage frequency of the high bypass ratio ducted fan engines that are expected to power the BWB.

  1. A study of interior noise levels, noise sources and transmission paths in light aircraft

    NASA Technical Reports Server (NTRS)

    Hayden, R. E.; Murray, B. S.; Theobald, M. A.

    1983-01-01

    The interior noise levels and spectral characteristics of 18 single-and twin-engine propeller-driven light aircraft, and source-path diagnosis of a single-engine aircraft which was considered representative of a large part of the fleet were studied. The purpose of the flight surveys was to measure internal noise levels and identify principal noise sources and paths under a carefully controlled and standardized set of flight procedures. The diagnostic tests consisted of flights and ground tests in which various parts of the aircraft, such as engine mounts, the engine compartment, exhaust pipe, individual panels, and the wing strut were instrumented to determine source levels and transmission path strengths using the transfer function technique. Predominant source and path combinations are identified. Experimental techniques are described. Data, transfer function calculations to derive source-path contributions to the cabin acoustic environment, and implications of the findings for noise control design are analyzed.

  2. Optical linear algebra processors - Noise and error-source modeling

    NASA Technical Reports Server (NTRS)

    Casasent, D.; Ghosh, A.

    1985-01-01

    The modeling of system and component noise and error sources in optical linear algebra processors (OLAPs) are considered, with attention to the frequency-multiplexed OLAP. General expressions are obtained for the output produced as a function of various component errors and noise. A digital simulator for this model is discussed.

  3. Optical linear algebra processors: noise and error-source modeling.

    PubMed

    Casasent, D; Ghosh, A

    1985-06-01

    The modeling of system and component noise and error sources in optical linear algebra processors (OLAP's) are considered, with attention to the frequency-multiplexed OLAP. General expressions are obtained for the output produced as a function of various component errors and noise. A digital simulator for this model is discussed.

  4. Active noise control using noise source having adaptive resonant frequency tuning through stiffness variation

    NASA Technical Reports Server (NTRS)

    Pla, Frederic G. (Inventor); Rajiyah, Harindra (Inventor); Renshaw, Anthony A. (Inventor); Hedeen, Robert A. (Inventor)

    1995-01-01

    A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of a noise radiating element is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency of the noise radiating element is tuned by a plurality of force transmitting mechanisms which contact the noise radiating element. Each one of the force transmitting mechanisms includes an expandable element and a spring in contact with the noise radiating element so that excitation of the element varies the spring force applied to the noise radiating element. The elements are actuated by a controller which receives input of a signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the elements and causes the spring force applied to the noise radiating element to be varied. The force transmitting mechanisms can be arranged to either produce bending or linear stiffness variations in the noise radiating element.

  5. System Noise Assessment and the Potential for a Low Noise Hybrid Wing Body Aircraft with Open Rotor Propulsion

    NASA Technical Reports Server (NTRS)

    Thomas, Russell H.; Burley, Casey L.; Lopes, Leonard V.; Bahr, Christopher J.; Gern, Frank H.; VanZante, Dale E.

    2014-01-01

    An aircraft system noise assessment was conducted for a hybrid wing body freighter aircraft concept configured with three open rotor engines. The primary objective of the study was to determine the aircraft system level noise given the significant impact of installation effects including shielding the open rotor noise by the airframe. The aircraft was designed to carry a payload of 100,000 lbs on a 6,500 nautical mile mission. An experimental database was used to establish the propulsion airframe aeroacoustic installation effects including those from shielding by the airframe planform, interactions with the control surfaces, and additional noise reduction technologies. A second objective of the study applied the impacts of projected low noise airframe technology and a projection of advanced low noise rotors appropriate for the NASA N+2 2025 timeframe. With the projection of low noise rotors and installation effects, the aircraft system level was 26.0 EPNLdB below Stage 4 level with the engine installed at 1.0 rotor diameters upstream of the trailing edge. Moving the engine to 1.5 rotor diameters brought the system level noise to 30.8 EPNLdB below Stage 4. At these locations on the airframe, the integrated level of installation effects including shielding can be as much as 20 EPNLdB cumulative in addition to lower engine source noise from advanced low noise rotors. And finally, an additional set of technology effects were identified and the potential impact at the system level was estimated for noise only without assessing the impact on aircraft performance. If these additional effects were to be included it is estimated that the potential aircraft system noise could reach as low as 38.0 EPNLdB cumulative below Stage 4.

  6. Propulsion Airframe Aeroacoustic Integration Effects for a Hybrid Wing Body Aircraft Configuration

    NASA Technical Reports Server (NTRS)

    Czech, Michael J.; Thomas, Russell H.; Elkoby, Ronen

    2010-01-01

    An extensive experimental investigation was performed to study the propulsion airframe aeroacoustic effects of a high bypass ratio engine for a hybrid wing body aircraft configuration where the engine is installed above the wing. The objective was to provide an understanding of the jet noise shielding effectiveness as a function of engine gas condition and location as well as nozzle configuration. A 4.7% scale nozzle of a bypass ratio seven engine was run at characteristic cycle points under static and forward flight conditions. The effect of the pylon and its orientation on jet noise was also studied as a function of bypass ratio and cycle condition. The addition of a pylon yielded significant spectral changes lowering jet noise by up to 4dB at high polar angles and increasing it by 2 to 3dB at forward angles. In order to assess jet noise shielding, a planform representation of the airframe model, also at 4.7% scale was traversed relative to the jet nozzle from downstream to several diameters upstream of the wing trailing edge. Installations at two fan diameters upstream of the wing trailing edge provided only limited shielding in the forward arc at high frequencies for both the axisymmetric and a conventional round nozzle with pylon. This was consistent with phased array measurements suggesting that the high frequency sources are predominantly located near the nozzle exit and, consequently, are amenable to shielding. The mid to low frequencies sources were observed further downstream and shielding was insignificant. Chevrons were designed and used to impact the distribution of sources with the more aggressive design showing a significant upstream migration of the sources in the mid frequency range. Furthermore, the chevrons reduced the low frequency source levels and the typical high frequency increase due to the application of chevron nozzles was successfully shielded. The pylon was further modified with a technology that injects air through the shelf of the

  7. Intrinsic Noise Level of Noise Cross-Correlation Functions and its Implication to Source Population of Ambient noises

    NASA Astrophysics Data System (ADS)

    Chen, Ying-Nien; Gung, Yuancheng; Chiao, Ling-Yun; Rhie, Junkee

    2017-01-01

    SUMMARYWe present a quantitative procedure to evaluate the intrinsic <span class="hlt">noise</span> level (INL) of the <span class="hlt">noise</span> cross-correlation function (NCF). The method is applied to realistic NCFs derived from the continuous data recorded by the seismic arrays in Taiwan and Korea. The obtained temporal evolution of NCF <span class="hlt">noise</span> level follows fairly the prediction of the theoretical formulation, confirming the feasibility of the method. We then apply the obtained INL to the assessment of data quality and the <span class="hlt">source</span> characteristics of ambient <span class="hlt">noise</span>. We show that the INL-based signal-to-<span class="hlt">noise</span> ratio provides an exact measure for the true <span class="hlt">noise</span> level within the NCF and better resolving power for the NCF quality, and such measurement can be implemented to any time windows of the NCFs to evaluate the quality of overtones or coda waves. Moreover, since NCF amplitudes are influenced by both the population and excitation strengths of <span class="hlt">noises</span>, while INL is primarily sensitive to the overall <span class="hlt">source</span> population, with information from both measurements, we may better constrain the <span class="hlt">source</span> characteristics of seismic ambient <span class="hlt">noises</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850048238&hterms=analytical+results+phase+noise&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Danalytical%2Bresults%2Bphase%2Bnoise','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850048238&hterms=analytical+results+phase+noise&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Danalytical%2Bresults%2Bphase%2Bnoise"><span>An improved <span class="hlt">source</span> model for aircraft interior <span class="hlt">noise</span> studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mahan, J. R.; Fuller, C. R.</p> <p>1985-01-01</p> <p>There is concern that advanced turboprop engines currently being developed may produce excessive aircraft cabin <span class="hlt">noise</span> level. This concern has stimulated renewed interest in developing aircraft interior <span class="hlt">noise</span> reduction methods that do not significnatly increase take off weight. An existing analytical model for <span class="hlt">noise</span> transmission into aircraft cabins was utilized to investigate the behavior of an improved propeller <span class="hlt">source</span> model for use in aircraft interior <span class="hlt">noise</span> studies. The new <span class="hlt">source</span> model, a virtually rotating dipole, is shown to adequately match measured fuselage sound pressure distributions, including the correct phase relationships, for published data. The virtually rotating dipole is used to study the sensitivity of synchrophasing effectiveness to the fuselage sound pressure trace velocity distribution. Results of calculations are presented which reveal the importance of correctly modeling the surface pressure phase relations in synchrophasing and other aircraft interior <span class="hlt">noise</span> studies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850009359','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850009359"><span>An improved <span class="hlt">source</span> model for aircraft interior <span class="hlt">noise</span> studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mahan, J. R.; Fuller, C. R.</p> <p>1985-01-01</p> <p>There is concern that advanced turboprop engines currently being developed may produce excessive aircraft cabin <span class="hlt">noise</span> levels. This concern has stimulated renewed interest in developing aircraft interior <span class="hlt">noise</span> reduction methods that do not significantly increase take off weight. An existing analytical model for <span class="hlt">noise</span> transmission into aircraft cabins was utilized to investigate the behavior of an improved propeller <span class="hlt">source</span> model for use in aircraft interior <span class="hlt">noise</span> studies. The new <span class="hlt">source</span> model, a virtually rotating dipole, is shown to adequately match measured fuselage sound pressure distributions, including the correct phase relationships, for published data. The virtually rotating dipole is used to study the sensitivity of synchrophasing effectiveness to the fuselage sound pressure trace velocity distribution. Results of calculations are presented which reveal the importance of correctly modeling the surface pressure phase relations in synchrophasing and other aircraft interior <span class="hlt">noise</span> studies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014RScI...85b4702G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014RScI...85b4702G"><span>Large bandwidth op-amp based white <span class="hlt">noise</span> current <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Giusi, Gino; Scandurra, Graziella; Ciofi, Carmine</p> <p>2014-02-01</p> <p>Electrical <span class="hlt">noise</span> <span class="hlt">sources</span> are basic building blocks in many measurement and instrumentation applications and in communication systems. In this paper, we propose a quite simple topology for the realization of a programmable, wide bandwidth, white <span class="hlt">noise</span> current <span class="hlt">source</span> that requires only two resistors and one operational amplifier. We validate the proposed approach by means of SPICE simulations and demonstrate, by means of proper measurements, the capability of generating a flat current <span class="hlt">noise</span> spectrum in a frequency range up to four decades from a few Hz up to 100 kHz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22489369','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22489369"><span>Demonstration of Johnson <span class="hlt">noise</span> thermometry with all-superconducting quantum voltage <span class="hlt">noise</span> <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Yamada, Takahiro Urano, Chiharu; Maezawa, Masaaki</p> <p>2016-01-25</p> <p>We present a Johnson <span class="hlt">noise</span> thermometry (JNT) system based on an integrated quantum voltage <span class="hlt">noise</span> <span class="hlt">source</span> (IQVNS) that has been fully implemented using superconducting circuit technology. To enable precise measurement of Boltzmann's constant, an IQVNS chip was designed to produce intrinsically calculable pseudo-white <span class="hlt">noise</span> to calibrate the JNT system. On-chip real-time generation of pseudo-random codes via simple circuits produced pseudo-voltage <span class="hlt">noise</span> with a harmonic tone interval of less than 1 Hz, which was one order of magnitude finer than the harmonic tone interval of conventional quantum voltage <span class="hlt">noise</span> <span class="hlt">sources</span>. We estimated a value for Boltzmann's constant experimentally by performing JNT measurements at the temperature of the triple point of water using the IQVNS chip.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080007426','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080007426"><span>Active <span class="hlt">noise</span> control using <span class="hlt">noise</span> <span class="hlt">source</span> having adaptive resonant frequency tuning through stress variation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pla, Frederic G. (Inventor); Rajiyah, Harindra (Inventor); Renshaw, Anthony A. (Inventor); Hedeen, Robert A. (Inventor)</p> <p>1995-01-01</p> <p>A <span class="hlt">noise</span> <span class="hlt">source</span> for an aircraft engine active <span class="hlt">noise</span> cancellation system in which the resonant frequency of a <span class="hlt">noise</span> radiating element is tuned to permit <span class="hlt">noise</span> cancellation over a wide range of frequencies. The resonant frequency of the <span class="hlt">noise</span> radiating element is tuned by an expandable ring embedded in the <span class="hlt">noise</span> radiating element. Excitation of the ring causes expansion or contraction of the ring, thereby varying the stress in the <span class="hlt">noise</span> radiating element. The ring is actuated by a controller which receives input of a feedback signal proportional to displacement of the <span class="hlt">noise</span> radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the ring, causing the ring to expand or contract. Instead of a single ring embedded in the <span class="hlt">noise</span> radiating panel, a first expandable ring can be bonded to one side of the <span class="hlt">noise</span> radiating element, and a second expandable ring can be bonded to the other side.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19810025404','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19810025404"><span>Computer program to predict aircraft <span class="hlt">noise</span> levels</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Clark, B. J.</p> <p>1981-01-01</p> <p>Methods developed at the NASA Lewis Research Center for predicting the <span class="hlt">noise</span> contributions from various aircraft <span class="hlt">noise</span> <span class="hlt">sources</span> were programmed to predict aircraft <span class="hlt">noise</span> levels either in flight or in ground tests. The <span class="hlt">noise</span> <span class="hlt">sources</span> include fan inlet and exhaust, jet, flap (for powered lift), core (combustor), turbine, and <span class="hlt">airframe</span>. <span class="hlt">Noise</span> propagation corrections are available for atmospheric attenuation, ground reflections, extra ground attenuation, and shielding. Outputs can include spectra, overall sound pressure level, perceived <span class="hlt">noise</span> level, tone-weighted perceived <span class="hlt">noise</span> level, and effective perceived <span class="hlt">noise</span> level at locations specified by the user. Footprint contour coordinates and approximate footprint areas can also be calculated. Inputs and outputs can be in either System International or U.S. customary units. The subroutines for each <span class="hlt">noise</span> <span class="hlt">source</span> and propagation correction are described. A complete listing is given.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19820024506','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19820024506"><span>Integrated <span class="hlt">airframe</span> propulsion control</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Fennell, R. E.; Black, S. B.</p> <p>1982-01-01</p> <p>Perturbation equations which describe flight dynamics and engine operation about a given operating point are combined to form an integrated aircraft/propulsion system model. Included in the model are the dependence of aerodynamic coefficients upon atmospheric variables along with the dependence of engine variables upon flight condition and inlet performance. An off-design engine performance model is used to identify interaction parameters in the model. Inclusion of subsystem interaction effects introduces coupling between flight and propulsion variables. To analyze interaction effects on control, consideration is first given to control requirements for separate flight and engine models. For the separate <span class="hlt">airframe</span> model, feedback control provides substantial improvement in short period damping. For the integrated system, feedback control compensates for the coupling present in the model and provides good overall system stability. However, this feedback control law involves many non-zero gains. Analysis of suboptimal control strategies indicates that performance of the closed loop integrated system can be maintained with a feedback matrix in which the number of non-zero gains is small relative to the number of components in the feedback matrix.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23505502','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23505502"><span>MEG <span class="hlt">source</span> localization using invariance of <span class="hlt">noise</span> space.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhang, Junpeng; Raij, Tommi; Hämäläinen, Matti; Yao, Dezhong</p> <p>2013-01-01</p> <p>We propose INvariance of <span class="hlt">Noise</span> (INN) space as a novel method for <span class="hlt">source</span> localization of magnetoencephalography (MEG) data. The method is based on the fact that modulations of <span class="hlt">source</span> strengths across time change the energy in signal subspace but leave the <span class="hlt">noise</span> subspace invariant. We compare INN with classical MUSIC, RAP-MUSIC, and beamformer approaches using simulated data while varying signal-to-<span class="hlt">noise</span> ratios as well as distance and temporal correlation between two <span class="hlt">sources</span>. We also demonstrate the utility of INN with actual auditory evoked MEG responses in eight subjects. In all cases, INN performed well, especially when the <span class="hlt">sources</span> were closely spaced, highly correlated, or one <span class="hlt">source</span> was considerably stronger than the other.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20130013993','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130013993"><span>Open Rotor Aeroacoustic Installation Effects for Conventional and Unconventional <span class="hlt">Airframes</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Czech, Michael J.; Thomas, Russell H.</p> <p>2013-01-01</p> <p>As extensive experimental campaign was performed to study the aeroacoustic installation effects of an open rotor with respect to both a conventional tube and wing type <span class="hlt">airframe</span> and an unconventional hybrid wing body <span class="hlt">airframe</span>. The open rotor rig had two counter rotating rows of blades each with eight blades of a design originally flight tested in the 1980s. The aeroacoustic installation effects measured in an aeroacoustic wind tunnel included those from flow effects due to inflow distortion or wake interaction and acoustic propagation effects such as shielding and reflection. The objective of the test campaign was to quantify the installation effects for a wide range of parameters and configurations derived from the two <span class="hlt">airframe</span> types. For the conventional <span class="hlt">airframe</span>, the open rotor was positioned in increments in front of and then over the main wing and then in positions representative of tail mounted aircraft with a conventional tail, a T-tail and a U-tail. The interaction of the wake of the open rotor as well as acoustic scattering results in an increase of about 10 dB when the rotor is positioned in front of the main wing. When positioned over the main wing a substantial amount of <span class="hlt">noise</span> reduction is obtained and this is also observed for tail-mounted installations with a large U-tail. For the hybrid wing body <span class="hlt">airframe</span>, the open rotor was positioned over the <span class="hlt">airframe</span> along the centerline as well as off-center representing a twin engine location. A primary result was the documentation of the <span class="hlt">noise</span> reduction from shielding as a function of the location of the open rotor upstream of the trailing edge of the hybrid wing body. The effects from vertical surfaces and elevon deflection were also measured. Acoustic lining was specially designed and inserted flush with the elevon and <span class="hlt">airframe</span> surface, the result was an additional reduction in open rotor <span class="hlt">noise</span> propagating to the far field microphones. Even with the older blade design used, the experiment provided</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080007425','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080007425"><span>Active <span class="hlt">noise</span> control using <span class="hlt">noise</span> <span class="hlt">source</span> having adaptive resonant frequency tuning through variable ring loading</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pla, Frederic G. (Inventor); Rajiyah, Harindra (Inventor); Renshaw, Anthony A. (Inventor); Hedeen, Robert A. (Inventor)</p> <p>1995-01-01</p> <p>A <span class="hlt">noise</span> <span class="hlt">source</span> for an aircraft engine active <span class="hlt">noise</span> cancellation system in which the resonant frequency of <span class="hlt">noise</span> radiating structure is tuned to permit <span class="hlt">noise</span> cancellation over a wide range of frequencies. The resonant frequency of the <span class="hlt">noise</span> radiating structure is tuned by a plurality of drivers arranged to contact the <span class="hlt">noise</span> radiating structure. Excitation of the drivers causes expansion or contraction of the drivers, thereby varying the edge loading applied to the <span class="hlt">noise</span> radiating structure. The drivers are actuated by a controller which receives input of a feedback signal proportional to displacement of the <span class="hlt">noise</span> radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the drivers, causing them to expand or contract. The <span class="hlt">noise</span> radiating structure may be either the outer shroud of the engine or a ring mounted flush with an inner wall of the shroud or disposed in the interior of the shroud.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20120006513','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20120006513"><span>Sub-Shot <span class="hlt">Noise</span> Power <span class="hlt">Source</span> for Microelectronics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Strekalov, Dmitry V.; Yu, Nan; Mansour, Kamjou</p> <p>2011-01-01</p> <p>Low-current, high-impedance microelectronic devices can be affected by electric current shot <span class="hlt">noise</span> more than they are affected by Nyquist <span class="hlt">noise</span>, even at room temperature. An approach to implementing a sub-shot <span class="hlt">noise</span> current <span class="hlt">source</span> for powering such devices is based on direct conversion of amplitude-squeezed light to photocurrent. The phenomenon of optical squeezing allows for the optical measurements below the fundamental shot <span class="hlt">noise</span> limit, which would be impossible in the domain of classical optics. This becomes possible by affecting the statistical properties of photons in an optical mode, which can be considered as a case of information encoding. Once encoded, the information describing the photon (or any other elementary excitations) statistics can be also transmitted. In fact, it is such information transduction from optics to an electronics circuit, via photoelectric effect, that has allowed the observation of the optical squeezing. It is very difficult, if not technically impossible, to directly measure the statistical distribution of optical photons except at extremely low light level. The photoelectric current, on the other hand, can be easily analyzed using RF spectrum analyzers. Once it was observed that the photocurrent <span class="hlt">noise</span> generated by a tested light <span class="hlt">source</span> in question is below the shot <span class="hlt">noise</span> limit (e.g. produced by a coherent light beam), it was concluded that the light <span class="hlt">source</span> in question possess the property of amplitude squeezing. The main novelty of this technology is to turn this well-known information transduction approach around. Instead of studying the statistical property of an optical mode by measuring the photoelectron statistics, an amplitude-squeezed light <span class="hlt">source</span> and a high-efficiency linear photodiode are used to generate photocurrent with sub-Poissonian electron statistics. By powering microelectronic devices with this current <span class="hlt">source</span>, their performance can be improved, especially their <span class="hlt">noise</span> parameters. Therefore, a room-temperature sub</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040070765','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040070765"><span>Jet <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Using Linear Phased Array</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Agboola, Ferni A.; Bridges, James</p> <p>2004-01-01</p> <p>A study was conducted to further clarify the interpretation and application of linear phased array microphone results, for localizing aeroacoustics <span class="hlt">sources</span> in aircraft exhaust jet. Two model engine nozzles were tested at varying power cycles with the array setup parallel to the jet axis. The array position was varied as well to determine best location for the array. The results showed that it is possible to resolve jet <span class="hlt">noise</span> <span class="hlt">sources</span> with bypass and other components separation. The results also showed that a focused near field image provides more realistic <span class="hlt">noise</span> <span class="hlt">source</span> localization at low to mid frequencies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20070007329','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20070007329"><span><span class="hlt">Source</span> <span class="hlt">Noise</span> Modeling Efforts for Fan <span class="hlt">Noise</span> in NASA Research Programs</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Huff, Dennis L.</p> <p>2006-01-01</p> <p>There has been considerable progress made in fan <span class="hlt">noise</span> prediction over the past 15 years. NASA has conducted and sponsored research that has improved both tone and broadband fan <span class="hlt">noise</span> prediction methods. This presentation highlights progress in these areas with emphasis on rotor/stator interaction <span class="hlt">noise</span> <span class="hlt">sources</span>. Tone <span class="hlt">noise</span> predictions are presented for an advanced prediction code called "LINFLUX". Comparisons with data are" included for individual fan duct modes. There has also been considerable work developing new fan broadband <span class="hlt">noise</span> prediction codes and validation data from wind tunnel model tests. Results from several code validation exercises are presented that show improvement of predicted sound power levels. A summary is included with recommendations for future work.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_6 --> <div id="page_7" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="121"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20170001228','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20170001228"><span>Computational Modeling of a Mechanized Benchtop Apparatus for Leading-Edge Slat <span class="hlt">Noise</span> Treatment Device Prototypes</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Turner, Travis L.; Moore, James B.; Long, David L.</p> <p>2017-01-01</p> <p><span class="hlt">Airframe</span> <span class="hlt">noise</span> is a growing concern in the vicinity of airports because of population growth and gains in engine <span class="hlt">noise</span> reduction that have rendered the <span class="hlt">airframe</span> an equal contributor during the approach and landing phases of flight for many transport aircraft. The leading-edge-slat device of a typical high-lift system for transport aircraft is a prominent <span class="hlt">source</span> of <span class="hlt">airframe</span> <span class="hlt">noise</span>. Two technologies have significant potential for slat <span class="hlt">noise</span> reduction; the slat-cove filler (SCF) and the slat-gap filler (SGF). Previous work was done on a 2D section of a transport-aircraft wing to demonstrate the implementation feasibility of these concepts. Benchtop hardware was developed in that work for qualitative parametric study. The benchtop models were mechanized for quantitative measurements of performance. Computational models of the mechanized benchtop apparatus for the SCF were developed and the performance of the system for five different SCF assemblies is demonstrated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020059663','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020059663"><span>General Aviation Interior <span class="hlt">Noise</span>. Part 1; <span class="hlt">Source</span>/Path Identification</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Unruh, James F.; Till, Paul D.; Palumbo, Daniel L. (Technical Monitor)</p> <p>2002-01-01</p> <p>There were two primary objectives of the research effort reported herein. The first objective was to identify and evaluate <span class="hlt">noise</span> <span class="hlt">source</span>/path identification technology applicable to single engine propeller driven aircraft that can be used to identify interior <span class="hlt">noise</span> <span class="hlt">sources</span> originating from structure-borne engine/propeller vibration, airborne propeller transmission, airborne engine exhaust <span class="hlt">noise</span>, and engine case radiation. The approach taken to identify the contributions of each of these possible <span class="hlt">sources</span> was first to conduct a Principal Component Analysis (PCA) of an in-flight <span class="hlt">noise</span> and vibration database acquired on a Cessna Model 182E aircraft. The second objective was to develop and evaluate advanced technology for <span class="hlt">noise</span> <span class="hlt">source</span> ranking of interior panel groups such as the aircraft windshield, instrument panel, firewall, and door/window panels within the cabin of a single engine propeller driven aircraft. The technology employed was that of Acoustic Holography (AH). AH was applied to the test aircraft by acquiring a series of in-flight microphone array measurements within the aircraft cabin and correlating the measurements via PCA. The <span class="hlt">source</span> contributions of the various panel groups leading to the array measurements were then synthesized by solving the inverse problem using the boundary element model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850004526','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850004526"><span>Algorithm for astronomical, point <span class="hlt">source</span>, signal to <span class="hlt">noise</span> ratio calculations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jayroe, R. R.; Schroeder, D. J.</p> <p>1984-01-01</p> <p>An algorithm was developed to simulate the expected signal to <span class="hlt">noise</span> ratios as a function of observation time in the charge coupled device detector plane of an optical telescope located outside the Earth's atmosphere for a signal star, and an optional secondary star, embedded in a uniform cosmic background. By choosing the appropriate input values, the expected point <span class="hlt">source</span> signal to <span class="hlt">noise</span> ratio can be computed for the Hubble Space Telescope using the Wide Field/Planetary Camera science instrument.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004RScI...75.1323R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004RScI...75.1323R"><span>Low flicker-<span class="hlt">noise</span> amplifier for 50 Ω <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rubiola, Enrico; Lardet-Vieudrin, Franck</p> <p>2004-05-01</p> <p>This article analyzes the design of a low-<span class="hlt">noise</span> amplifier intended as the input front-end for the measurement of the low-frequency components (below 10 Hz) of a 50 Ω <span class="hlt">source</span>. Low residual flicker is the main desired performance. This feature can only be appreciated if white <span class="hlt">noise</span> is sufficiently low, and if an appropriate design ensures dc stability. An optimal solution is proposed, in which the low-<span class="hlt">noise</span> and dc-stability features are achieved at a reasonable complexity. Gain is accurate to more than 100 kHz, which makes the amplifier an appealing external front-end for fast Fourier transform (FFT) analyzers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012PhBio...9b6002N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012PhBio...9b6002N"><span>Isolating intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span> in a stochastic genetic switch</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Newby, Jay M.</p> <p>2012-04-01</p> <p>The stochastic mutual repressor model is analysed using perturbation methods. This simple model of a gene circuit consists of two genes and three promotor states. Either of the two protein products can dimerize, forming a repressor molecule that binds to the promotor of the other gene. When the repressor is bound to a promotor, the corresponding gene is not transcribed and no protein is produced. Either one of the promotors can be repressed at any given time or both can be unrepressed, leaving three possible promotor states. This model is analysed in its bistable regime in which the deterministic limit exhibits two stable fixed points and an unstable saddle, and the case of small <span class="hlt">noise</span> is considered. On small timescales, the stochastic process fluctuates near one of the stable fixed points, and on large timescales, a metastable transition can occur, where fluctuations drive the system past the unstable saddle to the other stable fixed point. To explore how different intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span> affect these transitions, fluctuations in protein production and degradation are eliminated, leaving fluctuations in the promotor state as the only <span class="hlt">source</span> of <span class="hlt">noise</span> in the system. The process without protein <span class="hlt">noise</span> is then compared to the process with weak protein <span class="hlt">noise</span> using perturbation methods and Monte Carlo simulations. It is found that some significant differences in the random process emerge when the intrinsic <span class="hlt">noise</span> <span class="hlt">source</span> is removed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20030003692','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030003692"><span>Fan <span class="hlt">Noise</span> <span class="hlt">Source</span> Diagnostic Test Computation of Rotor Wake Turbulence <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nallasamy, M.; Envia, E.; Thorp, S. A.; Shabbir, A.</p> <p>2002-01-01</p> <p>An important <span class="hlt">source</span> mechanism of fan broadband <span class="hlt">noise</span> is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband <span class="hlt">noise</span> model that utilizes computed rotor flow turbulence from a RANS code is used to predict fan broadband <span class="hlt">noise</span> spectra. The <span class="hlt">noise</span> model is employed to examine the broadband <span class="hlt">noise</span> characteristics of the 22-inch <span class="hlt">Source</span> Diagnostic Test fan rig for which broadband <span class="hlt">noise</span> data were obtained in wind tunnel tests at the NASA Glenn Research Center. A 9-case matrix of three outlet guide vane configurations at three representative fan tip speeds are considered. For all cases inlet and exhaust acoustic power spectra are computed and compared with the measured spectra where possible. In general, the acoustic power levels and shape of the predicted spectra are in good agreement with the measured data. The predicted spectra show the experimentally observed trends with fan tip speed, vane count, and vane sweep. The results also demonstrate the validity of using CFD-based turbulence information for fan broadband <span class="hlt">noise</span> calculations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770003071','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770003071"><span>New developments in blown flap <span class="hlt">noise</span> technology</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gibson, J. S.</p> <p>1976-01-01</p> <p>The <span class="hlt">noise</span> technology relating to blown-flap systems is reviewed. There are three general <span class="hlt">sources</span> of <span class="hlt">noise</span>: turbomachinery, <span class="hlt">airframe</span>, and the interaction <span class="hlt">noise</span> of the jet blowing on the flaps. The latter <span class="hlt">noise-source</span> area is the most critical and the main subject dicussed. Characteristics of lower surface blown and upper surface blown systems are described, including <span class="hlt">noise</span> spectra, directivity, jet velocity characteristics, aircraft geometric variation effects, and aircraft forward speed effects. <span class="hlt">Noise</span> reduction concepts are described, including slowing down the jet flow field by devices and engine cycle modifications, structural geometry and shielding modifications, local flow field modifications of the passive and active type, and the absorption of <span class="hlt">noise</span>. It is concluded that, while there has been considerable progress in the past several years, low <span class="hlt">noise</span> characteristics in blown flap aircraft must be largely built in by better application of low <span class="hlt">noise</span> principles during the design.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19810012301','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19810012301"><span>NASA progress in aircraft <span class="hlt">noise</span> prediction</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Raney, J. P.; Padula, S. L.; Zorumski, W. E.</p> <p>1981-01-01</p> <p>Langley Research Center efforts to develop a methodology for predicting the effective perceived <span class="hlt">noise</span> level (EPNL) produced by jet-powered CTOL aircraft to an accuracy of + or - 1.5 dB are summarized with emphasis on the aircraft <span class="hlt">noise</span> prediction program (ANOPP) which contains a complete set of prediction methods for CTOL aircraft including propulsion system <span class="hlt">noise</span> <span class="hlt">sources</span>, aerodynamic or <span class="hlt">airframe</span> <span class="hlt">noise</span> <span class="hlt">sources</span>, forward speed effects, a layered atmospheric model with molecular absorption, ground impedance effects including excess ground attenuation, and a received <span class="hlt">noise</span> contouring capability. The present state of ANOPP is described and its accuracy and applicability to the preliminary aircraft design process is assessed. Areas are indicated where further theoretical and experimental research on <span class="hlt">noise</span> prediction are needed. Topics covered include the elements of the <span class="hlt">noise</span> prediction problem which are incorporated in ANOPP, results of comparisons of ANOPP calculations with measured <span class="hlt">noise</span> levels, and progress toward treating <span class="hlt">noise</span> as a design constraint in aircraft system studies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22280610','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22280610"><span>Perceptual interaction of the harmonic <span class="hlt">source</span> and <span class="hlt">noise</span> in voice.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kreiman, Jody; Gerratt, Bruce R</p> <p>2012-01-01</p> <p>Although the amount of inharmonic energy (<span class="hlt">noise</span>) present in a human voice is an important determinant of vocal quality, little is known about the perceptual interaction between harmonic and inharmonic aspects of the voice <span class="hlt">source</span>. This paper reports three experiments investigating this issue. Results indicate that perception of the harmonic slope and of <span class="hlt">noise</span> levels are both influenced by complex interactions between the spectral shape and relative levels of harmonic and <span class="hlt">noise</span> energy in the voice <span class="hlt">source</span>. Just-noticeable differences (JNDs) for the <span class="hlt">noise</span>-to-harmonics ratio (NHR) varied significantly with the NHR and harmonic spectral slope, but NHR had no effect on JNDs for NHR when harmonic slopes were steepest, and harmonic slope had no effect when NHRs were highest. Perception of changes in the harmonic <span class="hlt">source</span> slope depended on NHR and on the harmonic <span class="hlt">source</span> slope: JNDs increased when spectra rolled off steeply, with this effect in turn depending on NHR. Finally, all effects were modulated by the shape of the <span class="hlt">noise</span> spectrum. It thus appears that, beyond masking, understanding perception of individual parameters requires knowledge of the acoustic context in which they function, consistent with the view that voices are integral patterns that resist decomposition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AIPA....7b5014M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AIPA....7b5014M"><span>Developing general acoustic model for <span class="hlt">noise</span> <span class="hlt">sources</span> and parameters estimation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Madoliat, Reza; Nouri, Nowrouz Mohammad; Rahrovi, Ali</p> <p>2017-02-01</p> <p><span class="hlt">Noise</span> measured at various points around the environment can be evaluated by a series of acoustic <span class="hlt">sources</span>. Acoustic <span class="hlt">sources</span> with wide surface can be broken down in fluid environment using some smaller acoustic <span class="hlt">sources</span>. The aim of this study is to make a model to indicate the type, number, direction, position and strength of these <span class="hlt">sources</span> in a way that the main sound and the sound of equivalent <span class="hlt">sources</span> match together in an acceptable way. When position and direction of the <span class="hlt">source</span> is given, the strength of the <span class="hlt">source</span> can be found using inverse method. On the other hand, considering the non-uniqueness of solution in inverse method, a different acoustic strength is obtained for the <span class="hlt">sources</span> if different positions are selected. Selecting an arrangement of general <span class="hlt">source</span> and using the optimization algorithm, the least possible mismatch between the main sound and the sound of equivalent <span class="hlt">sources</span> can be achieved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.S51E..02S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.S51E..02S"><span>Seismic <span class="hlt">noise</span> frequency dependent P and S wave <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stutzmann, E.; Schimmel, M.; Gualtieri, L.; Farra, V.; Ardhuin, F.</p> <p>2013-12-01</p> <p>Seismic <span class="hlt">noise</span> in the period band 3-10 sec is generated in the oceans by the interaction of ocean waves. <span class="hlt">Noise</span> signal is dominated by Rayleigh waves but body waves can be extracted using a beamforming approach. We select the TAPAS array deployed in South Spain between June 2008 and September 2009 and we use the vertical and horizontal components to extract <span class="hlt">noise</span> P and S waves, respectively. Data are filtered in narrow frequency bands and we select beam azimuths and slownesses that correspond to the largest continuous <span class="hlt">sources</span> per day. Our procedure automatically discard earthquakes which are localized during short time durations. Using this approach, we detect many more <span class="hlt">noise</span> P-waves than S-waves. <span class="hlt">Source</span> locations are determined by back-projecting the detected slowness/azimuth. P and S waves are generated in nearby areas and both <span class="hlt">source</span> locations are frequency dependent. Long period <span class="hlt">sources</span> are dominantly in the South Atlantic and Indian Ocean whereas shorter period <span class="hlt">sources</span> are rather in the North Atlantic Ocean. We further show that the detected S-waves are dominantly Sv-waves. We model the observed body waves using an ocean wave model that takes into account all possible wave interactions including coastal reflection. We use the wave model to separate direct and multiply reflected phases for P and S waves respectively. We show that in the South Atlantic the complex <span class="hlt">source</span> pattern can be explained by the existence of both coastal and pelagic <span class="hlt">sources</span> whereas in the North Atlantic most body wave <span class="hlt">sources</span> are pelagic. For each detected <span class="hlt">source</span>, we determine the equivalent <span class="hlt">source</span> magnitude which is compared to the model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880053218&hterms=james+stewart&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Djames%2Bstewart','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880053218&hterms=james+stewart&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Djames%2Bstewart"><span><span class="hlt">Noise</span> tube <span class="hlt">sources</span> for the far IR and millimeter region</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Moller, K. D.; Zoeller, R. G.; Ugras, N. G.; Zablocky, P.; Heaney, James B.; Stewart, K. P.; Boucarut, R. A.</p> <p>1988-01-01</p> <p>The radiant output of a <span class="hlt">noise</span> tube designed for the 90-140-GHz (3.3-2.1-mm) frequency range has been compared with that from mercury lamps over the wavelength region from 0.4 to about 6 mm. Lamellar grating and Michelson Fourier transform spectrometers were used in conjunction with He cooled bolometers of NEP from 10 to the -12th to 10 to the -14th W/sq rt H2 to measure relative spectral irradiance. With this instrumental arrangement, the radiant power emitted by the <span class="hlt">noise</span> tube was observed to be less than that from a mercury lamp, at least to a 3-mm wavelength, but it produced less <span class="hlt">source</span> <span class="hlt">noise</span> than an ac operated mercury lamp. When the <span class="hlt">noise</span> tube operating current was reduced, the spectral irradiance peak shifted to longer wavelengths.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/814835','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/814835"><span>Review of Subcritical <span class="hlt">Source</span>-Driven <span class="hlt">Noise</span> Analysis Measurements</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Valentine, T.E.</p> <p>1999-11-24</p> <p>Subcritical <span class="hlt">source</span>-driven <span class="hlt">noise</span> measurements are simultaneous Rossi-{alpha} and randomly pulsed neutron measurements that provide measured quantities that can be related to the subcritical neutron multiplication factor. In fact, subcritical <span class="hlt">source</span>-driven <span class="hlt">noise</span> measurements should be performed in lieu of Rossi-{alpha} measurements because of the additional information that is obtained from <span class="hlt">noise</span> measurements such as the spectral ratio and the coherence functions. The basic understanding of <span class="hlt">source</span>-driven <span class="hlt">noise</span> analysis measurements can be developed from a point reactor kinetics model to demonstrate how the measured quantities relate to the subcritical neutron multiplication factor. More elaborate models can also be developed using a generalized stochastic model. These measurements can be simulated using Monte Carlo codes to determine the subcritical neutron multiplication factor or to determine the sensitivity of calculations to nuclear cross section data. The interpretation of the measurement using a Monte Carlo method is based on a perturbation model for the relationship between the spectral ratio and the subcritical neutron multiplication factor. The subcritical <span class="hlt">source</span>-driven <span class="hlt">noise</span> measurement has advantages over other subcritical measurement methods in that reference measurements at delayed critical are not required for interpreting the measurements. Therefore, benchmark or in-situ subcritical measurements can be performed outside a critical experiment facility. Furthermore, a certain ratio of frequency spectra has been shown to be independent of detection efficiency thereby making the measurement more robust and unaffected by drifts or changes in instrumentation during the measurement. Criteria have been defined for application of this measurement method for benchmarks and in-situ subcritical measurements. An extension of the <span class="hlt">source</span>-driven subcritical <span class="hlt">noise</span> measurement has also been discussed that eliminates the few technical challenges for in-situ applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JSV...333.1356L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JSV...333.1356L"><span>Propeller sheet cavitation <span class="hlt">noise</span> <span class="hlt">source</span> modeling and inversion</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Keunhwa; Lee, Jaehyuk; Kim, Dongho; Kim, Kyungseop; Seong, Woojae</p> <p>2014-02-01</p> <p>Propeller sheet cavitation is the main contributor to high level of <span class="hlt">noise</span> and vibration in the after body of a ship. Full measurement of the cavitation-induced hull pressure over the entire surface of the affected area is desired but not practical. Therefore, using a few measurements on the outer hull above the propeller in a cavitation tunnel, empirical or semi-empirical techniques based on physical model have been used to predict the hull-induced pressure (or hull-induced force). In this paper, with the analytic <span class="hlt">source</span> model for sheet cavitation, a multi-parameter inversion scheme to find the positions of <span class="hlt">noise</span> <span class="hlt">sources</span> and their strengths is suggested. The inversion is posed as a nonlinear optimization problem, which is solved by the optimization algorithm based on the adaptive simplex simulated annealing algorithm. Then, the resulting hull pressure can be modeled with boundary element method from the inverted cavitation <span class="hlt">noise</span> <span class="hlt">sources</span>. The suggested approach is applied to the hull pressure data measured in a cavitation tunnel of the Samsung Heavy Industry. Two monopole <span class="hlt">sources</span> are adequate to model the propeller sheet cavitation <span class="hlt">noise</span>. The inverted <span class="hlt">source</span> information is reasonable with the cavitation dynamics of the propeller and the modeled hull pressure shows good agreement with cavitation tunnel experimental data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19800004564','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19800004564"><span>A study of the prediction of cruise <span class="hlt">noise</span> and laminar flow control <span class="hlt">noise</span> criteria for subsonic air transports</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Swift, G.; Mungur, P.</p> <p>1979-01-01</p> <p>General procedures for the prediction of component <span class="hlt">noise</span> levels incident upon <span class="hlt">airframe</span> surfaces during cruise are developed. Contributing <span class="hlt">noise</span> <span class="hlt">sources</span> are those associated with the propulsion system, the <span class="hlt">airframe</span> and the laminar flow control (LFC) system. Transformation procedures from the best prediction base of each <span class="hlt">noise</span> <span class="hlt">source</span> to the transonic cruise condition are established. Two approaches to LFC/acoustic criteria are developed. The first is a semi-empirical extension of the X-21 LFC/acoustic criteria to include sensitivity to the spectrum and directionality of the sound field. In the second, the more fundamental problem of how sound excites boundary layer disturbances is analyzed by deriving and solving an inhomogeneous Orr-Sommerfeld equation in which the <span class="hlt">source</span> terms are proportional to the production and dissipation of sound induced fluctuating vorticity. Numerical solutions are obtained and compared with corresponding measurements. Recommendations are made to improve and validate both the cruise <span class="hlt">noise</span> prediction methods and the LFC/acoustic criteria.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010RScI...81f4706W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010RScI...81f4706W"><span>A battery-based, low-<span class="hlt">noise</span> voltage <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wagner, Anke; Sturm, Sven; Schabinger, Birgit; Blaum, Klaus; Quint, Wolfgang</p> <p>2010-06-01</p> <p>A highly stable, low-<span class="hlt">noise</span> voltage <span class="hlt">source</span> was designed to improve the stability of the electrode bias voltages of a Penning trap. To avoid excess <span class="hlt">noise</span> and ground loops, the voltage <span class="hlt">source</span> is completely independent of the public electric network and uses a 12 V car battery to generate output voltages of ±15 and ±5 V. First, the dc supply voltage is converted into ac-voltage and gets amplified. Afterwards, the signal is rectified, filtered, and regulated to the desired output value. Each channel can deliver up to 1.5 A. The current as well as the battery voltage and the output voltages can be read out via a universal serial bus (USB) connection for monitoring purposes. With the presented design, a relative voltage stability of 7×10-7 over 6.5 h and a <span class="hlt">noise</span> level equal or smaller than 30 nV/√Hz is achieved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20590260','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20590260"><span>A battery-based, low-<span class="hlt">noise</span> voltage <span class="hlt">source</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wagner, Anke; Sturm, Sven; Schabinger, Birgit; Blaum, Klaus; Quint, Wolfgang</p> <p>2010-06-01</p> <p>A highly stable, low-<span class="hlt">noise</span> voltage <span class="hlt">source</span> was designed to improve the stability of the electrode bias voltages of a Penning trap. To avoid excess <span class="hlt">noise</span> and ground loops, the voltage <span class="hlt">source</span> is completely independent of the public electric network and uses a 12 V car battery to generate output voltages of +/-15 and +/-5 V. First, the dc supply voltage is converted into ac-voltage and gets amplified. Afterwards, the signal is rectified, filtered, and regulated to the desired output value. Each channel can deliver up to 1.5 A. The current as well as the battery voltage and the output voltages can be read out via a universal serial bus (USB) connection for monitoring purposes. With the presented design, a relative voltage stability of 7 x 10(-7) over 6.5 h and a <span class="hlt">noise</span> level equal or smaller than 30 nV/square root(Hz) is achieved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhDT........58O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhDT........58O"><span>Investigation of <span class="hlt">noise</span> <span class="hlt">sources</span> and propagation in external gear pumps</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Opperwall, Timothy J.</p> <p></p> <p>Oil hydraulics is widely accepted as the best technology for transmitting power in many engineering applications due to its advantages in power density, control, layout flexibility, and efficiency. Due to these advantages, hydraulic systems are present in many different applications including construction, agriculture, aerospace, automotive, forestry, medical, and manufacturing, just to identify a few. Many of these applications involve the systems in close proximity to human operators and passengers where <span class="hlt">noise</span> is one of the main constraints to the acceptance and spread of this technology. As a key component in power transfer, displacement machines can be major <span class="hlt">sources</span> of <span class="hlt">noise</span> in hydraulic systems. Thus, investigation into the <span class="hlt">sources</span> of <span class="hlt">noise</span> and discovering strategies to reduce <span class="hlt">noise</span> is a key part of applying fluid power systems to a wider range of applications, as well as improving the performance of current hydraulic systems. The present research aims to leverage previous efforts and develop new models and experimental techniques in the topic of <span class="hlt">noise</span> generation caused by hydrostatic units. This requires challenging and surpassing current accepted methods in the understanding of <span class="hlt">noise</span> in fluid power systems. This research seeks to expand on the previous experimental and modeling efforts by directly considering the effect that system and component design changes apply on the total sound power and the sound frequency components emitted from displacement machines and the attached lines. The case of external gear pumps is taken as reference for a new model to understand the generation and transmission of <span class="hlt">noise</span> from the <span class="hlt">sources</span> out to the environment. The lumped parameter model HYGESim (HYdraulic GEar machine Simulator) was expanded to investigate the dynamic forces on the solid bodies caused by the pump operation and to predict interactions with the attached system. Vibration and sound radiation were then predicted using a combined finite element and boundary</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19740002804','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19740002804"><span>Aircraft <span class="hlt">noise</span> reduction technology. [to show impact on individuals and communities, component <span class="hlt">noise</span> <span class="hlt">sources</span>, and operational procedures to reduce impact</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1973-01-01</p> <p>Aircraft and airport <span class="hlt">noise</span> reduction technology programs conducted by NASA are presented. The subjects discussed are: (1) effects of aircraft <span class="hlt">noise</span> on individuals and communities, (2) status of aircraft <span class="hlt">source</span> <span class="hlt">noise</span> technology, (3) operational procedures to reduce the impact of aircraft <span class="hlt">noise</span>, and (4) NASA relations with military services in aircraft <span class="hlt">noise</span> problems. References to more detailed technical literature on the subjects discussed are included.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002ASAJ..111.2336H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002ASAJ..111.2336H"><span>Identification and classification of <span class="hlt">noise</span> <span class="hlt">sources</span> in a chain conveyor</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Homer, John P.; Vipperman, Jeffrey S.; Reeves, Efrem R.</p> <p>2002-05-01</p> <p><span class="hlt">Noise</span> induced hearing loss (NIHL) is one of the most significant disabilities of workers in the mining industry. In response, the National Institute of Occupational Safety and Health (NIOSH) is conducting a study associated with mining equipment. This study outlines the analysis of a chain conveyor. Band-limited accelerometer, sound-intensity, far-field and near-field microphone measurements were taken along the conveyor section. The sound intensity measurements were used to identify areas with high <span class="hlt">noise</span> as well as to calculate and 1/3-octave sound power levels. The total sound power results were used to classify the dominant <span class="hlt">noise</span> <span class="hlt">sources</span> where the 1/3-octave sound power results were used to identify the most contributive frequency bands to the overall <span class="hlt">noise</span> of the system. Coherence analysis was performed between accelerometer and microphone measurements to identify structure-borne and air-borne <span class="hlt">noise</span> paths of the system. Summary results from the analysis include recommendations for transmission control and damping devices and their ability to reduce <span class="hlt">noise</span> to regulatory acceptable levels.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_7 --> <div id="page_8" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="141"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010APS..4CF.H5005M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010APS..4CF.H5005M"><span>A simple-<span class="hlt">source</span> model of military jet aircraft <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Morgan, Jessica; Gee, Kent L.; Neilsen, Tracianne; Wall, Alan T.</p> <p>2010-10-01</p> <p>The jet plumes produced by military jet aircraft radiate significant amounts of <span class="hlt">noise</span>. A need to better understand the characteristics of the turbulence-induced aeroacoustic <span class="hlt">sources</span> has motivated the present study. The purpose of the study is to develop a simple-<span class="hlt">source</span> model of jet <span class="hlt">noise</span> that can be compared to the measured data. The study is based off of acoustic data collected near a tied-down F-22 Raptor. The simplest model consisted of adjusting the origin of a monopole above a rigid planar reflector until the locations of the predicted and measured interference nulls matched. The model has developed into an extended Rayleigh distribution of partially correlated monopoles which fits the measured data from the F-22 significantly better. The results and basis for the model match the current prevailing theory that jet <span class="hlt">noise</span> consists of both correlated and uncorrelated <span class="hlt">sources</span>. In addition, this simple-<span class="hlt">source</span> model conforms to the theory that the peak <span class="hlt">source</span> location moves upstream with increasing frequency and lower engine conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.V33A2608M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.V33A2608M"><span>Volcanic jet <span class="hlt">noise</span>: infrasonic <span class="hlt">source</span> processes and atmospheric propagation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Matoza, R. S.; Fee, D.; Ogden, D. E.</p> <p>2011-12-01</p> <p>Volcanic eruption columns are complex flows consisting of (possibly supersonic) injections of ash-gas mixtures into the atmosphere. A volcanic eruption column can be modeled as a lower momentum-driven jet (the gas-thrust region), which transitions with altitude into a thermally buoyant plume. Matoza et al. [2009] proposed that broadband infrasonic signals recorded during this type of volcanic activity represent a low-frequency form of jet <span class="hlt">noise</span>. Jet <span class="hlt">noise</span> is produced at higher acoustic frequencies by smaller-scale man-made jet flows (e.g., turbulent jet flow from jet engines and rockets). Jet <span class="hlt">noise</span> generation processes could operate at larger spatial scales and produce infrasonic frequencies in the lower gas-thrust portion of the eruption column. Jet-<span class="hlt">noise</span>-like infrasonic signals have been observed at ranges of tens to thousands of kilometers from sustained volcanic explosions at Mount St. Helens, WA; Tungurahua, Ecuador; Redoubt, AK; and Sarychev Peak, Kuril Islands. Over such distances, the atmosphere cannot be considered homogeneous. Long-range infrasound propagation takes place primarily in waveguides formed by vertical gradients in temperature and horizontal winds, and exhibits strong spatiotemporal variability. The timing and location of volcanic explosions can be estimated from remote infrasonic data and could be used with ash cloud dispersion forecasts for hazard mitigation. <span class="hlt">Source</span> studies of infrasonic volcanic jet <span class="hlt">noise</span>, coupled with infrasound propagation modeling, hold promise for being able to constrain more detailed eruption jet parameters with remote, ground-based geophysical data. Here we present recent work on the generation and propagation of volcanic jet <span class="hlt">noise</span>. Matoza, R. S., D. Fee, M. A. Garcés, J. M. Seiner, P. A. Ramón, and M. A. H. Hedlin (2009), Infrasonic jet <span class="hlt">noise</span> from volcanic eruptions, Geophys. Res. Lett., 36, L08303, doi:10.1029/2008GL036486.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19840025761','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19840025761"><span>A formulation of rotor-<span class="hlt">airframe</span> coupling for design analysis of vibrations of helicopter <span class="hlt">airframes</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kvaternik, R. G.; Walton, W. C., Jr.</p> <p>1982-01-01</p> <p>A linear formulation of rotor <span class="hlt">airframe</span> coupling intended for vibration analysis in <span class="hlt">airframe</span> structural design is presented. The <span class="hlt">airframe</span> is represented by a finite element analysis model; the rotor is represented by a general set of linear differential equations with periodic coefficients; and the connections between the rotor and <span class="hlt">airframe</span> are specified through general linear equations of constraint. Coupling equations are applied to the rotor and <span class="hlt">airframe</span> equations to produce one set of linear differential equations governing vibrations of the combined rotor <span class="hlt">airframe</span> system. These equations are solved by the harmonic balance method for the system steady state vibrations. A feature of the solution process is the representation of the <span class="hlt">airframe</span> in terms of forced responses calculated at the rotor harmonics of interest. A method based on matrix partitioning is worked out for quick recalculations of vibrations in design studies when only relatively few <span class="hlt">airframe</span> members are varied. All relations are presented in forms suitable for direct computer implementation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20090030602','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20090030602"><span>Proceedings of the <span class="hlt">Airframe</span> Icing Workshop</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Colantonio, Ron O. (Editor)</p> <p>2009-01-01</p> <p>The NASA Glenn Research Center (GRC) has a long history of working with its partners towards the understanding of ice accretion formation and its associated degradation of aerodynamic performance. The June 9, 2009, <span class="hlt">Airframe</span> Icing Workshop held at GRC provided an opportunity to examine the current NASA <span class="hlt">airframe</span> icing research program and to dialogue on remaining and emerging <span class="hlt">airframe</span> icing issues and research with the external community. Some of the <span class="hlt">airframe</span> icing gaps identified included, but are not limited to, ice accretion simulation enhancements, three-dimensional benchmark icing database development, three-dimensional iced aerodynamics modeling, and technology development for a smart icing system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA468464','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA468464"><span>The Mitigation of Radio <span class="hlt">Noise</span> from External <span class="hlt">Sources</span> at Receiving Sites</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2007-05-01</p> <p>receiving site. Step 2—Understand <span class="hlt">sources</span> and <span class="hlt">source</span> mechanisms . Step 3—Locate <span class="hlt">sources</span>. Step 4—Identify the hardware which is generating <span class="hlt">noise</span>...Typical <span class="hlt">noise</span> problems at a receiving site are described in Section 1. Typical <span class="hlt">sources</span>, <span class="hlt">source</span> mechanisms and the temporal and spectral properties...Two common types of <span class="hlt">noise</span> will be encountered along with several less common types. These types are closely related to the <span class="hlt">source</span> mechanisms</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19830017227','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19830017227"><span>Limits on the prediction of helicopter rotor <span class="hlt">noise</span> using thickness and loading <span class="hlt">sources</span>: Validation of helicopter <span class="hlt">noise</span> prediction techniques</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Succi, G. P.</p> <p>1983-01-01</p> <p>The techniques of helicopter rotor <span class="hlt">noise</span> prediction attempt to describe precisely the details of the <span class="hlt">noise</span> field and remove the empiricisms and restrictions inherent in previous methods. These techniques require detailed inputs of the rotor geometry, operating conditions, and blade surface pressure distribution. The Farassat <span class="hlt">noise</span> prediction techniques was studied, and high speed helicopter <span class="hlt">noise</span> prediction using more detailed representations of the thickness and loading <span class="hlt">noise</span> <span class="hlt">sources</span> was investigated. These predictions were based on the measured blade surface pressures on an AH-1G rotor and compared to the measured sound field. Although refinements in the representation of the thickness and loading <span class="hlt">noise</span> <span class="hlt">sources</span> improve the calculation, there are still discrepancies between the measured and predicted sound field. Analysis of the blade surface pressure data indicates shocks on the blades, which are probably responsible for these discrepancies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880007253','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880007253"><span>Advanced composite <span class="hlt">airframe</span> program: Today's technology</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Good, Danny E.; Mazza, L. Thomas</p> <p>1988-01-01</p> <p>The Advanced Composite <span class="hlt">Airframe</span> Program (ACAP) was undertaken to demonstrate the advantages of the application of advanced composite materials and structural design concepts to the <span class="hlt">airframe</span> structure on helicopters designed to stringent military requirements. The primary goals of the program were the reduction of <span class="hlt">airframe</span> production costs and <span class="hlt">airframe</span> weight by 17 and 22 percent respectively. The ACAP effort consisted of a preliminary design phase, detail design, and design support testing, full-scale fabrication, laboratory testing, and a ground/flight test demonstration. Since the completion of the flight test demonstration programs follow-on efforts were initiated to more fully evaluate a variety of military characteristics of the composite <span class="hlt">airframe</span> structures developed under the original ACAP advanced development contracts. An overview of the ACAP program is provided and some of the design features, design support testing, manufacturing approaches, and the results of the flight test evaluation, as well as, an overview of Militarization Test and Evaluation efforts are described.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19990028361','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19990028361"><span><span class="hlt">Source</span> Methodology for Turbofan <span class="hlt">Noise</span> Prediction (<span class="hlt">SOURCE</span>3D Technical Documentation)</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Meyer, Harold D.</p> <p>1999-01-01</p> <p>This report provides the analytical documentation for the <span class="hlt">SOURCE</span>3D Rotor Wake/Stator Interaction Code. It derives the equations for the rotor scattering coefficients and stator <span class="hlt">source</span> vector and scattering coefficients that are needed for use in the TFANS (Theoretical Fan <span class="hlt">Noise</span> Design/Prediction System). <span class="hlt">SOURCE</span>3D treats the rotor and stator as isolated <span class="hlt">source</span> elements. TFANS uses this information, along with scattering coefficients for inlet and exit elements, and provides complete <span class="hlt">noise</span> solutions for turbofan engines. <span class="hlt">SOURCE</span>3D is composed of a collection of FORTRAN programs that have been obtained by extending the approach of the earlier V072 Rotor Wake/Stator Interaction Code. Similar to V072, it treats the rotor and stator as a collection of blades and vanes having zero thickness and camber contained in an infinite, hardwall annular duct. <span class="hlt">SOURCE</span>3D adds important features to the V072 capability-a rotor element, swirl flow and vorticity waves, actuator disks for flow turning, and combined rotor/actuator disk and stator/actuator disk elements. These items allow reflections from the rotor, frequency scattering, and mode trapping, thus providing more complete <span class="hlt">noise</span> predictions than previously. The code has been thoroughly verified through comparison with D.B. Hanson's CUP2D two- dimensional code using a narrow annulus test case.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160005092','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160005092"><span><span class="hlt">Noise</span> Scaling and Community <span class="hlt">Noise</span> Metrics for the Hybrid Wing Body Aircraft</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Burley, Casey L.; Brooks, Thomas F.; Hutcheson, Florence V.; Doty, Michael J.; Lopes, Leonard V.; Nickol, Craig L.; Vicroy, Dan D.; Pope, D. Stuart</p> <p>2014-01-01</p> <p>An aircraft system <span class="hlt">noise</span> assessment was performed for the hybrid wing body aircraft concept, known as the N2A-EXTE. This assessment is a result of an effort by NASA to explore a realistic HWB design that has the potential to substantially reduce <span class="hlt">noise</span> and fuel burn. Under contract to NASA, Boeing designed the aircraft using practical aircraft design princip0les with incorporation of <span class="hlt">noise</span> technologies projected to be available in the 2020 timeframe. NASA tested 5.8% scale-mode of the design in the NASA Langley 14- by 22-Foot Subsonic Tunnel to provide <span class="hlt">source</span> <span class="hlt">noise</span> directivity and installation effects for aircraft engine and <span class="hlt">airframe</span> configurations. Analysis permitted direct scaling of the model-scale jet, <span class="hlt">airframe</span>, and engine shielding effect measurements to full-scale. Use of these in combination with ANOPP predictions enabled computations of the cumulative (CUM) <span class="hlt">noise</span> margins relative to FAA Stage 4 limits. The CUM margins were computed for a baseline N2A-EXTE configuration and for configurations with added <span class="hlt">noise</span> reduction strategies. The strategies include reduced approach speed, over-the-rotor line and soft-vane fan technologies, vertical tail placement and orientation, and modified landing gear designs with fairings. Combining the inherent HWB engine shielding by the <span class="hlt">airframe</span> with added <span class="hlt">noise</span> technologies, the cumulative <span class="hlt">noise</span> was assessed at 38.7 dB below FAA Stage 4 certification level, just 3.3 dB short of the NASA N+2 goal of 42 dB. This new result shows that the NASA N+2 goal is approachable and that significant reduction in overall aircraft <span class="hlt">noise</span> is possible through configurations with <span class="hlt">noise</span> reduction technologies and operational changes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050175875','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050175875"><span>Fan <span class="hlt">Noise</span> <span class="hlt">Source</span> Diagnostic Test: Rotor Alone Aerodynamic Performance Results</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hughes, Christopher E.; Jeracki, Robert J.; Woodward, Richard P.; Miller, Christopher J.</p> <p>2005-01-01</p> <p>The aerodynamic performance of an isolated fan or rotor alone model was measured in the NASA Glenn Research Center 9- by 15- Foot Low Speed Wind Tunnel as part of the Fan Broadband <span class="hlt">Source</span> Diagnostic Test conducted at NASA Glenn. The <span class="hlt">Source</span> Diagnostic Test was conducted to identify the <span class="hlt">noise</span> <span class="hlt">sources</span> within a wind tunnel scale model of a turbofan engine and quantify their contribution to the overall system <span class="hlt">noise</span> level. The fan was part of a 1/5th scale model representation of the bypass stage of a current technology turbofan engine. For the rotor alone testing, the fan and nacelle, including the inlet, external cowl, and fixed area fan exit nozzle, were modeled in the test hardware; the internal outlet guide vanes located behind the fan were removed. Without the outlet guide vanes, the velocity at the nozzle exit changes significantly, thereby affecting the fan performance. As part of the investigation, variations in the fan nozzle area were tested in order to match as closely as possible the rotor alone performance with the fan performance obtained with the outlet guide vanes installed. The fan operating performance was determined using fixed pressure/temperature combination rakes and the corrected weight flow. The performance results indicate that a suitable nozzle exit was achieved to be able to closely match the rotor alone and fan/outlet guide vane configuration performance on the sea level operating line. A small shift in the slope of the sea level operating line was measured, which resulted in a slightly higher rotor alone fan pressure ratio at take-off conditions, matched fan performance at cutback conditions, and a slightly lower rotor alone fan pressure ratio at approach conditions. However, the small differences in fan performance at all fan conditions were considered too small to affect the fan acoustic performance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4014398','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4014398"><span>Axonal <span class="hlt">Noise</span> as a <span class="hlt">Source</span> of Synaptic Variability</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Neishabouri, Ali; Faisal, A. Aldo</p> <p>2014-01-01</p> <p>Post-synaptic potential (PSP) variability is typically attributed to mechanisms inside synapses, yet recent advances in experimental methods and biophysical understanding have led us to reconsider the role of axons as highly reliable transmission channels. We show that in many thin axons of our brain, the action potential (AP) waveform and thus the Ca++ signal controlling vesicle release at synapses will be significantly affected by the inherent variability of ion channel gating. We investigate how and to what extent fluctuations in the AP waveform explain observed PSP variability. Using both biophysical theory and stochastic simulations of central and peripheral nervous system axons from vertebrates and invertebrates, we show that channel <span class="hlt">noise</span> in thin axons (<1 µm diameter) causes random fluctuations in AP waveforms. AP height and width, both experimentally characterised parameters of post-synaptic response amplitude, vary e.g. by up to 20 mV and 0.5 ms while a single AP propagates in C-fibre axons. We show how AP height and width variabilities increase with a ¾ power-law as diameter decreases and translate these fluctuations into post-synaptic response variability using biophysical data and models of synaptic transmission. We find for example that for mammalian unmyelinated axons with 0.2 µm diameter (matching cerebellar parallel fibres) axonal <span class="hlt">noise</span> alone can explain half of the PSP variability in cerebellar synapses. We conclude that axonal variability may have considerable impact on synaptic response variability. Thus, in many experimental frameworks investigating synaptic transmission through paired-cell recordings or extracellular stimulation of presynaptic neurons, causes of variability may have been confounded. We thereby show how bottom-up aggregation of molecular <span class="hlt">noise</span> <span class="hlt">sources</span> contributes to our understanding of variability observed at higher levels of biological organisation. PMID:24809823</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150005710','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150005710"><span>The Prediction of Scattered Broadband Shock-Associated <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Miller, Steven A. E.</p> <p>2015-01-01</p> <p>A mathematical model is developed for the prediction of scattered broadband shock-associated <span class="hlt">noise</span>. Model arguments are dependent on the vector Green's function of the linearized Euler equations, steady Reynolds-averaged Navier-Stokes solutions, and the two-point cross-correlation of the equivalent <span class="hlt">source</span>. The equivalent <span class="hlt">source</span> is dependent on steady Reynolds-averaged Navier-Stokes solutions of the jet flow, that capture the nozzle geometry and <span class="hlt">airframe</span> surface. Contours of the time-averaged streamwise velocity component and turbulent kinetic energy are examined with varying <span class="hlt">airframe</span> position relative to the nozzle exit. Propagation effects are incorporated by approximating the vector Green's function of the linearized Euler equations. This approximation involves the use of ray theory and an assumption that broadband shock-associated <span class="hlt">noise</span> is relatively unaffected by the refraction of the jet shear layer. A non-dimensional parameter is proposed that quantifies the changes of the broadband shock-associated <span class="hlt">noise</span> <span class="hlt">source</span> with varying jet operating condition and <span class="hlt">airframe</span> position. Scattered broadband shock-associated <span class="hlt">noise</span> possesses a second set of broadband lobes that are due to the effect of scattering. Presented predictions demonstrate relatively good agreement compared to a wide variety of measurements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020084621','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020084621"><span>Fan <span class="hlt">Noise</span> <span class="hlt">Source</span> Diagnostic Test: Vane Unsteady Pressure Results</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Envia, Edmane</p> <p>2002-01-01</p> <p>To investigate the nature of fan outlet guide vane pressure fluctuations and their link to rotor-stator interaction <span class="hlt">noise</span>, time histories of vane fluctuating pressures were digitally acquired as part of the Fan <span class="hlt">Noise</span> <span class="hlt">Source</span> Diagnostic Test. Vane unsteady pressures were measured at seven fan tip speeds for both a radial and a swept vane configuration. Using time-domain averaging and spectral analysis, the blade passing frequency (BPF) harmonic and broadband contents of the vane pressures were individually analyzed. Significant Sound Pressure Level (SPL) reductions were observed for the swept vane relative to the radial vane for the BPF harmonics of vane pressure, but vane broadband reductions due to sweep turned out to be much smaller especially on an average basis. Cross-correlation analysis was used to establish the level of spatial coherence of broadband pressures between different locations on the vane and integral length scales of pressure fluctuations were estimated from these correlations. Two main results of this work are: (1) the average broadband level on the vane (in dB) increases linearly with the fan tip speed for both the radial and swept vanes, and (2) the broadband pressure distribution on the vane is nearly homogeneous and its integral length scale is a monotonically decreasing function of fan tip speed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880031424&hterms=hawking&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dhawking','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880031424&hterms=hawking&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dhawking"><span>Quadrupole <span class="hlt">source</span> in prediction of the <span class="hlt">noise</span> of rotating blades - A new <span class="hlt">source</span> description</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Farassat, F.</p> <p>1987-01-01</p> <p>The aim of this paper is to perform a theoretical study of the quadrupole term of the Ffowcs Williams-Hawkings (FW-H) equation to obtain practical results for applications to rotating blades. The quadrupole term of the FW-H equation is algebraically manipulated into volume, surface and line <span class="hlt">sources</span> using generalized function theory and differential geometry. The volume <span class="hlt">source</span> is of the type in Lighthill's jet <span class="hlt">noise</span> theory. The surface <span class="hlt">sources</span> are on the blade and shock surfaces and the line <span class="hlt">source</span> is at the trailing edge. It is shown that contribution of volume <span class="hlt">sources</span> in the boundary layer and wakes can be written in the form of surface integrals. It is argued that the surface and line <span class="hlt">sources</span> and the part of the volume <span class="hlt">sources</span> in the boundary layer, wakes and vortices near the blades should be sufficient in calculation of the <span class="hlt">noise</span> of high speed rotating blades. The integrals correspoding to the various <span class="hlt">sources</span> appearing in the formula for calculation of the acoustic pressure are briefly derived.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020053652','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020053652"><span>General Aviation Interior <span class="hlt">Noise</span>. Part 2; In-Flight <span class="hlt">Source</span>/Verification</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Unruh, James F.; Till, Paul D.; Palumbo, Daniel L. (Technical Monitor)</p> <p>2002-01-01</p> <p>The technical approach made use of the Cessna Model 182E aircraft used in the previous effort as a test bed for <span class="hlt">noise</span> control application. The present phase of the project reports on flight test results during application of various passive <span class="hlt">noise</span> treatments in an attempt to verify the <span class="hlt">noise</span> <span class="hlt">sources</span> and paths for the aircraft. The data presented establishes the level of interior <span class="hlt">noise</span> control that can be expected for various passive <span class="hlt">noise</span> control applications within the aircraft cabin. Subsequent testing will address specific testing to demonstrate the technology available to meet a specified level of <span class="hlt">noise</span> control by application of passive and/or active <span class="hlt">noise</span> control technology.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080047421','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080047421"><span>Separating Turbofan Engine <span class="hlt">Noise</span> <span class="hlt">Sources</span> Using Auto and Cross Spectra from Four Microphones</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Miles, Jeffrey Hilton</p> <p>2008-01-01</p> <p>The study of core <span class="hlt">noise</span> from turbofan engines has become more important as <span class="hlt">noise</span> from other <span class="hlt">sources</span> such as the fan and jet were reduced. A multiple-microphone and acoustic-<span class="hlt">source</span> modeling method to separate correlated and uncorrelated <span class="hlt">sources</span> is discussed. The auto- and cross spectra in the frequency range below 1000 Hz are fitted with a <span class="hlt">noise</span> propagation model based on a <span class="hlt">source</span> couplet consisting of a single incoherent monopole <span class="hlt">source</span> with a single coherent monopole <span class="hlt">source</span> or a <span class="hlt">source</span> triplet consisting of a single incoherent monopole <span class="hlt">source</span> with two coherent monopole point <span class="hlt">sources</span>. Examples are presented using data from a Pratt& Whitney PW4098 turbofan engine. The method separates the low-frequency jet <span class="hlt">noise</span> from the core <span class="hlt">noise</span> at the nozzle exit. It is shown that at low power settings, the core <span class="hlt">noise</span> is a major contributor to the <span class="hlt">noise</span>. Even at higher power settings, it can be more important than jet <span class="hlt">noise</span>. However, at low frequencies, uncorrelated broadband <span class="hlt">noise</span> and jet <span class="hlt">noise</span> become the important factors as the engine power setting is increased.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730023214','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730023214"><span>Aircraft <span class="hlt">noise</span> <span class="hlt">source</span> and computer programs - User's guide</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Crowley, K. C.; Jaeger, M. A.; Meldrum, D. F.</p> <p>1973-01-01</p> <p>The application of computer programs for predicting the <span class="hlt">noise</span>-time histories and <span class="hlt">noise</span> contours for five types of aircraft is reported. The aircraft considered are: (1) turbojet, (2) turbofan, (3) turboprop, (4) V/STOL, and (5) helicopter. Three principle considerations incorporated in the design of the <span class="hlt">noise</span> prediction program are core effectiveness, limited input, and variable output reporting.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28287041','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28287041"><span><span class="hlt">Noise</span> disturbance in open-plan study environments: a field study on <span class="hlt">noise</span> <span class="hlt">sources</span>, student tasks and room acoustic parameters.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Braat-Eggen, P Ella; van Heijst, Anne; Hornikx, Maarten; Kohlrausch, Armin</p> <p>2017-04-03</p> <p>The aim of this study is to gain more insight in the assessment of <span class="hlt">noise</span> in open-plan study environments and to reveal correlations between <span class="hlt">noise</span> disturbance experienced by students and the <span class="hlt">noise</span> <span class="hlt">sources</span> they perceive, the tasks they perform and the acoustic parameters of the open-plan study environment they work in. Data were collected in five open-plan study environments at universities in the Netherlands. A questionnaire was used to investigate student tasks, perceived sound <span class="hlt">sources</span> and their perceived disturbance, and sound measurements were performed to determine the room acoustic parameters. This study shows that 38% of the surveyed students are disturbed by background <span class="hlt">noise</span> in an open-plan study environment. Students are mostly disturbed by speech when performing complex cognitive tasks like studying for an exam, reading and writing. Significant but weak correlations were found between the room acoustic parameters and <span class="hlt">noise</span> disturbance of students. Practitioner Summary: A field study was conducted to gain more insight in the assessment of <span class="hlt">noise</span> in open-plan study environments at universities in the Netherlands. More than one third of the students was disturbed by <span class="hlt">noise</span>. An interaction effect was found for task type, <span class="hlt">source</span> type and room acoustic parameters.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SPIE.9783E..10L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SPIE.9783E..10L"><span><span class="hlt">Noise</span> characteristics of CT perfusion imaging: how does <span class="hlt">noise</span> propagate from <span class="hlt">source</span> images to final perfusion maps?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Ke; Chen, Guang-Hong</p> <p>2016-03-01</p> <p>Cerebral CT perfusion (CTP) imaging is playing an important role in the diagnosis and treatment of acute ischemic strokes. Meanwhile, the reliability of CTP-based ischemic lesion detection has been challenged due to the noisy appearance and low signal-to-<span class="hlt">noise</span> ratio of CTP maps. To reduce <span class="hlt">noise</span> and improve image quality, a rigorous study on the <span class="hlt">noise</span> transfer properties of CTP systems is highly desirable to provide the needed scientific guidance. This paper concerns how <span class="hlt">noise</span> in the CTP <span class="hlt">source</span> images propagates to the final CTP maps. Both theoretical deviations and subsequent validation experiments demonstrated that, the <span class="hlt">noise</span> level of background frames plays a dominant role in the <span class="hlt">noise</span> of the cerebral blood volume (CBV) maps. This is in direct contradiction with the general belief that <span class="hlt">noise</span> of non-background image frames is of greater importance in CTP imaging. The study found that when radiation doses delivered to the background frames and to all non-background frames are equal, lowest <span class="hlt">noise</span> variance is achieved in the final CBV maps. This novel equality condition provides a practical means to optimize radiation dose delivery in CTP data acquisition: radiation exposures should be modulated between background frames and non-background frames so that the above equality condition is satisïnAed. For several typical CTP acquisition protocols, numerical simulations and in vivo canine experiment demonstrated that <span class="hlt">noise</span> of CBV can be effectively reduced using the proposed exposure modulation method.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20136203','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20136203"><span><span class="hlt">Noise</span>-induced annoyance from transportation <span class="hlt">noise</span>: short-term responses to a single <span class="hlt">noise</span> <span class="hlt">source</span> in a laboratory.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kim, Jaehwan; Lim, Changwoo; Hong, Jiyoung; Lee, Soogab</p> <p>2010-02-01</p> <p>An experimental study was performed to compare the annoyances from civil-aircraft <span class="hlt">noise</span>, military-aircraft <span class="hlt">noise</span>, railway <span class="hlt">noise</span>, and road-traffic <span class="hlt">noise</span>. Two-way within-subjects designs were applied in this research. Fifty-two subjects, who were naive listeners, were given various stimuli with varying levels through a headphone in an anechoic chamber. Regardless of the frequency weighting network, even under the same average energy level, civil-aircraft <span class="hlt">noise</span> was the most annoying, followed by military-aircraft <span class="hlt">noise</span>, railway <span class="hlt">noise</span>, and road-traffic <span class="hlt">noise</span>. In particular, penalties in the time-averaged, A-weighted sound level (TAL) of about 8, 5, and 5 dB, respectively, were found in the civil-aircraft, military-aircraft, and railway <span class="hlt">noises</span>. The reason could be clarified through the high-frequency component and the variability in the level. When people were exposed to sounds with the same maximum A-weighted level, a railway bonus of about 3 dB was found. However, transportation <span class="hlt">noise</span> has been evaluated by the time-averaged A-weighted level in most countries. Therefore, in the present situation, the railway bonus is not acceptable for railway vehicles with diesel-electric engines.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_8 --> <div id="page_9" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="161"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19740003484','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19740003484"><span>Radially leaned outlet guide vanes for fan <span class="hlt">source</span> <span class="hlt">noise</span> reduction</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kazin, S. B.</p> <p>1973-01-01</p> <p>Two quiet engine program half scale fans one with a subsonic and the other with a supersonic fan tip speed at takeoff were run with 30 degree leaned and radial outlet guide vanes. Acoustic data at takeoff fan speed on the subsonic tip speed fan showed decreases in 200-foot sideline <span class="hlt">noise</span> of from 1 to 2 PNdb. The supersonic tip speed fan a takeoff fan speed, however, showed <span class="hlt">noise</span> increases of up 3 PNdb and a decrease in fan efficiency. At approach fan speed, the subsonic tip speed fan showed a <span class="hlt">noise</span> decrease of 2.3 PNdb at the 200-foot sideline maximum angle and an increase in efficiency. The supersonic tip speed fan showed <span class="hlt">noise</span> increase of 3.5 PNdb and no change in efficiency. The decrease in fan efficiency and the nature of the <span class="hlt">noise</span> increase largely high frequency broadband <span class="hlt">noise</span> lead to the speculation that an aerodynamic problem occurred.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.S34B..01F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.S34B..01F"><span><span class="hlt">Source</span>-structure trade-offs in ambient <span class="hlt">noise</span> correlations: Theory and numerical examples</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fichtner, A.; Sager, K.; Ermert, L. A.</p> <p>2015-12-01</p> <p>We analyse the physics and geometry of trade-offs between Earth structure and <span class="hlt">noise</span> <span class="hlt">sources</span> in inter-station <span class="hlt">noise</span> correlations. Our approach is based on the computation of off-diagonal Hessian elements that describe the extent to which variations in <span class="hlt">noise</span> <span class="hlt">sources</span> can compensate for variations in Earth structure without changing the misfit beyond the measurement uncertainty. Despite the fact that all ambient <span class="hlt">noise</span> inverse problems are special in terms of their receiver configuration and data, some general statements concerning <span class="hlt">source</span>-structure trade-offs can be made: (i) While <span class="hlt">source</span>-structure trade-offs may be reduced to some extent by clever measurement design, there are inherent trade-offs that can generally not be avoided. These inherent trade-offs may lead to a mispositioning of structural heterogeneities when the <span class="hlt">noise</span> <span class="hlt">source</span> distribution is unknown. (ii) When attenuation is weak, <span class="hlt">source</span>-structure trade-offs in ambient <span class="hlt">noise</span> correlations are a global phenomenon, meaning that there is no <span class="hlt">noise</span> <span class="hlt">source</span> perturbation that does not trade-off with some Earth structure, and vice versa. (iii) The most significant <span class="hlt">source</span>-structure trade-offs occur within two elliptically shaped regions connecting a potential <span class="hlt">noise</span> <span class="hlt">source</span> perturbation to each one of the receivers. (iv) Far from these elliptical regions, only small-scale structure can trade off against changes in the <span class="hlt">noise</span> <span class="hlt">source</span>. (v) While <span class="hlt">source</span>-structure trade-offs mostly decay with increasing attenuation, they are nearly unaffected by attenuation when the <span class="hlt">noise</span> <span class="hlt">source</span> perturbation is located near the receiver-receiver line. We complement these theoretical considerations by numerical experiments where we model ambient <span class="hlt">noise</span> correlations for arbitrary <span class="hlt">source</span> geometries. The experiments illustrate how and to which extent unknown <span class="hlt">noise</span> <span class="hlt">sources</span> may map into spurious Earth structure. This work is intended to contribute to the development of joint <span class="hlt">source</span>-structure inversions of ambient <span class="hlt">noise</span> correlations, and in particular</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5031880','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5031880"><span>/sup 252/Cf-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mihalczo, J.T.; King, W.T.; Blakeman, E.D.</p> <p>1985-01-01</p> <p>The /sup 252/Cf-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method has been tested in a wide variety of experiments that have indicated the broad range of applicability of the method. The neutron multiplication factor k/sub eff/ has been satisfactorily detemined for a variety of materials including uranium metal, light water reactor fuel pins, fissile solutions, fuel plates in water, and interacting cylinders. For a uranyl nitrate solution tank which is typical of a fuel processing or reprocessing plant, the k/sub eff/ values were satisfactorily determined for values between 0.92 and 0.5 using a simple point kinetics interpretation of the experimental data. The short measurement times, in several cases as low as 1 min, have shown that the development of this method can lead to a practical subcriticality monitor for many in-plant applications. The further development of the method will require experiments oriented toward particular applications including dynamic experiments and the development of theoretical methods to predict the experimental observables.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MarGR..37..257H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MarGR..37..257H"><span>The suppression of coherent <span class="hlt">noise</span> from another airgun <span class="hlt">source</span> in marine multi-channel seismic data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hsu, Ho-Han; Liu, Char-Shine; Chang, Jih-Hsin; Tsai, You-Tsung; Chiu, Shye-Donq</p> <p>2016-12-01</p> <p>During seismic investigations, multiple and unexpected <span class="hlt">sources</span> may cause serious interference on seismic records, and coherent <span class="hlt">noise</span> generated by another unwanted active <span class="hlt">source</span> could result in extremely poor data quality. Because airgun arrays have been widely used as the sound <span class="hlt">source</span> in marine seismic surveys, the <span class="hlt">noise</span> generated by another airgun array usually has similar characteristics to the primary signals in both frequency bands and wave forms, so the suppression of this type of coherent <span class="hlt">noise</span> is very difficult. In practice, seismic crews try to avoid conducting multiple surveys simultaneously in a same area, so the <span class="hlt">source</span> interference problem normally does not occur, and suppression of coherent <span class="hlt">noise</span> from another active <span class="hlt">source</span> has rarely been discussed and proposed before. This paper presents a dataset in which part of the records are contaminated by shot <span class="hlt">noise</span> from another seismic vessel, and proposes a hybrid approach to suppress the coherent <span class="hlt">noise</span> from that unwanted seismic <span class="hlt">source</span>. <span class="hlt">Noise</span> subtraction and primary signal preservation within different data properties are considered to begin the <span class="hlt">noise</span> suppression. Based on different <span class="hlt">noise</span> characteristics from various <span class="hlt">source</span> directions and wave propagation paths, coherence <span class="hlt">noise</span> can be separated from primary signals in frequency-wave number (F-K), frequency-time (F-T) and intercept time-slowness (tau-p) domains, respectively. This hybrid coherent <span class="hlt">noise</span> suppression approach involves applying three different filters, F-K, F-T and tau-p, to the contaminated dataset. Our results show that most of the coherent <span class="hlt">noise</span> generated by another seismic <span class="hlt">source</span> could be suppressed, and seismic images could be substantially improved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150010120','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150010120"><span>Jet-Surface Interaction Test: Phased Array <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Results</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Podboy, Gary</p> <p>2012-01-01</p> <p>Subsonic jets are relatively simple. The peak <span class="hlt">noise</span> <span class="hlt">source</span> location gradually moves upstream toward the nozzle as frequency increases. 2) Supersonic jets are more complicated. The peak <span class="hlt">noise</span> <span class="hlt">source</span> location moves downstream as frequency increases through a BBSN hump. 3) In both subsonic and supersonic jets the peak <span class="hlt">noise</span> <span class="hlt">source</span> location corresponding to a given frequency of <span class="hlt">noise</span> moves downstream as jet Mach number increases. 4) The <span class="hlt">noise</span> generated at a given frequency in a BBSN hump is generated by a small number of shocks, not from all the shocks at the same time. 5) Single microphone spectrum levels decrease when the <span class="hlt">noise</span> <span class="hlt">source</span> locations measured with the phased array are blocked by a shielding surface. This consistency validates the phased array data and the stationary monopole <span class="hlt">source</span> model used to process it. 6) Reflecting surface data illustrate that the law of reflection must be satisfied for <span class="hlt">noise</span> to reflect off a surface toward an observer. Depending on the relative locations of the jet, the surface and the observer only some of the jet <span class="hlt">noise</span> <span class="hlt">sources</span> may satisfy this requirement. 7) The low frequency <span class="hlt">noise</span> created when a jet flow impinges on a surface comes primarily from the trailing edge regardless of the axial extent impacted by the flow.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110015387','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110015387"><span>Embedded Acoustic Sensor Array for Engine Fan <span class="hlt">Noise</span> <span class="hlt">Source</span> Diagnostic Test: Feasibility of <span class="hlt">Noise</span> Telemetry via Wireless Smart Sensors</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zaman, Afroz; Bauch, Matthew; Raible, Daniel</p> <p>2011-01-01</p> <p>Aircraft engines have evolved into a highly complex system to meet ever-increasing demands. The evolution of engine technologies has primarily been driven by fuel efficiency, reliability, as well as engine <span class="hlt">noise</span> concerns. One of the <span class="hlt">sources</span> of engine <span class="hlt">noise</span> is pressure fluctuations that are induced on the stator vanes. These local pressure fluctuations, once produced, propagate and coalesce with the pressure waves originating elsewhere on the stator to form a spinning pressure pattern. Depending on the duct geometry, air flow, and frequency of fluctuations, these spinning pressure patterns are self-sustaining and result in <span class="hlt">noise</span> which eventually radiate to the far-field from engine. To investigate the nature of vane pressure fluctuations and the resulting engine <span class="hlt">noise</span>, unsteady pressure signatures from an array of embedded acoustic sensors are recorded as a part of vane <span class="hlt">noise</span> <span class="hlt">source</span> diagnostics. Output time signatures from these sensors are routed to a control and data processing station adding complexity to the system and cable loss to the measured signal. "Smart" wireless sensors have data processing capability at the sensor locations which further increases the potential of wireless sensors. Smart sensors can process measured data locally and transmit only the important information through wireless communication. The aim of this wireless <span class="hlt">noise</span> telemetry task was to demonstrate a single acoustic sensor wireless link for unsteady pressure measurement, and thus, establish the feasibility of distributed smart sensors scheme for aircraft engine vane surface unsteady pressure data transmission and characterization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19740006271','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19740006271"><span>Sonic inlet <span class="hlt">noise</span> attenuation and performance with a J-85 turbojet engine as a <span class="hlt">noise</span> <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Groth, H. W.</p> <p>1974-01-01</p> <p>A static test program was conducted to investigate aerodynamic and acoustic performance of a sonic inlet used as a <span class="hlt">noise</span> suppressor. A translating centerbody type inlet with radial vanes was tested ahead of a J85-GE-13 turbojet engine. The inlet when fully choked, maintained high recovery with low distortions while dramatically reducing <span class="hlt">noise</span> emanating from the compressor. Recoveries of 98.1% at simulated takeoff and 95% at approach were attained with associated sound attenuation of 40 db and 38 db respectively. Inlet lip shape was found to have significant effects on <span class="hlt">noise</span> attenuation at these static conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhRvL.115g7002W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhRvL.115g7002W"><span>Candidate <span class="hlt">Source</span> of Flux <span class="hlt">Noise</span> in SQUIDs: Adsorbed Oxygen Molecules</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Hui; Shi, Chuntai; Hu, Jun; Han, Sungho; Yu, Clare C.; Wu, R. Q.</p> <p>2015-08-01</p> <p>A major obstacle to using superconducting quantum interference devices (SQUIDs) as qubits is flux <span class="hlt">noise</span>. We propose that the heretofore mysterious spins producing flux <span class="hlt">noise</span> could be O2 molecules adsorbed on the surface. Using density functional theory calculations, we find that an O2 molecule adsorbed on an α-alumina surface has a magnetic moment of ˜1.8 μB . The spin is oriented perpendicular to the axis of the O-O bond, the barrier to spin rotations is about 10 mK. Monte Carlo simulations of ferromagnetically coupled, anisotropic X Y spins on a square lattice find 1 /f magnetization <span class="hlt">noise</span>, consistent with flux <span class="hlt">noise</span> in Al SQUIDs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160009107','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160009107"><span>Potential for Landing Gear <span class="hlt">Noise</span> Reduction on Advanced Aircraft Configurations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Thomas, Russell H.; Nickol, Craig L.; Burley, Casey L.; Guo, Yueping</p> <p>2016-01-01</p> <p>The potential of significantly reducing aircraft landing gear <span class="hlt">noise</span> is explored for aircraft configurations with engines installed above the wings or the fuselage. An innovative concept is studied that does not alter the main gear assembly itself but does shorten the main strut and integrates the gear in pods whose interior surfaces are treated with acoustic liner. The concept is meant to achieve maximum <span class="hlt">noise</span> reduction so that main landing gears can be eliminated as a major <span class="hlt">source</span> of <span class="hlt">airframe</span> <span class="hlt">noise</span>. By applying this concept to an aircraft configuration with 2025 entry-into-service technology levels, it is shown that compared to <span class="hlt">noise</span> levels of current technology, the main gear <span class="hlt">noise</span> can be reduced by 10 EPNL dB, bringing the main gear <span class="hlt">noise</span> close to a floor established by other components such as the nose gear. The assessment of the <span class="hlt">noise</span> reduction potential accounts for design features for the advanced aircraft configuration and includes the effects of local flow velocity in and around the pods, gear <span class="hlt">noise</span> reflection from the <span class="hlt">airframe</span>, and reflection and attenuation from acoustic liner treatment on pod surfaces and doors. A technical roadmap for maturing this concept is discussed, and the possible drag increase at cruise due to the addition of the pods is identified as a challenge, which needs to be quantified and minimized possibly with the combination of detailed design and application of drag reduction technologies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AnRFM..49..277I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AnRFM..49..277I"><span>Combustion and Engine-Core <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ihme, Matthias</p> <p>2017-01-01</p> <p>The implementation of advanced low-emission aircraft engine technologies and the reduction of <span class="hlt">noise</span> from <span class="hlt">airframe</span>, fan, and jet exhaust have made <span class="hlt">noise</span> contributions from an engine core increasingly important. Therefore, meeting future ambitious <span class="hlt">noise</span>-reduction goals requires the consideration of engine-core <span class="hlt">noise</span>. This article reviews progress on the fundamental understanding, experimental analysis, and modeling of engine-core <span class="hlt">noise</span>; addresses limitations of current techniques; and identifies opportunities for future research. After identifying core-<span class="hlt">noise</span> contributions from the combustor, turbomachinery, nozzles, and jet exhaust, they are examined in detail. Contributions from direct combustion <span class="hlt">noise</span>, originating from unsteady combustion, and indirect combustion <span class="hlt">noise</span>, resulting from the interaction of flow-field perturbations with mean-flow variations in turbine stages and nozzles, are analyzed. A new indirect <span class="hlt">noise-source</span> contribution arising from mixture inhomogeneities is identified by extending the theory. Although typically omitted in core-<span class="hlt">noise</span> analysis, the impact of mean-flow variations and nozzle-upstream perturbations on the jet-<span class="hlt">noise</span> modulation is examined, providing potential avenues for future core-<span class="hlt">noise</span> mitigation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150010121','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150010121"><span>Jet-Surface Interaction Test: Phased Array <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Results</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Podboy, Gary G.</p> <p>2012-01-01</p> <p>An experiment was conducted to investigate the effect that a planar surface located near a jet flow has on the <span class="hlt">noise</span> radiated to the far-field. Two different configurations were tested: 1) a shielding configuration in which the surface was located between the jet and the far-field microphones, and 2) a reflecting configuration in which the surface was mounted on the opposite side of the jet, and thus the jet <span class="hlt">noise</span> was free to reflect off the surface toward the microphones. Both conventional far-field microphone and phased array <span class="hlt">noise</span> <span class="hlt">source</span> localization measurements were obtained. This paper discusses phased array results, while a companion paper discusses far-field results. The phased array data show that the axial distribution of <span class="hlt">noise</span> <span class="hlt">sources</span> in a jet can vary greatly depending on the jet operating condition and suggests that it would first be necessary to know or be able to predict this distribution in order to be able to predict the amount of <span class="hlt">noise</span> reduction to expect from a given shielding configuration. The data obtained on both subsonic and supersonic jets show that the <span class="hlt">noise</span> <span class="hlt">sources</span> associated with a given frequency of <span class="hlt">noise</span> tend to move downstream, and therefore, would become more difficult to shield, as jet Mach number increases. The <span class="hlt">noise</span> <span class="hlt">source</span> localization data obtained on cold, shock-containing jets suggests that the constructive interference of sound waves that produces <span class="hlt">noise</span> at a given frequency within a broadband shock <span class="hlt">noise</span> hump comes primarily from a small number of shocks, rather than from all the shocks at the same time. The reflecting configuration data illustrates that the law of reflection must be satisfied in order for jet <span class="hlt">noise</span> to reflect off of a surface to an observer, and depending on the relative locations of the jet, the surface, and the observer, only some of the jet <span class="hlt">noise</span> <span class="hlt">sources</span> may satisfy this requirement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.S43B2527V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.S43B2527V"><span>Investigation of Apparent Seismic Velocity Changes Caused by Microseism <span class="hlt">Noise</span> <span class="hlt">Source</span> Variability</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Volk, M. F.; Bean, C. J.; Lokmer, I.; Craig, D.</p> <p>2013-12-01</p> <p>Currently there is strong interest in monitoring temporal changes in seismic wave velocity in various geological settings. These settings can range from volcano monitoring to reservoir monitoring amongst others. Green's functions are often used to observe temporal variations in seismic wave velocity as their arrival times contain information about velocity changes. Green's functions are typically retrieved by cross correlating ambient <span class="hlt">noise</span> recorded at given pair of stations. Theoretically the recorded wavefields used for the cross correlation should be diffuse. For applications in seismic imagery, the background <span class="hlt">noise</span> <span class="hlt">sources</span> should be uniformly distributed in space or the wavefield must be highly scattered but neither condition typically occur in nature. However temporal and spatial variations of non-uniformly distributed <span class="hlt">noise</span> <span class="hlt">sources</span> may lead to apparent changes in Green's functions which are related to the <span class="hlt">source</span> not the path. This could lead to a misinterpretation of temporal changes in wave velocity. We track the spatial and temporal distribution of the <span class="hlt">noise</span> <span class="hlt">sources</span> using seismic arrays, located in Ireland. It is a good location in which to study these effects, as it is tectonically very quiet and is relatively close to large microseism <span class="hlt">noise</span> <span class="hlt">sources</span> in the North Atlantic, allowing a quantification of <span class="hlt">noise</span> <span class="hlt">source</span> heterogeneity. The temporal variations in seismic wave velocity are calculated and compared to the temporal and spatial distribution of the microseism <span class="hlt">noise</span> <span class="hlt">sources</span>. The initial results show how the direct arrival waveform and the arrival time of the Green's functions correlate with spatial and temporal variability of the microseism <span class="hlt">noise</span> <span class="hlt">sources</span>. Under these conditions we also explore the minimum <span class="hlt">noise</span> trace length required for the Green's functions to converge. We quantify the degree to which apparent velocity variations using direct arrivals are caused by changes in the <span class="hlt">sources</span> and assess the use of coda wave arrivals in mitigating <span class="hlt">source</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Nanos...8..835S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Nanos...8..835S"><span>Nanoscale direct mapping of localized and induced <span class="hlt">noise</span> <span class="hlt">sources</span> on conducting polymer films</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shekhar, Shashank; Cho, Duckhyung; Lee, Hyungwoo; Cho, Dong-Guk; Hong, Seunghun</p> <p>2015-12-01</p> <p>The localized <span class="hlt">noise-sources</span> and those induced by external-stimuli were directly mapped by using a conducting-AFM integrated with a custom-designed <span class="hlt">noise</span> measurement set-up. In this method, current and <span class="hlt">noise</span> images of a poly(9,9-dioctylfluorene)-polymer-film on a conducting-substrate were recorded simultaneously, enabling the mapping of the resistivity and <span class="hlt">noise</span> <span class="hlt">source</span> density (NT). The polymer-films exhibited separate regions with high or low resistivities, which were attributed to the ordered or disordered phases, respectively. A larger number of <span class="hlt">noise-sources</span> were observed in the disordered-phase-regions than in the ordered-phase regions, due to structural disordering. Increased bias-voltages on the disordered-phase-regions resulted in increased NT, which is explained by the structural deformation at high bias-voltages. On photo-illumination, the ordered-phase-regions exhibited a rather large increase in the conductivity and NT. Presumably, the illumination released carriers from deep-traps which should work as additional <span class="hlt">noise-sources</span>. These results show that our methods provide valuable insights into <span class="hlt">noise-sources</span> and, thus, can be powerful tools for basic research and practical applications of conducting polymer films.The localized <span class="hlt">noise-sources</span> and those induced by external-stimuli were directly mapped by using a conducting-AFM integrated with a custom-designed <span class="hlt">noise</span> measurement set-up. In this method, current and <span class="hlt">noise</span> images of a poly(9,9-dioctylfluorene)-polymer-film on a conducting-substrate were recorded simultaneously, enabling the mapping of the resistivity and <span class="hlt">noise</span> <span class="hlt">source</span> density (NT). The polymer-films exhibited separate regions with high or low resistivities, which were attributed to the ordered or disordered phases, respectively. A larger number of <span class="hlt">noise-sources</span> were observed in the disordered-phase-regions than in the ordered-phase regions, due to structural disordering. Increased bias-voltages on the disordered-phase-regions resulted in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880003323','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880003323"><span>The 8.4-GHz low-<span class="hlt">noise</span> maser pump <span class="hlt">source</span> assembly</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cardenas, R.</p> <p>1987-01-01</p> <p>Improved pump <span class="hlt">source</span> assemblies and new 8.4-GHz low <span class="hlt">noise</span> traveling-wave masers (TWMs) were installed at the same time at Deep Space Stations 14 and 43 as part of the Mark IVA DSCC Antenna Microwave Subsystems upgrade. The pump <span class="hlt">source</span> assemblies are part of the new 8.4-GHz TWMs, which are identified as Block IIA Low-<span class="hlt">Noise</span> TWMs. Improved reliability of the pump <span class="hlt">source</span> assemblies was required to meet stress analysis criteria.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992cacn.agar.....P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992cacn.agar.....P"><span>A brief review of the <span class="hlt">source</span> <span class="hlt">noise</span> technology applicable to fixed-wing military aircraft</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pinker, R. A.</p> <p>1992-04-01</p> <p>Although the last two decades have seen major reductions in the <span class="hlt">noise</span> from civil aircraft, <span class="hlt">noise</span> from military operations, both around airfields and from low-flying aircraft, continues to be a <span class="hlt">source</span> of irritation and a potential health hazard. Because of the continuing concern about the <span class="hlt">noise</span> levels produced by combat aircraft, the following paper is intended to provide some of the background to the main conclusions and recommendations reached in the final report of the NATO/Committee on the Challenges of a Modern Society (CCMS) Pilot Study on aircraft <span class="hlt">noise</span>. Although biased towards fixed wing combat aircraft <span class="hlt">noise</span>, the paper also considers other fixed wing military aircraft, but specifically excludes sonic booms and rotary wing aircraft as they both have their own particular <span class="hlt">noise</span> <span class="hlt">sources</span> and problems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930066851&hterms=Natural+gases&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DNatural%2Bgases','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930066851&hterms=Natural+gases&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DNatural%2Bgases"><span>Natural <span class="hlt">noise</span> above 50 MHZ from terrestrial and extraterrestrial <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smith, E. K.; Flock, W. L.</p> <p>1991-01-01</p> <p>This paper offers a brief overview of natural radio <span class="hlt">noise</span> for frequencies above 50 MHz in terms of brightness temperature as observed from two vantage points. The first is from an Earth station located at 40 degrees north latitude and observing at elevation angles from 0 to 90 degrees with an ideal antenna. The second is a satellite in geostationary orbit communicating with the Earth. Earth station <span class="hlt">noise</span> at VHF and UHF is dominated by galactic and solar <span class="hlt">noise</span>. Emission from the atmosphere, gases and hydrometeors, are dominant at EHF and SHF. Radiative transfer theory is invoked in the calculation of brightness temperature from the atmosphere. The situation is not vastly different from geostationary orbit if communications is with the Earth. Emission from the land and sea, even under idealized conditions, enters significantly. Land is a much more effective emitter than sea water, but at frequencies above 30 GHz the differential becomes much less due to the increasing significance of atmospheric emission.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2012-title14-vol2/pdf/CFR-2012-title14-vol2-sec65-85.pdf','CFR2012'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2012-title14-vol2/pdf/CFR-2012-title14-vol2-sec65-85.pdf"><span>14 CFR 65.85 - <span class="hlt">Airframe</span> rating; additional privileges.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2012&page.go=Go">Code of Federal Regulations, 2012 CFR</a></p> <p></p> <p>2012-01-01</p> <p>... (CONTINUED) AIRMEN CERTIFICATION: AIRMEN OTHER THAN FLIGHT CREWMEMBERS Mechanics § 65.85 <span class="hlt">Airframe</span> rating; additional privileges. (a) Except as provided in paragraph (b) of this section, a certificated mechanic with...) A certificated mechanic with an <span class="hlt">airframe</span> rating can approve and return to service an <span class="hlt">airframe</span>,...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2013-title14-vol2/pdf/CFR-2013-title14-vol2-sec65-85.pdf','CFR2013'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2013-title14-vol2/pdf/CFR-2013-title14-vol2-sec65-85.pdf"><span>14 CFR 65.85 - <span class="hlt">Airframe</span> rating; additional privileges.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2013&page.go=Go">Code of Federal Regulations, 2013 CFR</a></p> <p></p> <p>2013-01-01</p> <p>... (CONTINUED) AIRMEN CERTIFICATION: AIRMEN OTHER THAN FLIGHT CREWMEMBERS Mechanics § 65.85 <span class="hlt">Airframe</span> rating; additional privileges. (a) Except as provided in paragraph (b) of this section, a certificated mechanic with...) A certificated mechanic with an <span class="hlt">airframe</span> rating can approve and return to service an <span class="hlt">airframe</span>,...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2014-title14-vol2/pdf/CFR-2014-title14-vol2-sec65-85.pdf','CFR2014'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2014-title14-vol2/pdf/CFR-2014-title14-vol2-sec65-85.pdf"><span>14 CFR 65.85 - <span class="hlt">Airframe</span> rating; additional privileges.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2014&page.go=Go">Code of Federal Regulations, 2014 CFR</a></p> <p></p> <p>2014-01-01</p> <p>... (CONTINUED) AIRMEN CERTIFICATION: AIRMEN OTHER THAN FLIGHT CREWMEMBERS Mechanics § 65.85 <span class="hlt">Airframe</span> rating; additional privileges. (a) Except as provided in paragraph (b) of this section, a certificated mechanic with...) A certificated mechanic with an <span class="hlt">airframe</span> rating can approve and return to service an <span class="hlt">airframe</span>,...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2011-title14-vol2/pdf/CFR-2011-title14-vol2-sec65-85.pdf','CFR2011'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2011-title14-vol2/pdf/CFR-2011-title14-vol2-sec65-85.pdf"><span>14 CFR 65.85 - <span class="hlt">Airframe</span> rating; additional privileges.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2011&page.go=Go">Code of Federal Regulations, 2011 CFR</a></p> <p></p> <p>2011-01-01</p> <p>... (CONTINUED) AIRMEN CERTIFICATION: AIRMEN OTHER THAN FLIGHT CREWMEMBERS Mechanics § 65.85 <span class="hlt">Airframe</span> rating; additional privileges. (a) Except as provided in paragraph (b) of this section, a certificated mechanic with...) A certificated mechanic with an <span class="hlt">airframe</span> rating can approve and return to service an <span class="hlt">airframe</span>,...</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_9 --> <div id="page_10" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="181"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2010-title14-vol2/pdf/CFR-2010-title14-vol2-sec65-85.pdf','CFR'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2010-title14-vol2/pdf/CFR-2010-title14-vol2-sec65-85.pdf"><span>14 CFR 65.85 - <span class="hlt">Airframe</span> rating; additional privileges.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2010&page.go=Go">Code of Federal Regulations, 2010 CFR</a></p> <p></p> <p>2010-01-01</p> <p>... (CONTINUED) AIRMEN CERTIFICATION: AIRMEN OTHER THAN FLIGHT CREWMEMBERS Mechanics § 65.85 <span class="hlt">Airframe</span> rating; additional privileges. (a) Except as provided in paragraph (b) of this section, a certificated mechanic with...) A certificated mechanic with an <span class="hlt">airframe</span> rating can approve and return to service an <span class="hlt">airframe</span>,...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930045406&hterms=Sound+waves&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DSound%2Bwaves','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930045406&hterms=Sound+waves&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DSound%2Bwaves"><span>High-speed helicopter rotor <span class="hlt">noise</span> - Shock waves as a potent <span class="hlt">source</span> of sound</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Farassat, F.; Lee, Yung-Jang; Tadghighi, H.; Holz, R.</p> <p>1991-01-01</p> <p>In this paper we discuss the problem of high speed rotor <span class="hlt">noise</span> prediction. In particular, we propose that from the point of view of the acoustic analogy, shocks around rotating blades are <span class="hlt">sources</span> of sound. We show that, although for a wing at uniform steady rectilinear motion with shocks the volume quadrupole and shock <span class="hlt">sources</span> cancel in the far field to the order of 1/r, this cannot happen for rotating blades. In this case, some cancellation between volume quadrupoles and shock <span class="hlt">sources</span> occurs, yet the remaining shock <span class="hlt">noise</span> contribution is still potent. A formula for shock <span class="hlt">noise</span> prediction is presented based on mapping the deformable shock surface to a time independent region. The resulting equation is similar to Formulation 1A of Langley. Shock <span class="hlt">noise</span> prediction for a hovering model rotor for which experimental <span class="hlt">noise</span> data exist is presented. The comparison of measured and predicted acoustic data shows good agreement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19810013374','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19810013374"><span><span class="hlt">Sources</span>, control, and effects of <span class="hlt">noise</span> from aircraft propellers and rotors</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mixson, J. S.; Greene, G. C.; Dempsey, T. K.</p> <p>1981-01-01</p> <p>Recent NASA and NASA sponsored research on the prediction and control of propeller and rotor <span class="hlt">source</span> <span class="hlt">noise</span>, on the analysis and design of fuselage sidewall <span class="hlt">noise</span> control treatments, and on the measurement and quantification of the response of passengers to aircraft <span class="hlt">noise</span> is described. <span class="hlt">Source</span> <span class="hlt">noise</span> predictions are compared with measurements for conventional low speed propellers, for new high speed propellers (propfans), and for a helicopter. Results from a light aircraft demonstration program are considered which indicates that about 5 dB reduction of flyover <span class="hlt">noise</span> can be obtained without significant performance penalty. Sidewall design studies are examined for interior <span class="hlt">noise</span> control in light general aviation aircraft and in large transports using propfan propulsion. The weight of the added acoustic treatment is estimated and tradeoffs between weight and <span class="hlt">noise</span> reduction are discussed. A laboratory study of passenger response to combined broadband and tonal propeller-like <span class="hlt">noise</span> is described. Subject discomfort ratings of combined tone broadband <span class="hlt">noises</span> are compared with ratings of broadband (boundary layer) <span class="hlt">noise</span> alone and the relative importance of the propeller tones is examined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19870007383','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870007383"><span>Identification and proposed control of helicopter transmission <span class="hlt">noise</span> at the <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Coy, John J.; Handschuh, Robert F.; Lewicki, David G.; Huff, Ronald G.; Krejsa, Eugene A.; Karchmer, Allan M.</p> <p>1987-01-01</p> <p>Helicopter cabin interiors require <span class="hlt">noise</span> treatment which is expensive and adds weight. The gears inside the main power transmission are major <span class="hlt">sources</span> of cabin <span class="hlt">noise</span>. Work conducted by the NASA Lewis Research Center in measuring cabin interior <span class="hlt">noise</span> and in relating the <span class="hlt">noise</span> spectrum to the gear vibration of the Army OH-58 helicopter is described. Flight test data indicate that the planetary gear train is a major <span class="hlt">source</span> of cabin <span class="hlt">noise</span> and that other low frequency <span class="hlt">sources</span> are present that could dominate the cabin <span class="hlt">noise</span>. Companion vibration measurements were made in a transmission test stand, revealing that the single largest contributor to the transmission vibration was the spiral bevel gear mesh. The current understanding of the nature and causes of gear and transmission <span class="hlt">noise</span> is discussed. It is believed that the kinematical errors of the gear mesh have a strong influence on that <span class="hlt">noise</span>. The completed NASA/Army sponsored research that applies to transmission <span class="hlt">noise</span> reduction is summarized. The continuing research program is also reviewed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880007264','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880007264"><span>Identification and proposed control of helicopter transmission <span class="hlt">noise</span> at the <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Coy, John J.; Handschuh, Robert F.; Lewicki, David G.; Huff, Ronald G.; Krejsa, Eugene A.; Karchmer, Allan M.; Coy, John J.</p> <p>1988-01-01</p> <p>Helicopter cabin interiors require <span class="hlt">noise</span> treatment which is expensive and adds weight. The gears inside the main power transmission are major <span class="hlt">sources</span> of cabin <span class="hlt">noise</span>. Work conducted by the NASA Lewis Research Center in measuring cabin interior <span class="hlt">noise</span> and in relating the <span class="hlt">noise</span> spectrum to the gear vibration of the Army OH-58 helicopter is described. Flight test data indicate that the planetary gear train is a major <span class="hlt">source</span> of cabin <span class="hlt">noise</span> and that other low frequency <span class="hlt">sources</span> are present that could dominate the cabin <span class="hlt">noise</span>. Companion vibration measurements were made in a transmission test stand, revealing that the single largest contributor to the transmission vibration was the spiral bevel gear mesh. The current understanding of the nature and causes of gear and transmission <span class="hlt">noise</span> is discussed. It is believed that the kinematical errors of the gear mesh have a strong influence on that <span class="hlt">noise</span>. The completed NASA/Army sponsored research that applies to transmission <span class="hlt">noise</span> reduction is summarized. The continuing research program is also reviewed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19750022793','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19750022793"><span>Study of <span class="hlt">noise</span> <span class="hlt">sources</span> in a subsonic fan using measured blade pressures and acoustic theory</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hanson, D. B.</p> <p>1975-01-01</p> <p><span class="hlt">Sources</span> of <span class="hlt">noise</span> in a 1.4 m (4.6 ft) diameter subsonic tip speed propulsive fan running statically outdoors are studied using a combination of techniques. Signals measured with pressure transducers on a rotor blade are plotted in a format showing the space-time history of inlet distortion. Study of these plots visually and with statistical correlation analysis confirms that the inlet flow contains long, thin eddies of turbulence. Turbulence generated in the boundary layer of the shroud upstream of the rotor tips was not found to be an important <span class="hlt">noise</span> <span class="hlt">source</span>. Fan <span class="hlt">noise</span> is diagnosed by computing narrowband spectra of rotor and stator sound power and comparing these with measured sound power spectra. Rotor <span class="hlt">noise</span> is computed from spectra of the measured blade pressures and stator <span class="hlt">noise</span> is computed using the author's stator <span class="hlt">noise</span> theory. It is concluded that the rotor and stator <span class="hlt">sources</span> contribute about equally at frequencies in the vicinity of the first three harmonics of blade passing frequency. At higher frequencies, the stator contribution diminishes rapidly and the rotor/inlet turbulence mechanism dominates. Two parametric studies are performed by using the rotor <span class="hlt">noise</span> calculation procedure which was correlated with test. In the first study, the effects on <span class="hlt">noise</span> spectrum and directivity are calculated for changes in turbulence properties, rotational Mach number, number of blades, and stagger angle. In the second study the influences of design tip speed and blade number on <span class="hlt">noise</span> are evaluated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160013856','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160013856"><span>Full-Scale Turbofan Engine <span class="hlt">Noise-Source</span> Separation Using a Four-Signal Method</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hultgren, Lennart S.; Arechiga, Rene O.</p> <p>2016-01-01</p> <p>Contributions from the combustor to the overall propulsion <span class="hlt">noise</span> of civilian transport aircraft are starting to become important due to turbofan design trends and expected advances in mitigation of other <span class="hlt">noise</span> <span class="hlt">sources</span>. During on-ground, static-engine acoustic tests, combustor <span class="hlt">noise</span> is generally sub-dominant to other engine <span class="hlt">noise</span> <span class="hlt">sources</span> because of the absence of in-flight effects. Consequently, <span class="hlt">noise-source</span> separation techniques are needed to extract combustor-<span class="hlt">noise</span> information from the total <span class="hlt">noise</span> signature in order to further progress. A novel four-signal <span class="hlt">source</span>-separation method is applied to data from a static, full-scale engine test and compared to previous methods. The new method is, in a sense, a combination of two- and three-signal techniques and represents an attempt to alleviate some of the weaknesses of each of those approaches. This work is supported by the NASA Advanced Air Vehicles Program, Advanced Air Transport Technology Project, Aircraft <span class="hlt">Noise</span> Reduction Subproject and the NASA Glenn Faculty Fellowship Program.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22087938','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22087938"><span>Effects of <span class="hlt">noise</span> levels and call types on the <span class="hlt">source</span> levels of killer whale calls.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Holt, Marla M; Noren, Dawn P; Emmons, Candice K</p> <p>2011-11-01</p> <p>Accurate parameter estimates relevant to the vocal behavior of marine mammals are needed to assess potential effects of anthropogenic sound exposure including how masking <span class="hlt">noise</span> reduces the active space of sounds used for communication. Information about how these animals modify their vocal behavior in response to <span class="hlt">noise</span> exposure is also needed for such assessment. Prior studies have reported variations in the <span class="hlt">source</span> levels of killer whale sounds, and a more recent study reported that killer whales compensate for vessel masking <span class="hlt">noise</span> by increasing their call amplitude. The objectives of the current study were to investigate the <span class="hlt">source</span> levels of a variety of call types in southern resident killer whales while also considering background <span class="hlt">noise</span> level as a likely factor related to call <span class="hlt">source</span> level variability. The <span class="hlt">source</span> levels of 763 discrete calls along with corresponding background <span class="hlt">noise</span> were measured over three summer field seasons in the waters surrounding the San Juan Islands, WA. Both <span class="hlt">noise</span> level and call type were significant factors on call <span class="hlt">source</span> levels (1-40 kHz band, range of 135.0-175.7 dB(rms) re 1 [micro sign]Pa at 1 m). These factors should be considered in models that predict how anthropogenic masking <span class="hlt">noise</span> reduces vocal communication space in marine mammals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015FNL....1450005V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015FNL....1450005V"><span>GIS-Based <span class="hlt">Noise</span> Simulation Open <span class="hlt">Source</span> Software: N-GNOIS</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vijay, Ritesh; Sharma, A.; Kumar, M.; Shende, V.; Chakrabarti, T.; Gupta, Rajesh</p> <p>2015-12-01</p> <p>Geographical information system (GIS)-based <span class="hlt">noise</span> simulation software (N-GNOIS) has been developed to simulate the <span class="hlt">noise</span> scenario due to point and mobile <span class="hlt">sources</span> considering the impact of geographical features and meteorological parameters. These have been addressed in the software through attenuation modules of atmosphere, vegetation and barrier. N-GNOIS is a user friendly, platform-independent and open geospatial consortia (OGC) compliant software. It has been developed using open <span class="hlt">source</span> technology (QGIS) and open <span class="hlt">source</span> language (Python). N-GNOIS has unique features like cumulative impact of point and mobile <span class="hlt">sources</span>, building structure and honking due to traffic. Honking is the most common phenomenon in developing countries and is frequently observed on any type of roads. N-GNOIS also helps in designing physical barrier and vegetation cover to check the propagation of <span class="hlt">noise</span> and acts as a decision making tool for planning and management of <span class="hlt">noise</span> component in environmental impact assessment (EIA) studies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100032967','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100032967"><span>Phased Array Radiometer Calibration Using a Radiated <span class="hlt">Noise</span> <span class="hlt">Source</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Srinivasan, Karthik; Limaye, Ashutoch S.; Laymon, Charles A.; Meyer, Paul J.</p> <p>2010-01-01</p> <p>Electronic beam steering capability of phased array antenna systems offer significant advantages when used in real aperture imaging radiometers. The sensitivity of such systems is limited by the ability to accurately calibrate variations in the antenna circuit characteristics. Passive antenna systems, which require mechanical rotation to scan the beam, have stable characteristics and the <span class="hlt">noise</span> figure of the antenna can be characterized with knowledge of its physical temperature [1],[2]. Phased array antenna systems provide the ability to electronically steer the beam in any desired direction. Such antennas make use of active components (amplifiers, phase shifters) to provide electronic scanning capability while maintaining a low antenna <span class="hlt">noise</span> figure. The gain fluctuations in the active components can be significant, resulting in substantial calibration difficulties [3]. In this paper, we introduce two novel calibration techniques that provide an end-to-end calibration of a real-aperture, phased array radiometer system. Empirical data will be shown to illustrate the performance of both methods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850004525','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850004525"><span>Algorithm for astronomical, extended <span class="hlt">source</span>, signal-to-<span class="hlt">noise</span> radio calculations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jayroe, R. R.</p> <p>1984-01-01</p> <p>An algorithm was developed to simulate the expected signal-to-<span class="hlt">noise</span> ratio as a function of observation time in the charge coupled device detector plane of an optical telescope located outside the Earth's atmosphere for an extended, uniform astronomical <span class="hlt">source</span> embedded in a uniform cosmic background. By choosing the appropriate input values, the expected extended <span class="hlt">source</span> signal-to-<span class="hlt">noise</span> ratios can be computed for the Hubble Space Telescope using the Wide Field/Planetary Camera science instrument.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017NatSR...743411C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017NatSR...743411C"><span>Direct mapping of electrical <span class="hlt">noise</span> <span class="hlt">sources</span> in molecular wire-based devices</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cho, Duckhyung; Lee, Hyungwoo; Shekhar, Shashank; Yang, Myungjae; Park, Jae Yeol; Hong, Seunghun</p> <p>2017-02-01</p> <p>We report a <span class="hlt">noise</span> mapping strategy for the reliable identification and analysis of <span class="hlt">noise</span> <span class="hlt">sources</span> in molecular wire junctions. Here, different molecular wires were patterned on a gold substrate, and the current-<span class="hlt">noise</span> map on the pattern was measured and analyzed, enabling the quantitative study of <span class="hlt">noise</span> <span class="hlt">sources</span> in the patterned molecular wires. The frequency spectra of the <span class="hlt">noise</span> from the molecular wire junctions exhibited characteristic 1/f2 behavior, which was used to identify the electrical signals from molecular wires. This method was applied to analyze the molecular junctions comprising various thiol molecules on a gold substrate, revealing that the <span class="hlt">noise</span> in the junctions mainly came from the fluctuation of the thiol bonds. Furthermore, we quantitatively compared the frequencies of such bond fluctuations in different molecular wire junctions and identified molecular wires with lower electrical <span class="hlt">noise</span>, which can provide critical information for designing low-<span class="hlt">noise</span> molecular electronic devices. Our method provides valuable insights regarding <span class="hlt">noise</span> phenomena in molecular wires and can be a powerful tool for the development of molecular electronic devices.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5324066','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5324066"><span>Direct mapping of electrical <span class="hlt">noise</span> <span class="hlt">sources</span> in molecular wire-based devices</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Cho, Duckhyung; Lee, Hyungwoo; Shekhar, Shashank; Yang, Myungjae; Park, Jae Yeol; Hong, Seunghun</p> <p>2017-01-01</p> <p>We report a <span class="hlt">noise</span> mapping strategy for the reliable identification and analysis of <span class="hlt">noise</span> <span class="hlt">sources</span> in molecular wire junctions. Here, different molecular wires were patterned on a gold substrate, and the current-<span class="hlt">noise</span> map on the pattern was measured and analyzed, enabling the quantitative study of <span class="hlt">noise</span> <span class="hlt">sources</span> in the patterned molecular wires. The frequency spectra of the <span class="hlt">noise</span> from the molecular wire junctions exhibited characteristic 1/f2 behavior, which was used to identify the electrical signals from molecular wires. This method was applied to analyze the molecular junctions comprising various thiol molecules on a gold substrate, revealing that the <span class="hlt">noise</span> in the junctions mainly came from the fluctuation of the thiol bonds. Furthermore, we quantitatively compared the frequencies of such bond fluctuations in different molecular wire junctions and identified molecular wires with lower electrical <span class="hlt">noise</span>, which can provide critical information for designing low-<span class="hlt">noise</span> molecular electronic devices. Our method provides valuable insights regarding <span class="hlt">noise</span> phenomena in molecular wires and can be a powerful tool for the development of molecular electronic devices. PMID:28233821</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015MeScT..26i5010Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015MeScT..26i5010Z"><span>Diesel engine <span class="hlt">noise</span> <span class="hlt">source</span> identification based on EEMD, coherent power spectrum analysis and improved AHP</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Junhong; Wang, Jian; Lin, Jiewei; Bi, Fengrong; Guo, Qian; Chen, Kongwu; Ma, Liang</p> <p>2015-09-01</p> <p>As the essential foundation of <span class="hlt">noise</span> reduction, many <span class="hlt">noise</span> <span class="hlt">source</span> identification methods have been developed and applied to engineering practice. To identify the <span class="hlt">noise</span> <span class="hlt">source</span> in the board-band frequency of different engine parts at various typical speeds, this paper presents an integrated <span class="hlt">noise</span> <span class="hlt">source</span> identification method based on the ensemble empirical mode decomposition (EEMD), the coherent power spectrum analysis, and the improved analytic hierarchy process (AHP). The measured <span class="hlt">noise</span> is decomposed into several IMFs with physical meaning, which ensures the coherence analysis of the IMFs and the vibration signals are meaningful. An improved AHP is developed by introducing an objective weighting function to replace the traditional subjective evaluation, which makes the results no longer dependent on the subject performances and provides a better consistency in the meantime. The proposed <span class="hlt">noise</span> identification model is applied to identifying a diesel engine surface radiated <span class="hlt">noise</span>. As a result, the frequency-dependent contributions of different engine parts to different test points at different speeds are obtained, and an overall weight order is obtained as oil pan  >  left body  >  valve chamber cover  >  gear chamber casing  >  right body  >  flywheel housing, which provides an effectual guidance for the <span class="hlt">noise</span> reduction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1160107','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1160107"><span>How Common are <span class="hlt">Noise</span> <span class="hlt">Sources</span> on the Crash Arc of Malaysian Flight 370</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Fenimore, Edward E.; Kunkle, Thomas David; Stead, Richard J.</p> <p>2014-10-21</p> <p>Malaysian Flight 370 disappeared nearly without a trace. Besides some communication handshakes to the INMASAT satellite, the Comprehensive Test Ban Treaty monitoring system could have heard the aircraft crash into the southern Indian Ocean. One <span class="hlt">noise</span> event from Cape Leeuwin has been suggested by Stead as the crash and occurs within the crash location suggested by Kunkle at el. We analyze the hydrophone data from Cape Leeuwin to understand how common such <span class="hlt">noise</span> events are on the arc of possible locations where Malaysian Flight 370 might have crashed. Few other <span class="hlt">noise</span> <span class="hlt">sources</span> were found on the arc. The <span class="hlt">noise</span> event found by Stead is the strongest. No <span class="hlt">noise</span> events are seen within the Australian Transportation Safety Board (ATSB) new search location until the 10<sup>th</sup> strongest event, an event which is very close to the <span class="hlt">noise</span> level.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20711517','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20711517"><span>Can lightning be a <span class="hlt">noise</span> <span class="hlt">source</span> for a spherical gravitational wave antenna?</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Magalhaes, Nadja Simao; Marinho, Rubens de Melo Jr.; Aguiar, Odylio Denys de; Frajuca, Carlos</p> <p>2005-11-15</p> <p>The detection of gravitational waves is a very active research field at the moment. In Brazil the gravitational wave detector is called Mario SCHENBERG. Because of its high sensitivity it is necessary to model mathematically all known <span class="hlt">noise</span> <span class="hlt">sources</span> so that digital filters can be developed that maximize the signal-to-<span class="hlt">noise</span> ratio. One of the <span class="hlt">noise</span> <span class="hlt">sources</span> that must be considered are the disturbances caused by electromagnetic pulses due to lightnings close to the experiment. Such disturbances may influence the vibrations of the antenna's normal modes and mask possible gravitational wave signals. In this work we model the interaction between lightnings and SCHENBERG antenna and calculate the intensity of the <span class="hlt">noise</span> due to a close lightning stroke in the detected signal. We find that the <span class="hlt">noise</span> generated does not disturb the experiment significantly.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1227010','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1227010"><span>Analytic treatment of <span class="hlt">source</span> photon emission times to reduce <span class="hlt">noise</span> in implicit Monte Carlo calculations</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Trahan, Travis J.; Gentile, Nicholas A.</p> <p>2012-09-10</p> <p>Statistical uncertainty is inherent to any Monte Carlo simulation of radiation transport problems. In space-angle-frequency independent radiative transfer calculations, the uncertainty in the solution is entirely due to random sampling of <span class="hlt">source</span> photon emission times. We have developed a modification to the Implicit Monte Carlo algorithm that eliminates <span class="hlt">noise</span> due to sampling of the emission time of <span class="hlt">source</span> photons. In problems that are independent of space, angle, and energy, the new algorithm generates a smooth solution, while a standard implicit Monte Carlo solution is noisy. For space- and angle-dependent problems, the new algorithm exhibits reduced <span class="hlt">noise</span> relative to standard implicit Monte Carlo in some cases, and comparable <span class="hlt">noise</span> in all other cases. In conclusion, the improvements are limited to short time scales; over long time scales, <span class="hlt">noise</span> due to random sampling of spatial and angular variables tends to dominate the <span class="hlt">noise</span> reduction from the new algorithm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20130003185','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130003185"><span>High Bypass Ratio Jet <span class="hlt">Noise</span> Reduction and Installation Effects Including Shielding Effectiveness</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Thomas, Russell H.; Czech, Michael J.; Doty, Michael J.</p> <p>2013-01-01</p> <p>An experimental investigation was performed to study the propulsion <span class="hlt">airframe</span> aeroacoustic installation effects of a separate flow jet nozzle with a Hybrid Wing Body aircraft configuration where the engine is installed above the wing. Prior understanding of the jet <span class="hlt">noise</span> shielding effectiveness was extended to a bypass ratio ten application as a function of nozzle configuration, chevron type, axial spacing, and installation effects from additional <span class="hlt">airframe</span> components. Chevron types included fan chevrons that are uniform circumferentially around the fan nozzle and T-fan type chevrons that are asymmetrical circumferentially. In isolated testing without a pylon, uniform chevrons compared to T-fan chevrons showed slightly more low frequency reduction offset by more high frequency increase. Phased array localization shows that at this bypass ratio chevrons still move peak jet <span class="hlt">noise</span> <span class="hlt">source</span> locations upstream but not to nearly the extent, as a function of frequency, as for lower bypass ratio jets. For baseline nozzles without chevrons, the basic pylon effect has been greatly reduced compared to that seen for lower bypass ratio jets. Compared to Tfan chevrons without a pylon, the combination with a standard pylon results in more high frequency <span class="hlt">noise</span> increase and an overall higher <span class="hlt">noise</span> level. Shielded by an <span class="hlt">airframe</span> surface 2.17 fan diameters from nozzle to <span class="hlt">airframe</span> trailing edge, the T-fan chevron nozzle can produce reductions in jet <span class="hlt">noise</span> of as much as 8 dB at high frequencies and upstream angles. <span class="hlt">Noise</span> reduction from shielding decreases with decreasing frequency and with increasing angle from the jet inlet. Beyond an angle of 130 degrees there is almost no <span class="hlt">noise</span> reduction from shielding. Increasing chevron immersion more than what is already an aggressive design is not advantageous for <span class="hlt">noise</span> reduction. The addition of <span class="hlt">airframe</span> control surfaces, including vertical stabilizers and elevon deflection, showed only a small overall impact. Based on the test results, the best</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994SPIE.2245..202D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994SPIE.2245..202D"><span>Dual-band infrared imaging to detect corrosion damage within <span class="hlt">airframes</span> and concrete structures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>DelGrande, Nancy; Durbin, Philip F.</p> <p>1994-03-01</p> <p>We are developing dual-band IR (DBIR) imaging and detection techniques to inspect <span class="hlt">airframes</span> and concrete bridge decks for hidden corrosion damage. Using selective DBIR image ratios, we enhanced surface temperature contrast and removed surface emissivity <span class="hlt">noise</span> associated with clutter. Our surface temperature maps depicted defect sites, which heat and cool at different rates than their surroundings. Our emissivity-ratio maps tagged and removed the masking effects of surface clutter. For <span class="hlt">airframe</span> inspections, we used time-resolved DBIR temperature, emissivity-ratio and composite thermal inertia maps to locate corrosion-thinning effects within a flash-heated Boeing 737 <span class="hlt">airframe</span>. Emissivity-ratio maps tagged and removed clutter sites from uneven paint, dirt and surface markers. Temperature and thermal inertia maps characterized defect sites, types, sizes, thicknesses, thermal properties and material-loss effects from <span class="hlt">airframe</span> corrosion. For concrete inspections, we mapped DBIR temperature and emissivity-ratio patterns to better interpret surrogate delamination sites within naturally- heated, concrete slabs and removed the clutter mask from sand pile-up, grease stains, rocks and other surface objects.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4150400','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4150400"><span>Volterra dendritic stimulus processors and biophysical spike generators with intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Lazar, Aurel A.; Zhou, Yiyin</p> <p>2014-01-01</p> <p>We consider a class of neural circuit models with internal <span class="hlt">noise</span> <span class="hlt">sources</span> arising in sensory systems. The basic neuron model in these circuits consists of a dendritic stimulus processor (DSP) cascaded with a biophysical spike generator (BSG). The dendritic stimulus processor is modeled as a set of nonlinear operators that are assumed to have a Volterra series representation. Biophysical point neuron models, such as the Hodgkin-Huxley neuron, are used to model the spike generator. We address the question of how intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span> affect the precision in encoding and decoding of sensory stimuli and the functional identification of its sensory circuits. We investigate two intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span> arising (i) in the active dendritic trees underlying the DSPs, and (ii) in the ion channels of the BSGs. <span class="hlt">Noise</span> in dendritic stimulus processing arises from a combined effect of variability in synaptic transmission and dendritic interactions. Channel <span class="hlt">noise</span> arises in the BSGs due to the fluctuation of the number of the active ion channels. Using a stochastic differential equations formalism we show that encoding with a neuron model consisting of a nonlinear DSP cascaded with a BSG with intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span> can be treated as generalized sampling with noisy measurements. For single-input multi-output neural circuit models with feedforward, feedback and cross-feedback DSPs cascaded with BSGs we theoretically analyze the effect of <span class="hlt">noise</span> <span class="hlt">sources</span> on stimulus decoding. Building on a key duality property, the effect of <span class="hlt">noise</span> parameters on the precision of the functional identification of the complete neural circuit with DSP/BSG neuron models is given. We demonstrate through extensive simulations the effects of <span class="hlt">noise</span> on encoding stimuli with circuits that include neuron models that are akin to those commonly seen in sensory systems, e.g., complex cells in V1. PMID:25225477</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_10 --> <div id="page_11" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="201"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920023706&hterms=noise+environment&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dnoise%2Benvironment','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920023706&hterms=noise+environment&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dnoise%2Benvironment"><span>MD-80 aft cabin <span class="hlt">noise</span> control: A case history</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lang, M. A.; Lorch, D. R.; May, D. N.; Simpson, M. A.</p> <p>1992-01-01</p> <p>The interior <span class="hlt">noise</span> technology program to improve the <span class="hlt">noise</span> environment in the aft cabin of the MD-80 twin jet aircraft is discussed. Two potential <span class="hlt">noise</span> control treatments were identified: vibration absorber devices for the <span class="hlt">airframe</span> and for the engine. A series of ground and flight tests using in-service aircraft was then conducted. These tests showed that the vibration absorbers for the <span class="hlt">airframe</span> and engine decreased aircraft <span class="hlt">noise</span> significantly.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992acin.work...13L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992acin.work...13L"><span>MD-80 aft cabin <span class="hlt">noise</span> control: A case history</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lang, M. A.; Lorch, D. R.; May, D. N.; Simpson, M. A.</p> <p>1992-07-01</p> <p>The interior <span class="hlt">noise</span> technology program to improve the <span class="hlt">noise</span> environment in the aft cabin of the MD-80 twin jet aircraft is discussed. Two potential <span class="hlt">noise</span> control treatments were identified: vibration absorber devices for the <span class="hlt">airframe</span> and for the engine. A series of ground and flight tests using in-service aircraft was then conducted. These tests showed that the vibration absorbers for the <span class="hlt">airframe</span> and engine decreased aircraft <span class="hlt">noise</span> significantly.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22357037','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22357037"><span>Suppression of fiber modal <span class="hlt">noise</span> induced radial velocity errors for bright emission-line calibration <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mahadevan, Suvrath; Halverson, Samuel; Ramsey, Lawrence; Venditti, Nick</p> <p>2014-05-01</p> <p>Modal <span class="hlt">noise</span> in optical fibers imposes limits on the signal-to-<span class="hlt">noise</span> ratio (S/N) and velocity precision achievable with the next generation of astronomical spectrographs. This is an increasingly pressing problem for precision radial velocity spectrographs in the near-infrared (NIR) and optical that require both high stability of the observed line profiles and high S/N. Many of these spectrographs plan to use highly coherent emission-line calibration <span class="hlt">sources</span> like laser frequency combs and Fabry-Perot etalons to achieve precision sufficient to detect terrestrial-mass planets. These high-precision calibration <span class="hlt">sources</span> often use single-mode fibers or highly coherent <span class="hlt">sources</span>. Coupling light from single-mode fibers to multi-mode fibers leads to only a very low number of modes being excited, thereby exacerbating the modal <span class="hlt">noise</span> measured by the spectrograph. We present a commercial off-the-shelf solution that significantly mitigates modal <span class="hlt">noise</span> at all optical and NIR wavelengths, and which can be applied to spectrograph calibration systems. Our solution uses an integrating sphere in conjunction with a diffuser that is moved rapidly using electrostrictive polymers, and is generally superior to most tested forms of mechanical fiber agitation. We demonstrate a high level of modal <span class="hlt">noise</span> reduction with a narrow bandwidth 1550 nm laser. Our relatively inexpensive solution immediately enables spectrographs to take advantage of the innate precision of bright state-of-the art calibration <span class="hlt">sources</span> by removing a major <span class="hlt">source</span> of systematic <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012ApPhL.101v1112B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012ApPhL.101v1112B"><span>An extremely low-<span class="hlt">noise</span> heralded single-photon <span class="hlt">source</span>: A breakthrough for quantum technologies</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brida, G.; Degiovanni, I. P.; Genovese, M.; Piacentini, F.; Traina, P.; Della Frera, A.; Tosi, A.; Bahgat Shehata, A.; Scarcella, C.; Gulinatti, A.; Ghioni, M.; Polyakov, S. V.; Migdall, A.; Giudice, A.</p> <p>2012-11-01</p> <p>Low <span class="hlt">noise</span> single-photon <span class="hlt">sources</span> are a critical element for quantum technologies. We present a heralded single-photon <span class="hlt">source</span> with an extremely low level of residual background photons, by implementing low-jitter detectors and electronics and a fast custom-made pulse generator controlling an optical shutter (a LiNbO3 waveguide optical switch) on the output of the <span class="hlt">source</span>. This <span class="hlt">source</span> has a second-order autocorrelation g(2)(0)=0.005(7), and an output <span class="hlt">noise</span> factor (defined as the ratio of the number of <span class="hlt">noise</span> photons to total photons at the <span class="hlt">source</span> output channel) of 0.25(1)%. These are the best performance characteristics reported to date.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140002889','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140002889"><span>Jet-Surface Interaction Test: Phased Array <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Results</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Podboy, Gary G.</p> <p>2013-01-01</p> <p>An experiment was conducted to investigate the effect that a planar surface located near a jet flow has on the <span class="hlt">noise</span> radiated to the far-field. Two different configurations were tested: 1) a shielding configuration in which the surface was located between the jet and the far-field microphones, and 2) a reflecting configuration in which the surface was mounted on the opposite side of the jet, and thus the jet <span class="hlt">noise</span> was free to reflect off the surface toward the microphones. Both conventional far-field microphone and phased array <span class="hlt">noise</span> <span class="hlt">source</span> localization measurements were obtained. This paper discusses phased array results, while a companion paper (Brown, C.A., "Jet-Surface Interaction Test: Far-Field <span class="hlt">Noise</span> Results," ASME paper GT2012-69639, June 2012.) discusses far-field results. The phased array data show that the axial distribution of <span class="hlt">noise</span> <span class="hlt">sources</span> in a jet can vary greatly depending on the jet operating condition and suggests that it would first be necessary to know or be able to predict this distribution in order to be able to predict the amount of <span class="hlt">noise</span> reduction to expect from a given shielding configuration. The data obtained on both subsonic and supersonic jets show that the <span class="hlt">noise</span> <span class="hlt">sources</span> associated with a given frequency of <span class="hlt">noise</span> tend to move downstream, and therefore, would become more difficult to shield, as jet Mach number increases. The <span class="hlt">noise</span> <span class="hlt">source</span> localization data obtained on cold, shock-containing jets suggests that the constructive interference of sound waves that produces <span class="hlt">noise</span> at a given frequency within a broadband shock <span class="hlt">noise</span> hump comes primarily from a small number of shocks, rather than from all the shocks at the same time. The reflecting configuration data illustrates that the law of reflection must be satisfied in order for jet <span class="hlt">noise</span> to reflect off of a surface to an observer, and depending on the relative locations of the jet, the surface, and the observer, only some of the jet <span class="hlt">noise</span> <span class="hlt">sources</span> may satisfy this requirement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1988hmrn.rept.....B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1988hmrn.rept.....B"><span>Helicopter main-rotor <span class="hlt">noise</span>: Determination of <span class="hlt">source</span> contributions using scaled model data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brooks, Thomas F.; Jolly, J. Ralph, Jr.; Marcolini, Michael A.</p> <p>1988-08-01</p> <p>Acoustic data from a test of a 40 percent model MBB BO-105 helicopter main rotor are scaled to equivalent full-scale flyover cases. The test was conducted in the anechoic open test section of the German-Dutch Windtunnel (DNW). The measured data are in the form of acoustic pressure time histories and spectra from two out-of-flow microphones underneath and foward of the model. These are scaled to correspond to measurements made at locations 150 m below the flight path of a full-scale rotor. For the scaled data, a detailed analysis is given for the identification in the data of the <span class="hlt">noise</span> contributions from different rotor <span class="hlt">noise</span> <span class="hlt">sources</span>. Key results include a component breakdown of the <span class="hlt">noise</span> contributions, in terms of <span class="hlt">noise</span> criteria calculations of a weighted sound pressure level (dBA) and perceived <span class="hlt">noise</span> level (PNL), as functions of rotor advance ratio and descent angle. It is shown for the scaled rotor that, during descent, impulsive blade-vortex interaction (BVI) <span class="hlt">noise</span> is the dominant contributor to the <span class="hlt">noise</span>. In level flight and mild climb, broadband blade-turbulent wake interaction (BWI) <span class="hlt">noise</span> is dominant due to the absence of BVI activity. At high climb angles, BWI is reduced and self-<span class="hlt">noise</span> from blade boundary-layer turbulence becomes the most prominent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880017523','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880017523"><span>Helicopter main-rotor <span class="hlt">noise</span>: Determination of <span class="hlt">source</span> contributions using scaled model data</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Brooks, Thomas F.; Jolly, J. Ralph, Jr.; Marcolini, Michael A.</p> <p>1988-01-01</p> <p>Acoustic data from a test of a 40 percent model MBB BO-105 helicopter main rotor are scaled to equivalent full-scale flyover cases. The test was conducted in the anechoic open test section of the German-Dutch Windtunnel (DNW). The measured data are in the form of acoustic pressure time histories and spectra from two out-of-flow microphones underneath and foward of the model. These are scaled to correspond to measurements made at locations 150 m below the flight path of a full-scale rotor. For the scaled data, a detailed analysis is given for the identification in the data of the <span class="hlt">noise</span> contributions from different rotor <span class="hlt">noise</span> <span class="hlt">sources</span>. Key results include a component breakdown of the <span class="hlt">noise</span> contributions, in terms of <span class="hlt">noise</span> criteria calculations of a weighted sound pressure level (dBA) and perceived <span class="hlt">noise</span> level (PNL), as functions of rotor advance ratio and descent angle. It is shown for the scaled rotor that, during descent, impulsive blade-vortex interaction (BVI) <span class="hlt">noise</span> is the dominant contributor to the <span class="hlt">noise</span>. In level flight and mild climb, broadband blade-turbulent wake interaction (BWI) <span class="hlt">noise</span> is dominant due to the absence of BVI activity. At high climb angles, BWI is reduced and self-<span class="hlt">noise</span> from blade boundary-layer turbulence becomes the most prominent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19790006704','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19790006704"><span>Basic research in fan <span class="hlt">source</span> <span class="hlt">noise</span>: Inlet distortion and turbulence <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kantola, R. A.; Warren, R. E.</p> <p>1978-01-01</p> <p>A widely recognized problem in jet engine fan <span class="hlt">noise</span> is the discrepancy between inflight and static tests. This discrepancy consists of blade passing frequency tones, caused by ingested turbulence that appear in the static tests but not in flight. To reduce the ingested distortions and turbulence in an anechoic chamber, a reverse cone inlet is used to guide the air into the fan. This inlet also has provisions for boundary layer suction and is used in conjunction with a turbulence control structure (TCS) to condition the air impinging on the fan. The program was very successful in reducing the ingested turbulence, to the point where reductions in the acoustic power at blade passing frequency are as high as 18 db for subsonic tip speeds. Even with this large subsonic tone suppression, the supersonic tip speed tonal content remains largely unchanged, indicating that the TCS did not appreciably attenuate the <span class="hlt">noise</span> but effects the generation via turbulence reduction. Turbulence mapping of the inlet confirmed that the tone reductions are due to a reduction in turbulence, as the low frequency power spectra of the streamwise and transverse turbulence were reduced by up to ten times and 100 times, respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012RScI...83d4701C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012RScI...83d4701C"><span>A low phase <span class="hlt">noise</span> microwave <span class="hlt">source</span> for atomic spin squeezing experiments in 87Rb</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, Zilong; Bohnet, Justin G.; Weiner, Joshua M.; Thompson, James K.</p> <p>2012-04-01</p> <p>We describe and characterize a simple, low cost, low phase <span class="hlt">noise</span> microwave <span class="hlt">source</span> that operates near 6.800 GHz for agile, coherent manipulation of ensembles of 87Rb. Low phase <span class="hlt">noise</span> is achieved by directly multiplying a low phase <span class="hlt">noise</span> 100 MHz crystal to 6.8 GHz using a nonlinear transmission line and filtering the output with custom band-pass filters. The fixed frequency signal is single sideband modulated with a direct digital synthesis frequency <span class="hlt">source</span> to provide the desired phase, amplitude, and frequency control. Before modulation, the <span class="hlt">source</span> has a single sideband phase <span class="hlt">noise</span> near -140 dBc/Hz in the range of 10 kHz-1 MHz offset from the carrier frequency and -130 dBc/Hz after modulation. The resulting <span class="hlt">source</span> is estimated to contribute added spin-<span class="hlt">noise</span> variance 16 dB below the quantum projection <span class="hlt">noise</span> level during quantum nondemolition measurements of the clock transition in an ensemble 7 × 105 87Rb atoms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22072287','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22072287"><span>A low phase <span class="hlt">noise</span> microwave <span class="hlt">source</span> for atomic spin squeezing experiments in {sup 87}Rb</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Chen Zilong; Bohnet, Justin G.; Weiner, Joshua M.; Thompson, James K.</p> <p>2012-04-15</p> <p>We describe and characterize a simple, low cost, low phase <span class="hlt">noise</span> microwave <span class="hlt">source</span> that operates near 6.800 GHz for agile, coherent manipulation of ensembles of {sup 87}Rb. Low phase <span class="hlt">noise</span> is achieved by directly multiplying a low phase <span class="hlt">noise</span> 100 MHz crystal to 6.8 GHz using a nonlinear transmission line and filtering the output with custom band-pass filters. The fixed frequency signal is single sideband modulated with a direct digital synthesis frequency <span class="hlt">source</span> to provide the desired phase, amplitude, and frequency control. Before modulation, the <span class="hlt">source</span> has a single sideband phase <span class="hlt">noise</span> near -140 dBc/Hz in the range of 10 kHz-1 MHz offset from the carrier frequency and -130 dBc/Hz after modulation. The resulting <span class="hlt">source</span> is estimated to contribute added spin-<span class="hlt">noise</span> variance 16 dB below the quantum projection <span class="hlt">noise</span> level during quantum nondemolition measurements of the clock transition in an ensemble 7 x 10{sup 5} {sup 87}Rb atoms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22559559','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22559559"><span>A low phase <span class="hlt">noise</span> microwave <span class="hlt">source</span> for atomic spin squeezing experiments in 87Rb.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chen, Zilong; Bohnet, Justin G; Weiner, Joshua M; Thompson, James K</p> <p>2012-04-01</p> <p>We describe and characterize a simple, low cost, low phase <span class="hlt">noise</span> microwave <span class="hlt">source</span> that operates near 6.800 GHz for agile, coherent manipulation of ensembles of (87)Rb. Low phase <span class="hlt">noise</span> is achieved by directly multiplying a low phase <span class="hlt">noise</span> 100 MHz crystal to 6.8 GHz using a nonlinear transmission line and filtering the output with custom band-pass filters. The fixed frequency signal is single sideband modulated with a direct digital synthesis frequency <span class="hlt">source</span> to provide the desired phase, amplitude, and frequency control. Before modulation, the <span class="hlt">source</span> has a single sideband phase <span class="hlt">noise</span> near -140 dBc/Hz in the range of 10 kHz-1 MHz offset from the carrier frequency and -130 dBc/Hz after modulation. The resulting <span class="hlt">source</span> is estimated to contribute added spin-<span class="hlt">noise</span> variance 16 dB below the quantum projection <span class="hlt">noise</span> level during quantum nondemolition measurements of the clock transition in an ensemble 7 × 10(5) (87)Rb atoms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4336190','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4336190"><span>Exposures to Transit and Other <span class="hlt">Sources</span> of <span class="hlt">Noise</span> among New York City Residents</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Neitzel, Richard L.; Gershon, Robyn R. M.; McAlexander, Tara P.; Magda, Lori A.; Pearson, Julie M.</p> <p>2015-01-01</p> <p>To evaluate the contributions of common <span class="hlt">noise</span> <span class="hlt">sources</span> to total annual <span class="hlt">noise</span> exposures among urban residents and workers, we estimated exposures associated with five common <span class="hlt">sources</span> (use of mass transit, occupational and non-occupational activities, MP3 player and stereo use, and time at home and doing other miscellaneous activities) among a sample of over 4500 individuals in New York City (NYC). We then evaluated the contributions of each <span class="hlt">source</span> to total <span class="hlt">noise</span> exposure and also compared our estimated exposures to the recommended 70 dBA annual exposure limit. We found that one in ten transit users had <span class="hlt">noise</span> exposures in excess of the recommended exposure limit from their transit use alone. When we estimated total annual exposures, 90% of NYC transit users and 87% of nonusers exceeded the recommended limit. MP3 player and stereo use, which represented a small fraction of the total annual hours for each subject on average, was the primary <span class="hlt">source</span> of exposure among the majority of urban dwellers we evaluated. Our results suggest that the vast majority of urban mass transit riders may be at risk of permanent, irreversible <span class="hlt">noise</span>-induced hearing loss and that, for many individuals, this risk is driven primarily by exposures other than occupational <span class="hlt">noise</span>. PMID:22088203</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001RaSc...36.1659N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001RaSc...36.1659N"><span>Statistical addition method for external <span class="hlt">noise</span> <span class="hlt">sources</span> affecting HF-MF-LF systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Neudegg, David</p> <p>2001-01-01</p> <p>The current statistical method for the addition of external component <span class="hlt">noise</span> <span class="hlt">sources</span> in the LF, MF, and lower HF band (100 kHz to 3 MHz) produces total median <span class="hlt">noise</span> levels that may be less than the largest-component median in some cases. Several case studies illustrate this anomaly. Methods used to sum the components rely on their power (decibels) distributions being represented as normal by the statistical parameters. The atmospheric <span class="hlt">noise</span> component is not correctly represented by its decile values when it is assumed to have a normal distribution, causing anomalies in the <span class="hlt">noise</span> summation when components are similar in magnitude. A revised component summation method is proposed, and the way it provides a more physically realistic total <span class="hlt">noise</span> median for LF, MF, and lower HF frequencies is illustrated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20060019177','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20060019177"><span>Reducing Propulsion <span class="hlt">Airframe</span> Aeroacoustic Interactions with Uniquely Tailored Chevrons. 1.; Isolated Nozzles</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mengle, Vinod G.; Elkroby, Ronen; Brunsniak, Leon; Thomas, Russ H.</p> <p>2006-01-01</p> <p>The flow/acoustic environment surrounding an engine nozzle installed on an airplane, say, under the wing, is asymmetric due to the pylon, the wing and the interaction of the exhaust jet with flaps on the wing. However, the conventional chevrons, which are azimuthally uniform serrations on the nozzle lip, do not exploit the asymmetry due to these propulsion <span class="hlt">airframe</span> aeroacoustic interactions to reduce jet <span class="hlt">noise</span>. In this pioneering study we use this non-axisymmetry to our advantage and examine if the total jet-related <span class="hlt">noise</span> radiated to the ground can be reduced by using different types of azimuthally varying chevrons (AVC) which vary the mixing around the nozzle periphery. Several scale models of the isolated nozzle, representative of high bypass ratio engine nozzles, were made with a pylon and azimuthally varying chevrons on both fan and core nozzles to enhance mixing at the top (near the pylon) with less mixing at the bottom (away from the pylon) or vice versa. Various combinations of fan and core AVC nozzles were systematically tested at typical take-off conditions inside a free jet wind-tunnel and, here, in Part 1 we analyze the acoustics results for the isolated nozzle with a pylon, with installation effects reported in Parts 2 and 3. Several interesting results are discovered: amongst the fan AVCs the top-enhanced mixing T-fan chevron nozzle is quieter in combination with any core AVC nozzle when compared to conventional chevrons; however, the bottom-mixing B-fan chevrons, as well as the core AVC nozzles, by themselves, are noisier. Further, the low-frequency <span class="hlt">source</span> strengths in the jet plume, obtained via phased microphone arrays, also corroborate the far field sound, and for the T-fan chevrons such <span class="hlt">sources</span> move further downstream than those for baseline or conventional chevron nozzles.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhyC..518...85Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhyC..518...85Y"><span>Design and test of component circuits of an integrated quantum voltage <span class="hlt">noise</span> <span class="hlt">source</span> for Johnson <span class="hlt">noise</span> thermometry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yamada, Takahiro; Maezawa, Masaaki; Urano, Chiharu</p> <p>2015-11-01</p> <p>We present design and testing of a pseudo-random number generator (PRNG) and a variable pulse number multiplier (VPNM) which are digital circuit subsystems in an integrated quantum voltage <span class="hlt">noise</span> <span class="hlt">source</span> for Jonson <span class="hlt">noise</span> thermometry. Well-defined, calculable pseudo-random patterns of single flux quantum pulses are synthesized with the PRNG and multiplied digitally with the VPNM. The circuit implementation on rapid single flux quantum technology required practical circuit scales and bias currents, 279 junctions and 33 mA for the PRNG, and 1677 junctions and 218 mA for the VPNM. We confirmed the circuit operation with sufficiently wide margins, 80-120%, with respect to the designed bias currents.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSV...375...53F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSV...375...53F"><span>Spatial resolution limits for the localization of <span class="hlt">noise</span> <span class="hlt">sources</span> using direct sound mapping</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fernandez Comesaña, D.; Holland, K. R.; Fernandez-Grande, E.</p> <p>2016-08-01</p> <p>One of the main challenges arising from <span class="hlt">noise</span> and vibration problems is how to identify the areas of a device, machine or structure that produce significant acoustic excitation, i.e. the localization of main <span class="hlt">noise</span> <span class="hlt">sources</span>. The direct visualization of sound, in particular sound intensity, has extensively been used for many years to locate sound <span class="hlt">sources</span>. However, it is not yet well defined when two <span class="hlt">sources</span> should be regarded as resolved by means of direct sound mapping. This paper derives the limits of the direct representation of sound pressure, particle velocity and sound intensity by exploring the relationship between spatial resolution, <span class="hlt">noise</span> level and geometry. The proposed expressions are validated via simulations and experiments. It is shown that particle velocity mapping yields better results for identifying closely spaced sound <span class="hlt">sources</span> than sound pressure or sound intensity, especially in the acoustic near-field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970003410','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970003410"><span>Definition of 1992 Technology Aircraft <span class="hlt">Noise</span> Levels and the Methodology for Assessing Airplane <span class="hlt">Noise</span> Impact of Component <span class="hlt">Noise</span> Reduction Concepts</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kumasaka, Henry A.; Martinez, Michael M.; Weir, Donald S.</p> <p>1996-01-01</p> <p>This report describes the methodology for assessing the impact of component <span class="hlt">noise</span> reduction on total airplane system <span class="hlt">noise</span>. The methodology is intended to be applied to the results of individual study elements of the NASA-Advanced Subsonic Technology (AST) <span class="hlt">Noise</span> Reduction Program, which will address the development of <span class="hlt">noise</span> reduction concepts for specific components. Program progress will be assessed in terms of <span class="hlt">noise</span> reduction achieved, relative to baseline levels representative of 1992 technology airplane/engine design and performance. In this report, the 1992 technology reference levels are defined for assessment models based on four airplane sizes - an average business jet and three commercial transports: a small twin, a medium sized twin, and a large quad. Study results indicate that component changes defined as program final goals for nacelle treatment and engine/<span class="hlt">airframe</span> <span class="hlt">source</span> <span class="hlt">noise</span> reduction would achieve from 6-7 EPNdB reduction of total airplane <span class="hlt">noise</span> at FAR 36 Stage 3 <span class="hlt">noise</span> certification conditions for all of the airplane <span class="hlt">noise</span> assessment models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006JSV...295..781V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006JSV...295..781V"><span>Experimental determination of the tonal <span class="hlt">noise</span> <span class="hlt">sources</span> in a centrifugal fan</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Velarde-Suárez, Sandra; Ballesteros-Tajadura, Rafael; Pablo Hurtado-Cruz, Juan; Santolaria-Morros, Carlos</p> <p>2006-08-01</p> <p>In this work, an experimental study about the aerodynamic tonal <span class="hlt">noise</span> <span class="hlt">sources</span> in a centrifugal fan with backward-curved blades has been carried out. Acoustic pressure measurements at the fan exit duct and pressure fluctuation measurements on the volute surface have been made for different flow rates. A correlation study of both pressure signals has been made in order to explain some of the features of the aerodynamic tonal <span class="hlt">noise</span> generation. A strong <span class="hlt">source</span> of <span class="hlt">noise</span> caused by the interaction between the fluctuating flow leaving the impeller and the volute tongue is appreciated. The unsteady forces exerted on the fan blades constitute another <span class="hlt">noise</span> generation mechanism, which affects the whole extension of the impeller, thus transmitting pressure fluctuations to the entire volute casing. The relative importance of this mechanism compared to the impeller-tongue interaction depends on the flow rate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040191552','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040191552"><span>Development in <span class="hlt">Source</span> Modeling and Sound Propagation for Jet <span class="hlt">Noise</span> Predictions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Leib, Steward</p> <p>2004-01-01</p> <p>The purpose of the research carried out under this cooperative agreement was to develop tools that could be used to improve upon the current state of the art in the prediction of <span class="hlt">noise</span> emitted by turbulent exhaust jets. Both the <span class="hlt">source</span> modeling and sound propagation aspects of the prediction of jet <span class="hlt">noise</span> by acoustic analogy were examined with a view toward the development of methods which yield improved predictions over a wider range of operating conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040086700','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040086700"><span>NASA's Subsonic Jet Transport <span class="hlt">Noise</span> Reduction Research</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Powell, Clemans A.; Preisser, John S.</p> <p>2000-01-01</p> <p>Although new jet transport airplanes in today s fleet are considerably quieter than the first jet transports introduced about 40 years ago, airport community <span class="hlt">noise</span> continues to be an important environmental issue. NASA s Advanced Subsonic Transport (AST) <span class="hlt">Noise</span> Reduction program was begun in 1994 as a seven-year effort to develop technology to reduce jet transport <span class="hlt">noise</span> 10 dB relative to 1992 technology. This program provides for reductions in engine <span class="hlt">source</span> <span class="hlt">noise</span>, improvements in nacelle acoustic treatments, reductions in the <span class="hlt">noise</span> generated by the <span class="hlt">airframe</span>, and improvements in the way airplanes are operated in the airport environs. These <span class="hlt">noise</span> reduction efforts will terminate at the end of 2001 and it appears that the objective will be met. However, because of an anticipated 3-8% growth in passenger and cargo operations well into the 21st Century and the slow introduction of new the <span class="hlt">noise</span> reduction technology into the fleet, world aircraft <span class="hlt">noise</span> impact will remain essentially constant until about 2020 to 2030 and thereafter begin to rise. Therefore NASA has begun planning with the Federal Aviation Administration, industry, universities and environmental interest groups in the USA for a new <span class="hlt">noise</span> reduction initiative to provide technology for significant further reductions.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_11 --> <div id="page_12" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="221"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADB055403','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADB055403"><span>Combat Maintenance Concepts and Repair Techniques for Helicopter <span class="hlt">Airframe</span> Structures</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1981-01-01</p> <p>helicopter <span class="hlt">airframe</span> and to de- velop concepts for the assessment and repair of <span class="hlt">airframe</span> combat damage. A computer model was developed to generate...random simulated hallistic strikes on the Black Hawk helicopter <span class="hlt">airframe</span>. Random shotlines were generated with the model , and cases involving damage...Distribution of Ballistic Hits on Helicopters from Southeast Asia Combat Experience 23 Shotline Simulation Model 24 Conventions for Azimuth and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050031174','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050031174"><span><span class="hlt">Airframe</span> Technology Development for Next Generation Launch Vehicles</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Glass, David E.</p> <p>2004-01-01</p> <p>The <span class="hlt">Airframe</span> subproject within NASA's Next Generation Launch Technology (NGLT) program has the responsibility to develop <span class="hlt">airframe</span> technology for both rocket and airbreathing vehicles for access to space. The <span class="hlt">Airframe</span> sub-project pushes the state-of-the-art in <span class="hlt">airframe</span> technology for low-cost, reliable, and safe space transportation. Both low and medium technology readiness level (TRL) activities are being pursued. The key technical areas being addressed include design and integration, hot and integrated structures, cryogenic tanks, and thermal protection systems. Each of the technologies in these areas are discussed in this paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10141287','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10141287"><span>An improved assessment approach for <span class="hlt">noise</span> impacts from stationary point and traffic <span class="hlt">sources</span> on humans and wildlife</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Chang, Young-Soo; Chun, K.C.</p> <p>1994-04-01</p> <p>This paper presents an improved, efficient approach for assessing <span class="hlt">noise</span> impacts associated with a complex set of <span class="hlt">noise</span> <span class="hlt">sources</span> at multiple receptor locations; <span class="hlt">noise</span> impacts form typical remedial activities at a contaminated industrial site are used as an example. The <span class="hlt">noise</span> <span class="hlt">sources</span> associated with remedial activities at the site and surrounding areas are described, the <span class="hlt">noise</span>-propagation modeling methods and results are presented, and an impact assessment of the contaminated site is discussed with regard to applicable regulatory standards and individual and community responses. Also discussed is the improved <span class="hlt">noise</span> assessment approach. The improved features demonstrated are automate approaches for (1) inputting long-term hourly meterorological data (e.g., 8,760 hours for a one-year period) into a long-range <span class="hlt">noise</span>-propagation model for computing <span class="hlt">noise</span>-level increases at receptor locations and (2) analyzing potential individual and community responses to intrusive <span class="hlt">noises</span> using the IAP and modified CNR.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002JSV...251..457G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002JSV...251..457G"><span>Active Control of a Moving <span class="hlt">Noise</span> SOURCE—EFFECT of Off-Axis <span class="hlt">Source</span> Position</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>GUO, J.; PAN, J.; HODGSON, M.</p> <p>2002-03-01</p> <p>An optimally arranged multiple-channel active-control system is known to be able to create a large quiet zone in free space for a stationary primary <span class="hlt">noise</span> <span class="hlt">source</span>. When the primary <span class="hlt">noise</span> <span class="hlt">source</span> moves, the active control of the <span class="hlt">noise</span> becomes much more difficult, as the primary <span class="hlt">noise</span> field changes with time in space. In this case, the controller of the control system must respond fast enough to compensate for the change; much research has been focused on this issue. In this paper, it is shown that a moving <span class="hlt">source</span> also causes difficulties from an acoustical perspective. A moving <span class="hlt">source</span> not only changes continuously the strengths and phases of the sound field in the space, but also changes the wavefront of the primary sound field continuously. It is known that the efficiency of active <span class="hlt">noise</span> control is determined mainly by the wavefront matching between the primary and control fields. To keep the control system effective in the case of a moving <span class="hlt">source</span>, the wavefront of the control field needs to change, in order to continuously match the primary-wavefront change. This paper shows that there are limitations to the control-wavefront change. An optimally pre-arranged, multiple-channel control system is not able to construct a matching wavefront when the primary <span class="hlt">source</span> moves outside a certain range. In other words, the control system is still able to create a large quiet zone only when the primary <span class="hlt">source</span> moves within a range around the central axis of the control system. Both the location and the size of the quiet zone change with the location of the primary <span class="hlt">source</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770020173','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770020173"><span>Preliminary study of a hydrogen peroxide rocket for use in moving <span class="hlt">source</span> jet <span class="hlt">noise</span> tests</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Plencner, R. M.</p> <p>1977-01-01</p> <p>A preliminary investigation was made of using a hydrogen peroxide rocket to obtain pure moving <span class="hlt">source</span> jet <span class="hlt">noise</span> data. The thermodynamic cycle of the rocket was analyzed. It was found that the thermodynamic exhaust properties of the rocket could be made to match those of typical advanced commercial supersonic transport engines. The rocket thruster was then considered in combination with a streamlined ground car for moving <span class="hlt">source</span> jet <span class="hlt">noise</span> experiments. When a nonthrottlable hydrogen peroxide rocket was used to accelerate the vehicle, propellant masses and/or acceleration distances became too large. However, when a throttlable rocket or an auxiliary system was used to accelerate the vehicle, reasonable propellant masses could be obtained.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JSV...386..283C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JSV...386..283C"><span>Nonlinear secondary <span class="hlt">noise</span> <span class="hlt">sources</span> for passive defect detection using ultrasound sensors</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chehami, Lynda; Moulin, Emmanuel; de Rosny, Julien; Prada, Claire; Chatelet, Eric; Lacerra, Giovanna; Gryllias, Konstantinos; Massi, Francesco</p> <p>2017-01-01</p> <p>This paper introduces the concept of secondary <span class="hlt">noise</span> <span class="hlt">sources</span> for passive defect detection and localization in structures. The proposed solution allows for the exploitation of the principle of Green's function reconstruction from <span class="hlt">noise</span> correlation, even in the absence of an adequate ambient <span class="hlt">noise</span>. The main principle is to convert a part of low-frequency modal vibrations into high-frequency <span class="hlt">noise</span> by exploiting the frictional contact nonlinearities. The device consists of a mass-spring resonator coupled to a flexible beam by a rough frictional interface. The extremity of the beam, attached to the surface of a plate, excites efficiently flexural waves in the plate up to 30 kHz when the primary resonator vibrates around its natural frequency, i.e. a few dozens Hz. A set of such devices is placed at random positions on the plate surface, and low-frequency excitation is provided by a shaker. The generated high-frequency <span class="hlt">noise</span> is recorded by an array of eight piezoelectric transducers attached to the plate. A differential correlation matrix is constructed by subtracting correlation functions computed from <span class="hlt">noise</span> signals at each sensor pairs, before and after the introduction of a local heterogeneity mimicking a defect. A simple array processing then allows for the detection and estimation of the defect location from this differential correlation matrix. Beyond the successful proof of concept, influence of experimental parameters, such as the number of secondary <span class="hlt">sources</span> or the variability of the position of the shaker application point, is also investigated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/788041','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/788041"><span>Further development of low <span class="hlt">noise</span> MEVVA ion <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Oks, Efim; Yushkov, George; Litovko, Irina; Anders, Andre; Brown, Ian</p> <p>2001-08-28</p> <p>Based on the idea of a space-charge-limited mode of operation, the influence of a pair of electrostatic meshes on the beam parameters of the LBNL MEVVA-5 ion <span class="hlt">source</span> was investigated. The meshes were placed in the expansion zone of the vacuum arc plasma. Apart from reducing the level of beam current fluctuations, this mode of operation provides significant control over the ion charge state distribution of the extracted beam. These effects can be understood taking not only space charge but also the high-directed ion drift velocities into account that are the same for different ion charge states of a material. The results of simulations of the processes involved are in good agreement with the experimental results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26157639','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26157639"><span>Powerline <span class="hlt">noise</span> elimination in biomedical signals via blind <span class="hlt">source</span> separation and wavelet analysis.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Akwei-Sekyere, Samuel</p> <p>2015-01-01</p> <p>The distortion of biomedical signals by powerline <span class="hlt">noise</span> from recording biomedical devices has the potential to reduce the quality and convolute the interpretations of the data. Usually, powerline <span class="hlt">noise</span> in biomedical recordings are extinguished via band-stop filters. However, due to the instability of biomedical signals, the distribution of signals filtered out may not be centered at 50/60 Hz. As a result, self-correction methods are needed to optimize the performance of these filters. Since powerline <span class="hlt">noise</span> is additive in nature, it is intuitive to model powerline <span class="hlt">noise</span> in a raw recording and subtract it from the raw data in order to obtain a relatively clean signal. This paper proposes a method that utilizes this approach by decomposing the recorded signal and extracting powerline <span class="hlt">noise</span> via blind <span class="hlt">source</span> separation and wavelet analysis. The performance of this algorithm was compared with that of a 4th order band-stop Butterworth filter, empirical mode decomposition, independent component analysis and, a combination of empirical mode decomposition with independent component analysis. The proposed method was able to expel sinusoidal signals within powerline <span class="hlt">noise</span> frequency range with higher fidelity in comparison with the mentioned techniques, especially at low signal-to-<span class="hlt">noise</span> ratio.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22370652','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22370652"><span><span class="hlt">Noise</span> power spectral density of a fibre scattered-light interferometer with a semiconductor laser <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Alekseev, A E; Potapov, V T</p> <p>2013-10-31</p> <p>Spectral characteristics of the <span class="hlt">noise</span> intensity fluctuations at the output of a scattered-light interferometer, caused by phase fluctuations of semiconductor laser radiation are considered. This kind of <span class="hlt">noise</span> is one of the main factors limiting sensitivity of interferometric sensors. For the first time, to our knowledge, the expression is obtained for the average <span class="hlt">noise</span> power spectral density at the interferometer output versus the degree of a light <span class="hlt">source</span> coherence and length of the scattering segment. Also, the approximate expressions are considered which determine the power spectral density in the low-frequency range (up to 200 kHz) and in the limiting case of extended scattering segments. The expression obtained for the <span class="hlt">noise</span> power spectral density agrees with experimental normalised power spectra with a high accuracy. (interferometry of radiation)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PrAeS..68...27F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PrAeS..68...27F"><span>Aircraft <span class="hlt">noise</span> prediction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Filippone, Antonio</p> <p>2014-07-01</p> <p>This contribution addresses the state-of-the-art in the field of aircraft <span class="hlt">noise</span> prediction, simulation and minimisation. The point of view taken in this context is that of comprehensive models that couple the various aircraft systems with the acoustic <span class="hlt">sources</span>, the propagation and the flight trajectories. After an exhaustive review of the present predictive technologies in the relevant fields (<span class="hlt">airframe</span>, propulsion, propagation, aircraft operations, trajectory optimisation), the paper addresses items for further research and development. Examples are shown for several airplanes, including the Airbus A319-100 (CFM engines), the Bombardier Dash8-Q400 (PW150 engines, Dowty R408 propellers) and the Boeing B737-800 (CFM engines). Predictions are done with the flight mechanics code FLIGHT. The transfer function between flight mechanics and the <span class="hlt">noise</span> prediction is discussed in some details, along with the numerical procedures for validation and verification. Some code-to-code comparisons are shown. It is contended that the field of aircraft <span class="hlt">noise</span> prediction has not yet reached a sufficient level of maturity. In particular, some parametric effects cannot be investigated, issues of accuracy are not currently addressed, and validation standards are still lacking.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996AAS...188.5515T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996AAS...188.5515T"><span>Analysis of the Low-Frequency Radio <span class="hlt">Noise</span> Environment at Satellite Heights from Terrestrial <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Taylor, M. F.; Basart, J. P.; McCoy, M.; Rios, E.</p> <p>1996-05-01</p> <p>We have investigated the propagation of terrestrial radio <span class="hlt">sources</span> from 1 to 30 MHz (HF spectral region) through the ionosphere for the purpose of characterizing the interference spectrum on potential space-based, low-frequency-radio telescopes. A recent survey of the HF <span class="hlt">noise</span> environment at satellite heights from 1 to 14 MHz has been conducted using the WIND spacecraft. Radio frequencies for which the interference appears to be sufficiently low for radio telescopes are 1.3, 2.9, 3.1, 8.2, and 11.4 MHz. A model was developed to predict the HF <span class="hlt">noise</span> environment. Our current model includes a <span class="hlt">source</span> model, an ionospheric model, and a ray tracing model. The <span class="hlt">source</span> model was developed using known commercial broadcast stations found in the World Radio TV Handbook. The ICED ionospheric model was used to generate a model ionosphere. By ray tracing a terrestrially based broadcast <span class="hlt">source</span> through the model ionosphere, an ionospheric transfer function (ITF) was developed. By modifying the <span class="hlt">source</span> model using the ITF, we were able to simulate the expected <span class="hlt">noise</span> environment at satellite heights. Comparison of modeled and measured spectra show the majority of the <span class="hlt">noise</span> environment is due to known commercial broadcasters. Improved modeling is necessary because the slopes of the simulated spectra above the plasma frequency are too shallow, and the plasma cutoff frequencies are too high compared to the measured data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100019469','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100019469"><span>Phased Array <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Measurements Made on a Williams International FJ44 Engine</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Podboy, Gary G.; Horvath, Csaba</p> <p>2010-01-01</p> <p>A 48-microphone planar phased array system was used to acquire <span class="hlt">noise</span> <span class="hlt">source</span> localization data on a full-scale Williams International FJ44 turbofan engine. Data were acquired with the array at three different locations relative to the engine, two on the side and one in front of the engine. At the two side locations the planar microphone array was parallel to the engine centerline; at the front location the array was perpendicular to the engine centerline. At each of the three locations, data were acquired at eleven different engine operating conditions ranging from engine idle to maximum (take off) speed. Data obtained with the array off to the side of the engine were spatially filtered to separate the inlet and nozzle <span class="hlt">noise</span>. Tones occurring in the inlet and nozzle spectra were traced to the low and high speed spools within the engine. The phased array data indicate that the Inflow Control Device (ICD) used during this test was not acoustically transparent; instead, some of the <span class="hlt">noise</span> emanating from the inlet reflected off of the inlet lip of the ICD. This reflection is a <span class="hlt">source</span> of error for far field <span class="hlt">noise</span> measurements made during the test. The data also indicate that a total temperature rake in the inlet of the engine is a <span class="hlt">source</span> of fan <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=Aerodynamics&pg=7&id=ED302630','ERIC'); return false;" href="http://eric.ed.gov/?q=Aerodynamics&pg=7&id=ED302630"><span>Aviation Maintenance Technology. <span class="hlt">Airframe</span>. A201. <span class="hlt">Airframe</span> Structures and Non-Metallic Structural Repairs. Instructor Material.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Oklahoma State Board of Vocational and Technical Education, Stillwater. Curriculum and Instructional Materials Center.</p> <p></p> <p>This teacher's guide is designed to aid teachers in leading students through a module on <span class="hlt">airframe</span> structures and nonmetallic structural repairs. The module contains four units that cover the following topics: (1) identifying aerodynamic and construction characteristics of aircraft structures; (2) inspecting wooden structures; (3) inspecting and…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140002732','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140002732"><span>Psychoacoustic Analysis of Synthesized Jet <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Okcu, Selen; Rathsam, Jonathan; Rizzi, Stephen A.</p> <p>2013-01-01</p> <p>An aircraft <span class="hlt">noise</span> synthesis capability is being developed so the annoyance caused by proposed aircraft can be assessed during the design stage. To make synthesized signals as realistic as possible, high fidelity simulation is required for <span class="hlt">source</span> (e.g., engine <span class="hlt">noise</span>, <span class="hlt">airframe</span> <span class="hlt">noise</span>), propagation and receiver effects. This psychoacoustic study tests whether the jet <span class="hlt">noise</span> component of synthesized aircraft engine <span class="hlt">noise</span> can be made more realistic using a low frequency oscillator (LFO) technique to simulate fluctuations in level observed in recordings. Jet <span class="hlt">noise</span> predictions are commonly made in the frequency domain based on models of time-averaged empirical data. The synthesis process involves conversion of the frequency domain prediction into an audible pressure time history. However, because the predictions are time-invariant, the synthesized sound lacks fluctuations observed in recordings. Such fluctuations are hypothesized to be perceptually important. To introduce time-varying characteristics into jet <span class="hlt">noise</span> synthesis, a method has been developed that modulates measured or predicted 1/3-octave band levels with a (<20Hz) LFO. The LFO characteristics are determined through analysis of laboratory jet <span class="hlt">noise</span> recordings. For the aft emission angle, results indicate that signals synthesized using a generic LFO are perceived as more similar to recordings than those using no LFO, and signals synthesized with an angle-specific LFO are more similar to recordings than those synthesized with a generic LFO.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19720023233&hterms=frame+type+structure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dframe%2Btype%2Bstructure','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19720023233&hterms=frame+type+structure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dframe%2Btype%2Bstructure"><span>Advanced design concepts for shuttle <span class="hlt">airframe</span> structure</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Card, M. F.; Davis, J. G., Jr.; Shideler, J. L.</p> <p>1972-01-01</p> <p>The development of weight-saving advanced design concepts for shuttle <span class="hlt">airframe</span> structure is presented. Design concepts under investigation employ selective composite reinforcement and/or efficient geometric arrangements. An effort to develop metallic panel designs which exploit the relaxation of smooth external-surface requirements for skin structure is reviewed. Available highlights from research and development studies which investigate the application of composite reinforcement to the design of two types of fuselage panels, a shear web, a large fuselage frame, and a landing-gear-door assembly are presented. Preliminary results from these studies suggest weight savings of 25 percent can be obtained.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19860010915','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19860010915"><span>Optimal <span class="hlt">airframe</span> synthesis for gust loads</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hajela, P.</p> <p>1986-01-01</p> <p>An optimization capability for sizing <span class="hlt">airframe</span> structures that are subjected to a combination of deterministic and random flight loads was established. The random vibration environment introduces the need for selecting a statistical process that best describes the random loads and permits computation of the dynamic response parameters of interest. Furthermore, it requires a formulation of design constraints that would minimize the conservativeness in the design and retain computational viability. The random loads are treated as a stationary, homogeneous process with a Gaussian probability distribution. The formulation of the analysis problem, the structure of the optimization programming system and a representative numerical example are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850002601','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850002601"><span>Fuel efficiency through new <span class="hlt">airframe</span> technology</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Leonard, R. W.</p> <p>1982-01-01</p> <p>In its Aircraft Energy Efficiency Program, NASA has expended approximately 200 million dollars toward development and application of advanced <span class="hlt">airframe</span> technologies to United States's commercial transports. United States manufacturers have already been given a significant boost toward early application of advanced composite materials to control surface and empennage structures and toward selected applications of active controls and advanced aerodynamic concepts. In addition, significant progress in definition and development of innovative, but realistic systems for laminar flow control over the wings of future transports has already been made.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110011597','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110011597"><span>The Effects of Ambient Conditions on Helicopter Rotor <span class="hlt">Source</span> <span class="hlt">Noise</span> Modeling</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schmitz, Frederic H.; Greenwood, Eric</p> <p>2011-01-01</p> <p>A new physics-based method called Fundamental Rotorcraft Acoustic Modeling from Experiments (FRAME) is used to demonstrate the change in rotor harmonic <span class="hlt">noise</span> of a helicopter operating at different ambient conditions. FRAME is based upon a non-dimensional representation of the governing acoustic and performance equations of a single rotor helicopter. Measured external <span class="hlt">noise</span> is used together with parameter identification techniques to develop a model of helicopter external <span class="hlt">noise</span> that is a hybrid between theory and experiment. The FRAME method is used to evaluate the main rotor harmonic <span class="hlt">noise</span> of a Bell 206B3 helicopter operating at different altitudes. The variation with altitude of Blade-Vortex Interaction (BVI) <span class="hlt">noise</span>, known to be a strong function of the helicopter s advance ratio, is dependent upon which definition of airspeed is flown by the pilot. If normal flight procedures are followed and indicated airspeed (IAS) is held constant, the true airspeed (TAS) of the helicopter increases with altitude. This causes an increase in advance ratio and a decrease in the speed of sound which results in large changes to BVI <span class="hlt">noise</span> levels. Results also show that thickness <span class="hlt">noise</span> on this helicopter becomes more intense at high altitudes where advancing tip Mach number increases because the speed of sound is decreasing and advance ratio increasing for the same indicated airspeed. These results suggest that existing measurement-based empirically derived helicopter rotor <span class="hlt">noise</span> <span class="hlt">source</span> models may give incorrect <span class="hlt">noise</span> estimates when they are used at conditions where data were not measured and may need to be corrected for mission land-use planning purposes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18465745','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18465745"><span>Mapping the signal-to-<span class="hlt">noise</span>-ratios of cortical <span class="hlt">sources</span> in magnetoencephalography and electroencephalography.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Goldenholz, Daniel M; Ahlfors, Seppo P; Hämäläinen, Matti S; Sharon, Dahlia; Ishitobi, Mamiko; Vaina, Lucia M; Stufflebeam, Steven M</p> <p>2009-04-01</p> <p>Although magnetoencephalography (MEG) and electroencephalography (EEG) have been available for decades, their relative merits are still debated. We examined regional differences in signal-to-<span class="hlt">noise</span>-ratios (SNRs) of cortical <span class="hlt">sources</span> in MEG and EEG. Data from four subjects were used to simulate focal and extended <span class="hlt">sources</span> located on the cortical surface reconstructed from high-resolution magnetic resonance images. The SNR maps for MEG and EEG were found to be complementary. The SNR of deep <span class="hlt">sources</span> was larger in EEG than in MEG, whereas the opposite was typically the case for superficial <span class="hlt">sources</span>. Overall, the SNR maps were more uniform for EEG than for MEG. When using a <span class="hlt">noise</span> model based on uniformly distributed random <span class="hlt">sources</span> on the cortex, the SNR in MEG was found to be underestimated, compared with the maps obtained with <span class="hlt">noise</span> estimated from actual recorded MEG and EEG data. With extended <span class="hlt">sources</span>, the total area of cortex in which the SNR was higher in EEG than in MEG was larger than with focal <span class="hlt">sources</span>. Clinically, SNR maps in a patient explained differential sensitivity of MEG and EEG in detecting epileptic activity. Our results emphasize the benefits of recording MEG and EEG simultaneously.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2882168','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2882168"><span>Mapping the Signal-To-<span class="hlt">Noise</span>-Ratios of Cortical <span class="hlt">Sources</span> in Magnetoencephalography and Electroencephalography</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Goldenholz, Daniel M.; Ahlfors, Seppo P.; Hämäläinen, Matti S.; Sharon, Dahlia; Ishitobi, Mamiko; Vaina, Lucia M.; Stufflebeam, Steven M.</p> <p>2010-01-01</p> <p>Although magnetoencephalography (MEG) and electroencephalography (EEG) have been available for decades, their relative merits are still debated. We examined regional differences in signal-to-<span class="hlt">noise</span>-ratios (SNRs) of cortical <span class="hlt">sources</span> in MEG and EEG. Data from four subjects were used to simulate focal and extended <span class="hlt">sources</span> located on the cortical surface reconstructed from high-resolution magnetic resonance images. The SNR maps for MEG and EEG were found to be complementary. The SNR of deep <span class="hlt">sources</span> was larger in EEG than in MEG, whereas the opposite was typically the case for superficial <span class="hlt">sources</span>. Overall, the SNR maps were more uniform for EEG than for MEG. When using a <span class="hlt">noise</span> model based on uniformly distributed random <span class="hlt">sources</span> on the cortex, the SNR in MEG was found to be underestimated, compared with the maps obtained with <span class="hlt">noise</span> estimated from actual recorded MEG and EEG data. With extended <span class="hlt">sources</span>, the total area of cortex in which the SNR was higher in EEG than in MEG was larger than with focal <span class="hlt">sources</span>. Clinically, SNR maps in a patient explained differential sensitivity of MEG and EEG in detecting epileptic activity. Our results emphasize the benefits of recording MEG and EEG simultaneously. PMID:18465745</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_12 --> <div id="page_13" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="241"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100024453','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100024453"><span>On Acoustic <span class="hlt">Source</span> Specification for Rotor-Stator Interaction <span class="hlt">Noise</span> Prediction</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nark, Douglas M.; Envia, Edmane; Burley, Caesy L.</p> <p>2010-01-01</p> <p>This paper describes the use of measured <span class="hlt">source</span> data to assess the effects of acoustic <span class="hlt">source</span> specification on rotor-stator interaction <span class="hlt">noise</span> predictions. Specifically, the acoustic propagation and radiation portions of a recently developed coupled computational approach are used to predict tonal rotor-stator interaction <span class="hlt">noise</span> from a benchmark configuration. In addition to the use of full measured data, randomization of <span class="hlt">source</span> mode relative phases is also considered for specification of the acoustic <span class="hlt">source</span> within the computational approach. Comparisons with sideline <span class="hlt">noise</span> measurements are performed to investigate the effects of various <span class="hlt">source</span> descriptions on both inlet and exhaust predictions. The inclusion of additional modal <span class="hlt">source</span> content is shown to have a much greater influence on the inlet results. Reasonable agreement between predicted and measured levels is achieved for the inlet, as well as the exhaust when shear layer effects are taken into account. For the number of trials considered, phase randomized predictions follow statistical distributions similar to those found in previous statistical <span class="hlt">source</span> investigations. The shape of the predicted directivity pattern relative to measurements also improved with phase randomization, having predicted levels generally within one standard deviation of the measured levels.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20030107607','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030107607"><span>Relationship between Aircraft <span class="hlt">Noise</span> Contour Area and <span class="hlt">Noise</span> Levels at Certification Points</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Powell, Clemans A.</p> <p>2003-01-01</p> <p>The use of sound exposure level contour area reduction has been proposed as an alternative or supplemental metric of progress and success for the NASA Quiet Aircraft Technology program, which currently uses the average of predicted <span class="hlt">noise</span> reductions at three community locations. As the program has expanded to include reductions in <span class="hlt">airframe</span> <span class="hlt">noise</span> as well as reduction due to optimization of operating procedures for lower <span class="hlt">noise</span>, there is concern that the three-point methodology may not represent a fair measure of benefit to airport communities. This paper addresses several topics related to this proposal: (1) an analytical basis for a relationship between certification <span class="hlt">noise</span> levels and <span class="hlt">noise</span> contour areas for departure operations is developed, (2) the relationship between predicted <span class="hlt">noise</span> contour area and the <span class="hlt">noise</span> levels measured or predicted at the certification measurement points is examined for a wide range of commercial and business aircraft, and (3) reductions in contour area for low-<span class="hlt">noise</span> approach scenarios are predicted and equivalent reductions in <span class="hlt">source</span> <span class="hlt">noise</span> are determined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5362733','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5362733"><span>Computational Acoustic Beamforming for <span class="hlt">Noise</span> <span class="hlt">Source</span> Identification for Small Wind Turbines</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Lien, Fue-Sang</p> <p>2017-01-01</p> <p>This paper develops a computational acoustic beamforming (CAB) methodology for identification of <span class="hlt">sources</span> of small wind turbine <span class="hlt">noise</span>. This methodology is validated using the case of the NACA 0012 airfoil trailing edge <span class="hlt">noise</span>. For this validation case, the predicted acoustic maps were in excellent conformance with the results of the measurements obtained from the acoustic beamforming experiment. Following this validation study, the CAB methodology was applied to the identification of <span class="hlt">noise</span> <span class="hlt">sources</span> generated by a commercial small wind turbine. The simulated acoustic maps revealed that the blade tower interaction and the wind turbine nacelle were the two primary mechanisms for sound generation for this small wind turbine at frequencies between 100 and 630 Hz. PMID:28378012</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050207443','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050207443"><span>Identification of <span class="hlt">Noise</span> <span class="hlt">Sources</span> in High Speed Jets via Correlation Measurements: A Review</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bridges, James (Technical Monitor); Panda, Jayanta</p> <p>2005-01-01</p> <p>Significant advancement has been made in the last few years to identify <span class="hlt">noise</span> <span class="hlt">sources</span> in high speed jets via direct correlation measurements. In this technique turbulent fluctuations in the flow are correlated with far field acoustics signatures. In the 1970 s there was a surge of work using mostly intrusive probes, and a few using Laser Doppler Velocimetry, to measure turbulent fluctuations. The later experiments established "shear <span class="hlt">noise</span>" as the primary <span class="hlt">source</span> for the shallow angle <span class="hlt">noise</span>. Various interpretations and criticisms from this time are described in the review. Recent progress in the molecular Rayleigh scattering based technique has provided a completely non-intrusive means of measuring density and velocity fluctuations. This has brought a renewed interest on correlation measurements. We have performed five different sets of experiments in single stream jets of different Mach number, temperature ratio and nozzle configurations. The present paper tries to summarize the correlation data from these works.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28378012','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28378012"><span>Computational Acoustic Beamforming for <span class="hlt">Noise</span> <span class="hlt">Source</span> Identification for Small Wind Turbines.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ma, Ping; Lien, Fue-Sang; Yee, Eugene</p> <p>2017-01-01</p> <p>This paper develops a computational acoustic beamforming (CAB) methodology for identification of <span class="hlt">sources</span> of small wind turbine <span class="hlt">noise</span>. This methodology is validated using the case of the NACA 0012 airfoil trailing edge <span class="hlt">noise</span>. For this validation case, the predicted acoustic maps were in excellent conformance with the results of the measurements obtained from the acoustic beamforming experiment. Following this validation study, the CAB methodology was applied to the identification of <span class="hlt">noise</span> <span class="hlt">sources</span> generated by a commercial small wind turbine. The simulated acoustic maps revealed that the blade tower interaction and the wind turbine nacelle were the two primary mechanisms for sound generation for this small wind turbine at frequencies between 100 and 630 Hz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23498706','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23498706"><span>Methodology of selecting the reference <span class="hlt">source</span> for an active <span class="hlt">noise</span> control system in a car.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Dąbrowski, Zbigniew; Stankiewicz, Bartosz</p> <p>2013-01-01</p> <p>At the end of the 20th century, a significant development in digital technologies of signal processing made it possible to apply active <span class="hlt">noise</span> control methods in new domains. A proper selection of the reference signal <span class="hlt">source</span> is a main problem in implementing such systems. This paper presents an estimation method based on an indicator of the coherent power level. It also presents a simple system of active <span class="hlt">noise</span> control in a car, operating according to the proposed method of optimising the positioning of reference <span class="hlt">sources</span>. This system makes it possible to considerably increase the comfort of work of drivers in various kinds of road transport without a great increase in cost. This is especially significant in the case of trucks and vans. Passive barriers are considerably more expensive in them, which results in a higher level of <span class="hlt">noise</span> than in passenger cars.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100019161','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100019161"><span>A Parameter Identification Method for Helicopter <span class="hlt">Noise</span> <span class="hlt">Source</span> Identification and Physics-Based Semi-Empirical Modeling</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Greenwood, Eric, II; Schmitz, Fredric H.</p> <p>2010-01-01</p> <p>A new physics-based parameter identification method for rotor harmonic <span class="hlt">noise</span> <span class="hlt">sources</span> is developed using an acoustic inverse simulation technique. This new method allows for the identification of individual rotor harmonic <span class="hlt">noise</span> <span class="hlt">sources</span> and allows them to be characterized in terms of their individual non-dimensional governing parameters. This new method is applied to both wind tunnel measurements and ground <span class="hlt">noise</span> measurements of two-bladed rotors. The method is shown to match the parametric trends of main rotor Blade-Vortex Interaction (BVI) <span class="hlt">noise</span>, allowing accurate estimates of BVI <span class="hlt">noise</span> to be made for operating conditions based on a small number of measurements taken at different operating conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADD020003','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADD020003"><span>Method and Apparatus for Reducing <span class="hlt">Noise</span> from Near Ocean Surface <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2001-10-01</p> <p>reducing the acoustic <span class="hlt">noise</span> from near-surface 4 <span class="hlt">sources</span> using an array processing technique that utilizes 5 Multiple Signal Classification ( MUSIC ...<span class="hlt">sources</span> without 13 degrading the signal level and quality of the TOI. The present 14 invention utilizes a unique application of the MUSIC beamforming...specific algorithm that utilizes a 5 MUSIC technique and estimates the direction of arrival (DOA) of 6 the acoustic signal signals and generates output</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20130003187','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130003187"><span>Auralization of Hybrid Wing Body Aircraft Flyover <span class="hlt">Noise</span> from System <span class="hlt">Noise</span> Predictions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Rizzi, Stephen A.; Aumann, Aric R.; Lopes, Leonvard V.; Burley, Casey L.</p> <p>2013-01-01</p> <p>System <span class="hlt">noise</span> assessments of a state-of-the-art reference aircraft (similar to a Boeing 777-200ER with GE90-like turbofan engines) and several hybrid wing body (HWB) aircraft configurations were recently performed using NASA engine and aircraft system analysis tools. The HWB aircraft were sized to an equivalent mission as the reference aircraft and assessments were performed using measurements of <span class="hlt">airframe</span> shielding from a series of propulsion <span class="hlt">airframe</span> aeroacoustic experiments. The focus of this work is to auralize flyover <span class="hlt">noise</span> from the reference aircraft and the best HWB configuration using <span class="hlt">source</span> <span class="hlt">noise</span> predictions and shielding data based largely on the earlier assessments. For each aircraft, three flyover conditions are auralized. These correspond to approach, sideline, and cutback operating states, but flown in straight and level flight trajectories. The auralizations are performed using synthesis and simulation tools developed at NASA. Audio and visual presentations are provided to allow the reader to experience the flyover from the perspective of a listener in the simulated environment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110011070','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110011070"><span>Use of a Microphone Phased Array to Determine <span class="hlt">Noise</span> <span class="hlt">Sources</span> in a Rocket Plume</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Panda, J.; Mosher, R.</p> <p>2010-01-01</p> <p>A 70-element microphone phased array was used to identify <span class="hlt">noise</span> <span class="hlt">sources</span> in the plume of a solid rocket motor. An environment chamber was built and other precautions were taken to protect the sensitive condenser microphones from rain, thunderstorms and other environmental elements during prolonged stay in the outdoor test stand. A camera mounted at the center of the array was used to photograph the plume. In the first phase of the study the array was placed in an anechoic chamber for calibration, and validation of the indigenous Matlab(R) based beamform software. It was found that the "advanced" beamform methods, such as CLEAN-SC was partially successful in identifying speaker <span class="hlt">sources</span> placed closer than the Rayleigh criteria. To participate in the field test all equipments were shipped to NASA Marshal Space Flight Center, where the elements of the array hardware were rebuilt around the test stand. The sensitive amplifiers and the data acquisition hardware were placed in a safe basement, and 100m long cables were used to connect the microphones, Kulites and the camera. The array chamber and the microphones were found to withstand the environmental elements as well as the shaking from the rocket plume generated <span class="hlt">noise</span>. The beamform map was superimposed on a photo of the rocket plume to readily identify the <span class="hlt">source</span> distribution. It was found that the plume made an exceptionally long, >30 diameter, <span class="hlt">noise</span> <span class="hlt">source</span> over a large frequency range. The shock pattern created spatial modulation of the <span class="hlt">noise</span> <span class="hlt">source</span>. Interestingly, the concrete pad of the horizontal test stand was found to be a good acoustic reflector: the beamform map showed two distinct <span class="hlt">source</span> distributions- the plume and its reflection on the pad. The array was found to be most effective in the frequency range of 2kHz to 10kHz. As expected, the classical beamform method excessively smeared the <span class="hlt">noise</span> <span class="hlt">sources</span> at lower frequencies and produced excessive side-lobes at higher frequencies. The "advanced" beamform</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19820026312','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19820026312"><span><span class="hlt">Noise</span> measurement in wind tunnels, workshop summary</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hickley, D. H.; Williams, J.</p> <p>1982-01-01</p> <p>In reviewing the progress made in acoustic measurements in wind tunnels over the 5-yr span of the workshops, it is evident that a great deal of progress has occurred. Specialized facilities are now on line, special measurement techniques were developed, and corrections were devised and proven. This capability is in the process of creating a new and more correct data bank on acoustic phenomena, and represents a major step forward in acoustics technology. Additional work is still required, but now, rather than concentrating on facilities and techniques, researchers may more profitably concentrate on <span class="hlt">noise-source</span> modeling, with the simulation of propulsor <span class="hlt">noise</span> <span class="hlt">source</span> (in flight) and of propulsor/<span class="hlt">airframe</span> airflow characteristics. Promising developments in directional acoustic receivers and other discrimination/correlation techniques should now be regularly exploited, in part for model <span class="hlt">noise-source</span> diagnosis, but also to expedite extraction of the lone <span class="hlt">source</span> signal from any residual background <span class="hlt">noise</span> and reverberation in the working chamber and from parasitic <span class="hlt">noise</span> due to essential rigs or instrumentation inside the airstream.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23556597','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23556597"><span>Localizing the <span class="hlt">sources</span> of two independent <span class="hlt">noises</span>: role of time varying amplitude differences.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Yost, William A; Brown, Christopher A</p> <p>2013-04-01</p> <p>Listeners localized the free-field <span class="hlt">sources</span> of either one or two simultaneous and independently generated <span class="hlt">noise</span> bursts. Listeners' localization performance was better when localizing one rather than two sound <span class="hlt">sources</span>. With two sound <span class="hlt">sources</span>, localization performance was better when the listener was provided prior information about the location of one of them. Listeners also localized two simultaneous <span class="hlt">noise</span> bursts that had sinusoidal amplitude modulation (AM) applied, in which the modulation envelope was in-phase across the two <span class="hlt">source</span> locations or was 180° out-of-phase. The AM was employed to investigate a hypothesis as to what process listeners might use to localize multiple sound <span class="hlt">sources</span>. The results supported the hypothesis that localization of two sound <span class="hlt">sources</span> might be based on temporal-spectral regions of the combined waveform in which the sound from one <span class="hlt">source</span> was more intense than that from the other <span class="hlt">source</span>. The interaural information extracted from such temporal-spectral regions might provide reliable estimates of the sound <span class="hlt">source</span> location that produced the more intense sound in that temporal-spectral region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20020048663&hterms=turbulent+jet&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dturbulent%2Bjet','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20020048663&hterms=turbulent+jet&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dturbulent%2Bjet"><span><span class="hlt">Noise</span> <span class="hlt">Sources</span> in a Low-Reynolds-Number Turbulent Jet at Mach 0.9</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Freund, Jonathan B.</p> <p>2001-01-01</p> <p>The mechanisms of sound generation in a Mach 0.9, Reynolds number 3600 turbulent jet are investigated by direct numerical simulation. Details of the numerical method are briefly outlined and results are validated against an experiment at the same flow conditions. Lighthill's theory is used to define a nominal acoustic <span class="hlt">source</span> in the jet, and a numerical solution of Lighthill's equation is compared to the simulation to verify the computational procedures. The acoustic <span class="hlt">source</span> is Fourier transformed in the axial coordinate and time and then filtered in order to identify and separate components capable of radiating to the far field. This procedure indicates that the peak radiating component of the <span class="hlt">source</span> is coincident with neither the peak of the full unfiltered <span class="hlt">source</span> nor that of the turbulent kinetic energy. The phase velocities of significant components range from approximately 5% to 50% of the ambient sound speed which calls into question the commonly made assumption that the <span class="hlt">noise</span> <span class="hlt">sources</span> convect at a single velocity. Space-time correlations demonstrate that the <span class="hlt">sources</span> are not acoustically compact in the streamwise direction and that the portion of the <span class="hlt">source</span> that radiates at angles greater than 45 deg. is stationary. Filtering non-radiating wavenumber components of the <span class="hlt">source</span> at single frequencies reveals that a simple modulated wave forms for the <span class="hlt">source</span>, as might be predicted by linear stability analysis. At small angles from the jet axis the <span class="hlt">noise</span> from these modes is highly directional, better described by an exponential than a standard Doppler factor.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080004428','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080004428"><span>Active control of aircraft engine inlet <span class="hlt">noise</span> using compact sound <span class="hlt">sources</span> and distributed error sensors</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Burdisso, Ricardo (Inventor); Fuller, Chris R. (Inventor); O'Brien, Walter F. (Inventor); Thomas, Russell H. (Inventor); Dungan, Mary E. (Inventor)</p> <p>1994-01-01</p> <p>An active <span class="hlt">noise</span> control system using a compact sound <span class="hlt">source</span> is effective to reduce aircraft engine duct <span class="hlt">noise</span>. The fan <span class="hlt">noise</span> from a turbofan engine is controlled using an adaptive filtered-x LMS algorithm. Single multi channel control systems are used to control the fan blade passage frequency (BPF) tone and the BPF tone and the first harmonic of the BPF tone for a plane wave excitation. A multi channel control system is used to control any spinning mode. The multi channel control system to control both fan tones and a high pressure compressor BPF tone simultaneously. In order to make active control of turbofan inlet <span class="hlt">noise</span> a viable technology, a compact sound <span class="hlt">source</span> is employed to generate the control field. This control field sound <span class="hlt">source</span> consists of an array of identical thin, cylindrically curved panels with an inner radius of curvature corresponding to that of the engine inlet. These panels are flush mounted inside the inlet duct and sealed on all edges to prevent leakage around the panel and to minimize the aerodynamic losses created by the addition of the panels. Each panel is driven by one or more piezoelectric force transducers mounted on the surface of the panel. The response of the panel to excitation is maximized when it is driven at its resonance; therefore, the panel is designed such that its fundamental frequency is near the tone to be canceled, typically 2000-4000 Hz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080004134','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080004134"><span>Active control of aircraft engine inlet <span class="hlt">noise</span> using compact sound <span class="hlt">sources</span> and distributed error sensors</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Burdisso, Ricardo (Inventor); Fuller, Chris R. (Inventor); O'Brien, Walter F. (Inventor); Thomas, Russell H. (Inventor); Dungan, Mary E. (Inventor)</p> <p>1996-01-01</p> <p>An active <span class="hlt">noise</span> control system using a compact sound <span class="hlt">source</span> is effective to reduce aircraft engine duct <span class="hlt">noise</span>. The fan <span class="hlt">noise</span> from a turbofan engine is controlled using an adaptive filtered-x LMS algorithm. Single multi channel control systems are used to control the fan blade passage frequency (BPF) tone and the BPF tone and the first harmonic of the BPF tone for a plane wave excitation. A multi channel control system is used to control any spinning mode. The multi channel control system to control both fan tones and a high pressure compressor BPF tone simultaneously. In order to make active control of turbofan inlet <span class="hlt">noise</span> a viable technology, a compact sound <span class="hlt">source</span> is employed to generate the control field. This control field sound <span class="hlt">source</span> consists of an array of identical thin, cylindrically curved panels with an inner radius of curvature corresponding to that of the engine inlet. These panels are flush mounted inside the inlet duct and sealed on all edges to prevent leakage around the panel and to minimize the aerodynamic losses created by the addition of the panels. Each panel is driven by one or more piezoelectric force transducers mounted on the surface of the panel. The response of the panel to excitation is maximized when it is driven at its resonance; therefore, the panel is designed such that its fundamental frequency is near the tone to be canceled, typically 2000-4000 Hz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.S31C..02P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.S31C..02P"><span>Ocean-Based Seismic <span class="hlt">Noise</span> <span class="hlt">Sources</span> Recorded by a Moderate Aperture Array in Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pratt, M. J.; Winberry, J. P.; Wiens, D.; Anandakrishnan, S.; Euler, G. G.</p> <p>2015-12-01</p> <p>The deployment of a temporary, 60 km aperture, broadband seismic array on the Whillans Ice Stream (WIS), West Antarctica provides an opportunity to analyze ocean-derived seismic <span class="hlt">noise</span> <span class="hlt">sources</span>. The location of Antarctica, surrounded by the Southern Ocean and the seasonal effect of sea ice on shallow water <span class="hlt">noise</span> production, allows for an intriguing experiment as to the production of primary and secondary microseisms. The WIS array was deployed for 2 months between December 2010-January 2011 with its primary objective to study WIS stick-slip events and glacial microseismicity. However, daylong stacks of station-to-station correlograms show directionality of the ambient <span class="hlt">noise</span> field within the frequency bands of the primary and secondary microseisms. Although the WIS array is located close to the grounding line, it lies 700 km from the nearest open water at the end of the austral summer. The array consists of 17 broadband stations arranged in a series of offset concentric circles that minimizes spatial artifacts with regards to the array response. We use beamforming analysis to show that primary microseisms (~15 s) are <span class="hlt">sourced</span> from three azimuthal directions with some ice-free coastline: Antarctic Peninsula, Victoria Land, and Dronning-Maude Land. Long-period secondary microseisms (~10 s) appear to be <span class="hlt">sourced</span> in the deep Southern Ocean and track storm systems. Short-period secondary microseisms (~6 s) show much more dependence on the continental shelf and possibly coastal reflections. This is consistent with year-long <span class="hlt">noise</span> spectra showing diminishment in the 15 s and 6 s bands [Grob et al. 2011]. Modeling of secondary microseism <span class="hlt">sources</span> [Ardhuin et al. 2011] provides insight on the <span class="hlt">sources</span> of surface wave <span class="hlt">noise</span> at higher frequencies. We backproject daily P and PKPbc body wave microseism signals found at lower ray parameters <span class="hlt">sourced</span> at distances of ~20-90° and ~145-155° respectively. The ocean <span class="hlt">sources</span> for these arrivals remain fairly consistent, suggesting a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110013150','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110013150"><span>Landing gear <span class="hlt">noise</span> attenuation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Moe, Jeffrey W. (Inventor); Whitmire, Julia (Inventor); Kwan, Hwa-Wan (Inventor); Abeysinghe, Amal (Inventor)</p> <p>2011-01-01</p> <p>A landing gear <span class="hlt">noise</span> attenuator mitigates <span class="hlt">noise</span> generated by <span class="hlt">airframe</span> deployable landing gear. The <span class="hlt">noise</span> attenuator can have a first position when the landing gear is in its deployed or down position, and a second position when the landing gear is in its up or stowed position. The <span class="hlt">noise</span> attenuator may be an inflatable fairing that does not compromise limited space constraints associated with landing gear retraction and stowage. A truck fairing mounted under a truck beam can have a compliant edge to allow for non-destructive impingement of a deflected fire during certain conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040082332','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040082332"><span>Further Progress in <span class="hlt">Noise</span> <span class="hlt">Source</span> Identification in High Speed Jets via Causality Principle</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Panda, J.; Seasholtz, R. G.; Elam, K. A.</p> <p>2004-01-01</p> <p>To locate <span class="hlt">noise</span> <span class="hlt">sources</span> in high-speed jets, the sound pressure fluctuations p/, measured at far field locations, were correlated with each of density p, axial velocity u, radial velocity v, puu and pvv fluctuations measured from various points in fully expanded, unheated plumes of Mach number 0.95, 1.4 and 1.8. The velocity and density fluctuations were measured simultaneously using a recently developed, non-intrusive, point measurement technique based on molecular Rayleigh scattering (Seasholtz, Panda, and Elam, AIAA Paper 2002-0827). The technique uses a continuous wave, narrow line-width laser, Fabry-Perot interferometer and photon counting electronics. The far field sound pressure fluctuations at 30 to the jet axis provided the highest correlation coefficients with all flow variables. The correlation coefficients decreased sharply with increased microphone polar angle, and beyond about 60 all correlation mostly fell below the experimental <span class="hlt">noise</span> floor. Among all correlations < puu; p/> showed the highest values. Interestingly, <p; p/>, in all respects, were very similar to <puu; p/>. The <v;p/> and <pvv;p/> correlations with 90deg microphone fell below the <span class="hlt">noise</span> floor. By moving the laser probe at various locations in the jet it was found that the strongest <span class="hlt">noise</span> <span class="hlt">source</span> lies downstream of the end of the potential core and extends many diameters beyond. Correlation measurement from the lip shear layer showed a Mach number dependency. While significant correlations were measured in Mach 1.8 jet, values were mostly below the <span class="hlt">noise</span> floor for subsonic Mach 0.95 jet. Various additional analyses showed that fluctuations from large organized structures mostly contributed to the measured correlation, while that from small scale structures fell below the <span class="hlt">noise</span> floor.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012SSEle..73...64M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012SSEle..73...64M"><span>RF dynamic and <span class="hlt">noise</span> performance of Metallic <span class="hlt">Source</span>/Drain SOI n-MOSFETs</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Martin, Maria J.; Pascual, Elena; Rengel, Raúl</p> <p>2012-07-01</p> <p>This paper presents a detailed study of the RF and <span class="hlt">noise</span> performance of n-type Schottky barrier (SB) MOSFETs with a particular focus on the influence of the Schottky barrier height (SBH) on the main dynamic and <span class="hlt">noise</span> figures of merit. With this aim, a 2D Monte Carlo simulator including tunnelling transport across Schottky interfaces has been developed, with special care to consider quantum transmission coefficients and the influence of image charge effects at the Schottky junctions. Particular attention is paid to the microscopic transport features, including carrier mean free paths or number of scattering events along the channel for investigating the optimization of the device topology and the strategic concepts related to the <span class="hlt">noise</span> performance of this new architecture. A more effective control of the gate electrode over drain current for low SBH (discussed in terms of internal physical quantities) is translated into an enhanced transconductance gm, cut-off frequency fT, and non-quasistatic dynamic parameters. The drain and gate intrinsic <span class="hlt">noise</span> <span class="hlt">sources</span> show a noteworthy degradation with the SBH reduction due to the increased current, influence of hot carriers and reduced number of phonon scatterings. However, the results evidence that this effect is counterbalanced by the extremely improved dynamic performance in terms of gm and fT. Therefore, the deterioration of the intrinsic <span class="hlt">noise</span> performance of the SB-MOSFET has no significant impact on high-frequency <span class="hlt">noise</span> FoMs as NFmin, Rn and Gass for low SBH and large gate overdrive conditions. The role of the SBH on Γopt, optimum <span class="hlt">noise</span> reactance and susceptance has been also analyzed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19870008968','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870008968"><span>Methods for designing treatments to reduce interior <span class="hlt">noise</span> of predominant <span class="hlt">sources</span> and paths in a single engine light aircraft</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hayden, Richard E.; Remington, Paul J.; Theobald, Mark A.; Wilby, John F.</p> <p>1985-01-01</p> <p>The <span class="hlt">sources</span> and paths by which <span class="hlt">noise</span> enters the cabin of a small single engine aircraft were determined through a combination of flight and laboratory tests. The primary <span class="hlt">sources</span> of <span class="hlt">noise</span> were found to be airborne <span class="hlt">noise</span> from the propeller and engine casing, airborne <span class="hlt">noise</span> from the engine exhaust, structureborne <span class="hlt">noise</span> from the engine/propeller combination and <span class="hlt">noise</span> associated with air flow over the fuselage. For the propeller, the primary airborne paths were through the firewall, windshield and roof. For the engine, the most important airborne path was through the firewall. Exhaust <span class="hlt">noise</span> was found to enter the cabin primarily through the panels in the vicinity of the exhaust outlet although exhaust <span class="hlt">noise</span> entering the cabin through the firewall is a distinct possibility. A number of <span class="hlt">noise</span> control techniques were tried, including firewall stiffening to reduce engine and propeller airborne <span class="hlt">noise</span>, to stage isolators and engine mounting spider stiffening to reduce structure-borne <span class="hlt">noise</span>, and wheel well covers to reduce air flow <span class="hlt">noise</span>.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <div id="page_14" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="261"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985bbn..rept.....H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985bbn..rept.....H"><span>Methods for designing treatments to reduce interior <span class="hlt">noise</span> of predominant <span class="hlt">sources</span> and paths in a single engine light aircraft</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hayden, Richard E.; Remington, Paul J.; Theobald, Mark A.; Wilby, John F.</p> <p>1985-03-01</p> <p>The <span class="hlt">sources</span> and paths by which <span class="hlt">noise</span> enters the cabin of a small single engine aircraft were determined through a combination of flight and laboratory tests. The primary <span class="hlt">sources</span> of <span class="hlt">noise</span> were found to be airborne <span class="hlt">noise</span> from the propeller and engine casing, airborne <span class="hlt">noise</span> from the engine exhaust, structureborne <span class="hlt">noise</span> from the engine/propeller combination and <span class="hlt">noise</span> associated with air flow over the fuselage. For the propeller, the primary airborne paths were through the firewall, windshield and roof. For the engine, the most important airborne path was through the firewall. Exhaust <span class="hlt">noise</span> was found to enter the cabin primarily through the panels in the vicinity of the exhaust outlet although exhaust <span class="hlt">noise</span> entering the cabin through the firewall is a distinct possibility. A number of <span class="hlt">noise</span> control techniques were tried, including firewall stiffening to reduce engine and propeller airborne <span class="hlt">noise</span>, to stage isolators and engine mounting spider stiffening to reduce structure-borne <span class="hlt">noise</span>, and wheel well covers to reduce air flow <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002PMB....47.2547J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002PMB....47.2547J"><span>Fast accurate MEG <span class="hlt">source</span> localization using a multilayer perceptron trained with real brain <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jun, Sung Chan; Pearlmutter, Barak A.; Nolte, Guido</p> <p>2002-07-01</p> <p>Iterative gradient methods such as Levenberg-Marquardt (LM) are in widespread use for <span class="hlt">source</span> localization from electroencephalographic (EEG) and magnetoencephalographic (MEG) signals. Unfortunately, LM depends sensitively on the initial guess, necessitating repeated runs. This, combined with LM's high per-step cost, makes its computational burden quite high. To reduce this burden, we trained a multilayer perceptron (MLP) as a real-time localizer. We used an analytical model of quasistatic electromagnetic propagation through a spherical head to map randomly chosen dipoles to sensor activities according to the sensor geometry of a 4D Neuroimaging Neuromag-122 MEG system, and trained a MLP to invert this mapping in the absence of <span class="hlt">noise</span> or in the presence of various sorts of <span class="hlt">noise</span> such as white Gaussian <span class="hlt">noise</span>, correlated <span class="hlt">noise</span>, or real brain <span class="hlt">noise</span>. A MLP structure was chosen to trade off computation and accuracy. This MLP was trained four times, with each type of <span class="hlt">noise</span>. We measured the effects of initial guesses on LM performance, which motivated a hybrid MLP-start-LM method, in which the trained MLP initializes LM. We also compared the localization performance of LM, MLPs, and hybrid MLP-start-LMs for realistic brain signals. Trained MLPs are much faster than other methods, while the hybrid MLP-start-LMs are faster and more accurate than fixed-4-start-LM. In particular, the hybrid MLP-start-LM initialized by a MLP trained with the real brain <span class="hlt">noise</span> dataset is 60 times faster and is comparable in accuracy to random-20-start-LM, and this hybrid system (localization error: 0.28 cm, computation time: 36 ms) shows almost as good performance as optimal-1-start-LM (localization error: 0.23 cm, computation time: 22 ms), which initializes LM with the correct dipole location. MLPs trained with <span class="hlt">noise</span> perform better than the MLP trained without <span class="hlt">noise</span>, and the MLP trained with real brain <span class="hlt">noise</span> is almost as good an initial guesser for LM as the correct dipole location.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007EJASP2008..247C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007EJASP2008..247C"><span>Maximum Likelihood DOA Estimation of Multiple Wideband <span class="hlt">Sources</span> in the Presence of Nonuniform Sensor <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, C. E.; Lorenzelli, F.; Hudson, R. E.; Yao, K.</p> <p>2007-12-01</p> <p>We investigate the maximum likelihood (ML) direction-of-arrival (DOA) estimation of multiple wideband <span class="hlt">sources</span> in the presence of unknown nonuniform sensor <span class="hlt">noise</span>. New closed-form expression for the direction estimation Cramér-Rao-Bound (CRB) has been derived. The performance of the conventional wideband uniform ML estimator under nonuniform <span class="hlt">noise</span> has been studied. In order to mitigate the performance degradation caused by the nonuniformity of the <span class="hlt">noise</span>, a new deterministic wideband nonuniform ML DOA estimator is derived and two associated processing algorithms are proposed. The first algorithm is based on an iterative procedure which stepwise concentrates the log-likelihood function with respect to the DOAs and the <span class="hlt">noise</span> nuisance parameters, while the second is a noniterative algorithm that maximizes the derived approximately concentrated log-likelihood function. The performance of the proposed algorithms is tested through extensive computer simulations. Simulation results show the stepwise-concentrated ML algorithm (SC-ML) requires only a few iterations to converge and both the SC-ML and the approximately-concentrated ML algorithm (AC-ML) attain a solution close to the derived CRB at high signal-to-<span class="hlt">noise</span> ratio.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25831324','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25831324"><span>Phase <span class="hlt">noise</span> measurement of wideband microwave <span class="hlt">sources</span> based on a microwave photonic frequency down-converter.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhu, Dengjian; Zhang, Fangzheng; Zhou, Pei; Pan, Shilong</p> <p>2015-04-01</p> <p>An approach for phase <span class="hlt">noise</span> measurement of microwave signal <span class="hlt">sources</span> based on a microwave photonic frequency down-converter is proposed. Using the same optical carrier, the microwave signal under test is applied to generate two +1st-order optical sidebands by two stages of electro-optical modulations. A time delay is introduced between the two sidebands through a span of fiber. By beating the two +1st-order sidebands at a photodetector, frequency down-conversion is implemented, and phase <span class="hlt">noise</span> of the signal under test can be calculated thereafter. The system has a very large operation bandwidth thanks to the frequency conversion in the optical domain, and good phase <span class="hlt">noise</span> measurement sensitivity can be achieved since the signal degradation caused by electrical amplifiers is avoided. An experiment is carried out. The phase <span class="hlt">noise</span> measured by the proposed system agrees well with that measured by a commercial spectrum analyzer or provided by the datasheet. A large operation bandwidth of 5-40 GHz is demonstrated using the proposed system. Moreover, good phase <span class="hlt">noise</span> floor is achieved (-123  dBc/Hz at 1 kHz and -137  dBc/Hz at 10 kHz at 10 GHz), which is nearly constant over the full measurement range.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27455301','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27455301"><span>Windmill <span class="hlt">Noise</span> Annoyance, Visual Aesthetics, and Attitudes towards Renewable Energy <span class="hlt">Sources</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Klæboe, Ronny; Sundfør, Hanne Beate</p> <p>2016-07-23</p> <p>A small focused socio-acoustic after-study of annoyance from a windmill park was undertaken after local health officials demanded a health impact study to look into neighborhood complaints. The windmill park consists of 31 turbines and is located in the South of Norway where it affects 179 dwellings. Simple exposure-effect relationships indicate stronger reactions to windmills and wind turbine <span class="hlt">noise</span> than shown internationally, with the caveat that the sample size is small (n = 90) and responses are colored by the existing local conflict. Pulsating swishing sounds and turbine engine hum are the main causes of <span class="hlt">noise</span> annoyance. About 60 per cent of those who participated in the survey were of the opinion that windmills degrade the landscape aesthetically, and were far from convinced that land-based windmills are desirable as a renewable energy <span class="hlt">source</span> (hydropower is an important alternative <span class="hlt">source</span> of renewables in Norway). Attitudes play an important role in addition to visual aesthetics in determining the acceptance of windmills and the resulting <span class="hlt">noise</span> annoyance. To compare results from different wind turbine <span class="hlt">noise</span> studies it seems necessary to assess the impact of important modifying factors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4997432','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4997432"><span>Windmill <span class="hlt">Noise</span> Annoyance, Visual Aesthetics, and Attitudes towards Renewable Energy <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Klæboe, Ronny; Sundfør, Hanne Beate</p> <p>2016-01-01</p> <p>A small focused socio-acoustic after-study of annoyance from a windmill park was undertaken after local health officials demanded a health impact study to look into neighborhood complaints. The windmill park consists of 31 turbines and is located in the South of Norway where it affects 179 dwellings. Simple exposure-effect relationships indicate stronger reactions to windmills and wind turbine <span class="hlt">noise</span> than shown internationally, with the caveat that the sample size is small (n = 90) and responses are colored by the existing local conflict. Pulsating swishing sounds and turbine engine hum are the main causes of <span class="hlt">noise</span> annoyance. About 60 per cent of those who participated in the survey were of the opinion that windmills degrade the landscape aesthetically, and were far from convinced that land-based windmills are desirable as a renewable energy <span class="hlt">source</span> (hydropower is an important alternative <span class="hlt">source</span> of renewables in Norway). Attitudes play an important role in addition to visual aesthetics in determining the acceptance of windmills and the resulting <span class="hlt">noise</span> annoyance. To compare results from different wind turbine <span class="hlt">noise</span> studies it seems necessary to assess the impact of important modifying factors. PMID:27455301</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19960009924','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19960009924"><span>An advanced arc track resistant <span class="hlt">airframe</span> wire</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Beatty, J.</p> <p>1995-01-01</p> <p>Tensolite, a custom cable manufacturer specializing in high temperature materials as the dielectric medium, develops an advance arc track resistant <span class="hlt">airframe</span> wire called Tufflite 2000. Tufflite 2000 has the following advantages over the other traditional wires: lighter weight and smaller in diameter; excellent wet and dry arc track resistance; superior dynamic cut-through performance even at elevated temperatures; flight proven performance on Boeing 737 and 757 airplanes; and true 260 C performance by utilizing Nickel plated copper conductors. This paper reports the different tests performed on Tufflite 2000: accelerated aging, arc resistance (wet and dry), dynamic cut through, humidity resistance, wire-to-wire abrasion, flammability, smoke, weight, notch sensitivity, flexibility, and markability. It particularly focuses on the BSI (British Standards Institute) dry arc resistance test and BSI wet arc tracking.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1981STIN...8223257T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1981STIN...8223257T"><span>Aerodynamics of a rolling <span class="hlt">airframe</span> missile</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tisserand, L. E.</p> <p>1981-05-01</p> <p>For guidance-related reasons, there is considerable interest in rolling missiles having single-plane steering capability. To aid the aerodynamic design of these <span class="hlt">airframes</span>, a unique investigation into the aerodynamics of a rolling, steering missile has been carried out. It represents the first known attempt to measure in a wind tunnel the aerodynamic forces and moments that act on a spinning body-canard-tail configuration that exercises canard steering in phase with body roll position. Measurements were made with the model spinning at steady-state roll rates ranging from 15 to 40 Hz over an angle-of-attack range up to about 16 deg. This short, exploratory investigation has demonstrated that a better understanding and a more complete definition of the aerodynamics of rolling, steering vehicles can be developed by way of simulative wind-tunnel testing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19820025859','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19820025859"><span>Crashworthy <span class="hlt">airframe</span> design concepts: Fabrication and testing</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cronkhite, J. D.; Berry, V. L.</p> <p>1982-01-01</p> <p>Crashworthy floor concepts applicable to general aviation aircraft metal <span class="hlt">airframe</span> structures were investigated. Initially several energy absorbing lower fuselage structure concepts were evaluated. Full scale floor sections representative of a twin engine, general aviation airplane lower fuselage structure were designed and fabricated. The floors featured an upper high strength platform with an energy absorbing, crushable structure underneath. Eighteen floors were fabricated that incorporated five different crushable subfloor concepts. The floors were then evaluated through static and dynamic testing. Computer programs NASTRAN and KRASH were used for the static and dynamic analysis of the floor section designs. Two twin engine airplane fuselages were modified to incorporate the most promising crashworthy floor sections for test evaluation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1989apmf.confR....P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1989apmf.confR....P"><span>Robotic dry stripping of <span class="hlt">airframes</span> - Phase II</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pauli, Robert A.; Wittenberg, Art M.</p> <p>1989-03-01</p> <p>This paper describes a program for the development of a dust-free closed-cycle robotic system for dry stripping of <span class="hlt">airframes</span>, designed to insure dust-free work environment and reduce plastic-media loss, the contamination risk, and the media inventory requirement. Phase I of the program involved building a prototype of the proposed robotic arm and its dust enclosure to prove basic automation concepts, showing reasonable paint removal rate from a curved surface, and establishing that the process is dust-free and recovers plastic media in a closed-cycle fashion. This paper contains calculations on the effect of different blasting parameters in order to determine optimum values required for the completion of Phase I. Also presented is the progress achieved by the Phase II of the program, which is to prove the total concept by building the complete system and demonstrating its capability.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20090041558','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20090041558"><span><span class="hlt">Noise-Source</span> Separation Using Internal and Far-Field Sensors for a Full-Scale Turbofan Engine</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hultgren, Lennart S.; Miles, Jeffrey H.</p> <p>2009-01-01</p> <p><span class="hlt">Noise-source</span> separation techniques for the extraction of the sub-dominant combustion <span class="hlt">noise</span> from the total <span class="hlt">noise</span> signatures obtained in static-engine tests are described. Three methods are applied to data from a static, full-scale engine test. Both 1/3-octave and narrow-band results are discussed. The results are used to assess the combustion-<span class="hlt">noise</span> prediction capability of the Aircraft <span class="hlt">Noise</span> Prediction Program (ANOPP). A new additional phase-angle-based discriminator for the three-signal method is also introduced.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JSV...338..250B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JSV...338..250B"><span><span class="hlt">Source</span> localization of turboshaft engine broadband <span class="hlt">noise</span> using a three-sensor coherence method</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Blacodon, Daniel; Lewy, Serge</p> <p>2015-03-01</p> <p>Turboshaft engines can become the main <span class="hlt">source</span> of helicopter <span class="hlt">noise</span> at takeoff. Inlet radiation mainly comes from the compressor tones, but aft radiation is more intricate: turbine tones usually are above the audible frequency range and do not contribute to the weighted sound levels; jet is secondary and radiates low <span class="hlt">noise</span> levels. A broadband component is the most annoying but its <span class="hlt">sources</span> are not well known (it is called internal or core <span class="hlt">noise</span>). Present study was made in the framework of the European project TEENI (Turboshaft Engine Exhaust <span class="hlt">Noise</span> Identification). Its main objective was to localize the broadband <span class="hlt">sources</span> in order to better reduce them. Several diagnostic techniques were implemented by the various TEENI partners. As regards ONERA, a first attempt at separating <span class="hlt">sources</span> was made in the past with Turbomeca using a three-signal coherence method (TSM) to reject background non-acoustic <span class="hlt">noise</span>. The main difficulty when using TSM is the assessment of the frequency range where the results are valid. This drawback has been circumvented in the TSM implemented in TEENI. Measurements were made on a highly instrumented Ardiden turboshaft engine in the Turbomeca open-air test bench. Two engine powers (approach and takeoff) were selected to apply TSM. Two internal pressure probes were located in various cross-sections, either behind the combustion chamber (CC), the high-pressure turbine (HPT), the free-turbine first stage (TL), or in four nozzle sections. The third transducer was a far-field microphone located around the maximum of radiation, at 120° from the intake centerline. The key result is that coherence increases from CC to HPT and TL, then decreases in the nozzle up to the exit. Pressure fluctuations from HPT and TL are very coherent with the far-field acoustic spectra up to 700 Hz. They are thus the main acoustic <span class="hlt">source</span> and can be attributed to indirect combustion <span class="hlt">noise</span> (accuracy decreases above 700 Hz because coherence is lower, but far-field sound spectra</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhDT........38M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhDT........38M"><span>Prediction of jet <span class="hlt">noise</span> shielding with forward flight effects</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mayoral, Salvador</p> <p></p> <p>Aircraft <span class="hlt">noise</span> continues to be a major concern among airport-neighboring communities. A strong component of aircraft <span class="hlt">noise</span> is the jet <span class="hlt">noise</span> that is generated from the turbulent mixing between the jet exhaust and ambient medium. The hybrid wing body aircraft suppresses jet <span class="hlt">noise</span> by mounting the engines over-the-wing so that the <span class="hlt">airframe</span> may shield ground observers from jet <span class="hlt">noise</span> <span class="hlt">sources</span>. Subscale jet <span class="hlt">noise</span> shielding measurements of a scaled-down turbofan nozzle and a model of the hybrid wing body planform are taken with two 12-microphone polar arrays. Chevrons and wedge-type fan flow deflectors are integrated into the baseline bypass ratio 10 (BPR10) nozzle to modify the mean flow and alter the <span class="hlt">noise</span> <span class="hlt">source</span> behavior. Acoustic results indicate that the baseline BPR10 nozzle produces a long <span class="hlt">noise</span> <span class="hlt">source</span> region that the <span class="hlt">airframe</span> has difficulty shielding, even when the nozzle is translated two fan diameters upstream of its nominal position. The integration of either chevrons or fan flow deflectors into the nozzle is essential for jet <span class="hlt">noise</span> shielding because they translate peak intensities upstream, closer to the fan exit plane. The numerical counterpart of this study transforms the system of equations governing the acoustic diffraction with forward flight into the wave equation. Two forward flight formulations are considered: uniform flow over slender body; and non-uniform potential flow at low Mach number. The wave equation is solved numerically in the frequency domain using the boundary element method. The equivalent jet <span class="hlt">noise</span> <span class="hlt">source</span> is modeled using the combination of a wavepacket and a monopole. The wavepacket is parameterized using the experimental far-field acoustic autospectra of the BPR10 jets and knowledge of their peak <span class="hlt">noise</span> locations. It is shown that the <span class="hlt">noise</span> <span class="hlt">source</span> compacts with increasing Mach number and consequently there is an increase in shielding. An assessment of the error associated with the non-uniform formulation for forward flight shows that the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PPNL...14..219O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PPNL...14..219O"><span>Low-<span class="hlt">noise</span> pulsed current <span class="hlt">source</span> for magnetic-field measurements of magnets for accelerators</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Omelyanenko, M. M.; Borisov, V. V.; Donyagin, A. M.; Khodzhibagiyan, H. G.; Kostromin, S. A.; Makarov, A. A.; Shemchuk, A. V.</p> <p>2017-01-01</p> <p>The schematic diagram, design, and technical characteristics of the pulsed current <span class="hlt">source</span> developed and produced for the magnetic-field measurement system of superconducting magnets for accelerators are described. The current <span class="hlt">source</span> is based on the current regulator with pass transistor bank in the linear mode. Output current pulses (0-100 A) are produced by utilizing the energy of the preliminarily charged capacitor bank (5-40 V), which is additionally charged between pulses. The output current does not have the mains frequency and harmonics ripple. The relative <span class="hlt">noise</span> level is less than-100 dB (or 10-5) of RMS value (it is defined as the ratio of output RMS <span class="hlt">noise</span> current to a maximal output current of 100 A within the operating bandwidth, expressed in dB). The work was performed at the Veksler and Baldin Laboratory of High Energy Physics, Joint Institute for Nuclear Research (JINR).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040201023','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040201023"><span>Sound <span class="hlt">Source</span> Identification Through Flow Density Measurement and Correlation With Far Field <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Panda, J.; Seasholtz, R. G.</p> <p>2001-01-01</p> <p>Sound <span class="hlt">sources</span> in the plumes of unheated round jets, in the Mach number range 0.6 to 1.8, were investigated experimentally using "casuality" approach, where air density fluctuations in the plumes were correlated with the far field <span class="hlt">noise</span>. The air density was measured using a newly developed Molecular Rayleigh scattering based technique, which did not require any seeding. The reference at the end provides a detailed description of the measurement technique.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoJI.tmp..387L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoJI.tmp..387L"><span>Ambient <span class="hlt">noise</span> tomography with non-uniform <span class="hlt">noise</span> <span class="hlt">sources</span> and low aperture networks: case study of deep geothermal reservoirs in northern Alsace, France</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lehujeur, Maximilien; Vergne, Jérôme; Maggi, Alessia; Schmittbuhl, Jean</p> <p>2016-10-01</p> <p>We developed and applied a method for ambient <span class="hlt">noise</span> surface wave tomography that can deal with <span class="hlt">noise</span> cross-correlation functions governed to first order by a non-uniform distribution of the ambient seismic <span class="hlt">noise</span> <span class="hlt">sources</span>. The method inverts the azimuthal distribution of <span class="hlt">noise</span> <span class="hlt">sources</span> that are assumed to be far from the network, together with the spatial variations of the phase and group velocities on an optimized irregular grid. Direct modeling of the two-sided <span class="hlt">noise</span> correlation functions avoids dispersion curve picking on every station pair and minimizes analyst intervention. The method involves station pairs spaced by distances down to a fraction of a wavelength, thereby bringing additional information for tomography. After validating the method on synthetic data, we applied it to a set of long-term continuous waveforms acquired around the geothermal sites at Soultz-sous-Forêts and Rittershoffen (Northern Alsace, France). For networks with limited aperture, we show that taking the azimuthal variations of the <span class="hlt">noise</span> energy into account has significant impact on the surface wave dispersion maps. We obtained regional phase and group velocity models in the 1-7 s period range, which is sensitive to the structures encompassing the geothermal reservoirs. The ambient <span class="hlt">noise</span> in our dataset originates from two main directions, the northern Atlantic Ocean and the Mediterranean Sea, and is dominated by the first Rayleigh wave overtone in the 2 - 5 s period range.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoJI.208..193L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoJI.208..193L"><span>Ambient <span class="hlt">noise</span> tomography with non-uniform <span class="hlt">noise</span> <span class="hlt">sources</span> and low aperture networks: case study of deep geothermal reservoirs in northern Alsace, France</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lehujeur, Maximilien; Vergne, Jérôme; Maggi, Alessia; Schmittbuhl, Jean</p> <p>2017-01-01</p> <p>We developed and applied a method for ambient <span class="hlt">noise</span> surface wave tomography that can deal with <span class="hlt">noise</span> cross-correlation functions governed to first order by a non-uniform distribution of the ambient seismic <span class="hlt">noise</span> <span class="hlt">sources</span>. The method inverts the azimuthal distribution of <span class="hlt">noise</span> <span class="hlt">sources</span> that are assumed to be far from the network, together with the spatial variations of the phase and group velocities on an optimized irregular grid. Direct modelling of the two-sided <span class="hlt">noise</span> correlation functions avoids dispersion curve picking on every station pair and minimizes analyst intervention. The method involves station pairs spaced by distances down to a fraction of a wavelength, thereby bringing additional information for tomography. After validating the method on synthetic data, we applied it to a set of long-term continuous waveforms acquired around the geothermal sites at Soultz-sous-Forêts and Rittershoffen (Northern Alsace, France). For networks with limited aperture, we show that taking the azimuthal variations of the <span class="hlt">noise</span> energy into account has significant impact on the surface wave dispersion maps. We obtained regional phase and group velocity models in the 1-7 s period range, which is sensitive to the structures encompassing the geothermal reservoirs. The ambient <span class="hlt">noise</span> in our dataset originates from two main directions, the northern Atlantic Ocean and the Mediterranean Sea, and is dominated by the first Rayleigh wave overtone in the 2-5 s period range.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4749559','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4749559"><span><span class="hlt">Sources</span> of <span class="hlt">noise</span> during accumulation of evidence in unrestrained and voluntarily head-restrained rats</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Scott, Benjamin B; Constantinople, Christine M; Erlich, Jeffrey C; Tank, David W; Brody, Carlos D</p> <p>2015-01-01</p> <p>Decision-making behavior is often characterized by substantial variability, but its <span class="hlt">source</span> remains unclear. We developed a visual accumulation of evidence task designed to quantify <span class="hlt">sources</span> of <span class="hlt">noise</span> and to be performed during voluntary head restraint, enabling cellular resolution imaging in future studies. Rats accumulated discrete numbers of flashes presented to the left and right visual hemifields and indicated the side that had the greater number of flashes. Using a signal-detection theory-based model, we found that the standard deviation in their internal estimate of flash number scaled linearly with the number of flashes. This indicates a major <span class="hlt">source</span> of <span class="hlt">noise</span> that, surprisingly, is not consistent with the widely used 'drift-diffusion modeling' (DDM) approach but is instead closely related to proposed models of numerical cognition and counting. We speculate that this form of <span class="hlt">noise</span> could be important in accumulation of evidence tasks generally. DOI: http://dx.doi.org/10.7554/eLife.11308.001 PMID:26673896</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23988431','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23988431"><span>Improved PHIP polarization using a precision, low <span class="hlt">noise</span>, voltage controlled current <span class="hlt">source</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Agraz, Jose; Grunfeld, Alexander; Cunningham, Karl; Li, Debiao; Wagner, Shawn</p> <p>2013-10-01</p> <p>Existing para-hydrogen induced polarization (PHIP) instrumentation relies on magnetic fields to hyperpolarize substances. These hyperpolarized substances have enhanced magnetic resonance imaging (MRI) signals over 10,000 fold, allowing for MRI at the molecular level. Required magnetic fields are generated by energizing a solenoid coil with current produced by a voltage controlled voltage <span class="hlt">source</span> (VCVS), also known as a power supply. A VCVS lacks the current regulation necessary to keep magnetic field fluctuations to a minimum, which results in low PHIP polarization. A voltage controlled current <span class="hlt">source</span> (VCCS) is an electric circuit that generates a steady flow of electrons proportional to an input voltage. A low <span class="hlt">noise</span> VCCS provides the solenoid current flow regulation necessary to generate a stable static magnetic field (Bo). We discuss the design and implementation of a low <span class="hlt">noise</span>, high stability, VCCS for magnetic field generation with minimum variations. We show that a precision, low <span class="hlt">noise</span>, voltage reference driving a metal oxide semiconductor field effect transistor (MOSFET) based current sink, results in the current flow control necessary for generating a low <span class="hlt">noise</span> and high stability Bo. In addition, this work: (1) compares current stability for ideal VCVS and VCCS models using transfer functions (TF), (2) develops our VCCS design's TF, (3) measures our VCCS design's thermal & 1/f <span class="hlt">noise</span>, and (4) measures and compares hydroxyethyl-propionate (HEP) polarization obtained using a VCVS and our VCCS. The hyperpolarization of HEP was done using a PHIP instrument developed in our lab. Using our VCCS design, HEP polarization magnitude data show a statistically significant increase in polarization over using a VCVS. Circuit schematic, bill of materials, board layout, TF derivation, and Matlab simulations code are included as supplemental files.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20070002014','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20070002014"><span>A Landing Gear <span class="hlt">Noise</span> Reduction Study Based on Computational Simulations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Khorrami, Mehdi R.; Lockard, David P.</p> <p>2006-01-01</p> <p>Landing gear is one of the more prominent <span class="hlt">airframe</span> <span class="hlt">noise</span> <span class="hlt">sources</span>. Techniques that diminish gear <span class="hlt">noise</span> and suppress its radiation to the ground are highly desirable. Using a hybrid computational approach, this paper investigates the <span class="hlt">noise</span> reduction potential of devices added to a simplified main landing gear model without small scale geometric details. The Ffowcs Williams and Hawkings equation is used to predict the <span class="hlt">noise</span> at far-field observer locations from surface pressure data provided by unsteady CFD calculations. Because of the simplified nature of the model, most of the flow unsteadiness is restricted to low frequencies. The wheels, gear boxes, and oleo appear to be the primary <span class="hlt">sources</span> of unsteadiness at these frequencies. The addition of fairings around the gear boxes and wheels, and the attachment of a splitter plate on the downstream side of the oleo significantly reduces the <span class="hlt">noise</span> over a wide range of frequencies, but a dramatic increase in <span class="hlt">noise</span> is observed at one frequency. The increased flow velocities, a consequence of the more streamlined bodies, appear to generate extra unsteadiness around other parts giving rise to the additional <span class="hlt">noise</span>. Nonetheless, the calculations demonstrate the capability of the devices to improve overall landing gear <span class="hlt">noise</span>.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1035153','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1035153"><span>Non-Uniform Contrast and <span class="hlt">Noise</span> Correction for Coded <span class="hlt">Source</span> Neutron Imaging</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Santos-Villalobos, Hector J; Bingham, Philip R</p> <p>2012-01-01</p> <p>Since the first application of neutron radiography in the 1930s, the field of neutron radiography has matured enough to develop several applications. However, advances in the technology are far from concluded. In general, the resolution of scintillator-based detection systems is limited to the $10\\mu m$ range, and the relatively low neutron count rate of neutron <span class="hlt">sources</span> compared to other illumination <span class="hlt">sources</span> restricts time resolved measurement. One path toward improved resolution is the use of magnification; however, to date neutron optics are inefficient, expensive, and difficult to develop. There is a clear demand for cost-effective scintillator-based neutron imaging systems that achieve resolutions of $1 \\mu m$ or less. Such imaging system would dramatically extend the application of neutron imaging. For such purposes a coded <span class="hlt">source</span> imaging system is under development. The current challenge is to reduce artifacts in the reconstructed coded <span class="hlt">source</span> images. Artifacts are generated by non-uniform illumination of the <span class="hlt">source</span>, gamma rays, dark current at the imaging sensor, and system <span class="hlt">noise</span> from the reconstruction kernel. In this paper, we describe how to pre-process the coded signal to reduce <span class="hlt">noise</span> and non-uniform illumination, and how to reconstruct the coded signal with three reconstruction methods correlation, maximum likelihood estimation, and algebraic reconstruction technique. We illustrates our results with experimental examples.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080047683','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080047683"><span>A Numerical Investigation of Turbine <span class="hlt">Noise</span> <span class="hlt">Source</span> Hierarchy and Its Acoustic Transmission Characteristics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>VanZante, Dale; Envia, Edmane</p> <p>2008-01-01</p> <p>Understanding the relative importance of the various turbine <span class="hlt">noise</span> generation mechanisms and the characteristics of the turbine acoustic transmission loss are essential ingredients in developing robust reduced-order models for predicting the turbine <span class="hlt">noise</span> signature. A computationally based investigation has been undertaken to help guide the development of a turbine <span class="hlt">noise</span> prediction capability that does not rely on empiricism. The investigation relies on highly detailed numerical simulations of the unsteady flowfield inside a modern high-pressure turbine (HPT). The simulations are developed using TURBO, which is an unsteady Reynolds-averaged Navier-Stokes (URANS) code capable of multi-stage simulations. The purpose of this study is twofold. First, to determine an estimate of the relative importance of the contributions to the coherent part of the acoustic signature of a turbine from the three potential <span class="hlt">sources</span> of turbine <span class="hlt">noise</span> generation, namely, blade-row viscous interaction, potential field interaction, and entropic <span class="hlt">source</span> associated with the interaction of the blade rows with the temperature nonuniformities caused by the incomplete mixing of the hot fluid and the cooling flow. Second, to develop an understanding of the turbine acoustic transmission characteristics and to assess the applicability of existing empirical and analytical transmission loss models to realistic geometries and flow conditions for modern turbine designs. The investigation so far has concentrated on two simulations: (1) a single-stage HPT and (2) a two-stage HPT and the associated inter-turbine duct/strut segment. The simulations are designed to resolve up to the second harmonic of the blade passing frequency tone in accordance with accepted rules for second order solvers like TURBO. The calculations include blade and vane cooling flows and a radial profile of pressure and temperature at the turbine inlet. The calculation can be modified later to include the combustor pattern factor at the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20050186648&hterms=gear+teeth+torque&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dgear%2Bteeth%2Btorque','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20050186648&hterms=gear+teeth+torque&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dgear%2Bteeth%2Btorque"><span>Experimentation Toward the Analysis of Gear <span class="hlt">Noise</span> <span class="hlt">Sources</span> Controlled by Sliding Friction and Surface Roughness</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Asnani, Vivake M.</p> <p>2004-01-01</p> <p>In helicopters and other rotorcraft, the gearbox is a major <span class="hlt">source</span> of <span class="hlt">noise</span> and vibration (N&V). The two N&V excitation mechanisms are the relative displacements between mating gears (transmission errors) and the friction associated with sliding between gear teeth. Historically, transmission errors have been minimized via improved manufacturing accuracies and tooth modifications. Yet, at high torque loads, <span class="hlt">noise</span> levels are still relatively high though transmission errors might be somewhat minimal. This suggests that sliding friction is indeed a dominant <span class="hlt">noise</span> <span class="hlt">source</span> for high power density rotorcraft gearboxes. In reality, friction <span class="hlt">source</span> mechanism is associated with surface roughness, lubrication regime properties, time-varying friction forces/torques and gear-mesh interface dynamics. Currently, the nature of these mechanisms is not well understood, while there is a definite need for analytical tools that incorporate sliding resistance and surface roughness, and predict their effects on the vibro- acoustic behavior of gears. Toward this end, an experiment was conducted to collect sound and vibration data on the NASA Glenn Gear-<span class="hlt">Noise</span> Rig. Three iterations of the experiment were accomplished: Iteration 1 tested a baseline set of gears to establish a benchmark. Iteration 2 used a gear-set with low surface asperities to reduce the sliding friction excitation. Iteration 3 incorporated low viscosity oil with the baseline set of gears to examine the effect of lubrication. The results from this experiment will contribute to a two year project in collaboration with the Ohio State University to develop the necessary mathematical and computer models for analyzing geared systems and explain key physical phenomena seen in experiments. Given the importance of sliding friction in the gear dynamic and vibro-acoustic behavior of rotorcraft gearboxes, there is considerable potential for research & developmental activities. Better models and understanding will lead to quiet and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080023403','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080023403"><span>Engine Validation of <span class="hlt">Noise</span> and Emission Reduction Technology Phase I</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Weir, Don (Editor)</p> <p>2008-01-01</p> <p>This final report has been prepared by Honeywell Aerospace, Phoenix, Arizona, a unit of Honeywell International, Inc., documenting work performed during the period December 2004 through August 2007 for the NASA Glenn Research Center, Cleveland, Ohio, under the Revolutionary Aero-Space Engine Research (RASER) Program, Contract No. NAS3-01136, Task Order 8, Engine Validation of <span class="hlt">Noise</span> and Emission Reduction Technology Phase I. The NASA Task Manager was Dr. Joe Grady of the NASA Glenn Research Center. The NASA Contract Officer was Mr. Albert Spence of the NASA Glenn Research Center. This report is for a test program in which NASA funded engine validations of integrated technologies that reduce aircraft engine <span class="hlt">noise</span>. These technologies address the reduction of engine fan and jet <span class="hlt">noise</span>, and <span class="hlt">noise</span> associated with propulsion/<span class="hlt">airframe</span> integration. The results of these tests will be used by NASA to identify the engineering tradeoffs associated with the technologies that are needed to enable advanced engine systems to meet stringent goals for the reduction of <span class="hlt">noise</span>. The objectives of this program are to (1) conduct system engineering and integration efforts to define the engine test-bed configuration; (2) develop selected <span class="hlt">noise</span> reduction technologies to a technical maturity sufficient to enable engine testing and validation of those technologies in the FY06-07 time frame; (3) conduct engine tests designed to gain insight into the <span class="hlt">sources</span>, mechanisms and characteristics of <span class="hlt">noise</span> in the engines; and (4) establish baseline engine <span class="hlt">noise</span> measurements for subsequent use in the evaluation of <span class="hlt">noise</span> reduction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoJI.205..715W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoJI.205..715W"><span>Correction of phase velocity bias caused by strong directional <span class="hlt">noise</span> <span class="hlt">sources</span> in high-frequency ambient <span class="hlt">noise</span> tomography: a case study in Karamay, China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Kai; Luo, Yinhe; Yang, Yingjie</p> <p>2016-05-01</p> <p>We collect two months of ambient <span class="hlt">noise</span> data recorded by 35 broad-band seismic stations in a 9 × 11 km area (1-3 km station interval) near Karamay, China, and do cross-correlation of <span class="hlt">noise</span> data between all station pairs. Array beamforming analysis of the ambient <span class="hlt">noise</span> data shows that ambient <span class="hlt">noise</span> <span class="hlt">sources</span> are unevenly distributed and the most energetic ambient <span class="hlt">noise</span> mainly comes from azimuths of 40°-70°. As a consequence of the strong directional <span class="hlt">noise</span> <span class="hlt">sources</span>, surface wave components of the cross-correlations at 1-5 Hz show clearly azimuthal dependence, and direct dispersion measurements from cross-correlations are strongly biased by the dominant <span class="hlt">noise</span> energy. This bias renders that the dispersion measurements from cross-correlations do not accurately reflect the interstation velocities of surface waves propagating directly from one station to the other, that is, the cross-correlation functions do not retrieve empirical Green's functions accurately. To correct the bias caused by unevenly distributed <span class="hlt">noise</span> <span class="hlt">sources</span>, we adopt an iterative inversion procedure. The iterative inversion procedure, based on plane-wave modeling, includes three steps: (1) surface wave tomography, (2) estimation of ambient <span class="hlt">noise</span> energy and biases and (3) phase velocities correction. First, we use synthesized data to test the efficiency and stability of the iterative procedure for both homogeneous and heterogeneous media. The testing results show that: (1) the amplitudes of phase velocity bias caused by directional <span class="hlt">noise</span> <span class="hlt">sources</span> are significant, reaching ˜2 and ˜10 per cent for homogeneous and heterogeneous media, respectively; (2) phase velocity bias can be corrected by the iterative inversion procedure and the convergence of inversion depends on the starting phase velocity map and the complexity of the media. By applying the iterative approach to the real data in Karamay, we further show that phase velocity maps converge after 10 iterations and the phase velocity maps obtained using</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22225031','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22225031"><span>A comparison between exposure-response relationships for wind turbine annoyance and annoyance due to other <span class="hlt">noise</span> <span class="hlt">sources</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Janssen, Sabine A; Vos, Henk; Eisses, Arno R; Pedersen, Eja</p> <p>2011-12-01</p> <p>Surveys have shown that <span class="hlt">noise</span> from wind turbines is perceived as annoying by a proportion of residents living in their vicinity, apparently at much lower <span class="hlt">noise</span> levels than those inducing annoyance due to other environmental <span class="hlt">sources</span>. The aim of the present study was to derive the exposure-response relationship between wind turbine <span class="hlt">noise</span> exposure in L(den) and the expected percentage annoyed residents and to compare it to previously established relationships for industrial <span class="hlt">noise</span> and transportation <span class="hlt">noise</span>. In addition, the influence of several individual and situational factors was assessed. On the basis of available data from two surveys in Sweden (N=341, N=754) and one survey in the Netherlands (N=725), a relationship was derived for annoyance indoors and for annoyance outdoors at the dwelling. In comparison to other <span class="hlt">sources</span> of environmental <span class="hlt">noise</span>, annoyance due to wind turbine <span class="hlt">noise</span> was found at relatively low <span class="hlt">noise</span> exposure levels. Furthermore, annoyance was lower among residents who received economical benefit from wind turbines and higher among residents for whom the wind turbine was visible from the dwelling. Age and <span class="hlt">noise</span> sensitivity had similar effects on annoyance to those found in research on annoyance by other <span class="hlt">sources</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011PhDT.......106D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011PhDT.......106D"><span>Supersonic jet <span class="hlt">noise</span> prediction and <span class="hlt">noise</span> <span class="hlt">source</span> investigation for realistic baseline and chevron nozzles based on hybrid RANS/LES simulations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Du, Yongle</p> <p></p> <p>Jet <span class="hlt">noise</span> simulations have been performed for a military-style baseline nozzle and a chevron nozzle with design Mach numbers of Md = 1:5 operating at several off-design conditions. The objective of the current numerical study is to provide insight into the <span class="hlt">noise</span> generation mechanisms of shock-containing supersonic hot jets and the <span class="hlt">noise</span> reduction mechanisms of chevron nozzles. A hybrid methodology combining advanced CFD technologies and the acoustic analogy is used for supersonic jet <span class="hlt">noise</span> simulations. Unsteady Reynolds-averaged Navier-Stokes (URANS) equations are solved to predict the turbulent <span class="hlt">noise</span> <span class="hlt">sources</span> in the jet flows. A modified version of the Detached Eddy Simulation (DES) approach is used to avoid excessive damping of fine scale turbulent fluctuations. A multiblock structured mesh topology is used to represent complex nozzle geometries, including the faceted inner contours and finite nozzle thickness. A block interface condition is optimized for the complex multiblock mesh topology to avoid the centerline singularity. A fourth-order Dispersion-Relation-Preserving (DRP) scheme is used for spatial discretization. To enable efficient calculations, a dual time-stepping method is used in addition to parallel computation using MPI. Both multigrid and implicit residual smoothing are used to accelerate the convergence rate of sub-iterations in the fictitious time domain. <span class="hlt">Noise</span> predictions are made with the permeable surface Ffowcs Williams and Hawkings (FWH) solution. All the numerical methods have been implemented in the jet flow simulation code "CHOPA" and the <span class="hlt">noise</span> prediction code "PSJFWH". The computer codes have been validated with several benchmark cases. A preliminary study has been performed for an under-expanded baseline nozzle jet with Mj = 1:56 to validate the accuracy of the jet <span class="hlt">noise</span> simulations. The results show that grid refinement around the jet potential core and the use of a lower artificial dissipation improve the resolution of the predicted</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28000727','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28000727"><span>Evidence of Cnidarians sensitivity to sound after exposure to low frequency <span class="hlt">noise</span> underwater <span class="hlt">sources</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Solé, Marta; Lenoir, Marc; Fontuño, José Manuel; Durfort, Mercè; van der Schaar, Mike; André, Michel</p> <p>2016-12-21</p> <p>Jellyfishes represent a group of species that play an important role in oceans, particularly as a food <span class="hlt">source</span> for different taxa and as a predator of fish larvae and planktonic prey. The massive introduction of artificial sound <span class="hlt">sources</span> in the oceans has become a concern to science and society. While we are only beginning to understand that non-hearing specialists like cephalopods can be affected by anthropogenic <span class="hlt">noises</span> and regulation is underway to measure European water <span class="hlt">noise</span> levels, we still don't know yet if the impact of sound may be extended to other lower level taxa of the food web. Here we exposed two species of Mediterranean Scyphozoan medusa, Cotylorhiza tuberculata and Rhizostoma pulmo to a sweep of low frequency sounds. Scanning electron microscopy (SEM) revealed injuries in the statocyst sensory epithelium of both species after exposure to sound, that are consistent with the manifestation of a massive acoustic trauma observed in other species. The presence of acoustic trauma in marine species that are not hearing specialists, like medusa, shows the magnitude of the problem of <span class="hlt">noise</span> pollution and the complexity of the task to determine threshold values that would help building up regulation to prevent permanent damage of the ecosystems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5175278','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5175278"><span>Evidence of Cnidarians sensitivity to sound after exposure to low frequency <span class="hlt">noise</span> underwater <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Solé, Marta; Lenoir, Marc; Fontuño, José Manuel; Durfort, Mercè; van der Schaar, Mike; André, Michel</p> <p>2016-01-01</p> <p>Jellyfishes represent a group of species that play an important role in oceans, particularly as a food <span class="hlt">source</span> for different taxa and as a predator of fish larvae and planktonic prey. The massive introduction of artificial sound <span class="hlt">sources</span> in the oceans has become a concern to science and society. While we are only beginning to understand that non-hearing specialists like cephalopods can be affected by anthropogenic <span class="hlt">noises</span> and regulation is underway to measure European water <span class="hlt">noise</span> levels, we still don’t know yet if the impact of sound may be extended to other lower level taxa of the food web. Here we exposed two species of Mediterranean Scyphozoan medusa, Cotylorhiza tuberculata and Rhizostoma pulmo to a sweep of low frequency sounds. Scanning electron microscopy (SEM) revealed injuries in the statocyst sensory epithelium of both species after exposure to sound, that are consistent with the manifestation of a massive acoustic trauma observed in other species. The presence of acoustic trauma in marine species that are not hearing specialists, like medusa, shows the magnitude of the problem of <span class="hlt">noise</span> pollution and the complexity of the task to determine threshold values that would help building up regulation to prevent permanent damage of the ecosystems. PMID:28000727</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3460980','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3460980"><span><span class="hlt">Noise</span> suppression of a dipole <span class="hlt">source</span> by tensioned membrane with side-branch cavities</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Liu, Y.; Choy, Y. S.; Huang, L.; Cheng, L.</p> <p>2012-01-01</p> <p>Reducing the ducted-fan <span class="hlt">noise</span> at the low frequency range remains a big technical challenge. This study presents a passive approach to directly suppress the dipole sound radiation from an axial-flow fan housed by a tensioned membrane with cavity backing. The method aims at achieving control of low frequency <span class="hlt">noise</span> with an appreciable bandwidth. The use of the membrane not only eliminates the aerodynamic loss of flow, but also provides flexibility in controlling the range of the stopband with high insertion loss by varying its tension and mass. A three-dimensional model is presented which allows the performance of the proposed device to be explored analytically. With the proper design, this device can achieve a <span class="hlt">noise</span> reduction of 5 dB higher than the empty expansion cavity recently proposed by Huang et al. [J. Acoust. Soc. Am. 128, 152–163 (2010)]. Through the detailed modal analysis, even in vacuo modes of the membrane vibration are found to play an important role in the suppression of sound radiation from the dipole <span class="hlt">source</span>. Experimental validation is conducted with a loudspeaker as the dipole <span class="hlt">source</span> and good agreement between the predicted and measured insertion loss is achieved. PMID:22978868</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22978868','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22978868"><span><span class="hlt">Noise</span> suppression of a dipole <span class="hlt">source</span> by tensioned membrane with side-branch cavities.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Liu, Y; Choy, Y S; Huang, L; Cheng, L</p> <p>2012-09-01</p> <p>Reducing the ducted-fan <span class="hlt">noise</span> at the low frequency range remains a big technical challenge. This study presents a passive approach to directly suppress the dipole sound radiation from an axial-flow fan housed by a tensioned membrane with cavity backing. The method aims at achieving control of low frequency <span class="hlt">noise</span> with an appreciable bandwidth. The use of the membrane not only eliminates the aerodynamic loss of flow, but also provides flexibility in controlling the range of the stopband with high insertion loss by varying its tension and mass. A three-dimensional model is presented which allows the performance of the proposed device to be explored analytically. With the proper design, this device can achieve a <span class="hlt">noise</span> reduction of 5 dB higher than the empty expansion cavity recently proposed by Huang et al. [J. Acoust. Soc. Am. 128, 152-163 (2010)]. Through the detailed modal analysis, even in vacuo modes of the membrane vibration are found to play an important role in the suppression of sound radiation from the dipole <span class="hlt">source</span>. Experimental validation is conducted with a loudspeaker as the dipole <span class="hlt">source</span> and good agreement between the predicted and measured insertion loss is achieved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatSR...637979S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatSR...637979S"><span>Evidence of Cnidarians sensitivity to sound after exposure to low frequency <span class="hlt">noise</span> underwater <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Solé, Marta; Lenoir, Marc; Fontuño, José Manuel; Durfort, Mercè; van der Schaar, Mike; André, Michel</p> <p>2016-12-01</p> <p>Jellyfishes represent a group of species that play an important role in oceans, particularly as a food <span class="hlt">source</span> for different taxa and as a predator of fish larvae and planktonic prey. The massive introduction of artificial sound <span class="hlt">sources</span> in the oceans has become a concern to science and society. While we are only beginning to understand that non-hearing specialists like cephalopods can be affected by anthropogenic <span class="hlt">noises</span> and regulation is underway to measure European water <span class="hlt">noise</span> levels, we still don’t know yet if the impact of sound may be extended to other lower level taxa of the food web. Here we exposed two species of Mediterranean Scyphozoan medusa, Cotylorhiza tuberculata and Rhizostoma pulmo to a sweep of low frequency sounds. Scanning electron microscopy (SEM) revealed injuries in the statocyst sensory epithelium of both species after exposure to sound, that are consistent with the manifestation of a massive acoustic trauma observed in other species. The presence of acoustic trauma in marine species that are not hearing specialists, like medusa, shows the magnitude of the problem of <span class="hlt">noise</span> pollution and the complexity of the task to determine threshold values that would help building up regulation to prevent permanent damage of the ecosystems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AIPC.1495..242C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AIPC.1495..242C"><span>A perspective on 30 years of progress in ambient <span class="hlt">noise</span>: <span class="hlt">Source</span> mechanisms and the characteristics of the sound field</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cato, Douglas H.</p> <p>2012-11-01</p> <p>The last 30 years has seen substantial progress in ocean ambient <span class="hlt">noise</span> research, particularly in understanding the mechanisms of sound generation by the <span class="hlt">sources</span> of ambient <span class="hlt">noise</span>, the way in which the <span class="hlt">noise</span> field is affected by sound propagation, and improvements in quantifying the relationship between <span class="hlt">noise</span> and environmental parameters. This has led to significant improvements in <span class="hlt">noise</span> prediction. Activity was probably strongest in the 1980s and 1990s, as evident, for example, in the Sea Surface Sound conferences and their published proceedings (four over 10 years). Although much of the application has been to sonar, there has also been interest in using ambient <span class="hlt">noise</span> to measure properties of the environment and in its significance to marine life. There have been significant changes in the ambient <span class="hlt">noise</span> itself over the last 30 years. The contribution from human activities appears to have increased, particularly that due to increases in shipping numbers. Biological <span class="hlt">noise</span> has also increased with the significant increases in populations of some whale species following the cessation of broad scale whaling in the 1960s and early 1970s. Concern about the effects of <span class="hlt">noise</span> on marine animals as well as the way they exploit the <span class="hlt">noise</span> has led to renewed interest in ambient <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140008691','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140008691"><span>Comparison of <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Data with Flow Field Data Obtained in Cold Supersonic Jets and Implications Regarding Broadband Shock <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Podboy, Gary; Wernet, Mark; Clem, Michelle; Fagan, Amy</p> <p>2013-01-01</p> <p>Phased array <span class="hlt">noise</span> <span class="hlt">source</span> localization have been compared with 2 types of flow field data (BOS and PIV). The data show that: 1) the higher frequency <span class="hlt">noise</span> in a BBSN hump is generated further downstream than the lower frequency <span class="hlt">noise</span>. This is due to a) the shock spacing decreasing and b) the turbulent structure size increasing with distance downstream. 2) BBSN can be created by very weak shocks. 3) BBSN is not created by the strong shocks just downstream of the nozzle because the turbulent structures have not grown large enough to match the shock spacing. 4) The point in the flow where the shock spacing equals the average size of the turbulent structures is a hot spot for shock <span class="hlt">noise</span>. 5) Some of the shocks responsible for producing the first hump also produce the second hump.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920012279','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920012279"><span>Hypersonic airbreathing propulsion/<span class="hlt">airframe</span> integration</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Weidner, John P.</p> <p>1992-01-01</p> <p>Recent interest in airbreathing hypersonic flight has centered around the need to develop advanced space launch systems which can reduce the cost of inserting payloads in orbit and make space more accessible. An effect of the thermal environment is to require the vehicle to operate at high altitudes, in very thin air, to maintain aircraft structural load limits. The high altitudes at which the hypersonic vehicle must operate give rise to the concept of an <span class="hlt">airframe</span> integrated propulsion system to provide a much larger inlet and nozzle to process the required volume of air at low density, atmospheric conditions. In the integrated system, the forward portion of the vehicle compresses the air flow and serves as the external portion of the inlet; the aftbody completes the expansion process for the nozzle. In addition, the engine, which is contained between the body and the forebody shock wave, lends itself to a modular integration of a number of separate engines. In this manner, a relatively small engine can be defined to allow engine development in existing ground facilities.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AIPC..922...95R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AIPC..922...95R"><span>Study of MOSFET Low Frequency <span class="hlt">Noise</span> <span class="hlt">Source</span> Fluctuation Using a New Fully Programmable Test Set-up</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rochereau, K.; Blanc, C.; Marin, M.</p> <p>2007-07-01</p> <p>In this paper we aim to demonstrate the huge spread that can be seen on flicker (1/f) <span class="hlt">noise</span> figures of advanced MOS devices. In order to do so, we set up a new fully programmable test bench including low frequency <span class="hlt">noise</span> (1Hz-few Mhz) measurement capability. Once all the hurdles we faced during measurement optimization have been overpassed, we show indeed 1/f <span class="hlt">noise</span> dispersion over wafer is far larger than simple drive current one. We introduce the first steps of a global study of <span class="hlt">noise</span> <span class="hlt">source</span> fluctuation that has still to be led.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970028895','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970028895"><span>Low Speed, 2-D Rotor/Stator Active <span class="hlt">Noise</span> Control at the <span class="hlt">Source</span> Demonstration</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Simonich, John C.; Kousen, Ken A.; Zander, Anthony C.; Bak, Michael; Topol, David A.</p> <p>1997-01-01</p> <p>Wake/blade-row interaction <span class="hlt">noise</span> produced by the Annular Cascade Facility at Purdue University has been modeled using the LINFLO analysis. Actuator displacements needed for complete cancellation of the propagating acoustic response modes have been determined, along with the associated actuator power requirements. As an alternative, weighted least squares minimization of the total far-field sound power using individual actuators has also been examined. Attempts were made to translate the two-dimensional aerodynamic results into three-dimensional actuator requirements. The results lie near the limit of present actuator technology. In order to investigate the concept of <span class="hlt">noise</span> control at the <span class="hlt">source</span> for active rotor/stator <span class="hlt">noise</span> control at the <span class="hlt">source</span>, various techniques for embedding miniature actuators into vanes were examined. Numerous miniature speaker arrangements were tested and analyzed to determine their suitability as actuators for a demonstration test in the Annular Cascade Facility at Purdue. The best candidates demonstrated marginal performance. An alternative concept to using vane mounted speakers as control actuators was developed and tested. The concept uses compression drivers which are mounted externally to the stator vanes. Each compression driver is connected via a tube to an air cavity in the stator vane, from which the driver signal radiates into the working section of the experimental rig. The actual locations and dimensions of the actuators were used as input parameters for a LINFLO computational analysis of the actuator displacements required for complete cancellation of tones in the Purdue experimental rig. The actuators were designed and an arrangement determined which is compatible with the Purdue experimental rig and instrumentation. Experimental tests indicate that the actuators are capable of producing equivalent displacements greater than the requirements predicted by the LINFLO analysis. The acoustic output of the actuators was also found</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.S52C..03A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.S52C..03A"><span>Numerical wave modelling for seismo-acoustic <span class="hlt">noise</span> <span class="hlt">sources</span>: wave model accuracy issues and evidence for variable seismic attenuation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ardhuin, F.; Lavanant, T.; Obrebski, M. J.; Marié, L.; Royer, J.</p> <p>2012-12-01</p> <p>Nonlinear wave-wave interactions generate <span class="hlt">noise</span> that numerical ocean wave models may simulate. The accuracy of the <span class="hlt">noise</span> <span class="hlt">source</span> predicted by the theory of Longuet-Higgins (1950) and Hasselmann (1963) depends on the realism of the directional wave distribution, which is generally not very well known. Numerical <span class="hlt">noise</span> models developed by Kedar et al. (2008) and Ardhuin et al. (2010) also suffer from poorly known seismic wave propagation and attenuation properties. Here, several seismic and ocean pressure records are used here to assess the effects of wave modelling errors on the magnitude of <span class="hlt">noise</span> <span class="hlt">sources</span>. Measurements within 200~m from the sea surface are dominated by acoustic-gravity modes, for which bottom effects are negligible. These data show that directional wave spectra are well enough reproduced to estimate seismo-acoustic <span class="hlt">noise</span> <span class="hlt">sources</span> at frequencies below 0.3~Hz, whith an underestimation of the <span class="hlt">noise</span> level by about 50%. In larger water depths, the comparison of a numerical <span class="hlt">noise</span> model with hydrophone records from two open-ocean sites near Hawaii and Kerguelen islands reveal that a) deep ocean acoustic <span class="hlt">noise</span> at frequencies 0.1 to 1 Hz is consistent with the Rayleigh wave theory, and is well predicted up to 0.4~Hz. b) In particular, evidence of the vertical modes expected theoretically is given by the local maxima in the <span class="hlt">noise</span> spectrum. c) <span class="hlt">noise</span> above 0.6 Hz is not well modeled probably due to a poor estimate of the directional properties of high frequency wind-waves, d) the <span class="hlt">noise</span> level is strongly influenced by bottom properties, in particular the presence of sediments. Further, for continental coastal seismic stations, an accurate model of <span class="hlt">noise</span> level variability near the <span class="hlt">noise</span> spectral peak requires an accurate modelling of coastal reflection (Ardhuin and Roland JGR 2012). In cases where <span class="hlt">noise</span> <span class="hlt">sources</span> are confined to a small area (e.g. Obrebski et al. GRL 2012), the <span class="hlt">source</span> amplitude may be factored out, allowing an estimate of seismic attenuation rates</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040139604','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040139604"><span>Integration of Propulsion-<span class="hlt">Airframe</span>-Aeroacoustic Technologies and Design Concepts for a Quiet Blended-Wing-Body Transport</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hill, G. A.; Brown, S. A.; Geiselhart, K. A.</p> <p>2004-01-01</p> <p>This paper summarizes the results of studies undertaken to investigate revolutionary propulsion-<span class="hlt">airframe</span> configurations that have the potential to achieve significant <span class="hlt">noise</span> reductions over present-day commercial transport aircraft. Using a 300 passenger Blended-Wing-Body (BWB) as a baseline, several alternative low-<span class="hlt">noise</span> propulsion-<span class="hlt">airframe</span>-aeroacoustic (PAA) technologies and design concepts were investigated both for their potential to reduce the overall BWB <span class="hlt">noise</span> levels, and for their impact on the weight, performance, and cost of the vehicle. Two evaluation frameworks were implemented for the assessments. The first was a Multi-Attribute Decision Making (MADM) process that used a Pugh Evaluation Matrix coupled with the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). This process provided a qualitative evaluation of the PAA technologies and design concepts and ranked them based on how well they satisfied chosen design requirements. From the results of the evaluation, it was observed that almost all of the PAA concepts gave the BWB a <span class="hlt">noise</span> benefit, but degraded its performance. The second evaluation framework involved both deterministic and probabilistic systems analyses that were performed on a down-selected number of BWB propulsion configurations incorporating the PAA technologies and design concepts. These configurations included embedded engines with Boundary Layer Ingesting Inlets, Distributed Exhaust Nozzles installed on podded engines, a High Aspect Ratio Rectangular Nozzle, Distributed Propulsion, and a fixed and retractable aft <span class="hlt">airframe</span> extension. The systems analyses focused on the BWB performance impacts of each concept using the mission range as a measure of merit. <span class="hlt">Noise</span> effects were also investigated when enough information was available for a tractable analysis. Some tentative conclusions were drawn from the results. One was that the Boundary Layer Ingesting Inlets provided improvements to the BWB's mission range, by</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20120003366','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20120003366"><span>Emerging Community <span class="hlt">Noise</span> Reduction Approaches</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Envia, Edmane</p> <p>2012-01-01</p> <p>An overview of the current NASA research portfolio in the area of aircraft <span class="hlt">noise</span> reduction is presented. The emphasis of the research described herein is on meeting the aggressive near- and mid-term national goals for reducing aircraft <span class="hlt">noise</span> emissions, which NASA internal studies have shown to be feasible using <span class="hlt">noise</span> reduction technologies currently being developed in-house or in partnership with NASA s industry and academic partners. While NASA has an active research effort in <span class="hlt">airframe</span> <span class="hlt">noise</span> reduction, this overview focuses on propulsion <span class="hlt">noise</span> reduction only.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSV...362...39X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSV...362...39X"><span><span class="hlt">Noise</span> control of dipole <span class="hlt">source</span> by using micro-perforated panel housing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xi, Q.; Choy, Y. S.; Cheng, L.; Tang, S. K.</p> <p>2016-02-01</p> <p>Mitigating low-frequency <span class="hlt">noise</span> in a small ducted fan system such as hairdryer is still a technical challenge. Traditional duct lining with porous materials work ineffectively due to the limitation of its thickness and length of small domestic product with ducted fans. This study presents a passive approach to directly suppress the sound radiation from the fan housed by a short microperforated panel covered with a shallow cavity backing. The <span class="hlt">noise</span> suppression is achieved by the sound cancellation between sound fields from a fan of a dipole nature and sound radiation from a vibrating panel via vibro-acoustic coupling and by sound absorption in micro-perforations to widen the stopband. A two-dimensional theoretical model, capable of dealing with strong coupling among the vibrating micro-perforated panel, sound radiation from the dipole <span class="hlt">source</span>, sound fields inside the cavity and the duct is developed. Through modal analysis, it is found that the even modes of the panel vibration are very important to cancel the sound radiation from the dipole <span class="hlt">source</span>. Experimental validation is conducted with a loudspeaker to simulate the dipole <span class="hlt">source</span>, and good agreement between the predicted and measured insertion loss (IL) is achieved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRB..121.4031S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRB..121.4031S"><span>Sensitivity of earthquake <span class="hlt">source</span> inversions to atmospheric <span class="hlt">noise</span> and corrections of InSAR data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scott, Chelsea Phipps; Lohman, Rowena Benfer</p> <p>2016-05-01</p> <p>Tropospheric phase delays pose a major challenge to InSAR (interferometric synthetic aperture radar)-based studies of tectonic deformation. One approach to the mitigation of effects from tropospheric <span class="hlt">noise</span> is the application of elevation-dependent corrections based on empirical fits between elevation and interferometric phase. We quantify the effects of corrections with a range of complexity on inferred earthquake <span class="hlt">source</span> parameters using synthetic interferograms with known atmospheric characteristics. We infer statistical properties of the stratified component of the atmosphere using pressure, temperature, and water vapor data from the North America Regional Reanalysis model over our region of interest in the Basin and Range province of the western United States. The statistics of the simulated atmospheric turbulence are estimated from InSAR and Global Positioning System data. We demonstrate potentially significant improvements in the precision of earthquake magnitude, depth, and dip estimates for several synthetic earthquake focal mechanisms following a correction for spatially variable atmospheric characteristics, relative to cases where the correction is based on a uniform delay versus elevation relationship or where no correction is applied. We apply our approach to the 1992 M5.6 Little Skull Mountain, Nevada, earthquake and demonstrate that the earthquake <span class="hlt">source</span> parameter error bounds decrease in size after applying the atmospheric corrections. Our approach for evaluating the impact of atmospheric <span class="hlt">noise</span> on inferred fault parameters is easily adaptable to other regions and <span class="hlt">source</span> mechanisms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5665180','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5665180"><span>Subcritical measurements using the /sup 252/Cf <span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mihalczo, J.T.; Blakeman, E.D.; Ragan, G.E.; Kryter, R.C.</p> <p>1985-01-01</p> <p>This paper describes recent measurements of the subcritical neutron multiplication factor using the /sup 252/Cf <span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method. This work was supported by a program of collaboration between the United States Department of Energy and the Power Reactor and Nuclear Fuel Development Corporation of Japan related to the development of fast breeder technology. The experiment reported consists of a configuration of two interacting tanks of uranyl nitrate aqueous solution with different uranium concentrations in each tank. The /sup 252/Cf-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method obtains the subcriticality from the signals of three detectors: the first, a parallel plate ionization chamber with /sup 252/Cf electroplated on one of its plates that is located in or near the system containing the fissile material, and produces an electrical pulse for every spontaneous fission that occurs and thereby serves as a timed <span class="hlt">source</span> of fission neutrons; and the second and third detectors that are placed in or near the system containing fissile material and serve to detect particles from the fission chain multiplication process. 9 refs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011RScI...82c3513S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011RScI...82c3513S"><span>Low <span class="hlt">noise</span> Kα-band hopping reflectometer based on yttrium iron garnet <span class="hlt">sources</span> at TEXTOR</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Soldatov, S.; Krämer-Flecken, A.; Zorenko, O.</p> <p>2011-03-01</p> <p>The heterodyne hopping reflectometer system based on wide-tuned low <span class="hlt">noise</span> yttrium iron garnet <span class="hlt">sources</span> was developed for TEXTOR experiment. Being installed in 1998 it successfully operates more than 10 years providing the measurements of plasma density fluctuations. Owing to the advance multihorn antennae systems installed at three different positions around the tokamak, the correlation properties as well as the propagation measurements of plasma density fluctuations are realized. The reflectometer operates in ordinary polarization mode providing the access mostly to plasma gradient and pedestal region. The capabilities of the diagnostic are illustrated with the examples of measured fluctuation characteristics in the variety of TEXTOR plasmas.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080047422','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080047422"><span>Time Delay Analysis of Turbofan Engine Direct and Indirect Combustion <span class="hlt">Noise</span> <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Miles, Jeffrey Hilton</p> <p>2008-01-01</p> <p>The core <span class="hlt">noise</span> components of a dual spool turbofan engine were separated by the use of a coherence function. A <span class="hlt">source</span> location technique based on adjusting the time delay between the combustor pressure sensor signal and the far-field microphone signal to maximize the coherence and remove as much variation of the phase angle with frequency as possible was used. The discovery was made that for the 130o microphone a 90.027 ms time shift worked best for the frequency band from 0 to 200 Hz while a 86.975 ms time shift worked best for the frequency band from 200 to 400 Hz. Hence, the 0 to 200 Hz band signal took more time than the 200 to 400 Hz band signal to travel the same distance. This suggests the 0 to 200 Hz coherent cross spectral density band is partly due to indirect combustion <span class="hlt">noise</span> attributed to entropy fluctuations, which travel at the flow velocity, interacting with the turbine. The signal in the 200 to 400 Hz frequency band is attributed mostly to direct combustion <span class="hlt">noise</span>. Results are presented herein for engine power settings of 48, 54, and 60 percent of the maximum power setting</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27106340','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27106340"><span>Military jet <span class="hlt">noise</span> <span class="hlt">source</span> imaging using multisource statistically optimized near-field acoustical holography.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wall, Alan T; Gee, Kent L; Neilsen, Tracianne B; McKinley, Richard L; James, Michael M</p> <p>2016-04-01</p> <p>The identification of acoustic <span class="hlt">sources</span> is critical to targeted <span class="hlt">noise</span> reduction efforts for jets on high-performance tactical aircraft. This paper describes the imaging of acoustic <span class="hlt">sources</span> from a tactical jet using near-field acoustical holography techniques. The measurement consists of a series of scans over the hologram with a dense microphone array. Partial field decomposition methods are performed to generate coherent holograms. Numerical extrapolation of data beyond the measurement aperture mitigates artifacts near the aperture edges. A multisource equivalent wave model is used that includes the effects of the ground reflection on the measurement. Multisource statistically optimized near-field acoustical holography (M-SONAH) is used to reconstruct apparent <span class="hlt">source</span> distributions between 20 and 1250 Hz at four engine powers. It is shown that M-SONAH produces accurate field reconstructions for both inward and outward propagation in the region spanned by the physical hologram measurement. Reconstructions across the set of engine powers and frequencies suggests that directivity depends mainly on estimated <span class="hlt">source</span> location; <span class="hlt">sources</span> farther downstream radiate at a higher angle relative to the inlet axis. At some frequencies and engine powers, reconstructed fields exhibit multiple radiation lobes originating from overlapped <span class="hlt">source</span> regions, which is a phenomenon relatively recently reported for full-scale jets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880064715&hterms=vibration+helicopter&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dvibration%2Bhelicopter','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880064715&hterms=vibration+helicopter&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dvibration%2Bhelicopter"><span>Optimization of helicopter <span class="hlt">airframe</span> structures for vibration reduction considerations, formulations and applications</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Murthy, T. Sreekanta</p> <p>1988-01-01</p> <p>Several key issues involved in the application of formal optimization technique to helicopter <span class="hlt">airframe</span> structures for vibration reduction are addressed. Considerations which are important in the optimization of real <span class="hlt">airframe</span> structures are discussed. Considerations necessary to establish relevant set of design variables, constraints and objectives which are appropriate to conceptual, preliminary, detailed design, ground and flight test phases of <span class="hlt">airframe</span> design are discussed. A methodology is suggested for optimization of <span class="hlt">airframes</span> in various phases of design. Optimization formulations that are unique to helicopter <span class="hlt">airframes</span> are described and expressions for vibration related functions are derived. Using a recently developed computer code, the optimization of a Bell AH-1G helicopter <span class="hlt">airframe</span> is demonstrated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1811553N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1811553N"><span>Identifying seismic <span class="hlt">noise</span> <span class="hlt">sources</span> and their amplitude from P wave microseisms.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Neale, Jennifer; Harmon, Nicholas; Srokosz, Meric</p> <p>2016-04-01</p> <p>Understanding <span class="hlt">sources</span> of seismic <span class="hlt">noise</span> is important for a range of applications including seismic imagery, time-lapse, and climate studies. For locating <span class="hlt">sources</span> from seismic data, body waves offer an advantage over surface waves because they can reveal the distance to the <span class="hlt">source</span> as well as direction. Studies have found that body waves do originate from regions predicted by models (Obrebski et al., 2013), where wave interaction intensity and site effect combine to produce the <span class="hlt">source</span> (Ardhuin & Herbers, 2013). Here, we undertake a quantitative comparison between observed body wave microseisms and modelled <span class="hlt">sources</span>- in terms of location, amplitude, and spectral shape- with the aim of understanding how well <span class="hlt">sources</span> are observed and potentially what they reveal about the underlying ocean wavefield. We used seismic stations from the Southern California Seismic Network, and computed beamformer output as a function of time, frequency, slowness and azimuth. During winter months (October - mid March) the dominant arrivals at frequencies 0.18-0.22 Hz were P waves that originated from the North Pacific, whilst arrivals from the North Atlantic dominated at slightly lower frequencies of 0.16-0.18 Hz. Based on this, we chose to focus on P waves during winter, and back-projected the beamformer energy onto a global grid using P wave travel timetables (following Gerstoft et al., 2008). We modelled the seismic <span class="hlt">sources</span> using Wavewatch III and site effect coefficients calculated following Ardhuin and Herbers (2013). We output the beamformer and the modelled <span class="hlt">sources</span> on a 2° global grid averaged over 6 hour periods from September 2012 to September 2014, at seismic frequencies of 0.06 to 0.3 Hz. We then integrated the spectra over the full frequency range. Here we focus on results from the first winter in the North Pacific. Preliminary results indicate that the logarithm of the modelled <span class="hlt">source</span> and the logarithm of the beamformer output are well described by a two-term exponential model</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20060020690','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20060020690"><span>Reducing Propulsion <span class="hlt">Airframe</span> Aeroacoustic Interactions with Uniquely Tailored Chevrons. 2; Installed Nozzles</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mengle, Vinod G.; Elkoby, Ronen; Brusniak, Leon; Thomas, Russ H.</p> <p>2006-01-01</p> <p>Propulsion <span class="hlt">airframe</span> aeroacoustic (PAA) interactions arise due to the manner in which an engine is installed on the <span class="hlt">airframe</span> and lead to an asymmetry in the flow/acoustic environment, for example, for under-the-wing installations due to the pylon, the wing and the high-lift devices. In this work we study how we can affect these PAA interactions to reduce the overall jet-related installed <span class="hlt">noise</span> by tailoring the chevron shapes on fan and core nozzles in a unique fashion to take advantage of this asymmetry. In part 1 of this trio of papers we introduced the concept of azimuthally varying chevrons (AVC) and showed how some types of AVCs can be more beneficial than the conventional chevrons when tested on "isolated" scaled nozzles inclusive of the pylon effect. In this paper, we continue to study the effect of installing these AVC nozzles under a typical scaled modern wing with high-lift devices placed in a free jet. The <span class="hlt">noise</span> benefits of these installed nozzles, as well as their installation effects are systematically studied for several fan/core AVC combinations at typical take-off conditions with high bypass ratio. We show, for example, that the top-enhanced mixing T-fan AVC nozzle (with enhanced mixing near the pylon and less mixing away from it) when combined with conventional chevrons on the core nozzle is quieter than conventional chevrons on both nozzles, and hardly produces any high-frequency lift, just as in the isolated case; however, its installed nozzle benefit is less than its isolated nozzle benefit. This suppression of take-off <span class="hlt">noise</span> benefit under installed conditions, compared to its isolated nozzle benefit, is seen for all other chevron nozzles. We show how these relative <span class="hlt">noise</span> benefits are related to the relative installation effects of AVCs and baseline nozzles.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19820025272','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19820025272"><span>A computer program for the prediction of near field <span class="hlt">noise</span> of aircraft in cruising flight: User's guide</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Tibbetts, J. G.</p> <p>1980-01-01</p> <p>Detailed instructions for using the near field cruise <span class="hlt">noise</span> prediction program, a program listing, and a sample case with output are presented. The total <span class="hlt">noise</span> for free field lossless conditions at selected observer locations is obtained by summing the contributions from up to nine acoustic <span class="hlt">sources</span>. These <span class="hlt">noise</span> <span class="hlt">sources</span>, selected at the user's option, include the fan/compressor, turbine, core (combustion), jet, shock, and <span class="hlt">airframe</span> (trailing edge and turbulent boundary layers). The effects of acoustic suppression materials such as engine inlet treatment may also be included in the <span class="hlt">noise</span> prediction. The program is available for use on the NASA/Langley Research Center CDC computer. Comparisons of the program predictions with measured data are also given, and some possible reasons for their lack of agreement presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=acoustic+AND+reduction+AND+noise&pg=2&id=EJ091713','ERIC'); return false;" href="http://eric.ed.gov/?q=acoustic+AND+reduction+AND+noise&pg=2&id=EJ091713"><span>Control of Environmental <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Jensen, Paul</p> <p>1973-01-01</p> <p>Discusses the physical properties, <span class="hlt">sources</span>, physiological effects, and legislation pertaining to <span class="hlt">noise</span>, especially <span class="hlt">noise</span> characteristics in the community. Indicates that <span class="hlt">noise</span> reduction steps can be taken more intelligently after determination of the true <span class="hlt">noise</span> <span class="hlt">sources</span> and paths. (CC)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140011422','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140011422"><span>Identification of <span class="hlt">Noise</span> <span class="hlt">Sources</span> During Rocket Engine Test Firings and a Rocket Launch Using a Microphone Phased-Array</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Panda, Jayanta; Mosher, Robert N.; Porter, Barry J.</p> <p>2013-01-01</p> <p>A 70 microphone, 10-foot by 10-foot, microphone phased array was built for use in the harsh environment of rocket launches. The array was setup at NASA Wallops launch pad 0A during a static test firing of Orbital Sciences' Antares engines, and again during the first launch of the Antares vehicle. It was placed 400 feet away from the pad, and was hoisted on a scissor lift 40 feet above ground. The data sets provided unprecedented insight into rocket <span class="hlt">noise</span> <span class="hlt">sources</span>. The duct exit was found to be the primary <span class="hlt">source</span> during the static test firing; the large amount of water injected beneath the nozzle exit and inside the plume duct quenched all other <span class="hlt">sources</span>. The maps of the <span class="hlt">noise</span> <span class="hlt">sources</span> during launch were found to be time-dependent. As the engines came to full power and became louder, the primary <span class="hlt">source</span> switched from the duct inlet to the duct exit. Further elevation of the vehicle caused spilling of the hot plume, resulting in a distributed <span class="hlt">noise</span> map covering most of the pad. As the entire plume emerged from the duct, and the ondeck water system came to full power, the plume itself became the loudest <span class="hlt">noise</span> <span class="hlt">source</span>. These maps of the <span class="hlt">noise</span> <span class="hlt">sources</span> provide vital insight for optimization of sound suppression systems for future Antares launches.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1988hias.rept.....G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1988hias.rept.....G"><span>A high intensity acoustic <span class="hlt">source</span> for active attenuation of exhaust <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Glendinning, A. G.; Elliott, S. J.; Nelson, P. A.</p> <p>1988-04-01</p> <p>An electropneumatic sound <span class="hlt">source</span> was developed for active <span class="hlt">noise</span> control systems applied in hostile environments such as the exhaust systems of gas turbines and internal combustion engines. It employs a gas bearing to support the friction free motion of a sliding plate which is used to modulate the supply of compressed air. The sliding plate is driven by an electrodynamic vibrator. Experimental results demonstrate that this arrangement reduces harmonic distortion to at least 20 dB below the fundamental driving frequency for most operating conditions. A theoretical analysis of the transducer enables predictions to be made of the acoustic volume velocity (<span class="hlt">source</span> strength) produced by the transducer as a function of the upstream pressure and displacement of the sliding valve. Applicability of the transducer to gas turbine and internal combustion engine exhaust systems was tested, and net power consumption resulting from the operation of the device was estimated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910009732','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910009732"><span>Inflight <span class="hlt">source</span> <span class="hlt">noise</span> of an advanced full-scale single-rotation propeller</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Woodward, Richard P.; Loeffler, Irvin J.</p> <p>1991-01-01</p> <p>Flight tests to define the far field tone <span class="hlt">source</span> at cruise conditions were completed on the full scale SR-7L advanced turboprop which was installed on the left wing of a Gulfstream II aircraft. This program, designated Propfan Test Assessment (PTA), involved aeroacoustic testing of the propeller over a range of test conditions. These measurements defined <span class="hlt">source</span> levels for input into long distance propagation models to predict en route <span class="hlt">noise</span>. Inflight data were taken for 7 test cases. The sideline directivities measured by the Learjet showed expected maximum levels near 105 degrees from the propeller upstream axis. However, azimuthal directivities based on the maximum observed sideline tone levels showed highest levels below the aircraft. An investigation of the effect of propeller tip speed showed that the tone level of reduction associated with reductions in propeller tip speed is more significant in the horizontal plane than below the aircraft.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/166026','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/166026"><span><span class="hlt">Source</span> impedance, transient response, and <span class="hlt">noise</span> characterization of the TOPAZ 2 reactors</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kusnierkiewicz, D.Y.</p> <p>1995-01-20</p> <p>Electrical measurements have been performed on the TOPAZ 2 V-71 and Ya-21 Reactors, in order to characterize the <span class="hlt">source</span> impedance as a function of DC operating point and frequency. The response of the reactor to step changes in load current, as well as the frequency content of the electrical <span class="hlt">noise</span> generated by the reactor have also been measured. These parameters are important to know in order to design power regulation circuitry which maintains a constant load on the reactor during spacecraft operations for any flight application of the TOPAZ 2 reactors. Voltage spikes at the reactor interface induced by load transients must be limited; the power regulation circuitry must have adequate bandwidth to compensate for spacecraft load dynamics. The methods used to make these measurements will be discussed. Results of the measurements on the Ya-21 reactor indicate the <span class="hlt">source</span> impedance is dominated by a series resistance and inductance. The equivalent DC leakage resistance from the reactor output to structure was also measured. The self generated <span class="hlt">noise</span> of the reactor is benign; load induced transients will be sufficiently controlled with capacitive filtering and active regulation circuitry external to the reactor/power distribution system. {copyright} 1995 {ital American} {ital Institute} {ital of} {ital Physics}</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S43B4558B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S43B4558B"><span>Empirical sensitivity kernels of <span class="hlt">noise</span> correlations with respect to virtual <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Boué, P.; Stehly, L.; Nakata, N.; Beroza, G. C.</p> <p>2014-12-01</p> <p>Cross-correlation of time-series, or interferometry, applied to the ambient seismic field is an established method to observe the propagation of waves between pairs of sensors without involving transient <span class="hlt">sources</span>. These reconstructed waves are routinely used to develop high-resolution images of the crust and upper mantle, or in mapping the time-dependent velocity changes associated with tectonic events. Using similar methods, recent work have highlighted more challenging observations, such as higher mode surface wave propagation and body wave reconstruction at various scales of the Earth: from the industrial surveys at the reservoir scale to the global scale. Furthermore, the reconstruction of the correct amplitude information can be used to image the anelastic attenuation of the medium and has led to a new type of ground motion prediction using virtual earthquakes method. The dependability of such amplitude retrieval had been debated and represents a difficult challenge due to uneven <span class="hlt">source</span> distribution. In this study, we discuss the possibility to use the correlation of ambient <span class="hlt">noise</span> correlation (similar to C3 method) to map the contribution of different <span class="hlt">source</span> locations for Rayleigh wave reconstruction between receiver pairs. These maps constructed in terms of traveltime or amplitude perturbations of the Green's function, can be considered as empirical sensitivity kernels with respect to the contribution of each virtual <span class="hlt">source</span>. We propose for the first time to map these kernels using a dataset of continuous records from a dense array of about 2600 sensors deployed at the local-scale in Long Beach (CA, USA). Finally, these maps are used to analyze the impact of the original ambient <span class="hlt">noise</span> directivity on the recovered Green's functions and discuss the effects of the velocity lateral heterogeneity within the array. We aim at understanding, and thereby reducing, the bias in ambient field measurements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JSV...329..786K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JSV...329..786K"><span>Turbulence and heat excited <span class="hlt">noise</span> <span class="hlt">sources</span> in single and coaxial jets</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koh, Seong Ryong; Schröder, Wolfgang; Meinke, Matthias</p> <p>2010-03-01</p> <p>The generation of <span class="hlt">noise</span> in subsonic high Reynolds number single and coaxial turbulent jets is analyzed by a hybrid method. The computational approach is based on large-eddy simulations (LES) and solutions of the acoustic perturbation equations (APE). The method is used to investigate the acoustic fields of one isothermal single stream jet at a Mach number 0.9 and a Reynolds number 400,000 based on the nozzle diameter and two coaxial jets whose Mach number and Reynolds number based on the secondary jet match the values of the single jet. One coaxial jet configuration possesses a cold primary flow, whereas the other configuration has a hot primary jet. Thus, the configurations allow in a first step the analysis of the relationship of the flow and acoustic fields of a single and a cold coaxial jet and in a second step the investigation of the differences of the fluid mechanics and aeroacoustics of cold and hot coaxial jets. For the isothermal single jet the present hybrid acoustic computation shows convincing agreement with the direct acoustic simulation based on large-eddy simulations. The analysis of the acoustic field of the coaxial jets focuses on two <span class="hlt">noise</span> <span class="hlt">sources</span>, the Lamb vector fluctuations and the entropy <span class="hlt">sources</span> of the APE equations. The power spectral density (PSD) distributions evidence the Lamb vector fluctuations to represent the major acoustic <span class="hlt">sources</span> of the isothermal jet. Especially the typical downstream and sideline acoustic generations occur on a cone-like surface being wrapped around the end of the potential core. Furthermore, when the coaxial jet possesses a hot primary jet, the acoustic core being characterized by the entropy <span class="hlt">source</span> terms increases the low frequency acoustics by up to 5 dB, i.e., the sideline acoustics is enhanced by the pronounced temperature gradient.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SPIE.9783E..1UW','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SPIE.9783E..1UW"><span>Multi-gamma-<span class="hlt">source</span> CT imaging system: a feasibility study with the Poisson <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wi, Sunhee; Cho, Seungryong</p> <p>2016-03-01</p> <p>This study was performed to test the feasibility of multi-gamma-<span class="hlt">source</span> CT imaging system. Gamma-<span class="hlt">source</span> CT employs radioisotopes that emit monochromatic energy gamma-rays. The advantages of gamma-<span class="hlt">source</span> CT include its immunity to beam hardening artifacts, its capacity of quantitative CT imaging, and its higher performance in low contrast imaging compared to the conventional x-ray CT. Radioisotope should be shielded by use of a pin-hole collimator so as to make a fine focal spot. Due to its low gamma-ray flux in general, the reconstructed image from a single gamma-<span class="hlt">source</span> CT would suffer from high <span class="hlt">noise</span> in data. To address this problem, we proposed a multi-gamma <span class="hlt">source</span> CT imaging system and developed an iterative image reconstruction algorithm accordingly in this work. Conventional imaging model assumes a single linear imaging system typically represented by Mf = g. In a multi-gamma-<span class="hlt">source</span> CT system however, the inversion problem is not any more based on a single linear system since one cannot separate a detector pixel value into multiple ones that are corresponding to each rays from the <span class="hlt">sources</span>. Instead, the imaging model can be constructed by a set of linear system models each of which assumes an estimated measurement g. Based on this model, the proposed algorithm has a weighting step which distributes each projection data into multiple estimated measurements. We used two gamma <span class="hlt">sources</span> at various positions and with varying intensities in this numerical study to demonstrate its feasibility. Therefore, the measured projection data(g) is separated into each estimated projection data(g1, g2) in this study. The proposed imaging protocol is believed to contribute to both medical and industrial applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020062991','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020062991"><span><span class="hlt">Airframe</span> Research and Technology for Hypersonic Airbreathing Vehicles</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Glass, David E.; Merski, N. Ronald; Glass, Christopher E.</p> <p>2002-01-01</p> <p>The Hypersonics Investment Area (HIA) within NASA's Advanced Space Transportation Program (ASTP) has the responsibility to develop hypersonic airbreathing vehicles for access to space. The <span class="hlt">Airframe</span> Research and Technology (AR and T) Project, as one of six projects in the HIA, will push the state-of-the-art in <span class="hlt">airframe</span> and vehicle systems for low-cost, reliable, and safe space transportation. The individual technologies within the project are focused on advanced, breakthrough technologies in <span class="hlt">airframe</span> and vehicle systems and cross-cutting activities that are the basis for improvements in these disciplines. Both low and medium technology readiness level (TRL) activities are being pursued. The key technical areas that will be addressed by the project include analysis and design tools, integrated vehicle health management (IVHM), composite (polymer, metal, and ceramic matrix) materials development, thermal/structural wall concepts, thermal protection systems, seals, leading edges, aerothermodynamics, and <span class="hlt">airframe</span>/propulsion flowpath technology. Each of the technical areas or sub-projects within the <span class="hlt">Airframe</span> R and T Project is described in this paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.7382C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.7382C"><span>Extraction of the local phase velocity and the group velocity from surface <span class="hlt">noise</span> <span class="hlt">source</span> in microseismic monitoring.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chmiel, Malgorzata; Roux, Philippe; Bardainne, Thomas</p> <p>2015-04-01</p> <p>The aim of this work is to demonstrate the extraction of the local phase velocity and the group velocity from surface <span class="hlt">noise</span> <span class="hlt">source</span> in microseismic monitoring. One of the biggest challenges in microseismic monitoring is surface seismic <span class="hlt">noise</span>. Microseismic surface studies are often contaminated with instrumental and ambient seismic <span class="hlt">noise</span>, originating from both natural (wind, rain) and anthropogenic <span class="hlt">sources</span> (injection, pumps, infrastructure, traffic). The two primary ways to attenuate the undesired surface <span class="hlt">noise</span> <span class="hlt">sources</span> are via processing and acquisition strategies. At the acquisition stage, one solution is through the use of patch array. One patch is a group of 48 vertical sensors densely distributed on the area of~150m*150m, and one trace is the array of 12 vertical geophones. In the present work, 44 patches were sparsely distributed on a 41 square kilometer area. Benefitting from continuous recording, we used Matched Field Processing (MFP) methods to extract local phase and group velocities over the whole area. The aim of this technique is to detect and locate uncoherent <span class="hlt">noise</span> <span class="hlt">sources</span> while using array-processing methods. The method is based on the comparison between a recorded wave field per patch (the data vector) and a theoretical (or modeled) wave-field (the replica vector) in the frequency domain. The replica vector is a Green's function at a given frequency, which depends on the following parameters: position (x,y) in 2D-grid and a phase velocity. The <span class="hlt">noise</span> <span class="hlt">source</span> location is obtained by matching the data vector with the replica vector using a linear "low-resolution" algorithm or a nonlinear "high-resolution" adaptive processor. These algorithms are defined for each point in the 2D - grid and for each phase velocity. The phase velocity per patch is optimal if it maximizes the processor output. As a result, an ambiguity surface is produced which shows the probability of presence of primary <span class="hlt">noise</span> <span class="hlt">sources</span> per patch. The combination of all the maps per patch</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25330772','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25330772"><span>Two-microphone spatial filtering improves speech reception for cochlear-implant users in reverberant conditions with multiple <span class="hlt">noise</span> <span class="hlt">sources</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Goldsworthy, Raymond L</p> <p>2014-10-20</p> <p>This study evaluates a spatial-filtering algorithm as a method to improve speech reception for cochlear-implant (CI) users in reverberant environments with multiple <span class="hlt">noise</span> <span class="hlt">sources</span>. The algorithm was designed to filter sounds using phase differences between two microphones situated 1 cm apart in a behind-the-ear hearing-aid capsule. Speech reception thresholds (SRTs) were measured using a Coordinate Response Measure for six CI users in 27 listening conditions including each combination of reverberation level (T60=0, 270, and 540 ms), number of <span class="hlt">noise</span> <span class="hlt">sources</span> (1, 4, and 11), and signal-processing algorithm (omnidirectional response, dipole-directional response, and spatial-filtering algorithm). <span class="hlt">Noise</span> <span class="hlt">sources</span> were time-reversed speech segments randomly drawn from the Institute of Electrical and Electronics Engineers sentence recordings. Target speech and <span class="hlt">noise</span> <span class="hlt">sources</span> were processed using a room simulation method allowing precise control over reverberation times and sound-<span class="hlt">source</span> locations. The spatial-filtering algorithm was found to provide improvements in SRTs on the order of 6.5 to 11.0 dB across listening conditions compared with the omnidirectional response. This result indicates that such phase-based spatial filtering can improve speech reception for CI users even in highly reverberant conditions with multiple <span class="hlt">noise</span> <span class="hlt">sources</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22308867','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22308867"><span>The differential Howland current <span class="hlt">source</span> with high signal to <span class="hlt">noise</span> ratio for bioimpedance measurement system</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Liu, Jinzhen; Li, Gang; Lin, Ling; Qiao, Xiaoyan; Wang, Mengjun; Zhang, Weibo</p> <p>2014-05-15</p> <p>The stability and signal to <span class="hlt">noise</span> ratio (SNR) of the current <span class="hlt">source</span> circuit are the important factors contributing to enhance the accuracy and sensitivity in bioimpedance measurement system. In this paper we propose a new differential Howland topology current <span class="hlt">source</span> and evaluate its output characters by simulation and actual measurement. The results include (1) the output current and impedance in high frequencies are stabilized after compensation methods. And the stability of output current in the differential current <span class="hlt">source</span> circuit (DCSC) is 0.2%. (2) The output impedance of two current circuits below the frequency of 200 KHz is above 1 MΩ, and below 1 MHz the output impedance can arrive to 200 KΩ. Then in total the output impedance of the DCSC is higher than that of the Howland current <span class="hlt">source</span> circuit (HCSC). (3) The SNR of the DCSC are 85.64 dB and 65 dB in the simulation and actual measurement with 10 KHz, which illustrates that the DCSC effectively eliminates the common mode interference. (4) The maximum load in the DCSC is twice as much as that of the HCSC. Lastly a two-dimensional phantom electrical impedance tomography is well reconstructed with the proposed HCSC. Therefore, the measured performance shows that the DCSC can significantly improve the output impedance, the stability, the maximum load, and the SNR of the measurement system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150002347','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150002347"><span>Acoustics of Jet Surface Interaction - Scrubbing <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Khavaran, Abbas</p> <p>2014-01-01</p> <p>Concepts envisioned for the future of civil air transport consist of unconventional propulsion systems in the close proximity to the structure or embedded in the <span class="hlt">airframe</span>. While such integrated systems are intended to shield <span class="hlt">noise</span> from the community, they also introduce new <span class="hlt">sources</span> of sound. Sound generation due to interaction of a jet flow past a nearby solid surface is investigated here using the generalized acoustic analogy theory. The analysis applies to the boundary layer <span class="hlt">noise</span> generated at and near a wall, and excludes the scattered <span class="hlt">noise</span> component that is produced at the leading or the trailing edge. While compressibility effects are relatively unimportant at very low Mach numbers, frictional heat generation and thermal gradient normal to the surface could play important roles in generation and propagation of sound in high speed jets of practical interest. A general expression is given for the spectral density of the far field sound as governed by the variable density Pridmore-Brown equation. The propagation Green's function is solved numerically for a high aspect-ratio rectangular jet starting with the boundary conditions on the surface and subject to specified mean velocity and temperature profiles between the surface and the observer. It is shown the magnitude of the Green's function decreases with increasing <span class="hlt">source</span> frequency and/or jet temperature. The phase remains constant for a rigid surface, but varies with <span class="hlt">source</span> location when subject to an impedance type boundary condition. The Green's function in the absence of the surface, and flight effects are also investigated</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040110379','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040110379"><span>Propulsion <span class="hlt">Airframe</span> Aeroacoustics Technology Evaluation and Selection Using a Multi-Attribute Decision Making Process and Non-Deterministic Design</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Burg, Cecile M.; Hill, Geoffrey A.; Brown, Sherilyn A.; Geiselhart, Karl A.</p> <p>2004-01-01</p> <p>The Systems Analysis Branch at NASA Langley Research Center has investigated revolutionary Propulsion <span class="hlt">Airframe</span> Aeroacoustics (PAA) technologies and configurations for a Blended-Wing-Body (BWB) type aircraft as part of its research for NASA s Quiet Aircraft Technology (QAT) Project. Within the context of the long-term NASA goal of reducing the perceived aircraft <span class="hlt">noise</span> level by a factor of 4 relative to 1997 state of the art, major configuration changes in the propulsion <span class="hlt">airframe</span> integration system were explored with <span class="hlt">noise</span> as a primary design consideration. An initial down-select and assessment of candidate PAA technologies for the BWB was performed using a Multi-Attribute Decision Making (MADM) process consisting of organized brainstorming and decision-making tools. The assessments focused on what effect the PAA technologies had on both the overall <span class="hlt">noise</span> level of the BWB and what effect they had on other major design considerations such as weight, performance and cost. A probabilistic systems analysis of the PAA configurations that presented the best <span class="hlt">noise</span> reductions with the least negative impact on the system was then performed. Detailed results from the MADM study and the probabilistic systems analysis will be published in the near future.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140002895','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140002895"><span>Analysis-Driven Design Optimization of a SMA-Based Slat-Cove Filler for Aeroacoustic <span class="hlt">Noise</span> Reduction</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Scholten, William; Hartl, Darren; Turner, Travis</p> <p>2013-01-01</p> <p><span class="hlt">Airframe</span> <span class="hlt">noise</span> is a significant component of environmental <span class="hlt">noise</span> in the vicinity of airports. The <span class="hlt">noise</span> associated with the leading-edge slat of typical transport aircraft is a prominent <span class="hlt">source</span> of <span class="hlt">airframe</span> <span class="hlt">noise</span>. Previous work suggests that a slat-cove filler (SCF) may be an effective <span class="hlt">noise</span> treatment. Hence, development and optimization of a practical slat-cove-filler structure is a priority. The objectives of this work are to optimize the design of a functioning SCF which incorporates superelastic shape memory alloy (SMA) materials as flexures that permit the deformations involved in the configuration change. The goal of the optimization is to minimize the actuation force needed to retract the slat-SCF assembly while satisfying constraints on the maximum SMA stress and on the SCF deflection under static aerodynamic pressure loads, while also satisfying the condition that the SCF self-deploy during slat extension. A finite element analysis model based on a physical bench-top model is created in Abaqus such that automated iterative analysis of the design could be performed. In order to achieve an optimized design, several design variables associated with the current SCF configuration are considered, such as the thicknesses of SMA flexures and the dimensions of various components, SMA and conventional. Designs of experiment (DOE) are performed to investigate structural response to an aerodynamic pressure load and to slat retraction and deployment. DOE results are then used to inform the optimization process, which determines a design minimizing actuator forces while satisfying the required constraints.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160012296','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160012296"><span>A Review of <span class="hlt">Noise</span> and Vibration Control Technologies for Rotorcraft Transmissions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Scheidler, Justin J.; Asnani, Vivake M.</p> <p>2016-01-01</p> <p>An expanded commercial use of rotorcraft can alleviate runway congestion and improve the accessibility of routine air travel. To date, commercial use has been hindered by excessive cabin <span class="hlt">noise</span>. The primary <span class="hlt">noise</span> <span class="hlt">source</span> is structure-borne vibration originating from the main rotor gearbox. Despite significant advancements in gear design, the gear mesh tones generated often exceed 100 dB. This paper summarizes the findings of a literature survey of vibration control technologies that serve to attenuate this vibration near the <span class="hlt">source</span>, before it spreads into the <span class="hlt">airframe</span> and produces <span class="hlt">noise</span>. The scope is thus limited to vibration control treatments and modifications of the gears, driveline, housing structures, and the strut connections to the <span class="hlt">airframe</span>. The findings of the literature are summarized and persistent and unresolved issues are identified. An emphasis is placed on components and systems that have been demonstrated in flight vehicles. Then, a discussion is presented of emerging technologies that have the potential to make significant advancements over the state of the art.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014MeScT..25g5204C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014MeScT..25g5204C"><span>Exploiting continuous scanning laser Doppler vibrometry (CSLDV) in time domain correlation methods for <span class="hlt">noise</span> <span class="hlt">source</span> identification</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chiariotti, Paolo; Martarelli, Milena; Revel, Gian Marco</p> <p>2014-07-01</p> <p>This paper proposes the use of continuous scanning laser Doppler vibrometry (CSLDV) in time domain correlation techniques that aim at characterizing the structure-borne contributions of the <span class="hlt">noise</span> emission of a mechanical system. The time domain correlation technique presented in this paper is based on the use of FIR (finite impulse response) filters obtained from the vibro-acoustic transfer matrix when vibration data are collected by laser Doppler vibrometry (LDV) exploited in continuous scan mode (CSLDV). The advantages, especially in terms of <span class="hlt">source</span> decorrelation capabilities, related to the use of CSLDV for such purpose, with respect to standard discrete scan (SLDV), are discussed throughout the paper. To validate this approach, vibro-acoustic measurements were performed on a planetary gear motor for home appliances. The analysis of results is also supported by a simulation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22391461','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22391461"><span>Reduction of beam current <span class="hlt">noise</span> in the FNAL magnetron ion <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bollinger, D. S. Karns, P. R. Tan, C. Y.</p> <p>2015-04-08</p> <p>The new FNAL Injector Line with a circular dimple magnetron ion <span class="hlt">source</span> has been operational since December of 2012. Since the new injector came on line there have been variations in the H- beam current flattop observed near the downstream end of the Linac. Several different cathode geometries including a hollow cathode suggested by Dudnikov [1] were tried. Previous studies also showed that different mixtures of hydrogen and nitrogen had an effect on beam current <span class="hlt">noise</span> [2]. We expanded on those studies by trying mixtures ranging from (0.25% nitrogen, 99.75% hydrogen) to (3% nitrogen, 97% hydrogen). The results of these studies in our test stand will be presented in this paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19800006956','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19800006956"><span>Combustion <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Strahle, W. C.</p> <p>1977-01-01</p> <p>A review of the subject of combustion generated <span class="hlt">noise</span> is presented. Combustion <span class="hlt">noise</span> is an important <span class="hlt">noise</span> <span class="hlt">source</span> in industrial furnaces and process heaters, turbopropulsion and gas turbine systems, flaring operations, Diesel engines, and rocket engines. The state-of-the-art in combustion <span class="hlt">noise</span> importance, understanding, prediction and scaling is presented for these systems. The fundamentals and available theories of combustion <span class="hlt">noise</span> are given. Controversies in the field are discussed and recommendations for future research are made.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140002894','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140002894"><span>Development of a SMA-Based Slat-Cove Filler for Reduction of Aeroacoustic <span class="hlt">Noise</span> Associated With Transport-Class Aircraft Wings</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Turner, Travis L.; Kidd, Reggie T.; Hartl, Darren J.; Scholten, William D.</p> <p>2013-01-01</p> <p><span class="hlt">Airframe</span> <span class="hlt">noise</span> is a significant part of the overall <span class="hlt">noise</span> produced by typical, transport-class aircraft during the approach and landing phases of flight. Leading-edge slat <span class="hlt">noise</span> is a prominent <span class="hlt">source</span> of <span class="hlt">airframe</span> <span class="hlt">noise</span>. The concept of a slat-cove filler was proposed in previous work as an effective means of mitigating slat <span class="hlt">noise</span>. Bench-top models were deployed at 75% scale to study the feasibility of producing a functioning slat-cove filler. Initial results from several concepts led to a more-focused effort investigating a deformable structure based upon pseudoelastic SMA materials. The structure stows in the cavity between the slat and main wing during cruise and deploys simultaneously with the slat to guide the aerodynamic flow suitably for low <span class="hlt">noise</span>. A qualitative parametric study of SMA-enabled, slat-cove filler designs was performed on the bench-top. Computational models were developed and analyses were performed to assess the displacement response under representative aerodynamic load. The bench-top and computational results provide significant insight into design trades and an optimal design.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20000101661','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20000101661"><span>Current Background <span class="hlt">Noise</span> <span class="hlt">Sources</span> and Levels in the NASA Ames 40- by 80-Foot Wind Tunnel: A Status Report</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Allen, Christopher S.; Jaeger, Stephen; Soderman, Paul; Koga, Dennis (Technical Monitor)</p> <p>1999-01-01</p> <p>Background <span class="hlt">noise</span> measurements were made of the acoustic environment in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel (40x80) at NASA Ames Research Center. The measurements were acquired subsequent to the 40x80 Aeroacoustic Modernization Project, which was undertaken to improve the anechoic characteristics of the 40x80's closed test section as well as reduce the levels of background <span class="hlt">noise</span> in the facility. The resulting 40x80 anechoic environment was described by Soderman et. al., and the current paper describes the resulting 40x80 background <span class="hlt">noise</span>, discusses the <span class="hlt">sources</span> of the <span class="hlt">noise</span>, and draws comparisons to previous 40x80 background <span class="hlt">noise</span> levels measurements. At low wind speeds or low frequencies, the 40x80 background <span class="hlt">noise</span> is dominated by the fan drive system. To obtain the lowest fan drive <span class="hlt">noise</span> for a given tunnel condition, it is possible in the 40x80 to reduce the fans' rotational speed and adjust the fans' blade pitch, as described by Schmidtz et. al. This idea is not new, but has now been operationally implemented with modifications for increased power at low rotational speeds. At low to mid-frequencies and at higher wind speeds, the dominant <span class="hlt">noise</span> mechanism was thought to be caused by the surface interface of the previous test section floor acoustic lining. In order to reduce this <span class="hlt">noise</span> mechanism, the new test section floor lining was designed to resist the pumping of flow in and out of the space between the grating slats required to support heavy equipment. In addition, the lining/flow interface over the entire test section was designed to be smoother and quieter than the previous design. At high wind speeds or high frequencies, the dominant <span class="hlt">source</span> of background <span class="hlt">noise</span> in the 40x80 is believed to be caused by the response of the in-flow microphone probes (required by the nature of the closed test section) to the fluctuations in the freestream flow. The resulting background <span class="hlt">noise</span> levels are also different for probes of various</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910010809','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910010809"><span>IMPAC: An Integrated Methodology for Propulsion and <span class="hlt">Airframe</span> Control</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Garg, Sanjay; Ouzts, Peter J.; Lorenzo, Carl F.; Mattern, Duane L.</p> <p>1991-01-01</p> <p>The National Aeronautics and Space Administration is actively involved in the development of enabling technologies that will lead towards aircraft with new/enhanced maneuver capabilities such as Short Take-Off Vertical Landing (STOVL) and high angle of attack performance. Because of the high degree of dynamic coupling between the <span class="hlt">airframe</span> and propulsion systems of these types of aircraft, one key technology is the integration of the flight and propulsion control. The NASA Lewis Research Center approach to developing Integrated Flight Propulsion Control (IFPC) technologies is an in-house research program referred to as IMPAC (Integrated Methodology for Propulsion and <span class="hlt">Airframe</span> Control). The goals of IMPAC are to develop a viable alternative to the existing integrated control design methodologies that will allow for improved system performance and simplicity of control law synthesis and implementation, and to demonstrate the applicability of the methodology to a supersonic STOVL fighter aircraft. Based on some preliminary control design studies that included evaluation of the existing methodologies, the IFPC design methodology that is emerging at the Lewis Research Center consists of considering the <span class="hlt">airframe</span> and propulsion system as one integrated system for an initial centralized controller design and then partitioning the centralized controller into separate <span class="hlt">airframe</span> and propulsion system subcontrollers to ease implementation and to set meaningful design requirements for detailed subsystem control design and evaluation. An overview of IMPAC is provided and detailed discussion of the various important design and evaluation steps in the methodology are included.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19840010086','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19840010086"><span><span class="hlt">Airframe</span> technology for aircraft energy efficiency. [economic factors</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>James, R. L., Jr.; Maddalon, D. V.</p> <p>1984-01-01</p> <p>The economic factors that resulted in the implementation of the aircraft energy efficiency program (ACEE) are reviewed and <span class="hlt">airframe</span> technology elements including content, progress, applications, and future direction are discussed. The program includes the development of laminar flow systems, advanced aerodynamics, active controls, and composite structures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920016668','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920016668"><span>Computational Structures Technology for <span class="hlt">Airframes</span> and Propulsion Systems</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Noor, Ahmed K. (Compiler); Housner, Jerrold M. (Compiler); Starnes, James H., Jr. (Compiler); Hopkins, Dale A. (Compiler); Chamis, Christos C. (Compiler)</p> <p>1992-01-01</p> <p>This conference publication contains the presentations and discussions from the joint University of Virginia (UVA)/NASA Workshops. The presentations included NASA Headquarters perspectives on High Speed Civil Transport (HSCT), goals and objectives of the UVA Center for Computational Structures Technology (CST), NASA and Air Force CST activities, CST activities for <span class="hlt">airframes</span> and propulsion systems in industry, and CST activities at Sandia National Laboratory.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AcAau.111..178D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AcAau.111..178D"><span>Novel inlet-<span class="hlt">airframe</span> integration methodology for hypersonic waverider vehicles</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ding, Feng; Liu, Jun; Shen, Chi-bing; Huang, Wei</p> <p>2015-06-01</p> <p>With the aim of integrating a ramjet or scramjet with an <span class="hlt">airframe</span>, a novel inlet-<span class="hlt">airframe</span> integration methodology for the hypersonic waverider vehicle is proposed. For this newly proposed design concept and for the specified flight conditions, not only the forebody of the vehicle but also its engine cowl and wings can ride on the bow shock wave, causing the bow shock wave to remain attached to the leading edge for the entire length of the vehicle. Thus, this integrated vehicle can take full advantage of the waverider's high lift-to-drag ratio characteristics and the ideal pre-compression surface for the engine. In this work, a novel inlet-<span class="hlt">airframe</span> integrated axisymmetric basic flow model that accounts for both external and internal flows is first designed using the method of characteristics and the streamline tracing technique. Subsequently, the design of the inlet-<span class="hlt">airframe</span> integrated waverider vehicle is generated from the integrated axisymmetric basic flow model using the streamline tracing technique. Then, the design methodologies of both the integrated axisymmetric basic flow model and the integrated waverider vehicle are verified by a computational numerical method. Finally, the viscous effects and performance of both the integrated axisymmetric basic flow model and the integrated waverider vehicle are analysed under the design condition using the numerical computation. The obtained results show that the proposed approach is effective in designing the integrated hypersonic waverider vehicle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920013401','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920013401"><span>Design of an integrated <span class="hlt">airframe</span>/propulsion control system architecture</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cohen, Gerald C.; Lee, C. William; Strickland, Michael J.; Torkelson, Thomas C.</p> <p>1990-01-01</p> <p>The design of an integrated <span class="hlt">airframe</span>/propulsion control system architecture is described. The design is based on a prevalidation methodology that uses both reliability and performance. A detailed account is given for the testing associated with a subset of the architecture and concludes with general observations of applying the methodology to the architecture.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=tungsten&pg=3&id=ED302632','ERIC'); return false;" href="http://eric.ed.gov/?q=tungsten&pg=3&id=ED302632"><span>Aviation Maintenance Technology. <span class="hlt">Airframe</span>. A204. Aircraft Welding. Instructor Material.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Oklahoma State Board of Vocational and Technical Education, Stillwater. Curriculum and Instructional Materials Center.</p> <p></p> <p>This teacher's guide is designed to aid teachers in leading students through a module on aircraft welding on <span class="hlt">airframes</span>. The module contains four units that cover the following topics: (1) gas welding and cutting; (2) brazing and soldering; (3) shielded metal arc welding; and (4) gas tungsten arc welding. Each unit follows a standardized format…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2014-title14-vol3/pdf/CFR-2014-title14-vol3-part147-appC.pdf','CFR2014'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2014-title14-vol3/pdf/CFR-2014-title14-vol3-part147-appC.pdf"><span>14 CFR Appendix C to Part 147 - <span class="hlt">Airframe</span> Curriculum Subjects</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2014&page.go=Go">Code of Federal Regulations, 2014 CFR</a></p> <p></p> <p>2014-01-01</p> <p>... titanium. (1) 18. Solder stainless steel. (1) 19. Fabricate tubular structures. (2) 20. Solder, braze, gas... control systems. j. fire protection systems (1) 54. Inspect, check, and service smoke and carbon monoxide... of proficiency at which that item must be taught. I. <span class="hlt">Airframe</span> Structures Teaching level a....</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2012-title14-vol3/pdf/CFR-2012-title14-vol3-part147-appC.pdf','CFR2012'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2012-title14-vol3/pdf/CFR-2012-title14-vol3-part147-appC.pdf"><span>14 CFR Appendix C to Part 147 - <span class="hlt">Airframe</span> Curriculum Subjects</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2012&page.go=Go">Code of Federal Regulations, 2012 CFR</a></p> <p></p> <p>2012-01-01</p> <p>... titanium. (1) 18. Solder stainless steel. (1) 19. Fabricate tubular structures. (2) 20. Solder, braze, gas... control systems. j. fire protection systems (1) 54. Inspect, check, and service smoke and carbon monoxide... of proficiency at which that item must be taught. I. <span class="hlt">Airframe</span> Structures Teaching level a....</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2013-title14-vol3/pdf/CFR-2013-title14-vol3-part147-appC.pdf','CFR2013'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2013-title14-vol3/pdf/CFR-2013-title14-vol3-part147-appC.pdf"><span>14 CFR Appendix C to Part 147 - <span class="hlt">Airframe</span> Curriculum Subjects</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2013&page.go=Go">Code of Federal Regulations, 2013 CFR</a></p> <p></p> <p>2013-01-01</p> <p>... titanium. (1) 18. Solder stainless steel. (1) 19. Fabricate tubular structures. (2) 20. Solder, braze, gas... control systems. j. fire protection systems (1) 54. Inspect, check, and service smoke and carbon monoxide... of proficiency at which that item must be taught. I. <span class="hlt">Airframe</span> Structures Teaching level a....</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2011-title14-vol3/pdf/CFR-2011-title14-vol3-part147-appC.pdf','CFR2011'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2011-title14-vol3/pdf/CFR-2011-title14-vol3-part147-appC.pdf"><span>14 CFR Appendix C to Part 147 - <span class="hlt">Airframe</span> Curriculum Subjects</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2011&page.go=Go">Code of Federal Regulations, 2011 CFR</a></p> <p></p> <p>2011-01-01</p> <p>... titanium. (1) 18. Solder stainless steel. (1) 19. Fabricate tubular structures. (2) 20. Solder, braze, gas... control systems. j. fire protection systems (1) 54. Inspect, check, and service smoke and carbon monoxide... of proficiency at which that item must be taught. I. <span class="hlt">Airframe</span> Structures Teaching level a....</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22779457','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22779457"><span>Shipping <span class="hlt">noise</span> in whale habitat: characteristics, <span class="hlt">sources</span>, budget, and impact on belugas in Saguenay-St. Lawrence Marine Park hub.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gervaise, Cédric; Simard, Yvan; Roy, Nathalie; Kinda, Bazile; Ménard, Nadia</p> <p>2012-07-01</p> <p>A continuous car ferry line crossing the Saguenay Fjord mouth and traffic from the local whale-watching fleet introduce high levels of shipping <span class="hlt">noise</span> in the heart of the Saguenay-St. Lawrence Marine Park. To characterize this <span class="hlt">noise</span> and examine its potential impact on belugas, a 4-hydrophone array was deployed in the area and continuously recorded for five weeks in May-June 2009. The <span class="hlt">source</span> levels of the different vessel types showed little dependence on vessel size or speed increase. Their spectral range covered 33 dB. Lowest <span class="hlt">noise</span> levels occurred at night, when ferry crossing pace was reduced, and daytime <span class="hlt">noise</span> peaked during whale-watching tour departures and arrivals. Natural ambient <span class="hlt">noise</span> prevailed 9.4% of the time. Ferry traffic added 30-35 dB to ambient levels above 1 kHz during crossings, which contributed 8 to 14 dB to hourly averages. The whale-watching fleet added up to 5.6 dB during peak hours. Assuming no behavioral or auditory compensation, half of the time, beluga potential communication range was reduced to less than ~30% of its expected value under natural <span class="hlt">noise</span> conditions, and to less than ~15% for one quarter of the time, with little dependence on call frequency. The echolocation band for this population of belugas was also affected by the shipping <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFD.D4009R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFD.D4009R"><span>Towards the characterization of <span class="hlt">noise</span> <span class="hlt">sources</span> in a supersonic three-stream jet using advanced analysis tools</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ruscher, Christopher; Gogineni, Sivaram</p> <p>2016-11-01</p> <p>Strict <span class="hlt">noise</span> regulation set by governing bodies currently make supersonic commercial aviation impractical. One of the many challenges that exist in developing practical supersonic commercial aircraft is the <span class="hlt">noise</span> produced by the engine's exhaust jet. A promising method of jet <span class="hlt">noise</span> reduction for supersonic applications is through the addition of extra exhaust streams. Data for an axisymmetric three-stream nozzle were generated using the Naval Research Laboratory's JENRE code. This data will be compared to experimental results obtained by NASA for validation purposes. Once the simulation results show satisfactory agreement to the experiments, advanced analysis tools will be applied to the simulation data to characterize potential <span class="hlt">noise</span> <span class="hlt">sources</span>. The tools to be applied include methods that are based on proper orthogonal decomposition, wavelet decomposition, and stochastic estimation. Additionally, techniques such as empirical mode decomposition and momentum potential theorem will be applied to the data as well.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770007084','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770007084"><span>Further studies of static to flight effects on fan tone <span class="hlt">noise</span> using inlet distortion control for <span class="hlt">source</span> identification</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hodder, B. K.</p> <p>1976-01-01</p> <p>Current experimental investigations have linked static inflow distortion phenomena such as the ground vortex, atmospheric turbulence, and teststand structure interference to the generation of fan tone <span class="hlt">noise</span> at the blade passing frequency. Since such distortions do not exist in flight, it is important to remove them from the static test environment and thereby improve the static-to-flight tone-<span class="hlt">noise</span> correlation. In the course of providing evidence for this position, a recent investigation used a distortion control inlet with a modern day turbofan engine to assess atmospheric turbulence effects. Although the initial results were encouraging, they were incomplete. The present investigation continues this work and shows more completely the effect of atmospheric turbulence on tone-<span class="hlt">noise</span> generation. Further, use is made of the distortion control inlet to identify other competing tone-<span class="hlt">noise</span> <span class="hlt">sources</span> in the test engine such as a rotor-core stator interaction which was confirmed by engine modifications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20130000448','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130000448"><span>Hybrid Wing Body Shielding Studies Using an Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> Generating Simple Modes</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sutliff, Daniel, L.; Brown, Clifford, A.; Walker, Bruce, E.</p> <p>2012-01-01</p> <p>An Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> (UCFANS) was designed, built, and tested in support of the Langley Research Center s 14- by 22-Foot wind tunnel test of the Hybrid Wing Body (HWB) full three-dimensional 5.8 percent scale model. The UCFANS is a 5.8 percent rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of candidate engines using artificial <span class="hlt">sources</span> (no flow). The purpose of the test was to provide an estimate of the acoustic shielding benefits possible from mounting the engine on the upper surface of an HWB aircraft and to provide a database for shielding code validation. A range of frequencies, and a parametric study of modes were generated from exhaust and inlet nacelle configurations. Radiated acoustic data were acquired from a traversing linear array of 13 microphones, spanning 36 in. Two planes perpendicular to the axis of the nacelle (in its 0 orientation) and three planes parallel were acquired from the array sweep. In each plane the linear array traversed five sweeps, for a total span of 160 in. acquired. The resolution of the sweep is variable, so that points closer to the model are taken at a higher resolution. Contour plots of Sound Pressure Level, and integrated Power Levels are presented in this paper; as well as the in-duct modal structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70047737','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70047737"><span>Ground motion in the presence of complex topography: Earthquake and ambient <span class="hlt">noise</span> <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hartzell, Stephen; Meremonte, Mark; Ramírez-Guzmán, Leonardo; McNamara, Daniel</p> <p>2014-01-01</p> <p>To study the influence of topography on ground motion, eight seismic recorders were deployed for a period of one year over Poverty Ridge on the east side of the San Francisco Bay Area, California. This location is desirable because of its proximity to local earthquake <span class="hlt">sources</span> and the significant topographic relief of the array (439 m). Topographic amplification is evaluated as a function of frequency using a variety of methods, including reference‐site‐based spectral ratios and single‐station horizontal‐to‐vertical spectral ratios using both shear waves from earthquakes and ambient <span class="hlt">noise</span>. Field observations are compared with the predicted ground motion from an accurate digital model of the topography and a 3D local velocity model. Amplification factors from the theoretical calculations are consistent with observations. The fundamental resonance of the ridge is prominently observed in the spectra of data and synthetics; however, higher‐frequency peaks are also seen primarily for <span class="hlt">sources</span> in line with the major axis of the ridge, perhaps indicating higher resonant modes. Excitations of lateral ribs off of the main ridge are also seen at frequencies consistent with their dimensions. The favored directions of resonance are shown to be transverse to the major axes of the topographic features.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JSV...393..425T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JSV...393..425T"><span>Algorithmic localisation of <span class="hlt">noise</span> <span class="hlt">sources</span> in the tip region of a low-speed axial flow fan</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tóth, Bence; Vad, János</p> <p>2017-04-01</p> <p>An objective and algorithmised methodology is proposed to analyse beamform data obtained for axial fans. Its application is demonstrated in a case study regarding the tip region of a low-speed cooling fan. First, beamforming is carried out in a co-rotating frame of reference. Then, a distribution of <span class="hlt">source</span> strength is extracted along the circumference of the rotor at the blade tip radius in each analysed third-octave band. The circumferential distributions are expanded into Fourier series, which allows for filtering out the effects of perturbations, on the basis of an objective criterion. The remaining Fourier components are then considered as base <span class="hlt">sources</span> to determine the blade-passage-periodic flow mechanisms responsible for the broadband <span class="hlt">noise</span>. Based on their frequency and angular location, the base <span class="hlt">sources</span> are grouped together. This is done using the fuzzy c-means clustering method to allow the overlap of the <span class="hlt">source</span> mechanisms. The number of clusters is determined in a validity analysis. Finally, the obtained clusters are assigned to <span class="hlt">source</span> mechanisms based on the literature. Thus, turbulent boundary layer - trailing edge interaction <span class="hlt">noise</span>, tip leakage flow <span class="hlt">noise</span>, and double leakage flow <span class="hlt">noise</span> are identified.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26611074','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26611074"><span>Potential Uses of Anthropogenic <span class="hlt">Noise</span> as a <span class="hlt">Source</span> of Information in Animal Sensory and Communication Systems.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Stansbury, Amanda; Deecke, Volker; Götz, Thomas; Janik, Vincent M</p> <p>2016-01-01</p> <p>Although current research on the impact of anthropogenic <span class="hlt">noise</span> has focused on the detrimental effects, there is a range of ways by which animals could benefit from increased <span class="hlt">noise</span> levels. Here we discuss two potential uses of anthropogenic <span class="hlt">noise</span>. First, local variations in the ambient-<span class="hlt">noise</span> field could be used to perceive objects and navigate within an environment. Second, introduced sound cues could be used as a signal for prey detection or orientation and navigation. Although the disadvantages of <span class="hlt">noise</span> pollution will likely outweigh any positive effects, it is important to acknowledge that such changes may benefit some species.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/10641846','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/10641846"><span>Analysis of light <span class="hlt">noise</span> <span class="hlt">sources</span> in a recycled Michelson interferometer with Fabry-Perot arms.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Camp, J B; Yamamoto, H; Whitcomb, S E; McClelland, D E</p> <p>2000-01-01</p> <p>We present a method by which the effect of laser field variations on the signal output of an interferometric gravitational wave detector is rigorously determined. Using the Laser Interferometer Gravitational Wave Observatory (LIGO) optical configuration of a power recycled Michelson interferometer with Fabry-Perot arm cavities as an example, we calculate the excess <span class="hlt">noise</span> after the input filter cavity (mode cleaner) and the dependence of the detector strain sensitivity on laser frequency and amplitude <span class="hlt">noise</span>, radio frequency oscillator <span class="hlt">noise</span>, and scattered-light phase <span class="hlt">noise</span>. We find that <span class="hlt">noise</span> on the radio frequency sidebands generally limits the detector's sensitivity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25608189','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25608189"><span><span class="hlt">Noise</span> <span class="hlt">sources</span> and improved performance of a mid-wave infrared uncooled silicon carbide optical photodetector.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lim, Geunsik; Manzur, Tariq; Kar, Aravinda</p> <p>2014-12-20</p> <p>An uncooled photon detector is fabricated for the mid-wave infrared (MWIR) wavelength of 4.21 μm by doping an n-type 4H-SiC substrate with gallium using a laser doping technique. The dopant creates a p-type energy level of 0.3 eV, which is the energy of a photon corresponding to the MWIR wavelength 4.21 μm. This energy level was confirmed by optical absorption spectroscopy. The detection mechanism involves photoexcitation of carriers by the photons of this wavelength absorbed in the semiconductor. The resulting changes in the carrier densities at different energy levels modify the refractive index and, therefore, the reflectance of the semiconductor. This change in the reflectance constitutes the optical response of the detector, which can be probed remotely with a laser beam such as a He-Ne laser and the power of the reflected probe beam can be measured with a conventional laser power meter. The <span class="hlt">noise</span> mechanisms in the probe laser, silicon carbide MWIR detector, and laser power meter affect the performance of the detector in regards to aspects such as the responsivity, <span class="hlt">noise</span> equivalent temperature difference (NETD), and detectivity. For the MWIR wavelengths of 4.21 and 4.63 μm, the experimental detectivity of the optical photodetector of this study was found to be 1.07×10(10)  cm·Hz(1/2)/W, while the theoretical value was 1.11×10(10)  cm·Hz(1/2)/W. The values of NETD are 404 and 15.5 mK based on experimental data for an MWIR radiation <span class="hlt">source</span> with a temperature of 25°C and theoretical calculations, respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850006357','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850006357"><span><span class="hlt">Sources</span>, paths, and concepts for reduction of <span class="hlt">noise</span> in the test section of the NASA Langley 4x7m wind tunnel</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hayden, R. E.; Wilby, J. F.</p> <p>1984-01-01</p> <p>NASA is investigating the feasibility of modifying the 4x7m Wind Tunnel at the Langley Research Center to make it suitable for a variety of aeroacoustic testing applications, most notably model helicopter rotors. The amount of <span class="hlt">noise</span> reduction required to meet NASA's goal for test section background <span class="hlt">noise</span> was determined, the predominant <span class="hlt">sources</span> and paths causing the background <span class="hlt">noise</span> were quantified, and trade-off studies between schemes to reduce fan <span class="hlt">noise</span> at the <span class="hlt">source</span> and those to attenuate the sound generated in the circuit between the <span class="hlt">sources</span> and the test section were carried out. An extensive data base is also presented on circuit <span class="hlt">sources</span> and paths.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17879798','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17879798"><span>Characterization of <span class="hlt">noise</span> <span class="hlt">sources</span> for two generations of computed radiography systems using powder and crystalline photostimulable phosphors.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mackenzie, Alistair; Honey, Ian D</p> <p>2007-08-01</p> <p>The performances of two generations of computed radiography (CR) were tested and compared in terms of resolution and <span class="hlt">noise</span> characteristics. The main aim was to characterize and quantify the <span class="hlt">noise</span> <span class="hlt">sources</span> in the images. The systems tested were (1) Agfa CR 25.0, a flying spot reader with powder phosphor image plates (MD 40.0); and (2) the Agfa DX-S, a line-scanning CR reader with needle crystal phosphor image plates (HD 5.0). For both systems, the standard metrics of presampled modulation transfer function (MTF), normalized <span class="hlt">noise</span> power spectra (NNPS) and detective quantum efficiency (DQE) were measured using standard radiation quality RQA5 as defined by the International Electrotechnical Commission. The various <span class="hlt">noise</span> <span class="hlt">sources</span> contributing to the NNPS were separated by using knowledge of their relationship with air kerma, MTF, absorption efficiency and antialiasing filters. The DX-S MTF was superior compared with the CR 25.0. The maximum difference in MTF between the DX-S scan and CR 25.0 subscan directions was 0.13 at 1.3 mm(-1). For a nominal detector air kerma of 4 microGy, the peak DQE of the DX-S was 43 (+/-3)%, which was over double that of the CR 25.0 of 18 (+/-2)%. The additive electronic <span class="hlt">noise</span> was negligible on the CR 25.0 but calculated to be constant 3.4 x 10(-7) (+/-0.4 x 10(-7)) mm2 at 3.9 microGy on the DX-S. The DX-S has improved image quality compared with a traditional flying spot reader. The separation of the <span class="hlt">noise</span> <span class="hlt">sources</span> indicates that the improvements in DQE of the DX-S are due not only to the higher quantum, efficiency and MTF, but also the lower structure, secondary quantum, and excess <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20953510','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20953510"><span>Characterization of <span class="hlt">noise</span> <span class="hlt">sources</span> for two generations of computed radiography systems using powder and crystalline photostimulable phosphors</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mackenzie, Alistair; Honey, Ian D.</p> <p>2007-08-15</p> <p>The performances of two generations of computed radiography (CR) were tested and compared in terms of resolution and <span class="hlt">noise</span> characteristics. The main aim was to characterize and quantify the <span class="hlt">noise</span> <span class="hlt">sources</span> in the images. The systems tested were (1) Agfa CR 25.0, a flying spot reader with powder phosphor image plates (MD 40.0); and (2) the Agfa DX-S, a line-scanning CR reader with needle crystal phosphor image plates (HD 5.0). For both systems, the standard metrics of presampled modulation transfer function (MTF), normalized <span class="hlt">noise</span> power spectra (NNPS) and detective quantum efficiency (DQE) were measured using standard radiation quality RQA5 as defined by the International Electrotechnical Commission. The various <span class="hlt">noise</span> <span class="hlt">sources</span> contributing to the NNPS were separated by using knowledge of their relationship with air kerma, MTF, absorption efficiency and antialiasing filters. The DX-S MTF was superior compared with the CR 25.0. The maximum difference in MTF between the DX-S scan and CR 25.0 subscan directions was 0.13 at 1.3 mm{sup -1}. For a nominal detector air kerma of 4 {mu}Gy, the peak DQE of the DX-S was 43({+-}3)%, which was over double that of the CR 25.0 of 18({+-}2)%. The additive electronic <span class="hlt">noise</span> was negligible on the CR 25.0 but calculated to be constant 3.4x10{sup -7} ({+-}0.4x10{sup -7}) mm{sup 2} at 3.9 {mu}Gy on the DX-S. The DX-S has improved image quality compared with a traditional flying spot reader. The separation of the <span class="hlt">noise</span> <span class="hlt">sources</span> indicates that the improvements in DQE of the DX-S are due not only to the higher quantum, efficiency and MTF, but also the lower structure, secondary quantum, and excess <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880014855','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880014855"><span><span class="hlt">Sources</span> and levels of background <span class="hlt">noise</span> in the NASA Ames 40- by 80-foot wind tunnel</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Soderman, Paul T.</p> <p>1988-01-01</p> <p>Background <span class="hlt">noise</span> levels are measured in the NASA Ames Research Center 40- by 80-Foot Wind Tunnel following installation of a sound-absorbent lining on the test-section walls. Results show that the fan-drive <span class="hlt">noise</span> dominated the empty test-section background <span class="hlt">noise</span> at airspeeds below 120 knots. Above 120 knots, the test-section broadband background <span class="hlt">noise</span> was dominated by wind-induced dipole <span class="hlt">noise</span> (except at lower harmonics of fan blade-passage tones) most likely generated at the microphone or microphone support strut. Third-octave band and narrow-band spectra are presented for several fan operating conditions and test-section airspeeds. The background <span class="hlt">noise</span> levels can be reduced by making improvements to the microphone wind screen or support strut. Empirical equations are presented relating variations of fan <span class="hlt">noise</span> with fan speed or blade-pitch angle. An empirical expression for typical fan <span class="hlt">noise</span> spectra is also presented. Fan motor electric power consumption is related to the <span class="hlt">noise</span> generation. Preliminary measurements of sound absorption by the test-section lining indicate that the 152 mm thick lining will adequately absorb test-section model <span class="hlt">noise</span> at frequencies above 300 Hz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/6005410','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6005410"><span>A portable measurement system for subcriticality measurements by the Cf-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mihalczo, J.T.; Ragan, G.E.; Blakeman, E.D.</p> <p>1987-01-01</p> <p>A portable measurement system consisting of a personal computer used as a Fourier analyzer and three detection channels (with associated electronics that provide the signals to analog-to-digital (A/D) convertors) has been assembled to measure subcriticality by the /sup 252/Cf-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method. 8 refs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20050186590&hterms=Input+Interaction&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DInput%2BInteraction','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20050186590&hterms=Input+Interaction&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DInput%2BInteraction"><span>Improving Rotor-Stator Interaction <span class="hlt">Noise</span> Code Through Analysis of Input Parameters</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Unton, Timothy J.</p> <p>2004-01-01</p> <p>There are two major <span class="hlt">sources</span> of aircraft <span class="hlt">noise</span>. The first is from the <span class="hlt">airframe</span> and the second is from the engines. The focus of the acoustics branch at NASA Glenn is on the engine <span class="hlt">noise</span> <span class="hlt">sources</span>. There are two major <span class="hlt">sources</span> of engine <span class="hlt">noise</span>; fan <span class="hlt">noise</span> and jet <span class="hlt">noise</span>. Fan <span class="hlt">noise</span>, produced by rotating machinery of the engine, consists of both tonal <span class="hlt">noise</span>, which occurs at discrete frequencies, and broadband <span class="hlt">noise</span>, which occurs across a wide range of frequencies. The focus of my assignment is on the broadband <span class="hlt">noise</span> generated by the interaction of fan flow turbulence and the stator blades. such as the sweep and stagger angles and blade count, as well as the flow parameters such as intensity of turbulence in the flow. The tool I employed in this work is a computer program that predicts broadband <span class="hlt">noise</span> from fans. The program assumes that the complex shape of the curved blade can be represented as a single flat plate, allowing it to use fairly simple equations that can be solved in a reasonable amount of time. While the results from such representation provided reasonable estimates of the broadband <span class="hlt">noise</span> levels, they did not usually represent the entire spectrum accurately. My investigation found that the discrepancy between data and theory can be improved if the leading edge and the trailing edge of the blade are treated separately. Using this approach, I reduced the maximum error in <span class="hlt">noise</span> level from a high of 30% to less than 5% for the cases investigated. Detailed results of this investigation will be discussed at my presentation. The objective of this study is to investigate the influence of geometric parameters</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4593122','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4593122"><span>A phantom road experiment reveals traffic <span class="hlt">noise</span> is an invisible <span class="hlt">source</span> of habitat degradation</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ware, Heidi E.; McClure, Christopher J. W.; Carlisle, Jay D.; Barber, Jesse R.</p> <p>2015-01-01</p> <p>Decades of research demonstrate that roads impact wildlife and suggest traffic <span class="hlt">noise</span> as a primary cause of population declines near roads. We created a “phantom road” using an array of speakers to apply traffic <span class="hlt">noise</span> to a roadless landscape, directly testing the effect of <span class="hlt">noise</span> alone on an entire songbird community during autumn migration. Thirty-one percent of the bird community avoided the phantom road. For individuals that stayed despite the <span class="hlt">noise</span>, overall body condition decreased by a full SD and some species showed a change in ability to gain body condition when exposed to traffic <span class="hlt">noise</span> during migratory stopover. We conducted complementary laboratory experiments that implicate foraging-vigilance behavior as one mechanism driving this pattern. Our results suggest that <span class="hlt">noise</span> degrades habitat that is otherwise suitable, and that the presence of a species does not indicate the absence of an impact. PMID:26324924</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5923513','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5923513"><span>The sup 252 Cf-<span class="hlt">source</span>-driven <span class="hlt">noise</span> measurements of unreflected uranium hydride cylinder subcriticality</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mihalczo, J.T.; Pare, V.K.; Blakeman, E.D. )</p> <p>1991-01-01</p> <p>Subcritical neutron multiplication factors have been measured by the {sup 252}Cf-<span class="hlt">source</span>-driven <span class="hlt">noise</span> analysis method for unreflected, 15.0-cm-diam uranium hydride cylinders of varying heights. Because of the difficulty and cost of controlling the H/U ratio in damp uranium (93.2 wt% {sup 235}U) oxide power and fabricating sufficient material for experiments, few experiments have been performed with materials of low H/U ratios. These measurements may provide alternate information that can be used for verifying calculational methods since the H/U ratio for this material is 3.00. These measurements, which are the first application of this method to uranium hydride, were performed at the Los Alamos National Laboratory Critical Experiments Facility in 1989. These measurements were used to demonstrate the capability of this measurement method for this type of material and to provide a benchmark experiment for calculational methods with slightly moderated systems. Previous experiments by this method were for a wide variety of well-moderated systems or unmoderated uranium metal cylinders.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970001748','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970001748"><span>Active Control of Fan <span class="hlt">Noise</span>: Feasibility Study. Volume 6; Theoretical Analysis for Coupling of Active <span class="hlt">Noise</span> Control Actuator Ring <span class="hlt">Sources</span> to an Annular Duct with Flow</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kraft, R. E.</p> <p>1996-01-01</p> <p>The objective of this effort is to develop an analytical model for the coupling of active <span class="hlt">noise</span> control (ANC) piston-type actuators that are mounted flush to the inner and outer walls of an annular duct to the modes in the duct generated by the actuator motion. The analysis will be used to couple the ANC actuators to the modal analysis propagation computer program for the annular duct, to predict the effects of active suppression of fan-generated engine <span class="hlt">noise</span> <span class="hlt">sources</span>. This combined program will then be available to assist in the design or evaluation of ANC systems in fan engine annular exhaust ducts. An analysis has been developed to predict the modes generated in an annular duct due to the coupling of flush-mounted ring actuators on the inner and outer walls of the duct. The analysis has been combined with a previous analysis for the coupling of modes to a cylindrical duct in a FORTRAN computer program to perform the computations. The method includes the effects of uniform mean flow in the duct. The program can be used for design or evaluation purposes for active <span class="hlt">noise</span> control hardware for turbofan engines. Predictions for some sample cases modeled after the geometry of the NASA Lewis ANC Fan indicate very efficient coupling in both the inlet and exhaust ducts for the m = 6 spinning mode at frequencies where only a single radial mode is cut-on. Radial mode content in higher order cut-off modes at the <span class="hlt">source</span> plane and the required actuator displacement amplitude to achieve 110 dB SPL levels in the desired mode were predicted. Equivalent cases with and without flow were examined for the cylindrical and annular geometry, and little difference was found for a duct flow Mach number of 0.1. The actuator ring coupling program will be adapted as a subroutine to the cylindrical duct modal analysis and the exhaust duct modal analysis. This will allow the fan <span class="hlt">source</span> to be defined in terms of characteristic modes at the fan <span class="hlt">source</span> plane and predict the propagation to the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19760025884','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19760025884"><span>Static and wind tunnel near-field/far-field jet <span class="hlt">noise</span> measurements from model scale single-flow baseline and suppressor nozzles. Volume 1: <span class="hlt">Noise</span> <span class="hlt">source</span> locations and extrapolation of static free-field jet <span class="hlt">noise</span> data</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jaeck, C. L.</p> <p>1976-01-01</p> <p>A test was conducted in the Boeing Large Anechoic Chamber to determine static jet <span class="hlt">noise</span> <span class="hlt">source</span> locations of six baseline and suppressor nozzle models, and establish a technique for extrapolating near field data into the far field. The test covered nozzle pressure ratios from 1.44 to 2.25 and jet velocities from 412 to 594 m/s at a total temperature of 844 K.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050214793','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050214793"><span>Sound <span class="hlt">Sources</span> Identified in High-Speed Jets by Correlating Flow Density Fluctuations With Far-Field <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Panda, Jayanta; Seasholtz, Richard G.</p> <p>2003-01-01</p> <p><span class="hlt">Noise</span> <span class="hlt">sources</span> in high-speed jets were identified by directly correlating flow density fluctuation (cause) to far-field sound pressure fluctuation (effect). The experimental study was performed in a nozzle facility at the NASA Glenn Research Center in support of NASA s initiative to reduce the <span class="hlt">noise</span> emitted by commercial airplanes. Previous efforts to use this correlation method have failed because the tools for measuring jet turbulence were intrusive. In the present experiment, a molecular Rayleigh-scattering technique was used that depended on laser light scattering by gas molecules in air. The technique allowed accurate measurement of air density fluctuations from different points in the plume. The study was conducted in shock-free, unheated jets of Mach numbers 0.95, 1.4, and 1.8. The turbulent motion, as evident from density fluctuation spectra was remarkably similar in all three jets, whereas the <span class="hlt">noise</span> <span class="hlt">sources</span> were significantly different. The correlation study was conducted by keeping a microphone at a fixed location (at the peak <span class="hlt">noise</span> emission angle of 30 to the jet axis and 50 nozzle diameters away) while moving the laser probe volume from point to point in the flow. The following figure shows maps of the nondimensional coherence value measured at different Strouhal frequencies ([frequency diameter]/jet speed) in the supersonic Mach 1.8 and subsonic Mach 0.95 jets. The higher the coherence, the stronger the <span class="hlt">source</span> was.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23297894','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23297894"><span>Investigation of contact acoustic nonlinearities on metal and composite <span class="hlt">airframe</span> structures via intensity based health monitoring.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Romano, P Q; Conlon, S C; Smith, E C</p> <p>2013-01-01</p> <p>Nonlinear structural intensity (NSI) and nonlinear structural surface intensity (NSSI) based damage detection techniques were improved and extended to metal and composite <span class="hlt">airframe</span> structures. In this study, the measurement of NSI maps at sub-harmonic frequencies was completed to provide enhanced understanding of the energy flow characteristics associated with the damage induced contact acoustic nonlinearity mechanism. Important results include NSI <span class="hlt">source</span> localization visualization at ultra-subharmonic (nf/2) frequencies, and damage detection results utilizing structural surface intensity in the nonlinear domain. A detection metric relying on modulated wave spectroscopy was developed and implemented using the NSSI feature. The data fusion of the intensity formulation provided a distinct advantage, as both the single interrogation frequency NSSI and its modulated wave extension (NSSI-MW) exhibited considerably higher sensitivities to damage than using single-sensor (strain or acceleration) nonlinear detection metrics. The active intensity based techniques were also extended to composite materials, and results show both NSSI and NSSI-MW can be used to detect damage in the bond line of an integrally stiffened composite plate structure with high sensitivity. Initial damage detection measurements made on an OH-58 tailboom (Penn State Applied Research Laboratory, State College, PA) indicate the techniques can be transitioned to complex <span class="hlt">airframe</span> structures achieving high detection sensitivities with minimal sensors and actuators.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MNRAS.459.3314F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MNRAS.459.3314F"><span>The 154 MHz radio sky observed by the Murchison Widefield Array: <span class="hlt">noise</span>, confusion, and first <span class="hlt">source</span> count analyses</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Franzen, T. M. O.; Jackson, C. A.; Offringa, A. R.; Ekers, R. D.; Wayth, R. B.; Bernardi, G.; Bowman, J. D.; Briggs, F.; Cappallo, R. J.; Deshpande, A. A.; Gaensler, B. M.; Greenhill, L. J.; Hazelton, B. J.; Johnston-Hollitt, M.; Kaplan, D. L.; Lonsdale, C. J.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Morgan, J.; Oberoi, D.; Ord, S. M.; Prabu, T.; Seymour, N.; Shankar, N. Udaya; Srivani, K. S.; Subrahmanyan, R.; Tingay, S. J.; Trott, C. M.; Webster, R. L.; Williams, A.; Williams, C. L.</p> <p>2016-07-01</p> <p>We analyse a 154 MHz image made from a 12 h observation with the Murchison Widefield Array (MWA) to determine the <span class="hlt">noise</span> contribution and behaviour of the <span class="hlt">source</span> counts down to 30 mJy. The MWA image has a bandwidth of 30.72 MHz, a field-of-view within the half-power contour of the primary beam of 570 deg2, a resolution of 2.3 arcmin and contains 13 458 <span class="hlt">sources</span> above 5σ. The rms <span class="hlt">noise</span> in the centre of the image is 4-5 mJy beam-1. The MWA counts are in excellent agreement with counts from other instruments and are the most precise ever derived in the flux density range 30-200 mJy due to the sky area covered. Using the deepest available <span class="hlt">source</span> count data, we find that the MWA image is affected by sidelobe confusion <span class="hlt">noise</span> at the ≈3.5 mJy beam-1 level, due to incompletely peeled and out-of-image <span class="hlt">sources</span>, and classical confusion becomes apparent at ≈1.7 mJy beam-1. This work highlights that (i) further improvements in ionospheric calibration and deconvolution imaging techniques would be required to probe to the classical confusion limit and (ii) the shape of low-frequency <span class="hlt">source</span> counts, including any flattening towards lower flux densities, must be determined from deeper ≈150 MHz surveys as it cannot be directly inferred from higher frequency data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19820014389','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19820014389"><span>Advanced general aviation comparative engine/<span class="hlt">airframe</span> integration study</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Huggins, G. L.; Ellis, D. R.</p> <p>1981-01-01</p> <p>The NASA Advanced Aviation Comparative Engine/<span class="hlt">Airframe</span> Integration Study was initiated to help determine which of four promising concepts for new general aviation engines for the 1990's should be considered for further research funding. The engine concepts included rotary, diesel, spark ignition, and turboprop powerplants; a conventional state-of-the-art piston engine was used as a baseline for the comparison. Computer simulations of the performance of single and twin engine pressurized aircraft designs were used to determine how the various characteristics of each engine interacted in the design process. Comparisons were made of how each engine performed relative to the others when integrated into an <span class="hlt">airframe</span> and required to fly a transportation mission.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040086814','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040086814"><span><span class="hlt">Airframe</span> Integration Trade Studies for a Reusable Launch Vehicle</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dorsey, John T.; Wu, Chauncey; Rivers, Kevin; Martin, Carl; Smith, Russell</p> <p>1999-01-01</p> <p>Future launch vehicles must be lightweight, fully reusable and easily maintained if low-cost access to space is to be achieved. The goal of achieving an economically viable Single-Stage-to-Orbit (SSTO) Reusable Launch Vehicle (RLV) is not easily achieved and success will depend to a large extent on having an integrated and optimized total system. A series of trade studies were performed to meet three objectives. First, to provide structural weights and parametric weight equations as inputs to configuration-level trade studies. Second, to identify, assess and quantify major weight drivers for the RLV <span class="hlt">airframe</span>. Third, using information on major weight drivers, and considering the RLV as an integrated thermal structure (composed of thrust structures, tanks, thermal protection system, insulation and control surfaces), identify and assess new and innovative approaches or concepts that have the potential for either reducing <span class="hlt">airframe</span> weight, improving operability, and/or reducing cost.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910003376&hterms=integrated+systems&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dintegrated%2Bsystems','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910003376&hterms=integrated+systems&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dintegrated%2Bsystems"><span>The Integrated <span class="hlt">Airframe</span>/Propulsion Control System Architecture program (IAPSA)</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Palumbo, Daniel L.; Cohen, Gerald C.; Meissner, Charles W.</p> <p>1990-01-01</p> <p>The Integrated <span class="hlt">Airframe</span>/Propulsion Control System Architecture program (IAPSA) is a two-phase program which was initiated by NASA in the early 80s. The first phase, IAPSA 1, studied different architectural approaches to the problem of integrating engine control systems with <span class="hlt">airframe</span> control systems in an advanced tactical fighter. One of the conclusions of IAPSA 1 was that the technology to construct a suitable system was available, yet the ability to create these complex computer architectures has outpaced the ability to analyze the resulting system's performance. With this in mind, the second phase of IAPSA approached the same problem with the added constraint that the system be designed for validation. The intent of the design for validation requirement is that validation requirements should be shown to be achievable early in the design process. IAPSA 2 has demonstrated that despite diligent efforts, integrated systems can retain characteristics which are difficult to model and, therefore, difficult to validate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA098795','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA098795"><span>FET <span class="hlt">Noise</span> Studies.</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1981-03-01</p> <p>The predominant <span class="hlt">sources</span> of nonlinearity in the FET, relevant to oscillator analysis, are the transconductance gm and the <span class="hlt">source</span>-gate capacitance C sg...two general categories of <span class="hlt">noise</span> mechanisms in an FET: intrinsic <span class="hlt">sources</span>, i.e., <span class="hlt">noise</span> associated with the FET operation itself, and extrinsic <span class="hlt">noise</span>...very high drain voltages, also produces white <span class="hlt">noise</span>. <span class="hlt">Noise</span> produced by para- sitic resistance, one of the extrinsic <span class="hlt">noise</span> <span class="hlt">sources</span>, is also flat. These</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JAG...128....1J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JAG...128....1J"><span>A de-<span class="hlt">noising</span> algorithm based on wavelet threshold-exponential adaptive window width-fitting for ground electrical <span class="hlt">source</span> airborne transient electromagnetic signal</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ji, Yanju; Li, Dongsheng; Yu, Mingmei; Wang, Yuan; Wu, Qiong; Lin, Jun</p> <p>2016-05-01</p> <p>The ground electrical <span class="hlt">source</span> airborne transient electromagnetic system (GREATEM) on an unmanned aircraft enjoys considerable prospecting depth, lateral resolution and detection efficiency, etc. In recent years it has become an important technical means of rapid resources exploration. However, GREATEM data are extremely vulnerable to stationary white <span class="hlt">noise</span> and non-stationary electromagnetic <span class="hlt">noise</span> (sferics <span class="hlt">noise</span>, aircraft engine <span class="hlt">noise</span> and other human electromagnetic <span class="hlt">noises</span>). These <span class="hlt">noises</span> will cause degradation of the imaging quality for data interpretation. Based on the characteristics of the GREATEM data and major <span class="hlt">noises</span>, we propose a de-<span class="hlt">noising</span> algorithm utilizing wavelet threshold method and exponential adaptive window width-fitting. Firstly, the white <span class="hlt">noise</span> is filtered in the measured data using the wavelet threshold method. Then, the data are segmented using data window whose step length is even logarithmic intervals. The data polluted by electromagnetic <span class="hlt">noise</span> are identified within each window based on the discriminating principle of energy detection, and the attenuation characteristics of the data slope are extracted. Eventually, an exponential fitting algorithm is adopted to fit the attenuation curve of each window, and the data polluted by non-stationary electromagnetic <span class="hlt">noise</span> are replaced with their fitting results. Thus the non-stationary electromagnetic <span class="hlt">noise</span> can be effectively removed. The proposed algorithm is verified by the synthetic and real GREATEM signals. The results show that in GREATEM signal, stationary white <span class="hlt">noise</span> and non-stationary electromagnetic <span class="hlt">noise</span> can be effectively filtered using the wavelet threshold-exponential adaptive window width-fitting algorithm, which enhances the imaging quality.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JSV...332.3517L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JSV...332.3517L"><span>Landing-gear <span class="hlt">noise</span> prediction using high-order finite difference schemes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, Wen; Wook Kim, Jae; Zhang, Xin; Angland, David; Caruelle, Bastien</p> <p>2013-07-01</p> <p>Aerodynamic <span class="hlt">noise</span> from a generic two-wheel landing-gear model is predicted by a CFD/FW-H hybrid approach. The unsteady flow-field is computed using a compressible Navier-Stokes solver based on high-order finite difference schemes and a fully structured grid. The calculated time history of the surface pressure data is used in an FW-H solver to predict the far-field <span class="hlt">noise</span> levels. Both aerodynamic and aeroacoustic results are compared to wind tunnel measurements and are found to be in good agreement. The far-field <span class="hlt">noise</span> was found to vary with the 6th power of the free-stream velocity. Individual contributions from three components, i.e. wheels, axle and strut of the landing-gear model are also investigated to identify the relative contribution to the total <span class="hlt">noise</span> by each component. It is found that the wheels are the dominant <span class="hlt">noise</span> <span class="hlt">source</span> in general. Strong vortex shedding from the axle is the second major contributor to landing-gear <span class="hlt">noise</span>. This work is part of Airbus LAnding Gear <span class="hlt">nOise</span> database for CAA validatiON (LAGOON) program with the general purpose of evaluating current CFD/CAA and experimental techniques for <span class="hlt">airframe</span> <span class="hlt">noise</span> prediction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20090030607','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20090030607"><span>NASA <span class="hlt">Airframe</span> Icing Research Overview Past and Current</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Potapczuk, Mark</p> <p>2009-01-01</p> <p>This slide presentation reviews the past and current research that NASA has done in the area of <span class="hlt">airframe</span> icing. Both the history experimental efforts and model development to understand the process and problem of ice formation are reviewed. This has resulted in the development of new experimental methods, advanced icing simulation software, flight dynamics and experimental databases that have an impact on design, testing, construction and certification and qualification of the aircraft and its sub-systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19790009409','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19790009409"><span>An integrated computer procedure for sizing composite <span class="hlt">airframe</span> structures</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sobieszczanski-Sobieski, J.</p> <p>1979-01-01</p> <p>A computerized algorithm to generate cross-sectional dimensions and fiber orientations for composite <span class="hlt">airframe</span> structures is described, and its application in a wing structural synthesis is established. The algorithm unifies computations of aeroelastic loads, stresses, and deflections, as well as optimal structural sizing and fiber orientations in an open-ended system of integrated computer programs. A finite-element analysis and a mathematical-optimization technique are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950008070','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950008070"><span>Analysis of small crack behavior for <span class="hlt">airframe</span> applications</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mcclung, R. C.; Chan, K. S.; Hudak, S. J., Jr.; Davidson, D. L.</p> <p>1994-01-01</p> <p>The small fatigue crack problem is critically reviewed from the perspective of <span class="hlt">airframe</span> applications. Different types of small cracks-microstructural, mechanical, and chemical-are carefully defined and relevant mechanisms identified. Appropriate analysis techniques, including both rigorous scientific and practical engineering treatments, are briefly described. Important materials data issues are addressed, including increased scatter in small crack data and recommended small crack test methods. Key problems requiring further study are highlighted.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19820014394','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19820014394"><span>Advanced general aviation engine/<span class="hlt">airframe</span> integration study</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zmroczek, L. A.</p> <p>1982-01-01</p> <p>A comparison of the in-<span class="hlt">airframe</span> performance and efficiency of the advanced engine concepts is presented. The results indicate that the proposed advanced engines can significantly improve the performance and economy of general aviation airplanes. The engine found to be most promising is the highly advanced version of a rotary combustion (Wankel) engine. The low weight and fuel consumption of this engine, as well as its small size, make it suited for aircraft use.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920013400','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920013400"><span>Design of an integrated <span class="hlt">airframe</span>/propulsion control system architecture</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cohen, Gerald C.; Lee, C. William; Strickland, Michael J.</p> <p>1990-01-01</p> <p>The design of an integrated <span class="hlt">airframe</span>/propulsion control system architecture is described. The design is based on a prevalidation methodology that used both reliability and performance tools. An account is given of the motivation for the final design and problems associated with both reliability and performance modeling. The appendices contain a listing of the code for both the reliability and performance model used in the design.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19421292','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19421292"><span>Signal-to-<span class="hlt">noise</span> analysis for detection sensitivity of small absorbing heterogeneity in turbid media with single-<span class="hlt">source</span> and dual-interfering-<span class="hlt">source</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chen, Y; Mu, C; Intes, X; Chance, B</p> <p>2001-08-13</p> <p>Previous studies have suggested that the phased-array detection can achieve high sensitivity in detecting and localizing inhomogeneities embedded in turbid media by illuminating with dual interfering <span class="hlt">sources</span>. In this paper, we analyze the sensitivity of single-<span class="hlt">source</span> and dual-interfering-<span class="hlt">source</span> (phased array) systems with signal-to-<span class="hlt">noise</span> ratio criteria. Analytical solutions are presented to investigate the sensitivity of detection using different degrees of absorption perturbation by varying the size and contrast of the object under similar configurations for single- and dual-<span class="hlt">source</span> systems. The results suggest that dual-<span class="hlt">source</span> configuration can provide higher detection sensitivity. The relation between the amplitude and phase signals for both systems is also analyzed using a vector model. The results can be helpful for optimizing the experimental design by combining the advantages of both single- and dual-<span class="hlt">source</span> systems in object detection and localization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.S53C2506W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.S53C2506W"><span>Application of the discontinuous Galerkin method to study the <span class="hlt">source</span> mechanisms for Love waves in ambient <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wenk, S.; Hadziioannou, C.; Igel, H.</p> <p>2012-12-01</p> <p>To produce detailed images of the crust using <span class="hlt">noise</span> correlation studies and to understand the ocean - solid Earth interaction processes we investigate the behavior and distribution of ambient <span class="hlt">noise</span> <span class="hlt">sources</span>, especially focused on the relative contribution of Love waves to the ambient <span class="hlt">noise</span> field. Therefore, we apply the discontinuous Galerkin (DG) method, which makes use of unstructured tetrahedral meshes combined with a time integration scheme solving the arbitrary high-order derivative (ADER) Riemann problem. The ADER-DG method is high-order accurate in space and time, beneficial for reliable simulations of high-frequency wavefields over long propagation distances. Due to the ease with which tetrahedral grids can be adapted to complex geometries, undulating topography of the Earth's surface and interior interfaces can be readily implemented in the computational domain.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SPIE.9801E..03S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SPIE.9801E..03S"><span>Fluidic actuators for active flow control on <span class="hlt">airframe</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schueller, M.; Weigel, P.; Lipowski, M.; Meyer, M.; Schlösser, P.; Bauer, M.</p> <p>2016-04-01</p> <p>One objective of the European Projects AFLoNext and Clean Sky 2 is to apply Active Flow Control (AFC) on the <span class="hlt">airframe</span> in critical aerodynamic areas such as the engine/wing junction or the outer wing region for being able to locally improve the aerodynamics in certain flight conditions. At the engine/wing junction, AFC is applied to alleviate or even eliminate flow separation at low speeds and high angle of attacks likely to be associated with the integration of underwing- mounted Ultra High Bypass Ratio (UHBR) engines and the necessary slat-cut-outs. At the outer wing region, AFC can be used to allow more aggressive future wing designs with improved performance. A relevant part of the work on AFC concepts for <span class="hlt">airframe</span> application is the development of suitable actuators. Fluidic Actuated Flow Control (FAFC) has been introduced as a Flow Control Technology that influences the boundary layer by actively blowing air through slots or holes out of the aircraft skin. FAFC actuators can be classified by their Net Mass Flux and accordingly divided into ZNMF (Zero Net Mass Flux) and NZNMF (Non Zero Net-Mass-Flux) actuators. In the frame of both projects, both types of the FAFC actuator concepts are addressed. In this paper, the objectives of AFC on the <span class="hlt">airframe</span> is presented and the actuators that are used within the project are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015APS..DFDKP1075S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015APS..DFDKP1075S"><span>Experimental Analysis of Flow over a Highly Maneuverable <span class="hlt">Airframe</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Spirnak, Jonathan; Benson, Michael; van Poppel, Bret; Elkins, Christopher; Eaton, John; Team HMA Team</p> <p>2015-11-01</p> <p>One way to reduce the collateral damage in war is by increasing the accuracy of indirect fire weapons. The Army Research Laboratory is currently developing a Highly Maneuverable <span class="hlt">Airframe</span> (HMA) consisting of four deflecting canards to provide in-flight maneuverability while fins maintain short duration aerodynamic stability. An experiment was conducted using Magnetic Resonance Velocimetry (MRV) techniques to gather three dimensional, three-component velocity data for fluid flow over a scaled down HMA model. Tests were performed at an angle of attack of 2.3° and canard deflection angles of 0° and 2°. The resulting data serve to both validate computational fluid dynamics (CFD) simulations and understand the flow over this complex geometry. Particular interest is given to the development of the tip and inboard vortices that originate at the canard/body junction and the canard tips to determine their effects on <span class="hlt">airframe</span> stability. Results show the development of a strong tip vortex and four weaker inboard vortices off each canard. Although the weaker inboard vortices dissipate rapidly downstream of the canard trailing edges, the stronger tip vortices persist until reaching the fins approximately six chord lengths downstream of the canard trailing edges. Team HMA designed and built the water channel and <span class="hlt">airframe</span> for this experiment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140011934','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140011934"><span>Impact Testing and Simulation of Composite <span class="hlt">Airframe</span> Structures</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jackson, Karen E.; Littell, Justin D.; Horta, Lucas G.; Annett, Martin S.; Fasanella, Edwin L.; Seal, Michael D., II</p> <p>2014-01-01</p> <p>Dynamic tests were performed at NASA Langley Research Center on composite <span class="hlt">airframe</span> structural components of increasing complexity to evaluate their energy absorption behavior when subjected to impact loading. A second objective was to assess the capabilities of predicting the dynamic response of composite <span class="hlt">airframe</span> structures, including damage initiation and progression, using a state-of-the-art nonlinear, explicit transient dynamic finite element code, LS-DYNA. The test specimens were extracted from a previously tested composite prototype fuselage section developed and manufactured by Sikorsky Aircraft Corporation under the US Army's Survivable Affordable Repairable <span class="hlt">Airframe</span> Program (SARAP). Laminate characterization testing was conducted in tension and compression. In addition, dynamic impact tests were performed on several components, including I-beams, T-sections, and cruciform sections. Finally, tests were conducted on two full-scale components including a subfloor section and a framed fuselage section. These tests included a modal vibration and longitudinal impact test of the subfloor section and a quasi-static, modal vibration, and vertical drop test of the framed fuselage section. Most of the test articles were manufactured of graphite unidirectional tape composite with a thermoplastic resin system. However, the framed fuselage section was constructed primarily of a plain weave graphite fabric material with a thermoset resin system. Test data were collected from instrumentation such as accelerometers and strain gages and from full-field photogrammetry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.9164V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.9164V"><span><span class="hlt">Sources</span> of high frequency seismic <span class="hlt">noise</span>: insights from a dense network of ~250 stations in northern Alsace (France)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vergne, Jerome; Blachet, Antoine; Lehujeur, Maximilien</p> <p>2015-04-01</p> <p>Monitoring local or regional seismic activity requires stations having a low level of background seismic <span class="hlt">noise</span> at frequencies higher than few tenths of Hertz. Network operators are well aware that the seismic quality of a site depends on several aspects, among them its geological setting and the proximity of roads, railways, industries or trees. Often, the impact of each <span class="hlt">noise</span> <span class="hlt">source</span> is only qualitatively known which precludes estimating the quality of potential future sites before they are tested or installed. Here, we want to take advantage of a very dense temporary network deployed in Northern Alsace (France) to assess the effect of various kinds of potential <span class="hlt">sources</span> on the level of seismic <span class="hlt">noise</span> observed in the frequency range 0.2-50 Hz. In September 2014, more than 250 seismic stations (FairfieldNodal@ Zland nodes with 10Hz vertical geophone) have been installed every 1.5 km over a ~25km diameter disc centred on the deep geothermal sites of Soultz-sous-Forêts and Rittershoffen. This region exhibits variable degrees of human imprints from quite remote areas to sectors with high traffic roads and big villages. It also encompasses both the deep sedimentary basin of the Rhine graben and the piedmont of the Vosges massif with exposed bedrock. For each site we processed the continuous data to estimate probability density functions of the power spectral densities. At frequencies higher than 1 Hz most sites show a clear temporal modulation of seismic <span class="hlt">noise</span> related to human activity with the well-known variations between day and night and between weekdays and weekends. Moreover we observe a clear evolution of the spatial distribution of seismic <span class="hlt">noise</span> levels with frequency. Basically, between 0.5 and 4 Hz the geological setting modulates the level of seismic <span class="hlt">noise</span>. At higher frequencies, the amplitude of seismic <span class="hlt">noise</span> appears mostly related to the distance to nearby roads. Based on road maps and traffic estimation, a forward approach is performed to model the induced</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..1512286J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..1512286J"><span>Applying the seismic interferometry method to vertical seismic profile data using tunnel excavation <span class="hlt">noise</span> as <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jurado, Maria Jose; Teixido, Teresa; Martin, Elena; Segarra, Miguel; Segura, Carlos</p> <p>2013-04-01</p> <p>In the frame of the research conducted to develop efficient strategies for investigation of rock properties and fluids ahead of tunnel excavations the seismic interferometry method was applied to analyze the data acquired in boreholes instrumented with geophone strings. The results obtained confirmed that seismic interferometry provided an improved resolution of petrophysical properties to identify heterogeneities and geological structures ahead of the excavation. These features are beyond the resolution of other conventional geophysical methods but can be the cause severe problems in the excavation of tunnels. Geophone strings were used to record different types of seismic <span class="hlt">noise</span> generated at the tunnel head during excavation with a tunnelling machine and also during the placement of the rings covering the tunnel excavation. In this study we show how tunnel construction activities have been characterized as <span class="hlt">source</span> of seismic signal and used in our research as the seismic <span class="hlt">source</span> signal for generating a 3D reflection seismic survey. The data was recorded in vertical water filled borehole with a borehole seismic string at a distance of 60 m from the tunnel trace. A reference pilot signal was obtained from seismograms acquired close the tunnel face excavation in order to obtain best signal-to-<span class="hlt">noise</span> ratio to be used in the interferometry processing (Poletto et al., 2010). The seismic interferometry method (Claerbout 1968) was successfully applied to image the subsurface geological structure using the seismic wave field generated by tunneling (tunnelling machine and construction activities) recorded with geophone strings. This technique was applied simulating virtual shot records related to the number of receivers in the borehole with the seismic transmitted events, and processing the data as a reflection seismic survey. The pseudo reflective wave field was obtained by cross-correlation of the transmitted wave data. We applied the relationship between the transmission</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JEMat..45.4769J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JEMat..45.4769J"><span>Dislocations as a <span class="hlt">Noise</span> <span class="hlt">Source</span> in LWIR HgCdTe Photodiodes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jóźwikowski, Krzysztof; Jóźwikowska, Alina; Martyniuk, Andrzej</p> <p>2016-10-01</p> <p>The effect of dislocation on the 1/ f <span class="hlt">noise</span> current in long-wavelength infrared (LWIR) reverse biased HgCdTe photodiodes working at liquid nitrogen (LN) temperature was analyzed theoretically by using a phenomenological model of dislocations as an additional Shockley-Read-Hall (SRH) generation-recombination (G-R) channel in heterostructure. Numerical analysis was involved to solve the set of transport equations in order to find a steady state values of physical parameters of the heterostructure. Next, the set of transport equations for fluctuations (TEFF) was formulated and solved to obtain the spectral densities (SD) of the fluctuations of electrical potential, quasi-Fermi levels, and temperature. The SD of mobility fluctuations, shot G-R <span class="hlt">noise</span>, and thermal <span class="hlt">noise</span> were also taken into account in TEFF. Additional expressions for SD of 1/ f fluctuations of the G-R processes were derived. Numerical values of the SD of <span class="hlt">noise</span> current were compared with the experimental results of Johnson et al. Theoretical analysis has shown that the dislocations increase the G-R processes and this way cause the growth of G-R dark current. Despite the fact that dislocations increase both shot G-R <span class="hlt">noise</span> and 1/ f G-R <span class="hlt">noise</span>, the main cause of 1/ f current <span class="hlt">noise</span> in LN cooled LWIR photodiodes are fluctuations of the carriers mobility determined by 1/ f fluctuations of relaxation times. As the <span class="hlt">noise</span> current is proportional to the total diode current, growth of G-R dark current caused by dislocations leads to the growth of <span class="hlt">noise</span> current.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100033097','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100033097"><span>Phased Array <span class="hlt">Noise</span> <span class="hlt">Source</span> Localization Measurements of an F404 Nozzle Plume at Both Full and Model Scale</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Podboy, Gary G.; Bridges, James E.; Henderson, Brenda S.</p> <p>2010-01-01</p> <p>A 48-microphone planar phased array system was used to acquire jet <span class="hlt">noise</span> <span class="hlt">source</span> localization data on both a full-scale F404-GE-F400 engine and on a 1/4th scale model of a F400 series nozzle. The full-scale engine test data show the location of the dominant <span class="hlt">noise</span> <span class="hlt">sources</span> in the jet plume as a function of frequency for the engine in both baseline (no chevron) and chevron configurations. Data are presented for the engine operating both with and without afterburners. Based on lessons learned during this test, a set of recommendations are provided regarding how the phased array measurement system could be modified in order to obtain more useful acoustic <span class="hlt">source</span> localization data on high-performance military engines in the future. The data obtained on the 1/4th scale F400 series nozzle provide useful insights regarding the full-scale engine jet <span class="hlt">noise</span> <span class="hlt">source</span> mechanisms, and document some of the differences associated with testing at model-scale versus fullscale.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730024885','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730024885"><span><span class="hlt">Noise</span> pollution resources compendium</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1973-01-01</p> <p>Abstracts of reports concerning <span class="hlt">noise</span> pollution are presented. The abstracts are grouped in the following areas of activity: (1) <span class="hlt">sources</span> of <span class="hlt">noise</span>, (2) <span class="hlt">noise</span> detection and measurement, (3) <span class="hlt">noise</span> abatement and control, (4) physical effects of <span class="hlt">noise</span> and (5) social effects of <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910032600&hterms=source+study&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dsource%2Bstudy','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910032600&hterms=source+study&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dsource%2Bstudy"><span>Can shock waves on helicopter rotors generate <span class="hlt">noise</span>? - A study of the quadrupole <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Farassat, F.; Tadghighi, H.</p> <p>1990-01-01</p> <p>An analysis has previously established that local shock surfaces attached to helicopter rotor blades moving at high subsonic speeds are potent <span class="hlt">noise</span> generators; in pursuit of this insight, a novel formulation is presented for the prediction of the <span class="hlt">noise</span> of a deformable shock, whose area changes as a function of the azimuthal position of the blade. The derivation of this formulation has its basis in a mapping of the moving shock to a time-independent region. In virtue of this mapping, the implementation of the main result on a computer becomes straightforward enough for incorporation into the available rotor-<span class="hlt">noise</span> prediction code. A problem illustrating the importance of rotor shocks in the generation of high-intensity <span class="hlt">noise</span> is presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950008072','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950008072"><span>Advanced method and processing technology for complicated shape <span class="hlt">airframe</span> part forming</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Miodushevsky, P. V.; Rajevskaya, G. A.</p> <p>1994-01-01</p> <p>Slow deformation modes of forming give considerably higher residual fatigue life of the <span class="hlt">airframe</span> part. It has experimentally proven that fatigue life of complicated shape integral <span class="hlt">airframe</span> panels made of high strength aluminum alloys is significantly increased after creep deformation process. To implement the slow deformation mode forming methods, universal automated equipment was developed. Multichannel forming systems provide high accuracy of <span class="hlt">airframe</span> part shape eliminating residual stresses and spring effect. Forming process multizone control technology was developed and experimentally proved that static/fatigue properties of formed <span class="hlt">airframe</span> parts are increased.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009JAG....67...66A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009JAG....67...66A"><span>A seismic field test with a Low-level Acoustic Combustion <span class="hlt">Source</span> and Pseudo-<span class="hlt">Noise</span> codes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Askeland, Bjørn; Ruud, Bent Ole; Hobæk, Halvor; Mjelde, Rolf</p> <p>2009-01-01</p> <p>The Low-level Acoustic Combustion <span class="hlt">Source</span> (LACS) which can fire its pulses at a high rate, has been tested successfully as a seismic marine <span class="hlt">source</span> on shallow ice-age sediments in Byfjorden at Bergen, Norway. Pseudo-<span class="hlt">Noise</span> pulsed signals with spiky autocorrelation functions were used to detect the sediments. Each transmitted sequence lasted 10 s and contained 43 pulses. While correlation gave a blurry result, deconvolution between the near-field recordings and the streamer recordings gave a clear seismic section. Compared to the section acquired with single air-gun shots along the same profile, the LACS gave a more clear presentation of the sediments and basement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150000743','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150000743"><span>Acoustics of Jet Surface Interaction-Scrubbing <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Khavaran, Abbas</p> <p>2014-01-01</p> <p>Concepts envisioned for the future of civil air transport consist of unconventional propulsion systems in the close proximity of the structure or embedded in the <span class="hlt">airframe</span>. While such integrated systems are intended to shield <span class="hlt">noise</span> from community, they also introduce new <span class="hlt">sources</span> of sound. Sound generation due to interaction of a jet flow past a nearby solid surface is investigated here using the generalized acoustic analogy theory. The analysis applies to the boundary layer <span class="hlt">noise</span> generated at and near a wall, and excludes the scattered <span class="hlt">noise</span> component that is produced at the leading or the trailing edge. While compressibility effects are relatively unimportant at very low Mach numbers, frictional heat generation and thermal gradient normal to the surface could play important roles in generation and propagation of sound in high speed jets of practical interest. A general expression is given for the spectral density of the far field sound as governed by the variable density Pridmore-Brown equation. The propagation Greens function is solved numerically for a high aspect-ratio rectangular jet starting with the boundary conditions on the surface and subject to specified mean velocity and temperature profiles between the surface and the observer. It is shown the magnitude of the Greens function decreases with increasing <span class="hlt">source</span> frequency andor jet temperature. The phase remains constant for a rigid surface, but varies with <span class="hlt">source</span> location when subject to an impedance type boundary condition. The Greens function in the absence of the surface, and flight effect are also investigated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20030000834','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030000834"><span>Measurement of Trailing Edge <span class="hlt">Noise</span> Using Directional Array and Coherent Output Power Methods</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hutcheson, Florence V.; Brooks, Thomas F.</p> <p>2002-01-01</p> <p>The use of a directional (or phased) array of microphones for the measurement of trailing edge (TE) <span class="hlt">noise</span> is described and tested. The capabilities of this method arc evaluated via measurements of TE <span class="hlt">noise</span> from a NACA 63-215 airfoil model and from a cylindrical rod. This TE <span class="hlt">noise</span> measurement approach is compared to one that is based on thc cross spectral analysis of output signals from a pair of microphones placed on opposite sides of an <span class="hlt">airframe</span> model (COP method). Advantages and limitations of both methods arc examined. It is shown that the microphone array can accurately measures TE <span class="hlt">noise</span> and captures its two-dimensional characteristic over a large frequency range for any TE configuration as long as <span class="hlt">noise</span> contamination from extraneous <span class="hlt">sources</span> is within bounds. The COP method is shown to also accurately measure TE <span class="hlt">noise</span> but over a more limited frequency range that narrows for increased TE thickness. Finally, the applicability and generality of an airfoil self-<span class="hlt">noise</span> prediction method was evaluated via comparison to the experimental data obtained using the COP and array measurement methods. The predicted and experimental results are shown to agree over large frequency ranges.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19960003376','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19960003376"><span>Active Control of Fan <span class="hlt">Noise</span>-Feasibility Study. Volume 2: Canceling <span class="hlt">Noise</span> <span class="hlt">Source</span>-Design of an Acoustic Plate Radiator Using Piezoceramic Actuators</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pla, F. G.; Rajiyah, H.</p> <p>1995-01-01</p> <p>The feasibility of using acoustic plate radiators powered by piezoceramic thin sheets as canceling <span class="hlt">sources</span> for active control of aircraft engine fan <span class="hlt">noise</span> is demonstrated. Analytical and numerical models of actuated beams and plates are developed and validated. An optimization study is performed to identify the optimum combination of design parameters that maximizes the plate volume velocity for a given resonance frequency. Fifteen plates with various plate and actuator sizes, thicknesses, and bonding layers were fabricated and tested using results from the optimization study. A maximum equivalent piston displacement of 0.39 mm was achieved with the optimized plate samples tested with only one actuator powered, corresponding to a plate deflection at the center of over 1 millimeter. This is very close to the deflection required for a full size engine application and represents a 160-fold improvement over previous work. Experimental results further show that performance is limited by the critical stress of the piezoceramic actuator and bonding layer rather than by the maximum moment available from the actuator. Design enhancements are described in detail that will lead to a flight-worthy acoustic plate radiator by minimizing actuator tensile stresses and reducing nonlinear effects. Finally, several adaptive tuning methods designed to increase the bandwidth of acoustic plate radiators are analyzed including passive, active, and semi-active approaches. The back chamber pressurization and volume variation methods are investigated experimentally and shown to be simple and effective ways to obtain substantial control over the resonance frequency of a plate radiator. This study shows that piezoceramic-based plate radiators can be a viable acoustic <span class="hlt">source</span> for active control of aircraft engine fan <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/776581','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/776581"><span>Simultaneous ballistic deficit immunity and resilience to parallel <span class="hlt">noise</span> <span class="hlt">sources</span>: A new pulse shaping technique</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Fabris, Lorenzo; Becker, John A.; Goulding, Frederick S.; Madden, Norman W.</p> <p>2000-10-11</p> <p>A new and different time variant pulse processing system has been developed based on a simple CR-RC filter and two analog switches. The new pulse processing technique combines both ballistic deficit immunity and resilience to parallel <span class="hlt">noise</span> without a significant compromise to the low energy resolution, generally considered a mutually exclusive requirement. The filter is realized by combining two different pulse-shaping techniques. One of the techniques creates a low rate of curvature at the pulse peak, which reduces ballistic deficit, while the second technique increases the tolerance to low frequency <span class="hlt">noise</span> by modifying the <span class="hlt">noise</span> history. Several experimental measurements are presented, including tests on a co-planar grid CdZnTe detector. Improvements on both the resolution and line shape are shown for the 662 keV line of 137Cs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/95297','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/95297"><span><span class="hlt">Noise</span> measurements in shunted, shorted, and fully electroded quartz gauges in the Saturn plasma radiation <span class="hlt">source</span> x-ray simulator</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Barrett, W.H.; Greenwoll, J.I.; Smith, C.W.; Johnson, D.E.; De La Cruz, C.F.</p> <p>1995-08-01</p> <p>This paper describes recent work to improve the measurement of the stress response of materials to intense, short pulses of radiation. When Saturn fires, large prompt electrical <span class="hlt">noise</span> pulses are induced in stress measurement circuits. The conventional wisdom has been that the shorted guard ring quartz gauge was the only configuration with acceptable prompt signal-to-<span class="hlt">noise</span> characteristics for stress measurements in this pulsed radiation environment. However, because of abnormal signal distortion, the shorted guard ring gauge is restricted to a maximum stress of about 8 kbars. Below this level, the normal, quantified signal distortion is correctable with analytical deconvolution techniques. The shunted guard ring gauge is acceptable for Egli fidelity measurements to about 25 kbars with negligible signal distortion. Experiments were conducted on the Saturn soft x-ray <span class="hlt">source</span> which show that higher fidelity shunted guard ring gauges can successfully measure stress with acceptable induced <span class="hlt">noise</span>. We also found that a 50-ohm impedance matching resistor at the gauge reduced the prompt <span class="hlt">noise</span> amplitude and improved the baseline quality of the measurement prior to shock wave arrival.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19780011153','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19780011153"><span>Study of hypersonic propulsion/<span class="hlt">airframe</span> integration technology</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hartill, W. R.; Goebel, T. P.; Vancamp, V. V.</p> <p>1978-01-01</p> <p>An assessment is done of current and potential ground facilities, and analysis and flight test techniques for establishing a hypersonic propulsion/<span class="hlt">airframe</span> integration technology base. A mach 6 cruise prototype aircraft incorporating integrated Scramjet engines was considered the baseline configuration, and the assessment focused on the aerodynamic and configuration aspects of the integration technology. The study describes the key technology milestones that must be met to permit a decision on development of a prototype vehicle, and defines risk levels for these milestones. Capabilities and limitations of analysis techniques, current and potential ground test facilities, and flight test techniques are described in terms of the milestones and risk levels.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19790013253','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19790013253"><span><span class="hlt">Airframe</span>-integrated propulsion system for hypersonic cruise vehicles</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jones, R. A.; Huber, P. W.</p> <p>1978-01-01</p> <p>Research on a new, hydrogen burning, airbreathing engine concept which offers good potential for efficient hypersonic cruise vehicles is considered. Features of the engine which lead to good performance include; extensive engine-<span class="hlt">airframe</span> integration, fixed geometry, low cooling, and the control of heat release in the supersonic combustor by mixed-modes of fuel injection from the combustor entrance. The engine concept is described along with results from inlet tests, direct-connect combustor tests, and tests of two subscale boiler-plate research engines presently underway at conditions which simulate flight at Mach 4 and 7.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110003022','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110003022"><span>Reliability-Based Design Optimization of a Composite <span class="hlt">Airframe</span> Component</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pai, Shantaram S.; Coroneos, Rula; Patnaik, Surya N.</p> <p>2011-01-01</p> <p>A stochastic optimization methodology (SDO) has been developed to design <span class="hlt">airframe</span> structural components made of metallic and composite materials. The design method accommodates uncertainties in load, strength, and material properties that are defined by distribution functions with mean values and standard deviations. A response parameter, like a failure mode, has become a function of reliability. The primitive variables like thermomechanical loads, material properties, and failure theories, as well as variables like depth of beam or thickness of a membrane, are considered random parameters with specified distribution functions defined by mean values and standard deviations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA275673','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA275673"><span>Damage Tolerance: Assessment Handbook. Volume 2: <span class="hlt">Airframe</span> Damage Tolerance Evaluation</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1993-10-01</p> <p><span class="hlt">Airframe</span> Damage Tolerance Evaluation NJ 084u5 DTIC FLE 15 1994 Research and Special Programs Administration John A. Volpe National Transportation Systems...permission of John Wiley and Sons, New York, N.Y.] (4-5] CORRODED END Magnes;um Magnesium alloys Zinc Galvanized steel or galvanized wrought iron Aluminum...Reprinted from M M. Ratwani and D.P. Wilhem , iDeelopment andEvaluation of Methods of Plane Strain Fractuire Analysis, Northrop Corporation, AFFDL-TR-73-42</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19810003587','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19810003587"><span>Should we attempt global (inlet engine <span class="hlt">airframe</span>) control design?</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Carlin, C. M.</p> <p>1980-01-01</p> <p>The feasibility of multivariable design of the entire airplane control system is briefly addressed. An intermediate step in that direction is to design a control for an inlet engine augmentor system by using multivariable techniques. The supersonic cruise large scale inlet research program is described which will provide an opportunity to develop, integrate, and wind tunnel test a control for a mixed compression inlet and variable cycle engine. The integrated propulsion <span class="hlt">airframe</span> control program is also discussed which will introduce the problem of implementing MVC within a distributed processing avionics architecture, requiring real time decomposition of the global design into independent modules in response to hardware communication failures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910043630&hterms=noise+linear&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DTitle%26N%3D0%26No%3D20%26Ntt%3Dnoise%2Bin%2Blinear','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910043630&hterms=noise+linear&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DTitle%26N%3D0%26No%3D20%26Ntt%3Dnoise%2Bin%2Blinear"><span>Effect of mean load on the non-linear behavior of spur gear <span class="hlt">noise</span> <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kahraman, Ahmet; Singh, Rajendra</p> <p>1989-01-01</p> <p>An analytical technique for estimating <span class="hlt">noise</span> generation by spur-gear pairs with backlash is developed using the results obtained by Comparin and Singh (1989). The derivation of the governing equations is outlined, and numerical results for sample problems are presented in graphs. Good agreement with published experimental data (Munro, 1962) is demonstrated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA205758','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA205758"><span>A Standard Definition for Wind-Generated, Low-Frequency Ambient <span class="hlt">Noise</span> <span class="hlt">Source</span> Levels</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1989-02-09</p> <p>FUNDING NUMBERS PROGR.AM PROJECT ITASK IWORK UNIT ELEMENT 14O. NO. NO. IACCESSION NO. I I ritLE (include Security Caiafaon) I7Ol A STANDARD DEFINITION...use of a specific propagation code (PE, RAYTRACE, ASTRAL , NORMAL MODE, etc). The specification of <span class="hlt">noise</span> intensity per unit area with respect to/ /P</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160005908','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160005908"><span>Open Rotor <span class="hlt">Noise</span> Shielding by Blended-Wing-Body Aircraft</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Guo, Yueping; Czech, Michael J.; Thomas, Russell H.</p> <p>2015-01-01</p> <p>This paper presents an analysis of open rotor <span class="hlt">noise</span> shielding by Blended Wing Body (BWB) aircraft by using model scale test data acquired in the Boeing Low Speed Aeroacoustic Facility (LSAF) with a legacy F7/A7 rotor model and a simplified BWB platform. The objective of the analysis is the understanding of the shielding features of the BWB and the method of application of the shielding data for <span class="hlt">noise</span> studies of BWB aircraft with open rotor propulsion. By studying the directivity patterns of individual tones, it is shown that though the tonal energy distribution and the spectral content of the wind tunnel test model, and thus its total <span class="hlt">noise</span>, may differ from those of more advanced rotor designs, the individual tones follow directivity patterns that characterize far field radiations of modern open rotors, ensuring the validity of the use of this shielding data. Thus, open rotor tonal <span class="hlt">noise</span> shielding should be categorized into front rotor tones, aft rotor tones and interaction tones, not only because of the different directivities of the three groups of tones, but also due to the differences in their <span class="hlt">source</span> locations and coherence features, which make the respective shielding characteristics of the three groups of tones distinctly different from each other. To reveal the parametric trends of the BWB shielding effects, results are presented with variations in frequency, far field emission angle, rotor operational condition, engine installation geometry, and local <span class="hlt">airframe</span> features. These results prepare the way for the development of parametric models for the shielding effects in prediction tools.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19750009957','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19750009957"><span>Generalized wave envelope analysis of sound propagation in ducts with stepped <span class="hlt">noise</span> <span class="hlt">source</span> profiles and variable axial impedance</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Baumeister, K. J.</p> <p>1975-01-01</p> <p>A finite difference formulation is presented for sound propagation in a rectangular two-dimensional duct without steady flow. Before the difference equations are formulated, the governing Helmholtz equation is first transformed to a form whose solution tends not to oscillate along the length of the duct. This transformation reduces the required number of grid points by an order of magnitude. Example solutions indicate that stepped <span class="hlt">noise</span> <span class="hlt">source</span> profiles have much higher attenuation than plane waves in a uniform impedance liner. Also, multiple stepped impedance liners are shown to have higher attenuation than uniform ducts if the impedances are chosen properly. For optimum <span class="hlt">noise</span> reduction with axial variations in impedance, the numerical analysis indicates that for a plane wave input the resistance should be near zero at the entrance of a suppressor duct, while the reactance should be near the optimum value associated with the least-attenuated mode in a uniform duct.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920005567','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920005567"><span>Interior <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mixson, John S.; Wilby, John F.</p> <p>1991-01-01</p> <p>The generation and control of flight vehicle interior <span class="hlt">noise</span> is discussed. Emphasis is placed on the mechanisms of transmission through airborne and structure-borne paths and the control of cabin <span class="hlt">noise</span> by path modification. Techniques for identifying the relative contributions of the various <span class="hlt">source</span>-path combinations are also discussed along with methods for the prediction of aircraft interior <span class="hlt">noise</span> such as those based on the general modal theory and statistical energy analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770013556','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770013556"><span>Development, documentation and correlation of a NASTRAN vibration model of the AH-1G helicopter <span class="hlt">airframe</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cronkhite, J. D.</p> <p>1976-01-01</p> <p>NASTRAN was evaluated for vibration analysis of the helicopter <span class="hlt">airframe</span>. The first effort involved development of a NASTRAN model of the AH-1G helicopter <span class="hlt">airframe</span> and comprehensive documentation of the model. The next effort was to assess the validity of the NASTRAN model by comparisons with static and vibration tests.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17519199','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17519199"><span>Computational aeroelastic modelling of <span class="hlt">airframes</span> and turbomachinery: progress and challenges.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bartels, R E; Sayma, A I</p> <p>2007-10-15</p> <p>Computational analyses such as computational fluid dynamics and computational structural dynamics have made major advances towards maturity as engineering tools. Computational aeroelasticity (CAE) is the integration of these disciplines. As CAE matures, it also finds an increasing role in the design and analysis of aerospace vehicles. This paper presents a survey of the current state of CAE with a discussion of recent research, success and continuing challenges in its progressive integration into multidisciplinary aerospace design. It approaches CAE from the perspective of the two main areas of application: <span class="hlt">airframe</span> and turbomachinery design. An overview will be presented of the different prediction methods used for each field of application. Differing levels of nonlinear modelling will be discussed with insight into accuracy versus complexity and computational requirements. Subjects will include current advanced methods (linear and nonlinear), nonlinear flow models, use of order reduction techniques and future trends in incorporating structural nonlinearity. Examples in which CAE is currently being integrated into the design of <span class="hlt">airframes</span> and turbomachinery will be presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19940036051&hterms=vibration+helicopter&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dvibration%2Bhelicopter','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19940036051&hterms=vibration+helicopter&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dvibration%2Bhelicopter"><span>Investigation on the use of optimization techniques for helicopter <span class="hlt">airframe</span> vibrations design studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sreekanta Murthy, T.</p> <p>1992-01-01</p> <p>Results of the investigation of formal nonlinear programming-based numerical optimization techniques of helicopter <span class="hlt">airframe</span> vibration reduction are summarized. The objective and constraint function and the sensitivity expressions used in the formulation of <span class="hlt">airframe</span> vibration optimization problems are presented and discussed. Implementation of a new computational procedure based on MSC/NASTRAN and CONMIN in a computer program system called DYNOPT for optimizing <span class="hlt">airframes</span> subject to strength, frequency, dynamic response, and dynamic stress constraints is described. An optimization methodology is proposed which is thought to provide a new way of applying formal optimization techniques during the various phases of the <span class="hlt">airframe</span> design process. Numerical results obtained from the application of the DYNOPT optimization code to a helicopter <span class="hlt">airframe</span> are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910065117&hterms=Input+Interaction&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DInput%2BInteraction','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910065117&hterms=Input+Interaction&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DInput%2BInteraction"><span>Analysis of <span class="hlt">airframe</span>/engine interactions in integrated flight and propulsion control</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schierman, John D.; Schmidt, David K.</p> <p>1991-01-01</p> <p>An analysis framework for the assessment of dynamic cross-coupling between <span class="hlt">airframe</span> and engine systems from the perspective of integrated flight/propulsion control is presented. This analysis involves to determining the significance of the interactions with respect to deterioration in stability robustness and performance, as well as critical frequency ranges where problems may occur due to these interactions. The analysis illustrated here investigates both the <span class="hlt">airframe</span>'s effects on the engine control loops and the engine's effects on the <span class="hlt">airframe</span> control loops in two case studies. The second case study involves a multi-input/multi-output analysis of the <span class="hlt">airframe</span>. Sensitivity studies are performed on critical interactions to examine the degradations in the system's stability robustness and performance. Magnitudes of the interactions required to cause instabilities, as well as the frequencies at which the instabilities occur are recorded. Finally, the analysis framework is expanded to include control laws which contain cross-feeds between the <span class="hlt">airframe</span> and engine systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA219535','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA219535"><span>Identification and Proposed Control of Helicopter Transmission <span class="hlt">Noise</span> at the <span class="hlt">Source</span></span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1987-03-19</p> <p>future work on helicopter <span class="hlt">noise</span> are presented. OH-SB HELICOPTER & TRANSMISION The OH-58C Helicopter is the Army’s Light Scout/Attack helicopter...grinding machine . As currently manufactured, spiral bevel gears do not have conjugate action. Spiral bevel gears with conjugate action were examined...was lost. The process of grinding teeth on a spiral bevel gear is a function of many different settings on the gear grinding machine . Nominally similar</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22984278','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22984278"><span><span class="hlt">Source</span> of statistical <span class="hlt">noises</span> in the Monte Carlo sampling techniques for coherently scattered photons.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Muhammad, Wazir; Lee, Sang Hoon</p> <p>2013-01-01</p> <p>Detailed comparisons of the predictions of the Relativistic Form Factors (RFFs) and Modified Form Factors (MFFs) and their advantages and shortcomings in calculating elastic scattering cross sections can be found in the literature. However, the issues related to their implementation in the Monte Carlo (MC) sampling for coherently scattered photons is still under discussion. Secondly, the linear interpolation technique (LIT) is a popular method to draw the integrated values of squared RFFs/MFFs (i.e. A(Z, v(i)²)) over squared momentum transfer (v(i)² = v(1)²,......, v(59)²). In the current study, the role/issues of RFFs/MFFs and LIT in the MC sampling for the coherent scattering were analyzed. The results showed that the relative probability density curves sampled on the basis of MFFs are unable to reveal any extra scientific information as both the RFFs and MFFs produced the same MC sampled curves. Furthermore, no relationship was established between the multiple small peaks and irregular step shapes (i.e. statistical <span class="hlt">noise</span>) in the PDFs and either RFFs or MFFs. In fact, the <span class="hlt">noise</span> in the PDFs appeared due to the use of LIT. The density of the <span class="hlt">noise</span> depends upon the interval length between two consecutive points in the input data table of A(Z, v(i)²) and has no scientific background. The probability density function curves became smoother as the interval lengths were decreased. In conclusion, these statistical <span class="hlt">noises</span> can be efficiently removed by introducing more data points in the A(Z, v(i)²) data tables.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA133958','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA133958"><span>Experimental and Analytical Studies of Shielding Concepts for Point <span class="hlt">Sources</span> and Jet <span class="hlt">Noise</span>.</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1983-05-01</p> <p>fundarentac property of barriers, permits significant <span class="hlt">noise</span> reduction onit it rilerate an ; Fig. 2-25 %. On the whole, however, a lighter scoop shield...the radiated sound field of a turbulent jet can Localized Extension .57 be derived from the self preservation properties of the turbulence in the...Helmholtz -0 integral states that if some physical property of a sound field such as It can be Shown that when 7.1-e) is satisfied the contribution to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA598418','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA598418"><span>Auditory Masking Patterns in Bottlenose Dolphins from Anthropogenic and Natural <span class="hlt">Noise</span> <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2013-09-30</p> <p>e.g., critical ratios ) are often used to describe and predict auditory masking. For this task, detection thresholds for a 10 kHz tone were measured in...unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 2 determine the relationship between <span class="hlt">noise</span> metrics and masked tonal ...the residual errors (FIG 3) demonstrates that the two-parameter model produces much better fits than critical ratio predictions, while still being</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1984aiaa.meetT....W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1984aiaa.meetT....W"><span>Prediction of <span class="hlt">sources</span> moving at high speed as applied to helicopter and propeller <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wright, S. E.; Lee, D. J.</p> <p>1984-01-01</p> <p>This paper analyzes the linear acoustic solution concerning the radiation from a rigid body in motion. The body displacement <span class="hlt">source</span> is used as the monopole <span class="hlt">source</span> description, rather than the traditional volume flow rate. The point <span class="hlt">source</span> behavior, particularly in circular motion, and the onset of noncompactness is considered. The effect of finite <span class="hlt">source</span> distributions is established and an efficient method developed to calculate the effect of finite chord and span distributions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1008624','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1008624"><span>Auditory and Subjective Effects of Airborne <span class="hlt">Noise</span> from Industrial Ultrasonic <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Acton, W. I.; Carson, M. B.</p> <p>1967-01-01</p> <p>This investigation was undertaken primarily to examine the possibility of hearing damage from industrial ultrasonic equipment. In the factory concerned, ultrasonic washers and drills were used at a number of different locations, and girls working 12 ft (3·6 m.) away from one bank of three small washers complained of unpleasant subjective effects which included fatigue, persistent headaches, nausea, and tinnitus. As personnel working in the vicinity of similar washers in other parts of the factory did not complain of these effects, it seemed possible that the <span class="hlt">noise</span> had been transmitted along a column of air in a bank of dryboxes. Enclosure of these washers by a sliding screen of Perspex had completely abated the trouble. Sound pressure level measurements taken in the positions occupied by the operators indicated that, when the effects occur, they are probably caused by high sound levels at the upper audio-frequencies present with the ultrasonic <span class="hlt">noise</span>, and this was supported by a limited laboratory investigation. Audiometric investigation showed that hearing damage due to <span class="hlt">noise</span> from these industrial ultrasonic devices is unlikely. However, extrapolations of currently accepted hearing damage risk criteria may be valid in predicting the occurrence of these subjective effects. Images PMID:6073088</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970017414','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970017414"><span>Fan <span class="hlt">Noise</span> Prediction System Development: <span class="hlt">Source</span>/Radiation Field Coupling and Workstation Conversion for the Acoustic Radiation Code</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Meyer, H. D.</p> <p>1993-01-01</p> <p>The Acoustic Radiation Code (ARC) is a finite element program used on the IBM mainframe to predict far-field acoustic radiation from a turbofan engine inlet. In this report, requirements for developers of internal aerodynamic codes regarding use of their program output an input for the ARC are discussed. More specifically, the particular input needed from the Bolt, Beranek and Newman/Pratt and Whitney (turbofan <span class="hlt">source</span> <span class="hlt">noise</span> generation) Code (BBN/PWC) is described. In a separate analysis, a method of coupling the <span class="hlt">source</span> and radiation models, that recognizes waves crossing the interface in both directions, has been derived. A preliminary version of the coupled code has been developed and used for initial evaluation of coupling issues. Results thus far have shown that reflection from the inlet is sufficient to indicate that full coupling of the <span class="hlt">source</span> and radiation fields is needed for accurate <span class="hlt">noise</span> predictions ' Also, for this contract, the ARC has been modified for use on the Sun and Silicon Graphics Iris UNIX workstations. Changes and additions involved in this effort are described in an appendix.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008spa..book.1005F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008spa..book.1005F"><span>Community Response to <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fidell, Sandy</p> <p></p> <p>The primary effects of community <span class="hlt">noise</span> on residential populations are speech interference, sleep disturbance, and annoyance. This chapter focuses on transportation <span class="hlt">noise</span> in general and on aircraft <span class="hlt">noise</span> in particular because aircraft <span class="hlt">noise</span> is one of the most prominent community <span class="hlt">noise</span> <span class="hlt">sources</span>, because airport/community controversies are often the most contentious and widespread, and because industrial and other specialized formsofcommunitynoise generally posemorelocalized problems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150010713','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150010713"><span>Jet Surface Interaction Scrubbing <span class="hlt">Noise</span> from High Aspect-Ratio Rectangular Jets</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Khavaran, Abbas; Bozak, Richard F.</p> <p>2015-01-01</p> <p>Concepts envisioned for the future of civil air transport consist of unconventional propulsion systems in the close proximity of the <span class="hlt">airframe</span>. Distributed propulsion system with exhaust configurations that resemble a high aspect ratio rectangular jet are among geometries of interest. Nearby solid surfaces could provide <span class="hlt">noise</span> shielding for the purpose of reduced community <span class="hlt">noise</span>. Interaction of high-speed jet exhaust with structure could also generate new <span class="hlt">sources</span> of sound as a result of flow scrubbing past the structure, and or scattered <span class="hlt">noise</span> from sharp edges. The present study provides a theoretical framework to predict the scrubbing <span class="hlt">noise</span> component from a high aspect ratio rectangular exhaust in proximity of a solid surface. The analysis uses the Greens function (GF) to the variable density Pridmore-Brown equation in a transversely sheared mean flow. <span class="hlt">Sources</span> of sound are defined as the auto-covariance function of second-rank velocity fluctuations in the jet plume, and are modeled using a RANS-based acoustic analogy approach. Acoustic predictions are presented in an 8:1 aspect ratio rectangular exhaust at three subsonic Mach numbers. The effect of nearby surface on the scrubbing <span class="hlt">noise</span> component is shown on both reflected and shielded sides of the plate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSV...377...90S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSV...377...90S"><span>Concurrent identification of aero-acoustic scattering and <span class="hlt">noise</span> <span class="hlt">sources</span> at a flow duct singularity in low Mach number flow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sovardi, Carlo; Jaensch, Stefan; Polifke, Wolfgang</p> <p>2016-09-01</p> <p>A numerical method to concurrently characterize both aeroacoustic scattering and <span class="hlt">noise</span> <span class="hlt">sources</span> at a duct singularity is presented. This approach combines Large Eddy Simulation (LES) with techniques of System Identification (SI): In a first step, a highly resolved LES with external broadband acoustic excitation is carried out. Subsequently, time series data extracted from the LES are post-processed by means of SI to model both acoustic propagation and <span class="hlt">noise</span> generation. The present work studies the aero-acoustic characteristics of an orifice placed in a duct at low flow Mach numbers with the "LES-SI" method. Parametric SI based on the Box-Jenkins mathematical structure is employed, with a prediction error approach that utilizes correlation analysis of the output residuals to avoid overfitting. Uncertainties of model parameters due to the finite length of times series are quantified in terms of confidence intervals. Numerical results for acoustic scattering matrices and power spectral densities of broad-band <span class="hlt">noise</span> are validated against experimental measurements over a wide range of frequencies below the cut-off frequency of the duct.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/262465','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/262465"><span>Field and laboratory studies of moving and temporally variable <span class="hlt">noise</span> <span class="hlt">sources</span> (aircraft); perception of location, movement, and direction.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gunn, W J; Shigehisa, T; Shepherd, W T</p> <p>1979-10-01</p> <p>The conditions were examined under which more valid and reliable estimates could be made of the effects of aircraft <span class="hlt">noise</span> on people. In Exper. 1, 12 Ss in 2 different houses directly under the flight path of a major airport (JFK) indicated 1 of 12 possible flight paths (4 directly overhead and 8 to one side) for each of 3 jet aircraft flyovers: 3% of cases in House A and 56% in House B (which had open windows) were correctly identified. Despite judgment inaccuracy, Ss were more than moderately certain of the correctness of their judgments. In Exper. II. Ss either inside or outside of 2 houses in Wallops Station, Virginia, indicated on diagrams the direction of flyovers. Each of 4 aircraft (Boeing 737, C-54, UE-1 helicopter, Queenaire) made 8 flyovers directly over the houses and 8 to one side. Windows were either open or closed. All flyovers and conditions were counterbalanced. All sound <span class="hlt">sources</span> under all conditions were usually judged to be overhead and moving, but for Ss indoors with windows closed the to-the-side flyovers were judged to be off to the side in 24% of cases. Outdoor Ss reported correct direction in 75% of cases while indoor Ss were correct in only 25% (windows open) or 18% (windows closed). Judgments "to the side" were significantly better (p = less than .02) with windows open vs closed, while with windows closed judgments were significantly better (p = less than .05) for flyovers overhead vs to the side. In Exper. III, Ss localized in azimuth and in the vertical plane recorded <span class="hlt">noises</span> (10 1-oct <span class="hlt">noise</span> bands of CF = 28.12 c/s - 14.4kc/s, spoken voice, and jet aircraft takeoffs and landings), presented through 1, 2, or 4 floor-level loudspeakers at each corner of a simulated living room (4.2 x 5.4m)built inside an IAC soundproof room. Aircraft <span class="hlt">noises</span> presented by 4 loudspeakers were localized as "directly" overhead 80% of the time and "generally overhead" about 90% of the time; other sounds were so localized about 50% and 75% of the time respectively</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA241141','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA241141"><span>Aeroacoustics of Flight Vehicles: Theory and Practice. Volume 1. <span class="hlt">Noise</span> <span class="hlt">Sources</span></span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1991-08-01</p> <p>coso kl (32) -2 [mB(Mr2cosO- M,) ] = t 1 +kMx BD (33) and the phase lag due to sweep is 2Mrt mB MCA _r I _ _’cs - k - (34)Ms- r k1-Mzcos6 k D In equation...indicates sound at blade-passage frequency and its multiples, just as with the steady-loading formulas discussed previously. The factor ( r /C%) - t indicates...Pressures. AIAA-80-0977, June 1980 36 Chou, S - T .; and George, A. R .. Effect of Angle of Attack on Rotor Trading-Edge <span class="hlt">Noise</span>. AIAA J, vol. 22, no 12, Dec</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930016947','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930016947"><span>Bibliography on propulsion <span class="hlt">airframe</span> integration technologies for high-speed civil transport applications, 1980-1991</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Anderson, David J.; Mizukami, Masashi</p> <p>1993-01-01</p> <p>NASA has initiated the High Speed Research (HSR) program with the goal to develop technologies for a new generation, economically viable, environmentally acceptable, supersonic transport (SST) called the High Speed Civil Transport (HSCT). A significant part of this effort is expected to be in multidisciplinary systems integration, such as in propulsion <span class="hlt">airframe</span> integration (PAI). In order to assimilate the knowledge database on PAI for SST type aircraft, a bibliography on this subject was compiled. The bibliography with over 1200 entries, full abstracts, and indexes. Related topics are also covered, such as the following: engine inlets, engine cycles, nozzles, existing supersonic cruise aircraft, <span class="hlt">noise</span> issues, computational fluid dynamics, aerodynamics, and external interference. All identified documents from 1980 through early 1991 are included; this covers the latter part of the NASA Supersonic Cruise Research (SCR) program and the beginnings of the HSR program. In addition, some pre-1980 documents of significant merit or reference value are also included. The references were retrieved via a computerized literature search using the NASA RECON database system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19870026322&hterms=Propellers+aircraft&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DPropellers%2Baircraft','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19870026322&hterms=Propellers+aircraft&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DPropellers%2Baircraft"><span>Comparison of two propeller <span class="hlt">source</span> models for aircraft interior <span class="hlt">noise</span> studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mahan, J. R.; Fuller, C. R.</p> <p>1986-01-01</p> <p>The sensitivity of the predicted synchrophasing (SP) effectiveness trends to the propeller <span class="hlt">source</span> model issued is investigated with reference to the development of advanced turboprop engines for transport aircraft. SP effectiveness is shown to be sensitive to the type of <span class="hlt">source</span> model used. For the virtually rotating dipole <span class="hlt">source</span> model, the SP effectiveness is sensitive to the direction of rotation at some frequencies but not at others. The SP effectiveness obtained from the virtually rotating dipole model is not very sensitive to the radial location of the <span class="hlt">source</span> distribution within reasonable limits. Finally, the predicted SP effectiveness is shown to be more sensitive to the details of the <span class="hlt">source</span> model used for the case of corotation than for the case of counterrotation.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012GeoJI.188.1303Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012GeoJI.188.1303Y"><span>Exploiting seismic signal and <span class="hlt">noise</span> in an intracratonic environment to constrain crustal structure and <span class="hlt">source</span> parameters of infrequent earthquakes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Young, Mallory K.; Tkalčić, Hrvoje; Rawlinson, Nicholas; Reading, Anya M.</p> <p>2012-03-01</p> <p>In many regions of the world characterized by a relatively low rate of seismicity, the determination of local and regional seismic <span class="hlt">source</span> parameters is often restricted to an analysis of the first onsets of P waves (or first motion analysis) due to incomplete information about Earth structure and the small size of the events. When rare large earthquakes occur in these regions, their waveforms can be used to model Earth structure. This, however, makes the nature of the earthquake <span class="hlt">source</span> determination problem circular, as <span class="hlt">source</span> information is mapped as structure. Presented here is one possible remedy to this situation, where through a two-step approach we first constrain Earth structure using data independent of the earthquake of interest. In this study, we focus on a region in Western Australia with low seismicity and minimal instrument coverage and use the CAPRA/LP temporary deployment to demonstrate that reliable structural models of the upper lithosphere can be obtained from an independent collection of teleseismic and ambient <span class="hlt">noise</span> datasets. Apart from teleseismic receiver functions (RFs), we obtain group velocities from the cross-correlation of ambient <span class="hlt">noise</span> and phase velocities from the traditional two-station method using carefully selected teleseismic earthquakes and station pairs. Crustal models are then developed through the joint inversion of dispersion data and RFs, and structural Green's functions are computed from a layered composite model. In the second step of this comprehensive approach, we apply full waveform inversion (three-component body and surface waves) to the 2007 ML= 5.3 Shark Bay, Western Australia, earthquake to estimate its <span class="hlt">source</span> parameters (seismic moment, focal mechanism, and depth). We conclude that the full waveform inversion analysis provides constraints on the orientation of fault planes superior to a first motion interpretation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950008051','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950008051"><span>Corrosion and corrosion fatigue of <span class="hlt">airframe</span> aluminum alloys</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Chen, G. S.; Gao, M.; Harlow, D. G.; Wei, R. P.</p> <p>1994-01-01</p> <p>Localized corrosion and corrosion fatigue crack nucleation and growth are recognized as degradation mechanisms that effect the durability and integrity of commercial transport aircraft. Mechanically based understanding is needed to aid the development of effective methodologies for assessing durability and integrity of <span class="hlt">airframe</span> components. As a part of the methodology development, experiments on pitting corrosion, and on corrosion fatigue crack nucleation and early growth from these pits were conducted. Pitting was found to be associated with constituent particles in the alloys and pit growth often involved coalescence of individual particle-nucleated pits, both laterally and in depth. Fatigue cracks typically nucleated from one of the larger pits that formed by a cluster of particles. The size of pit at which fatigue crack nucleates is a function of stress level and fatigue loading frequency. The experimental results are summarized, and their implications on service performance and life prediction are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140010018','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140010018"><span>Simulating the Impact Response of Composite <span class="hlt">Airframe</span> Components</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jackson, Karen E.; Littell, Justin D.; Fasanella, Edwin L.</p> <p>2014-01-01</p> <p>In 2010, NASA Langley Research Center obtained residual hardware from the US Army's Survivable Affordable Repairable <span class="hlt">Airframe</span> Program (SARAP). The hardware consisted of a composite fuselage section that was representative of the center section of a Black Hawk helicopter. The section was fabricated by Sikorsky Aircraft Corporation and designated the Test Validation Article (TVA). The TVA was subjected to a vertical drop test in 2008 to evaluate a tilting roof concept to limit the intrusion of overhead mass items, such as the rotor transmission, into the fuselage cabin. As a result of the 2008 test, damage to the hardware was limited primarily to the roof. Consequently, when the post-test article was obtained in 2010, the roof area was removed and the remaining structure was cut into six different types of test specimens including: (1) tension and compression coupons for material property characterization, (2) I-beam sections, (3) T-sections, (4) cruciform sections, (5) a large subfloor section, and (6) a forward framed fuselage section. In 2011, NASA and Sikorsky entered into a cooperative research agreement to study the impact responses of composite <span class="hlt">airframe</span> structures and to evaluate the capabilities of the explicit transient dynamic finite element code, LS-DYNA®, to simulate these responses including damage initiation and progressive failure. Finite element models of the composite specimens were developed and impact simulations were performed. The properties of the composite material were represented using both a progressive in-plane damage model (Mat 54) and a continuum damage mechanics model (Mat 58) in LS-DYNA. This paper provides test-analysis comparisons of time history responses and the location and type of damage for representative I-beam, T-section, and cruciform section components.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20090022184','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20090022184"><span>Reliability-Based Design Optimization of a Composite <span class="hlt">Airframe</span> Component</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Patnaik, Surya N.; Pai, Shantaram S.; Coroneos, Rula M.</p> <p>2009-01-01</p> <p>A stochastic design optimization methodology (SDO) has been developed to design components of an <span class="hlt">airframe</span> structure that can be made of metallic and composite materials. The design is obtained as a function of the risk level, or reliability, p. The design method treats uncertainties in load, strength, and material properties as distribution functions, which are defined with mean values and standard deviations. A design constraint or a failure mode is specified as a function of reliability p. Solution to stochastic optimization yields the weight of a structure as a function of reliability p. Optimum weight versus reliability p traced out an inverted-S-shaped graph. The center of the inverted-S graph corresponded to 50 percent (p = 0.5) probability of success. A heavy design with weight approaching infinity could be produced for a near-zero rate of failure that corresponds to unity for reliability p (or p = 1). Weight can be reduced to a small value for the most failure-prone design with a reliability that approaches zero (p = 0). Reliability can be changed for different components of an <span class="hlt">airframe</span> structure. For example, the landing gear can be designed for a very high reliability, whereas it can be reduced to a small extent for a raked wingtip. The SDO capability is obtained by combining three codes: (1) The MSC/Nastran code was the deterministic analysis tool, (2) The fast probabilistic integrator, or the FPI module of the NESSUS software, was the probabilistic calculator, and (3) NASA Glenn Research Center s optimization testbed CometBoards became the optimizer. The SDO capability requires a finite element structural model, a material model, a load model, and a design model. The stochastic optimization concept is illustrated considering an academic example and a real-life raked wingtip structure of the Boeing 767-400 extended range airliner made of metallic and composite materials.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S41A4419T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S41A4419T"><span>Directionality of Ambient <span class="hlt">Noise</span> on the Juan de Fuca Plate: Implications for <span class="hlt">Source</span> Locations of the Primary and Secondary Microseism</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tian, Y.; Ritzwoller, M. H.</p> <p>2014-12-01</p> <p>Based on cross-correlations computed from 61 ocean bottom seismometers (OBSs) within the Juan de Fuca plate from the Cascadia Initiative experiment and 42 continental stations near the western US coast, we investigate the generation locations of the primary (11-20 sec period) and secondary (5-10 sec period) microseisms in the northern Pacific Ocean by analyzing the directionality of the microseism signals received in this region. (1) Ambient <span class="hlt">noise</span> observed across the array is much different in the primary and secondary microseism bands, both in its azimuthal content and seasonal variation, indicating different <span class="hlt">source</span> generation locations. (2) The principal secondary microseism signals propagate toward the east, consistent with <span class="hlt">source</span> generation in deep water of the North Pacific, perhaps coincident with the region of body wave excitation observed by Gerstoft et al. [2008] and Landès et al. [2010]. (3) Local primary microseism <span class="hlt">sources</span> within and near the Juan de Fuca plate are implied by observations of the azimuthal dependence of the fundamental mode Rayleigh wave amplitudes as well as observations of precursory arrivals in cross-correlations of ambient <span class="hlt">noise</span>. The strongest local generation region is observed northwest of the Juan de Fuca plate near the coast of British Columbia perhaps near Graham Island. Weaker local <span class="hlt">sources</span> appear to be oceanward of Vancouver Island and southern Oregon. (4) High quality Green's functions are derived from cross-correlations between deep water OBSs and continental stations proving that deep water generated signals can efficiently propagate onto the continent and are well recorded by continental seismic stations, at least at periods longer than about 5 sec.In conclusion, the primary and secondary microseisms are generated at different locations, with the secondary microseism dominantly coming from deep-water <span class="hlt">sources</span> and the <span class="hlt">source</span> of primary microseism having a significant component in the shallow waters of the eastern Pacific</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006JSV...293.1029J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006JSV...293.1029J"><span>Evaluation of the interim measurement protocol for railway <span class="hlt">noise</span> <span class="hlt">source</span> description</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Janssens, M. H. A.; Jansen, H. W.; Dittrich, M. G.</p> <p>2006-06-01</p> <p>The Dutch national calculation scheme for railway <span class="hlt">noise</span> has been declared the default interim method for railway <span class="hlt">noise</span> calculation by the EU, until the introduction of results from the Harmonoise project. It includes a measurement protocol for determining emission input data in the format suitable for the present calculation scheme. The calculation scheme contains a fixed database of emission data for common Dutch rolling stock. The measurement protocol provides for the addition of emission data of new or foreign rolling stock. This is relevant for the Netherlands, as such rolling stock increasingly appears on the network, but also for other European countries that are going to use the interim method, since emission data for their rolling stock have to be established. The protocol features two procedures. Procedure A allows using the existing fixed database of emission data. Selection of a particular dataset (or 'category') can be based on external appearance of rolling stock (without measurements) or pass-by sound pressure level measurements at a site with known rail roughness. If a user finds that none of the existing data sets properly represent its rolling stock, the optional procedure B is available. This procedure assesses pass-by levels, track and wheel roughness levels. The measurement protocol is based on a type-test-like procedure requiring controlled conditions for the vehicle and track. A measurement campaign has been undertaken to test procedures A and B. This campaign coincided with a Swiss campaign to establish the sound emission of freight vehicles equipped with composite block brakes. The test of the protocol was focussed both on the practicability of the required measurements and on the unambiguity and comprehensiveness of the test. Open questions, findings, resulting conclusions and recommendations regarding the protocol are discussed here.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011JGRA..116.3104S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011JGRA..116.3104S"><span>Constraints on coronal turbulence models from <span class="hlt">source</span> sizes of <span class="hlt">noise</span> storms at 327 MHz</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Subramanian, Prasad; Cairns, Iver</p> <p>2011-03-01</p> <p>We seek to reconcile observations of small <span class="hlt">source</span> sizes in the solar corona at 327 MHz with predictions of scattering models that incorporate refractive index effects, inner scale effects, and a spherically diverging wavefront. We use an empirical prescription for the turbulence amplitude CN2(R) based on very long baseline interferometry observations by Spangler et al. of compact radio <span class="hlt">sources</span> against the solar wind for heliocentric distances R ≈ 10-50 R⊙. We use the Coles and Harmon model for the inner scale li(R), which is presumed to arise from cyclotron damping. In view of the prevalent uncertainty in the power law index that characterizes solar wind turbulence at various heliocentric distances, we retain this index as a free parameter. We find that the inclusion of spherical divergence effects suppresses the predicted <span class="hlt">source</span> size substantially. We also find that inner scale effects significantly reduce the predicted <span class="hlt">source</span> size. An important general finding for solar <span class="hlt">sources</span> is that the calculations substantially underpredict the observed <span class="hlt">source</span> size. Three possible, nonexclusive, interpretations of this general result are proposed. First and simplest, future observations with better angular resolution will detect much smaller <span class="hlt">sources</span>. Consistent with this, previous observations of small <span class="hlt">sources</span> in the corona at metric wavelengths are limited by the instrument resolution. Second, the spatially varying level of turbulence CN2(R) is much larger in the inner corona than predicted by straightforward extrapolation sunward of the empirical prescription, which was based on observations between 10 and 50 R⊙. Either the functional form or the constant of proportionality could be different. Third, perhaps the inner scale is smaller than the model, leading to increased scattering. These results and interpretations are discussed and compared with earlier work.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770012544','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770012544"><span>Correlation of AH-1G <span class="hlt">airframe</span> test data with a NASTRAN mathematical model</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cronkhite, J. D.; Berry, V. L.</p> <p>1976-01-01</p> <p>Test data was provided for evaluating a mathematical vibration model of the Bell AH-1G helicopter <span class="hlt">airframe</span>. The math model was developed and analyzed using the NASTRAN structural analysis computer program. Data from static and dynamic tests were used for comparison with the math model. Static tests of the fuselage and tailboom were conducted to verify the stiffness representation of the NASTRAN model. Dynamic test data were obtained from shake tests of the <span class="hlt">airframe</span> and were used to evaluate the NASTRAN model for representing the low frequency (below 30 Hz) vibration response of the <span class="hlt">airframe</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140010733','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140010733"><span>The Prediction of <span class="hlt">Noise</span> Due to Jet Turbulence Convecting Past Flight Vehicle Trailing Edges</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Miller, Steven A. E.</p> <p>2014-01-01</p> <p>High intensity acoustic radiation occurs when turbulence convects past <span class="hlt">airframe</span> trailing edges. A mathematical model is developed to predict this acoustic radiation. The model is dependent on the local flow and turbulent statistics above the trailing edge of the flight vehicle <span class="hlt">airframe</span>. These quantities are dependent on the jet and flight vehicle Mach numbers and jet temperature. A term in the model approximates the turbulent statistics of single-stream heated jet flows and is developed based upon measurement. The developed model is valid for a wide range of jet Mach numbers, jet temperature ratios, and flight vehicle Mach numbers. The model predicts traditional trailing edge <span class="hlt">noise</span> if the jet is not interacting with the <span class="hlt">airframe</span>. Predictions of mean-flow quantities and the cross-spectrum of static pressure near the <span class="hlt">airframe</span> trailing edge are compared with measurement. Finally, predictions of acoustic intensity are compared with measurement and the model is shown to accurately capture the phenomenon.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150021044','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150021044"><span>Acoustic Database for Turbofan Engine Core-<span class="hlt">Noise</span> <span class="hlt">Sources</span>. I; Volume</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gordon, Grant</p> <p>2015-01-01</p> <p>In this program, a database of dynamic temperature and dynamic pressure measurements were acquired inside the core of a TECH977 turbofan engine to support investigations of indirect combustion <span class="hlt">noise</span>. Dynamic temperature and pressure measurements were recorded for engine gas dynamics up to temperatures of 3100 degrees Fahrenheit and transient responses as high as 1000 hertz. These measurements were made at the entrance of the high pressure turbine (HPT) and at the entrance and exit of the low pressure turbine (LPT). Measurements were made at two circumferential clocking positions. In the combustor and inter-turbine duct (ITD), measurements were made at two axial locations to enable the exploration of time delays. The dynamic temperature measurements were made using dual thin-wire thermocouple probes. The dynamic pressure measurements were made using semi-infinite probes. Prior to the engine test, a series of bench, oven, and combustor rig tests were conducted to characterize the performance of the dual wire temperature probes and to define and characterize the data acquisition systems. A measurement solution for acquiring dynamic temperature and pressure data on the engine was defined. A suite of hardware modifications were designed to incorporate the dynamic temperature and pressure instrumentation into the TECH977 engine. In particular, a probe actuation system was developed to protect the delicate temperature probes during engine startup and transients in order to maximize sensor life. A set of temperature probes was procured and the TECH977 engine was assembled with the suite of new and modified hardware. The engine was tested at four steady state operating speeds, with repeats. Dynamic pressure and temperature data were acquired at each condition for at least one minute. At the two highest power settings, temperature data could not be obtained at the forward probe locations since the mean temperatures exceeded the capability of the probes. The temperature data</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985aimm.cong..407M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985aimm.cong..407M"><span>Use of acoustic intensity measurements in the characterization of jet <span class="hlt">noise</span> <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Musafir, R. E.; Slama, J. G.; Zindeluk, M.</p> <p></p> <p>The usefulness of two-microphone acoustic-intensity (AI) measurements for characterizing the acoustic field of a jet flow is investigated by means of numerical simulations. The theoretical principles and data basis for the simulations are explained, and the intensity patterns generated by the simulation are presented graphically. It is found that the vector information in AI data from the near field are useful in understanding complex <span class="hlt">sources</span>, but that far-field intensity charts cannot locate separate <span class="hlt">sources</span> and may be misleading if not analyzed in terms of a sound physical model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017RScI...88c5107B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017RScI...88c5107B"><span>A low <span class="hlt">noise</span> modular current <span class="hlt">source</span> for stable magnetic field control</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Biancalana, Valerio; Bevilacqua, Giuseppe; Chessa, Piero; Dancheva, Yordanka; Cecchi, Roberto; Stiaccini, Leonardo</p> <p>2017-03-01</p> <p>A low cost, stable, programmable, unipolar current <span class="hlt">source</span> is described. The circuit is designed in view of a modular arrangement, suitable for applications where several DC <span class="hlt">sources</span> must be controlled at once. A hybrid switching/linear design helps in improving the stability and in reducing the power dissipation and cross-talking. Multiple units can be supplied by a single DC power supply, while allowing for a variety of maximal current values and compliance voltages at the outputs. The circuit is analogically controlled by a unipolar voltage, enabling current programmability and control through commercial digital-to-analogue conversion cards.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005ASAJ..118.1848W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005ASAJ..118.1848W"><span>Acoustic emissions of digital data video projectors- Investigating <span class="hlt">noise</span> <span class="hlt">sources</span> and their change during product aging</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>White, Michael Shane</p> <p>2005-09-01</p> <p>Acoustic emission testing continues to be a growing part of IT and telecommunication product design, as product <span class="hlt">noise</span> is increasingly becoming a differentiator in the marketplace. This is especially true for digital/video display companies, such as InFocus Corporation, considering the market shift of these products to the home entertainment consumer as retail prices drop and performance factors increase. Projectors and displays using Digital Light Processing(tm) [DLP(tm)] technology incorporate a device known as a ColorWheel(tm) to generate the colors displayed at each pixel in the image. These ColorWheel(tm) devices spin at very high speeds and can generate high-frequency tones not typically heard in liquid crystal displays and other display technologies. Also, acoustic emission testing typically occurs at the beginning of product life and is a measure of acoustic energy emitted at this point in the lifecycle. Since the product is designed to be used over a long period of time, there is concern as to whether the acoustic emissions change over the lifecycle of the product, whether these changes will result in a level of nuisance to the average customer, and does this nuisance begin to develop prior to the intended lifetime of the product.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFDG20005X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFDG20005X"><span>New insights into insect's silent flight. Part II: sound <span class="hlt">source</span> and <span class="hlt">noise</span> control</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xue, Qian; Geng, Biao; Zheng, Xudong; Liu, Geng; Dong, Haibo</p> <p>2016-11-01</p> <p>The flapping flight of aerial animals has excellent aerodynamic performance but meanwhile generates low <span class="hlt">noise</span>. In this study, the unsteady flow and acoustic characteristics of the flapping wing are numerically investigated for three-dimensional (3D) models of Tibicen linnei cicada at free forward flight conditions. Single cicada wing is modelled as a membrane with prescribed motion reconstructed by Wan et al. (2015). The flow field and acoustic field around the flapping wing are solved with immersed-boundary-method based incompressible flow solver and linearized-perturbed-compressible-equations based acoustic solver. The 3D simulation allows examination of both directivity and frequency composition of the produced sound in a full space. The mechanism of sound generation of flapping wing is analyzed through correlations between acoustic signals and flow features. Along with a flexible wing model, a rigid wing model is also simulated. The results from these two cases will be compared to investigate the effects of wing flexibility on sound generation. This study is supported by NSF CBET-1313217 and AFOSR FA9550-12-1-0071.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=social+AND+network+AND+accuracy&pg=3&id=EJ1004715','ERIC'); return false;" href="http://eric.ed.gov/?q=social+AND+network+AND+accuracy&pg=3&id=EJ1004715"><span>Organizational Communication in Emergencies: Using Multiple Channels and <span class="hlt">Sources</span> to Combat <span class="hlt">Noise</span> and Capture Attention</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Stephens, Keri K.; Barrett, Ashley K.; Mahometa, Michael J.</p> <p>2013-01-01</p> <p>This study relies on information theory, social presence, and <span class="hlt">source</span> credibility to uncover what best helps people grasp the urgency of an emergency. We surveyed a random sample of 1,318 organizational members who received multiple notifications about a large-scale emergency. We found that people who received 3 redundant messages coming through at…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012IEITF..95..498L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012IEITF..95..498L"><span>A 24dB Gain 51-68GHz Common <span class="hlt">Source</span> Low <span class="hlt">Noise</span> Amplifier Using Asymmetric-Layout Transistors</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Ning; Bunsen, Keigo; Takayama, Naoki; Bu, Qinghong; Suzuki, Toshihide; Sato, Masaru; Kawano, Yoichi; Hirose, Tatsuya; Okada, Kenichi; Matsuzawa, Akira</p> <p></p> <p>At mm-wave frequency, the layout of CMOS transistors has a larger effect on the device performance than ever before in low frequency. In this work, the distance between the gate and drain contact (Dgd) has been enlarged to obtain a better maximum available gain (MAG). By using the asymmetric-layout transistor, a 0.6dB MAG improvement is realized when Dgd changes from 60nm to 200nm. A four-stage common-<span class="hlt">source</span> low <span class="hlt">noise</span> amplifier is implemented in a 65nm CMOS process. A measured peak power gain of 24dB is achieved with a power dissipation of 30mW from a 1.2-V power supply. An 18dB variable gain is also realized by adjusting the bias voltage. The measured 3-dB bandwidth is about 17GHz from 51GHz to 68GHz, and <span class="hlt">noise</span> figure (NF) is from 4.0dB to 7.6dB.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20120012957','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20120012957"><span>Assessment of NASA's Aircraft <span class="hlt">Noise</span> Prediction Capability</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dahl, Milo D. (Editor)</p> <p>2012-01-01</p> <p>A goal of NASA s Fundamental Aeronautics Program is the improvement of aircraft <span class="hlt">noise</span> prediction. This document provides an assessment, conducted from 2006 to 2009, on the current state of the art for aircraft <span class="hlt">noise</span> prediction by carefully analyzing the results from prediction tools and from the experimental databases to determine errors and uncertainties and compare results to validate the predictions. The error analysis is included for both the predictions and the experimental data and helps identify where improvements are required. This study is restricted to prediction methods and databases developed or sponsored by NASA, although in many cases they represent the current state of the art for industry. The present document begins with an introduction giving a general background for and a discussion on the process of this assessment followed by eight chapters covering topics at both the system and the component levels. The topic areas, each with multiple contributors, are aircraft system <span class="hlt">noise</span>, engine system <span class="hlt">noise</span>, <span class="hlt">airframe</span> <span class="hlt">noise</span>, fan <span class="hlt">noise</span>, liner physics, duct acoustics, jet <span class="hlt">noise</span>, and propulsion <span class="hlt">airframe</span> aeroacoustics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880060266&hterms=star+shots&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dstar%2Bshots','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880060266&hterms=star+shots&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dstar%2Bshots"><span>Shot <span class="hlt">noise</span> cross-correlation functions and cross spectra - Implications for models of QPO X-ray <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Shibazaki, N.; Elsner, R. F.; Bussard, R. W.; Ebisuzaki, T.; Weisskopf, M. C.</p> <p>1988-01-01</p> <p>The cross-correlation functions (CCFs) and cross spectra expected for quasi-periodic oscillation (QPO) shot <span class="hlt">noise</span> models are calculated under various assumptions, and the results are compared to observations. Effects due to possible coherence of the QPO oscillations are included. General formulas for the cross spectrum, the cross-phase spectrum, and the time-delay spectrum for QPO shot models are calculated and discussed. It is shown that the CCFs, cross spectra, and power spectra observed for Cyg X-e2 imply that the spectrum of the shots evolves with time, with important implications for the interpretation of these functions as well as of observed average energy spectra. The possible origins for the observed hard lags are discussed, and some physical difficulties for the Comptonization model are described. Classes of physical models for QPO <span class="hlt">sources</span> are briefly addressed, and it is concluded that models involving shot formation at the surface of neutron stars are favored by observation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940028997','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940028997"><span>Propulsion <span class="hlt">airframe</span> integration session overview and review of Lewis PAI efforts</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Batterton, Peter G.</p> <p>1992-01-01</p> <p>Propulsion/<span class="hlt">Airframe</span> Integration (PAI) is a key issue for the High Speed Civil Transport. The aircraft performance, economics, and environmental acceptability can be adversely affected if the integration of the propulsion system and the <span class="hlt">airframe</span> is not addressed properly or in a timely manner. Some of the goals are listed in this figure. In particular, these goals are highly influenced by how successfully the propulsion system and <span class="hlt">airframe</span> are integrated. These goals were grouped by the 'Aero' and 'Propulsion' categories to suggest which group of technologists will likely be addressing them. In terms of the NASA High Speed Research Program, the ultimate objective for propulsion/<span class="hlt">airframe</span> integration is to demonstrate the technologies for achievement of these goals on a 'single' integrated configuration.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150002348','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150002348"><span>Shielding Characteristics Using an Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> to Generate Modes - Experimental Measurements and Analytical Predictions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sutliff, Daniel L.; Walker, Bruce E.</p> <p>2014-01-01</p> <p>An Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> (UCFANS) was designed, built, and tested in support of the NASA Langley Research Center's 14x22 wind tunnel test of the Hybrid Wing Body (HWB) full 3-D 5.8% scale model. The UCFANS is a 5.8% rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of proposed engines using artificial <span class="hlt">sources</span> (no flow). The purpose of the program was to provide an estimate of the acoustic shielding benefits possible from mounting an engine on the upper surface of a wing; a flat plate model was used as the shielding surface. Simple analytical simulations were used to preview the radiation patterns - Fresnel knife-edge diffraction was coupled with a dense phased array of point <span class="hlt">sources</span> to compute shielded and unshielded sound pressure distributions for potential test geometries and excitation modes. Contour plots of sound pressure levels, and integrated power levels, from nacelle alone and shielded configurations for both the experimental measurements and the analytical predictions are presented in this paper.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20030065909','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030065909"><span>Computation of Large-Scale Structure Jet <span class="hlt">Noise</span> <span class="hlt">Sources</span> With Weak Nonlinear Effects Using Linear Euler</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dahl, Milo D.; Hixon, Ray; Mankbadi, Reda R.</p> <p>2003-01-01</p> <p>An approximate technique is presented for the prediction of the large-scale turbulent structure sound <span class="hlt">source</span> in a supersonic jet. A linearized Euler equations code is used to solve for the flow disturbances within and near a jet with a given mean flow. Assuming a normal mode composition for the wave-like disturbances, the linear radial profiles are used in an integration of the Navier-Stokes equations. This results in a set of ordinary differential equations representing the weakly nonlinear self-interactions of the modes along with their interaction with the mean flow. Solutions are then used to correct the amplitude of the disturbances that represent the <span class="hlt">source</span> of large-scale turbulent structure sound in the jet.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880037647&hterms=techniques+method&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dtechniques%252C%2Bmethod','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880037647&hterms=techniques+method&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dtechniques%252C%2Bmethod"><span>A <span class="hlt">noise</span> <span class="hlt">source</span> identification technique using an inverse Helmholtz integral equation method</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gardner, B. K.; Bernhard, R. J.</p> <p>1988-01-01</p> <p>A technique is developed which utilizes numerical models and field pressure information to characterize acoustic fields and identify acoustic <span class="hlt">sources</span>. The numerical models are based on boundary element numerical procedures. Either pressure, velocity, or passive boundary conditions, in the form of impedance boundary conditions, may be imposed on the numerical model. Alternatively, if no boundary information is known, a boundary condition can be left unspecified. Field pressure data may be specified to overdetermine the numerical problem. The problem is solved numerically for the complete sound field from which the acoustic <span class="hlt">sources</span> may be determined. The model can then be used to idenfify acoustic intensity paths in the field. The solution can be modified and the model used to evaluate design alternatives. In this investigation the method is tested analytically and verified. In addition, the sensitivity of the method to random and bias error in the input data is demonstrated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009SPIE.7258E..5NW','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009SPIE.7258E..5NW"><span>Dual <span class="hlt">source</span> CT (DSCT) imaging of obese patients: evaluation of CT number accuracy, uniformity, and <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Walz-Flannigan, A.; Schmidt, B.,; Apel, A.; Eusemann, C.; Yu, L.; McCollough, C. H.</p> <p>2009-02-01</p> <p>Obese patients present challenges in obtaining sufficient x-ray exposure over reasonable time periods for acceptable CT image quality. To overcome this limitation, the exposure can be divided between two x-ray <span class="hlt">sources</span> using a dualsource (DS) CT system. However, cross-scatter issues in DS CT may also compromise image quality. We evaluated a DS CT system optimized for imaging obese patients, comparing the CT number accuracy and uniformity to the same images obtained with a single-<span class="hlt">source</span> (SS) acquisition. The imaging modes were compared using both solid cylindrical PMMA phantoms and a semi-anthropomorphic thorax phantom fitted with extension rings to simulate different size patients. Clinical protocols were used and CTDIvol and kVp were held constant between SS and DS modes. Results demonstrated good agreement in CT number between SS and DS modes in CT number, with the DS mode showing better axial uniformity for the largest phantoms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA209804','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA209804"><span>Analysis of a System to Prevent Helicopter Rotor Blade-<span class="hlt">Airframe</span> Strikes</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1989-05-01</p> <p><span class="hlt">airframe</span> are particularly vulnerable: the tail boom, canopy and, in the case of the underslung, teetoring rotor, the rotor shaft. This latter case is...but they do occur. Three areas of the <span class="hlt">airframe</span> are particularly vulnerable: the tail boom, canopy and, in the case of the underslung, teetoring rotor...particular vulnerable, the tail boom, canopy and, in the case of the underslung, teetoring rotor, the rotor shaft. This latter case, known as "mast</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009SPIE.7307E..09S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009SPIE.7307E..09S"><span>Design of an <span class="hlt">airframe</span> agnostic roll-on/roll-off (AA-RORO) sensor platform</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sparks, Bruce; Wowczuk, Zenovy S.; Harrison, A. Jay</p> <p>2009-05-01</p> <p>The US military has recently taken tactical steps to increase its ISR capabilities to support military operations. Due to the dynamic capabilities of the terrorist threat, there is a need for a payload- and <span class="hlt">airframe</span>-agnostic, rapid-deployment sensor system that can be used on multiple <span class="hlt">airframes</span> for in-theater missions and for the test and evaluation of sensors prior to fielding. This "plug-and-play" system, based upon the Oculus Sensor Deployment System technology, uses a system-of-systems approach to modularize the base platform, thereby allowing the system to conform to aircraft such as the C-130, C-27, V-22, CH-47, CH-53 and CASA-235 without any modification to the <span class="hlt">airframe</span> itself. This type of system can be used as (1) a versatile, cost-effective test and evaluation platform for current and developmental sensors as well as (2) an in-theater ISR asset that can be used on readily available <span class="hlt">airframes</span> at a particular location. This paper illustrates the CONUS and OCONUS mission potential of this multi-<span class="hlt">airframe</span> system and outlines the novel design characteristics that the <span class="hlt">Airframe</span> Agnostic Roll-on/Roll-off (AA-RORO) sensor platform incorporates to make it the most versatile, rapid-deployment sensor platform available to support near-term U.S. military operations. The system concept was developed with the support of and input from multiple military agencies and the respective branches they represent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1326612','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1326612"><span>Reduction of Beam Current <span class="hlt">Noise</span> in the FNAL Magnetron Ion <span class="hlt">Source</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bollinger, D. S.; Karns, P. R.; Tan, C. Y.</p> <p>2014-01-01</p> <p>The new FNAL Injector Line with a circular dimple magnetron ion <span class="hlt">source</span> has been operational since December of 2013. Since the new injector came on line there have been variations in the H- beam current flattop observed near the downstream end of the linac. Several different cathode geometries including a hollow cathode suggested by Dudnikov [1] were tried. We expanded on those studies by trying mixtures ranging from 0.25%N, 99.75%H to 3%N, 97%H. The results of these studies in our test stand will be presented in this paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993PhDT.......194L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993PhDT.......194L"><span>Vibro-Acoustic Analysis of Computer Disk Drive Components with Emphasis on Electro-Mechanical <span class="hlt">Noise</span> <span class="hlt">Sources</span>.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Ming-Ran</p> <p></p> <p>Vibro-acoustic characteristics of compact electro -mechanical devices are not well understood. This study examines fundamental research issues in this area through the example case of a 3.5" personal computer hard disk drive. In particular, a narrow band mathematical model of the drive has been developed to predict prominent pure tones over the high frequency range (1-6.5 KHz). Through detailed analytical studies, it has been found that the motor torque pulsation of the brushless d.c. motor is the <span class="hlt">source</span> for this <span class="hlt">noise</span> problem. Accordingly, a simplified disk drive model consisting of motor driving a single disk is used to investigate key components, with emphasis on the development of new mathematical models to describe the <span class="hlt">source</span>, path and radiator characteristics. Two different mathematical models have been developed for brushless d.c. motor to predict the torque spectrum associated with invertor switching logic, pulse width modulation control scheme, eccentricity, and magnetic saturation. Frequency contents of predicted variables are identified and matched with measured sound data. Additionally, the Galerkin's method (or modified harmonic balance) is also employed successfully to develop an efficient computational scheme which predicts the Fourier coefficients of torque pulsations directly including various effects associated with inductance harmonics and the fluctuation of rotor angular velocity. For the radiator (annular disk), modal base formulations of sound radiation have been developed by approximating disk eigen-functions. Specifically, the effects of modal coupling and <span class="hlt">source</span> rotation on radiated sound are investigated. Analytical predictions match well with numerical results obtained by using a boundary element program. New mobility transfer functions (path) are derived to couple the <span class="hlt">source</span> and radiator formulations in order to construct an overall vibro-acoustic model. Potential areas of further research including experimental validation are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5875386','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5875386"><span>Acoustic <span class="hlt">noise</span> associated with the MOD-1 wind turbine: its <span class="hlt">source</span>, impact, and control</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kelley, N.D.; McKenna, H.E.; Hemphill, R.R.; Etter, C.L.; Garrelts, R.L.; Linn, N.C.</p> <p>1985-02-01</p> <p>This report summarizes extensive research by staff of the Solar Energy Research Institute and its subcontractors conducted to establish the origin and possible amelioration of acoustic disturbances associated with the operation of the DOE/NASA MOD-1 wind turbine installed in 1979 near Boone, North Carolina. Results have shown that the <span class="hlt">source</span> of this acoustic annoyance was the transient, unsteady aerodynamic lift imparted to the turbine blades as they passed through the lee wakes of the large, cylindrical tower supports. Nearby residents were annoyed by the low-frequency, acoustic impulses propagated into the structures in which the complainants lived. The situation was aggravated further by a complex sound propagation process controlled by terrain and atmospheric focusing. Several techniques for reducing the abrupt, unsteady blade load transients were researched and are discussed in the report.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5949122','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5949122"><span><span class="hlt">Sources</span> of <span class="hlt">noise</span> and vibration in a mechanical system with clearances</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Akay, A.; Bengisu, M.T.</p> <p>1982-01-01</p> <p>Inherent in the design of any mechanism with moving parts is the requirement for clearances. In the case of an engine, this requirement is enhanced by the extremes of both load and temperature under which some parts are expected to function. Collision of the parts in these connections where clearances exist are influenced by transient combustion forces as well as inertial forces. Impacts in the joints of a system are a major <span class="hlt">source</span> of sound, vibration and wear. The mechanism of sound generation follows the dynamic response of the system components. The resulting transient acoustic field is comprised of radiation from the forced and free vibrations of the system. Radiation due to inertial forces are generally of lower frequency whereas sounds produced by the impacts exhibit higher levels with higher spectral content. This study investigates the sound and vibration response of a four-bar mechanism in the absence of external forces.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUSM.G13A..01W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUSM.G13A..01W"><span>Glacial Isostatic Adjustment as a <span class="hlt">Source</span> of <span class="hlt">Noise</span> for the Interpretation of GRACE Data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wahr, J.; Velicogna, I.; Paulson, A.</p> <p>2009-05-01</p> <p>Viscoelastic relaxation in the Earth's mantle caused by wide-spread deglaciation following the last glacial maximum (LGM), can appear as a secular trend in measurements of the Earth's time-variable gravity field. The presence of this trend can provide an opportunity to use gravity observations to constrain models of the glacial isostatic adjustment (GIA) process. But it can also be a nuisance for people who are using the gravity observations to learn about other things. Gravity observations, whether from satellites or from ground-based gravimeters, can not distinguish between the gravitational effects of water/snow/ice variations on or near the surface, and those caused by density variations deep within the mantle. Unmodeled or mismodeled GIA signals can sometimes make it difficult to use gravity observations to learn about secular changes in water/snow/ice from such places as northern Canada, Scandinavia, Antarctica, and Greenland: places where there was considerable long-term deglaciation following the LGM. These issues have become particularly important since the 2002 launch of the GRACE gravity satellite mission. GIA signals in northern Canada and Scandinavia are clearly evident in the GRACE data. But the presence of GIA signals in these and other regions has sometimes caused problems for long-term hydrological and, especially, cryospheric studies with GRACE. GIA model errors, for example, are by far the largest <span class="hlt">source</span> of uncertainty when using GRACE to estimate present-day thinning rates of the Antarctic ice sheet. This talk will discuss the contributions of the GIA signal to GRACE time-variable gravity measurements; partly as an opportunity to study the GIA process, but mostly as a <span class="hlt">source</span> of uncertainty for other applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020068132','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020068132"><span>Design and Test of an Improved Crashworthiness Small Composite <span class="hlt">Airframe</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Terry, James E.; Hooper, Steven J.; Nicholson, Mark</p> <p>2002-01-01</p> <p>The purpose of this small business innovative research (SBIR) program was to evaluate the feasibility of developing small composite airplanes with improved crashworthiness. A combination of analysis and half scale component tests were used to develop an energy absorbing <span class="hlt">airframe</span>. Four full scale crash tests were conducted at the NASA Impact Dynamics Research Facility, two on a hard surface and two onto soft soil, replicating earlier NASA tests of production general aviation airplanes. Several seat designs and restraint systems including both an air bag and load limiting shoulder harnesses were tested. Tests showed that occupant loads were within survivable limits with the improved structural design and the proper combination of seats and restraint systems. There was no loss of cabin volume during the events. The analysis method developed provided design guidance but time did not allow extending the analysis to soft soil impact. This project demonstrated that survivability improvements are possible with modest weight penalties. The design methods can be readily applied by airplane designers using the examples in this report.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160006053','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160006053"><span>Variability in the Propagation Phase of CFD-Based <span class="hlt">Noise</span> Prediction: Summary of Results From Category 8 of the BANC-III Workshop</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lopes, Leonard; Redonnet, Stephane; Imamura, Taro; Ikeda, Tomoaki; Zawodny, Nikolas; Cunha, Guilherme</p> <p>2015-01-01</p> <p>The usage of Computational Fluid Dynamics (CFD) in <span class="hlt">noise</span> prediction typically has been a two part process: accurately predicting the flow conditions in the near-field and then propagating the <span class="hlt">noise</span> from the near-field to the observer. Due to the increase in computing power and the cost benefit when weighed against wind tunnel testing, the usage of CFD to estimate the local flow field of complex geometrical structures has become more routine. Recently, the Benchmark problems in <span class="hlt">Airframe</span> <span class="hlt">Noise</span> Computation (BANC) workshops have provided a community focus on accurately simulating the local flow field near the body with various CFD approaches. However, to date, little effort has been given into assessing the impact of the propagation phase of <span class="hlt">noise</span> prediction. This paper includes results from the BANC-III workshop which explores variability in the propagation phase of CFD-based <span class="hlt">noise</span> prediction. This includes two test cases: an analytical solution of a quadrupole <span class="hlt">source</span> near a sphere and a computational solution around a nose landing gear. Agreement between three codes was very good for the analytic test case, but CFD-based <span class="hlt">noise</span> predictions indicate that the propagation phase can introduce 3dB or more of variability in <span class="hlt">noise</span> predictions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040086964','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040086964"><span>Propulsion System <span class="hlt">Airframe</span> Integration Issues and Aerodynamic Database Development for the Hyper-X Flight Research Vehicle</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Engelund, Walter C.; Holland, Scott D.; Cockrell, Charles E., Jr.; Bittner, Robert D.</p> <p>1999-01-01</p> <p>NASA's Hyper-X Research Vehicle will provide a unique opportunity to obtain data on an operational <span class="hlt">airframe</span> integrated scramjet propulsion system at true flight conditions. The <span class="hlt">airframe</span> integrated nature of the scramjet engine with the Hyper-X vehicle results in a strong coupling effect between the propulsion system operation and the <span class="hlt">airframe</span> s basic aerodynamic characteristics. Comments on general <span class="hlt">airframe</span> integrated scramjet propulsion system effects on vehicle aerodynamic performance, stability, and control are provided, followed by examples specific to the Hyper-X research vehicle. An overview is provided of the current activities associated with the development of the Hyper-X aerodynamic database, including wind tunnel test activities and parallel CFD analysis efforts. A brief summary of the Hyper-X aerodynamic characteristics is provided, including the direct and indirect effects of the <span class="hlt">airframe</span> integrated scramjet propulsion system operation on the basic <span class="hlt">airframe</span> stability and control characteristics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19870004687','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870004687"><span>Effects of background <span class="hlt">noise</span> on total <span class="hlt">noise</span> annoyance</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Willshire, K. F.</p> <p>1987-01-01</p> <p>Two experiments were conducted to assess the effects of combined community <span class="hlt">noise</span> <span class="hlt">sources</span> on annoyance. The first experiment baseline relationships between annoyance and <span class="hlt">noise</span> level for three community <span class="hlt">noise</span> <span class="hlt">sources</span> (jet aircraft flyovers, traffic and air conditioners) presented individually. Forty eight subjects evaluated the annoyance of each <span class="hlt">noise</span> <span class="hlt">source</span> presented at four different <span class="hlt">noise</span> levels. Results indicated the slope of the linear relationship between annoyance and <span class="hlt">noise</span> level for the traffic <span class="hlt">noise</span> was significantly different from that of aircraft and of air conditioner <span class="hlt">noise</span>, which had equal slopes. The second experiment investigated annoyance response to combined <span class="hlt">noise</span> <span class="hlt">sources</span>, with aircraft <span class="hlt">noise</span> defined as the major <span class="hlt">noise</span> <span class="hlt">source</span> and traffic and air conditioner <span class="hlt">noise</span> as background <span class="hlt">noise</span> <span class="hlt">sources</span>. Effects on annoyance of <span class="hlt">noise</span> level differences between aircraft and background <span class="hlt">noise</span> for three total <span class="hlt">noise</span> levels and for both background <span class="hlt">noise</span> <span class="hlt">sources</span> were determined. A total of 216 subjects were required to make either total or <span class="hlt">source</span> specific annoyance judgements, or a combination of the two, for a wide range of combined <span class="hlt">noise</span> conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoJI.201..429T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoJI.201..429T"><span>Directionality of ambient <span class="hlt">noise</span> on the Juan de Fuca plate: implications for <span class="hlt">source</span> locations of the primary and secondary microseisms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tian, Ye; Ritzwoller, Michael H.</p> <p>2015-04-01</p> <p>Based on cross-correlations of ambient seismic <span class="hlt">noise</span> computed using 61 ocean bottom seismometers (OBSs) within the Juan de Fuca (JdF) plate from the Cascadia Initiative experiment and 42 continental stations near the coast of the western United States, we investigate the locations of generation of the primary (11-20 s period) and secondary (5-10 s period) microseisms in the northern Pacific Ocean by analysing the directionality and seasonality of the microseism (Rayleigh wave) signals received in this region. We conclude that (1) the ambient <span class="hlt">noise</span> observed across the array is much different in the primary and secondary microseism bands, both in its azimuthal content and seasonal variation. (2) The principal secondary microseism signals propagate towards the east, consistent with their generation in deep waters of the North Pacific, perhaps coincident both with the region of observed body wave excitation and the predicted wave-wave interaction region from recent studies. (3) The primary microseism, as indicated by observations of the azimuthal dependence of the fundamental mode Rayleigh wave as well as observations of precursory arrivals, derives significantly from the shallow waters of the eastern Pacific near to the JdF plate but also has a component generated at greater distance of unknown origin. (4) These observations suggest different physical mechanisms for generating the two microseisms: the secondary microseisms are likely to be generated by non-linear wave-wave interaction over the deep Pacific Ocean, while the primary microseism may couple directly into the solid earth locally in shallow waters from ocean gravity waves. (5) Above 5 s period, high quality empirical Green's functions are observed from cross-correlations between deep water OBSs and continental stations, which illustrates that microseisms propagate efficiently from either deep or shallow water <span class="hlt">source</span> regions onto the continent and are well recorded by continental seismic stations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970004793','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970004793"><span>The Influences of Lamination Angles on the Interior <span class="hlt">Noise</span> Levels of an Aircraft</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Fernholz, Christian M.; Robinson, Jay H.</p> <p>1996-01-01</p> <p>The feasibility of reducing the interior <span class="hlt">noise</span> levels of an aircraft passenger cabin through optimization of the composite lay up of the fuselage is investigated. MSC/NASTRAN, a commercially available finite element code, is used to perform the dynamic analysis and subsequent optimization of the fuselage. The numerical calculation of sensitivity of acoustic pressure to lamination angle is verified using a simple thin, cylindrical shell with point force excitations as <span class="hlt">noise</span> <span class="hlt">sources</span>. The thin shell used represents a geometry similar to the fuselage and analytic solutions are available for the cylindrical thin shell equations of motion. Optimization of lamination angle for the reduction of interior <span class="hlt">noise</span> is performed using a finite element model of an actual aircraft fuselage. The aircraft modeled for this study is the Beech Starship. Point forces simulate the structure borne <span class="hlt">noise</span> produced by the engines and are applied to the fuselage at the wing mounting locations. These forces are the <span class="hlt">noise</span> <span class="hlt">source</span> for the optimization problem. The acoustic pressure response is reduced at a number of points in the fuselage and over a number of frequencies. The objective function is minimized with the constraint that it be larger than the maximum sound pressure level at the response points in the passenger cabin for all excitation frequencies in the range of interest. Results from the study of the fuselage model indicate that a reduction in interior <span class="hlt">noise</span> levels is possible over a finite frequency range through optimal configuration of the lamination angles in the fuselage. <span class="hlt">Noise</span> reductions of roughly 4 dB were attained. For frequencies outside the optimization range, the acoustic pressure response may increase after optimization. The effects of changing lamination angle on the overall structural integrity of the <span class="hlt">airframe</span> are not considered in this study.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007PMB....52.1409K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007PMB....52.1409K"><span><span class="hlt">Noise</span>-tolerance analysis for detection and reconstruction of absorbing inhomogeneities with diffuse optical tomography using single- and phase-correlated dual-<span class="hlt">source</span> schemes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kanmani, B.; Vasu, R. M.</p> <p>2007-03-01</p> <p>An iterative reconstruction procedure is used to invert intensity data from both single- and phase-correlated dual-<span class="hlt">source</span> illuminations for absorption inhomogeneities. The Jacobian for the dual <span class="hlt">source</span> is constructed by an algebraic addition of the Jacobians estimated for the two <span class="hlt">sources</span> separately. By numerical simulations, it is shown that the dual-<span class="hlt">source</span> scheme performs superior to the single-<span class="hlt">source</span> system in regard to (i) <span class="hlt">noise</span> tolerance in data and (ii) ability to reconstruct smaller and lower contrast objects. The quality of reconstructions from single-<span class="hlt">source</span> data, as indicated by mean-square error at convergence, is markedly poorer compared to their dual-<span class="hlt">source</span> counterpart, when <span class="hlt">noise</span> in data was in excess of 2%. With fixed contrast and decreasing inhomogeneity diameter, our simulations showed that, for diameters below 7 mm, the dual-<span class="hlt">source</span> scheme has a higher percentage contrast recovery compared to the single-<span class="hlt">source</span> scheme. Similarly, the dual-<span class="hlt">source</span> scheme reconstructs to a higher percentage contrast recovery from lower contrast inhomogeneity, in comparison to the single-<span class="hlt">source</span> scheme.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040129607','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040129607"><span>Internal Shock Interactions in Propulsion/<span class="hlt">Airframe</span> Integrated Three-Dimensional Sidewall Compression Scramjet Inlets</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Holland, Scott D.; Perkins, John N.</p> <p>1992-01-01</p> <p>The advantages and design requirements of propulsion/<span class="hlt">airframe</span> integration for high Mach number flight have led to extensive study of the three-dimensional sidewall compression scramjet inlet in recent years. Recent research publications have indicated testing over a broad range of Mach number (2 to 18) in a variety of test gases, such as air, helium, and tetrafluoromethane. Multiple experimental techniques have been employed to obtain detailed internal shock interaction data, performance data, and inlet starting limits. Computational fluid dynamics has been effectively used for preliminary parametric studies as well as in parallel with experiments to aid in the explanation of unusual or unexpected flow phenomena. Inlets of this genre afford a relatively simple, generic geometry while producing a highly complex, three-dimensional flow field dominated by shock/shock and shock/boundary layer interactions. While the importance of the viscous effects in high speed inlet interactions is recognized, the present work addresses in a parametric fashion the inviscid effects of leading edge sweep, sidewall compression, and inflow Mach number on the internal shock structure in terms of inlet compression and mass capture. In the process, the <span class="hlt">source</span> of the of the Mach number invariance with leading edge sweep for a constant sidewall compression class of inlet is identified, and a previously undocumented spillage phenomenon in a constant effective wedge angle class of inlets is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040073464','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040073464"><span>A Deconvolution Approach for the Mapping of Acoustic <span class="hlt">Sources</span> (DAMAS) Determined from Phased Microphone Arrays</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Brooks, Thomas F.; Humphreys, William M., Jr.</p> <p>2004-01-01</p> <p>Current processing of acoustic array data is burdened with considerable uncertainty. This study reports an original methodology that serves to demystify array results, reduce misinterpretation, and accurately quantify position and strength of acoustic <span class="hlt">sources</span>. Traditional array results represent <span class="hlt">noise</span> <span class="hlt">sources</span> that are convolved with array beamform response functions, which depend on array geometry, size (with respect to <span class="hlt">source</span> position and distributions), and frequency. The Deconvolution Approach for the Mapping of Acoustic <span class="hlt">Sources</span> (DAMAS) method removes beamforming characteristics from output presentations. A unique linear system of equations accounts for reciprocal influence at different locations over the array survey region. It makes no assumption beyond the traditional processing assumption of statistically independent <span class="hlt">noise</span> <span class="hlt">sources</span>. The full rank equations are solved with a new robust iterative method. DAMAS is quantitatively validated using archival data from a variety of prior high-lift <span class="hlt">airframe</span> component <span class="hlt">noise</span> studies, including flap edge/cove, trailing edge, leading edge, slat, and calibration <span class="hlt">sources</span>. Presentations are explicit and straightforward, as the <span class="hlt">noise</span> radiated from a region of interest is determined by simply summing the mean-squared values over that region. DAMAS can fully replace existing array processing and presentations methodology in most applications. It appears to dramatically increase the value of arrays to the field of experimental acoustics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080015889','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080015889"><span>A Deconvolution Approach for the Mapping of Acoustic <span class="hlt">Sources</span> (DAMAS) Determined from Phased Microphone Arrays</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Brooks, Thomas F.; Humphreys, William M.</p> <p>2006-01-01</p> <p>Current processing of acoustic array data is burdened with considerable uncertainty. This study reports an original methodology that serves to demystify array results, reduce misinterpretation, and accurately quantify position and strength of acoustic <span class="hlt">sources</span>. Traditional array results represent <span class="hlt">noise</span> <span class="hlt">sources</span> that are convolved with array beamform response functions, which depend on array geometry, size (with respect to <span class="hlt">source</span> position and distributions), and frequency. The Deconvolution Approach for the Mapping of Acoustic <span class="hlt">Sources</span> (DAMAS) method removes beamforming characteristics from output presentations. A unique linear system of equations accounts for reciprocal influence at different locations over the array survey region. It makes no assumption beyond the traditional processing assumption of statistically independent <span class="hlt">noise</span> <span class="hlt">sources</span>. The full rank equations are solved with a new robust iterative method. DAMAS is quantitatively validated using archival data from a variety of prior high-lift <span class="hlt">airframe</span> component <span class="hlt">noise</span> studies, including flap edge/cove, trailing edge, leading edge, slat, and calibration <span class="hlt">sources</span>. Presentations are explicit and straightforward, as the <span class="hlt">noise</span> radiated from a region of interest is determined by simply summing the mean-squared values over that region. DAMAS can fully replace existing array processing and presentations methodology in most applications. It appears to dramatically increase the value of arrays to the field of experimental acoustics.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880005380','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880005380"><span>Development of rotorcraft interior <span class="hlt">noise</span> control concepts. Phase 3: Development of <span class="hlt">noise</span> control concepts</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Yoerkie, Charles A.; Gintoli, P. J.; Ingraham, S. T.; Moore, J. A.</p> <p>1986-01-01</p> <p>The goal of this research is the understanding of helicopter internal <span class="hlt">noise</span> mechanisms and the development, design, and testing of <span class="hlt">noise</span> control concepts which will produce significant reductions in the acoustic environment to which passengers are exposed. The Phase 3 effort involved the identification and evaluation of current and advanced treatment concepts, including isolation of structure-borne paths. In addition, a plan was devised for the full-scale evaluation of an isolation concept. Specific objectives were as follows: (1) identification and characterization of various <span class="hlt">noise</span> control concepts; (2) implementation of <span class="hlt">noise</span> control concepts within the S-76 SEA (statistical energy analysis) model; (3) definition and evaluation of a preliminary acoustic isolation design to reduce structure-borne transmission of acoustic frequency main gearbox gear clash vibrations into the <span class="hlt">airframe</span>; (4) formulation of a plan for the full-scale validation of the isolation concept; and (5) prediction of the cabin <span class="hlt">noise</span> environment with various <span class="hlt">noise</span> control concepts installed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20070010603','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20070010603"><span>Low <span class="hlt">Noise</span> Cruise Efficient Short Take-Off and Landing Transport Vehicle Study</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kim, Hyun D.; Berton, Jeffrey J.; Jones, Scott M.</p> <p>2007-01-01</p> <p>The saturation of the airspace around current airports combined with increasingly stringent community <span class="hlt">noise</span> limits represents a serious impediment to growth in world aviation travel. Breakthrough concepts that both increase throughput and reduce <span class="hlt">noise</span> impacts are required to enable growth in aviation markets. Concepts with a 25 year horizon must facilitate a 4x increase in air travel while simultaneously meeting community <span class="hlt">noise</span> constraints. Attacking these horizon issues holistically is the concept study of a Cruise Efficient Short Take-Off and Landing (CESTOL) high subsonic transport under the NASA's Revolutionary Systems Concepts for Aeronautics (RSCA) project. The concept is a high-lift capable <span class="hlt">airframe</span> with a partially embedded distributed propulsion system that takes a synergistic approach in propulsion-<span class="hlt">airframe</span>-integration (PAI) by fully integrating the <span class="hlt">airframe</span> and propulsion systems to achieve the benefits of both low-<span class="hlt">noise</span> short take-off and landing (STOL) operations and efficient high speed cruise. This paper presents a summary of the recent study of a distributed propulsion/<span class="hlt">airframe</span> configuration that provides low-<span class="hlt">noise</span> STOL operation to enable 24-hour use of the untapped regional and city center airports to increase the capacity of the overall airspace while still maintaining efficient high subsonic cruise flight capability.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19840023156','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19840023156"><span>Effect of external pressure environment on the internal <span class="hlt">noise</span> level due to a <span class="hlt">source</span> inside a cylindrical tank</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Clevenson, S. A.; Roussos, L. A.</p> <p>1984-01-01</p> <p>A small cylindrical tank was used to study the effect on the <span class="hlt">noise</span> environment within a tank of conditions of atmospheric (sea level) pressure or vacuum environments on the exterior. Experimentally determined absorption coefficients were used to calculate transmission loss, transmissibility coefficients and the sound pressure (<span class="hlt">noise</span>) level differences in the interior. The <span class="hlt">noise</span> level differences were also measured directly for the two exterior environments and compared to various analytical approximations with limited agreement. Trend study curves indicated that if the tank transmission loss is above 25 dB, the difference in interior <span class="hlt">noise</span> level between the vacuum and ambient pressure conditions are less than 2 dB.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150006713','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150006713"><span>Hybrid Wing Body Shielding Studies Using an Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> Generating Typical Turbofan Modes</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sutliff, Daniel L.; Brown, Cliff; Walker, Bruce E.</p> <p>2014-01-01</p> <p>An Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> (UCFANS) was designed, built, and tested in support of the NASA Langley Research Center's 14x22 wind tunnel test of the Hybrid Wing Body (HWB) full 3-D 5.8% scale model. The UCFANS is a 5.8% rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of proposed engines using artificial <span class="hlt">sources</span> (no flow). The purpose of the test was to provide an estimate of the acoustic shielding benefits possible from mounting the engine on the upper surface of an HWB aircraft using the projected signature of the engine currently proposed for the HWB. The modal structures at the rating points were generated from inlet and exhaust nacelle configurations - a flat plate model was used as the shielding surface and vertical control surfaces with correct plan form shapes were also tested to determine their additional impact on shielding. Radiated acoustic data were acquired from a traversing linear array of 13 microphones, spanning 36 inches. Two planes perpendicular, and two planes parallel, to the axis of the nacelle were acquired from the array sweep. In each plane the linear array traversed 4 sweeps, for a total span of 168 inches acquired. The resolution of the sweep is variable, so that points closer to the model are taken at a higher resolution. Contour plots of Sound Pressure Levels, and integrated Power Levels, from nacelle alone and shielded configurations are presented in this paper; as well as the in-duct mode power levels.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140005372','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140005372"><span>Hybrid Wing Body Shielding Studies Using an Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> Generating Typical Turbofan Modes</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sutliff, Daniel l.; Brown, Clifford A.; Walker, Bruce E.</p> <p>2014-01-01</p> <p>An Ultrasonic Configurable Fan Artificial <span class="hlt">Noise</span> <span class="hlt">Source</span> (UCFANS) was designed, built, and tested in support of the NASA Langley Research Center's 14- by 22-ft wind tunnel test of the Hybrid Wing Body (HWB) full 3-D 5.8 percent scale model. The UCFANS is a 5.8 percent rapid prototype scale model of a high-bypass turbofan engine that can generate the tonal signature of proposed engines using artificial <span class="hlt">sources</span> (no flow). The purpose of the test was to provide an estimate of the acoustic shielding benefits possible from mounting the engine on the upper surface of an HWB aircraft using the projected signature of the engine currently proposed for the HWB. The modal structures at the rating points were generated from inlet and exhaust nacelle configurations--a flat plate model was used as the shielding surface and vertical control surfaces with correct plan form shapes were also tested to determine their additional impact on shielding. Radiated acoustic data were acquired from a traversing linear array of 13 microphones, spanning 36 in. Two planes perpendicular, and two planes parallel, to the axis of the nacelle were acquired from the array sweep. In each plane the linear array traversed four sweeps, for a total span of 168 in. acquired. The resolution of the sweep is variable, so that points closer to the model are taken at a higher resolution. Contour plots of Sound Pressure Levels, and integrated Power Levels, from nacelle alone and shielded configurations are presented in this paper; as well as the in-duct mode power levels</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910004020','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910004020"><span>Calculation of rotor impedance for use in design analysis of helicopter <span class="hlt">airframe</span> vibrations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nygren, Kip P.</p> <p>1990-01-01</p> <p>Excessive vibration is one of the most prevalent technical obstacles encountered in the development of new rotorcraft. The inability to predict these vibrations is primarily due to deficiencies in analysis and simulation tools. The Langley Rotorcraft Structural Dynamics Program was instituted in 1984 to meet long term industry needs in the area of rotorcraft vibration prediction. As a part of the Langley program, this research endeavors to develop an efficient means of coupling the rotor to the <span class="hlt">airframe</span> for preliminary design analysis of helicopter <span class="hlt">airframe</span> vibrations. The main effort was to modify the existing computer program for modeling the dynamic and aerodynamic behavior of rotorcraft called DYSCO (DYnamic System COupler) to calculate the rotor impedance. DYSCO was recently developed for the U.S. Army and has proven to be adaptable for the inclusion of new solution methods. The solution procedure developed to use DYSCO for the calculation of rotor impedance is presented. Verification of the procedure by comparison with a known solution for a simple wind turbine model is about 75 percent completed, and initial results are encouraging. After the wind turbine impedance is confirmed, the verification effort will continue by comparison to solutions of a more sophisticated rotorcraft model. Future work includes determination of the sensitivity of the rotorcraft <span class="hlt">airframe</span> vibrations to helicopter flight conditions and rotor modeling assumptions. When completed, this research will ascertain the feasibility and efficiency of the impedance matching method of rotor-<span class="hlt">airframe</span> coupling for use in the analysis of <span class="hlt">airframe</span> vibrations during the preliminary rotorcraft design process.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19277078','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19277078"><span>Phase <span class="hlt">noise</span> optimization in temporal phase-shifting digital holography with partial coherence light <span class="hlt">sources</span> and its application in quantitative cell imaging.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Remmersmann, Christian; Stürwald, Stephan; Kemper, Björn; Langehanenberg, Patrik; von Bally, Gert</p> <p>2009-03-10</p> <p>In temporal phase-shifting-based digital holographic microscopy, high-resolution phase contrast imaging requires optimized conditions for hologram recording and phase retrieval. To optimize the phase resolution, for the example of a variable three-step algorithm, a theoretical analysis on statistical errors, digitalization errors, uncorrelated errors, and errors due to a misaligned temporal phase shift is carried out. In a second step the theoretically predicted results are compared to the measured phase <span class="hlt">noise</span> obtained from comparative experimental investigations with several coherent and partially coherent light <span class="hlt">sources</span>. Finally, the applicability for <span class="hlt">noise</span> reduction is demonstrated by quantitative phase contrast imaging of pancreas tumor cells.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009JOptA..11j3001Q','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009JOptA..11j3001Q"><span>REVIEW ARTICLE: Harmonically mode-locked semiconductor-based lasers as high repetition rate ultralow <span class="hlt">noise</span> pulse train and optical frequency comb <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Quinlan, F.; Ozharar, S.; Gee, S.; Delfyett, P. J.</p> <p>2009-10-01</p> <p>Recent experimental work on semiconductor-based harmonically mode-locked lasers geared toward low <span class="hlt">noise</span> applications is reviewed. Active, harmonic mode-locking of semiconductor-based lasers has proven to be an excellent way to generate 10 GHz repetition rate pulse trains with pulse-to-pulse timing jitter of only a few femtoseconds without requiring active feedback stabilization. This level of timing jitter is achieved in long fiberized ring cavities and relies upon such factors as low <span class="hlt">noise</span> rf <span class="hlt">sources</span> as mode-lockers, high optical power, intracavity dispersion management and intracavity phase modulation. When a high finesse etalon is placed within the optical cavity, semiconductor-based harmonically mode-locked lasers can be used as optical frequency comb <span class="hlt">sources</span> with 10 GHz mode spacing. When active mode-locking is replaced with regenerative mode-locking, a completely self-contained comb <span class="hlt">source</span> is created, referenced to the intracavity etalon.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19860035113&hterms=sound+temperature&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dsound%2Btemperature','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19860035113&hterms=sound+temperature&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dsound%2Btemperature"><span>Laboratory study of the effects of sidewall treatment, <span class="hlt">source</span> directivity and temperature on the interior <span class="hlt">noise</span> of a light aircraft fuselage</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Heitman, K. E.; Mixson, J. S.</p> <p>1986-01-01</p> <p>This paper describes a laboratory study of add-on {coustic treatments for a twin-engine, propeller-driven aircraft fuselage. The sound <span class="hlt">source</span> was a pneumatic-driver, with attached horn to simulate propeller <span class="hlt">noise</span> distribution, powered by a white <span class="hlt">noise</span> signal. Treatments included a double-wall, production-line treatment and various fiberglass and lead-vinyl treatments. Insertion losses, space-averaged across six interior microphone positions, were used to evaluate the treatments. In addition, the effects of sound <span class="hlt">source</span> angle and ambient temperature on interior sound pressure level are presented. The sound <span class="hlt">source</span> angle is shown to have a significant effect on one-third octave band localized sound pressure level. While changes in ambient temperature are shown to have little effect on one-third octave band localized sound pressure level, the change in narrowband localized sound pressure level may be dramatic.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/977119','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/977119"><span>Transcriptional Bursting from the HIV-1 Promoter is a Significant <span class="hlt">Source</span> of Stochastic <span class="hlt">Noise</span> in HIV-1 Gene Expression</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Singh, A; Razooky, B; Cox, Chris D.; Simpson, Michael L; Weinberger, Leor S.</p> <p>2010-01-01</p> <p>Analysis of <span class="hlt">noise</span> in gene expression has proven a powerful approach for analyzing gene regulatory architecture. To probe the regulatory mechanisms controlling expression of HIV-1, we analyze <span class="hlt">noise</span> in gene-expression from HIV-1 s long terminal repeat (LTR) promoter at different HIV-1 integration sites across the human genome. Flow cytometry analysis of GFP expression from the HIV-1 LTR shows high variability (<span class="hlt">noise</span>) at each integration site. Notably, the measured <span class="hlt">noise</span> levels are inconsistent with constitutive gene expression models. Instead, quantification of expression <span class="hlt">noise</span> indicates that HIV-1 gene expression occurs through randomly timed bursts of activity from the LTR and that each burst generates an average of 2 10 mRNA transcripts before the promoter returns to an inactive state. These data indicate that transcriptional bursting can generate high variability in HIV-1 early gene products, which may critically influence the viral fate-decision between active replication and proviral latency.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150000893','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150000893"><span>Experiments on Exhaust <span class="hlt">Noise</span> of Tightly Integrated Propulsion Systems</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bridges, James E.; Brown, Clifford A.; Bozak, Richard F.</p> <p>2014-01-01</p> <p>A wide-ranging series of tests have been completed that seek to map the effects of installation, including jet by jet interaction effects, on exhaust <span class="hlt">noise</span> from various nozzles in forward flight. The primary data was far-field acoustic spectral directivity. The goals of the test series were (i) to generate enough data for empirical models of the different effects, and (ii) to provide data for advanced computational <span class="hlt">noise</span> predictions methods applied to simplified yet realistic configurations. Data is presented that demonstrate several checks on data quality and that provide an overview of trends observed to date. Among the findings presented here: (i) Data was repeatable between jet rigs for single nozzles with and without surfaces to within +/- 0.5 dB. (ii) The presence of a second jet caused a strong reduction of the summed <span class="hlt">noise</span> in the plane of the two plumes and an increase over the expected <span class="hlt">source</span> doubling in most other azimuthal planes. (iii) The impact of the second jet was reduced when the jets were unheated. (iv) The impact of adding a second isolated rectangular jet was relatively independent of the nozzle aspect ratio up to aspect ratio 8:1. (v) Forward flight had similar impact on a high aspect ratio (8:1) jet as on an axisymmetric jet, except at the peak <span class="hlt">noise</span> angle where the impact was less. (vi) The effect of adding a second round jet to a tightly integrated nozzle where the nozzle lip was less than a diameter from the surface was very dependent upon the length of the surface downstream of the nozzle. (vii) When the nozzles were rectangular and tightly integrated with the <span class="hlt">airframe</span> surface the impact of a second jet was very dependent upon how close together the two jets were. This paper serves as an overview of the test; other papers presented in the same conference will give more detailed analysis of the results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/174678','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/174678"><span>Inductively coupled plasma spectrometry: <span class="hlt">Noise</span> characteristics of aerosols, application of generalized standard additions method, and Mach disk as an emission <span class="hlt">source</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Luan, Shen</p> <p>1995-10-06</p> <p>This dissertation is focused on three problem areas in the performance of inductively coupled plasma (ICP) <span class="hlt">source</span>. The <span class="hlt">noise</span> characteristics of aerosols produced by ICP nebulizers are investigated. A laser beam is scattered by aerosol and detected by a photomultiplier tube and the <span class="hlt">noise</span> amplitude spectrum of the scattered radiation is measured by a spectrum analyzer. Discrete frequency <span class="hlt">noise</span> in the aerosol generated by a Meinhard nebulizer or a direct injection nebulizer is primarily caused by pulsation in the liquid flow from the pump. A Scott-type spray chamber suppresses white <span class="hlt">noise</span>, while a conical, straight-pass spray chamber enhances white <span class="hlt">noise</span>, relative to the <span class="hlt">noise</span> seen from the primary aerosol. Simultaneous correction for both spectral interferences and matrix effects in ICP atomic emission spectrometry (AES) can be accomplished by using the generalized standard additions method (GSAM). Results obtained with the application of the GSAM to the Perkin-Elmer Optima 3000 ICP atomic emission spectrometer are presented. The echelle-based polychromator with segmented-array charge-coupled device detectors enables the direct, visual examination of the overlapping lines Cd (1) 228.802 nm and As (1) 228.812 nm. The slit translation capability allows a large number of data points to be sampled, therefore, the advantage of <span class="hlt">noise</span> averaging is gained. An ICP is extracted into a small quartz vacuum chamber through a sampling orifice in a water-cooled copper plate. Optical emission from the Mach disk region is measured with a new type of echelle spectrometer equipped with two segmented-array charge-coupled-device detectors, with an effort to improve the detection limits for simultaneous multielement analysis by ICP-AES.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040086735','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040086735"><span>Microstructural and Mechanical Characterization of Shear Formed Aluminum Alloys for <span class="hlt">Airframe</span> and Space Applications</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Troeger, L. P.; Domack, M. S.; Wagner, J. A.</p> <p>1998-01-01</p> <p>Advanced manufacturing processes such as near-net-shape forming can reduce production costs and increase the reliability of launch vehicle and <span class="hlt">airframe</span> structural components through the reduction of material scrap and part count and the minimization of joints. The current research is an investigation of the processing-microstructure-property relationship for shear formed cylinders of the Al-Cu-Li-Mg-Ag alloy 2195 for space applications and the Al-Cu-Mg-Ag alloy C415 for <span class="hlt">airframe</span> applications. Cylinders which have undergone various amounts of shear-forming strain have been studied to assess the microstructure and mechanical properties developed during and after shear forming.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADB073386','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADB073386"><span>ICAM Manufacturing Cost/Design Guide. Volume 3. <span class="hlt">Airframes</span>. User’s Manual.</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1983-01-01</p> <p>PER MATERIAL CUBIC INCH POUND ALUMINUM 705F -T6 -T652 r-T7352 TITANIUM 0.16 $30Ti6AI-4V LOW ALLOY STEEL 0.28 $3 4340 PH CRES $0.28 $7 15 - 5PH FIGURE...DG ...... ................ ... 3-3 3.3 Utilization of Learning Curve . . . . . . . . . 3-6 3.4 Cost Worksheet for <span class="hlt">Airframe</span> Designers ...... 3-9 3.4.1...for <span class="hlt">Airframe</span> Assemblies . 4.2- 15 4.2.5 Ground Rules for Mechanically Fastened Assembly Section .............. 4.2-27 4.2.5.1 General Ground Rules</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21476618','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21476618"><span><span class="hlt">Airframe</span> structural damage detection: a non-linear structural surface intensity based technique.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Semperlotti, Fabio; Conlon, Stephen C; Barnard, Andrew R</p> <p>2011-04-01</p> <p>The non-linear structural surface intensity (NSSI) based damage detection technique is extended to <span class="hlt">airframe</span> applications. The selected test structure is an upper cabin <span class="hlt">airframe</span> section from a UH-60 Blackhawk helicopter (Sikorsky Aircraft, Stratford, CT). Structural damage is simulated through an impact resonator device, designed to simulate the induced vibration effects typical of non-linear behaving damage. An experimental study is conducted to prove the applicability of NSSI on complex mechanical systems as well as to evaluate the minimum sensor and actuator requirements. The NSSI technique is shown to have high damage detection sensitivity, covering an extended substructure with a single sensing location.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19860005829','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19860005829"><span>An examination of the relations between rotor vibratory loads and <span class="hlt">airframe</span> vibrations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Niebanck, C. F.</p> <p>1985-01-01</p> <p>Harmonic rotor hub loads and <span class="hlt">airframe</span> interactions in steady flight are reviewed, with regard to the objective of achieving lower <span class="hlt">airframe</span> vibration by modifying blade root loads. Flight test and wind tunnel data are reviewed, along with sample fuselage response data. Trends which could provide a generalized approach to the above objective are found to be very limited. Recent analytical and corresponding experimental blade tuning modifications are reviewed and compared. Rotor vibratory load modification and substantial vibration changes were achieved over a wide range of rotor operating conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015jsrs.conf...100','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015jsrs.conf...100"><span>Phobos mass estimations from MEX and Viking 1 data: influence of different <span class="hlt">noise</span> <span class="hlt">sources</span> and estimation strategies</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kudryashova, M.; Rosenblatt, P.; Marty, J.-C.</p> <p>2015-08-01</p> <p>The mass of Phobos is an important parameter which, together with second-order gravity field coefficients and libration amplitude, constrains internal structure and nature of the moon. And thus, it needs to be known with high precision. Nevertheless, Phobos mass (GM, more precisely) estimated by different authors based on diverse data-sets and methods, varies by more than their 1-sigma error. The most complete lists of GM values are presented in the works of R. Jacobson (2010) and M. Paetzold et al. (2014) and include the estimations in the interval from (5.39 ± 0:03).10^5 (Smith et al., 1995) till (8.5 ± 0.7).10^5[m^3/s^2] (Williams et al., 1988). Furthermore, even the comparison of the estimations coming from the same estimation procedure applied to the consecutive flybys of the same spacecraft (s/c) shows big variations in GMs. The indicated behavior is very pronounced in the GM estimations stemming from the Viking1 flybys in February 1977 (as well as from MEX flybys, though in a smaller amplitude) and in this work we made an attempt to figure out its roots. The errors of Phobos GM estimations depend on the precision of the model (e.g. accuracy of Phobos a priori ephemeris and its a priori GM value) as well as on the radio-tracking measurements quality (<span class="hlt">noise</span>, coverage, flyby distance). In the present work we are testing the impact of mentioned above error <span class="hlt">sources</span> by means of simulations. We also consider the effect of the uncertainties in a priori Phobos positions on the GM estimations from real observations. Apparently, the strategy (i.e. splitting real observations in data-arcs, whether they stem from the close approaches of Phobos by spacecraft or from analysis of the s/c orbit evolution around Mars) of the estimations has an impact on the Phobos GM estimation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/6219178','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6219178"><span>A portable measurement system for subcriticality measurements by the CF-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mihalczo, J.T.; Ragan, G.E.</p> <p>1987-01-01</p> <p>A portable system has been assembled that is capable of measuring the subcriticality of fissile materials using the /sup 252/CF-<span class="hlt">source</span>-driven neutron <span class="hlt">noise</span> analysis method. The measurement system consists of a parallel-plate ionization chamber containing /sup 252/CF, two /sup 3/He proportional counters with their associated electronics, and a small computer containing anti-aliasing filters and A/D convertors. The system Fourier analyzes the digitized data and forms the appropriate auto and cross-power spectral densities. These spectra are used to form a ratio of spectral densities, G/sub 12/G/sub 13//G/sub 11/G/sub 23/, where 1 refers to the ionization chamber, and 2 and 3 refer to the /sup 3/He counters, from which subcriticality can be determined. The chamber and detectors are located appropriately near the fissile material. The system is capable of sampling signals at rates of up to 80 kHz and processing these data at rates of 2 kHz to form the appropriate spectra. The presently configured system is a two-channel system, hence the measurement of G/sub 12/, G/sub 13/, and G/sub 23/ must be done sequentially before the ratio of spectral densities is obtained. Future improvements of the system will allow simultaneous measurement of all spectra and will further reduce size, thereby enhancing portability. This measurement system can provide reliable, cost effective, and convenient determination of the subcriticality of a wide variety of fissile materials and moderators.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26950131','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26950131"><span>A Low-<span class="hlt">Noise</span> CMOS THz Imager Based on <span class="hlt">Source</span> Modulation and an In-Pixel High-Q Passive Switched-Capacitor N-Path Filter.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Boukhayma, Assim; Dupret, Antoine; Rostaing, Jean-Pierre; Enz, Christian</p> <p>2016-03-03</p> <p>This paper presents the first low <span class="hlt">noise</span> complementary metal oxide semiconductor (CMOS) deletedCMOS terahertz (THz) imager based on <span class="hlt">source</span> modulation and in-pixel high-Q filtering. The 31 × 31 focal plane array has been fully integrated in a 0 . 13 μ m standard CMOS process. The sensitivity has been improved significantly by modulating the active THz <span class="hlt">source</span> that lights the scene and performing on-chip high-Q filtering. Each pixel encompass a broadband bow tie antenna coupled to an N-type metal-oxide-semiconductor (NMOS) detector that shifts the THz radiation, a low <span class="hlt">noise</span> adjustable gain amplifier and a high-Q filter centered at the modulation frequency. The filter is based on a passive switched-capacitor (SC) N-path filter combined with a continuous-time broad-band Gm-C filter. A simplified analysis that helps in designing and tuning the passive SC N-path filter is provided. The characterization of the readout chain shows that a Q factor of 100 has been achieved for the filter with a good matching between the analytical calculation and the measurement results. An input-referred <span class="hlt">noise</span> of 0 . 2 μ V RMS has been measured. Characterization of the chip with different THz wavelengths confirms the broadband feature of the antenna and shows that this THz imager reaches a total <span class="hlt">noise</span> equivalent power of 0 . 6 nW at 270 GHz and 0 . 8 nW at 600 GHz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20090035729','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20090035729"><span>Separation of Main and Tail Rotor <span class="hlt">Noise</span> <span class="hlt">Sources</span> from Ground-Based Acoustic Measurements Using Time-Domain De-Dopplerization</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Greenwood, Eric II; Schmitz, Fredric H.</p> <p>2009-01-01</p> <p>A new method of separating the contributions of helicopter main and tail rotor <span class="hlt">noise</span> <span class="hlt">sources</span> is presented, making use of ground-based acoustic measurements. The method employs time-domain de-Dopplerization to transform the acoustic pressure time-history data collected from an array of ground-based microphones to the equivalent time-history signals observed by an array of virtual inflight microphones traveling with the helicopter. The now-stationary signals observed by the virtual microphones are then periodically averaged with the main and tail rotor once per revolution triggers. The averaging process suppresses <span class="hlt">noise</span> which is not periodic with the respective rotor, allowing for the separation of main and tail rotor pressure time-histories. The averaged measurements are then interpolated across the range of directivity angles captured by the microphone array in order to generate separate acoustic hemispheres for the main and tail rotor <span class="hlt">noise</span> <span class="hlt">sources</span>. The new method is successfully applied to ground-based microphone measurements of a Bell 206B3 helicopter and demonstrates the strong directivity characteristics of harmonic <span class="hlt">noise</span> radiation from both the main and tail rotors of that helicopter.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_24 --> <div id="page_25" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="481"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880013482','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880013482"><span>Propulsion and <span class="hlt">airframe</span> aerodynamic interactions of supersonic V/STOL configurations. Volume 1: Wind tunnel test pressure data report</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zilz, D. E.; Devereaux, P. A.</p> <p>1985-01-01</p> <p>A wind tunnel model of a supersonic V/STOL fighter configuration has been tested to measure the aerodynamic interaction effects which can result from geometrically close-coupled propulsion system/<span class="hlt">airframe</span> components. The approach was to configure the model to represent two different test techniques. One was a conventional test technique composed of two test modes. In the Flow-Through mode, absolute configuration aerodynamics are measured, including inlet/<span class="hlt">airframe</span> interactions. In the Jet-Effects mode, incremental nozzle/<span class="hlt">airframe</span> interactions are measured. The other test technique is a propulsion simulator approach, where a sub-scale, externally powered engine is mounted in the model. This allows proper measurement of inlet/<span class="hlt">airframe</span> and nozzle/<span class="hlt">airframe</span> interactions simultaneously. This is Volume 1 of 2: Wind Tunnel Test Pressure Data Report.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JOpt...18b5601M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JOpt...18b5601M"><span>Analysis of SNR penalty in Brillouin optical time-domain analysis sensors induced by laser <span class="hlt">source</span> phase <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Minardo, A.; Bernini, R.; Zeni, L.</p> <p>2016-02-01</p> <p>In this paper, we analyze numerically the effect of phase <span class="hlt">noise</span> from the laser in Brillouin optical time-domain analysis (BOTDA) sensors. Due to laser phase <span class="hlt">noise</span>, the phase shift between pump and probe beams is a stochastic variable with zero mean and variance changing with the position along the fiber. The numerical results, carried out for various fiber lengths and pump pulse durations, show that laser phase <span class="hlt">noise</span> induces a reduction of the average Brillouin gain, as well as an increase of the overall system <span class="hlt">noise</span>. Preliminary experimental results, carried out by use of a conventional BOTDA system and two DFB diode lasers having different linewidth (63 and 900 kHz), support the numerical analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160009106','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160009106"><span>Modeling and Prediction of Krueger Device <span class="hlt">Noise</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Guo, Yueping; Burley, Casey L.; Thomas, Russell H.</p> <p>2016-01-01</p> <p>This paper presents the development of a <span class="hlt">noise</span> prediction model for aircraft Krueger flap devices that are considered as alternatives to leading edge slotted slats. The prediction model decomposes the total Krueger <span class="hlt">noise</span> into four components, generated by the unsteady flows, respectively, in the cove under the pressure side surface of the Krueger, in the gap between the Krueger trailing edge and the main wing, around the brackets supporting the Krueger device, and around the cavity on the lower side of the main wing. For each <span class="hlt">noise</span> component, the modeling follows a physics-based approach that aims at capturing the dominant <span class="hlt">noise</span>-generating features in the flow and developing correlations between the <span class="hlt">noise</span> and the flow parameters that control the <span class="hlt">noise</span> generation processes. The far field <span class="hlt">noise</span> is modeled using each of the four <span class="hlt">noise</span> component's respective spectral functions, far field directivities, Mach number dependencies, component amplitudes, and other parametric trends. Preliminary validations are carried out by using small scale experimental data, and two applications are discussed; one for conventional aircraft and the other for advanced configurations. The former focuses on the parametric trends of Krueger <span class="hlt">noise</span> on design parameters, while the latter reveals its importance in relation to other <span class="hlt">airframe</span> <span class="hlt">noise</span> components.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011JSV...330.4180S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011JSV...330.4180S"><span>Initial <span class="hlt">noise</span> predictions for rudimentary landing gear</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Spalart, Philippe R.; Shur, Mikhail L.; Strelets, Mikhail Kh.; Travin, Andrey K.</p> <p>2011-08-01</p> <p>A four-wheel "rudimentary" landing gear (RLG) truck was designed for public-domain research, with a level of complexity which is manageable in current numerical simulations, and a weak Reynolds-number sensitivity. Experimental measurements of wall-pressure fluctuations are allowing a meaningful test of unsteady simulations with emphasis on <span class="hlt">noise</span> generation. We present three Detached-Eddy Simulations (DES) using up to 18 million points in the high-order NTS code. The first is incompressible with the model placed in the wind tunnel, as requested for the 2010 workshop on Benchmark problems for <span class="hlt">Airframe</span> <span class="hlt">Noise</span> Computations (BANC-I), intended for force and surface-pressure studies. The second and third are at Mach 0.115 and Mach 0.23, with only one wall, a "ceiling" analogous to a wing (but infinite and inviscid), and are used to exercise far-field <span class="hlt">noise</span> prediction by coupling the Detached-Eddy Simulations and a Ffowcs-Williams/Hawkings calculation. The results include wall-pressure, and far-field-<span class="hlt">noise</span> intensities and spectra. The wall pressure signals in the three simulations are very similar and, in a comparison published separately, agree well with experiment and other simulations. In the absence of experimental <span class="hlt">noise</span> data, the attention is focused on internal quality checks, by varying the permeable Ffowcs-Williams/Hawkings calculation surface and then by using only the solid surface. An unexpected finding at these Mach numbers is an apparent strong role for quadrupoles, revealed by a typical deficit of 3 dB in the solid-surface results, relative to the permeable-surface results. The solid-surface approach has variants, related to the presence of the ceiling (a plane of symmetry), which can increase this error further; there is little consensus on the exact configuration of the solid surfaces in the Ffowcs-Williams/Hawkings calculation procedure. Tentative theoretical arguments suggest that a balance somewhat in favor of quadrupoles over dipoles is plausible at Mach</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140010022','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140010022"><span>Aerodynamic Measurements of a Gulfstream Aircraft Model With and Without <span class="hlt">Noise</span> Reduction Concepts</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Neuhart, Dan H.; Hannon, Judith A.; Khorrami, Mehdi R.</p> <p>2014-01-01</p> <p>Steady and unsteady aerodynamic measurements of a high-fidelity, semi-span 18% scale Gulfstream aircraft model are presented. The aerodynamic data were collected concurrently with acoustic measurements as part of a larger aeroacoustic study targeting <span class="hlt">airframe</span> <span class="hlt">noise</span> associated with main landing gear/flap components, gear-flap interaction <span class="hlt">noise</span>, and the viability of related <span class="hlt">noise</span> mitigation technologies. The aeroacoustic tests were conducted in the NASA Langley Research Center 14- by 22-Foot Subsonic Wind Tunnel with the facility in the acoustically treated open-wall (jet) mode. Most of the measurements were obtained with the model in landing configuration with the flap deflected at 39º and the main landing gear on and off. Data were acquired at Mach numbers of 0.16, 0.20, and 0.24. Global forces (lift and drag) and extensive steady and unsteady surface pressure measurements were obtained. Comparison of the present results with those acquired during a previous test shows a significant reduction in the lift experienced by the model. The underlying cause was traced to the likely presence of a much thicker boundary layer on the tunnel floor, which was acoustically treated for the present test. The steady and unsteady pressure fields on the flap, particularly in the regions of predominant <span class="hlt">noise</span> <span class="hlt">sources</span> such as the inboard and outboard tips, remained unaffected. It is shown that the changes in lift and drag coefficients for model configurations fitted with gear/flap <span class="hlt">noise</span> abatement technologies fall within the repeatability of the baseline configuration. Therefore, the <span class="hlt">noise</span> abatement technologies evaluated in this experiment have no detrimental impact on the aerodynamic performance of the aircraft model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160006501','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160006501"><span>Overview of the Transport Rotorcraft <span class="hlt">Airframe</span> Crash Testbed (TRACT) Full Scale Crash Tests</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Annett, Martin; Littell, Justin</p> <p>2015-01-01</p> <p>The Transport Rotorcraft <span class="hlt">Airframe</span> Crash Testbed (TRACT) full-scale tests were performed at NASA Langley Research Center's Landing and Impact Research Facility in 2013 and 2014. Two CH-46E <span class="hlt">airframes</span> were impacted at 33-ft/s forward and 25-ft/s vertical combined velocities onto soft soil, which represents a severe, but potentially survivable impact scenario. TRACT 1 provided a baseline set of responses, while TRACT 2 included retrofits with composite subfloors and other crash system improvements based on TRACT 1. For TRACT 2, a total of 18 unique experiments were conducted to evaluate Anthropomorphic Test Devices (ATD) responses, seat and restraint performance, cargo restraint effectiveness, patient litter behavior, and activation of emergency locator transmitters and crash sensors. Combinations of Hybrid II, Hybrid III, and ES-2 ATDs were placed in forward and side facing seats and occupant results were compared against injury criteria. The structural response of the <span class="hlt">airframe</span> was assessed based on accelerometers located throughout the <span class="hlt">airframe</span> and using three-dimensional photogrammetric techniques. Analysis of the photogrammetric data indicated regions of maximum deflection and permanent deformation. The response of TRACT 2 was noticeably different in the horizontal direction due to changes in the cabin configuration and soil surface, with higher acceleration and damage occurring in the cabin. Loads from ATDs in energy absorbing seats and restraints were within injury limits. Severe injury was likely for ATDs in forward facing passenger seats.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://files.eric.ed.gov/fulltext/ED222762.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/ED222762.pdf"><span><span class="hlt">Airframe</span> Repair Specialist, 2-3. Military Curriculum Materials for Vocational and Technical Education.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Ohio State Univ., Columbus. National Center for Research in Vocational Education.</p> <p></p> <p>These military-developed curriculum materials consist of five volumes of individualized, self-paced training manuals for use by those studying to be <span class="hlt">airframe</span> repair technicians. Covered in the individual volumes are the following topics: fundamentals of organization and management (ground safety, aircraft ground safety, and aerospace and power…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19720010361','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19720010361"><span>Design of a convective cooling system for a Mach 6 hypersonic transport <span class="hlt">airframe</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Helenbrook, R. G.; Anthony, F. M.</p> <p>1971-01-01</p> <p>Results of analytical and design studies are presented for a water-glycol convective cooling system for the <span class="hlt">airframe</span> structure of a hypersonic transport. System configurations and weights are compared. The influences of system pressure drop and flow control schedules on system weight are defined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160005922','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160005922"><span>Evaluation of the Second Transport Rotorcraft <span class="hlt">Airframe</span> Crash Testbed (TRACT 2) Full Scale Crash Test</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Annett, Martin; Littell, Justin</p> <p>2015-01-01</p> <p>Two Transport Rotorcraft <span class="hlt">Airframe</span> Crash Testbed (TRACT) full-scale tests were performed at NASA Langley Research Center's Landing and Impact Research Facility in 2013 and 2014. Two CH-46E <span class="hlt">airframes</span> were impacted at 33-ft/s forward and 25-ft/s vertical combined velocities onto soft soil, which represents a severe, but potentially survivable impact scenario. TRACT 1 provided a baseline set of responses, while TRACT 2 included retrofits with composite subfloors and other crash system improvements based on TRACT 1. For TRACT 2, a total of 18 unique experiments were conducted to evaluate ATD responses, seat and restraint performance, cargo restraint effectiveness, patient litter behavior, and activation of emergency locator transmitters and crash sensors. Combinations of Hybrid II, Hybrid III, and ES-2 Anthropomorphic Test Devices (ATDs) were placed in forward and side facing seats and occupant results were compared against injury criteria. The structural response of the <span class="hlt">airframe</span> was assessed based on accelerometers located throughout the <span class="hlt">airframe</span> and using three-dimensional photogrammetric techniques. Analysis of the photogrammetric data indicated regions of maximum deflection and permanent deformation. The response of TRACT 2 was noticeably different in the longitudinal direction due to changes in the cabin configuration and soil surface, with higher acceleration and damage occurring in the cabin. Loads from ATDs in energy absorbing seats and restraints were within injury limits. Severe injury was likely for ATDs in forward facing passenger seats.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=trim&pg=6&id=ED302631','ERIC'); return false;" href="http://eric.ed.gov/?q=trim&pg=6&id=ED302631"><span>Aviation Maintenance Technology. <span class="hlt">Airframe</span>. A203. Aircraft Fabric Covering, Painting, and Finishing. Instructor Material.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Oklahoma State Board of Vocational and Technical Education, Stillwater. Curriculum and Instructional Materials Center.</p> <p></p> <p>This teacher's guide is designed to aid teachers in leading students through a module on <span class="hlt">airframe</span> building and repair, including fabric covering, painting, and finishing. The module contains two units that cover the following topics: (1) inspecting, testing, and installing aircraft fabric coverings and (2) applying dope, paint, and trim. Each unit…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002PhDT.......109H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002PhDT.......109H"><span>Optimal actuator placement and active structure design for control of helicopter <span class="hlt">airframe</span> vibrations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Heverly, David Ellsworth, II</p> <p></p> <p>A comprehensive research program on active control of rotorcraft <span class="hlt">airframe</span> vibration is detailed in this thesis. A systematic design methodology, to realize an active vibration control system, is proposed and studied. The methodology is a four-part design cycle and relies heavily on numerical computation, modeling, and analysis. The various analytical tools, models, and processes required to execute the methodology are described. Two dynamic models of the helicopter <span class="hlt">airframe</span> and an optimization procedure for actuator placement are utilized within the methodology. The optimization procedure simultaneously determines the type of actuation, the locations to apply actuation, and the corresponding active control actions. A feasibility study is conducted to examine the effectiveness of helicopter vibration control by distributing actuators at optimal locations within the <span class="hlt">airframe</span>, rather than confining actuation to a centralized region. Results indicate that distributed actuation is capable of greater vibration suppression and requires less control effort than a centralized actuation configuration. An analytical and experimental investigation is conducted on a scaled model of a helicopter tailboom. The scaled tailboom model is used to study the actuation design and realization issues associated with integrating dual-point actuation into a semi-monocoque <span class="hlt">airframe</span> structure. A piezoelectric stack actuator configuration is designed and installed within the tailboom model. Experimental tests indicate the stack actuator configuration is able to produce a bending moment within the structure to suppress vibration without causing excessive localized stress in the structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016LaPhL..13b5101Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016LaPhL..13b5101Y"><span>Ultrahigh-resolution optical coherence tomography at 1.3 μm central wavelength by using a supercontinuum <span class="hlt">source</span> pumped by <span class="hlt">noise</span>-like pulses</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>You, Yi-Jing; Wang, Chengming; Lin, Yi-Lun; Zaytsev, Alexey; Xue, Ping; Pan, Ci-Ling</p> <p>2016-02-01</p> <p>We report on the ultrahigh-resolution optical coherence tomography (OCT) with a novel high-power supercontinuum (SC) light <span class="hlt">source</span> generated by <span class="hlt">noise</span>-like pulses from an Yb-doped fiber laser. The SC spectrum is flat with a bandwidth of 420 nm centered around ~1.3 μm. The light <span class="hlt">source</span> is successfully employed in a time-domain OCT (TD-OCT), achieving an axial resolution of 2.3 μm. High resolution fiber-based spectral-domain OCT (SD-OCT) imaging of bio-tissue was also demonstrated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920023704','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920023704"><span>Fourth Aircraft Interior <span class="hlt">Noise</span> Workshop</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Stephens, David G. (Compiler)</p> <p>1992-01-01</p> <p>The fourth in a series of NASA/SAE Interior <span class="hlt">Noise</span> Workshops was held on May 19 and 20, 1992. The theme of the workshop was new technology and applications for aircraft <span class="hlt">noise</span> with emphasis on <span class="hlt">source</span> <span class="hlt">noise</span> prediction; cabin <span class="hlt">noise</span> prediction; cabin <span class="hlt">noise</span> control, including active and passive methods; and cabin interior <span class="hlt">noise</span> procedures. This report is a compilation of the presentations made at the meeting which addressed the above issues.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26831958','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26831958"><span>Ultra-compact Watt-level flat supercontinuum <span class="hlt">source</span> pumped by <span class="hlt">noise</span>-like pulse from an all-fiber oscillator.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chen, He; Zhou, Xuanfeng; Chen, Sheng-Ping; Jiang, Zong-Fu; Hou, Jing</p> <p>2015-12-28</p> <p>We demonstrate Watt-level flat visible supercontinuum (SC) generation in photonic crystal fibers, which is directly pumped by broadband <span class="hlt">noise</span>-like pulses from an Yb-doped all-fiber oscillator. The novel SC generator is featured with elegant all-fiber-integrated architecture, high spectral flatness and high efficiency. Wide optical spectrum spanning from 500 nm to 2300 nm with 1.02 W optical power is obtained under the pump of 1.4 W <span class="hlt">noise</span>-like pulse. The flatness of the spectrum in the range of 700 nm~1600 nm is less than 5 dB (including the pump residue). The exceptional simplicity, economical efficiency and the comparable performances make the <span class="hlt">noise</span>-like pulse oscillator a competitive candidate to the widely used cascade amplified coherent pulse as the pump <span class="hlt">source</span> of broadband SC. To the best of our knowledge, this is the first demonstration of SC generation which is directly pumped by an all-fiber <span class="hlt">noise</span>-like pulse oscillator.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhDT........59F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhDT........59F"><span>West Texas array experiment: <span class="hlt">Noise</span> and <span class="hlt">source</span> characterization of short-range infrasound and acoustic signals, along with lab and field evaluation of Intermountain Laboratories infrasound microphones</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fisher, Aileen</p> <p></p> <p>The term infrasound describes atmospheric sound waves with frequencies below 20 Hz, while acoustics are classified within the audible range of 20 Hz to 20 kHz. Infrasound and acoustic monitoring in the scientific community is hampered by low signal-to-<span class="hlt">noise</span> ratios and a limited number of studies on regional and short-range <span class="hlt">noise</span> and <span class="hlt">source</span> characterization. The JASON Report (2005) suggests the infrasound community focus on more broad-frequency, observational studies within a tactical distance of 10 km. In keeping with that recommendation, this paper presents a study of regional and short-range atmospheric acoustic and infrasonic <span class="hlt">noise</span> characterization, at a desert site in West Texas, covering a broad frequency range of 0.2 to 100 Hz. To spatially sample the band, a large number of infrasound gauges was needed. A laboratory instrument analysis is presented of the set of low-cost infrasound sensors used in this study, manufactured by Inter-Mountain Laboratories (IML). Analysis includes spectra, transfer functions and coherences to assess the stability and range of the gauges, and complements additional instrument testing by Sandia National Laboratories. The IMLs documented here have been found reliably coherent from 0.1 to 7 Hz without instrument correction. Corrections were built using corresponding time series from the commercially available and more expensive Chaparral infrasound gauge, so that the corrected IML outputs were able to closely mimic the Chaparral output. Arrays of gauges are needed for atmospheric sound signal processing. Our West Texas experiment consisted of a 1.5 km aperture, 23-gauge infrasound/acoustic array of IMLs, with a compact, 12 m diameter grid-array of rented IMLs at the center. To optimize signal recording, signal-to-<span class="hlt">noise</span> ratio needs to be quantified with respect to both frequency band and coherence length. The higher-frequency grid array consisted of 25 microphones arranged in a five by five pattern with 3 meter spacing, without</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140000601','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140000601"><span>On <span class="hlt">Noise</span> Assessment for Blended Wing Body Aircraft</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Guo, Yueping; Burley, Casey L; Thomas, Russell H.</p> <p>2014-01-01</p> <p>A system <span class="hlt">noise</span> study is presented for the blended-wing-body (BWB) aircraft configured with advanced technologies that are projected to be available in the 2025 timeframe of the NASA N+2 definition. This system <span class="hlt">noise</span> assessment shows that the <span class="hlt">noise</span> levels of the baseline configuration, measured by the cumulative Effective Perceived <span class="hlt">Noise</span> Level (EPNL), have a large margin of 34 dB to the aircraft <span class="hlt">noise</span> regulation of Stage 4. This confirms the acoustic benefits of the BWB shielding of engine <span class="hlt">noise</span>, as well as other projected <span class="hlt">noise</span> reduction technologies, but the <span class="hlt">noise</span> margins are less than previously published assessments and are short of meeting the NASA N+2 <span class="hlt">noise</span> goal. In establishing the relevance of the acoustic assessment framework, the design of the BWB configuration, the technical approach of the <span class="hlt">noise</span> analysis, the databases and prediction tools used in the assessment are first described and discussed. The predicted <span class="hlt">noise</span> levels and the component decomposition are then analyzed to identify the ranking order of importance of various <span class="hlt">noise</span> components, revealing the prominence of <span class="hlt">airframe</span> <span class="hlt">noise</span>, which holds up the levels at all three <span class="hlt">noise</span> certification locations and renders engine <span class="hlt">noise</span> reduction technologies less effective. When projected <span class="hlt">airframe</span> component <span class="hlt">noise</span> reduction is added to the HWB configuration, it is shown that the cumulative <span class="hlt">noise</span> margin to Stage 4 can reach 41.6 dB, nearly at the NASA goal. These results are compared with a previous NASA assessment with a different study framework. The approaches that yield projections of such low <span class="hlt">noise</span> levels are discussed including aggressive assumptions on future technologies, assumptions on flight profile management, engine installation, and component <span class="hlt">noise</span> reduction technologies. It is shown that reliable predictions of component <span class="hlt">noise</span> also play an important role in the system <span class="hlt">noise</span> assessment. The comparisons and discussions illustrate the importance of practical feasibilities and constraints in aircraft</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014MeScT..25l5111L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014MeScT..25l5111L"><span>A <span class="hlt">source</span> of illumination for low-<span class="hlt">noise</span> ‘Violin-Mode’ shadow sensors, intended for use in interferometric gravitational wave detectors</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lockerbie, N. A.; Tokmakov, K. V.; Strain, K. A.</p> <p>2014-12-01</p> <p>A low-<span class="hlt">noise</span> <span class="hlt">source</span> of illumination is described for shadow sensors having a displacement sensitivity of (69  ±  13) picometres (rms)/√Hz, at 500 Hz, over a measuring span of ±0.1 mm. These sensors were designed to detect ‘Violin-Mode’ resonances in the suspension fibres of the test-masses/mirrors for the Advanced LIGO (Laser Interferometer Gravitational wave Observatory) gravitational wave detectors. The <span class="hlt">source</span> of illumination (emitter) described here used a single column of 8 × miniature near infrared LEDs (λ = 890 nm). These emitters cast the shadows of 400 μm diameter fused silica suspension fibres onto their complementary shadow-displacement detectors, located at a distance of 74 fibre diameters (29.6 mm) behind the axes of the fibres themselves. Violin-Mode vibrations of each fibre were sensed as differential ac photocurrents in the corresponding ‘split-photodiode’ detector. This paper describes the design, construction, <span class="hlt">noise</span> analysis, and measures that were taken in the conception of the emitters, in order to produce high-contrast shadows at such distant detectors. In this way it proved possible to obtain, simultaneously, a very high transfer sensitivity to Violin-Mode vibration of the fibres, and a very low level of detection noise—close to the fundamental shot <span class="hlt">noise</span> limit—whilst remaining within the constraints of this simple design of emitter. The shadow detector is described in an accompanying paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1990PASP..102.1420A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1990PASP..102.1420A"><span>Signal-to-<span class="hlt">noise</span> ratios in IUE SWP-LO spectra of chromospheric emission-line <span class="hlt">sources</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ayres, Thomas R.</p> <p>1990-12-01</p> <p>The short-wavelength-prime (SWP) detector of the International Ultraviolet Explorer should operate near the photon-counting limit, but the <span class="hlt">noise</span> levels in flat-field images are several times higher. The exaggerated <span class="hlt">noise</span> can be traced to the incomplete removal of the pixel-to-pixel granularity of the television frames by the prevailing spectral image processing system. An empirical <span class="hlt">noise</span> model for the current-epoch photometric linearization strategy and one for a hypothetical processing system that achieves complete flat fielding of the raw images are derived. A formula is then proposed to predict the signal-to-<span class="hlt">noise</span> ratio in the measured flux of an emission line (possibly superimposed on a smooth continuum) in an IUE low-dispersion (5 A resolution) far-ultraviolet (1150 A-1950 A) spectrum as recorded with the SWP camera. For illustration, the formula is specialized to the important C IV 1549 A feature of F-K stars. The S/N relation permits one to determine sensitivity limits, upper limits in faint exposures, and optimum exposure times.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002ASAJ..111.2336V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002ASAJ..111.2336V"><span>Dragline <span class="hlt">noise</span> survey</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vipperman, Jeffrey S.; Bauer, Eric R.</p> <p>2002-05-01</p> <p>It is estimated that 70%-90% of miners have enough <span class="hlt">noise</span> induced hearing loss (NIHL) to be classified as a disability (NIOSH, Publication No. 76-172, 1976; Franks, NIOSH Internal Report, 1996). In response, NIOSH is conducting a cross-sectional survey of the mining industry in order to determine the <span class="hlt">sources</span> of mining <span class="hlt">noise</span> and offer recommendations on how to mitigate high <span class="hlt">noise</span> levels, and bring mining operations into compliance with the recent mining <span class="hlt">noise</span> regulation: 30CFR, Part 62. This paper will outline the results from <span class="hlt">noise</span> surveys of eight draglines which operate in above-ground coal mining operations. The data recorded include <span class="hlt">noise</span> dosimetry in conjunction with time-at-task studies and 1/3-octave sound level (Leq, Lmin, and Lmax) measurements. The 1/3-octave band readings were used to create <span class="hlt">noise</span> contour maps which allowed the spatial and frequency information of the <span class="hlt">noise</span> to be considered. Comparison of Lmin and Lmax levels offer insight into the variability of the <span class="hlt">noise</span> levels inside the dragline. The potential for administrative controls is limited due to consistently high <span class="hlt">noise</span> levels throughout the deck. Implementation of engineering controls is also hindered by the size and number of the <span class="hlt">noise</span> <span class="hlt">sources</span> and the frequency content of the <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110013067','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110013067"><span>Measurement of Model <span class="hlt">Noise</span> in a Hard-Wall Wind Tunnel</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Soderman, Paul T.</p> <p>2006-01-01</p> <p>Identification, analysis, and control of fluid-mechanically-generated sound from models of aircraft and automobiles in special low-<span class="hlt">noise</span>, semi-anechoic wind tunnels are an important research endeavor. Such studies can also be done in aerodynamic wind tunnels that have hard walls if phased microphone arrays are used to focus on the <span class="hlt">noise-source</span> regions and reject unwanted reflections or background <span class="hlt">noise</span>. Although it may be difficult to simulate the total flyover or drive-by <span class="hlt">noise</span> in a closed wind tunnel, individual <span class="hlt">noise</span> <span class="hlt">sources</span> can be isolated and analyzed. An acoustic and aerodynamic study was made of a 7-percent-scale aircraft model in a NASA Ames 7-by-10-ft (about 2-by-3-m) wind tunnel for the purpose of identifying and attenuating <span class="hlt">airframe</span> <span class="hlt">noise</span> <span class="hlt">sources</span>. Simulated landing, takeoff, and approach configurations were evaluated at Mach 0.26. Using a phased microphone array mounted in the ceiling over the inverted model, various <span class="hlt">noise</span> <span class="hlt">sources</span> in the high-lift system, landing gear, fins, and miscellaneous other components were located and compared for sound level and frequency at one flyover location. Numerous <span class="hlt">noise</span>-alleviation devices and modifications of the model were evaluated. Simultaneously with acoustic measurements, aerodynamic forces were recorded to document aircraft conditions and any performance changes caused by geometric modifications. Most modern microphone-array systems function in the frequency domain in the sense that spectra of the microphone outputs are computed, then operations are performed on the matrices of microphone-signal cross-spectra. The entire acoustic field at one station in such a system is acquired quickly and interrogated during postprocessing. Beam-forming algorithms are employed to scan a plane near the model surface and locate <span class="hlt">noise</span> <span class="hlt">sources</span> while rejecting most background <span class="hlt">noise</span> and spurious reflections. In the case of the system used in this study, previous studies in the wind tunnel have identified <span class="hlt">noise</span> <span class="hlt">sources</span> up to 19 d</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_25 --> <center> <div class="footer-extlink text-muted"><small>Some links on this page may take you to non-federal websites. Their policies may differ from this site.</small> </div> </center> <div id="footer-wrapper"> <div class="footer-content"> <div id="footerOSTI" class=""> <div class="row"> <div class="col-md-4 text-center col-md-push-4 footer-content-center"><small><a href="http://www.science.gov/disclaimer.html">Privacy and Security</a></small> <div class="visible-sm visible-xs push_footer"></div> </div> <div class="col-md-4 text-center col-md-pull-4 footer-content-left"> <img src="https://www.osti.gov/images/DOE_SC31.png" alt="U.S. Department of Energy" usemap="#doe" height="31" width="177"><map style="display:none;" name="doe" id="doe"><area shape="rect" coords="1,3,107,30" href="http://www.energy.gov" alt="U.S. Deparment of Energy"><area shape="rect" coords="114,3,165,30" href="http://www.science.energy.gov" alt="Office of Science"></map> <a ref="http://www.osti.gov" style="margin-left: 15px;"><img src="https://www.osti.gov/images/footerimages/ostigov53.png" alt="Office of Scientific and Technical Information" height="31" width="53"></a> <div class="visible-sm visible-xs push_footer"></div> </div> <div class="col-md-4 text-center footer-content-right"> <a href="http://www.science.gov"><img src="https://www.osti.gov/images/footerimages/scigov77.png" alt="science.gov" height="31" width="98"></a> <a href="http://worldwidescience.org"><img src="https://www.osti.gov/images/footerimages/wws82.png" alt="WorldWideScience.org" height="31" width="90"></a> </div> </div> </div> </div> </div> <p><br></p> </div><!-- container --> <script type="text/javascript"><!-- // var lastDiv = ""; function showDiv(divName) { // hide last div if (lastDiv) { document.getElementById(lastDiv).className = "hiddenDiv"; } //if value of the box is not nothing and an object with that name exists, then change the class if (divName && document.getElementById(divName)) { document.getElementById(divName).className = "visibleDiv"; lastDiv = divName; } } //--> </script> <script> /** * Function that tracks a click on an outbound link in Google Analytics. * This function takes a valid URL string as an argument, and uses that URL string * as the event label. */ var trackOutboundLink = function(url,collectionCode) { try { h = window.open(url); setTimeout(function() { ga('send', 'event', 'topic-page-click-through', collectionCode, url); }, 1000); } catch(err){} }; </script> <!-- Google Analytics --> <script> (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){ (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o), m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m) })(window,document,'script','//www.google-analytics.com/analytics.js','ga'); ga('create', 'UA-1122789-34', 'auto'); ga('send', 'pageview'); </script> <!-- End Google Analytics --> <script> showDiv('page_1') </script> </body> </html>