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Sample records for aerodynamic noise sources

  1. 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.

  2. Fan Noise Source Diagnostic Test: Rotor Alone Aerodynamic Performance Results

    NASA Technical Reports Server (NTRS)

    Hughes, Christopher E.; Jeracki, Robert J.; Woodward, Richard P.; Miller, Christopher J.

    2005-01-01

    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 Source Diagnostic Test conducted at NASA Glenn. The Source Diagnostic Test was conducted to identify the noise sources within a wind tunnel scale model of a turbofan engine and quantify their contribution to the overall system noise 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.

  3. New aspects of subsonic aerodynamic noise theory

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Howes, W. L.

    1973-01-01

    A theory of aerodynamic noise is presented which differs from Lighthill's theory primarily in the way in which convection of the noise sources is treated. The sound directivity pattern obtained from the present theory agrees better with jet-noise directivity data than does that obtained from Lighthill's theory. The results imply that the shear-noise contribution to jet noise is smaller than previously expected.

  4. 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.

  5. A new technique for aerodynamic noise calculation

    NASA Technical Reports Server (NTRS)

    Hardin, J. C.; Pope, D. S.

    1992-01-01

    A novel method for the numerical analysis of aerodynamic noise generation is presented. The method involves first solving for the time-dependent incompressible flow for the given geometry. This fully nonlinear method that is tailored to extract the relevant acoustic fluctuations seems to be an efficient approach to the numerical analysis of aerodynamic noise generation.

  6. Direct Numerical Simulation of Aerodynamic Noise

    DTIC Science & Technology

    1989-09-29

    Noise First Annual Progress Report ONR Grant N00014-88-K-0592 Principal Investigator : Parviz Main Sr. Research Associate: Sanjiva K. Lele Research...of Aerodynamic Noise ONR Grant N00014-88-K-0592 Principal Investigator : Parviz Moin Sr. Research Associate : Sanjiva K. Lele Research Assistant : Tim

  7. On aerodynamic noise generation from vortex shedding in rotating blades

    NASA Astrophysics Data System (ADS)

    Martin, B. T.; Bies, D. A.

    1992-06-01

    The interaction of the shed wakes of plates in a cascade with each following plate is investigated in a water tunnel and shown to provide an explanation for an observed very powerful aerodynamic noise source. In particular, the noise generation of an idling circular saw may be explained as due to the interaction of the wake shed by an upstream tooth with the leading edge of the following downstream tooth. When a vortex travelling downstream in the gullet between teeth encounters the leading edge of the downstream tooth it is deflected out of the gullet into the main stream. The associated impulses which the teeth encounter give rise to the radiated noise.

  8. Aerodynamic noise emission from turbulent shear layers.

    NASA Technical Reports Server (NTRS)

    Pao, S. P.

    1973-01-01

    The Phillips (1960) convected wave equation is employed in this paper to study aerodynamic noise emission processes in subsonic and supersonic shear layers. The wave equation in three spatial dimensions is first reduced to an ordinary differential equation by Fourier transformation and then solved via the WKBJ method. Three typical solutions are required for discussions in this paper. The current results are different from the classical conclusions. The effects of refraction, convection, Mach-number dependence and temperature dependence of turbulent noise emission are analyzed in the light of solutions to the Phillips equation.

  9. Aircraft Noise Prediction Program theoretical manual: Propeller aerodynamics and noise

    NASA Technical Reports Server (NTRS)

    Zorumski, W. E. (Editor); Weir, D. S. (Editor)

    1986-01-01

    The prediction sequence used in the aircraft noise prediction program (ANOPP) is described. The elements of the sequence are called program modules. The first group of modules analyzes the propeller geometry, the aerodynamics, including both potential and boundary-layer flow, the propeller performance, and the surface loading distribution. This group of modules is based entirely on aerodynamic strip theory. The next group of modules deals with the first group. Predictions of periodic thickness and loading noise are determined with time-domain methods. Broadband noise is predicted by a semiempirical method. Near-field predictions of fuselage surface pressrues include the effects of boundary layer refraction and scattering. Far-field predictions include atmospheric and ground effects.

  10. Modelling Aerodynamically Generated Sound: Recent Advances in Rotor Noise Prediction

    NASA Technical Reports Server (NTRS)

    Brentner, Kenneth S.

    2000-01-01

    A great deal of progress has been made in the modeling of aerodynamically generated sound for rotors over the past decade. The Ffowcs Williams-Hawkings (FW-H ) equation has been the foundation for much of the development. Both subsonic and supersonic quadrupole noise formulations have been developed for the prediction of high-speed impulsive noise. In an effort to eliminate the need to compute the quadrupole contribution, the FW-H has also been utilized on permeable surfaces surrounding all physical noise sources. Comparison of the Kirchhoff formulation for moving surfaces with the FW-H equation have shown that the Kirchhoff formulation for moving surfaces can give erroneous results for aeroacoustic problems.

  11. Diagnostic techniques for measurement of aerodynamic noise in free field and reverberant environment of wind tunnels

    NASA Technical Reports Server (NTRS)

    El-Sum, H. M. A.; Mawardi, O. K.

    1973-01-01

    Techniques for studying aerodynamic noise generating mechanisms without disturbing the flow in a free field, and in the reverberation environment of the ARC wind tunnel were investigated along with the design and testing of an acoustic antenna with an electronic steering control. The acoustic characteristics of turbojet as a noise source, detection of direct sound from a source in a reverberant background, optical diagnostic methods, and the design characteristics of a high directivity acoustic antenna. Recommendations for further studies are included.

  12. Aerodynamic Performance Measurements for a Forward Swept Low Noise Fan

    NASA Technical Reports Server (NTRS)

    Fite, E. Brian

    2006-01-01

    One source of noise in high tip speed turbofan engines, caused by shocks, is called multiple pure tone noise (MPT's). A new fan, called the Quiet High Speed Fan (QHSF), showed reduced noise over the part speed operating range, which includes MPT's. The QHSF showed improved performance in most respects relative to a baseline fan; however, a partspeed instability discovered during testing reduced the operating range below acceptable limits. The measured QHSF adiabatic efficiency on the fixed nozzle acoustic operating line was 85.1 percent and the baseline fan 82.9 percent, a 2.2 percent improvement. The operating line pressure rise at design point rotational speed and mass flow was 1.764 and 1.755 for the QHSF and baseline fan, respectively. Weight flow at design point speed was 98.28 lbm/sec for the QHSF and 97.97 lbm/sec for the baseline fan. The operability margin for the QHSF approached 0 percent at the 75 percent speed operating condition. The baseline fan maintained sufficient margin throughout the operating range as expected. Based on the stage aerodynamic measurements, this concept shows promise for improved performance over current technology if the operability limitations can be solved.

  13. 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.

  14. Analysis of aerodynamic noise generated from inclined circular cylinder

    NASA Astrophysics Data System (ADS)

    Haramoto, Yasutake; Yasuda, Shouji; Matsuzaki, Kazuyoshi; Munekata, Mizue; Ohba, Hideki

    2000-06-01

    Making clear the generation mechanism of fluid dynamic noise is essential to reduce noise deriving from turbomachinery. The analysis of the aerodynamic noise generated from circular cylinder is carried out numerically and experimentally in a low noise wind tunnel. In this study, aerodynamic sound radiated from a circular cylinder in uniform flow is predicted numerically by the following two step method. First, the three-dimensional unsteady incompressible Navier-Stokes equation is solved using the high order accurate upwind scheme. Next, the sound pressure level at the observed point is calculated from the fluctuating surface pressure on the cylinder, based on modified Lighthill-Curl’s equation. It is worth to note that the noise generated from the model is reduced rapidly when it is inclined against the mean flow. In other words, the peak level of the radiated noise decreases rapidly with inclination of the circular cylinder. The simulated SPL for the inclined circular cylinder is compared with the measured value, and good agreement is obtained for the peak spectrum frequency of the sound pressure level and tendency of noise reduction. So we expect that the change of flow structures makes reduction of the aerodynamic noise from the inclined models.

  15. A method for characterizing aerodynamic sound sources in turbomachines

    NASA Astrophysics Data System (ADS)

    Mongeau, L.; Thompson, D. E.; Mclaughlin, D. K.

    1995-03-01

    A method based on Weidemann's acoustic similarity laws [1] was used to investigate the aerodynamic sound generated by a partially ducted centrifugal pump rotor. The primary objective of the method was to determine the spectral characteristics of the sound source by isolating the effects of acoustic phenomena such as duct resonances or sound reflections. Pump-radiated sound pressure spectra were measured for different impeller rotational speeds, keeping the operating condition constant. The spectra, assumed to be expressed as the product of a source spectral distribution function and an acoustic frequency response function, were then decomposed into a product form following a computer-implemented algorithm. The method was successful in accurately determining the spectral distribution of the broadband aerodynamic noise generating mechanisms involved and that of the acoustic frequency response of the system. The absolute levels of the source function and the acoustic function were established by assuming that, over a limited low frequency range, the average gain of the frequency response function is unity so that comparisons between different pump operating conditions could be made. The source spectral distribution was found to be independent of the microphone location and the acoustic loading. When applicable, this method therefore allows the characterization of aerodynamic sound sources by measuring ordinary sound pressure spectra, at any one point around the source, without having to isolate the source from the system. The source characterization method was instrumental in the study of sound generation by rotating stall presented in a previous publication [2].

  16. Component-based model to predict aerodynamic noise from high-speed train pantographs

    NASA Astrophysics Data System (ADS)

    Latorre Iglesias, E.; Thompson, D. J.; Smith, M. G.

    2017-04-01

    At typical speeds of modern high-speed trains the aerodynamic noise produced by the airflow over the pantograph is a significant source of noise. Although numerical models can be used to predict this they are still very computationally intensive. A semi-empirical component-based prediction model is proposed to predict the aerodynamic noise from train pantographs. The pantograph is approximated as an assembly of cylinders and bars with particular cross-sections. An empirical database is used to obtain the coefficients of the model to account for various factors: incident flow speed, diameter, cross-sectional shape, yaw angle, rounded edges, length-to-width ratio, incoming turbulence and directivity. The overall noise from the pantograph is obtained as the incoherent sum of the predicted noise from the different pantograph struts. The model is validated using available wind tunnel noise measurements of two full-size pantographs. The results show the potential of the semi-empirical model to be used as a rapid tool to predict aerodynamic noise from train pantographs.

  17. Advanced Noise Control Fan Aerodynamic Performance

    NASA Technical Reports Server (NTRS)

    Bozak, Richard F., Jr.

    2009-01-01

    The Advanced Noise Control Fan at the NASA Glenn Research Center is used to experimentally analyze fan generated acoustics. In order to determine how a proposed noise reduction concept affects fan performance, flow measurements can be used to compute mass flow. Since tedious flow mapping is required to obtain an accurate mass flow, an equation was developed to correlate the mass flow to inlet lip wall static pressure measurements. Once this correlation is obtained, the mass flow for future configurations can be obtained from the nonintrusive wall static pressures. Once the mass flow is known, the thrust and fan performance can be evaluated. This correlation enables fan acoustics and performance to be obtained simultaneously without disturbing the flow.

  18. Active aerodynamic control of wake-airfoil interaction noise - Experiment

    NASA Astrophysics Data System (ADS)

    Simonich, J. C.; Lavrich, P. L.; Sofrin, T. G.; Topol, D. A.

    A proof of concept experiment is conducted that shows the potential for active aerodynamic control of rotor wake/stator interaction noise in a simplified manner. A single airfoil model representing the stator was fitted with a moveable trailing edge flap controlled by a servo motor. The control system moves the motor driven flap in the correct angular displacement phase and rate to reduce the unsteady load on the airfoil during the wake interaction.

  19. Aerodynamic Performance of Scale-Model Turbofan Outlet Guide Vanes Designed for Low Noise

    NASA Technical Reports Server (NTRS)

    Hughes, Christopher E.

    2001-01-01

    The design of effective new technologies to reduce aircraft propulsion noise is dependent on an understanding of the noise sources and noise generation mechanisms in the modern turbofan engine. In order to more fully understand the physics of noise in a turbofan engine, a comprehensive aeroacoustic wind tunnel test programs was conducted called the 'Source Diagnostic Test.' The text was cooperative effort between NASA and General Electric Aircraft Engines, as part of the NASA Advanced Subsonic Technology Noise Reduction Program. A 1/5-scale model simulator representing the bypass stage of a current technology high bypass ratio turbofan engine was used in the test. The test article consisted of the bypass fan and outlet guide vanes in a flight-type nacelle. The fan used was a medium pressure ratio design with 22 individual, wide chord blades. Three outlet guide vane design configurations were investigated, representing a 54-vane radial Baseline configuration, a 26-vane radial, wide chord Low Count configuration and a 26-vane, wide chord Low Noise configuration with 30 deg of aft sweep. The test was conducted in the NASA Glenn Research Center 9 by 15-Foot Low Speed Wind Tunnel at velocities simulating the takeoff and approach phases of the aircraft flight envelope. The Source Diagnostic Test had several acoustic and aerodynamic technical objectives: (1) establish the performance of a scale model fan selected to represent the current technology turbofan product; (2) assess the performance of the fan stage with each of the three distinct outlet guide vane designs; (3) determine the effect of the outlet guide vane configuration on the fan baseline performance; and (4) conduct detailed flowfield diagnostic surveys, both acoustic and aerodynamic, to characterize and understand the noise generation mechanisms in a turbofan engine. This paper addresses the fan and stage aerodynamic performance results from the Source Diagnostic Test.

  20. Aerodynamics and interaction noise of streamlined bodies in nonuniform flows

    NASA Astrophysics Data System (ADS)

    Atassi, H. M.; Logue, M. M.

    2011-08-01

    The unsteady aerodynamics and interaction noise of streamlined bodies are modeled in terms of the Euler equations linearized about a nonuniform flow. The validity of the inviscid approach is supported by recent LES simulations of an airfoil in a gust indicating that for not-too-small impinging excitations, the interaction process is dominated by inertia forces. Results in the present paper are focused on the aerodynamics and interaction noise of a turbofan modeled as an annular cascade. The model accounts for the inflow-fan-duct coupling and the high frequency of the interaction process. Two high-order numerical algorithms are developed with body-fitted coordinate system. One algorithm uses a primitive variable formulation, the other uses an efficient velocity splitting algorithm and is suitable for broadband computations. Analytical and numerical analysis of disturbances in rotational flows is developed and exact inflow/outflow boundary conditions are derived, yielding directly the radiated acoustics. The upstream disturbances evolve in rotational flows and as a result the aerodynamic-aeroacoustic response of the annular cascade depends on the initial conditions location. Computational results show that the three-dimensional geometry of the annular cascade, the mean flow swirl, and the blade geometry have strong influence on the blade sectional lift and the radiated sound. These results also show the inadequacy of using the popular linear cascade model particularly for realistic fan geometry and inflow conditions.

  1. Aerodynamic Measurements of a Gulfstream Aircraft Model With and Without Noise Reduction Concepts

    NASA Technical Reports Server (NTRS)

    Neuhart, Dan H.; Hannon, Judith A.; Khorrami, Mehdi R.

    2014-01-01

    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 airframe noise associated with main landing gear/flap components, gear-flap interaction noise, and the viability of related noise 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 noise sources 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 noise abatement technologies fall within the repeatability of the baseline configuration. Therefore, the noise abatement technologies evaluated in this experiment have no detrimental impact on the aerodynamic performance of the aircraft model.

  2. Some useful hybrid approaches for predicting aerodynamic noise

    NASA Astrophysics Data System (ADS)

    Bailly, Christophe; Bogey, Christophe; Gloerfelt, Xavier

    2005-09-01

    In recent years, several numerical studies have shown the feasibility of Direct Noise Computation (DNC) where the turbulent flow and the radiated acoustic field are obtained simultaneously by solving the compressible Navier-Stokes equations. The acoustic radiation obtained by DNC can be used as reference solution to investigate hybrid methods in which the sound field is usually calculated as a by-product of the flow field obtained by a more conventional Navier-Stokes solver. A hybrid approach is indeed of practical interest when only the non-acoustic part of the aerodynamic field is available. In this review, some acoustic analogies or hybrid approaches are revisited in the light of CAA. To cite this article: C. Bailly et al., C. R. Mecanique 333 (2005).

  3. Experimental investigation on the effect of slat geometrical configurations on aerodynamic noise

    NASA Astrophysics Data System (ADS)

    Pagani, Carlos C.; Souza, Daniel S.; Medeiros, Marcello A. F.

    2017-04-01

    Relatively few studies have addressed the slat noise dependence on gap, overlap and deflection angle, although slat noise level and spectral content are topics of increasing concern in the aeronautical industry. This paper presents new experimental data on the subject. An array of microphones placed in a closed-section wind tunnel was used in the experiments. Beamforming signal processing enhanced by DAMAS (Deconvolution Approach for the Mapping of Acoustic Sources) was applied to the data. The experimental data covered a range of angles of attack and Mach numbers, for which the typical slat noise signature features high-level narrow-band peaks, broadband noise and a single broad tone. The narrow-band peaks often dominate the slat noise spectra and arise at Strouhal numbers up to approximately 5. The broadband noise is well characterized for Strouhal numbers between 5 and 20, whereas the broad tone arises for Strouhal above 20. A total of 10 different slat configurations, including variations in gap, overlap and deflection angle were tested. The slat noise dependence on gap, overlap and slat deflection angle was assessed by letting each of them vary separately. The slat configuration exerted a substantial effect on all slat noise components, with variations of up to 20 dB/Hz in the level of the narrow-band peaks. In general, the level of the narrow-band peaks reduced and the high frequency content increased as the gap, overlap, angle of attack and slat deflection increased separately or in combination. The aerodynamically optimized baseline configuration is very distinct from the lowest noise one.

  4. Lobed Mixer Design for Noise Suppression Acoustic and Aerodynamic Test Data Analysis

    NASA Technical Reports Server (NTRS)

    Mengle, Vinod G.; Dalton, William N.; Boyd, Kathleen (Technical Monitor); Bridges, James (Technical Monitor)

    2002-01-01

    A comprehensive database for the acoustic and aerodynamic characteristics of several model-scale lobe mixers of bypass ratio 5 to 6 has been created for mixed jet speeds up to 1080 ft/s at typical take-off (TO) conditions of small-to-medium turbofan engines. The flight effect was simulated for Mach numbers up to 0.3. The static thrust performance and plume data were also obtained at typical TO and cruise conditions. The tests were done at NASA Lewis anechoic dome and ASK's FluiDyne Laboratories. The effect of several lobe mixer and nozzle parameters, such as, lobe scalloping, lobe count, lobe penetration and nozzle length was examined in terms of flyover noise at constant altitude. Sound in the nozzle reference frame was analyzed to understand the source characteristics. Several new concepts, mechanisms and methods are reported for such lobed mixers, such as, "boomerang" scallops, "tongue" mixer, detection of "excess" internal noise sources, and extrapolation of flyover noise data from one flight speed to different flight speeds. Noise reduction of as much as 3 EPNdB was found with a deeply scalloped mixer compared to annular nozzle at net thrust levels of 9500 lb for a 29 in. diameter nozzle after optimizing the nozzle length.

  5. 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

  6. Piloted Simulation Study of the Effects of High-Lift Aerodynamics on the Takeoff Noise of a Representative High-Speed Civil Transport

    NASA Technical Reports Server (NTRS)

    Glaab, Louis J.; Riley, Donald R.; Brandon, Jay M.; Person, Lee H., Jr.; Glaab, Patricia C.

    1999-01-01

    As part of an effort between NASA and private industry to reduce airport-community noise for high-speed civil transport (HSCT) concepts, a piloted simulation study was initiated for the purpose of predicting the noise reduction benefits that could result from improved low-speed high-lift aerodynamic performance for a typical HSCT configuration during takeoff and initial climb. Flight profile and engine information from the piloted simulation were coupled with the NASA Langley Aircraft Noise Prediction Program (ANOPP) to estimate jet engine noise and to propagate the resulting source noise to ground observer stations. A baseline aircraft configuration, which also incorporated different levels of projected improvements in low-speed high-lift aerodynamic performance, was simulated to investigate effects of increased lift and lift-to-drag ratio on takeoff noise levels. Simulated takeoff flights were performed with the pilots following a specified procedure in which either a single thrust cutback was performed at selected altitudes ranging from 400 to 2000 ft, or a multiple-cutback procedure was performed where thrust was reduced by a two-step process. Results show that improved low-speed high-lift aerodynamic performance provides at least a 4 to 6 dB reduction in effective perceived noise level at the FAA downrange flyover measurement station for either cutback procedure. However, improved low-speed high-lift aerodynamic performance reduced maximum sideline noise levels only when using the multiple-cutback procedures.

  7. Numerical modeling of wind turbine aerodynamic noise in the time domain.

    PubMed

    Lee, Seunghoon; Lee, Seungmin; Lee, Soogab

    2013-02-01

    Aerodynamic noise from a wind turbine is numerically modeled in the time domain. An analytic trailing edge noise model is used to determine the unsteady pressure on the blade surface. The far-field noise due to the unsteady pressure is calculated using the acoustic analogy theory. By using a strip theory approach, the two-dimensional noise model is applied to rotating wind turbine blades. The numerical results indicate that, although the operating and atmospheric conditions are identical, the acoustical characteristics of wind turbine noise can be quite different with respect to the distance and direction from the wind turbine.

  8. Interaction of aerodynamic noise with laminar boundary layers in supersonic wind tunnels

    NASA Technical Reports Server (NTRS)

    Schopper, M. R.

    1984-01-01

    The interaction between incoming aerodynamic noise and the supersonic laminar boundary layer is studied. The noise field is modeled as a Mach wave radiation field consisting of discrete waves emanating from coherent turbulent entities moving downstream within the supersonic turbulent boundary layer. The individual disturbances are likened to miniature sonic booms and the laminar boundary layer is staffed by the waves as the sources move downstream. The mean, autocorrelation, and power spectral density of the field are expressed in terms of the wave shapes and their average arrival rates. Some consideration is given to the possible appreciable thickness of the weak shock fronts. The emphasis in the interaction analysis is on the behavior of the shocklets in the noise field. The shocklets are shown to be focused by the laminar boundary layer in its outer region. Borrowing wave propagation terminology, this region is termed the caustic region. Using scaling laws from sonic boom work, focus factors at the caustic are estimated to vary from 2 to 6 for incoming shocklet strengths of 1 to .01 percent of the free stream pressure level. The situation regarding experimental evidence of the caustic region is reviewed.

  9. Blade-Vortex Interaction (BVI) Noise and Airload Prediction Using Loose Aerodynamic/Structural Coupling

    NASA Technical Reports Server (NTRS)

    Sim, B. W.; Lim, J. W.

    2007-01-01

    Predictions of blade-vortex interaction (BVI) noise, using blade airloads obtained from a coupled aerodynamic and structural methodology, are presented. This methodology uses an iterative, loosely-coupled trim strategy to cycle information between the OVERFLOW-2 (CFD) and CAMRAD-II (CSD) codes. Results are compared to the HART-II baseline, minimum noise and minimum vibration conditions. It is shown that this CFD/CSD state-of-the-art approach is able to capture blade airload and noise radiation characteristics associated with BVI. With the exception of the HART-II minimum noise condition, predicted advancing and retreating side BVI for the baseline and minimum vibration conditions agrees favorably with measured data. Although the BVI airloads and noise amplitudes are generally under-predicted, this CFD/CSD methodology provides an overall noteworthy improvement over the lifting line aerodynamics and free-wake models typically used in CSD comprehensive analysis codes.

  10. 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

  11. Effects of Nozzle Geometry and Intermittent Injection of Aerodynamic Tab on Supersonic Jet Noise

    NASA Astrophysics Data System (ADS)

    Araki, Mikiya; Sano, Takayuki; Fukuda, Masayuki; Kojima, Takayuki; Taguchi, Hideyuki; Shiga, Seiichi; Obokata, Tomio

    Effects of the nozzle geometry and intermittent injection of aerodynamic tabs on exhaust noise from a rectangular plug nozzle were investigated experimentally. In JAXA (Japan Aerospace Exploration Agency), a pre-cooled turbojet engine for an HST (Hypersonic transport) is planned. A 1/100-scaled model of the rectangular plug nozzle is manufactured, and the noise reduction performance of aerodynamic tabs, which is small air jet injection from the nozzle wall, was investigated. Compressed air is injected through the rectangular plug nozzle into the atmosphere at the nozzle pressure ratio of 2.7, which corresponds to the take-off condition of the vehicle. Aerodynamic tabs were installed at the sidewall ends, and 4 kinds of round nozzles and 2 kinds of wedge nozzles were applied. Using a high-frequency solenoid valve, intermittent gas injection is also applied. It is shown that, by use of wedge nozzles, the aerodynamic tab mass flow rate, necessary to gain 2.3dB reduction in OASPL (Overall sound pressure level), decreases by 29% when compared with round nozzles. It is also shown that, by use of intermittent injection, the aerodynamic tab mass flow rate, necessary to gain 2.3dB reduction in OASPL, decreases by about 40% when compared with steady injection. By combination of wedge nozzles and intermittent injection, the aerodynamic tab mass flow rate significantly decreases by 57% when compared with the conventional strategy.

  12. Effect of Two Advanced Noise Reduction Technologies on the Aerodynamic Performance of an Ultra High Bypass Ratio Fan

    NASA Technical Reports Server (NTRS)

    Hughes, Christoper E.; Gazzaniga, John A.

    2013-01-01

    A wind tunnel experiment was conducted in the NASA Glenn Research Center anechoic 9- by 15-Foot Low-Speed Wind Tunnel to investigate two new advanced noise reduction technologies in support of the NASA Fundamental Aeronautics Program Subsonic Fixed Wing Project. The goal of the experiment was to demonstrate the noise reduction potential and effect on fan model performance of the two noise reduction technologies in a scale model Ultra-High Bypass turbofan at simulated takeoff and approach aircraft flight speeds. The two novel noise reduction technologies are called Over-the-Rotor acoustic treatment and Soft Vanes. Both technologies were aimed at modifying the local noise source mechanisms of the fan tip vortex/fan case interaction and the rotor wake-stator interaction. For the Over-the-Rotor acoustic treatment, two noise reduction configurations were investigated. The results showed that the two noise reduction technologies, Over-the-Rotor and Soft Vanes, were able to reduce the noise level of the fan model, but the Over-the-Rotor configurations had a significant negative impact on the fan aerodynamic performance; the loss in fan aerodynamic efficiency was between 2.75 to 8.75 percent, depending on configuration, compared to the conventional solid baseline fan case rubstrip also tested. Performance results with the Soft Vanes showed that there was no measurable change in the corrected fan thrust and a 1.8 percent loss in corrected stator vane thrust, which resulted in a total net thrust loss of approximately 0.5 percent compared with the baseline reference stator vane set.

  13. Unified aeroacoustics analysis for high speed turboprop aerodynamics and noise. Volume 3: Application of theory for blade loading, wakes, noise, and wing shielding

    NASA Technical Reports Server (NTRS)

    Hanson, D. B.; Mccolgan, C. J.; Ladden, R. M.; Klatte, R. J.

    1991-01-01

    Results of the program for the generation of a computer prediction code for noise of advanced single rotation, turboprops (prop-fans) such as the SR3 model are presented. The code is based on a linearized theory developed at Hamilton Standard in which aerodynamics and acoustics are treated as a unified process. Both steady and unsteady blade loading are treated. Capabilities include prediction of steady airload distributions and associated aerodynamic performance, unsteady blade pressure response to gust interaction or blade vibration, noise fields associated with thickness and steady and unsteady loading, and wake velocity fields associated with steady loading. The code was developed on the Hamilton Standard IBM computer and has now been installed on the Cray XMP at NASA-Lewis. The work had its genesis in the frequency domain acoustic theory developed at Hamilton Standard in the late 1970s. It was found that the method used for near field noise predictions could be adapted as a lifting surface theory for aerodynamic work via the pressure potential technique that was used for both wings and ducted turbomachinery. In the first realization of the theory for propellers, the blade loading was represented in a quasi-vortex lattice form. This was upgraded to true lifting surface loading. Originally, it was believed that a purely linear approach for both aerodynamics and noise would be adequate. However, two sources of nonlinearity in the steady aerodynamics became apparent and were found to be a significant factor at takeoff conditions. The first is related to the fact that the steady axial induced velocity may be of the same order of magnitude as the flight speed and the second is the formation of leading edge vortices which increases lift and redistribute loading. Discovery and properties of prop-fan leading edge vortices were reported in two papers. The Unified AeroAcoustic Program (UAAP) capabilites are demonstrated and the theory verified by comparison with the

  14. The Effect of Bypass Nozzle Exit Area on Fan Aerodynamic Performance and Noise in a Model Turbofan Simulator

    NASA Technical Reports Server (NTRS)

    Hughes, Christopher E.; Podboy, Gary, G.; Woodward, Richard P.; Jeracki, Robert, J.

    2013-01-01

    The design of effective new technologies to reduce aircraft propulsion noise is dependent on identifying and understanding the noise sources and noise generation mechanisms in the modern turbofan engine, as well as determining their contribution to the overall aircraft noise signature. Therefore, a comprehensive aeroacoustic wind tunnel test program was conducted called the Fan Broadband Source Diagnostic Test as part of the NASA Quiet Aircraft Technology program. The test was performed in the anechoic NASA Glenn 9- by 15-Foot Low Speed Wind Tunnel using a 1/5 scale model turbofan simulator which represented a current generation, medium pressure ratio, high bypass turbofan aircraft engine. The investigation focused on simulating in model scale only the bypass section of the turbofan engine. The test objectives were to: identify the noise sources within the model and determine their noise level; investigate several component design technologies by determining their impact on the aerodynamic and acoustic performance of the fan stage; and conduct detailed flow diagnostics within the fan flow field to characterize the physics of the noise generation mechanisms in a turbofan model. This report discusses results obtained for one aspect of the Source Diagnostic Test that investigated the effect of the bypass or fan nozzle exit area on the bypass stage aerodynamic performance, specifically the fan and outlet guide vanes or stators, as well as the farfield acoustic noise level. The aerodynamic performance, farfield acoustics, and Laser Doppler Velocimeter flow diagnostic results are presented for the fan and four different fixed-area bypass nozzle configurations. The nozzles simulated fixed engine operating lines and encompassed the fan stage operating envelope from near stall to cruise. One nozzle was selected as a baseline reference, representing the nozzle area which would achieve the design point operating conditions and fan stage performance. The total area change from

  15. 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.

  16. Effects of Aerodynamic Tabs onExhaust Noise from a Rectangular Plug Nozzle

    NASA Astrophysics Data System (ADS)

    Araki, Mikiya; Sano, Takayuki; Kojima, Takayuki; Taguchi, Hideyuki; Shiga, Seiichi; Obokata, Tomio

    Effects of aerodynamic tabs on exhaust noise from a rectangular plug nozzle were investigated experimentally. In JAXA (Japan Aerospace Explanation Agency), a pre-cooled turbojet engine for the 1st stage propulsion of a TSTO (Two stage to orbit) is planned. In the present study, a 1/100-scaled model of the rectangular plug nozzle for the pre-cooled turbojet engine is manufactured and the exhaust noise characteristics were investigated. Compressed air is injected through the rectangular plug nozzle into the atmosphere. The nozzle pressure ratio was set at 2.7, which corresponds to the take-off condition of the vehicle. Aerodynamic tabs were installed at the ramp end (Upper AT), the cowl end (Lower AT) and the sidewall end (Side AT). The SPL (Sound pressure level) was measured with a high-frequency microphone. Without AT, the sound spectrum has a broadband peak at which the SPL is around 105dB. For Lower and Side ATs, the OASPL (Overall SPL) of the exhaust noise decreases, especially around ramp end. At the maximum, the OASPL was reduced by 2.4dB with about 2% loss of the main jet total pressure at the cowl exit. It is shown that the aerodynamic tabs are effective in noise reduction in a rectangular plug nozzle.

  17. Farfield viscous effects in nonlinear noise propagation. [in aerodynamics

    NASA Technical Reports Server (NTRS)

    Harris, W. L., Sr.

    1974-01-01

    Discussion of the method of parametric differentiation in application to predictions of farfield noise propagation in both lossless and dissipative media. It is shown that, in the lossless medium, the governing equation, transformed to parameter space, reduces to a wave equation in the farfield. In the dissipative medium, the system of nonlinear partial differential equations, transformed to parameter space, reduces to a linear partial differential equation of the propagating type which contains a third-order derivative as well as the wave operator.

  18. Estimation of aerodynamic noise generated by forced compressible round jets

    NASA Astrophysics Data System (ADS)

    Maidi, Mohamed

    2006-05-01

    An acoustic numerical code based on Ligthill's analogy is combined with large-eddy simulations techniques in order to evaluate the noise emitted by subsonic (M=0.7) and supersonic (M=1.4) round jets. We show first that, for centerline Mach number M=0.9 and Reynolds number Re=3.6×10, acoustic intensities compare satisfactorily with experimental data of the literature in terms of levels and directivity. Afterwards, high Reynolds number (Re=3.6×10) free and forced jets at Mach 0.7 and 1.4 are studied. Numerical results show that the jet noise intensity depends on the nature of the upstream mixing layer. Indeed, the subsonic jet is 4 dB quieter than the free jet when acting on this shear layer by superposing inlet varicose and flapping perturbations at preferred and first subharmonic frequency, respectively. The maximal acoustic level of the supersonic jet is, on the other hand, 3 dB lower than the free one with a flapping upstream perturbation at the second subharmonic. The results reported in this paper confirm previous works presented in the literature demonstrating that jet noise may be modified according to the inlet conditions. To cite this article: M. Maidi, C. R. Mecanique 334 (2006).

  19. Numerical Analysis of Aerodynamic Noise Radiation from a High-Speed Train Surface

    NASA Astrophysics Data System (ADS)

    SASSA, T.; SATO, T.; YATSUI, S.

    2001-10-01

    The aerodynamic noise radiation from a vestibule side door on a high-speed train surface is calculated by the combination of unsteady incompressible fluid flow analysis and acoustic analysis. Pressure fluctuation on a vestibule side door surface is measured to verify the results of fluid flow analysis. Analysis results agree with measured data very well at low frequencies. For high-frequency components, the solvable frequency is limited by the analysis mesh size. Required mesh size is typically one eighth of the wavelength of the pressure fluctuation on the model surface. The aerodynamic noise is mainly radiated from around the following corner where the vortices that are shed from the leading corner strongly interact with the train surface.

  20. 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.

  1. Experimental determination of the tonal noise sources in a centrifugal fan

    NASA Astrophysics Data System (ADS)

    Velarde-Suárez, Sandra; Ballesteros-Tajadura, Rafael; Pablo Hurtado-Cruz, Juan; Santolaria-Morros, Carlos

    2006-08-01

    In this work, an experimental study about the aerodynamic tonal noise sources 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 noise generation. A strong source of noise 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 noise 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.

  2. 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

  3. Follow-on Low Noise Fan Aerodynamic Study

    NASA Technical Reports Server (NTRS)

    Heidegger, Nathan J.; Hall, Edward J.; Delaney, Robert A.

    1999-01-01

    The focus of the project was to investigate the effects of turbulence models on the prediction of rotor wake structures. The Advanced Ducted Propfan Analysis (ADPAC) code was modified through the incorporation of the Spalart-Allmaras one-equation turbulence model. Suitable test cases were solved numerically using ADPAC employing the Spalart-Allmaras turbulence model and another prediction code for comparison. A near-wall spacing study was also completed to determine the adequate spacing of the first computational cell off the wall. Solutions were also collected using two versions of the algebraic Baldwin-Lomax turbulence model in ADPAC. The effects of the turbulence model on the rotor wake definition was examined by obtaining ADPAC solutions for the Low Noise Fan rotor-only steady-flow case using the standard algebraic Baldwin-Lomax turbulence model, a modified version of the Baldwin-Lomax turbulence model and the one-equation Spalart-Allmaras turbulence model. The results from the three different turbulence modeling techniques were compared with each other and the available experimental data. These results include overall rotor performance, spanwise exit profiles, and contours of axial velocity taken along constant axial locations and along blade-to-blade surfaces. Wake characterizations were also performed on the experimental and ADPAC predicted results including the definition of a wake correlation function. Correlations were evaluated for wake width and wake depth. Similarity profiles of the wake shape were also compared between all numerical solutions and experimental data.

  4. Effect of Trailing Edge Flow Injection on Fan Noise and Aerodynamic Performance

    NASA Technical Reports Server (NTRS)

    Fite, E. Brian; Woodward, Richard P.; Podboy, Gary G.

    2006-01-01

    An experimental investigation using trailing edge blowing for reducing fan rotor/guide vane wake interaction noise was completed in the NASA Glenn 9- by 15-foot Low Speed Wind Tunnel. Data were acquired to measure noise, aerodynamic performance, and flow features for a 22" tip diameter fan representative of modern turbofan technology. The fan was designed to use trailing edge blowing to reduce the fan blade wake momentum deficit. The test objective was to quantify noise reductions, measure impacts on fan aerodynamic performance, and document the flow field using hot-film anemometry. Measurements concentrated on approach, cutback, and takeoff rotational speeds as those are the primary conditions of acoustic interest. Data are presented for a 2% (relative to overall fan flow) trailing edge injection rate and show a 2 dB reduction in Overall Sound Power Level (OAPWL) at all fan test speeds. The reduction in broadband noise is nearly constant and is approximately 1.5 dB up to 20 kHz at all fan speeds. Measurements of tone noise show significant variation, as evidenced by reductions of up to 6 dB in the 2 BPF tone at 6700 rpm.: and increases of nearly 2 dB for the 4 BPF tone at approach speed. Aerodynamic performance measurements show the fan with 2 % injection has an overall efficiency that is comparable to the baseline fan and operates, as intended, with nearly the same pressure ratio and mass flow parameters. Hot-film measurements obtained at the approach operating condition indicate that mean blade wake filling in the tip region was not as significant as expected. This suggests that additional acoustic benefits could be realized if the trailing edge blowing could be modified to provide better filling of the wake momentum deficit. Nevertheless, the hot-film measurements indicate that the trailing edge blowing provided significant reductions in blade wake turbulence. Overall, these results indicate that further work may be required to fully understand the proper

  5. Two-stage, low noise advanced technology fan. Volume 2: Aerodynamic data

    NASA Technical Reports Server (NTRS)

    Harley, K. G.; Odegard, P. A.

    1975-01-01

    Aerodynamic data from static tests of a two-stage advanced technology fan designed to minimize noise are presented. Fan design conditions include delivery of 209.1kg/sec/sq m (42.85 lbm/sec/sq ft) specific corrected flow at an overall pressure ratio of 1.9 and an adiabatic efficiency of 85.3 percent. The 0.836m (2.74ft) diameter first stage rotor has a hub/tip ratio of 0.4 and 365.8m/sec (1200ft/sec) design tip speed. In addition to the moderate tip speed and pressure rise per stage, other noise control design features involve widely spaced blade rows and proper selection of blade-vane ratios. Aerodynamic data are presented for tests with unifrom and with hub and tip radially distorted inlet flow. Aerodynamic data are also presented for tests of this fan with acoustic treatments, including acoustically treated casing walls, a flowpath exit acoustic ring, and a translating centerbody sonic inlet device. A complete tabulation of the overall performance data, the blade element data, and the power spectral density information relating to turbulence levels generated by the sonic inlet obtained during these tests is included. For vol. 1, see N74-33789.

  6. Effect of anisotropic turbulence on aerodynamic noise. [Lighthill theory mathematical model for axisymmetric turbulence

    NASA Technical Reports Server (NTRS)

    Goldstein, M.; Rosenbaum, B.

    1973-01-01

    A model based on Lighthill's theory for predicting aerodynamic noise from a turbulent shear flow is developed. This model is a generalization of the one developed by Ribner. It does not require that the turbulent correlations factor into space and time-dependent parts. It replaces his assumption of isotropic turbulence by the more realistic one of axisymmetric turbulence. In the course of the analysis, a hierarchy of equations is developed wherein each succeeding equation involves more assumptions than the preceding equation but requires less experimental information for its use. The implications of the model for jet noise are discussed. It is shown that for the particular turbulence data considered anisotropy causes the high-frequency self-noise to be beamed downstream.

  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. Study of aerodynamic noise in low supersonic operation of an axial flow compressor

    NASA Technical Reports Server (NTRS)

    Arnoldi, R. A.

    1972-01-01

    A study of compressor noise is presented, based upon supersonic, part-speed operation of a high hub/tip ratio compressor designed for spanwise uniformity of aerodynamic conditions, having straight cylindrical inlet and exit passages for acoustic simplicity. Acoustic spectra taken in the acoustically-treated inlet plenum, are presented for five operating points at each of two speeds, corresponding to relative rotor tip Mach numbers of about 1.01 and 1.12 (60 and 67 percent design speed). These spectra are analyzed for low and high frequency broadband noise, blade passage frequency noise, combination tone noise and "haystack' noise (a very broad peak somewhat below blade passage frequency, which is occasionally observed in engines and fan test rigs). These types of noise are related to diffusion factor, total pressure ratio, and relative rotor tip Mach number. Auxiliary measurements of fluctuating wall static pressures and schlieren photographs of upstream shocks in the inlet are also presented and related to the acoustic and performance data.

  9. Cylinder wake influence on the tonal noise and aerodynamic characteristics of a NACA0018 airfoil

    NASA Astrophysics Data System (ADS)

    Takagi, Y.; Fujisawa, N.; Nakano, T.; Nashimoto, A.

    2006-11-01

    The influence of cylinder wake on discrete tonal noise and aerodynamic characteristics of a NACA0018 airfoil is studied experimentally in a uniform flow at a moderate Reynolds number. The experiments are carried out by measuring sound pressure levels and spectrum, separation and the reattachment points, pressure distribution, fluid forces, mean-flow and turbulence characteristics around the airfoil with and without the cylinder wake. Present results indicate that the tonal noise from the airfoil is suppressed by the influence of the cylinder wake and the aerodynamic characteristics are improved in comparison with the case without the cylinder wake. These are mainly due to the separation control of boundary layers over the airfoil caused by the wake-induced transition, which is observed by surface flow visualization with liquid- crystal coating. The PIV measurements of the flow field around the airfoil confirm that highly turbulent velocity fluctuation of the cylinder wake induces the transition of the boundary layers and produces an attached boundary layer over the airfoil. Then, the vortex shedding phenomenon near the trailing edge of pressure surface is removed by the influence of the wake and results in the suppression of tonal noise.

  10. 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.

  11. Lobed Mixer Design for Noise Suppression: Plume, Aerodynamic and Acoustic Data. Volume 2

    NASA Technical Reports Server (NTRS)

    Mengle, Vinod G.; Baker, V. David; Dalton, William N.; Bridges, James (Technical Monitor)

    2002-01-01

    A comprehensive database for the acoustic and aerodynamic characteristics of several model-scale lobe mixers of bypass ratio 5 to 6 has been created for mixed jet speeds up to 1080 ft per s at typical take-off (TO) conditions of small-to-medium turbofan engines. The flight effect was simulated for Mach numbers up to 0.3. The static thrust performance and plume data were also obtained at typical TO and cruise conditions. The tests were done at NASA Lewis anechoic dome and ASE's FluiDyne Laboratories. The effect of several lobe mixer and nozzle parameters, such as, lobe scalloping, lobe count, lobe penetration and nozzle length was examined in terms of flyover noise at constant altitude and also noise in the reference frame of the nozzle. This volume is divided into three parts: in the first two parts, we collate the plume survey data in graphical form (line, contour and surface plots) and analyze it; in part 3, we tabulate the aerodynamic data for the acoustics tests and the acoustic data in one-third octave band levels.

  12. 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.

  13. Unified Aeroacoustics Analysis for High Speed Turboprop Aerodynamics and Noise. Volume 1; Development of Theory for Blade Loading, Wakes, and Noise

    NASA Technical Reports Server (NTRS)

    Hanson, D. B.

    1991-01-01

    A unified theory for the aerodynamics and noise of advanced turboprops are presented. Aerodynamic topics include calculation of performance, blade load distribution, and non-uniform wake flow fields. Blade loading can be steady or unsteady due to fixed distortion, counter-rotating wakes, or blade vibration. The aerodynamic theory is based on the pressure potential method and is therefore basically linear. However, nonlinear effects associated with finite axial induction and blade vortex flow are included via approximate methods. Acoustic topics include radiation of noise caused by blade thickness, steady loading (including vortex lift), and unsteady loading. Shielding of the fuselage by its boundary layer and the wing are treated in separate analyses that are compatible but not integrated with the aeroacoustic theory for rotating blades.

  14. Aerodynamic and noise measurements on a quasi-two dimensional augmentor wing model with lobe-type nozzles

    NASA Technical Reports Server (NTRS)

    Aiken, T. N.

    1973-01-01

    An investigation was made of the static, wind-on aerodynamic and static noise characteristics of an augmentor wing having lobe type nozzles. The study was made in the Ames 7-by 10-Foot No. 1 Wind Tunnel using a small-scale, quasi-two-dimensional model. Several configurations of lobe nozzles as well as a normal slot nozzle were tested. Results indicate that lobe nozzles offer improved static and wind-on aerodynamics and reduced static noise relative to slot nozzles. Best wind-on performance was obtained when the tertiary gap was closed even though the static thrust augmentation was maximum with the gap open. Static thrust augmentation, wind-on lift and drag, and static noise directivity are presented as well as typical static and wind-on exit velocity profiles, surface pressure distributions and noise spectrums. The data are presented with limited discussion.

  15. Effects of aerodynamic interaction between main and tail rotors on helicopter hover performance and noise

    NASA Technical Reports Server (NTRS)

    Menger, R. P.; Wood, T. L.; Brieger, J. T.

    1983-01-01

    A model test was conducted to determine the effects of aerodynamic interaction between main rotor, tail rotor, and vertical fin on helicopter performance and noise in hover out of ground effect. The experimental data were obtained from hover tests performed with a .151 scale Model 222 main rotor, tail rotor and vertical fin. Of primary interest was the effect of location of the tail rotor with respect to the main rotor. Penalties on main rotor power due to interaction with the tail rotor ranged up to 3% depending upon tail rotor location and orientation. Penalties on tail rotor power due to fin blockage alone ranged up to 10% for pusher tail rotors and up to 50% for tractor tail rotors. The main rotor wake had only a second order effect on these tail rotor/fin interactions. Design charts are presented showing the penalties on main rotor power as a function of the relative location of the tail rotor.

  16. Inlet noise on 0.5-meter-diameter NASA QF-1 fan as measured in an unmodified compressor aerodynamic test facility and in an anechoic chamber

    NASA Technical Reports Server (NTRS)

    Gelder, T. F.; Soltis, R. F.

    1975-01-01

    Narrowband analysis revealed grossly similar sound pressure level spectra in each facility. Blade passing frequency (BPF) noise and multiple pure tone (MPT) noise were superimposed on a broadband (BB) base noise. From one-third octave bandwidth sound power analyses the BPF noise (harmonics combined), and the MPT noise (harmonics combined, excepting BPF's) agreed between facilities within 1.5 db or less over the range of speeds and flows tested. Detailed noise and aerodynamic performance is also presented.

  17. Radially leaned outlet guide vanes for fan source noise reduction

    NASA Technical Reports Server (NTRS)

    Kazin, S. B.

    1973-01-01

    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 noise of from 1 to 2 PNdb. The supersonic tip speed fan a takeoff fan speed, however, showed noise increases of up 3 PNdb and a decrease in fan efficiency. At approach fan speed, the subsonic tip speed fan showed a noise decrease of 2.3 PNdb at the 200-foot sideline maximum angle and an increase in efficiency. The supersonic tip speed fan showed noise increase of 3.5 PNdb and no change in efficiency. The decrease in fan efficiency and the nature of the noise increase largely high frequency broadband noise lead to the speculation that an aerodynamic problem occurred.

  18. 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.

  19. Computation of interactional aerodynamics for noise prediction of heavy lift rotorcraft

    NASA Astrophysics Data System (ADS)

    Hennes, Christopher C.

    Many computational tools are used when developing a modern helicopter. As the design space is narrowed, more accurate and time-intensive tools are brought to bear. These tools are used to determine the effect of a design decision on the performance, handling, stability and efficiency of the aircraft. One notable parameter left out of this process is acoustics. This is due in part to the difficulty in making useful acoustics calculations that reveal the differences between various design configurations. This thesis presents a new approach designed to bridge the gap in prediction capability between fast but low-fidelity Lagrangian particle methods, and slow but high-fidelity Eulerian computational fluid dynamics simulations. A multi-pronged approach is presented. First, a simple flow solver using well-understood and tested flow solution methodologies is developed specifically to handle bodies in arbitrary motion. To this basic flow solver two new technologies are added. The first is an Immersed Boundary technique designed to be tolerant of geometric degeneracies and low-resolution grids. This new technique allows easy inclusion of complex fuselage geometries at minimal computational cost, improving the ability of a solver to capture the complex interactional aerodynamic effects expected in modern rotorcraft design. The second new technique is an extension of a concept from flow visualization where the motion of tip vortices are tracked through the solution using massless particles convecting with the local flow. In this extension of that concept, the particles maintain knowledge of the expected and actual vortex strength. As a post-processing step, when the acoustic calculations are made, these particles are used to augment the loading noise calculation and reproduce the highly-impulsive character of blade-vortex interaction noise. In combination these new techniques yield a significant improvement to the state of the art in rotorcraft blade-vortex interaction noise

  20. Sonic inlet noise attenuation and performance with a J-85 turbojet engine as a noise source

    NASA Technical Reports Server (NTRS)

    Groth, H. W.

    1974-01-01

    A static test program was conducted to investigate aerodynamic and acoustic performance of a sonic inlet used as a noise 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 noise 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 noise attenuation at these static conditions.

  1. 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

  2. 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.

  3. 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

  4. Single stage, low noise, advanced technology fan. Volume 1: Aerodynamic design

    NASA Technical Reports Server (NTRS)

    Sullivan, T. J.; Younghans, J. L.; Little, D. R.

    1976-01-01

    The aerodynamic design for a half-scale fan vehicle, which would have application on an advanced transport aircraft, is described. The single stage advanced technology fan was designed to a pressure ratio of 1.8 at a tip speed of 503 m/sec 11,650 ft/sec). The fan and booster components are designed in a scale model flow size convenient for testing with existing facility and vehicle hardware. The design corrected flow per unit annulus area at the fan face is 215 kg/sec sq m (44.0 lb m/sec sq ft) with a hub-tip ratio of 0.38 at the leading edge of the fan rotor. This results in an inlet corrected airflow of 117.9 kg/sec (259.9 lb m/sec) for the selected rotor tip diameter if 90.37 cm (35.58 in.). The variable geometry inlet is designed utilizing a combination of high throat Mach number and acoustic treatment in the inlet diffuser for noise suppression (hybrid inlet). A variable fan exhaust nozzle was assumed in conjunction with the variable inlet throat area to limit the required area change of the inlet throat at approach and hence limit the overall diffusion and inlet length. The fan exit duct design was primarily influenced by acoustic requirements, including length of suppressor wall treatment; length, thickness and position on a duct splitter for additional suppressor treatment; and duct surface Mach numbers.

  5. Numerical study on reduction of aerodynamic noise around an airfoil with biomimetic structures

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Zhang, Chengchun; Wu, Zhengyang; Wharton, James; Ren, Luquan

    2017-04-01

    A biomimetic airfoil featuring leading edge waves, trailing edge serrations and surface ridges is proposed in this study, based on flow control with each section meeting the NACA 0012 airfoil profile. Numerical simulations have been conducted to compare aerodynamic and acoustic performances between the NACA 0012 and biomimetic airfoils. These simulations utilize the large eddy simulation (LES) method and aeroacoustic analogy at an angle of attack of 0° and a Reynolds number of 1.0×105, based on using the airfoil chord as the characteristic length. The simulation results reveal the overall sound pressure levels (OASPLs) for all frequencies and at the seven observer points around the biomimetic airfoil, and a decrease of 13.1-13.9 dB is observed, whereas the drag coefficient is almost unchanged. The biomimetic structures can transform the shedding vortices in laminar mode for the NACA 0012 airfoil to regular horseshoe-type vortices in the wake, and reduce the spanwise correlation of the large-scale vortices, thereby restrain the vortex shedding noise around the biomimetic airfoil.

  6. 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.

  7. 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.

  8. Simulation of Turbine Tone Noise Generation Using a Turbomachinery Aerodynamics Solver

    NASA Technical Reports Server (NTRS)

    VanZante, Dale; Envia, Edmane

    2010-01-01

    As turbofan engine bypass ratios continue to increase, the contribution of the turbine to the engine noise signature is receiving more attention. Understanding the relative importance of the various turbine noise generation mechanisms and the characteristics of the turbine acoustic transmission loss are essential ingredients in developing robust reduced-order models for predicting the turbine noise signature. A computationally based investigation has been undertaken to help guide the development of a turbine noise prediction capability that does not rely on empiricism. As proof-of-concept for this approach, two highly detailed numerical simulations of the unsteady flow field inside the first stage of a modern high-pressure turbine were carried out. The simulations were computed using TURBO, which is an unsteady Reynolds-Averaged Navier-Stokes code capable of multi-stage simulations. Spectral and modal analysis of the unsteady pressure data from the numerical simulation of the turbine stage show a circumferential modal distribution that is consistent with the Tyler-Sofrin rule. Within the high-pressure turbine, the interaction of velocity, pressure and temperature fluctuations with the downstream blade rows are all possible tone noise source mechanisms. We have taken the initial step in determining the source strength hierarchy by artificially reducing the level of temperature fluctuations in the turbine flowfield. This was accomplished by changing the vane cooling flow temperature in order to mitigate the vane thermal wake in the second of the two simulations. The results indicated that, despite a dramatic change in the vane cooling flow, the computed modal levels changed very little indicating that the contribution of temperature fluctuations to the overall pressure field is rather small compared with the viscous and potential field interaction mechanisms.

  9. 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.

  10. 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.

  11. 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.

  12. High frequency green function for aerodynamic noise in moving media. I - General theory. II - Noise from a spreading jet

    NASA Technical Reports Server (NTRS)

    Durbin, P. A.

    1983-01-01

    It is shown how a high frequency analysis can be made for general problems involving flow-generated noise. In the parallel shear flow problem treated by Balsa (1976) and Goldstein (1982), the equation governing sound propagation in the moving medium could be transformed into a wave equation for a stationary medium with an inhomogeneous index of refraction. It is noted that the procedure of Avila and Keller (1963) was then used to construct a high frequency Green function. This procedure involves matching a solution valid in an inner region around the point source to an outer, ray-acoustics solution. This same procedure is used here to construct the Green function for a source in an arbitrary mean flow. In view of the fact that there is no restriction to parallel flow, the governing equations cannot be transformed into a wave equation; the analysis therefore proceeds from the equations of motion themselves.

  13. Small scale noise and wind tunnel tests of upper surface blowing nozzle flap concepts. Volume 1. Aerodynamic test results

    NASA Technical Reports Server (NTRS)

    Renselaer, D. J.; Nishida, R. S.; Wilkin, C. A.

    1975-01-01

    The results and analyses of aerodynamic and acoustic studies conducted on the small scale noise and wind tunnel tests of upper surface blowing nozzle flap concepts are presented. Various types of nozzle flap concepts were tested. These are an upper surface blowing concept with a multiple slot arrangement with seven slots (seven slotted nozzle), an upper surface blowing type with a large nozzle exit at approximately mid-chord location in conjunction with a powered trailing edge flap with multiple slots (split flow or partially slotted nozzle). In addition, aerodynamic tests were continued on a similar multi-slotted nozzle flap, but with 14 slots. All three types of nozzle flap concepts tested appear to be about equal in overall aerodynamic performance but with the split flow nozzle somewhat better than the other two nozzle flaps in the landing approach mode. All nozzle flaps can be deflected to a large angle to increase drag without significant loss in lift. The nozzle flap concepts appear to be viable aerodynamic drag modulation devices for landing.

  14. NASA Aerodynamics Program Annual Report 1990

    DTIC Science & Technology

    1991-08-01

    95 ROTONET Phase IV System Multirotor Source Noise Module ...................................................... 97 Acoustic Results...94 Figure 6-7. ROTONET Phase IV System Multirotor Source Noise Module .................................. 96 Figure 6-8. Effects of Reduced...focusing on the areas of hybrid laminar flow technology and the reduction of aerodynamic interference between major aircraft components. A hybrid

  15. Experimental study of the aerodynamic noise radiated by cylinders with different cross-sections and yaw angles

    NASA Astrophysics Data System (ADS)

    Latorre Iglesias, E.; Thompson, D. J.; Smith, M. G.

    2016-01-01

    Vortex shedding from cylinders has been extensively studied due to its occurrence in many engineering fields. Many experimental studies reported in the literature focus on the aerodynamics of the vortex shedding process but the literature about the radiated noise is more scarce. The aim of the work presented here is to extend the available noise data. Aero-acoustic wind tunnel tests were carried out using cylinders with different cross-sections: circular, square, rectangular and elliptical. Flow speeds between 20 and 50 m/s were used, corresponding to Reynolds numbers in the range from 1.6×104 to 1.2×105. The dependence of the noise on the yaw angle, flow speed, cross-sectional shape, angle of attack and radiation angle (directivity) is assessed. The results obtained are compared, where possible, with those found in the literature for similar cases. It is intended that the results can be used for the validation and calibration of numerical and empirical aerodynamic noise prediction models.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. Active control of aircraft engine inlet noise using compact sound sources and distributed error sensors

    NASA Technical Reports Server (NTRS)

    Burdisso, Ricardo (Inventor); Fuller, Chris R. (Inventor); O'Brien, Walter F. (Inventor); Thomas, Russell H. (Inventor); Dungan, Mary E. (Inventor)

    1994-01-01

    An active noise control system using a compact sound source is effective to reduce aircraft engine duct noise. The fan noise 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 noise a viable technology, a compact sound source is employed to generate the control field. This control field sound source 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.

  6. Active control of aircraft engine inlet noise using compact sound sources and distributed error sensors

    NASA Technical Reports Server (NTRS)

    Burdisso, Ricardo (Inventor); Fuller, Chris R. (Inventor); O'Brien, Walter F. (Inventor); Thomas, Russell H. (Inventor); Dungan, Mary E. (Inventor)

    1996-01-01

    An active noise control system using a compact sound source is effective to reduce aircraft engine duct noise. The fan noise 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 noise a viable technology, a compact sound source is employed to generate the control field. This control field sound source 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.

  7. On the precise implications of acoustic analogies for aerodynamic noise at low Mach numbers

    NASA Astrophysics Data System (ADS)

    Spalart, Philippe R.

    2013-05-01

    We seek a clear statement of the scaling which may be expected with rigour for transportation or other noise at low Mach numbers M, based on Lighthill's and Curle's theories of 1952 and 1955. In the presence of compact solid bodies, the leading term in the acoustic intensity is of order M6. Contrary to the belief held since that time that it is of order M8, the contribution of quadrupoles, in the presence of dipoles, is of order only M7. Retarded-time-difference effects are also of order M7. Curle's widely used approximation based on unsteady forces neglects both effects. Its order of accuracy is thus lower than was thought, and the common estimates of the value of M below which it applies appear precarious. The M6 leading term is modified by powers up to the fourth of (1-Mr), where Mr is the relative Mach number between source and observer; at speeds of interest the effect is several dB. However, this is only one of the corrections of order M7, which makes its value debatable. The same applies to the difference between emission distance and reception distance. The scaling with M6 is theoretically correct to leading order, but this prediction may be so convincing, like the M8 scaling for jet noise, that some authors rush to confirm it when their measurements are in conflict with it. We survey experimental studies of landing-gear noise, and argue that the observed power of M is often well below 6. We also object to comparisons across Mach numbers at fixed frequency; they should be made at fixed Strouhal number St instead. Finally, the compact-source argument does not only require M≪1; it requires MSt≪1. This is more restrictive if the relevant St is well above 1, a situation which can be caused by interference with a boundary or by wake impingement, among other effects. The best length scales to define St for this purpose are discussed.

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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('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/2060/20080007425','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> </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_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li class="active"><span>5</span></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_5 --> <div id="page_6" 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_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> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="101"> <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('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 <span class="hlt">aerodynamic</span> 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 <span class="hlt">aerodynamic</span> 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://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> <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/2060/19910014536','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910014536"><span>Unified aeroacoustics analysis for high speed turboprop <span class="hlt">aerodynamics</span> and <span class="hlt">noise</span>. Volume 2: Development of theory for wing shielding</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Amiet, R. K.</p> <p>1991-01-01</p> <p>A unified theory for <span class="hlt">aerodynamics</span> and <span class="hlt">noise</span> of advanced turboprops is presented. The theory and a computer code developed for evaluation at the shielding benefits that might be expected by an aircraft wing in a wing-mounted propeller installation are presented. Several computed directivity patterns are presented to demonstrate the theory. Recently with the advent of the concept of using the wing of an aircraft for <span class="hlt">noise</span> shielding, the case of diffraction by a surface in a flow has been given attention. The present analysis is based on the case of diffraction of no flow. By combining a Galilean and a Lorentz transform, the wave equation with a mean flow can be reduced to the ordinary equation. Allowance is also made in the analysis for the case of a swept wing. The same combination of Galilean and Lorentz transforms lead to a problem with no flow but a different sweep. The solution procedures for the cases of leading and trailing edges are basically the same. Two normalizations of the solution are given by the computer program. FORTRAN computer programs are presented with detailed documentation. The output from these programs compares favorably with the results of other investigators.</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('https://www.ncbi.nlm.nih.gov/pubmed/18529018','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18529018"><span>Ambient <span class="hlt">aerodynamic</span> ionization <span class="hlt">source</span> for remote analyte sampling and mass spectrometric analysis.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Dixon, R Brent; Sampson, Jason S; Hawkridge, Adam M; Muddiman, David C</p> <p>2008-07-01</p> <p>The use of <span class="hlt">aerodynamic</span> devices in ambient ionization <span class="hlt">source</span> development has become increasingly prevalent in the field of mass spectrometry. In this study, an air ejector has been constructed from inexpensive, commercially available components to incorporate an electrospray ionization emitter within the exhaust jet of the device. This novel <span class="hlt">aerodynamic</span> device, herein termed remote analyte sampling, transport, and ionization relay (RASTIR) was used to remotely sample neutral species in the ambient and entrain them into an electrospray plume where they were subsequently ionized and detected using a linear ion trap Fourier transform mass spectrometer. Two sets of experiments were performed in the ambient environment to demonstrate the device's utility. The first involved the remote (approximately 1 ft) vacuum collection of pure sample particulates (i.e., dry powder) from a glass slide, entrainment and ionization at the ESI emitter, and mass spectrometric detection. The second experiment involved the capture (vacuum collection) of matrix-assisted laser desorbed proteins followed by entrainment in the ESI emitter plume, multiple charging, and mass spectrometric detection. This approach is in principle a RASTIR-assisted matrix-assisted laser desorption electrospray ionization <span class="hlt">source</span> (Sampson, J. S.; Hawkridge, A. M.; Muddiman, D. C. J. Am. Soc. Mass Spectrom. 2006, 17, 1712-1716; Rapid Commun. Mass Spectrom. 2007, 21, 1150-1154.). A detailed description of the device construction, operational parameters, and preliminary small molecule and protein data are presented.</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://hdl.handle.net/2060/20040073459','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040073459"><span>Investigation of Volumetric <span class="hlt">Sources</span> in Airframe <span class="hlt">Noise</span> Simulations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Casper, Jay H.; Lockard, David P.; Khorrami, Mehdi R.; Streett, Craig L.</p> <p>2004-01-01</p> <p>Hybrid methods for the prediction of airframe <span class="hlt">noise</span> 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 <span class="hlt">noise</span> predictions on the location of the integration surface used in the solution of the Ffowcs Williams and Hawkings equation. These differences in radiated <span class="hlt">noise</span> levels are most pronounced between solid-body surface integrals and off-body, permeable surface integrals. Such differences suggest that either a non-negligible volumetric <span class="hlt">source</span> 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 <span class="hlt">noise</span> predictions. The case study for this research is a computer simulation for a three-element, high-lift wing profile during landing conditions. The <span class="hlt">noise</span> radiated from this flow is predicted by a two-dimensional, frequency-domain formulation of the Ffowcs Williams and Hawkings equation. Radiated sound from volumetric <span class="hlt">sources</span> is assessed by comparison of a permeable surface integration with the sum of a solid-body surface integral and a volume integral. The separate <span class="hlt">noise</span> predictions are found in good agreement.</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/2060/19740025676','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19740025676"><span>Two stage low <span class="hlt">noise</span> advanced technology fan. 1: <span class="hlt">Aerodynamic</span>, structural, and acoustic design</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Messenger, H. E.; Ruschak, J. T.; Sofrin, T. G.</p> <p>1974-01-01</p> <p>A two-stage fan was designed to reduce <span class="hlt">noise</span> 20 db below current requirements. The first-stage rotor has a design tip speed of 365.8 m/sec and a hub/tip ratio of 0.4. The fan was designed to deliver a pressure ratio of 1.9 with an adiabatic efficiency of 85.3 percent at a specific inlet corrected flow of 209.2kg/sec/sq m. <span class="hlt">Noise</span> reduction devices include acoustically treated casing walls, a flowpath exit acoustic splitter, a translating centerbody sonic inlet device, widely spaced blade rows, and the proper ratio of blades and vanes. Multiple-circular-arc rotor airfoils, resettable stators, split outer casings, and capability to go to close blade-row spacing are also included.</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/2060/19870020101','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870020101"><span><span class="hlt">Aerodynamic</span> performance investigation of advanced mechanical suppressor and ejector nozzle concepts for jet <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>Wagenknecht, C. D.; Bediako, E. D.</p> <p>1985-01-01</p> <p>Advanced Supersonic Transport jet <span class="hlt">noise</span> may be reduced to Federal Air Regulation limits if recommended refinements to a recently developed ejector shroud exhaust system are successfully carried out. A two-part program consisting of a design study and a subscale model wind tunnel test effort conducted to define an acoustically treated ejector shroud exhaust system for supersonic transport application is described. Coannular, 20-chute, and ejector shroud exhaust systems were evaluated. Program results were used in a mission analysis study to determine aircraft takeoff gross weight to perform a nominal design mission, under Federal Aviation Regulation (1969), Part 36, Stage 3 <span class="hlt">noise</span> constraints. Mission trade study results confirmed that the ejector shroud was the best of the three exhaust systems studied with a significant takeoff gross weight advantage over the 20-chute suppressor nozzle which was the second best.</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> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910014538','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910014538"><span>Unified aeroacoustics analysis for high speed turboprop <span class="hlt">aerodynamics</span> and <span class="hlt">noise</span>. Volume 4: Computer user's manual for UAAP turboprop aeroacoustic code</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Menthe, R. W.; Mccolgan, C. J.; Ladden, R. M.</p> <p>1991-01-01</p> <p>The Unified AeroAcoustic Program (UAAP) code calculates the airloads on a single rotation prop-fan, or propeller, and couples these airloads with an acoustic radiation theory, to provide estimates of near-field or far-field <span class="hlt">noise</span> levels. The steady airloads can also be used to calculate the nonuniform velocity components in the propeller wake. The airloads are calculated using a three dimensional compressible panel method which considers the effects of thin, cambered, multiple blades which may be highly swept. These airloads may be either steady or unsteady. The acoustic model uses the blade thickness distribution and the steady or unsteady <span class="hlt">aerodynamic</span> loads to calculate the acoustic radiation. The users manual for the UAAP code is divided into five sections: general code description; input description; output description; system description; and error codes. The user must have access to IMSL10 libraries (MATH and SFUN) for numerous calls made for Bessel functions and matrix inversion. For plotted output users must modify the dummy calls to plotting routines included in the code to system-specific calls appropriate to the user's installation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1991hast.reptQ....M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1991hast.reptQ....M"><span>Unified aeroacoustics analysis for high speed turboprop <span class="hlt">aerodynamics</span> and <span class="hlt">noise</span>. Volume 4: Computer user's manual for UAAP turboprop aeroacoustic code</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Menthe, R. W.; McColgan, C. J.; Ladden, R. M.</p> <p>1991-05-01</p> <p>The Unified AeroAcoustic Program (UAAP) code calculates the airloads on a single rotation prop-fan, or propeller, and couples these airloads with an acoustic radiation theory, to provide estimates of near-field or far-field <span class="hlt">noise</span> levels. The steady airloads can also be used to calculate the nonuniform velocity components in the propeller wake. The airloads are calculated using a three dimensional compressible panel method which considers the effects of thin, cambered, multiple blades which may be highly swept. These airloads may be either steady or unsteady. The acoustic model uses the blade thickness distribution and the steady or unsteady <span class="hlt">aerodynamic</span> loads to calculate the acoustic radiation. The users manual for the UAAP code is divided into five sections: general code description; input description; output description; system description; and error codes. The user must have access to IMSL10 libraries (MATH and SFUN) for numerous calls made for Bessel functions and matrix inversion. For plotted output users must modify the dummy calls to plotting routines included in the code to system-specific calls appropriate to the user's installation.</p> </li> <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/2060/19760019109','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19760019109"><span>Two-stage, low <span class="hlt">noise</span> advanced technology fan. 4: <span class="hlt">Aerodynamic</span> final report</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Harley, K. G.; Keenan, M. J.</p> <p>1975-01-01</p> <p>A two-stage research fan was tested to provide technology for designing a turbofan engine for an advanced, long range commercial transport having a cruise Mach number of 0.85 -0.9 and a <span class="hlt">noise</span> level 20 EPNdB below current requirements. The fan design tip speed was 365.8m/sec (1200ft/sec);the hub/tip ratio was 0.4; the design pressure ratio was 1.9; and the design specific flow was 209.2 kg/sec/sq m(42.85lbm/sec/sq ft). Two fan-versions were tested: a baseline configuration, and an acoustically treated configuration with a sonic inlet device. The baseline version was tested with uniform inlet flow and with tip-radial and hub-radial inlet flow distortions. The baseline fan with uniform inlet flow attained an efficiency of 86.4% at design speed, but the stall margin was low. Tip-radial distortion increased stall margin 4 percentage points at design speed and reduced peak efficiency one percentage point. Hub-radial distortion decreased stall margin 4 percentage points at all speeds and reduced peak efficiency at design speed 8 percentage points. At design speed, the sonic inlet in the cruise position reduced stall margin one percentage point and efficiency 1.5 to 4.5 percentage points. The sonic inlet in the approach position reduced stall margin 2 percentage points.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910014539','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910014539"><span>Unified aeroacoustics analysis for high speed turboprop <span class="hlt">aerodynamics</span> and <span class="hlt">noise</span>. Volume 5: Propagation of propeller tone <span class="hlt">noise</span> through a fuselage boundary layer</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Magliozzi, B.; Hanson, D. B.</p> <p>1991-01-01</p> <p>An analysis of tone <span class="hlt">noise</span> propagation through a boundary layer and fuselage scattering effects was derived. This analysis is a three dimensional and the complete wave field is solved by matching analytical expressions for the incident and scattered waves in the outer flow to a numerical solution in the boundary layer flow. The outer wave field is constructed analytically from an incident wave appropriate to the <span class="hlt">source</span> and a scattered wave in the standard Hankel function form. For the incident wave, an existing function - domain propeller <span class="hlt">noise</span> radiation theory is used. In the boundary layer region, the wave equation is solved by numerical methods. The theoretical analysis is embodied in a computer program which allows the calculation of correction factors for the fuselage scattering and boundary layer refraction effects. The effects are dependent on boundary layer profile, flight speed, and frequency. Corrections can be derived for any point on the fuselage, including those on the opposite side from the <span class="hlt">source</span>. The theory was verified using limited cases and by comparing calculations with available measurements from JetStar tests of model prop-fans. For the JetStar model scale, the boundary layer refraction effects produce moderate fuselage pressure reinforcements aft of and near the plane of rotation and significant attenuation forward of the plane of rotation at high flight speeds. At lower flight speeds, the calculated boundary layer effects result in moderate amplification over the fuselage area of interest. Apparent amplification forward of the plane of rotation is a result of effective changes in the <span class="hlt">source</span> directivity due to boundary layer refraction effects. Full scale effects are calculated to be moderate, providing fuselage pressure amplification of about 5 dB at the peak <span class="hlt">noise</span> location. Evaluation using available <span class="hlt">noise</span> measurements was made under high-speed, high-altitude flight conditions. Comparisons of calculations made of free field <span class="hlt">noise</span>, using a</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 <span class="hlt">aerodynamic</span> 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://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/2060/20130013845','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130013845"><span>The Effects of Surfaces on the <span class="hlt">Aerodynamics</span> and Acoustics of Jet Flows</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smith, Matthew J.; Miller, Steven A. E.</p> <p>2013-01-01</p> <p>Aircraft <span class="hlt">noise</span> mitigation is an ongoing challenge for the aeronautics research community. In response to this challenge, low-<span class="hlt">noise</span> aircraft concepts have been developed that exhibit situations where the jet exhaust interacts with an airframe surface. Jet flows interacting with nearby surfaces manifest a complex behavior in which acoustic and <span class="hlt">aerodynamic</span> characteristics are altered. In this paper, the variation of the <span class="hlt">aerodynamics</span>, acoustic <span class="hlt">source</span>, and far-field acoustic intensity are examined as a large at plate is positioned relative to the nozzle exit. Steady Reynolds-Averaged Navier-Stokes solutions are examined to study the <span class="hlt">aerodynamic</span> changes in the field-variables and turbulence statistics. The mixing <span class="hlt">noise</span> model of Tam and Auriault is used to predict the <span class="hlt">noise</span> produced by the jet. To validate both the <span class="hlt">aerodynamic</span> and the <span class="hlt">noise</span> prediction models, results are compared with Particle Image Velocimetry (PIV) and free-field acoustic data respectively. The variation of the <span class="hlt">aerodynamic</span> quantities and <span class="hlt">noise</span> <span class="hlt">source</span> are examined by comparing predictions from various jet and at plate configurations with an isolated jet. To quantify the propulsion airframe aeroacoustic installation effects on the <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> <span class="hlt">source</span>, a non-dimensional number is formed that contains the flow-conditions and airframe installation parameters.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA100783','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA100783"><span><span class="hlt">Aerodynamic</span> <span class="hlt">Noise</span> and Suppressors,</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>1981-05-29</p> <p>not only disturbs people, it also excites the chickens and dogs, causes milk cows to stop producing milk , and pigs, horses, and cows to be affected...Figure 3.34, when the distance between holes is greater than the diameter of the holes, the acoustic impedance per area a is ZA - r, + llaMA , (3. 1)9</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 <span class="hlt">Aerodynamics</span> 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/2060/19830017227','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/2060/19990028361','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://adsabs.harvard.edu/abs/2015ESASP.730..201S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015ESASP.730..201S"><span>Open <span class="hlt">Source</span> Software Openfoam as a New <span class="hlt">Aerodynamical</span> Simulation Tool for Rocket-Borne Measurements</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Staszak, T.; Brede, M.; Strelnikov, B.</p> <p>2015-09-01</p> <p>The only way to do in-situ measurements, which are very important experimental studies for atmospheric science, in the mesoshere/lower thermosphere (MLT) is to use sounding rockets. The drawback of using rockets is the shock wave appearing because of the very high speed of the rocket motion (typically about 1000 mIs). This shock wave disturbs the density, the temperature and the velocity fields in the vicinity of the rocket, compared to undisturbed values of the atmosphere. This effect, however, can be quantified and the measured data has to be corrected not just to make it more precise but simply usable. The commonly accepted and widely used tool for this calculations is the Direct Simulation Monte Carlo (DSMC) technique developed by GA. Bird which is available as stand-alone program limited to use a single processor. Apart from complications with simulations of flows around bodies related to different flow regimes in the altitude range of MLT, that rise due to exponential density change by several orders of magnitude, a particular hardware configuration introduces significant difficulty for <span class="hlt">aerodynamical</span> calculations due to choice of the grid sizes mainly depending on the demands on adequate DSMCs and good resolution of geometries with scale differences of factor of iO~. This makes either the calculation time unreasonably long or even prevents the calculation algorithm from converging. In this paper we apply the free open <span class="hlt">source</span> software OpenFOAM (licensed under GNU GPL) for a three-dimensional CFD-Simulation of a flow around a sounding rocket instrumentation. An advantage of this software package, among other things, is that it can run on high performance clusters, which are easily scalable. We present the first results and discuss the potential of the new tool in applications for sounding rockets.</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/2010FlDyR..42a1001A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010FlDyR..42a1001A"><span>PREFACE: <span class="hlt">Aerodynamic</span> sound <span class="hlt">Aerodynamic</span> sound</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Akishita, Sadao</p> <p>2010-02-01</p> <p>The modern theory of <span class="hlt">aerodynamic</span> sound originates from Lighthill's two papers in 1952 and 1954, as is well known. I have heard that Lighthill was motivated in writing the papers by the jet-<span class="hlt">noise</span> emitted by the newly commercialized jet-engined airplanes at that time. The technology of <span class="hlt">aerodynamic</span> sound is destined for environmental problems. Therefore the theory should always be applied to newly emerged public nuisances. This issue of Fluid Dynamics Research (FDR) reflects problems of environmental sound in present Japanese technology. The Japanese community studying <span class="hlt">aerodynamic</span> sound has held an annual symposium since 29 years ago when the late Professor S Kotake and Professor S Kaji of Teikyo University organized the symposium. Most of the Japanese authors in this issue are members of the annual symposium. I should note the contribution of the two professors cited above in establishing the Japanese community of <span class="hlt">aerodynamic</span> sound research. It is my pleasure to present the publication in this issue of ten papers discussed at the annual symposium. I would like to express many thanks to the Editorial Board of FDR for giving us the chance to contribute these papers. We have a review paper by T Suzuki on the study of jet <span class="hlt">noise</span>, which continues to be important nowadays, and is expected to reform the theoretical model of generating mechanisms. Professor M S Howe and R S McGowan contribute an analytical paper, a valuable study in today's fluid dynamics research. They apply hydrodynamics to solve the compressible flow generated in the vocal cords of the human body. Experimental study continues to be the main methodology in <span class="hlt">aerodynamic</span> sound, and it is expected to explore new horizons. H Fujita's study on the Aeolian tone provides a new viewpoint on major, longstanding sound problems. The paper by M Nishimura and T Goto on textile fabrics describes new technology for the effective reduction of bluff-body <span class="hlt">noise</span>. The paper by T Sueki et al also reports new technology for the</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/2060/20020084621','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/2060/19970017414','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 <span class="hlt">aerodynamic</span> 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://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> <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://hdl.handle.net/2060/20040085745','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040085745"><span>Modeling <span class="hlt">Aerodynamically</span> Generated Sound of Helicopter Rotors</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Brentner, Kenneth S.; Farassat, F.</p> <p>2002-01-01</p> <p>A great deal of progress has been made in the modeling of <span class="hlt">aerodynamically</span> generated sound of rotors over the past decade. Although the modeling effort has focused on helicopter main rotors, the theory is generally valid for a wide range of rotor configurations. The Ffowcs Williams Hawkings (FW-H) equation has been the foundation for much of the development. The monopole and dipole <span class="hlt">source</span> terms of the FW-H equation account for the thickness and loading <span class="hlt">noise</span>, respectively. Bladevortex-interaction <span class="hlt">noise</span> and broadband <span class="hlt">noise</span> are important types of loading <span class="hlt">noise</span>, hence much research has been directed toward the accurate modeling of these <span class="hlt">noise</span> mechanisms. Both subsonic and supersonic quadrupole <span class="hlt">noise</span> formulations have been developed for the prediction of high-speed impulsive <span class="hlt">noise</span>. In an effort to eliminate the need to compute the quadrupole contribution, the FW-H equation has also been utilized on permeable surfaces surrounding all physical <span class="hlt">noise</span> <span class="hlt">sources</span>. Comparisons of the Kirchhoff formulation for moving surfaces with the FW-H equation have shown that the Kirchhoff formulation for moving surfaces can give erroneous results for aeroacoustic problems. Finally, significant progress has been made incorporating the rotor <span class="hlt">noise</span> models into full vehicle <span class="hlt">noise</span> prediction tools.</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('https://www.osti.gov/scitech/biblio/1021160','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1021160"><span>Aeroacoustics and <span class="hlt">aerodynamic</span> performance of a rotor with flatback airfoils.</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Paquette, Joshua A.; Barone, Matthew Franklin; Christiansen, Monica; Simley, Eric</p> <p>2010-06-01</p> <p>The <span class="hlt">aerodynamic</span> performance and aeroacoustic <span class="hlt">noise</span> <span class="hlt">sources</span> of a rotor employing flatback airfoils have been studied in field test campaign and companion modeling effort. The field test measurements of a sub-scale rotor employing nine meter blades include both performance measurements and acoustic measurements. The acoustic measurements are obtained using a 45 microphone beamforming array, enabling identification of both <span class="hlt">noise</span> <span class="hlt">source</span> amplitude and position. Semi-empirical models of flatback airfoil blunt trailing edge <span class="hlt">noise</span> are developed and calibrated using available aeroacoustic wind tunnel test data. The model results and measurements indicate that flatback airfoil <span class="hlt">noise</span> is less than drive train <span class="hlt">noise</span> for the current test turbine. It is also demonstrated that the commonly used Brooks, Pope, and Marcolini model for blunt trailing edge <span class="hlt">noise</span> may be over-conservative in predicting flatback airfoil <span class="hlt">noise</span> for wind turbine applications.</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://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('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2636590','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2636590"><span>The generation of diesel exhaust particle aerosols from a bulk <span class="hlt">source</span> in an <span class="hlt">aerodynamic</span> size range similar to atmospheric particles</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Cooney, Daniel J; Hickey, Anthony J</p> <p>2008-01-01</p> <p>The influence of diesel exhaust particles (DEP) on the lungs and heart is currently a topic of great interest in inhalation toxicology. Epidemiological data and animal studies have implicated airborne particulate matter and DEP in increased morbidity and mortality due to a number of cardiopulmonary diseases including asthma, chronic obstructive pulmonary disorder, and lung cancer. The pathogeneses of these diseases are being studied using animal models and cell culture techniques. Real-time exposures to freshly combusted diesel fuel are complex and require significant infrastructure including engine operations, dilution air, and monitoring and control of gases. A method of generating DEP aerosols from a bulk <span class="hlt">source</span> in an <span class="hlt">aerodynamic</span> size range similar to atmospheric DEP would be a desirable and useful alternative. Metered dose inhaler technology was adopted to generate aerosols from suspensions of DEP in the propellant hydrofluoroalkane 134a. Inertial impaction data indicated that the particle size distributions of the generated aerosols were trimodal, with count median <span class="hlt">aerodynamic</span> diameters less than 100 nm. Scanning electron microscopy of deposited particles showed tightly aggregated particles, as would be expected from an evaporative process. Chemical analysis indicated that there were no major changes in the mass proportion of 2 specific aromatic hydrocarbons (benzo[a]pyrene and benzo[k]fluoranthene) in the particles resulting from the aerosolization process. PMID:19337412</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://www.dtic.mil/docs/citations/ADA109848','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA109848"><span><span class="hlt">Aerodynamic</span> and Acoustic Tests of a 1/15 Scale Model Dry Cooled Jet Aircraft Runup <span class="hlt">Noise</span> Suppression System,</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>1975-10-01</p> <p>Temperature Contours for the Obround Augmenter with the Jet Centered (Position a, yp = 1.0) and Deflected Downward 3.60 165 Figure 7.3- 16 . Maximum Mixed...Acoustic Tests -8- r7 FLUIDYNE ENGINEERING CORPORATION I 2.0.3 Aero-Thermal Testing (Test Series 13 through 16 ) I The aero-thermal testing, Figure...Excessive Augmenter Exit Flow <span class="hlt">Noise</span> <span class="hlt">Noise</span> One Engine at Two Engines at Criteria Max. RPM Max. RPM at 250 ft. AA/ANT a AA/A NT 95 dBA 18 16 85 dBA 24</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('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>, <span class="hlt">aerodynamic</span> or airframe <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://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://ntrs.nasa.gov/search.jsp?R=19770059005&hterms=usb&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dusb','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19770059005&hterms=usb&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dusb"><span>Upper surface blowing <span class="hlt">aerodynamic</span> and acoustic characteristics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ryle, D. M., Jr.; Braden, J. A.; Gibson, J. S.</p> <p>1977-01-01</p> <p><span class="hlt">Aerodynamic</span> performance at cruise, and <span class="hlt">noise</span> effects due to variations in nacelle and wing geometry and mode of operation are studied using small aircraft models that simulate upper surface blowing (USB). At cruise speeds ranging from Mach .50 to Mach .82, the key determinants of drag/thrust penalties are found to be nozzle aspect ratio, boattailing angle, and chordwise position; number of nacelles; and streamlined versus symmetric configuration. Recommendations are made for obtaining favorable cruise configurations. The acoustic studies, which concentrate on the <span class="hlt">noise</span> created by the jet exhaust flow and its interaction with wing and flap surfaces, isolate several important <span class="hlt">sources</span> of USB <span class="hlt">noise</span>, including nozzle shape, exit velocity, and impingement angle; flow pathlength; and flap angle and radius of curvature. Suggestions for lessening <span class="hlt">noise</span> due to trailing edge flow velocity, flow pathlength, and flow spreading are given, though compromises between some design options may be necessary.</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> </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.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://adsabs.harvard.edu/abs/1997JSV...208..803C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997JSV...208..803C"><span>The Aeroacoustics and <span class="hlt">Aerodynamics</span> of High-Speed Coanda Devices, Part 2: Effects of Modifications for Flow Control and <span class="hlt">Noise</span> Reduction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Carpenter, P. W.; Smith, C.</p> <p>1997-12-01</p> <p>The paper describes two studies of the effects of flow control devices on the <span class="hlt">aerodynamics</span> and aeroacoustics of a high-speed Coanda flow that is formed when a supersonic jet issues from a radial nozzle and adheres to a tulip-shaped body of revolution. Shadowgraphy and other flow-visualization techniques are used to reveal the various features of the complex flow fields. The acoustic characteristics are obtained from far- and near-field measurements with an array of microphones in an anechoic chamber. First the effects of incorporating a step between the annular exit slot and the Coanda surface are investigated. The step is incorporated to ensure that the breakaway pressure is raised to a level well above the maximum operating pressure. It substantially increases the complexity of the flow field and acoustic characteristics. In particular, it promotes the generation of two groups of discrete tones. A theoretical model based on a self-generated feedback loop is proposed to explain how these tones are generated. The second study investigates the effects of replacing the annular exit slot with a saw-toothed one with the aim of eliminating the discrete tones and thereby substantially reducing the level of <span class="hlt">noise</span> generated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20070025191','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20070025191"><span><span class="hlt">Noise</span> Generation in Hot 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; Kenzakowski, Donald C.</p> <p>2007-01-01</p> <p>A prediction method based on the generalized acoustic analogy is presented, and used to evaluate <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> radiated from high speed hot jets. The set of Euler equations are split into their respective non-radiating and residual components. Under certain conditions, the residual equations are rearranged to form a wave equation. This equation consists of a third-order wave operator, plus a number of nonlinear terms that are identified with the equivalent <span class="hlt">sources</span> of sound and their statistical characteristics are modeled. A specialized RANS solver provides the base flow as well as turbulence quantities and temperature fluctuations that determine the <span class="hlt">source</span> strength. The main objective here is to evaluate the relative contribution from various <span class="hlt">source</span> elements to the far-field spectra and to show the significance of temperature fluctuations as a <span class="hlt">source</span> of <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> in hot jets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140002783','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140002783"><span>Limitations of Phased Array Beamforming in Open Rotor <span class="hlt">Noise</span> <span class="hlt">Source</span> Imaging</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Horvath, Csaba; Envia, Edmane; Podboy, Gary G.</p> <p>2013-01-01</p> <p>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 <span class="hlt">noise</span> 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 <span class="hlt">noise</span> <span class="hlt">sources</span> of the blade passing frequency tones and interaction tones appear at their nominal Mach radii instead of at the actual <span class="hlt">noise</span> <span class="hlt">sources</span>, 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 <span class="hlt">noise</span> <span class="hlt">sources</span> interact with the phased array, often giving misleading results, as the apparent <span class="hlt">sources</span> do not always show where the actual <span class="hlt">noise</span> <span class="hlt">sources</span> are located. This suggests that a more sophisticated <span class="hlt">source</span> model would be required to accurately locate the <span class="hlt">sources</span> of each tone. The results of this study also have implications with regard to the shielding of open rotor <span class="hlt">sources</span> by airframe empennages.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016IJMPS..4260173N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016IJMPS..4260173N"><span><span class="hlt">Aerodynamic</span> Characteristic of the Active Compliant Trailing Edge Concept</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nie, Rui; Qiu, Jinhao; Ji, Hongli; Li, Dawei</p> <p>2016-06-01</p> <p>This paper introduces a novel Morphing Wing structure known as the Active Compliant Trailing Edge (ACTE). ACTE structures are designed using the concept of “distributed compliance” and wing skins of ACTE are fabricated from high-strength fiberglass composites laminates. Through the relative sliding between upper and lower wing skins which are connected by a linear guide pairs, the wing is able to achieve a large continuous deformation. In order to present an investigation about <span class="hlt">aerodynamics</span> and <span class="hlt">noise</span> characteristics of ACTE, a series of 2D airfoil analyses are established. The <span class="hlt">aerodynamic</span> characteristics between ACTE and conventional deflection airfoil are analyzed and compared, and the impacts of different ACTE structure design parameters on <span class="hlt">aerodynamic</span> characteristics are discussed. The airfoils mentioned above include two types (NACA0012 and NACA64A005.92). The computing results demonstrate that: compared with the conventional plane flap airfoil, the morphing wing using ACTE structures has the capability to improve <span class="hlt">aerodynamic</span> characteristic and flow separation characteristic. In order to study the <span class="hlt">noise</span> level of ACTE, flow field analysis using LES model is done to provide <span class="hlt">noise</span> <span class="hlt">source</span> data, and then the FW-H method is used to get the far field <span class="hlt">noise</span> levels. The simulation results show that: compared with the conventional flap/aileron airfoil, the ACTE configuration is better to suppress the flow separation and lower the overall sound pressure level.</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> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770010117','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770010117"><span>Single-stage, low-<span class="hlt">noise</span>, advanced technology fan. Volume 4: Fan <span class="hlt">aerodynamics</span>. Section 1: Results and analysis</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sullivan, T. J.; Silverman, I.; Little, D. R.</p> <p>1977-01-01</p> <p>Test results at design speed show fan total pressure ratio, weight flow, and adiabatic efficiency to be 2.2, 2.9, and 1.8% lower than design goal values. The hybrid acoustic inlet (which utilizes a high throat Mach number and acoustic wall treatment for <span class="hlt">noise</span> suppression) demonstrated total pressure recoveries of 98.9% and 98.2% at takeoff and approach. Exhaust duct pressure losses differed between the hardwall duct and treated duct with splitter by about 0.6% to 2.0% in terms of fan exit average total pressure (depending on operating condition). When the measured results were used to estimate pressure losses, a cruise sfc penalty of 0.68%, due to the acoustically treated duct, was projected.</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> </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://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://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/2060/20040191552','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/2060/19930084698','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930084698"><span><span class="hlt">Aerodynamic</span> Mixing Downstream from Line <span class="hlt">Source</span> of Heat in High-intensity Sound Field</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mickelson, William R; Baldwin, Lionel V</p> <p>1956-01-01</p> <p>Theory and measurement showed that the heat wake downstream from a line <span class="hlt">source</span> is displaced by a transverse standing sound wave in a manner similar to a flag waving in a harmonic mode. With a 147 db, 104 cps standing wave, time-mean temperatures were reduced by an order of magnitude except near the displacement-pattern nodal points. The theory showed that a 161 db, 520 cps standing wave considerably increased the mixing in both the time-mean and instantaneous senses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19780016121','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19780016121"><span>USB <span class="hlt">noise</span> reduction by nozzle and flap modifications</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.</p> <p>1976-01-01</p> <p>The development of concepts for reducing upper surface blown flap <span class="hlt">noise</span> at the <span class="hlt">source</span> through flap modifications and special nozzles is reviewed. In particular, recent results obtained on the <span class="hlt">aerodynamic</span> and acoustic performance of flaps with porous surfaces near the trailing edge and multi-slotted nozzles are reviewed. Considerable reduction (6-10 db) of the characteristic low frequency peak is shown. The <span class="hlt">aerodynamic</span> performance is compared with conventional systems, and prospects for future improvements are discussed.</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://www.osti.gov/scitech/servlets/purl/1029824','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1029824"><span>Survey of techniques for reduction of wind turbine blade trailing edge <span class="hlt">noise</span>.</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Barone, Matthew Franklin</p> <p>2011-08-01</p> <p><span class="hlt">Aerodynamic</span> <span class="hlt">noise</span> from wind turbine rotors leads to constraints in both rotor design and turbine siting. The primary <span class="hlt">source</span> of <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> on wind turbine rotors is the interaction of turbulent boundary layers on the blades with the blade trailing edges. This report surveys concepts that have been proposed for trailing edge <span class="hlt">noise</span> reduction, with emphasis on concepts that have been tested at either sub-scale or full-scale. These concepts include trailing edge serrations, low-<span class="hlt">noise</span> airfoil designs, trailing edge brushes, and porous trailing edges. The demonstrated <span class="hlt">noise</span> reductions of these concepts are cited, along with their impacts on <span class="hlt">aerodynamic</span> performance. An assessment is made of future research opportunities in trailing edge <span class="hlt">noise</span> reduction for wind turbine rotors.</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/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://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_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://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('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/2060/20060048234','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20060048234"><span>An Assessment of NASA Glenn's Aeroacoustic Experimental and Predictive Capabilities for Installed Cooling Fans. Part 1; <span class="hlt">Aerodynamic</span> Performance</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>VanZante, Dale E.; Koch, L. Danielle; Wernet, Mark P.; Podboy, Gary G.</p> <p>2006-01-01</p> <p>Driven by the need for low production costs, electronics cooling fans have evolved differently than the bladed components of gas turbine engines which incorporate multiple technologies to enhance performance and durability while reducing <span class="hlt">noise</span> emissions. Drawing upon NASA Glenn's experience in the measurement and prediction of gas turbine engine aeroacoustic performance, tests have been conducted to determine if these tools and techniques can be extended for application to the <span class="hlt">aerodynamics</span> and acoustics of electronics cooling fans. An automated fan plenum installed in NASA Glenn's Acoustical Testing Laboratory was used to map the overall <span class="hlt">aerodynamic</span> and acoustic performance of a spaceflight qualified 80 mm diameter axial cooling fan. In order to more accurately identify <span class="hlt">noise</span> <span class="hlt">sources</span>, diagnose performance limiting <span class="hlt">aerodynamic</span> deficiencies, and validate <span class="hlt">noise</span> prediction codes, additional <span class="hlt">aerodynamic</span> measurements were recorded for two operating points: free delivery and a mild stall condition. Non-uniformities in the fan s inlet and exhaust regions captured by Particle Image Velocimetry measurements, and rotor blade wakes characterized by hot wire anemometry measurements provide some assessment of the fan <span class="hlt">aerodynamic</span> performance. The data can be used to identify fan installation/design changes which could enlarge the stable operating region for the fan and improve its <span class="hlt">aerodynamic</span> performance and reduce <span class="hlt">noise</span> emissions.</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('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/2060/20040065977','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040065977"><span>The Airframe <span class="hlt">Noise</span> Reduction Challenge</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lockhard, David P.; Lilley, Geoffrey M.</p> <p>2004-01-01</p> <p>The NASA goal of reducing external aircraft <span class="hlt">noise</span> 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 <span class="hlt">noise</span>. Acoustic and <span class="hlt">aerodynamic</span> effects will be discussed, along with the likelihood of industry accepting and implementing the different technologies. We investigate the lower bound, defined as <span class="hlt">noise</span> generated by an aircraft modified with a virtual retrofit capable of eliminating all <span class="hlt">noise</span> associated with the high lift system and landing gear. However, the airframe <span class="hlt">noise</span> 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 <span class="hlt">noise</span> reduction will require that additional <span class="hlt">noise</span> <span class="hlt">sources</span> be addressed. Research shows that energy in the turbulent boundary layer of a wing is scattered as it crosses trailing edge. <span class="hlt">Noise</span> generated by scattering is the dominant <span class="hlt">noise</span> 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 <span class="hlt">noise</span> reduction, we need to employ emerging technologies and improve landing procedures; modified landing patterns and zoning restrictions could help alleviate aircraft <span class="hlt">noise</span> in communities close to airports.</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://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 <span class="hlt">aerodynamic</span> 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('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> <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://hdl.handle.net/2060/20110002972','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110002972"><span>Computational <span class="hlt">Aerodynamic</span> Simulations of a Spacecraft Cabin Ventilation Fan Design</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Tweedt, Daniel L.</p> <p>2010-01-01</p> <p>Quieter working environments for astronauts are needed if future long-duration space exploration missions are to be safe and productive. Ventilation and payload cooling fans are known to be dominant <span class="hlt">sources</span> of <span class="hlt">noise</span>, with the International Space Station being a good case in point. To address this issue cost effectively, early attention to fan design, selection, and installation has been recommended, leading to an effort by NASA to examine the potential for small-fan <span class="hlt">noise</span> reduction by improving fan <span class="hlt">aerodynamic</span> design. As a preliminary part of that effort, the <span class="hlt">aerodynamics</span> of a cabin ventilation fan designed by Hamilton Sundstrand has been simulated using computational fluid dynamics codes, and the computed solutions analyzed to quantify various aspects of the fan <span class="hlt">aerodynamics</span> and performance. Four simulations were performed at the design rotational speed: two at the design flow rate and two at off-design flow rates. Following a brief discussion of the computational codes, various <span class="hlt">aerodynamic</span>- and performance-related quantities derived from the computed flow fields are presented along with relevant flow field details. The results show that the computed fan performance is in generally good agreement with stated design goals.</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://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('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 <span class="hlt">aerodynamic</span> 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('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/2060/20090041558','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://hdl.handle.net/2060/20110002741','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110002741"><span><span class="hlt">Aerodynamic</span> Design and Computational Analysis of a Spacecraft Cabin Ventilation Fan</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Tweedt, Daniel L.</p> <p>2010-01-01</p> <p>Quieter working environments for astronauts are needed if future long-duration space exploration missions are to be safe and productive. Ventilation and payload cooling fans are known to be dominant <span class="hlt">sources</span> of <span class="hlt">noise</span>, with the International Space Station being a good case in point. To address this issue in a cost-effective way, early attention to fan design, selection, and installation has been recommended. Toward that end, NASA has begun to investigate the potential for small-fan <span class="hlt">noise</span> reduction through improvements in fan <span class="hlt">aerodynamic</span> design. Using tools and methodologies similar to those employed by the aircraft engine industry, most notably computational fluid dynamics (CFD) codes, the <span class="hlt">aerodynamic</span> design of a new cabin ventilation fan has been developed, and its <span class="hlt">aerodynamic</span> performance has been predicted and analyzed. The design, intended to serve as a baseline for future work, is discussed along with selected CFD results</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/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/2060/20050209957','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050209957"><span>Three-Dimensional Application of DAMAS Methodology for Aeroacoustic <span class="hlt">Noise</span> <span class="hlt">Source</span> Definition</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>2005-01-01</p> <p>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 <span class="hlt">Sources</span> (DAMAS) was developed which decouples the array design and processing influence from the <span class="hlt">noise</span> being measured, using a simple and robust algorithm. For several prior airframe <span class="hlt">noise</span> studies, it was shown to permit an unambiguous and accurate determination of acoustic <span class="hlt">source</span> 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 <span class="hlt">source</span> 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 <span class="hlt">noise</span> 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 <span class="hlt">noise</span> <span class="hlt">source</span> distributions in a difficult hard-wall wind tunnel environment.</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://hdl.handle.net/2060/19980227963','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19980227963"><span><span class="hlt">Noise</span> Considerations for Manned Reentry Vehicles</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hilton, David A.; Mayes, William H.; Hubbard, Harvey H.</p> <p>1960-01-01</p> <p><span class="hlt">Noise</span> measurements pertaining mainly to the static firing, launch, 0 and exit flight phases are presented for three rocket-powered vehicles 4 in the Project Mercury test program. Both internal and external data 4 from onboard recordings are presented for a range of Mach numbers and dynamic pressures and for different external vehicle shapes. The main <span class="hlt">sources</span> of <span class="hlt">noise</span> are noted to be the rocket engines during static firing and launch and the <span class="hlt">aerodynamic</span> boundary layer during the high-dynamic-pressure portions of the flight. Rocket-engine <span class="hlt">noise</span> measurements along the surface of the Mercury Big Joe vehicle were noted to correlate well with data from small models and available data for other large rockets. Measurements have indicated that the <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> pressures increase approximately as the dynamic pressure increases and may vary according to the external shape of the vehicle, the highest <span class="hlt">noise</span> levels being associated with conditions of flow separation. There is also a trend for the <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> spectra to peak at higher frequencies as the flight Mach number increases.</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('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('http://hdl.handle.net/2060/19990110628','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19990110628"><span>Computation of Supersonic Jet Mixing <span class="hlt">Noise</span> Using PARC Code With a kappa-epsilon Turbulence Model</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Khavaran, A.; Kim, C. M.</p> <p>1999-01-01</p> <p>A number of modifications have been proposed in order to improve the jet <span class="hlt">noise</span> prediction capabilities of the MGB code. This code which was developed at General Electric, employees the concept of acoustic analogy for the prediction of turbulent mixing <span class="hlt">noise</span>. The <span class="hlt">source</span> convection and also refraction of sound due to the shrouding effect of the mean flow are accounted for by incorporating the high frequency solution to Lilley's equation for cylindrical jets (Balsa and Mani). The broadband shock-associated <span class="hlt">noise</span> is estimated using Harper-Bourne and Fisher's shock <span class="hlt">noise</span> theory. The proposed modifications are aimed at improving the <span class="hlt">aerodynamic</span> predictions (<span class="hlt">source</span>/spectrum computations) and allowing for the non- axisymmetric effects in the jet plume and nozzle geometry (sound/flow interaction). In addition, recent advances in shock <span class="hlt">noise</span> prediction as proposed by Tam can be employed to predict the shock-associated <span class="hlt">noise</span> as an addition to the jet mixing <span class="hlt">noise</span> when the flow is not perfectly expanded. Here we concentrate on the <span class="hlt">aerodynamic</span> predictions using the PARC code with a k-E turbulence model and the ensuing turbulent mixing <span class="hlt">noise</span>. The geometry under consideration is an axisymmetric convergent-divergent nozzle at its design operating conditions. <span class="hlt">Aerodynamic</span> and acoustic computations are compared with data as well as predictions due to the original MGB model using Reichardt's <span class="hlt">aerodynamic</span> theory.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23967933','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23967933"><span>On-road and wind-tunnel measurement of motorcycle helmet <span class="hlt">noise</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kennedy, J; Carley, M; Walker, I; Holt, N</p> <p>2013-09-01</p> <p>The <span class="hlt">noise</span> <span class="hlt">source</span> mechanisms involved in motorcycling include various <span class="hlt">aerodynamic</span> <span class="hlt">sources</span> and engine <span class="hlt">noise</span>. The problem of <span class="hlt">noise</span> <span class="hlt">source</span> identification requires extensive data acquisition of a type and level that have not previously been applied. Data acquisition on track and on road are problematic due to rider safety constraints and the portability of appropriate instrumentation. One way to address this problem is the use of data from wind tunnel tests. The validity of these measurements for <span class="hlt">noise</span> <span class="hlt">source</span> identification must first be demonstrated. In order to achieve this extensive wind tunnel tests have been conducted and compared with the results from on-track measurements. Sound pressure levels as a function of speed were compared between on track and wind tunnel tests and were found to be comparable. Spectral conditioning techniques were applied to separate engine and wind tunnel <span class="hlt">noise</span> from <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> and showed that the <span class="hlt">aerodynamic</span> components were equivalent in both cases. The spectral conditioning of on-track data showed that the contribution of engine <span class="hlt">noise</span> to the overall <span class="hlt">noise</span> is a function of speed and is more significant than had previously been thought. These procedures form a basis for accurate experimental measurements of motorcycle <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('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://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('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('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4116176','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4116176"><span>Adaptive Neuro-Fuzzy Methodology for <span class="hlt">Noise</span> Assessment of Wind Turbine</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Shamshirband, Shahaboddin; Petković, Dalibor; Hashim, Roslan; Motamedi, Shervin</p> <p>2014-01-01</p> <p>Wind turbine <span class="hlt">noise</span> is one of the major obstacles for the widespread use of wind energy. <span class="hlt">Noise</span> tone can greatly increase the annoyance factor and the negative impact on human health. <span class="hlt">Noise</span> annoyance caused by wind turbines has become an emerging problem in recent years, due to the rapid increase in number of wind turbines, triggered by sustainable energy goals set forward at the national and international level. Up to now, not all aspects of the generation, propagation and perception of wind turbine <span class="hlt">noise</span> are well understood. For a modern large wind turbine, <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> from the blades is generally considered to be the dominant <span class="hlt">noise</span> <span class="hlt">source</span>, provided that mechanical <span class="hlt">noise</span> is adequately eliminated. The <span class="hlt">sources</span> of <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> can be divided into tonal <span class="hlt">noise</span>, inflow turbulence <span class="hlt">noise</span>, and airfoil self-<span class="hlt">noise</span>. Many analytical and experimental acoustical studies performed the wind turbines. Since the wind turbine <span class="hlt">noise</span> level analyzing by numerical methods or computational fluid dynamics (CFD) could be very challenging and time consuming, soft computing techniques are preferred. To estimate <span class="hlt">noise</span> level of wind turbine, this paper constructed a process which simulates the wind turbine <span class="hlt">noise</span> levels in regard to wind speed and sound frequency with adaptive neuro-fuzzy inference system (ANFIS). This intelligent estimator is implemented using Matlab/Simulink and the performances are investigated. The simulation results presented in this paper show the effectiveness of the developed method. PMID:25075621</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25075621','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25075621"><span>Adaptive neuro-fuzzy methodology for <span class="hlt">noise</span> assessment of wind turbine.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Shamshirband, Shahaboddin; Petković, Dalibor; Hashim, Roslan; Motamedi, Shervin</p> <p>2014-01-01</p> <p>Wind turbine <span class="hlt">noise</span> is one of the major obstacles for the widespread use of wind energy. <span class="hlt">Noise</span> tone can greatly increase the annoyance factor and the negative impact on human health. <span class="hlt">Noise</span> annoyance caused by wind turbines has become an emerging problem in recent years, due to the rapid increase in number of wind turbines, triggered by sustainable energy goals set forward at the national and international level. Up to now, not all aspects of the generation, propagation and perception of wind turbine <span class="hlt">noise</span> are well understood. For a modern large wind turbine, <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> from the blades is generally considered to be the dominant <span class="hlt">noise</span> <span class="hlt">source</span>, provided that mechanical <span class="hlt">noise</span> is adequately eliminated. The <span class="hlt">sources</span> of <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> can be divided into tonal <span class="hlt">noise</span>, inflow turbulence <span class="hlt">noise</span>, and airfoil self-<span class="hlt">noise</span>. Many analytical and experimental acoustical studies performed the wind turbines. Since the wind turbine <span class="hlt">noise</span> level analyzing by numerical methods or computational fluid dynamics (CFD) could be very challenging and time consuming, soft computing techniques are preferred. To estimate <span class="hlt">noise</span> level of wind turbine, this paper constructed a process which simulates the wind turbine <span class="hlt">noise</span> levels in regard to wind speed and sound frequency with adaptive neuro-fuzzy inference system (ANFIS). This intelligent estimator is implemented using Matlab/Simulink and the performances are investigated. The simulation results presented in this paper show the effectiveness of the developed method.</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://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://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://hdl.handle.net/2060/19920001380','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920001380"><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="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hubbard, Harvey H. (Editor)</p> <p>1991-01-01</p> <p>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 <span class="hlt">noise</span>, rotor <span class="hlt">noise</span>, turbomachinery <span class="hlt">noise</span>, jet <span class="hlt">noise</span> classical theory and experiments, <span class="hlt">noise</span> from turbulent shear flows, jet <span class="hlt">noise</span> generated by large-scale coherent motion, airframe <span class="hlt">noise</span>, propulsive lift <span class="hlt">noise</span>, combustion and core <span class="hlt">noise</span>, and sonic booms.</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> </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('http://adsabs.harvard.edu/abs/1998ThCFD..10..135D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998ThCFD..10..135D"><span>Underwater Flow <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>Dowling, A. P.</p> <p></p> <p>Lighthill's theory of <span class="hlt">aerodynamic</span> sound provides an effective way of investigating underwater flow <span class="hlt">noise</span>. When combined with a model of the coherent vortical structures in a turbulent boundary layer, it predicts the wave-number frequency pressure spectrum on a rigid surface and, in particular, highlights the rôle of surface viscous stresses as a <span class="hlt">source</span> of low wave-number pressure fluctuations on a plane surface. The inclusion of surface curvature and flexibility enables the theory to be applied to acoustic streamers (sometimes known as towed arrays). The effect of the interior mechanical structure of the streamers on the flow <span class="hlt">noise</span> is investigated. Simple algebraic forms are derived for the comparative performance of liquid and visco-elastic-filled streamers. The introduction of porous foam into a liquid streamer is found to be a particularly effective way of attenuating low wave-number disturbances, and theoretical predictions are compared with experiment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA019525','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA019525"><span>Chaff <span class="hlt">Aerodynamics</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>1975-11-01</p> <p>further improve the contrast all of the interior surfaces of the test chamber are painted flat black and the bac!-,ground walls in view of the cameras...to be adequate to eliminate wall effects on the chaff <span class="hlt">aerodynamics</span>. Secondly, the chamber air mass had to be sufficiently small that it would damp out...independently- supported special rotating-shutter system to "strobe" the dipole images. The integral shutter in each lens assembly is also retained for</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MSSP...66..715N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MSSP...66..715N"><span>Potential of neuro-fuzzy methodology to estimate <span class="hlt">noise</span> level of wind turbines</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nikolić, Vlastimir; Petković, Dalibor; Por, Lip Yee; Shamshirband, Shahaboddin; Zamani, Mazdak; Ćojbašić, Žarko; Motamedi, Shervin</p> <p>2016-01-01</p> <p>Wind turbines <span class="hlt">noise</span> effect became large problem because of increasing of wind farms numbers since renewable energy becomes the most influential energy <span class="hlt">sources</span>. However, wind turbine <span class="hlt">noise</span> generation and propagation is not understandable in all aspects. Mechanical <span class="hlt">noise</span> of wind turbines can be ignored since <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> of wind turbine blades is the main <span class="hlt">source</span> of the <span class="hlt">noise</span> generation. Numerical simulations of the <span class="hlt">noise</span> effects of the wind turbine can be very challenging task. Therefore in this article soft computing method is used to evaluate <span class="hlt">noise</span> level of wind turbines. The main goal of the study is to estimate wind turbine <span class="hlt">noise</span> in regard of wind speed at different heights and for different sound frequency. Adaptive neuro-fuzzy inference system (ANFIS) is used to estimate the wind turbine <span class="hlt">noise</span> levels.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19950061734&hterms=jet+engine+works&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Djet%2Bengine%2Bworks','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19950061734&hterms=jet+engine+works&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Djet%2Bengine%2Bworks"><span>Significance of shock structure on supersonic jet mixing <span class="hlt">noise</span> of axisymmetric nozzles</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kim, Chan M.; Krejsa, Eugene A.; Khavaran, Abbas</p> <p>1994-01-01</p> <p>One of the key technical elements in NASA's high speed research program is reducing the <span class="hlt">noise</span> level to meet the federal <span class="hlt">noise</span> regulation. The dominant <span class="hlt">noise</span> <span class="hlt">source</span> is associated with the supersonic jet discharged from the engine exhaust system. Whereas the turbulence mixing is largely responsible for the generation of the jet <span class="hlt">noise</span>, a broadband shock-associated <span class="hlt">noise</span> is also generated when the nozzle operates at conditions other than its design. For both mixing and shock <span class="hlt">noise</span> components, because the <span class="hlt">source</span> of the <span class="hlt">noise</span> is embedded in the jet plume, one can expect that jet <span class="hlt">noise</span> can be predicted from the jet flowfield computation. Mani et al. developed a unified <span class="hlt">aerodynamic</span>/acoustic prediction scheme by applying an extension of Reichardt's <span class="hlt">aerodynamic</span> model to compute turbulent shear stresses which are utilized in estimating the strength of the <span class="hlt">noise</span> <span class="hlt">source</span>. Although this method produces a fast and practical estimate of the jet <span class="hlt">noise</span>, a modification by Khavaran et al. has led to an improvement in <span class="hlt">aerodynamic</span> solution. The most notable feature in this work is that Reichardt's model is replaced with the computational fluid dynamics (CFD) solution of Reynolds-averaged Navier-Stokes equations. The major advantage of this work is that the essential, <span class="hlt">noise</span>-related flow quantities such as turbulence intensity and shock strength can be better predicted. The predictions were limited to a shock-free design condition and the effect of shock structure on the jet mixing <span class="hlt">noise</span> was not addressed. The present work is aimed at investigating this issue. Under imperfectly expanded conditions the existence of the shock cell structure and its interaction with the convecting turbulence structure may not only generate a broadband shock-associated <span class="hlt">noise</span> but also change the turbulence structure, and thus the strength of the mixing <span class="hlt">noise</span> <span class="hlt">source</span>. Failure in capturing shock structures properly could lead to incorrect aeroacoustic predictions.</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://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/2060/20150002338','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150002338"><span>Contra-Rotating Open Rotor Tone <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>Envia, Edmane</p> <p>2014-01-01</p> <p>Reliable prediction of contra-rotating open rotor (CROR) <span class="hlt">noise</span> is an essential element of any strategy for the development of low-<span class="hlt">noise</span> open rotor propulsion systems that can meet both the community <span class="hlt">noise</span> regulations and cabin <span class="hlt">noise</span> limits. Since CROR <span class="hlt">noise</span> spectra exhibit a preponderance of tones, significant efforts have been directed towards predicting their tone content. To that end, there has been an ongoing effort at NASA to assess various in-house open rotor tone <span class="hlt">noise</span> prediction tools using a benchmark CROR blade set for which significant <span class="hlt">aerodynamic</span> and acoustic data have been acquired in wind tunnel tests. In the work presented here, the focus is on the nearfield <span class="hlt">noise</span> of the benchmark open rotor blade set at the cruise condition. Using an analytical CROR tone <span class="hlt">noise</span> model with input from high-fidelity <span class="hlt">aerodynamic</span> simulations, tone <span class="hlt">noise</span> spectra have been predicted and compared with the experimental data. Comparisons indicate that the theoretical predictions are in good agreement with the data, especially for the dominant tones and for the overall sound pressure level of tones. The results also indicate that, whereas the individual rotor tones are well predicted by the combination of the thickness and loading <span class="hlt">sources</span>, for the interaction tones it is essential that the quadrupole <span class="hlt">source</span> is also included in the analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150002087','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150002087"><span>Contra-Rotating Open Rotor Tone <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>Envia, Edmane</p> <p>2014-01-01</p> <p>Reliable prediction of contra-rotating open rotor (CROR) <span class="hlt">noise</span> is an essential element of any strategy for the development of low-<span class="hlt">noise</span> open rotor propulsion systems that can meet both the community <span class="hlt">noise</span> regulations and the cabin <span class="hlt">noise</span> limits. Since CROR <span class="hlt">noise</span> spectra typically exhibits a preponderance of tones, significant efforts have been directed towards predicting their tone spectra. To that end, there has been an ongoing effort at NASA to assess various in-house open rotor tone <span class="hlt">noise</span> prediction tools using a benchmark CROR blade set for which significant <span class="hlt">aerodynamic</span> and acoustic data had been acquired in wind tunnel tests. In the work presented here, the focus is on the near-field <span class="hlt">noise</span> of the benchmark open rotor blade set at the cruise condition. Using an analytical CROR tone <span class="hlt">noise</span> model with input from high-fidelity <span class="hlt">aerodynamic</span> simulations, detailed tone <span class="hlt">noise</span> spectral predictions have been generated and compared with the experimental data. Comparisons indicate that the theoretical predictions are in good agreement with the data, especially for the dominant CROR tones and their overall sound pressure level. The results also indicate that, whereas individual rotor tones are well predicted by the linear <span class="hlt">sources</span> (i.e., thickness and loading), for the interaction tones it is essential that the quadrupole <span class="hlt">sources</span> be included in the analysis.</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> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930035187&hterms=Aachen&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DAachen','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930035187&hterms=Aachen&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DAachen"><span>Advances in tilt rotor <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>George, A. R.; Coffen, C. D.; Ringler, T. D.</p> <p>1992-01-01</p> <p>The two most serious tilt rotor external <span class="hlt">noise</span> problems, hover <span class="hlt">noise</span> and blade-vortex interaction <span class="hlt">noise</span>, are studied. The results of flow visualization and inflow velocity measurements document a complex, recirculating highly unsteady and turbulent flow due to the rotor-wing-body interactions characteristic of tilt rotors. The wing under the rotor is found to obstruct the inflow, causing a deficit in the inflow velocities over the inboard region of the rotor. Discrete frequency harmonic thickness and loading <span class="hlt">noise</span> mechanisms in hover are examined by first modeling tilt rotor hover <span class="hlt">aerodynamics</span> and then applying various <span class="hlt">noise</span> prediction methods using the WOPWOP code. The analysis indicates that the partial ground plane created by the wing below the rotor results in a primary sound <span class="hlt">source</span> for hover.</p> </li> <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://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> </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('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/2060/19940029640','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940029640"><span>Coupled 2-dimensional cascade theory for <span class="hlt">noise</span> and unsteady <span class="hlt">aerodynamics</span> of blade row interaction in turbofans. Volume 1: Theory development and parametric studies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hanson, Donald B.</p> <p>1994-01-01</p> <p>Typical analytical models for interaction between rotor and stator in a turbofan analyze the effect of wakes from the rotor impinging on the stator, producing unsteady loading, and thereby generating <span class="hlt">noise</span>. Reflection/transmission characteristics of the rotor are sometimes added in a separate calculation. In those models, there is a one-to-one relationship between wake harmonics and <span class="hlt">noise</span> harmonics; that is, the BPF (blade passing frequency) wake harmonic causes only the BPF <span class="hlt">noise</span> harmonic, etc. This report presents a more complete model in which flow tangency boundary conditions are satisfied on two cascades in relative motion for several harmonics simultaneously. By an extension of S.N. Smith's code for two dimensional flat plate cascades, the <span class="hlt">noise</span> generation/frequency scattering/blade row reflection problem is solved in a single matrix inversion. It is found that the BPF harmonic excitation of the stator scatters considerable energy in the higher BPF harmonics due to relative motion between the blade rows. Furthermore, when swirl between the rotor and stator is modeled, a 'mode trapping' effect occurs which explains observations on fans operating at rotational speeds below BFP cuton: the BPF mode amplifies between blade rows by multiple reflections but cannot escape to the inlet and exit ducts. However, energy scattered into higher harmonics does propagate and dominates the spectrum at two and three times BPF. This report presents the complete derivation of the theory, comparison with a previous (more limited) coupled rotor/stator interaction theory due to Kaji and Okazaki, exploration of the mode trapping phenomenon, and parametric studies showing the effects of vane/blade ratio and rotor/stator interaction. For generality, the analysis applies to stages where the rotor is either upstream or downstream of the stator and to counter rotation stages. The theory has been coded in a FORTRAN program called CUP2D, documented in Volume 2 of this report. It is</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20130013862','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130013862"><span>The Effects of Crosswind Flight on Rotor Harmonic <span class="hlt">Noise</span> Radiation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Greenwood, Eric; Sim, Ben W.</p> <p>2013-01-01</p> <p>In order to develop recommendations for procedures for helicopter <span class="hlt">source</span> <span class="hlt">noise</span> characterization, the effects of crosswinds on main rotor harmonic <span class="hlt">noise</span> radiation are assessed using a model of the Bell 430 helicopter. Crosswinds are found to have a significant effect on Blade-Vortex Interaction (BVI) <span class="hlt">noise</span> radiation when the helicopter is trimmed with the fuselage oriented along the inertial flight path. However, the magnitude of BVI <span class="hlt">noise</span> remains unchanged when the pilot orients the fuselage along the <span class="hlt">aerodynamic</span> velocity vector, crabbing for zero <span class="hlt">aerodynamic</span> sideslip. The effects of wind gradients on BVI <span class="hlt">noise</span> are also investigated and found to be smaller in the crosswind direction than in the headwind direction. The effects of crosswinds on lower harmonic <span class="hlt">noise</span> <span class="hlt">sources</span> at higher flight speeds are also assessed. In all cases, the directivity of radiated <span class="hlt">noise</span> is somewhat changed by the crosswind. The model predictions agree well with flight test data for the Bell 430 helicopter captured under various wind conditions. The results of this investigation would suggest that flight paths for future acoustic flight testing are best aligned across the prevailing wind direction to minimize the effects of winds on <span class="hlt">noise</span> measurements when wind cannot otherwise be avoided.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880019498','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880019498"><span>Investigation of helicopter rotor blade/wake interactive impulsive <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>Miley, S. J.; Hall, G. F.; Vonlavante, E.</p> <p>1987-01-01</p> <p>An analysis of the Tip <span class="hlt">Aerodynamic</span>/Aeroacoustic Test (TAAT) data was performed to identify possible <span class="hlt">aerodynamic</span> <span class="hlt">sources</span> of blade/vortex interaction (BVI) impulsive <span class="hlt">noise</span>. The identification is based on correlation of measured blade pressure time histories with predicted blade/vortex intersections for the flight condition(s) where impulsive <span class="hlt">noise</span> was detected. Due to the location of the recording microphones, only <span class="hlt">noise</span> signatures associated with the advancing blade were available, and the analysis was accordingly restricted to the first and second azimuthal quadrants. The results show that the blade tip region is operating transonically in the azimuthal range where previous BVI experiments indicated the impulsive <span class="hlt">noise</span> to be. No individual blade/vortex encounter is identifiable in the pressure data; however, there is indication of multiple intersections in the roll-up region which could be the origin of the <span class="hlt">noise</span>. Discrete blade/vortex encounters are indicated in the second quadrant; however, if impulsive <span class="hlt">noise</span> were produced here, the directivity pattern would be such that it was not recorded by the microphones. It is demonstrated that the TAAT data base is a valuable resource in the investigation of rotor <span class="hlt">aerodynamic</span>/aeroacoustic behavior.</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://ntrs.nasa.gov/search.jsp?R=19850049838&hterms=advancing+blade&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dadvancing%2Bblade','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850049838&hterms=advancing+blade&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dadvancing%2Bblade"><span>Computerized <span class="hlt">aerodynamic</span> design of a transonically 'quiet' blade</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Tauber, M. E.</p> <p>1984-01-01</p> <p>The high <span class="hlt">noise</span> levels produced by helicopters are major <span class="hlt">sources</span> of concern. There are many <span class="hlt">sources</span> of the <span class="hlt">noise</span>, but during high-speed forward flight, impulsive <span class="hlt">noise</span> dominates the <span class="hlt">noise</span> spectrum. The cause of the high-speed impulsive <span class="hlt">noise</span> is the propagation into the far field of shock waves that form on the advancing blade. This mechanism has been labeled 'delocalization'. It has been shown, however, that by judicious design of the blade-tip planform, delocalization can be prevented. The objective of the present study is to illustrate how blade-tip configurations (both planform and airfoil shape) can be systematically varied to identify shapes that avoid delocalization and simultaneously improve <span class="hlt">aerodynamic</span> performance. This has been done using the latest version of the ROT22 transonic, full-potential, quasi-steady, rotor flow-field code. A hypothetical modern rotor blade was postulated, and tip modifications consisting of taper, sweep, and airfoil section alterations were investigated. Planform modifications were found to be most effective in eliminating delocalization.</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> </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('http://adsabs.harvard.edu/abs/1983iapn.rept.....T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983iapn.rept.....T"><span>Investigation of the <span class="hlt">aerodynamic</span> performance and <span class="hlt">noise</span> characteristics of a 1/5th scale model of the Dowty Rotol R212 propeller</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Trebble, W. J. G.</p> <p>1983-11-01</p> <p>The four-bladed Dowty Rotol R212 propeller (NACA 16 sections) was studied at 1/5th scale (0.7 m diameter) in 1.5 m acoustic tunnel. Propeller power absorption and thrust were measured over a range of rotational speeds up to 8000 rev/min at mainstream speeds from 15 to 60 m/sec for a range of blade settings. Slipstream wake surveys show outward movement of the position of the peak pressure as propeller loading is increased. <span class="hlt">Noise</span> analysis demonstrates the predominance of multiple tones whose number and intensity increase with helical-tip Mach number. An empirical formula shows that the fundamental tone sound pressure level varies with tip speed and power loading in an identical manner to that observed on an ARA-D section propeller.</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('http://hdl.handle.net/2060/19940029887','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940029887"><span>Introduction to Generalized Functions with Applications in <span class="hlt">Aerodynamics</span> and Aeroacoustics</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>1994-01-01</p> <p>Generalized functions have many applications in science and engineering. One useful aspect is that discontinuous functions can be handled as easily as continuous or differentiable functions and provide a powerful tool in formulating and solving many problems of <span class="hlt">aerodynamics</span> and acoustics. Furthermore, generalized function theory elucidates and unifies many ad hoc mathematical approaches used by engineers and scientists. We define generalized functions as continuous linear functionals on the space of infinitely differentiable functions with compact support, then introduce the concept of generalized differentiation. Generalized differentiation is the most important concept in generalized function theory and the applications we present utilize mainly this concept. First, some results of classical analysis, are derived with the generalized function theory. Other applications of the generalized function theory in <span class="hlt">aerodynamics</span> discussed here are the derivations of general transport theorems for deriving governing equations of fluid mechanics, the interpretation of the finite part of divergent integrals, the derivation of the Oswatitsch integral equation of transonic flow, and the analysis of velocity field discontinuities as <span class="hlt">sources</span> of vorticity. Applications in aeroacoustics include the derivation of the Kirchhoff formula for moving surfaces, the <span class="hlt">noise</span> from moving surfaces, and shock <span class="hlt">noise</span> <span class="hlt">source</span> strength based on the Ffowcs Williams-Hawkings equation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19840008070','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19840008070"><span>Special opportunities in helicopter <span class="hlt">aerodynamics</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mccroskey, W. J.</p> <p>1983-01-01</p> <p><span class="hlt">Aerodynamic</span> research relating to modern helicopters includes the study of three dimensional, unsteady, nonlinear flow fields. A selective review is made of some of the phenomenon that hamper the development of satisfactory engineering prediction techniques, but which provides a rich <span class="hlt">source</span> of research opportunities: flow separations, compressibility effects, complex vortical wakes, and <span class="hlt">aerodynamic</span> interference between components. Several examples of work in progress are given, including dynamic stall alleviation, the development of computational methods for transonic flow, rotor-wake predictions, and blade-vortex interactions.</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> <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('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://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://hdl.handle.net/2060/20130001702','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130001702"><span>Preliminary <span class="hlt">Aerodynamic</span> Investigation of Fan Rotor Blade Morphing</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Tweedt, Daniel L.</p> <p>2012-01-01</p> <p>Various new technologies currently under development may enable controlled blade shape variability, or so-called blade morphing, to be practically employed in aircraft engine fans and compressors in the foreseeable future. The current study is a relatively brief, preliminary computational fluid dynamics investigation aimed at partially demonstrating and quantifying the <span class="hlt">aerodynamic</span> potential of fan rotor blade morphing. The investigation is intended to provide information useful for near-term planning, as well as <span class="hlt">aerodynamic</span> solution data sets that can be subsequently analyzed using advanced acoustic diagnostic tools, for the purpose of making fan <span class="hlt">noise</span> comparisons. Two existing fan system models serve as baselines for the investigation: the Advanced Ducted Propulsor fan with a design tip speed of 806 ft/sec and a pressure ratio of 1.294, and the <span class="hlt">Source</span> Diagnostic Test fan with a design tip speed of 1215 ft/sec and a pressure ratio of 1.470. Both are 22-in. sub-scale, low-<span class="hlt">noise</span> research fan/nacelle models that have undergone extensive experimental testing in the 9- by 15-foot Low Speed Wind Tunnel at the NASA Glenn Research Center. The study, restricted to fan rotor blade morphing only, involves a fairly simple blade morphing technique. Specifically, spanwise-linear variations in rotor blade-section setting angle are applied to alter the blade shape; that is, the blade is linearly retwisted from hub to tip. <span class="hlt">Aerodynamic</span> performance comparisons are made between morphed-blade and corresponding baseline configurations on the basis of equal fan system thrust, where rotor rotational speed for the morphed-blade fan is varied to change the thrust level for that configuration. The results of the investigation confirm that rotor blade morphing could be a useful technology, with the potential to enable significant improvements in fan <span class="hlt">aerodynamic</span> performance. Even though the study is very limited in scope and confined to simple geometric perturbations of two existing fan</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('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/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> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19800006774','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19800006774"><span>Classical <span class="hlt">Aerodynamic</span> Theory</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jones, R. T. (Compiler)</p> <p>1979-01-01</p> <p>A collection of papers on modern theoretical <span class="hlt">aerodynamics</span> is presented. Included are theories of incompressible potential flow and research on the <span class="hlt">aerodynamic</span> forces on wing and wing sections of aircraft and on airship hulls.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20060028488','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20060028488"><span><span class="hlt">Aerodynamics</span> at NASA JSC</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Vicker, Darby</p> <p>2006-01-01</p> <p>A viewgraph presentation describing <span class="hlt">aerodynamics</span> at NASA Johnson Space Center is shown. The topics include: 1) Personal Background; 2) <span class="hlt">Aerodynamic</span> Tools; 3) The Overset Computational Fluid Dynamics (CFD) Process; and 4) Recent Applicatoins.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19900003236','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19900003236"><span>Nacelle <span class="hlt">aerodynamic</span> performance</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Obara, Clifford J.; Dodbele, S. S.</p> <p>1987-01-01</p> <p>The boundary layer transition location was measured on a nacelle shape using the sublimating chemical flow visualization technique. This technique involves coating the surface with a thin film of volatile chemical solid, which, during exposure to a free stream airflow, rapidly sublimates in the turbulent boundary layer as a result of high shear stress and high mass transfer near the surface. Transition is indicated because the chemical coating remains relatively unaffected in the laminar region due to lower shear and low mass transfer. The slow response time of the chemical in a laminar boundary allowed for two test conditions during the same flight. The aircraft was first flown at the desired airspeed and altitude with the <span class="hlt">noise</span> <span class="hlt">source</span> off. Once a pattern had developed, the <span class="hlt">noise</span> <span class="hlt">source</span> was turned on to the desired setting and a new chemical pattern was sought. In this fashion a direct comparison of the effect of the <span class="hlt">noise</span> could be determined.</p> </li> <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://hdl.handle.net/2060/19920015435','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920015435"><span>NASA <span class="hlt">aerodynamics</span> program</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Williams, Louis J.; Hessenius, Kristin A.; Corsiglia, Victor R.; Hicks, Gary; Richardson, Pamela F.; Unger, George; Neumann, Benjamin; Moss, Jim</p> <p>1992-01-01</p> <p>The annual accomplishments is reviewed for the <span class="hlt">Aerodynamics</span> Division during FY 1991. The program includes both fundamental and applied research directed at the full spectrum of aerospace vehicles, from rotorcraft to planetary entry probes. A comprehensive review is presented of the following <span class="hlt">aerodynamics</span> elements: computational methods and applications; CFD validation; transition and turbulence physics; numerical <span class="hlt">aerodynamic</span> simulation; test techniques and instrumentation; configuration <span class="hlt">aerodynamics</span>; aeroacoustics; aerothermodynamics; hypersonics; subsonics; fighter/attack aircraft and rotorcraft.</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('http://hdl.handle.net/2060/19760011062','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19760011062"><span>Exploratory study to induce fan <span class="hlt">noise</span> in the test section of the NASA Langley full-scale wind tunnel</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ver, I. L.; Hayden, R. E.; Myles, M. M.; Murray, B. E.</p> <p>1975-01-01</p> <p>Measures to reduce the intensity of fan <span class="hlt">noise</span> in the NASA Langley 30 ft x 60 ft subsonic wind tunnel were sought. Measurements were first performed to document existing <span class="hlt">aerodynamic</span> and acoustic conditions. The purpose of these experiments was to (1) obtain the transfer function between the sound power output of the fan and the sound pressure on the test platform, (2) evaluate the sound attenuation around the tunnel circuit, (3) measure simultaneously the flow profile and the turbulence spectrum of the inflow to the fan and the <span class="hlt">noise</span> on the test platform, and (4) perform flow observations and identify secondary <span class="hlt">noise</span> <span class="hlt">sources</span>. Subsequently, these data were used to predict (1) the relative contribution of the major <span class="hlt">aerodynamic</span> parameters to total fan <span class="hlt">noise</span> and (2) the effect of placing a dissipative silencer in the collector duct upstream of the fan. Promising <span class="hlt">noise</span> control measures were identified and recommendations were made on how to evaluate them.</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/2060/19940023275','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940023275"><span>Coupled 2-dimensional cascade theory for <span class="hlt">noise</span> an d unsteady <span class="hlt">aerodynamics</span> of blade row interaction in turbofans. Volume 2: Documentation for computer code CUP2D</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hanson, Donald B.</p> <p>1994-01-01</p> <p>A two dimensional linear aeroacoustic theory for rotor/stator interaction with unsteady coupling was derived and explored in Volume 1 of this report. Computer program CUP2D has been written in FORTRAN embodying the theoretical equations. This volume (Volume 2) describes the structure of the code, installation and running, preparation of the input file, and interpretation of the output. A sample case is provided with printouts of the input and output. The <span class="hlt">source</span> code is included with comments linking it closely to the theoretical equations in Volume 1.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19900007919','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19900007919"><span>NASA <span class="hlt">aerodynamics</span> program</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Holmes, Bruce J.; Schairer, Edward; Hicks, Gary; Wander, Stephen; Blankson, Isiaiah; Rose, Raymond; Olson, Lawrence; Unger, George</p> <p>1990-01-01</p> <p>Presented here is a comprehensive review of the following <span class="hlt">aerodynamics</span> elements: computational methods and applications, computational fluid dynamics (CFD) validation, transition and turbulence physics, numerical <span class="hlt">aerodynamic</span> simulation, drag reduction, test techniques and instrumentation, configuration <span class="hlt">aerodynamics</span>, aeroacoustics, aerothermodynamics, hypersonics, subsonic transport/commuter aviation, fighter/attack aircraft and rotorcraft.</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/2060/20070021689','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20070021689"><span>Tandem Cylinder <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>Lockhard, David P.; Khorrami, Mehdi R.; CHoudhari, Meelan M.; Hutcheson, Florence V.; Brooks, Thomas F.; Stead, Daniel J.</p> <p>2007-01-01</p> <p>In an effort to better understand landing-gear <span class="hlt">noise</span> <span class="hlt">sources</span>, we have been examining a simplified configuration that still maintains some of the salient features of landing-gear flow fields. In particular, tandem cylinders have been studied because they model a variety of component level interactions. The present effort is directed at the case of two identical cylinders spatially separated in the streamwise direction by 3.7 diameters. Experimental measurements from the Basic <span class="hlt">Aerodynamic</span> Research Tunnel (BART) and Quiet Flow Facility (QFF) at NASA Langley Research Center (LaRC) have provided steady surface pressures, detailed off-surface measurements of the flow field using Particle Image Velocimetry (PIV), hot-wire measurements in the wake of the rear cylinder, unsteady surface pressure data, and the radiated <span class="hlt">noise</span>. The experiments were conducted at a Reynolds number of 166 105 based on the cylinder diameter. A trip was used on the upstream cylinder to insure a fully turbulent shedding process and simulate the effects of a high Reynolds number flow. The parallel computational effort uses the three-dimensional Navier-Stokes solver CFL3D with a hybrid, zonal turbulence model that turns off the turbulence production term everywhere except in a narrow ring surrounding solid surfaces. The current calculations further explore the influence of the grid resolution and spanwise extent on the flow and associated radiated <span class="hlt">noise</span>. Extensive comparisons with the experimental data are used to assess the ability of the computations to simulate the details of the flow. The results show that the pressure fluctuations on the upstream cylinder, caused by vortex shedding, are smaller than those generated on the downstream cylinder by wake interaction. Consequently, the downstream cylinder dominates the <span class="hlt">noise</span> radiation, producing an overall directivity pattern that is similar to that of an isolated cylinder. Only calculations based on the full length of the model span were able to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910005490','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910005490"><span>Prediction of XV-15 tilt rotor discrete frequency aeroacoustic <span class="hlt">noise</span> with WOPWOP</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Coffen, Charles D.; George, Albert R.</p> <p>1990-01-01</p> <p>The results, methodology, and conclusions of <span class="hlt">noise</span> prediction calculations carried out to study several possible discrete frequency harmonic <span class="hlt">noise</span> mechanisms of the XV-15 Tilt Rotor Aircraft in hover and helicopter mode forward flight are presented. The mechanisms studied were thickness and loading <span class="hlt">noise</span>. In particular, the loading <span class="hlt">noise</span> caused by flow separation and the fountain/ground plane effect were predicted with calculations made using WOPWOP, a <span class="hlt">noise</span> prediction program developed by NASA Langley. The methodology was to model the geometry and <span class="hlt">aerodynamics</span> of the XV-15 rotor blades in hover and steady level flight and then create corresponding FORTRAN subroutines which were used an input for WOPWOP. The models are described and the simplifying assumptions made in creating them are evaluated, and the results of the computations are presented. The computations lead to the following conclusions: The fountain/ground plane effect is an important <span class="hlt">source</span> of <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> for the XV-15 in hover. Unsteady flow separation from the airfoil passing through the fountain at high angles of attack significantly affects the predicted sound spectra and may be an important <span class="hlt">noise</span> mechanism for the XV-15 in hover mode. The various models developed did not predict the sound spectra in helicopter forward flight. The experimental spectra indicate the presence of blade vortex interactions which were not modeled in these calculations. A need for further study and development of more accurate <span class="hlt">aerodynamic</span> models, including unsteady stall in hover and blade vortex interactions in forward flight.</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/2060/19960003376','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://adsabs.harvard.edu/abs/1990aiaa.confS....L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1990aiaa.confS....L"><span>Experimental study of <span class="hlt">noise</span> <span class="hlt">sources</span> and acoustic propagation in a turbofan model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lewy, S.; Canard-Caruana, S.; Julliard, J.</p> <p>1990-10-01</p> <p>Experimental studies of the acoustic radiation of subsonic fans mainly due to blade and vane presure fluctuations were performed in the SNECMA 5C2 compressor anechoic facility. A brief description of the test rig is presented noting that the CA5 turbojet engine model fan has a diameter of 47 cm, 48 blades, and a nominal rotation speed of 12,600 rpm. The two chief experiments discussed are the measurement of blade and vane pressure fluctuations by thin-film transducers and the spinning mode analysis of the sound field propagating in the intake duct. Several examples of applications are discussed, and it is shown that an inflow control device, as expected, reduces the <span class="hlt">aerodynamic</span> disturbances by about 10 dB. Rotor-stator interaction tones are determined by the modal analysis, and it is found that a duct lining with a length of one duct radius could give an insertion loss up to 20 dB in flight.</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://adsabs.harvard.edu/abs/2014JSV...333.3058R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JSV...333.3058R"><span>Wind turbine <span class="hlt">noise</span> measurement using a compact microphone array with advanced deconvolution algorithms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ramachandran, Rakesh C.; Raman, Ganesh; Dougherty, Robert P.</p> <p>2014-07-01</p> <p>This paper experimentally investigates the <span class="hlt">noise</span> from a large wind turbine (GE 1.5 MW) with a compact microphone array (OptiNav 24) using advanced deconvolution based beamforming methods, such as DAMAS and CLEAN-SC beamforming algorithms, for data reduction. Our study focuses on the ability of a compact microphone array to successfully locate both mechanical and <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> <span class="hlt">sources</span> on the wind turbine. Several interesting results have emerged from this study: (i) A compact microphone array is sufficient to perform a detailed study on wind turbine <span class="hlt">noise</span> if advanced deconvolution methods are applied. (ii) <span class="hlt">Noise</span> <span class="hlt">sources</span> on the blade and on the nacelle can clearly be separated. (iii) <span class="hlt">Noise</span> of the blades is dominated by trailing edge <span class="hlt">noise</span> which is frequency dependent and is distributed along the length of the blade with the dominant <span class="hlt">noise</span> <span class="hlt">source</span> closer to the tip of the blade. (iv) The LP and DAMAS algorithms represent the distributed trailing edge <span class="hlt">noise</span> <span class="hlt">source</span> better than CLEAN-SC and classical beamforming. (v) Additional tonal <span class="hlt">noise</span> produced during yawing operation is believed to be radiating from the tower of the wind turbine that acts like a resonator. (vi) Ground reflection is not believed to have a significant effect on <span class="hlt">noise</span> <span class="hlt">source</span> location estimates in this study.</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/2060/19750009957','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/2060/20140012747','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140012747"><span>The Prediction and Analysis of Jet Flows and Scattered Turbulent Mixing <span class="hlt">Noise</span> about Flight Vehicle Airframes</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>Jet flows interacting with nearby surfaces exhibit a complex behavior in which acoustic and <span class="hlt">aerodynamic</span> characteristics are altered. The physical understanding and prediction of these characteristics are essential to designing future low <span class="hlt">noise</span> aircraft. A new approach is created for predicting scattered jet mixing <span class="hlt">noise</span> that utilizes an acoustic analogy and steady Reynolds-averaged Navier-Stokes solutions. A tailored Green's function accounts for the propagation of mixing <span class="hlt">noise</span> about the airframe and is calculated numerically using a newly developed ray tracing method. The steady <span class="hlt">aerodynamic</span> statistics, associated unsteady sound <span class="hlt">source</span>, 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 <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> <span class="hlt">source</span> 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 <span class="hlt">noise</span> 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.</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/2060/20140010739','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140010739"><span>The Prediction and Analysis of Jet Flows and Scattered Turbulent Mixing <span class="hlt">Noise</span> About Flight Vehicle Airframes</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.</p> <p>2014-01-01</p> <p>Jet flows interacting with nearby surfaces exhibit a complex behavior in which acoustic and <span class="hlt">aerodynamic</span> characteristics are altered. The physical understanding and prediction of these characteristics are essential to designing future low <span class="hlt">noise</span> aircraft. A new approach is created for predicting scattered jet mixing <span class="hlt">noise</span> that utilizes an acoustic analogy and steady Reynolds-averaged Navier-Stokes solutions. A tailored Green's function accounts for the propagation of mixing <span class="hlt">noise</span> about the air-frame and is calculated numerically using a newly developed ray tracing method. The steady <span class="hlt">aerodynamic</span> statistics, associated unsteady sound <span class="hlt">source</span>, 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 <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> <span class="hlt">source</span> 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 <span class="hlt">noise</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1982PhDT........11V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1982PhDT........11V"><span><span class="hlt">Aerodynamics</span> of sounding rockets at supersonic speeds</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vira, N. R.</p> <p></p> <p>This dissertation presents a practical and low cost method of computing the <span class="hlt">aerodynamic</span> characteristics of vehicles such as sounding rockets, high speed bombs, projectiles and guided missiles in supersonic flight. The vehicle configuration consists of a slender axisymmetric body with a conical or ogive <span class="hlt">noise</span>, cylinders, shoulders and boattails, if any, and have sets of two, three or four fins. Geometry of the fin cross section can be single wedge, double wedge, modified single wedge or modified double wedge. First the <span class="hlt">aerodynamics</span> of the fins and the body are analyzed separately; then fin body and fore and aft fin interferences are accounted for when they are combined to form the total vehicle. Results and formulas documented in this work are the basis of the supersonic portion of the Theoretical <span class="hlt">Aerodynamic</span> Derivatives (TAD) computer program operating at the NASA Goddard Space Flight Center.</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://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://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('https://www.osti.gov/scitech/biblio/7039937','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/7039937"><span>Unsteady transonic <span class="hlt">aerodynamics</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Nixon, D.</p> <p>1989-01-01</p> <p>Various papers on unsteady transonic <span class="hlt">aerodynamics</span> are presented. The topics addressed include: physical phenomena associated with unsteady transonic flows, basic equations for unsteady transonic flow, practical problems concerning aircraft, basic numerical methods, computational methods for unsteady transonic flows, application of transonic flow analysis to helicopter rotor problems, unsteady <span class="hlt">aerodynamics</span> for turbomachinery aeroelastic applications, alternative methods for modeling unsteady transonic flows.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040139870','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040139870"><span>Uncertainty in Computational <span class="hlt">Aerodynamics</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Luckring, J. M.; Hemsch, M. J.; Morrison, J. H.</p> <p>2003-01-01</p> <p>An approach is presented to treat computational <span class="hlt">aerodynamics</span> as a process, subject to the fundamental quality assurance principles of process control and process improvement. We consider several aspects affecting uncertainty for the computational <span class="hlt">aerodynamic</span> process and present a set of stages to determine the level of management required to meet risk assumptions desired by the customer of the predictions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160011958','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160011958"><span>Unsteady <span class="hlt">Aerodynamic</span> Force Sensing from Measured Strain</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pak, Chan-Gi</p> <p>2016-01-01</p> <p>A simple approach for computing unsteady <span class="hlt">aerodynamic</span> forces from simulated measured strain data is proposed in this study. First, the deflection and slope of the structure are computed from the unsteady strain using the two-step approach. Velocities and accelerations of the structure are computed using the autoregressive moving average model, on-line parameter estimator, low-pass filter, and a least-squares curve fitting method together with analytical derivatives with respect to time. Finally, <span class="hlt">aerodynamic</span> forces over the wing are computed using modal <span class="hlt">aerodynamic</span> influence coefficient matrices, a rational function approximation, and a time-marching algorithm. A cantilevered rectangular wing built and tested at the NASA Langley Research Center (Hampton, Virginia, USA) in 1959 is used to validate the simple approach. Unsteady <span class="hlt">aerodynamic</span> forces as well as wing deflections, velocities, accelerations, and strains are computed using the CFL3D computational fluid dynamics (CFD) code and an MSC/NASTRAN code (MSC Software Corporation, Newport Beach, California, USA), and these CFL3D-based results are assumed as measured quantities. Based on the measured strains, wing deflections, velocities, accelerations, and <span class="hlt">aerodynamic</span> forces are computed using the proposed approach. These computed deflections, velocities, accelerations, and unsteady <span class="hlt">aerodynamic</span> forces are compared with the CFL3D/NASTRAN-based results. In general, computed <span class="hlt">aerodynamic</span> forces based on the lifting surface theory in subsonic speeds are in good agreement with the target <span class="hlt">aerodynamic</span> forces generated using CFL3D code with the Euler equation. Excellent aeroelastic responses are obtained even with unsteady strain data under the signal to <span class="hlt">noise</span> ratio of -9.8dB. The deflections, velocities, and accelerations at each sensor location are independent of structural and <span class="hlt">aerodynamic</span> models. Therefore, the distributed strain data together with the current proposed approaches can be used as distributed deflection</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160010139','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160010139"><span>Measured <span class="hlt">Noise</span> from Small Unmanned Aerial Vehicles</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cabell, Randolph; McSwain, Robert; Grosveld, Ferdinand</p> <p>2016-01-01</p> <p>Proposed uses of small unmanned aerial vehicles (UAVs), including home package delivery, have the potential to expose large portions of communities to a new <span class="hlt">noise</span> <span class="hlt">source</span>. This paper discusses results of flyover <span class="hlt">noise</span> measurements of four small UAVs, including an internal combustion-powered model airplane and three battery-powered multicopters. Basic <span class="hlt">noise</span> characteristics of these vehicles are discussed, including spectral properties and sound level metrics such as sound pressure level, effective perceived <span class="hlt">noise</span> level, and sound exposure level. The size and <span class="hlt">aerodynamic</span> characteristics of the multicopters in particular make their flight path susceptible to atmospheric disturbances such as wind gusts. These gusts, coupled with a flight control system that varies rotor speed to maintain vehicle stability, create an unsteady acoustic signature. The spectral variations resulting from this unsteadiness are explored, in both hover and flyover conditions for the multicopters. The time varying <span class="hlt">noise</span>, which differs from the relatively steady <span class="hlt">noise</span> generated by large transport aircraft, may complicate the prediction of human annoyance using conventional sound level metrics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005PrAeS..41..323B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005PrAeS..41..323B"><span>Iced-airfoil <span class="hlt">aerodynamics</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bragg, M. B.; Broeren, A. P.; Blumenthal, L. A.</p> <p>2005-07-01</p> <p>Past research on airfoil <span class="hlt">aerodynamics</span> in icing are reviewed. This review emphasizes the time period after the 1978 NASA Lewis workshop that initiated the modern icing research program at NASA and the current period after the 1994 ATR accident where <span class="hlt">aerodynamics</span> research has been more aircraft safety focused. Research pre-1978 is also briefly reviewed. Following this review, our current knowledge of iced airfoil <span class="hlt">aerodynamics</span> is presented from a flowfield-physics perspective. This article identifies four classes of ice accretions: roughness, horn ice, streamwise ice, and spanwise-ridge ice. For each class, the key flowfield features such as flowfield separation and reattachment are discussed and how these contribute to the known <span class="hlt">aerodynamic</span> effects of these ice shapes. Finally Reynolds number and Mach number effects on iced-airfoil <span class="hlt">aerodynamics</span> are summarized.</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> <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://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><span class="hlt">Aerodynamic</span> <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 <span class="hlt">aerodynamic</span> 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 airframe <span class="hlt">noise</span> prediction.</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://hdl.handle.net/2060/19940029016','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940029016"><span>HSCT high lift system <span class="hlt">aerodynamic</span> requirements</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Paulson, John A.</p> <p>1992-01-01</p> <p>The viewgraphs and discussion of high lift system <span class="hlt">aerodynamic</span> requirements are provided. Low speed <span class="hlt">aerodynamics</span> has been identified as critical to the successful development of a High Speed Civil Transport (HSCT). The airplane must takeoff and land at a sufficient number of existing or projected airports to be economically viable. At the same time, community <span class="hlt">noise</span> must be acceptable. Improvements in cruise drag, engine fuel consumption, and structural weight tend to decrease the wing size and thrust required of engines. Decreasing wing size increases the requirements for effective and efficient low speed characteristics. Current design concepts have already been compromised away from better cruise wings for low speed performance. Flap systems have been added to achieve better lift-to-drag ratios for climb and approach and for lower pitch attitudes for liftoff and touchdown. Research to achieve improvements in low speed <span class="hlt">aerodynamics</span> needs to be focused on areas most likely to have the largest effect on the wing and engine sizing process. It would be desirable to provide enough lift to avoid sizing the airplane for field performance and to still meet the <span class="hlt">noise</span> requirements. The airworthiness standards developed in 1971 will be the basis for performance requirements for an airplane that will not be critical to the airplane wing and engine size. The lift and drag levels that were required to meet the performance requirements of tentative airworthiness standards established in 1971 and that were important to community <span class="hlt">noise</span> are identified. Research to improve the low speed <span class="hlt">aerodynamic</span> characteristics of the HSCT needs to be focused in the areas of performance deficiency and where <span class="hlt">noise</span> can be reduced. Otherwise, the wing planform, engine cycle, or other parameters for a superior cruising airplane would have to be changed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150000546','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150000546"><span>Aeroacoustic Evaluation of Flap and Landing Gear <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>Khorrami, Mehdi R.; Humphreys, William M., Jr.; Lockard, David P.; Ravetta, Patricio A.</p> <p>2014-01-01</p> <p>Aeroacoustic measurements for a semi-span, 18% scale, high-fidelity Gulfstream aircraft model are presented. The model was used as a test bed to conduct detailed studies of flap and main landing gear <span class="hlt">noise</span> <span class="hlt">sources</span> and to determine the effectiveness of numerous <span class="hlt">noise</span> mitigation concepts. Using a traversing microphone array in the flyover direction, an extensive set of acoustic data was obtained in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel with the facility in the acoustically treated open-wall (jet) mode. Most of the information was acquired with the model in a landing configuration with the flap deflected 39 deg and the main landing gear alternately installed and removed. Data were obtained at Mach numbers of 0.16, 0.20, and 0.24 over directivity angles between 56 deg and 116 deg, with 90 deg representing the overhead direction. Measured acoustic spectra showed that several of the tested flap <span class="hlt">noise</span> reduction concepts decrease the sound pressure levels by 2 - 4 dB over the entire frequency range at all directivity angles. Slightly lower levels of <span class="hlt">noise</span> reduction from the main landing gear were obtained through the simultaneous application of various gear devices. Measured <span class="hlt">aerodynamic</span> forces indicated that the tested gear/flap <span class="hlt">noise</span> abatement technologies have a negligible impact on the <span class="hlt">aerodynamic</span> performance of the aircraft model.</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://adsabs.harvard.edu/abs/2004PhDT........59M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004PhDT........59M"><span><span class="hlt">Aerodynamic</span> control in compressible flow using microwave driven discharges</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McAndrew, Brendan</p> <p></p> <p>A new <span class="hlt">aerodynamic</span> control scheme based on heating of the free stream flow is developed. The design, construction, and operation of a unique small scale wind tunnel to perform experiments involving this control scheme is detailed. Free stream heating is achieved by means of microwave driven discharges, and the resulting flow perturbations are used to alter the pressure distribution around a model in the flow. The experimental facility is also designed to allow the injection of an electron beam into the free stream for control of the discharge. Appropriate models for the fluid flow and discharge physics are developed, and comparisons of calculations based on those models are made with experimental results. The calculations have also been used to explore trends in parameters beyond the range possible in the experiments. The results of this work have been (1) the development of an operating facility capable of supporting free stream heat addition experiments in supersonic flow, (2) the development of a compatible instrumented model designed to make lift and drag measurements in a low pressure, high electrical <span class="hlt">noise</span> environment, (3) a theoretical model to predict the change in breakdown threshold in the presence of an electron beam or other <span class="hlt">source</span> of ionization, and (4) successful demonstration of <span class="hlt">aerodynamic</span> control using free stream heat addition.</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('https://ntrs.nasa.gov/search.jsp?R=20010037017&hterms=analogy+mathematics&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Danalogy%2Bmathematics','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20010037017&hterms=analogy+mathematics&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Danalogy%2Bmathematics"><span>Implementation of New Turbulence Spectra in the Lighthill Analogy <span class="hlt">Source</span> Terms</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Woodruff, S. L.; Seiner, J. M.; Hussaini, M. Y.; Erlebacher, G.</p> <p>2000-01-01</p> <p>The industry-standard MGB approach to predicting the <span class="hlt">noise</span> generated by a given <span class="hlt">aerodynamic</span> flow field requires that the turbulence velocity correlation be specified so that the <span class="hlt">source</span> terms in the Lighthill acoustic analogy may be computed. The velocity correlation traditionally used in MGB Computations is inconsistent with a number of basic qualitative properties of turbulent flows. In the present investigation the effect on <span class="hlt">noise</span> prediction of using two alternative velocity correlations is examined.</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://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('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://eric.ed.gov/?q=Aerodynamics&pg=4&id=EJ410920','ERIC'); return false;" href="http://eric.ed.gov/?q=Aerodynamics&pg=4&id=EJ410920"><span><span class="hlt">Aerodynamic</span> Lifting Force.</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>Weltner, Klaus</p> <p>1990-01-01</p> <p>Describes some experiments showing both qualitatively and quantitatively that <span class="hlt">aerodynamic</span> lift is a reaction force. Demonstrates reaction forces caused by the acceleration of an airstream and the deflection of an airstream. Provides pictures of demonstration apparatus and mathematical expressions. (YP)</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> <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://hdl.handle.net/2060/20030003725','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030003725"><span>A Parametric Study of Fine-scale Turbulence Mixing <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; Bridges, James; Freund, Jonathan B.</p> <p>2002-01-01</p> <p>The present paper is a study of <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> spectra from model functions that describe the <span class="hlt">source</span>. The study is motivated by the need to improve the spectral shape of the MGBK jet <span class="hlt">noise</span> prediction methodology at high frequency. The predicted spectral shape usually appears less broadband than measurements and faster decaying at high frequency. Theoretical representation of the <span class="hlt">source</span> is based on Lilley's equation. Numerical simulations of high-speed subsonic jets as well as some recent turbulence measurements reveal a number of interesting statistical properties of turbulence correlation functions that may have a bearing on radiated <span class="hlt">noise</span>. These studies indicate that an exponential spatial function may be a more appropriate representation of a two-point correlation compared to its Gaussian counterpart. The effect of <span class="hlt">source</span> non-compactness on spectral shape is discussed. It is shown that <span class="hlt">source</span> non-compactness could well be the differentiating factor between the Gaussian and exponential model functions. In particular, the fall-off of the <span class="hlt">noise</span> spectra at high frequency is studied and it is shown that a non-compact <span class="hlt">source</span> with an exponential model function results in a broader spectrum and better agreement with data. An alternate <span class="hlt">source</span> model that represents the <span class="hlt">source</span> as a covariance of the convective derivative of fine-scale turbulence kinetic energy is also examined.</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('https://ntrs.nasa.gov/search.jsp?R=19920000102&hterms=Butterfly&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DButterfly','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920000102&hterms=Butterfly&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DButterfly"><span><span class="hlt">Aerodynamic</span> Shutoff Valve</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Horstman, Raymond H.</p> <p>1992-01-01</p> <p><span class="hlt">Aerodynamic</span> flow achieved by adding fixed fairings to butterfly valve. When valve fully open, fairings align with butterfly and reduce wake. Butterfly free to turn, so valve can be closed, while fairings remain fixed. Design reduces turbulence in flow of air in internal suction system. Valve aids in development of improved porous-surface boundary-layer control system to reduce <span class="hlt">aerodynamic</span> drag. Applications primarily aerospace. System adapted to boundary-layer control on high-speed land vehicles.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ChPhB..25f4301K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ChPhB..25f4301K"><span>Use of a plane jet for flow-induced <span class="hlt">noise</span> reduction of tandem rods</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kun, Zhao; Xi-xiang, Yang; Patrick, N. Okolo; Wei-hua, Zhang</p> <p>2016-06-01</p> <p>Unsteady wake from upstream components of landing gear impinging on downstream components could be a strong <span class="hlt">noise</span> <span class="hlt">source</span>. The use of a plane jet is proposed to reduce this flow-induced <span class="hlt">noise</span>. Tandem rods with different gap widths were utilized as the test body. Both acoustic and <span class="hlt">aerodynamic</span> tests were conducted in order to validate this technique. Acoustic test results proved that overall <span class="hlt">noise</span> emission from tandem rods could be lowered and tonal <span class="hlt">noise</span> could be removed with use of the plane jet. However, when the plane jet was turned on, in some frequency range it could be the subsequent main contributor instead of tandem rods to total <span class="hlt">noise</span> emission whilst in some frequency range rods could still be the main contributor. Moreover, <span class="hlt">aerodynamic</span> tests fundamentally studied explanations for the <span class="hlt">noise</span> reduction. Specifically, not only impinging speed to rods but speed and turbulence level to the top edge of the rear rod could be diminished by the upstream plane jet. Consequently, the vortex shedding induced by the rear rod was reduced, which was confirmed by the speed, Reynolds stress as well as the velocity fluctuation spectral measured in its wake. This study confirmed the potential use of a plane jet towards landing gear <span class="hlt">noise</span> reduction. Project partially supported by the European Union FP7 CleanSky Joint Technology Initiative “ALLEGRA” (Grant No. 308225).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19980032586','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19980032586"><span>Reduction of Helicopter Blade-Vortex Interaction <span class="hlt">Noise</span> by Active Rotor Control Technology</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Yu, Yung H.; Gmelin, Bernd; Splettstoesser, Wolf; Brooks, Thomas F.; Philippe, Jean J.; Prieur, Jean</p> <p>1997-01-01</p> <p>Helicopter blade-vortex interaction <span class="hlt">noise</span> is one of the most severe <span class="hlt">noise</span> <span class="hlt">sources</span> and is very important both in community annoyance and military detection. Research over the decades has substantially improved basic physical understanding of the mechanisms generating rotor blade-vortex interaction <span class="hlt">noise</span> and also of controlling techniques, particularly using active rotor control technology. This paper reviews active rotor control techniques currently available for rotor blade vortex interaction <span class="hlt">noise</span> reduction, including higher harmonic pitch control, individual blade control, and on-blade control technologies. Basic physical mechanisms of each active control technique are reviewed in terms of <span class="hlt">noise</span> reduction mechanism and controlling <span class="hlt">aerodynamic</span> or structural parameters of a blade. Active rotor control techniques using smart structures/materials are discussed, including distributed smart actuators to induce local torsional or flapping deformations, Published by Elsevier Science Ltd.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994JSV...172..277Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994JSV...172..277Y"><span>Vortex shedding <span class="hlt">noise</span> control in idling circular saws using air ejection at the teeth</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yanagimoto, K.; Mote, C. D.; Ichimiya, R.</p> <p>1994-04-01</p> <p><span class="hlt">Aerodynamically</span> induced <span class="hlt">noise</span> from an idling circular saw can be very intense. The purpose of the present investigation is <span class="hlt">noise</span> reduction through vortex shedding control in idling circular saws. Reduction of <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> in idling circular saws may be possible by controlling the shed vortices and flow structures in the space between teeth, based on the earlier observations.</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://hdl.handle.net/2060/19950005076','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950005076"><span>Potential impacts of advanced <span class="hlt">aerodynamic</span> technology on air transportation system productivity</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bushnell, Dennis M. (Editor)</p> <p>1994-01-01</p> <p>Summaries of a workshop held at NASA Langley Research Center in 1993 to explore the application of advanced <span class="hlt">aerodynamics</span> to airport productivity improvement are discussed. Sessions included discussions of terminal area productivity problems and advanced <span class="hlt">aerodynamic</span> technologies for enhanced high lift and reduced <span class="hlt">noise</span>, emissions, and wake vortex hazard with emphasis upon advanced aircraft configurations and multidisciplinary solution options.</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('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/2060/20000076806','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20000076806"><span>Future Challenges and Opportunities in <span class="hlt">Aerodynamics</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kumar, Ajay; Hefner, Jerry N.</p> <p>2000-01-01</p> <p>Investments in aeronautics research and technology have declined substantially over the last decade, in part due to the perception that technologies required in aircraft design are fairly mature and readily available. This perception is being driven by the fact that aircraft configurations, particularly the transport aircraft, have evolved only incrementally, over last several decades. If however, one considers that the growth in air travel is expected to triple in the next 20 years, it becomes quickly obvious that the evolutionary development of technologies is not going to meet the increased demands for safety, environmental compatibility, capacity, and economic viability. Instead, breakthrough technologies will he required both in traditional disciplines of <span class="hlt">aerodynamics</span>, propulsion, structures, materials, controls, and avionics as well as in the multidisciplinary integration of these technologies into the design of future aerospace vehicles concepts. The paper discusses challenges and opportunities in the field of <span class="hlt">aerodynamics</span> over the next decade. Future technology advancements in <span class="hlt">aerodynamics</span> will hinge on our ability, to understand, model, and control complex, three-dimensional, unsteady viscous flow across the speed range. This understanding is critical for developing innovative flow and <span class="hlt">noise</span> control technologies and advanced design tools that will revolutionize future aerospace vehicle systems and concepts. Specifically, the paper focuses on advanced vehicle concepts, flow and <span class="hlt">noise</span> control technologies, and advanced design and analysis tools.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20030057124','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030057124"><span>Review of Integrated <span class="hlt">Noise</span> Model (INM) Equations and Processes</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Shepherd, Kevin P. (Technical Monitor); Forsyth, David W.; Gulding, John; DiPardo, Joseph</p> <p>2003-01-01</p> <p>The FAA's Integrated <span class="hlt">Noise</span> Model (INM) relies on the methods of the SAE AIR-1845 'Procedure for the Calculation of Airplane <span class="hlt">Noise</span> in the Vicinity of Airports' issued in 1986. Simplifying assumptions for <span class="hlt">aerodynamics</span> and <span class="hlt">noise</span> calculation were made in the SAE standard and the INM based on the limited computing power commonly available then. The key objectives of this study are 1) to test some of those assumptions against Boeing <span class="hlt">source</span> data, and 2) to automate the manufacturer's methods of data development to enable the maintenance of a consistent INM database over time. These new automated tools were used to generate INM database submissions for six airplane types :737-700 (CFM56-7 24K), 767-400ER (CF6-80C2BF), 777-300 (Trent 892), 717-200 (BR7 15), 757-300 (RR535E4B), and the 737-800 (CFM56-7 26K).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20000062459','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20000062459"><span>Influence of Mean-Density Gradient on Small-Scale 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>Khavaran, Abbas</p> <p>2000-01-01</p> <p>A physics-based methodology is described to predict jet-mixing <span class="hlt">noise</span> due to small-scale turbulence. Both self- and shear-<span class="hlt">noise</span> <span class="hlt">source</span> teens of Lilley's equation are modeled and the far-field <span class="hlt">aerodynamic</span> <span class="hlt">noise</span> is expressed as an integral over the jet volume of the <span class="hlt">source</span> multiplied by an appropriate Green's function which accounts for <span class="hlt">source</span> convection and mean-flow refraction. Our primary interest here is to include transverse gradients of the mean density in the <span class="hlt">source</span> modeling. It is shown that, in addition to the usual quadrupole type <span class="hlt">sources</span> which scale to the fourth-power of the acoustic wave number, additional dipole and monopole <span class="hlt">sources</span> are present that scale to lower powers of wave number. Various two-point correlations are modeled and an approximate solution to <span class="hlt">noise</span> spectra due to multipole <span class="hlt">sources</span> of various orders is developed. Mean flow and turbulence information is provided through RANS-k(epsilon) solution. Numerical results are presented for a subsonic jet at a range of temperatures and Mach numbers. Predictions indicated a decrease in high frequency <span class="hlt">noise</span> with added heat, while changes in the low frequency <span class="hlt">noise</span> depend on jet velocity and observer angle.</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/2060/19920023021','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920023021"><span>Turbine disk cavity <span class="hlt">aerodynamics</span> and heat transfer</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Johnson, B. V.; Daniels, W. A.</p> <p>1992-01-01</p> <p>Experiments were conducted to define the nature of the <span class="hlt">aerodynamics</span> and heat transfer for the flow within the disk cavities and blade attachments of a large-scale model, simulating the Space Shuttle Main Engine (SSME) turbopump drive turbines. These experiments of the <span class="hlt">aerodynamic</span> driving mechanisms explored the following: (1) flow between the main gas path and the disk cavities; (2) coolant flow injected into the disk cavities; (3) coolant density; (4) leakage flows through the seal between blades; and (5) the role that each of these various flows has in determining the adiabatic recovery temperature at all of the critical locations within the cavities. The model and the test apparatus provide close geometrical and <span class="hlt">aerodynamic</span> simulation of all the two-stage cavity flow regions for the SSME High Pressure Fuel Turbopump and the ability to simulate the <span class="hlt">sources</span> and sinks for each cavity flow.</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/2060/20030025715','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030025715"><span>Sound Generation in the Presence of Moving Surfaces with Application to Internally Generated Aircraft Engine <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>Goldstein, Marvin E.; Envia, E.</p> <p>2002-01-01</p> <p>In many cases of technological interest solid boundaries play a direct role in the <span class="hlt">aerodynamic</span> sound generation process and their presence often results in a large increase in the acoustic radiation. A generalized treatment of the emission of sound from moving boundaries is presented. The approach is similar to that of Ffowcs Williams and Hawkings (1969) but the effect of the surrounding mean flow is explicitly accounted for. The results are used to develop a rational framework for the prediction of internally generated aero-engine <span class="hlt">noise</span>. The final formulas suggest some new <span class="hlt">noise</span> <span class="hlt">sources</span> that may be of practical significance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19780016103','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19780016103"><span>Powered-Lift <span class="hlt">Aerodynamics</span> and Acoustics. [conferences</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1976-01-01</p> <p>Powered lift technology is reviewed. Topics covered include: (1) high lift <span class="hlt">aerodynamics</span>; (2) high speed and cruise <span class="hlt">aerodynamics</span>; (3) acoustics; (4) propulsion <span class="hlt">aerodynamics</span> and acoustics; (5) <span class="hlt">aerodynamic</span> and acoustic loads; and (6) full-scale and flight research.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770011935','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770011935"><span>Advanced acoustic and <span class="hlt">aerodynamic</span> 20-inch fan program</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Erwin, J. R.; Heldenbrand, R. W.</p> <p>1977-01-01</p> <p>The <span class="hlt">aerodynamic</span> analyses, mechanical analyses, and stress tests of a 20-inch diameter advanced fan design intended for acoustic investigation by NASA-LeRC are discussed. A high tip speed transonic fan rotor was scaled directly to 20.0 inches (0.508 m) from a 28.74-inch (0.73-m) diameter rotor. A new stator was designed and fabricated for the fan and incorporated with a test rig housing and adapter hardware for installation in the NASA-LeRC Jet <span class="hlt">Noise</span> Facility for acoustic evaluation. The stator was designed to allow mounting at three axial locations, and the fan, housing, and adapters are reversible so that either the inlet or the exhaust ends of the assembly face the open room of the test facility. Excellent <span class="hlt">aerodynamic</span> performance is predicted, and a low <span class="hlt">noise</span> signature is expected since the unique <span class="hlt">aerodynamic</span> design features of this fan are directly conductive to producing minimum sound power.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PrAeS..84...48A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PrAeS..84...48A"><span>Mimicking the humpback whale: An <span class="hlt">aerodynamic</span> perspective</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aftab, S. M. A.; Razak, N. A.; Mohd Rafie, A. S.; Ahmad, K. A.</p> <p>2016-07-01</p> <p>This comprehensive review aims to provide a critical overview of the work on tubercles in the past decade. The humpback whale is of interest to <span class="hlt">aerodynamic</span>/hydrodynamic researchers, as it performs manoeuvres that baffle the imagination. Researchers have attributed these capabilities to the presence of lumps, known as tubercles, on the leading edge of the flipper. Tubercles generate a unique flow control mechanism, offering the humpback exceptional manoeuverability. Experimental and numerical studies have shown that the flow pattern over the tubercle wing is quite different from conventional wings. Research on the Tubercle Leading Edge (TLE) concept has helped to clarify <span class="hlt">aerodynamic</span> issues such as flow separation, tonal <span class="hlt">noise</span> and dynamic stall. TLE shows increased lift by delaying and restricting spanwise separation. A summary of studies on different airfoils and reported improvement in performance is outlined. The major contributions and limitations of previous work are also reported.</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://hdl.handle.net/2060/19950020229','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950020229"><span>CFD research, parallel computation and <span class="hlt">aerodynamic</span> optimization</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ryan, James S.</p> <p>1995-01-01</p> <p>Over five years of research in Computational Fluid Dynamics and its applications are covered in this report. Using CFD as an established tool, <span class="hlt">aerodynamic</span> optimization on parallel architectures is explored. The objective of this work is to provide better tools to vehicle designers. Submarine design requires accurate force and moment calculations in flow with thick boundary layers and large separated vortices. Low <span class="hlt">noise</span> production is critical, so flow into the propulsor region must be predicted accurately. The High Speed Civil Transport (HSCT) has been the subject of recent work. This vehicle is to be a passenger vehicle with the capability of cutting overseas flight times by more than half. A successful design must surpass the performance of comparable planes. Fuel economy, other operational costs, environmental impact, and range must all be improved substantially. For all these reasons, improved design tools are required, and these tools must eventually integrate optimization, external <span class="hlt">aerodynamics</span>, propulsion, structures, heat transfer and other disciplines.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950005976','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950005976"><span>High speed civil transport <span class="hlt">aerodynamic</span> optimization</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ryan, James S.</p> <p>1994-01-01</p> <p>This is a report of work in support of the Computational Aerosciences (CAS) element of the Federal HPCC program. Specifically, CFD and <span class="hlt">aerodynamic</span> optimization are being performed on parallel computers. The long-range goal of this work is to facilitate teraflops-rate multidisciplinary optimization of aerospace vehicles. This year's work is targeted for application to the High Speed Civil Transport (HSCT), one of four CAS grand challenges identified in the HPCC FY 1995 Blue Book. This vehicle is to be a passenger aircraft, with the promise of cutting overseas flight time by more than half. To meet fuel economy, operational costs, environmental impact, <span class="hlt">noise</span> production, and range requirements, improved design tools are required, and these tools must eventually integrate optimization, external <span class="hlt">aerodynamics</span>, propulsion, structures, heat transfer, controls, and perhaps other disciplines. The fundamental goal of this project is to contribute to improved design tools for U.S. industry, and thus to the nation's economic competitiveness.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19720025115','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19720025115"><span><span class="hlt">Aerodynamic</span> and Acoustic Performance of Two Choked-Flow Inlets Under Static Conditions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Miller, B. A.; Abbott, J. M.</p> <p>1972-01-01</p> <p>Tests were conducted to determine the <span class="hlt">aerodynamic</span> and acoustic performance of two choking flow inlets under static conditions. One inlet choked the flow in the cowl throat by an axial translation of the inlet centerbody. The other inlet employed a translating grid of airfoils to choke the flow. Both inlets were sized to fit a 13.97 cm diameter fan with a design weight flow of 2.49 kg/sec. The inlets were operated in both the choked and unchoked modes over a range of weight flows. Measurements were made of inlet pressure recovery, flow distortion, surface static pressure distribution, and fan <span class="hlt">noise</span> suppression. Choking of the translating centerbody inlet reduced blade passing frequency <span class="hlt">noise</span> by 29 db while yielding a total pressure recovery of 0.985. <span class="hlt">Noise</span> reductions were also measured at 1/3-octave band center frequencies of 2500, 5000, and 20,000 cycles. The translating grid inlet gave a total pressure recovery of 0.968 when operating close to the choking weight flow. However, an intermittent high intensity <span class="hlt">noise</span> <span class="hlt">source</span> was encountered with this inlet that precluded an accurate measurement of inlet <span class="hlt">noise</span> suppression.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6080168','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6080168"><span>Applied computational <span class="hlt">aerodynamics</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Henne, P.A.</p> <p>1990-01-01</p> <p>The present volume discusses the original development of the panel method, the mapping solutions and singularity distributions of linear potential schemes, the capabilities of full-potential, Euler, and Navier-Stokes schemes, the use of the grid-generation methodology in applied <span class="hlt">aerodynamics</span>, subsonic airfoil design, inverse airfoil design for transonic applications, the divergent trailing-edge airfoil innovation in CFD, Euler and potential computational results for selected <span class="hlt">aerodynamic</span> configurations, and the application of CFD to wing high-lift systems. Also discussed are high-lift wing modifications for an advanced-capability EA-6B aircraft, Navier-Stokes methods for internal and integrated propulsion system flow predictions, the use of zonal techniques for analysis of rotor-stator interaction, CFD applications to complex configurations, CFD applications in component <span class="hlt">aerodynamic</span> design of the V-22, Navier-Stokes computations of a complete F-16, CFD at supersonic/hypersonic speeds, and future CFD developments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19860019440','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19860019440"><span>An analysis of blade vortex interaction <span class="hlt">aerodynamics</span> and acoustics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lee, D. J.</p> <p>1985-01-01</p> <p>The impulsive <span class="hlt">noise</span> associated with helicopter flight due to Blade-Vortex Interaction, sometimes called blade slap is analyzed especially for the case of a close encounter of the blade-tip vortex with a following blade. Three parts of the phenomena are considered: the tip-vortex structure generated by the rotating blade, the unsteady pressure produced on the following blade during the interaction, and the acoustic radiation due to the unsteady pressure field. To simplify the problem, the analysis was confined to the situation where the vortex is aligned parallel to the blade span in which case the maximum acoustic pressure results. Acoustic radiation due to the interaction is analyzed in space-fixed coordinates and in the time domain with the unsteady pressure on the blade surface as the <span class="hlt">source</span> of chordwise compact, but spanwise non-compact radiation. Maximum acoustic pressure is related to the vortex core size and Reynolds number which are in turn functions of the blade-tip <span class="hlt">aerodynamic</span> parameters. Finally <span class="hlt">noise</span> reduction and performance are considered.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19840052515&hterms=importance+marketing&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dimportance%2Bmarketing','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19840052515&hterms=importance+marketing&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dimportance%2Bmarketing"><span>Computational <span class="hlt">aerodynamics</span> and design</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ballhaus, W. F., Jr.</p> <p>1982-01-01</p> <p>The role of computational <span class="hlt">aerodynamics</span> in design is reviewed with attention given to the design process; the proper role of computations; the importance of calibration, interpretation, and verification; the usefulness of a given computational capability; and the marketing of new codes. Examples of computational <span class="hlt">aerodynamics</span> in design are given with particular emphasis on the Highly Maneuverable Aircraft Technology. Finally, future prospects are noted, with consideration given to the role of advanced computers, advances in numerical solution techniques, turbulence models, complex geometries, and computational design procedures. Previously announced in STAR as N82-33348</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880004697','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880004697"><span>Nonlinear <span class="hlt">aerodynamic</span> wing design</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bonner, Ellwood</p> <p>1985-01-01</p> <p>The applicability of new nonlinear theoretical techniques is demonstrated for supersonic wing design. The new technology was utilized to define outboard panels for an existing advanced tactical fighter model. Mach 1.6 maneuver point design and multi-operating point compromise surfaces were developed and tested. High <span class="hlt">aerodynamic</span> efficiency was achieved at the design conditions. A corollary result was that only modest supersonic penalties were incurred to meet multiple <span class="hlt">aerodynamic</span> requirements. The nonlinear potential analysis of a practical configuration arrangement correlated well with experimental data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19840014138&hterms=computer+graphics&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dcomputer%2Bgraphics','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19840014138&hterms=computer+graphics&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dcomputer%2Bgraphics"><span>Computer graphics in <span class="hlt">aerodynamic</span> analysis</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cozzolongo, J. V.</p> <p>1984-01-01</p> <p>The use of computer graphics and its application to <span class="hlt">aerodynamic</span> analyses on a routine basis is outlined. The mathematical modelling of the aircraft geometries and the shading technique implemented are discussed. Examples of computer graphics used to display <span class="hlt">aerodynamic</span> flow field data and aircraft geometries are shown. A future need in computer graphics for <span class="hlt">aerodynamic</span> analyses is addressed.</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('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/2060/19950019972','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950019972"><span>Aircraft <span class="hlt">noise</span> prediction program theoretical manual: Rotorcraft System <span class="hlt">Noise</span> Prediction System (ROTONET), part 4</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Weir, Donald S.; Jumper, Stephen J.; Burley, Casey L.; Golub, Robert A.</p> <p>1995-01-01</p> <p>This document describes the theoretical methods used in the rotorcraft <span class="hlt">noise</span> prediction system (ROTONET), which is a part of the NASA Aircraft <span class="hlt">Noise</span> Prediction Program (ANOPP). The ANOPP code consists of an executive, database manager, and prediction modules for jet engine, propeller, and rotor <span class="hlt">noise</span>. The ROTONET subsystem contains modules for the prediction of rotor airloads and performance with momentum theory and prescribed wake <span class="hlt">aerodynamics</span>, rotor tone <span class="hlt">noise</span> with compact chordwise and full-surface solutions to the Ffowcs-Williams-Hawkings equations, semiempirical airfoil broadband <span class="hlt">noise</span>, and turbulence ingestion broadband <span class="hlt">noise</span>. Flight dynamics, atmosphere propagation, and <span class="hlt">noise</span> metric calculations are covered in NASA TM-83199, Parts 1, 2, and 3.</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://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> </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/2060/20090035729','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> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20010020392','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20010020392"><span>Global Design Optimization for <span class="hlt">Aerodynamics</span> and Rocket Propulsion Components</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Shyy, Wei; Papila, Nilay; Vaidyanathan, Rajkumar; Tucker, Kevin; Turner, James E. (Technical Monitor)</p> <p>2000-01-01</p> <p>Modern computational and experimental tools for <span class="hlt">aerodynamics</span> and propulsion applications have matured to a stage where they can provide substantial insight into engineering processes involving fluid flows, and can be fruitfully utilized to help improve the design of practical devices. In particular, rapid and continuous development in aerospace engineering demands that new design concepts be regularly proposed to meet goals for increased performance, robustness and safety while concurrently decreasing cost. To date, the majority of the effort in design optimization of fluid dynamics has relied on gradient-based search algorithms. Global optimization methods can utilize the information collected from various <span class="hlt">sources</span> and by different tools. These methods offer multi-criterion optimization, handle the existence of multiple design points and trade-offs via insight into the entire design space, can easily perform tasks in parallel, and are often effective in filtering the <span class="hlt">noise</span> intrinsic to numerical and experimental data. However, a successful application of the global optimization method needs to address issues related to data requirements with an increase in the number of design variables, and methods for predicting the model performance. In this article, we review recent progress made in establishing suitable global optimization techniques employing neural network and polynomial-based response surface methodologies. Issues addressed include techniques for construction of the response surface, design of experiment techniques for supplying information in an economical manner, optimization procedures and multi-level techniques, and assessment of relative performance between polynomials and neural networks. Examples drawn from wing <span class="hlt">aerodynamics</span>, turbulent diffuser flows, gas-gas injectors, and supersonic turbines are employed to help demonstrate the issues involved in an engineering design context. Both the usefulness of the existing knowledge to aid current design</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/2060/19920017948','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920017948"><span>Rarefied-flow <span class="hlt">aerodynamics</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Potter, J. Leith</p> <p>1992-01-01</p> <p>Means for relatively simple and quick procedures are examined for estimating <span class="hlt">aerodynamic</span> coefficients of lifting reentry vehicles. The methods developed allow aerospace designers not only to evaluate the <span class="hlt">aerodynamics</span> of specific shapes but also to optimize shapes under given constraints. The analysis was also studied of the effect of thermomolecular flow on pressures measured by an orifice near the nose of a Space Shuttle Orbiter at altitudes above 75 km. It was shown that pressures corrected for thermomolecular flow effect are in good agreement with values predicted by independent theoretical methods. An incidental product was the insight gained about the free molecular thermal accommodation coefficient applicable under 'real' conditions of high speed flow in the Earth's atmosphere. The results are presented as abstracts of referenced papers. One reference paper is presented in its entirety.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005ESASP.563..229C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005ESASP.563..229C"><span>HYSHOT-2 <span class="hlt">Aerodynamics</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cain, T.; Owen, R.; Walton, C.</p> <p>2005-02-01</p> <p>The scramjet flight test Hyshot-2, flew on the 30 July 2002. The programme, led by the University of Queensland, had the primary objective of obtaining supersonic combustion data in flight for comparison with measurements made in shock tunnels. QinetiQ was one of the sponsors, and also provided <span class="hlt">aerodynamic</span> data and trajectory predictions for the ballistic re-entry of the spinning sounding rocket. The unconventional missile geometry created by the nose-mounted asymmetric-scramjet in conjunction with the high angle of attack during re-entry makes the problem interesting. This paper presents the wind tunnel measurements and <span class="hlt">aerodynamic</span> calculations used as input for the trajectory prediction. Indirect comparison is made with data obtained in the Hyshot-2 flight using a 6 degree-of-freedom trajectory simulation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040086755','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040086755"><span>Advanced <span class="hlt">Aerodynamic</span> Control Effectors</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wood, Richard M.; Bauer, Steven X. S.</p> <p>1999-01-01</p> <p>A 1990 research program that focused on the development of advanced <span class="hlt">aerodynamic</span> control effectors (AACE) for military aircraft has been reviewed and summarized. Data are presented for advanced planform, flow control, and surface contouring technologies. The data show significant increases in lift, reductions in drag, and increased control power, compared to typical <span class="hlt">aerodynamic</span> designs. The results presented also highlighted the importance of planform selection in the design of a control effector suite. Planform data showed that dramatic increases in lift (greater than 25%) can be achieved with multiple wings and a sawtooth forebody. Passive porosity and micro drag generator control effector data showed control power levels exceeding that available from typical effectors (moving surfaces). Application of an advanced planform to a tailless concept showed benefits of similar magnitude as those observed in the generic studies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhRvF...1h4002G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhRvF...1h4002G"><span><span class="hlt">Aerodynamic</span> Leidenfrost effect</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gauthier, Anaïs; Bird, James C.; Clanet, Christophe; Quéré, David</p> <p>2016-12-01</p> <p>When deposited on a plate moving quickly enough, any liquid can levitate as it does when it is volatile on a very hot solid (Leidenfrost effect). In the <span class="hlt">aerodynamic</span> Leidenfrost situation, air gets inserted between the liquid and the moving solid, a situation that we analyze. We observe two types of entrainment. (i) The thickness of the air gap is found to increase with the plate speed, which is interpreted in the Landau-Levich-Derjaguin frame: Air is dynamically dragged along the surface and its thickness results from a balance between capillary and viscous effects. (ii) Air set in motion by the plate exerts a force on the levitating liquid. We discuss the magnitude of this <span class="hlt">aerodynamic</span> force and show that it can be exploited to control the liquid and even to drive it against gravity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100039466','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100039466"><span><span class="hlt">Aerodynamics</span>: The Wright Way</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cole, Jennifer Hansen</p> <p>2010-01-01</p> <p>This slide presentation reviews some of the basic principles of <span class="hlt">aerodynamics</span>. Included in the presentation are: a few demonstrations of the principles, an explanation of the concepts of lift, drag, thrust and weight, a description of Bernoulli's principle, the concept of the airfoil (i.e., the shape of the wing) and how that effects lift, and the method of controlling an aircraft by manipulating the four forces using control surfaces.</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://adsabs.harvard.edu/abs/2016JPhCS.753b2029B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JPhCS.753b2029B"><span>Validation and comparison of <span class="hlt">aerodynamic</span> modelling approaches for wind turbines</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Blondel, F.; Boisard, R.; Milekovic, M.; Ferrer, G.; Lienard, C.; Teixeira, D.</p> <p>2016-09-01</p> <p>The development of large capacity Floating Offshore Wind Turbines (FOWT) is an interdisciplinary challenge for the design solvers, requiring accurate modelling of both hydrodynamics, elasticity, servodynamics and <span class="hlt">aerodynamics</span> all together. Floating platforms will induce low-frequency unsteadiness, and for large capacity turbines, the blade induced vibrations will lead to high-frequency unsteadiness. While yawed inflow conditions are still a challenge for commonly used <span class="hlt">aerodynamic</span> methods such as the Blade Element Momentum method (BEM), the new <span class="hlt">sources</span> of unsteadiness involved by large turbine scales and floater motions have to be tackled accurately, keeping the computational cost small enough to be compatible with design and certification purposes. In the light of this, this paper will focus on the comparison of three <span class="hlt">aerodynamic</span> solvers based on BEM and vortex methods, on standard, yawed and unsteady inflow conditions. We will focus here on up-to-date wind tunnel experiments, such as the Unsteady <span class="hlt">Aerodynamics</span> Experiment (UAE) database and the MexNext international project.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110012465','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110012465"><span>Investigation of Flow Conditioners for Compact Jet Engine Simulator Rig <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>Doty, Michael J.; Haskin, Henry H.</p> <p>2011-01-01</p> <p>The design requirements for two new Compact Jet Engine Simulator (CJES) units for upcoming wind tunnel testing lead to the distinct possibility of rig <span class="hlt">noise</span> contamination. The acoustic and <span class="hlt">aerodynamic</span> properties of several flow conditioner devices are investigated over a range of operating conditions relevant to the CJES units to mitigate the risk of rig <span class="hlt">noise</span>. An impinging jet broadband <span class="hlt">noise</span> <span class="hlt">source</span> is placed in the upstream plenum of the test facility permitting measurements of not only flow conditioner self-<span class="hlt">noise</span>, but also <span class="hlt">noise</span> attenuation characteristics. Several perforated plate and honeycomb samples of high porosity show minimal self-<span class="hlt">noise</span> but also minimal attenuation capability. Conversely, low porosity perforated plate and sintered wire mesh conditioners exhibit noticeable attenuation but also unacceptable self-<span class="hlt">noise</span>. One fine wire mesh sample (DP450661) shows minimal selfnoise and reasonable attenuation, particularly when combined in series with a 15.6 percent open area (POA) perforated plate upstream. This configuration is the preferred flow conditioner system for the CJES, providing up to 20 dB of broadband attenuation capability with minimal self-<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 <span class="hlt">aerodynamic</span> 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 <span class="hlt">aerodynamic</span> 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 airframe <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, <span class="hlt">aerodynamic</span> 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> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/850252','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/850252"><span>Freight Wing Trailer <span class="hlt">Aerodynamics</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Graham, Sean; Bigatel, Patrick</p> <p>2004-10-17</p> <p>Freight Wing Incorporated utilized the opportunity presented by this DOE category one Inventions and Innovations grant to successfully research, develop, test, patent, market, and sell innovative fuel and emissions saving <span class="hlt">aerodynamic</span> attachments for the trucking industry. A great deal of past scientific research has demonstrated that streamlining box shaped semi-trailers can significantly reduce a truck's fuel consumption. However, significant design challenges have prevented past concepts from meeting industry needs. Market research early in this project revealed the demands of truck fleet operators regarding <span class="hlt">aerodynamic</span> attachments. Products must not only save fuel, but cannot interfere with the operation of the truck, require significant maintenance, add significant weight, and must be extremely durable. Furthermore, SAE/TMC J1321 tests performed by a respected independent laboratory are necessary for large fleets to even consider purchase. Freight Wing used this information to create a system of three practical <span class="hlt">aerodynamic</span> attachments for the front, rear and undercarriage of standard semi trailers. SAE/TMC J1321 Type II tests preformed by the Transportation Research Center (TRC) demonstrated a 7% improvement to fuel economy with all three products. If Freight Wing is successful in its continued efforts to gain market penetration, the energy and environmental savings would be considerable. Each truck outfitted saves approximately 1,100 gallons of fuel every 100,000 miles, which prevents over 12 tons of CO2 from entering the atmosphere. If all applicable trailers used the technology, the country could save approximately 1.8 billion gallons of diesel fuel, 18 million tons of emissions and 3.6 billion dollars annually.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19940002587&hterms=Armament&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DArmament','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19940002587&hterms=Armament&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DArmament"><span>TAD- THEORETICAL <span class="hlt">AERODYNAMICS</span> PROGRAM</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Barrowman, J.</p> <p>1994-01-01</p> <p>This theoretical <span class="hlt">aerodynamics</span> program, TAD, was developed to predict the <span class="hlt">aerodynamic</span> characteristics of vehicles with sounding rocket configurations. These slender, axisymmetric finned vehicle configurations have a wide range of aeronautical applications from rockets to high speed armament. Over a given range of Mach numbers, TAD will compute the normal force coefficient derivative, the center-of-pressure, the roll forcing moment coefficient derivative, the roll damping moment coefficient derivative, and the pitch damping moment coefficient derivative of a sounding rocket configured vehicle. The vehicle may consist of a sharp pointed nose of cone or tangent ogive shape, up to nine other body divisions of conical shoulder, conical boattail, or circular cylinder shape, and fins of trapezoid planform shape with constant cross section and either three or four fins per fin set. The characteristics computed by TAD have been shown to be accurate to within ten percent of experimental data in the supersonic region. The TAD program calculates the characteristics of separate portions of the vehicle, calculates the interference between separate portions of the vehicle, and then combines the results to form a total vehicle solution. Also, TAD can be used to calculate the characteristics of the body or fins separately as an aid in the design process. Input to the TAD program consists of simple descriptions of the body and fin geometries and the Mach range of interest. Output includes the <span class="hlt">aerodynamic</span> characteristics of the total vehicle, or user-selected portions, at specified points over the mach range. The TAD program is written in FORTRAN IV for batch execution and has been implemented on an IBM 360 computer with a central memory requirement of approximately 123K of 8 bit bytes. The TAD program was originally developed in 1967 and last updated in 1972.</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://www.dtic.mil/docs/citations/ADA038763','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA038763"><span>Prediction of <span class="hlt">Aerodynamic</span> Loading</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>1977-02-01</p> <p>predictable even with knowledge of the motion and the quasi- steady <span class="hlt">aerodynamic</span> coefficients . It sems likely that the unsteady boundary-layer...build up, which are explainable 41 terams of the stability coefficients . More research is needed on the former type of undemanded manoeuvre. In some...drag 81, 82... B5 body sections I. kg lift St strdke 1M kg m pitching moment N kg normal force T kg axial force a 0 angle of attack Coefficie its: CD, cD</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> </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/2060/19820012073','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19820012073"><span>Aircraft <span class="hlt">noise</span> prediction program theoretical manual, part 2</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zorumski, W. E.</p> <p>1982-01-01</p> <p>Detailed prediction methods for specific aircraft <span class="hlt">noise</span> <span class="hlt">sources</span> are given. These <span class="hlt">sources</span> are airframe <span class="hlt">noise</span>, combustion <span class="hlt">noise</span>, fan <span class="hlt">noise</span>, single and dual stream jet <span class="hlt">noise</span>, and turbine <span class="hlt">noise</span>. Modifications to the NASA methods which comply with the International Civil Aviation Organization standard method for aircraft <span class="hlt">noise</span> prediction are given.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20000025202','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20000025202"><span>Modeling the High Speed Research Cycle 2B Longitudinal <span class="hlt">Aerodynamic</span> Database Using Multivariate Orthogonal Functions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Morelli, E. A.; Proffitt, M. S.</p> <p>1999-01-01</p> <p>The data for longitudinal non-dimensional, <span class="hlt">aerodynamic</span> coefficients in the High Speed Research Cycle 2B <span class="hlt">aerodynamic</span> database were modeled using polynomial expressions identified with an orthogonal function modeling technique. The discrepancy between the tabular <span class="hlt">aerodynamic</span> data and the polynomial models was tested and shown to be less than 15 percent for drag, lift, and pitching moment coefficients over the entire flight envelope. Most of this discrepancy was traced to smoothing local measurement <span class="hlt">noise</span> and to the omission of mass case 5 data in the modeling process. A simulation check case showed that the polynomial models provided a compact and accurate representation of the nonlinear <span class="hlt">aerodynamic</span> dependencies contained in the HSR Cycle 2B tabular <span class="hlt">aerodynamic</span> database.</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://www.osti.gov/scitech/servlets/purl/1007921','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1007921"><span>Plasma <span class="hlt">Aerodynamic</span> Control Effectors for Improved Wind Turbine Performance</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mehul P. Patel; Srikanth Vasudevan; Robert C. Nelson; Thomas C. Corke</p> <p>2008-08-01</p> <p>Orbital Research Inc is developing an innovative Plasma <span class="hlt">Aerodynamic</span> Control Effectors (PACE) technology for improved performance of wind turbines. The PACE system is aimed towards the design of "smart" rotor blades to enhance energy capture and reduce <span class="hlt">aerodynamic</span> loading and <span class="hlt">noise</span> using flow-control. The PACE system will provide ability to change <span class="hlt">aerodynamic</span> loads and pitch distribution across the wind turbine blade without any moving surfaces. Additional benefits of the PACE system include reduced blade structure weight and complexity that should translate into a substantially reduced initial cost. During the Phase I program, the ORI-UND Team demonstrated (proof-of-concept) performance improvements on select rotor blade designs using PACE concepts. Control of both 2-D and 3-D flows were demonstrated. An analytical study was conducted to estimate control requirements for the PACE system to maintain control during wind gusts. Finally, independent laboratory experiments were conducted to identify promising dielectric materials for the plasma actuator, and to examine environmental effects (water and dust) on the plasma actuator operation. The proposed PACE system will be capable of capturing additional energy, and reducing <span class="hlt">aerodynamic</span> loading and <span class="hlt">noise</span> on wind turbines. Supplementary benefits from the PACE system include reduced blade structure weight and complexity that translates into reduced initial capital costs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=Aerodynamics&pg=4&id=EJ604499','ERIC'); return false;" href="http://eric.ed.gov/?q=Aerodynamics&pg=4&id=EJ604499"><span>On Wings: <span class="hlt">Aerodynamics</span> of Eagles.</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>Millson, David</p> <p>2000-01-01</p> <p>The <span class="hlt">Aerodynamics</span> Wing Curriculum is a high school program that combines basic physics, <span class="hlt">aerodynamics</span>, pre-engineering, 3D visualization, computer-assisted drafting, computer-assisted manufacturing, production, reengineering, and success in a 15-hour, 3-week classroom module. (JOW)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=Aerodynamics&id=EJ892012','ERIC'); return false;" href="http://eric.ed.gov/?q=Aerodynamics&id=EJ892012"><span><span class="hlt">Aerodynamics</span> of a Party Balloon</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>Cross, Rod</p> <p>2007-01-01</p> <p>It is well-known that a party balloon can be made to fly erratically across a room, but it can also be used for quantitative measurements of other aspects of <span class="hlt">aerodynamics</span>. Since a balloon is light and has a large surface area, even relatively weak <span class="hlt">aerodynamic</span> forces can be readily demonstrated or measured in the classroom. Accurate measurements…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4813900','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4813900"><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="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Boukhayma, Assim; Dupret, Antoine; Rostaing, Jean-Pierre; Enz, Christian</p> <p>2016-01-01</p> <p>This paper presents the first low <span class="hlt">noise</span> complementary metal oxide semiconductor (CMOS) 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 0.13μm 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 0.2μV 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. PMID:26950131</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985AnRFM..17..151M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985AnRFM..17..151M"><span><span class="hlt">Aerodynamics</span> of sports balls</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mehta, R. D.</p> <p></p> <p>Research data on the <span class="hlt">aerodynamic</span> behavior of baseballs and cricket and golf balls are summarized. Cricket balls and baseballs are roughly the same size and mass but have different stitch patterns. Both are thrown to follow paths that avoid a batter's swing, paths that can curve if <span class="hlt">aerodynamic</span> forces on the balls' surfaces are asymmetric. Smoke tracer wind tunnel tests and pressure taps have revealed that the unbalanced side forces are induced by tripping the boundary layer on the seam side and producing turbulence. More particularly, the greater pressures are perpendicular to the seam plane and only appear when the balls travel at velocities high enough so that the roughness length matches the seam heigh. The side forces, once tripped, will increase with spin velocity up to a cut-off point. The enhanced lift coefficient is produced by the Magnus effect. The more complex stitching on a baseball permits greater variations in the flight path curve and, in the case of a knuckleball, the unsteady flow effects. For golf balls, the dimples trip the boundary layer and the high spin rate produces a lift coefficient maximum of 0.5, compared to a baseball's maximum of 0.3. Thus, a golf ball travels far enough for gravitational forces to become important.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930091232','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930091232"><span>The <span class="hlt">Aerodynamic</span> Plane Table</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zahm, A F</p> <p>1924-01-01</p> <p>This report gives the description and the use of a specially designed <span class="hlt">aerodynamic</span> plane table. For the accurate and expeditious geometrical measurement of models in an <span class="hlt">aerodynamic</span> laboratory, and for miscellaneous truing operations, there is frequent need for a specially equipped plan table. For example, one may have to measure truly to 0.001 inch the offsets of an airfoil at many parts of its surface. Or the offsets of a strut, airship hull, or other carefully formed figure may require exact calipering. Again, a complete airplane model may have to be adjusted for correct incidence at all parts of its surfaces or verified in those parts for conformance to specifications. Such work, if but occasional, may be done on a planing or milling machine; but if frequent, justifies the provision of a special table. For this reason it was found desirable in 1918 to make the table described in this report and to equip it with such gauges and measures as the work should require.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850008602','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850008602"><span><span class="hlt">Aerodynamic</span> challenges of ALT</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hooks, I.; Homan, D.; Romere, P. O.</p> <p>1985-01-01</p> <p>The approach and landing test (ALT) of the Space Shuttle Orbiter presented a number of unique challenges in the area of <span class="hlt">aerodynamics</span>. The purpose of the ALT program was both to confirm the use of the Boeing 747 as a transport vehicle for ferrying the Orbiter across the country and to demonstrate the flight characteristics of the Orbiter in its approach and landing phase. Concerns for structural fatigue and performance dictated a tailcone be attached to the Orbiter for ferry and for the initial landing tests. The Orbiter with a tailcone attached presented additional challenges to the normal aft sting concept of wind tunnel testing. The landing tests required that the Orbiter be separated from the 747 at approximately 20,000 feet using <span class="hlt">aerodynamic</span> forces to fly the vehicles apart. The concept required a complex test program to determine the relative effects of the two vehicles on each other. Also of concern, and tested, was the vortex wake created by the 747 and the means for the Orbiter to avoid it following separation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850049027&hterms=Sport&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DSport','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850049027&hterms=Sport&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DSport"><span><span class="hlt">Aerodynamics</span> of sports balls</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mehta, R. D.</p> <p>1985-01-01</p> <p>Research data on the <span class="hlt">aerodynamic</span> behavior of baseballs and cricket and golf balls are summarized. Cricket balls and baseballs are roughly the same size and mass but have different stitch patterns. Both are thrown to follow paths that avoid a batter's swing, paths that can curve if <span class="hlt">aerodynamic</span> forces on the balls' surfaces are asymmetric. Smoke tracer wind tunnel tests and pressure taps have revealed that the unbalanced side forces are induced by tripping the boundary layer on the seam side and producing turbulence. More particularly, the greater pressures are perpendicular to the seam plane and only appear when the balls travel at velocities high enough so that the roughness length matches the seam heigh. The side forces, once tripped, will increase with spin velocity up to a cut-off point. The enhanced lift coefficient is produced by the Magnus effect. The more complex stitching on a baseball permits greater variations in the flight path curve and, in the case of a knuckleball, the unsteady flow effects. For golf balls, the dimples trip the boundary layer and the high spin rate produces a lift coefficient maximum of 0.5, compared to a baseball's maximum of 0.3. Thus, a golf ball travels far enough for gravitational forces to become important.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19890009892','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19890009892"><span>Unsteady <span class="hlt">aerodynamics</span> of blade rows</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Verdon, Joseph M.</p> <p>1989-01-01</p> <p>The requirements placed on an unsteady <span class="hlt">aerodynamic</span> theory intended for turbomachinery aeroelastic or aeroacoustic applications are discussed along with a brief description of the various theoretical models that are available to address these requirements. The major emphasis is placed on the description of a linearized inviscid theory which fully accounts for the affects of a nonuniform mean or steady flow on unsteady <span class="hlt">aerodynamic</span> response. Although this linearization was developed primarily for blade flutter prediction, more general equations are presented which account for unsteady excitations due to incident external <span class="hlt">aerodynamic</span> disturbances as well as those due to prescribed blade motions. The motivation for this linearized unsteady <span class="hlt">aerodynamic</span> theory is focused on, its physical and mathematical formulation is outlined and examples are presented to illustrate the status of numerical solution procedures and several effects of mean flow nonuniformity on unsteady <span class="hlt">aerodynamic</span> response.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JSV...357...95P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JSV...357...95P"><span>Suppression of tonal <span class="hlt">noise</span> in a centrifugal fan using guide vanes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Paramasivam, Kishokanna; Rajoo, Srithar; Romagnoli, Alessandro</p> <p>2015-11-01</p> <p>This paper presents the work aiming for tonal <span class="hlt">noise</span> reduction in a centrifugal fan. In previous studies, it is well documented that tonal <span class="hlt">noise</span> is the dominant <span class="hlt">noise</span> <span class="hlt">source</span> generated in centrifugal fans. Tonal <span class="hlt">noise</span> is generated due to the <span class="hlt">aerodynamic</span> interaction between the rotating impeller and stationary diffuser vanes. The generation of tonal <span class="hlt">noise</span> is related to the pressure fluctuation at the leading edge of the stationary vane. The tonal <span class="hlt">noise</span> is periodic in time which occurs at the blade passing frequency (BPF) and its harmonics. Much of previous studies, have shown that the stationary vane causes the tonal <span class="hlt">noise</span> and generation of non-rotational turbulent <span class="hlt">noise</span>. However, omitting stationary vanes will lead to the increase of non-rotational turbulent <span class="hlt">noise</span> resulted from the high velocity of the flow leaving the impeller. Hence in order to reduce the tonal <span class="hlt">noise</span> and the non-rotational <span class="hlt">noise</span>, guide vanes were designed as part of this study to replace the diffuser vanes, which were originally used in the chosen centrifugal fan. The leading edge of the guide vane is tapered. This modification reduces the strength of pressure fluctuation resulting from the interaction between the impeller outflow and stationary vane. The sound pressure level at blade passing frequency (BPF) is reduced by 6.8 dB, the 2nd BPF is reduced by 4.1 dB and the 3rd BPF reduced by about 17.5 dB. The overall reduction was 0.9 dB. The centrifugal fan with tapered guide vanes radiates lower tonal <span class="hlt">noise</span> compared to the existing diffuser vanes. These reductions are achieved without compromising the performance of the centrifugal fan. The behavior of the fluid flow was studied using computational fluid dynamics (CFD) tools and the acoustics characteristics were determined through experiments in an anechoic chamber.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SPIE.9347E..15Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SPIE.9347E..15Y"><span>Interferometric coherence measurement and radio frequency <span class="hlt">noise</span> characterization of the 1.3 μm femtosecond intense Stokes continuum from a TZDW <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>Yao, Yuhong; Knox, Wayne H.</p> <p>2015-02-01</p> <p>Photonic crystal fiber (PCF) with two closely spaced zero dispersion wavelengths (TZDW) offers a unique route to efficient energy transfer to two spectrally localized continua beyond either side of the ZDWs, which we have employed in previous work for mid-IR difference frequency generation and speckle-free red-green-blue generation. In this manuscript, we report the interferometric coherence characterization and radio frequency (RF) <span class="hlt">noise</span> measurements of the Stokes side TZDW component. With a custom-built 1.3 W, 1035 nm, 40 MHz, 240 fs Yb:fiber chirped pulse amplifier as the pump <span class="hlt">source</span>, we use 12 cm of commercially available TZDW PCF to excite the dual narrow-band continua from which the Stokes pulse is filtered out with a 1180 nm long wave pass filter. We achieve 0.8 to 3 nJ of narrow-band pulses within the spectral range of 1200 - 1315 nm at an average power conversion efficiency of 33%. Employing an un-balanced Michelson interferometer, measured mutual spectral coherence of the Stokes pulse is in excess of 0.76 with pump Soliton order as high as N ~70. Its measured RF <span class="hlt">noise</span> spectrum at the first harmonic of the laser repetition rate shows less than 8 dBc/Hz increase in relative intensity <span class="hlt">noise</span> (RIN) compared to that of the power amplifier, which is consistent with reported studies employing sub-100 fs pulses from relatively low <span class="hlt">noise</span> oscillators. In contrast to the broadband continuum from a single ZDW PCF wherein severe de-coherence is found with pumping at high soliton order and longer pump pulse width, the reported TZDW fiber <span class="hlt">source</span> shows preservation of intensity stability and phase coherence against variation in pump pulse parameters, which not only attests to the stability of our reported method for mid-IR generation, but also shows promising potential towards an all-fiber, efficient and low <span class="hlt">noise</span> ultrafast <span class="hlt">source</span> that can be helpful for applications such as biomedical deep-tissue imaging.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140002891','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140002891"><span>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>2013-01-01</p> <p>Generation of sound due to scrubbing of a jet flow past a nearby solid surface is investigated within the framework of 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 should be solved numerically starting with the boundary conditions on the surface and subject to specified mean velocity and temperature profiles between the surface and the observer. The equivalent <span class="hlt">sources</span> of <span class="hlt">aerodynamic</span> sound are associated with non-linear momentum flux and enthalpy flux terms that appear in the linearized Navier-Stokes equations. These multi-pole <span class="hlt">sources</span> should be modeled and evaluated with input from a Reynolds-Averaged Navier-Stokes (RANS) solver with an appropriate turbulence model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22391175','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22391175"><span><span class="hlt">Aerodynamic</span> and aeroacoustic for wind turbine</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mohamed, Maizi; Rabah, Dizene</p> <p>2015-03-10</p> <p>This paper describes a hybrid approach forpredicting <span class="hlt">noise</span> radiated from the rotating Wind Turbine (HAWT) blades, where the <span class="hlt">sources</span> are extracted from an unsteady Reynolds-Averaged-Navier Stocks (URANS) simulation, ANSYS CFX 11.0, was used to calculate The near-field flow parameters around the blade surface that are necessary for FW-H codes. Comparisons with NREL Phase II experimental results are presented with respect to the pressure distributions for validating a capacity of the solver to calculate the near-field flow on and around the wind turbine blades, The results show that numerical data have a good agreement with experimental. The acoustic pressure, presented as a sum of thickness and loading <span class="hlt">noise</span> components, is analyzed by means of a discrete fast Fourier transformation for the presentation of the time acoustic time histories in the frequency domain. The results convincingly show that dipole <span class="hlt">source</span> <span class="hlt">noise</span> is the dominant <span class="hlt">noise</span> <span class="hlt">source</span> for this wind turbine.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19840021597&hterms=train+noise&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dtrain%2Bnoise','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19840021597&hterms=train+noise&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dtrain%2Bnoise"><span><span class="hlt">Noise</span> reduction experience at Hughes Helicopter, Inc.</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Janakiram, D. S.</p> <p>1982-01-01</p> <p><span class="hlt">Noise</span> reduction is mostly limited to light helicopters whose <span class="hlt">noise</span> signature is dominated by their tail rotors. It is primarily hardware oriented. Well known <span class="hlt">noise</span> reduction techniques such as reduction of rotor speeds with an accompanying increase in solidity to maintain performance, engine <span class="hlt">noise</span> 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 <span class="hlt">noise</span> is also used. Engine <span class="hlt">noise</span> (exhaust <span class="hlt">noise</span>), power train <span class="hlt">noise</span> and airframe <span class="hlt">noise</span> becomes important at low rotor tip speeds and means must be found to reduce these <span class="hlt">noise</span> <span class="hlt">sources</span> if further <span class="hlt">noise</span> reductions are desired. The use of a special test rig aids in isolating the various <span class="hlt">noise</span> <span class="hlt">sources</span> and arriving at the penalties (performance or payload) involved in quieting them. Significant <span class="hlt">noise</span> reduction are achieved for the light helicopter with minimum performance or weight penalties because of the dominance of a single <span class="hlt">noise</span> <span class="hlt">source</span> (the tail rotor).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA094293','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA094293"><span>High Velocity Jet <span class="hlt">Noise</span> <span class="hlt">Source</span> Location and Reduction. Task 3 - Experimental Investigation of Suppression Principles. Volume I. Suppressor Concepts Optimization</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>1978-12-01</p> <p>multinational corporation in the 1960’s placed extreme emphasis on the need for effective and efficient <span class="hlt">noise</span> suppression devices. Phase I of work...through model and engine testing applicable to an afterburning turbojet engine. Suppressor designs were based primarily on empirical methods. Phase II...using "ray" acoustics. This method is in contrast to the purely empirical method which consists of the curve -fitting of normalized data. In order to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150006712','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150006712"><span>A Mode Propagation Database Suitable for Code Validation Utilizing the NASA Glenn Advanced <span class="hlt">Noise</span> Control Fan and Artificial <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>Sutliff, Daniel L.</p> <p>2014-01-01</p> <p>The NASA Glenn Research Center's Advanced <span class="hlt">Noise</span> Control Fan (ANCF) was developed in the early 1990s to provide a convenient test bed to measure and understand fan-generated acoustics, duct propagation, and radiation to the farfield. A series of tests were performed primarily for the use of code validation and tool validation. Rotating Rake mode measurements were acquired for parametric sets of: (1) mode blockage, (2) liner insertion loss, (3) short ducts, and (4) mode reflection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140005371','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140005371"><span>A Mode Propagation Database Suitable for Code Validation Utilizing the NASA Glenn Advanced <span class="hlt">Noise</span> Control Fan and Artificial <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>Sutliff, Daniel L.</p> <p>2014-01-01</p> <p>The NASA Glenn Research Center's Advanced <span class="hlt">Noise</span> Control Fan (ANCF) was developed in the early 1990s to provide a convenient test bed to measure and understand fan-generated acoustics, duct propagation, and radiation to the farfield. A series of tests were performed primarily for the use of code validation and tool validation. Rotating Rake mode measurements were acquired for parametric sets of: (i) mode blockage, (ii) liner insertion loss, (iii) short ducts, and (iv) mode reflection.</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://adsabs.harvard.edu/abs/2016JPhCS.744a2189L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JPhCS.744a2189L"><span>Active <span class="hlt">Noise</span> Control for Dishwasher <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>Lee, Nokhaeng; Park, Youngjin</p> <p>2016-09-01</p> <p>The dishwasher is a useful home appliance and continually used for automatically washing dishes. It's commonly placed in the kitchen with built-in style for practicality and better use of space. In this environment, people are easily exposed to dishwasher <span class="hlt">noise</span>, so it is an important issue for the consumers, especially for the people living in open and narrow space. Recently, the sound power levels of the <span class="hlt">noise</span> are about 40 - 50 dBA. It could be achieved by removal of <span class="hlt">noise</span> <span class="hlt">sources</span> and passive means of insulating acoustical path. For more reduction, such a quiet mode with the lower speed of cycle has been introduced, but this deteriorates the washing capacity. Under this background, we propose active <span class="hlt">noise</span> control for dishwasher <span class="hlt">noise</span>. It is observed that the <span class="hlt">noise</span> is propagating mainly from the lower part of the front side. Control speakers are placed in the part for the collocation. Observation part of estimating sound field distribution and control part of generating the anti-<span class="hlt">noise</span> are designed for active <span class="hlt">noise</span> control. Simulation result shows proposed active <span class="hlt">noise</span> control scheme could have a potential application for dishwasher <span class="hlt">noise</span> reduction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20384146','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20384146"><span>[Study of the effect of light <span class="hlt">source</span> stability on the signal to <span class="hlt">noise</span> ratio in degenerate four wave mixing experiment].</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, Wei-Bo; Chen, De-Ying; Fan, Rong-Wei; Xia, Yuan-Qin</p> <p>2010-02-01</p> <p>The effects of the stability of dye laser on the signal to <span class="hlt">noise</span> ratio in degenerate four-wave mixing (DFWM) were first investigated in iodine vapor using forward geometries. Frequency-doubled outputs from a multi-mode Nd : YAG laser pumped dye laser with laser dye PM580 dissolved in ethanol was used. With the help of forward compensated beam-split technique and imaging detecting system, the saturation intensity of DFWM spectrum in the iodine vapor at 5 554.013 nm was first measured to be 290 microJ under the condition of atmospheric pressure and room temperature. The features of the dye laser such as wavelength ranges, beam quality and energy conversion efficiency decreased gradually with increasing pumping service use, pulse number and intensity. Additionally, with the comparison of the stable and unstable dye laser output, it was found that the instability of dye laser output had greatly influenced the DFWM signal and decreased the signal to background <span class="hlt">noise</span> ratio. Shot to shot jitter and the broadening in the output frequency leads to an effective broadening of the recorded spectrum and loss of the DFWM signal to <span class="hlt">noise</span> ratio under the same pumping intensity at different time. The study is of importance to the detection of trace atom, molecule and radical in combustion diagnosis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSV...383..464F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSV...383..464F"><span>Beamforming of aeroacoustic <span class="hlt">sources</span> in the time domain: An investigation of the intermittency of the <span class="hlt">noise</span> radiated by a forward-facing step</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fischer, J.; Valeau, V.; Brizzi, L.-E.</p> <p>2016-11-01</p> <p>The present study investigates the intermittency of the broadband aeroacoustic <span class="hlt">noise</span> produced by a forward-facing step in a flow. The <span class="hlt">noise</span> <span class="hlt">source</span> is viewed as a random succession of the so-called intermittent events of short duration distributed spatially in a <span class="hlt">source</span> region in the flow. An array processing method based on time-domain beamforming has been developed in order to track systematically the intermittent events, both in the time and space domains. Based on a simulated model of the far-field pressure field, the method is validated in terms of event detection and of performance for recovering the pressure spectrum. The method is then applied to experimental array data taken in an anechoic wind-tunnel at low Mach numbers (not exceeding 0.15) for a forward-facing step of height 30 mm. The results show that some very short intermittent events (with a mean duration of the order of 0.15 ms) can be identified from the array data. The spatial distribution of the intermittent events is found to be in agreement with the frequency domain beamform maps. The probability density functions of the events, in terms of widths and apparition times, are shown to be governed by Gamma laws and indicate random phenomena; it is observed that the statistical distributions vary with the streamwise position downstream and upstream of the step, the trends being in agreement with the <span class="hlt">source</span> behavior as evidenced by using the frequency-domain beamforming methods. The proposed method is then shown to identify, in terms of emission time, location and temporal width, a succession of short acoustic events that participate to the broadband aeroacoustic <span class="hlt">noise</span> produced by the step; those random events are likely to be linked to the dynamics of the flow interacting with the step.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003JSV...267..675L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003JSV...267..675L"><span>Train <span class="hlt">noise</span> reduction scenarios for compliance with future <span class="hlt">noise</span> legislation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Leth, S.</p> <p>2003-10-01</p> <p>The Technical Specification for Interoperability (TSI) for high-speed trains on the European market includes limits on <span class="hlt">noise</span> emission. These and other future restrictions on exterior <span class="hlt">noise</span> of high-speed and intercity trains will require that train manufacturers implement <span class="hlt">noise</span> control measures early in the design phase. A fundamental problem faced by manufacturers during the design process is determining how much <span class="hlt">noise</span> reduction is required for each of the various <span class="hlt">noise</span> <span class="hlt">sources</span> on the train in order to achieve an optimal balance. To illustrate this process, estimates are presented of the contributions from different <span class="hlt">sources</span> on existing Bombardier trains, based on measured data, numerical calculations and empirical formulae. In addition, methods of achieving the required <span class="hlt">noise</span> reductions for different <span class="hlt">sources</span> are briefly discussed along with targets for future exterior <span class="hlt">noise</span> emission. Measurement results presented demonstrate the importance of track quality in <span class="hlt">noise</span> emission. <span class="hlt">Noise</span> restrictions, including future legislation, must give proper recognition to this important parameter.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992cacn.agarV....B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992cacn.agarV....B"><span>Reduction of propeller <span class="hlt">noise</span> by active <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>Bschorr, O.; Kubanke, D.</p> <p>1992-04-01</p> <p>Active <span class="hlt">noise</span> control, a method of cancelling <span class="hlt">noise</span> by means of interference with a secondary anti-<span class="hlt">noise</span> <span class="hlt">source</span>, is now in full development. The first commercial application of this technique is in the case of active electronically controlled head sets. The next step will be the active <span class="hlt">noise</span> cancellation in air ducts and in passenger cabins. The aim of this paper is to assess the possibilities of the anti-<span class="hlt">noise</span> technique for reducing propeller <span class="hlt">noise</span>. First, by a mathematical simulation the theoretical <span class="hlt">noise</span> reduction on the ground was calculated and found to be promising for further investigations. In the case of the periodic engine and propeller <span class="hlt">noise</span>, for example, with only a single anti-<span class="hlt">noise</span> <span class="hlt">source</span>, the <span class="hlt">noise</span> foot prints of the lower propeller harmonics can be reduced by up to 10 dB. In laboratory tests the theoretical values will be confirmed experimentally. For cancellation of the periodic <span class="hlt">noise</span> one can use synchronous anti-<span class="hlt">noise</span> generators. Compared with the engine and propeller <span class="hlt">noise</span> the reduction of jet <span class="hlt">noise</span> by the anti-<span class="hlt">noise</span> technique is much more difficult. Therefore a sensor and controlling unit are necessary because of the stochastic nature of jet <span class="hlt">noise</span>. Since aircraft <span class="hlt">noise</span> is a severe problem, all methods are to be considered.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015APS..DFDH27004B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015APS..DFDH27004B"><span><span class="hlt">Aerodynamics</span> of a freely flying owl from PIV measurements in the wake</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ben-Gida, Hadar; Gurka, Roi; Weihs, Daniel</p> <p>2015-11-01</p> <p>The mechanisms of the silent flight of owls have been the subject of scientific interest for many decades and a <span class="hlt">source</span> of inspiration in the context of reducing flight <span class="hlt">noise</span>. Over millions of years of evolution, owls have produced many specialized configurations to reduce the <span class="hlt">aerodynamic</span> <span class="hlt">noise</span>, which is found to be essential for successful hunting of potential prey. Here, we study how the three-dimensional flow field formed over the wing affect the vortical structures develop in the wake of a freely flying owl. We study the unique flight patterns of the Boobook owl; a mid-sized owl, which has the feature of stealth flight during both gliding and flapping flight. The owl was flown in a hypobaric avian wind tunnel at its comfort speed for various flight modes. The wake velocity field was sampled using long duration high speed PIV whilst the wing's kinematics were imaged using high speed video simultaneously with the PIV. The time series velocity maps acquired during few consecutive wingbeat cycles enabled to describe the various flow features as formed at the owl's wake by reconstructing the wake patterns and associate them with the various phases of the wingbeat cycle. The stealthy flight mode, which is a result of <span class="hlt">noise</span> reduction mechanisms, formed over the wings (presumably by the leading-edge serrations) results in a unique signature in the wake flow field, which is characterized using the present data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050111478','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050111478"><span>Low <span class="hlt">Noise</span> Exhaust Nozzle Technology Development</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Majjigi, R. K.; Balan, C.; Mengle, V.; Brausch, J. F.; Shin, H.; Askew, J. W.</p> <p>2005-01-01</p> <p>NASA and the U.S. aerospace industry have been assessing the economic viability and environmental acceptability of a second-generation supersonic civil transport, or High Speed Civil Transport (HSCT). Development of a propulsion system that satisfies strict airport <span class="hlt">noise</span> regulations and provides high levels of cruise and transonic performance with adequate takeoff performance, at an acceptable weight, is critical to the success of any HSCT program. The principal objectives were to: 1. Develop a preliminary design of an innovative 2-D exhaust nozzle with the goal of meeting FAR36 Stage III <span class="hlt">noise</span> levels and providing high levels of cruise performance with a high specific thrust for Mach 2.4 HSCT with a range of 5000 nmi and a payload of 51,900 lbm, 2. Employ advanced acoustic and <span class="hlt">aerodynamic</span> codes during preliminary design, 3. Develop a comprehensive acoustic and <span class="hlt">aerodynamic</span> database through scale-model testing of low-<span class="hlt">noise</span>, high-performance, 2-D nozzle configurations, based on the preliminary design, and 4. Verify acoustic and <span class="hlt">aerodynamic</span> predictions by means of scale-model testing. The results were: 1. The preliminary design of a 2-D, convergent/divergent suppressor ejector nozzle for a variable-cycle engine powered, Mach 2.4 HSCT was evolved, 2. <span class="hlt">Noise</span> goals were predicted to be achievable for three takeoff scenarios, and 3. Impact of <span class="hlt">noise</span> suppression, nozzle <span class="hlt">aerodynamic</span> performance, and nozzle weight on HSCT takeoff gross weight were assessed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20130011529','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130011529"><span><span class="hlt">Aerodynamic</span> Reconstruction Applied to Parachute Test Vehicle Flight Data Analysis</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cassady, Leonard D.; Ray, Eric S.; Truong, Tuan H.</p> <p>2013-01-01</p> <p>The <span class="hlt">aerodynamics</span>, both static and dynamic, of a test vehicle are critical to determining the performance of the parachute cluster in a drop test and for conducting a successful test. The Capsule Parachute Assembly System (CPAS) project is conducting tests of NASA's Orion Multi-Purpose Crew Vehicle (MPCV) parachutes at the Army Yuma Proving Ground utilizing the Parachute Test Vehicle (PTV). The PTV shape is based on the MPCV, but the height has been reduced in order to fit within the C-17 aircraft for extraction. Therefore, the <span class="hlt">aerodynamics</span> of the PTV are similar, but not the same as, the MPCV. A small series of wind tunnel tests and computational fluid dynamics cases were run to modify the MPCV <span class="hlt">aerodynamic</span> database for the PTV, but <span class="hlt">aerodynamic</span> reconstruction of the flights has proven an effective <span class="hlt">source</span> for further improvements to the database. The acceleration and rotational rates measured during free flight, before parachute inflation but during deployment, were used to con rm vehicle static <span class="hlt">aerodynamics</span>. A multibody simulation is utilized to reconstruct the parachute portions of the flight. <span class="hlt">Aerodynamic</span> or parachute parameters are adjusted in the simulation until the prediction reasonably matches the flight trajectory. Knowledge of the static <span class="hlt">aerodynamics</span> is critical in the CPAS project because the parachute riser load measurements are scaled based on forebody drag. PTV dynamic damping is critical because the vehicle has no reaction control system to maintain attitude - the vehicle dynamics must be understood and modeled correctly before flight. It will be shown here that <span class="hlt">aerodynamic</span> reconstruction has successfully contributed to the CPAS project.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19830003822','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19830003822"><span>QCSEE under-the-wing engine-wing-flap <span class="hlt">aerodynamic</span> profile characteristics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bloomer, H. E.; Samanich, N. E.</p> <p>1982-01-01</p> <p>As part of a broad-based NASA program to provide a technology base for future propulsion requirements for powered-lift aircraft, the Quiet, Clean, Short-Haul, Experimental Engine (QCSEE) program was begun by the Lewis Research Center in 1974. The initial buildup of the under-the-wing (UTW) engine was tested by the contractor at his test site. The UTW engine was delivered to Lewis in 1978 for further testing with wing and flap segments simulating an installation on a short-haul transport aircraft. The engine was also tested alone as an aid in identifying the various <span class="hlt">noise</span> <span class="hlt">sources</span> and their levels. As part of these tests the <span class="hlt">aerodynamic</span> profiles at the exhaust nozzle and on the surfaces and in the wake of the wing-flap system were measured. This report documents, in plots and tabular form, the significant results from those tests. The results are presented as tabulations of <span class="hlt">aerodynamic</span> data for all of the test points and as profiles of pressure, temperature, velocity, and normalized velocity and pressure for selected conditions. One of the main conclusions was that the measured flap surface temperatures were surprisingly low for both approach and takeoff flap settings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6698744','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6698744"><span>Environmental issues: <span class="hlt">noise</span>, rail <span class="hlt">noise</span>, and high-speed rail</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hall, F.L.; Welland, J.D.; Bragdon, C.R.; Houtman, J.W.; Immers, B.H.</p> <p>1987-01-01</p> <p>The six papers in the report deal with the following areas: the effect of <span class="hlt">noise</span> barriers on the market value of adjacent residential properties; control of airport- and aircraft-related <span class="hlt">noise</span> in the United States; a traffic-assignment model to reduce <span class="hlt">noise</span> annoyance in urban networks; a survey of railroad occupational <span class="hlt">noise</span> <span class="hlt">sources</span>; a prediction procedure for rail transportation ground-borne <span class="hlt">noise</span> and vibration; and high-speed rail in California: the dream, the process, and the reality.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19790042863&hterms=noise+linear&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DTitle%26N%3D0%26No%3D30%26Ntt%3Dnoise%2Bin%2Blinear','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19790042863&hterms=noise+linear&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DTitle%26N%3D0%26No%3D30%26Ntt%3Dnoise%2Bin%2Blinear"><span>A comparison of linear acoustic theory with experimental <span class="hlt">noise</span> data for a small-scale hovering rotor</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Farassat, F.; Morris, C. E. K., Jr.; Nystrom, P. A.</p> <p>1979-01-01</p> <p>Linear acoustic calculations based on full <span class="hlt">aerodynamic</span> data as input are presented and compared with measured cases reported by Boxwell et al. (1978). The full <span class="hlt">aerodynamic</span> data are obtained using three programs giving radial loading, chordwise loading, and chordwise position of transition. It is shown that in the theoretical results the most significant <span class="hlt">noise</span> <span class="hlt">source</span> mechanism is due to blade thickness. Thus the conclusions of Boxwell et al. as to the importance of nonlinearities around the blades are upheld. These conclusions concern the width, shape and the level of the acoustic pressure calculated from linear acoustic theory. Some of the approximations involved in the application of acoustic analogy using quadrupole <span class="hlt">sources</span> are discussed. It is necessary that the near- and far-field problems of rotating blades be treated together as shown for the case of an oscillating sphere.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730022198','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730022198"><span>A Study of Trailing Edge Blowing as a Means of Reducing <span class="hlt">Noise</span> Generated by the Interaction of Flow with a Surface</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Scharton, T. D.; Pinkel, B.; Wilby, J. F.</p> <p>1973-01-01</p> <p>A system for reducing the <span class="hlt">noise</span> generated when a jet impinges against a flap is described. The eddies formed by the alternate zones of positive and negative pressure on the flap surface are identified as the sound <span class="hlt">source</span>. In the proposed concept, a stream of low velocity secondary air is ejected from a slot near the trailing edge of the flap as a buffer between the flap and the primary air jet to reduce the intensity of the fluctuating surface pressure field near the flap edge and thus reduce the intensity of the <span class="hlt">aerodynamic</span> <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920021703&hterms=Ar&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3DAr','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920021703&hterms=Ar&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3DAr"><span>Vortex flow <span class="hlt">aerodynamics</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smith, J. H. B.; Campbell, J. F.; Young, A. D. (Editor)</p> <p>1992-01-01</p> <p>The principal emphasis of the meeting was to be on the understanding and prediction of separation-induced vortex flows and their effects on vehicle performance, stability, control, and structural design loads. This report shows that a substantial amount of the papers covering this area were received from a wide range of countries, together with an attendance that was even more diverse. In itself, this testifies to the current interest in the subject and to the appropriateness of the Panel's choice of topic and approach. An attempt is made to summarize each paper delivered, and to relate the contributions made in the papers and in the discussions to some of the important aspects of vortex flow <span class="hlt">aerodynamics</span>. This reveals significant progress and important clarifications, but also brings out remaining weaknesses in predictive capability and gaps in understanding. Where possible, conclusions are drawn and areas of continuing concern are identified.</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>Airframe <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 airframe <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 <span class="hlt">aerodynamic</span> 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 <span class="hlt">aerodynamic</span> 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/2060/20050192626','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050192626"><span><span class="hlt">Noise</span> Reduction Through Circulation Control</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Munro, Scott E.; Ahuja, K. K.; Englar, Robert J.</p> <p>2005-01-01</p> <p>Circulation control technology uses tangential blowing around a rounded trailing edge or a leading edge to change the force and moment characteristics of an <span class="hlt">aerodynamic</span> body. This technology has been applied to circular cylinders, wings, helicopter rotors, and even to automobiles for improved <span class="hlt">aerodynamic</span> performance. Only limited research has been conducted on the acoustic of this technology. Since wing flaps contribute to the environmental <span class="hlt">noise</span> of an aircraft, an alternate blown high lift system without complex mechanical flaps could prove beneficial in reducing the <span class="hlt">noise</span> of an approaching aircraft. Thus, in this study, a direct comparison of the acoustic characteristics of high lift systems employing a circulation control wing configuration and a conventional wing flapped configuration has been made. These results indicate that acoustically, a circulation control wing high lift system could be considerably more acceptable than a wing with conventional mechanical flaps.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930045413&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=19930045413&hterms=hawking&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dhawking"><span>The influence of quadrupole <span class="hlt">sources</span> in the boundary layer and wake of a blade on helicopter rotor <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>Farassat, F.; Brentner, Kenneth S.</p> <p>1991-01-01</p> <p>It is presently noted that, for an observer in or near the plane containing a helicopter rotor disk, and in the far field, part of the volume quadrupole <span class="hlt">sources</span>, and the blade and wake surface quadrupole <span class="hlt">sources</span>, completely cancel out. This suggests a novel quadrupole <span class="hlt">source</span> description for the Ffowcs Williams-Hawkings equation which retain quadrupoles with axes parallel to the rotor disk; in this case, the volume and shock surface sourse terms are dominant.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1991adst.conf..240T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1991adst.conf..240T"><span>Payload vehicle <span class="hlt">aerodynamic</span> reentry analysis</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tong, Donald</p> <p></p> <p>An approach for analyzing the dynamic behavior of a cone-cylinder payload vehicle during reentry to insure proper deployment of the parachute system and recovery of the payload is presented. This analysis includes the study of an <span class="hlt">aerodynamic</span> device that is useful in extending vehicle axial rotation through the maximum dynamic pressure region. Attention is given to vehicle configuration and reentry trajectory, the derivation of pitch static <span class="hlt">aerodynamics</span>, the derivation of the pitch damping coefficient, pitching moment modeling, <span class="hlt">aerodynamic</span> roll device modeling, and payload vehicle reentry dynamics. It is shown that the vehicle dynamics at parachute deployment are well within the design limit of the recovery system, thus ensuring successful payload recovery.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1984JVGR...22...59K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1984JVGR...22...59K"><span>Seismicity at Old Faithful Geyser: an isolated <span class="hlt">source</span> of geothermal <span class="hlt">noise</span> and possible analogue of volcanic seismicity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kieffer, Susan Werner</p> <p>1984-09-01</p> <p>Old Faithful Geyser in Yellowstone National Park, U.S.A., is a relatively isolated <span class="hlt">source</span> of seismic <span class="hlt">noise</span> and exhibits seismic behavior similar to that observed at many volcanoes, including "bubblequakes" that resemble B-type "earthquakes", harmonic tremor before and during eruptions, and periods of seismic quiet prior to eruptions. Although Old Faithful differs from volcanoes in that the conduit is continuously open, that rock-fracturing is not a process responsible for seismicity, and that the erupting fluid is inviscid H 2O rather than viscous magma, there are also remarkable similarities in the problems of heat and mass recharge to the system, in the eruption dynamics, and in the seismicity. Water rises irregularly into the immediate reservoir of Old Faithful as recharge occurs, a fact that suggests that there are two enlarged storage regions: one between 18 and 22 m (the base of the immediate reservoir) and one between about 10 and 12 m depth. Transport of heat from hot water or steam entering at the base of the recharging water column into cooler overlying water occurs by migration of steam bubbles upward and their collapse in the cooler water, and by episodes of convective overturn. An eruption occurs when the temperature of the near-surface water exceeds the boiling point if the entire water column is sufficiently close to the boiling curve that the propagation of pressure-release waves (rarefactions) down the column can bring the liquid water onto the boiling curve. The process of conversion of the liquid water in the conduit at the onset of an eruption into a two-phase liquid-vapor mixture takes on the order of 30 s. The seismicity is directly related to the sequence of filling and heating during the recharge cycle, and to the fluid mechanics of the eruption. Short (0.2-0.3 s), monochromatic, high-frequency events (20-60 Hz) resembling unsustained harmonic tremor and, in some instances, B-type volcanic earthquakes, occur when exploding or imploding</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70013910','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70013910"><span>Seismicity at Old Faithful Geyser: an isolated <span class="hlt">source</span> of geothermal <span class="hlt">noise</span> and possible analogue of volcanic seismicity</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Kieffer, S.W.</p> <p>1984-01-01</p> <p>Old Faithful Geyser in Yellowstone National Park, U.S.A., is a relatively isolated <span class="hlt">source</span> of seismic <span class="hlt">noise</span> and exhibits seismic behavior similar to that observed at many volcanoes, including "bubblequakes" that resemble B-type "earthquakes", harmonic tremor before and during eruptions, and periods of seismic quiet prior to eruptions. Although Old Faithful differs from volcanoes in that the conduit is continuously open, that rock-fracturing is not a process responsible for seismicity, and that the erupting fluid is inviscid H2O rather than viscous magma, there are also remarkable similarities in the problems of heat and mass recharge to the system, in the eruption dynamics, and in the seismicity. Water rises irregularly into the immediate reservoir of Old Faithful as recharge occurs, a fact that suggests that there are two enlarged storage regions: one between 18 and 22 m (the base of the immediate reservoir) and one between about 10 and 12 m depth. Transport of heat from hot water or steam entering at the base of the recharging water column into cooler overlying water occurs by migration of steam bubbles upward and their collapse in the cooler water, and by episodes of convective overturn. An eruption occurs when the temperature of the near-surface water exceeds the boiling point if the entire water column is sufficiently close to the boiling curve that the propagation of pressure-release waves (rarefactions) down the column can bring the liquid water onto the boiling curve. The process of conversion of the liquid water in the conduit at the onset of an eruption into a two-phase liquid-vapor mixture takes on the order of 30 s. The seismicity is directly related to the sequence of filling and heating during the recharge cycle, and to the fluid mechanics of the eruption. Short (0.2-0.3 s), monochromatic, high-frequency events (20-60 Hz) resembling unsustained harmonic tremor and, in some instances, B-type volcanic earthquakes, occur when exploding or imploding</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19720000047','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19720000047"><span>High <span class="hlt">noise</span> immunity one shot</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schaffer, G. L.</p> <p>1972-01-01</p> <p>Multivibrator circuit, which includes constant current <span class="hlt">source</span>, isolates line <span class="hlt">noise</span> from timing circuitry and field effect transistor controls circuit's operational modes. Circuit has high immunity to supply line <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_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. 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