Quasimodes instability analysis of uncertain asymmetric rotor system based on 3D solid element model
NASA Astrophysics Data System (ADS)
Zuo, Yanfei; Wang, Jianjun; Ma, Weimeng
2017-03-01
Uncertainties are considered in the equation of motion of an asymmetric rotor system. Based on Hill's determinant method, quasimodes stability analysis with uncertain parameters is used to get stochastic boundaries of unstable regions. Firstly, A 3D finite element rotor model was built in rotating frame with four parameterized coefficients, which is assumed as random parameters representing the uncertainties existing in the rotor system. Then the influences of uncertain coefficients on the distribution of the unstable region boundaries are analyzed. The results show that uncertain parameters have various influences on the size, boundary and number of unstable regions. At last, the statistic results of the minimum and maximum spin speeds of unstable regions were got by Monte Carlo simulation. The used method is suitable for real engineering rotor system, because arbitrary configuration of rotors can be modeled by 3D finite element.
Reflection-asymmetric rotor model of odd Aapprox. 219--229 nuclei
Leander, G.A.; Chen, Y.S.
1988-06-01
The low-energy spectroscopy of odd-A nuclei in the mass region Aapprox.219--229 is modeled by coupling states of a deformed shell model including octupole deformation to a reflection-asymmetric rotor core. Theory and experiment are compared for the nuclei in which data are available: /sup 219,221,223,225/Rn, /sup 221,223,225,227/Fr, /sup 219,221,223,225,227/Ra, /sup 219,223,225,227,229/Ac /sup 221,223,225,227,229/Th, and /sup 229/Pa. Overall agreement requires an octupole deformation ..beta../sub 3/approx.0.1. The results throughout the region are synthesized to evaluate the model.
The stability of an asymmetric rotor in damped supports
NASA Technical Reports Server (NTRS)
Smalley, A. J.; Tessarzik, J. M.; Badgley, R. H.
1978-01-01
A general-purpose method of evaluating the stability of an asymmetric flexible rotor, mounted in symmetric damped bearings, is defined. This method evaluates the complex eigenvalues of the rotor system by solving the equations of motion in a rotating coordinate frame. The application of this method to a rotor mounted in tilting-pad bearings is demonstrated. The observed behavior of a number of different rotor configurations is compared with corresponding predictions of stability. For the configurations predicted to be unstable, a distinct and unnegotiable threshold of instability is encountered. The sharpness of this threshold is emphasized by careful balancing at speeds fractionally below the threshold. In a final configuration predicted to be marginally stable, lightly damped resonant behavior, negotiable by balancing, is encountered in the region of the first critical speed.
NASA Astrophysics Data System (ADS)
Han, Qinkai; Chu, Fulei
2012-12-01
It is well known that either the asymmetric disk or transverse crack brings parametric inertia (or stiffness) excitation to the rotor-bearing system. When both of them appear in a rotor system, the parametric instability behaviors have not gained sufficient attentions. Thus, the effect of transverse crack upon parametric instability of a rotor-bearing system with an asymmetric disk is studied. First, the finite element equations of motion are established for the asymmetric rotor system. Both the open and breathing transverse cracks are taken into account in the model. Then, the discrete state transition matrix (DSTM) method is introduced for numerically acquiring the instability regions. Based upon these, some computations for a practical asymmetric rotor system with open or breathing transverse crack are conducted, respectively. Variations of the primary and combination instability regions induced by the asymmetric disk with the crack depth are observed, and the effect of the orientation angle between the crack and asymmetric disk on various instability regions are discussed in detail. It is shown that for the asymmetric angle around 0, the existence of transverse (either open or breathing) crack has attenuation effect upon the instability regions. Under certain crack depth, the instability regions could be vanished by the transverse crack. When the asymmetric angle is around π/2, increasing the crack depth would enhance the instability regions.
Methods and apparatus for reduction of asymmetric rotor loads in wind turbines
Moroz, Emilian Mieczyslaw; Pierce, Kirk Gee
2006-10-10
A method for reducing load and providing yaw alignment in a wind turbine includes measuring displacements or moments resulting from asymmetric loads on the wind turbine. These measured displacements or moments are used to determine a pitch for each rotor blade to reduce or counter asymmetric rotor loading and a favorable yaw orientation to reduce pitch activity. Yaw alignment of the wind turbine is adjusted in accordance with the favorable yaw orientation and the pitch of each rotor blade is adjusted in accordance with the determined pitch to reduce or counter asymmetric rotor loading.
Orientation dynamics of asymmetric rotors using random phase wave functions
NASA Astrophysics Data System (ADS)
Kallush, Shimshon; Fleischer, Sharly
2015-06-01
Intense terahertz-frequency pulses induce coherent rotational dynamics and orientation of polar molecular ensembles. Exact numerical methods for rotational dynamics at room temperature are computationally not feasible for the vast majority of molecular rotors: the asymmetric top molecules at ambient temperatures. We exemplify the use of random phase wave functions (RPWFs) by calculating the terahertz-induced rotational dynamics of sulfur dioxide at ambient temperatures and high-field strengths and show that the RPWF method gains efficiency with the increase in temperature and in the terahertz-field strengths. The present method provides wide-ranging computational access to rotational dynamical responses of molecules at experimental conditions that are far beyond the reach of exact numerical methods.
Open Rotor Aeroacoustic Modeling
NASA Technical Reports Server (NTRS)
Envia, Edmane
2012-01-01
Owing to their inherent fuel efficiency, there is renewed interest in developing open rotor propulsion systems that are both efficient and quiet. The major contributor to the overall noise of an open rotor system is the propulsor noise, which is produced as a result of the interaction of the airstream with the counter-rotating blades. As such, robust aeroacoustic prediction methods are an essential ingredient in any approach to designing low-noise open rotor systems. To that end, an effort has been underway at NASA to assess current open rotor noise prediction tools and develop new capabilities. Under this effort, high-fidelity aerodynamic simulations of a benchmark open rotor blade set were carried out and used to make noise predictions via existing NASA open rotor noise prediction codes. The results have been compared with the aerodynamic and acoustic data that were acquired for this benchmark open rotor blade set. The emphasis of this paper is on providing a summary of recent results from a NASA Glenn effort to validate an in-house open noise prediction code called LINPROP which is based on a high-blade-count asymptotic approximation to the Ffowcs-Williams Hawkings Equation. The results suggest that while predicting the absolute levels may be difficult, the noise trends are reasonably well predicted by this approach.
Open Rotor Aeroacoustic Modelling
NASA Technical Reports Server (NTRS)
Envia, Edmane
2012-01-01
Owing to their inherent fuel efficiency, there is renewed interest in developing open rotor propulsion systems that are both efficient and quiet. The major contributor to the overall noise of an open rotor system is the propulsor noise, which is produced as a result of the interaction of the airstream with the counter-rotating blades. As such, robust aeroacoustic prediction methods are an essential ingredient in any approach to designing low-noise open rotor systems. To that end, an effort has been underway at NASA to assess current open rotor noise prediction tools and develop new capabilities. Under this effort, high-fidelity aerodynamic simulations of a benchmark open rotor blade set were carried out and used to make noise predictions via existing NASA open rotor noise prediction codes. The results have been compared with the aerodynamic and acoustic data that were acquired for this benchmark open rotor blade set. The emphasis of this paper is on providing a summary of recent results from a NASA Glenn effort to validate an in-house open noise prediction code called LINPROP which is based on a high-blade-count asymptotic approximation to the Ffowcs-Williams Hawkings Equation. The results suggest that while predicting the absolute levels may be difficult, the noise trends are reasonably well predicted by this approach.
Macroscopic balance model for wave rotors
NASA Technical Reports Server (NTRS)
Welch, Gerard E.
1996-01-01
A mathematical model for multi-port wave rotors is described. The wave processes that effect energy exchange within the rotor passage are modeled using one-dimensional gas dynamics. Macroscopic mass and energy balances relate volume-averaged thermodynamic properties in the rotor passage control volume to the mass, momentum, and energy fluxes at the ports. Loss models account for entropy production in boundary layers and in separating flows caused by blade-blockage, incidence, and gradual opening and closing of rotor passages. The mathematical model provides a basis for predicting design-point wave rotor performance, port timing, and machine size. Model predictions are evaluated through comparisons with CFD calculations and three-port wave rotor experimental data. A four-port wave rotor design example is provided to demonstrate model applicability. The modeling approach is amenable to wave rotor optimization studies and rapid assessment of the trade-offs associated with integrating wave rotors into gas turbine engine systems.
NASA Technical Reports Server (NTRS)
Martin, R. M.; Burley, C. L.; Elliott, J. W.
1989-01-01
Acoustic data from a model scale main rotor and tail rotor experiment in the NASA Langley 14 by 22 Foot Subsonic Tunnel are presented for the main rotor and trail rotor in isolation and for the two rotors operating together. Results for the isolated main rotor show the importance of the rotor flapping conditions on mid-frequency noise content. High levels of main rotor retreating side blade-vortex interaction noise are shown to radiate downstream of the model. The isolated tail rotor noise results show the dominance of harmonic noise in the thrusting direction. The occurrence of tail rotor broadband noise is seen by the broadening of the tail rotor harmonics and is attributed to fuselage wake turbulence. The combined main and tail rotor data are presented to show the dominance of each rotor's different noise sources at different directivity locations.
Theoretical models of helicopter rotor noise
NASA Technical Reports Server (NTRS)
Hawkings, D. L.
1978-01-01
For low speed rotors, it is shown that unsteady load models are only partially successful in predicting experimental levels. A theoretical model is presented which leads to the concept of unsteady thickness noise. This gives better agreement with test results. For high speed rotors, it is argued that present models are incomplete and that other mechanisms are at work. Some possibilities are briefly discussed.
Rotor systems research aircraft simulation mathematical model
NASA Technical Reports Server (NTRS)
Houck, J. A.; Moore, F. L.; Howlett, J. J.; Pollock, K. S.; Browne, M. M.
1977-01-01
An analytical model developed for evaluating and verifying advanced rotor concepts is discussed. The model was used during in both open loop and real time man-in-the-loop simulation during the rotor systems research aircraft design. Future applications include: pilot training, preflight of test programs, and the evaluation of promising concepts before their implementation on the flight vehicle.
Xu, Gaohong; Liu, Guohai; Du, Xinxin; Bian, Fangfang
2017-01-01
This paper proposes a novel permanent magnet (PM) motor for high torque performance, in which hybrid PM material and asymmetric rotor design are applied. The hybrid PM material is adopted to reduce the consumption of rare-earth PM because ferrite PM is assisted to enhance the torque production. Meanwhile, the rotor structure is designed to be asymmetric by shifting the surface-insert PM (SPM), which is used to improve the torque performance, including average torque and torque ripple. Moreover, the reasons for improvement of the torque performance are explained by evaluation and analysis of the performances of the proposed motor. Compared with SPM motor and V-type motor, the merit of high utilization ratio of rare-earth PM is also confirmed, showing that the proposed motor can offer higher torque density and lower torque ripple simultaneously with less consumption of rare-earth PM. PMID:28382228
NASA Astrophysics Data System (ADS)
Sinha, Sunil K.
2013-04-01
Loss of a blade from a running turbofan rotor introduces not only huge imbalance into the dynamical system rather it makes the entire rotor asymmetric as well. In a nonsymmetric rotor, the various terms of mass, gyroscopic and stiffness matrices also become time-dependent. In this paper, all the dynamical equations include the effect of the rotary inertia and gyroscopic moments as a result of both shaft bending as well as staggered blades flexing in-and-out of the plane of the disk. The governing equations also account for internal material damping in the shaft and the external damping in the support bearing system. In addition to the unbalance load at the disk location, the shaft may also be subjected to a torque and axial forces. Here, the fan blades are modeled as pre-twisted thin shallow shells. They have coupled flexural-torsional motion in the lateral out-of-plane direction as well as extensional degrees-of-freedom in the longitudinal spanwise direction of the blade airfoil. The effect of blade tip rub forces being transmitted to the shaft are analyzed in terms of the dynamic stability of the rotor, especially during windmilling.
NASA Technical Reports Server (NTRS)
Mineck, R. E.
1977-01-01
Tests were conducted in the Langley V/STOL tunnel to determine the effect of the main-rotor wake on the aerodynamic characteristics of the rotor systems research aircraft. A 1/6-scale model with a 4-blade articulated rotor was used to determine the effect of the rotor wake for the compound configuration. Data were obtained over a range of angles of attack, angles of sideslip, auxiliary engine thrusts, rotor collective pitch angles, and rotor tip-path plane angles for several main-rotor advance ratios. Separate results are presented for the forces and moments on the airframe, the wing, and the tail. An analysis of the test data indicates significant changes in the aerodynamic characteristics. The rotor wake increases the longitudinal static stability, the effective dihedral, and the lateral static stability of the airframe. The rotor induces a downwash on the wing. This downwash decreases the wing lift and increases the drag. The asymmetrical rotor wake induces a differential lift across the wing and a subsequent rolling moment. These rotor induced effects on the wing become smaller with increasing forward speed.
Magnetic lumped parameter modeling of rotor eccentricity in brushless permanent-magnet motors
Wang, J.P.; Lieu, D.K.
1999-09-01
Vibration, giving rise to acoustical noise, is an important index of motor performance. The unbalanced force due to rotor eccentricity caused by manufacturing imprecision or bearing defects is one possible source of excitation to vibration. The previously developed fast design package for permanent magnet motors, based on magnetic lumped parameter modeling, is modified to predict the influence of rotor eccentricity. Both static and dynamic cases are investigated. Magnetic material nonlinearity is taken into consideration. A two-dimensional relative permeance function is derived by conformal transformation followed by the modification of permeances modeling the air gap. Static and dynamic rotor eccentricity bring different effects to symmetric and asymmetric motors and are discussed separately.
Simple theoretical models for composite rotor blades
NASA Technical Reports Server (NTRS)
Valisetty, R. R.; Rehfield, L. W.
1984-01-01
The development of theoretical rotor blade structural models for designs based upon composite construction is discussed. Care was exercised to include a member of nonclassical effects that previous experience indicated would be potentially important to account for. A model, representative of the size of a main rotor blade, is analyzed in order to assess the importance of various influences. The findings of this model study suggest that for the slenderness and closed cell construction considered, the refinements are of little importance and a classical type theory is adequate. The potential of elastic tailoring is dramatically demonstrated, so the generality of arbitrary ply layup in the cell wall is needed to exploit this opportunity.
Modeling Aerodynamically Generated Sound of Helicopter Rotors
NASA Technical Reports Server (NTRS)
Brentner, Kenneth S.; Farassat, F.
2002-01-01
A great deal of progress has been made in the modeling of aerodynamically 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 source terms of the FW-H equation account for the thickness and loading noise, respectively. Bladevortex-interaction noise and broadband noise are important types of loading noise, hence much research has been directed toward the accurate modeling of these noise mechanisms. 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 equation has also been utilized on permeable surfaces surrounding all physical noise sources. 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 noise models into full vehicle noise prediction tools.
HARP model rotor test at the DNW. [Hughes Advanced Rotor Program
NASA Technical Reports Server (NTRS)
Dawson, Seth; Jordan, David; Smith, Charles; Ekins, James; Silverthorn, Lou
1989-01-01
Data from a test of a dynamically scaled model of the Hughes Advanced Rotor Program (HARP) bearingless model main rotor and 369K tail rotor are reported. The history of the HARP program and its goals are reviewed, and the main and tail rotor models are described. The test facilities and instrumentation are described, and wind tunnel test data are presented on hover, forward flight performance, and blade-vortex interaction. Performance data, acoustic data, and dynamic data from near field/far field and shear layer studies are presented.
HARP model rotor test at the DNW. [Hughes Advanced Rotor Program
NASA Technical Reports Server (NTRS)
Dawson, Seth; Jordan, David; Smith, Charles; Ekins, James; Silverthorn, Lou
1989-01-01
Data from a test of a dynamically scaled model of the Hughes Advanced Rotor Program (HARP) bearingless model main rotor and 369K tail rotor are reported. The history of the HARP program and its goals are reviewed, and the main and tail rotor models are described. The test facilities and instrumentation are described, and wind tunnel test data are presented on hover, forward flight performance, and blade-vortex interaction. Performance data, acoustic data, and dynamic data from near field/far field and shear layer studies are presented.
Important Scaling Parameters for Testing Model-Scale Helicopter Rotors
NASA Technical Reports Server (NTRS)
Singleton, Jeffrey D.; Yeager, William T., Jr.
1998-01-01
An investigation into the effects of aerodynamic and aeroelastic scaling parameters on model scale helicopter rotors has been conducted in the NASA Langley Transonic Dynamics Tunnel. The effect of varying Reynolds number, blade Lock number, and structural elasticity on rotor performance has been studied and the performance results are discussed herein for two different rotor blade sets at two rotor advance ratios. One set of rotor blades were rigid and the other set of blades were dynamically scaled to be representative of a main rotor design for a utility class helicopter. The investigation was con-densities permits the acquisition of data for several Reynolds and Lock number combinations.
Development of a rotor wake-vortex model, volume 1
NASA Technical Reports Server (NTRS)
Majjigi, R. K.; Gliebe, P. R.
1984-01-01
Certain empirical rotor wake and turbulence relationships were developed using existing low speed rotor wave data. A tip vortex model was developed by replacing the annulus wall with a row of image vortices. An axisymmetric turbulence spectrum model, developed in the context of rotor inflow turbulence, was adapted to predicting the turbulence spectrum of the stator gust upwash.
Full Scale Rotor Aeroacoustic Predictions and the Link to Model Scale Rotor Data
NASA Technical Reports Server (NTRS)
Boyd, D. Douglas, Jr.; Burley, Casey L.; Conner, David A.
2004-01-01
The NASA Aeroacoustic Prediction System (NAPS) is used to establish a link between model-scale and full-scale rotor predictions and is partially validated against measured wind tunnel and flight aeroacoustic data. The prediction approach of NAPS couples a comprehensive rotorcraft analysis with acoustic source noise and propagation codes. The comprehensive analysis selected for this study is CAMRAD-II, which provides the performance/trim/wake solution for a given rotor or flight condition. The post-trim capabilities of CAMRAD-II are used to compute high-resolution sectional airloads for the acoustic tone noise analysis, WOPMOD. The tone noise is propagated to observers on the ground with the propagation code, RNM (Rotor Noise Model). Aeroacoustic predictions are made with NAPS for an isolated rotor and compared to results of the second Harmonic Aeroacoustic Rotor Test (HART-II) program, which tested a 40% dynamically and Mach-scaled BO-105 main rotor at the DNW. The NAPS is validated with comparisons for three rotor conditions: a baseline condition and two Higher Harmonic Control (HHC) conditions. To establish a link between model and full-scale rotor predictions, a full-scale BO-105 main rotor input deck for NAPS is created from the 40% scale rotor input deck. The full-scale isolated rotor predictions are then compared to the model predictions. The comparisons include aerodynamic loading, acoustic levels, and acoustic pressure time histories for each of the three conditions. With this link established, full-scale predictions are made for a range of descent flight conditions and compared with measured trends from the recent Rotorcraft Operational Noise Abatement Procedures (RONAP) flight test conducted by DLR and ONERA. Additionally, the effectiveness of two HHC conditions from the HART-II program is demonstrated for the full-scale rotor in flight.
NASA Technical Reports Server (NTRS)
McAlister, K. W.; Huang, S. S.; Abrego, A. I.
2001-01-01
A model rotor was mounted horizontally in the settling chamber of a wind tunnel to obtain performance and wake structure data under low climb conditions. The immediate wake of the rotor was carefully surveyed using 3-component particle image velocimetry to define the velocity and vortical content of the flow, and used in a subsequent study to validate a theory for the separate determination of induced and profile drag. Measurements were obtained for two collective pitch angles intended to render a predominately induced drag state and another with a marked increase in profile drag. A majority of the azimuthally directed vorticity in the wake was found to be concentrated in the tip vortices. However, adjacent layers of inboard vorticity with opposite sense were clearly present. At low collective, the close proximity of the tip vortex from the previous blade caused the wake from the most recent blade passage to be distorted. The deficit velocity component that was directed along the azimuth of the rotor blade was never more that 15 percent of the rotor tip speed, and except for the region of the tip vortex, appeared to have totally disappeared form the wake left by the previous blade.
Test results from a dynamic model dynaflex rotor
NASA Technical Reports Server (NTRS)
Niebanck, C. F.; Goodman, R. K.
1985-01-01
A one-fifth scale dynamic model of the Sikorsky Dynaflex rotor was tested in hover and in forward flight conditions in a wind tunnel. The Dynaflex rotor features an advanced composite structure which flexes to provide a constant speed universal joint action. Testing concentrated on confirming that the stability and dynamic response of the rotor were satisfactory. Lift conditions of up to .11 Ct/sigma and advance ratios as high as .46 were reached. Vibratory loads were compared to those of articulated rotors. The Dynaflex rotor concept appears to be a practical concept from the standpoint of dynamic response and stability.
Icing Research Tunnel test of a model helicopter rotor
NASA Technical Reports Server (NTRS)
Miller, Thomas L.; Bond, Thomas H.
1989-01-01
An experimental program has been conducted in the NASA Lewis Research Center Icing Research Tunnel (IRT) in which an OH-58 tail rotor assembly was operated in a horizontal plane to simulate the action of a typical main rotor. Ice was accreted on the blades in a variety of rotor and tunnel operating conditions and documentation of the resulting shapes was performed. Rotor torque and vibration are presented as functions of time for several representative test runs, and the effects of various parametric variations on the blade ice shapes are shown. This OH-58 test was the first of its kind in the United States and will encourage additional model rotor icing tunnel testing. Although not a scaled representative of any actual full-scale main rotor system, this rig has produced torque and vibration data which will be useful in assessing the quality of existing rotor icing analyses.
Icing research tunnel test of a model helicopter rotor
NASA Technical Reports Server (NTRS)
Miller, Thomas L.; Bond, Thomas H.
1989-01-01
An experimental program has been conducted in the NASA Lewis Research Center Icing Research Tunnel (IRT) in which an OH-58 tail rotor assembly was operated in a horizontal plane to simulate the action of a typical main rotor. Ice was accreted on the blades in a variety of rotor and tunnel operating conditions and documentation of the resulting shapes was performed. Rotor torque and vibration are presented as functions of time for several representative test runs, and the effects of various parametric variations on the blade ice shapes are shown. This OH-58 test was the first of its kind in the United States and will encourage additional model rotor icing tunnel testing. Although not a scaled representative of any actual full-scale main rotor system, this rig has produced torque and vibration data which will be useful in assessing the quality of existing rotor icing analyses.
Coupled transport in rotor models
NASA Astrophysics Data System (ADS)
Iubini, S.; Lepri, S.; Livi, R.; Politi, A.
2016-08-01
Steady nonequilibrium states are investigated in a one-dimensional setup in the presence of two thermodynamic currents. Two paradigmatic nonlinear oscillators models are investigated: an XY chain and the discrete nonlinear Schrödinger equation. Their distinctive feature is that the relevant variable is an angle in both cases. We point out the importance of clearly distinguishing between energy and heat flux. In fact, even in the presence of a vanishing Seebeck coefficient, a coupling between (angular) momentum and energy arises, mediated by the unavoidable presence of a coherent energy flux. Such a contribution is the result of the ‘advection’ induced by the position-dependent angular velocity. As a result, in the XY model, the knowledge of the two diagonal elements of the Onsager matrix suffices to reconstruct its transport properties. The analysis of the nonequilibrium steady states finally allows to strengthen the connection between the two models.
Wong, Bryan M; Fadri, Maria M; Raman, Sumathy
2008-02-01
The thermodynamic properties of three halocarbon molecules relevant in atmospheric and public health applications are presented from ab initio calculations. Our technique makes use of a reaction path-like Hamiltonian to couple all the vibrational modes to a large-amplitude torsion for 1,2-difluoroethane, 1,2-dichloroethane, and 1,2-dibromoethane, each of which possesses a heavy asymmetric rotor. Optimized ab initio energies and Hessians were calculated at the CCSD(T) and MP2 levels of theory, respectively. In addition, to investigate the contribution of electronically excited states to thermodynamic properties, several excited singlet and triplet states for each of the halocarbons were computed at the CASSCF/MRCI level. Using the resulting potentials and projected frequencies, the couplings of all the vibrational modes to the large-amplitude torsion are calculated using the new STAR-P 2.4.0 software platform that automatically parallelizes our codes with distributed memory via a familiar MATLAB interface. Utilizing the efficient parallelization scheme of STAR-P, we obtain thermodynamic properties for each of the halocarbons, with temperatures ranging from 298.15 to 1000 K. We propose that the free energies, entropies, and heat capacities obtained from our methods be used to supplement theoretical and experimental values found in current thermodynamic tables.
Asymmetric Top Rotors in Superfluid Para-Hydrogen Nano-Clusters
NASA Astrophysics Data System (ADS)
Zeng, Tao; Li, Hui; Roy, Pierre-Nicholas
2012-06-01
We present the first simulation study of bosonic clusters doped with an asymmetric top molecule. A variation of the path-integral Monte Carlo method is developed to study a para-water (pH_2O) impurity in para-hydrogen (pH_2) clusters. The growth pattern of the doped clusters is similar in nature to that of the pure clusters. The pH_2O molecule appears to rotate freely in the cluster due to its large rotational constants and the lack of adiabatic following. The presence of pH_2O substantially quenches the superfluid response of pH_2 with respect to the space fixed frame. We also study the behaviour of a sulphur dioxide (32S16O_2) dopant in the pH_2 clusters. For such a heavy rotor, the adiabatic following of the pH_2 molecules is established and the superfluid renormalization of the rotational constants is observed. The rotational structure of the SO_2-p(H_2)_N clusters' ro-vibrational spectra is predicted. The connection between the superfluid response respect to the external boundary rotation and the dopant rotation is discussed.
NASA Technical Reports Server (NTRS)
Magee, J. P.; Alexander, H. R.
1973-01-01
The rotor system designed for the Boeing Model 222 tilt rotor aircraft is a soft-in-plane hingeless rotor design, 26 feet in diameter. This rotor has completed two test programs in the NASA Ames 40' X 80' wind tunnel. The first test was a windmilling rotor test on two dynamic wing test stands. The rotor was tested up to an advance ratio equivalence of 400 knots. The second test used the NASA powered propeller test rig and data were obtained in hover, transition and low speed cruise flight. Test data were obtained in the areas of wing-rotor dynamics, rotor loads, stability and control, feedback controls, and performance to meet the test objectives. These data are presented.
Effect of Rotor Diameter on the Thermal Stresses of a Turbine Rotor Model
NASA Astrophysics Data System (ADS)
Dávalos, J. O.; García, J. C.; Urquiza, G.; Castro-Gómez, L. L.; Rodríguez, J. A.; De Santiago, O.
2016-04-01
Thermal stresses in a simplified steam turbine rotor model during a cold startup are analyzed using finite element analysis (FEA). In order to validate the numerical model, an experimental array is developed in which a hollow cylinder is heated with hot air in the external surface. At the thick wall of the cylinder, temperature distribution is measured in real time, while at the same time an algorithm computes thermal stresses. Additional computational fluid dynamics (CFD) calculations are made to obtain magnitudes of velocity and pressure in order to compute convective heat transfer coefficient. The experimental results show good agreement with the FEA computations. To evaluate the effect of rotor diameter size, FEA computations with variation in external and internal diameters are performed. Results show that thermal stresses are proportional to rotor diameter size. Also, zones of higher stress concentration are found in the external and internal surfaces of the rotor.
Results of a sub-scale model rotor icing test
NASA Technical Reports Server (NTRS)
Flemming, Robert J.; Bond, Thomas H.; Britton, Randall K.
1991-01-01
A heavily instrumented sub-scale model of a helicopter main rotor was tested in the NASA Lewis Research Center Icing Research Tunnel (IRT) in September and November 1989. The four-bladed main rotor had a diameter of 1.83 m (6.00 ft) and the 0.124 m (4.9 in) chord rotor blades were specially fabricated for this experiment. The instrumented rotor was mounted on a Sikorsky Aircraft Powered Force Model, which enclosed a rotor balance and other measurement systems. The model rotor was exposed to a range of icing conditions that included variations in temperature, liquid water content, and median droplet diameter, and was operated over ranges of advance ratio, shaft angle, tip Mach number (rotor speed) and weight coefficient to determine the effect of these parameters on ice accretion. In addition to strain gage and balance data, the test was documented with still, video, and high speed photography, ice profile tracings, and ice molds. The sensitivity of the model rotor to the test parameters, is given, and the result to theoretical predictions are compared. Test data quality was excellent, and ice accretion prediction methods and rotor performance prediction methods (using published icing lift and drag relationships) reproduced the performance trends observed in the test. Adjustments to the correlation coefficients to improve the level of correlation are suggested.
Establishment of a rotor model basis
NASA Technical Reports Server (NTRS)
Mcfarland, R. E.
1982-01-01
Radial-dimension computations in the RSRA's blade-element model are modified for both the acquisition of extensive baseline data and for real-time simulation use. The baseline data, which are for the evaluation of model changes, use very small increments and are of high quality. The modifications to the real-time simulation model are for accuracy improvement, especially when a minimal number of blade segments is required for real-time synchronization. An accurate technique for handling tip loss in discrete blade models is developed. The mathematical consistency and convergence properties of summation algorithms for blade forces and moments are examined and generalized integration coefficients are applied to equal-annuli midpoint spacing. Rotor conditions identified as 'constrained' and 'balanced' are used and the propagation of error is analyzed.
Two-Dimensional Computational Model for Wave Rotor Flow Dynamics
NASA Technical Reports Server (NTRS)
Welch, Gerard E.
1996-01-01
A two-dimensional (theta,z) Navier-Stokes solver for multi-port wave rotor flow simulation is described. The finite-volume form of the unsteady thin-layer Navier-Stokes equations are integrated in time on multi-block grids that represent the stationary inlet and outlet ports and the moving rotor passages of the wave rotor. Computed results are compared with three-port wave rotor experimental data. The model is applied to predict the performance of a planned four-port wave rotor experiment. Two-dimensional flow features that reduce machine performance and influence rotor blade and duct wall thermal loads are identified. The performance impact of rounding the inlet port wall, to inhibit separation during passage gradual opening, is assessed.
Effect of Turbulence Modeling on Hovering Rotor Flows
NASA Technical Reports Server (NTRS)
Yoon, Seokkwan; Chaderjian, Neal M.; Pulliam, Thomas H.; Holst, Terry L.
2015-01-01
The effect of turbulence models in the off-body grids on the accuracy of solutions for rotor flows in hover has been investigated. Results from the Reynolds-Averaged Navier-Stokes and Laminar Off-Body models are compared. Advection of turbulent eddy viscosity has been studied to find the mechanism leading to inaccurate solutions. A coaxial rotor result is also included.
An improved numerical model for wave rotor design and analysis
NASA Technical Reports Server (NTRS)
Paxson, Daniel E.; Wilson, Jack
1992-01-01
A numerical model has been developed which can predict both the unsteady flows within a wave rotor and the steady averaged flows in the ports. The model is based on the assumptions of one-dimensional, unsteady, and perfect gas flow. Besides the dominant wave behavior, it is also capable of predicting the effects of finite tube opening time, leakage from the tube ends, and viscosity. The relative simplicity of the model makes it useful for design, optimization, and analysis of wave rotor cycles for any application. This paper discusses some details of the model and presents comparisons between the model and two laboratory wave rotor experiments.
An improved numerical model for wave rotor design and analysis
NASA Technical Reports Server (NTRS)
Paxson, Daniel E.; Wilson, Jack
1993-01-01
A numerical model has been developed which can predict both the unsteady flows within a wave rotor and the steady averaged flows in the ports. The model is based on the assumptions of one-dimensional, unsteady, and perfect gas flow. Besides the dominant wave behavior, it is also capable of predicting the effects of finite tube opening time, leakage from the tube ends, and viscosity. The relative simplicity of the model makes it useful for design, optimization, and analysis of wave rotor cycles for any application. This paper discusses some details of the model and presents comparisons between the model and two laboratory wave rotor experiments.
Development of a rotor wake/vortex model. Volume 2: User's manual for computer program
NASA Technical Reports Server (NTRS)
Majjigi, R. K.; Gliebe, P. R.
1984-01-01
The principal objective was to establish a verified rotor wake/vortex model for specific application to fan and compressor rotor-stator interaction and resulting noise generation. A description and flow chart of the Rotor Wake/Vortex Model computer program, a listing of the program, definitions of the input/output parameters, a sample input/output case, and input files for Rotor 55, the JT15D rotor, and Rotor 67, Stage 1 are provided.
Two-dimensional CFD modeling of wave rotor flow dynamics
NASA Technical Reports Server (NTRS)
Welch, Gerard E.; Chima, Rodrick V.
1994-01-01
A two-dimensional Navier-Stokes solver developed for detailed study of wave rotor flow dynamics is described. The CFD model is helping characterize important loss mechanisms within the wave rotor. The wave rotor stationary ports and the moving rotor passages are resolved on multiple computational grid blocks. The finite-volume form of the thin-layer Navier-Stokes equations with laminar viscosity are integrated in time using a four-stage Runge-Kutta scheme. Roe's approximate Riemann solution scheme or the computationally less expensive advection upstream splitting method (AUSM) flux-splitting scheme is used to effect upwind-differencing of the inviscid flux terms, using cell interface primitive variables set by MUSCL-type interpolation. The diffusion terms are central-differenced. The solver is validated using a steady shock/laminar boundary layer interaction problem and an unsteady, inviscid wave rotor passage gradual opening problem. A model inlet port/passage charging problem is simulated and key features of the unsteady wave rotor flow field are identified. Lastly, the medium pressure inlet port and high pressure outlet port portion of the NASA Lewis Research Center experimental divider cycle is simulated and computed results are compared with experimental measurements. The model accurately predicts the wave timing within the rotor passages and the distribution of flow variables in the stationary inlet port region.
Wind tunnel test on a 1/4.622 Froude scale, hingeless rotor, tilt rotor model, volume 1
NASA Technical Reports Server (NTRS)
Magee, J. P.; Alexander, H. R.
1976-01-01
Wing tunnel test data on a 1/4.622 Froude scale, hingeless rotor, tilt rotor mode are reported for all potential flight conditions through hover and a wide envelope of transitions. A mathematical model was used to describe the rotor system in real time simulation by means of regression analyses. Details of the model, test program and data system are provided together with four data files for hover and transition.
New models for asymmetric kinks and branes
NASA Astrophysics Data System (ADS)
Menezes, R.; Moreira, D. C.
2017-08-01
We investigate new models for scalar fields in flat and curved spacetime. We note that the global reflection symmetry of the potential that identify the scalar field model does not exclude the presence of internal asymmetries that give rise to asymmetric structures. Despite the asymmetry, the new structures are linearly stable and in the braneworld scenario with an extra dimension of infinite extend, they may generate new families of asymmetric thick branes that are robust against small fluctuations in the warped geometry.
Technology Investigations With the Tilt Rotor Aeroacoustic Model (TRAM)
NASA Technical Reports Server (NTRS)
Young, Larry A.; Yamauchi, Gloria K.; Booth, Earl; Johnson, Jeff L.; Derby, Michael R.; Sullivan, Ken; Ralston, Scott; Shockey, Gerald; Dawson, Seth; Warmbrodt, William (Technical Monitor)
1998-01-01
This paper introduces the Tilt Rotor Aeroacoustic Model (TRAM) project. The TRAM project is a key infrastructure investment for NASA tiltrotor research. The TRAM project consists of the development and testing of two modular, hardware-compatible, test stands: an isolated rotor configuration and a fullspan model (dual rotors with a complete airframe representation). These two test stands are inclusively called the Tilt Rotor Aeroacoustic Model (TRAM). The baseline proprotors and airframe of the TRAM test stands are nominally 1/4-scale representative of the V-22 Osprey aircraft. The research objectives of the project, the TRAM hardware design features and capabilities, illustrative examples of the type and quality of data that can be acquired with the TRAM, and the current status of the overall project will be discussed in this paper.
Reference Model 2: %22Rev 0%22 Rotor Design.
Barone, Matthew F.; Berg, Jonathan Charles; Griffith, Daniel
2011-12-01
The preliminary design for a three-bladed cross-flow rotor for a reference marine hydrokinetic turbine is presented. A rotor performance design code is described, along with modifications to the code to allow prediction of blade support strut drag as well as interference between two counter-rotating rotors. The rotor is designed to operate in a reference site corresponding to a riverine environment. Basic rotor performance and rigid-body loads calculations are performed to size the rotor elements and select the operating speed range. The preliminary design is verified with a simple finite element model that provides estimates of bending stresses during operation. A concept for joining the blades and support struts is developed and analyzed with a separate finite element analysis. Rotor mass, production costs, and annual energy capture are estimated in order to allow calculations of system cost-of-energy. Evaluation Only. Created with Aspose.Pdf.Kit. Copyright 2002-2011 Aspose Pty Ltd Evaluation Only. Created with Aspose.Pdf.Kit. Copyright 2002-2011 Aspose Pty Ltd
Linear Time Invariant Models for Integrated Flight and Rotor Control
NASA Astrophysics Data System (ADS)
Olcer, Fahri Ersel
2011-12-01
Recent developments on individual blade control (IBC) and physics based reduced order models of various on-blade control (OBC) actuation concepts are opening up opportunities to explore innovative rotor control strategies for improved rotor aerodynamic performance, reduced vibration and BVI noise, and improved rotor stability, etc. Further, recent developments in computationally efficient algorithms for the extraction of Linear Time Invariant (LTI) models are providing a convenient framework for exploring integrated flight and rotor control, while accounting for the important couplings that exist between body and low frequency rotor response and high frequency rotor response. Formulation of linear time invariant (LTI) models of a nonlinear system about a periodic equilibrium using the harmonic domain representation of LTI model states has been studied in the literature. This thesis presents an alternative method and a computationally efficient scheme for implementation of the developed method for extraction of linear time invariant (LTI) models from a helicopter nonlinear model in forward flight. The fidelity of the extracted LTI models is evaluated using response comparisons between the extracted LTI models and the nonlinear model in both time and frequency domains. Moreover, the fidelity of stability properties is studied through the eigenvalue and eigenvector comparisons between LTI and LTP models by making use of the Floquet Transition Matrix. For time domain evaluations, individual blade control (IBC) and On-Blade Control (OBC) inputs that have been tried in the literature for vibration and noise control studies are used. For frequency domain evaluations, frequency sweep inputs are used to obtain frequency responses of fixed system hub loads to a single blade IBC input. The evaluation results demonstrate the fidelity of the extracted LTI models, and thus, establish the validity of the LTI model extraction process for use in integrated flight and rotor control
NASA Astrophysics Data System (ADS)
Colín Ocampo, Jorge; Gutiérrez Wing, Enrique S.; Ramírez Moroyoqui, Félix J.; Abúndez Pliego, Arturo; Blanco Ortega, Andrés; Mayén, Jan
2017-10-01
It is well known that some mechanical systems, as a two pole generator, exhibit two different stiffness on the main inertial axis of its transverse section, which leads to complex vibration modes and complicates the determination of the angular position of the unbalance force and, consequently, the balancing process by conventional methods. Therefore, a methodology for the angular position identification of the unbalance force, based on a two-degrees-of-freedom mathematical simplified model of a rotor with unequal principal moments of inertia of the shaft transverse section, is proposed in this work. The methodology requires the analysis of the response polar plots of the rotor, as well as the information of the vibration response of at least four points from the response polar plot: vibration amplitude, phase angle and the angular velocity of the rotor. The identification of the unbalance force angular position was numerically and experimentally validated using the response polar plots experimentally acquired from a Jeffcott type rotor, which exhibits unequal principal moments of inertia of shaft transverse section and two inertial disks, which were analyzed for several unbalance force angular positions. The results showed slight differences between the identified and the experimental angular positions.
A general numerical model for wave rotor analysis
NASA Technical Reports Server (NTRS)
Paxson, Daniel W.
1992-01-01
Wave rotors represent one of the promising technologies for achieving very high core temperatures and pressures in future gas turbine engines. Their operation depends upon unsteady gas dynamics and as such, their analysis is quite difficult. This report describes a numerical model which has been developed to perform such an analysis. Following a brief introduction, a summary of the wave rotor concept is given. The governing equations are then presented, along with a summary of the assumptions used to obtain them. Next, the numerical integration technique is described. This is an explicit finite volume technique based on the method of Roe. The discussion then focuses on the implementation of appropriate boundary conditions. Following this, some results are presented which first compare the numerical approximation to the governing differential equations and then compare the overall model to an actual wave rotor experiment. Finally, some concluding remarks are presented concerning the limitations of the simplifying assumptions and areas where the model may be improved.
Extension and validation of an unsteady wake model for rotors
NASA Technical Reports Server (NTRS)
Su, AY; Yoo, Kyung M.; Peters, David A.
1992-01-01
A new three-dimensional, finite-state induced-flow model is extended to treat nonlinearities associated with the mass flow induced through the rotor plane. This new theory is then applied to the correlation of a recent set of unsteady, hover laser Doppler velocimetry inflow measurements conducted in the Aeroelastic Rotor Test Chamber at Georgia Institute of Technology. Although the model is intended primarily as a representation of unsteady aerodynamics for aeroelasticity applications, the results show that it has an excellent capability in predicting the inflow distribution in hover except near the root and tip. In addition, the computed unsteady spanwise lift distribution of a rotor is compared with that from an unsteady vortex lattice method for pitch oscillations at various frequencies. The new model is shown to be capable of prediction of unsteady loads typical of aeroelastic response.
A general numerical model for wave rotor analysis
NASA Astrophysics Data System (ADS)
Paxson, Daniel W.
1992-07-01
Wave rotors represent one of the promising technologies for achieving very high core temperatures and pressures in future gas turbine engines. Their operation depends upon unsteady gas dynamics and as such, their analysis is quite difficult. This report describes a numerical model which has been developed to perform such an analysis. Following a brief introduction, a summary of the wave rotor concept is given. The governing equations are then presented, along with a summary of the assumptions used to obtain them. Next, the numerical integration technique is described. This is an explicit finite volume technique based on the method of Roe. The discussion then focuses on the implementation of appropriate boundary conditions. Following this, some results are presented which first compare the numerical approximation to the governing differential equations and then compare the overall model to an actual wave rotor experiment. Finally, some concluding remarks are presented concerning the limitations of the simplifying assumptions and areas where the model may be improved.
Rotor Broadband Noise Prediction with Comparison to Model Data
NASA Technical Reports Server (NTRS)
Brooks, Thomas F.; Burley, Casey L.
2001-01-01
This paper reports an analysis and prediction development of rotor broadband noise. The two primary components of this noise are Blade-Wake Interaction (BWI) noise, due to the blades' interaction with the turbulent wakes of the preceding blades, and "Self" noise, due to the development and shedding of turbulence within the blades' boundary layers. Emphasized in this report is the new code development for Self noise. The analysis and validation employs data from the HART program, a model BO-105 rotor wind tunnel test conducted in the German-Dutch Wind Tunnel (DNW). The BWI noise predictions are based on measured pressure response coherence functions using cross-spectral methods. The Self noise predictions are based on previously reported semiempirical modeling of Self noise obtained from isolated airfoil sections and the use of CAMRAD.Modl to define rotor performance and local blade segment flow conditions. Both BWI and Self noise from individual blade segments are Doppler shifted and summed at the observer positions. Prediction comparisons with measurements show good agreement for a range of rotor operating conditions from climb to steep descent. The broadband noise predictions, along with those of harmonic and impulsive Blade-Vortex Interaction (BVI) noise predictions, demonstrate a significant advance in predictive capability for main rotor noise.
Effects of different rub models on simulated rotor dynamics
NASA Technical Reports Server (NTRS)
Kascak, A. F.; Tomko, J. J.
1984-01-01
Using a direct integration, transient response rotor dynamics computer code, the response of turbine engine rotors to two different blade tip - seal interference rub models was studied. The first model, an abradable seal rub model, is based on an energy-loss-per-unit-volume theory (applicable to a ceramic turbine blade tip seal). The second, a smearin model, is based on viscous hydrodynamic theory (applicable to a metallic blade tip seal). The results from these two models were compared with those from a previously studied model based on dry friction theory. The abradable model was very senitive to small changes in the energy per unit volume, and once a threshold was exceeded, the rotor went into a backward whirl. The amplitude seemed to grow without limit. This was similar to the dry friction model when the coefficient of friction exceeded a particular threshold. The smearing model was not as sensitive to small changes in the viscosity, but a threshold viscosity was found. When it was exceeded, the rotor went into backward whirl, but the amplitude seemed to grow to a finite limit.
A mathematical model for the doubly fed wound rotor generator
NASA Technical Reports Server (NTRS)
Brady, F. J.
1983-01-01
A mathematical analysis of a doubly-fed wound rotor machine used as a constant frequency generator is presented. The purpose of this analysis is to derive a consistent set of circuit equations which produce constant stator frequency and constant stator voltage. Starting with instantaneous circuit equations, the necessary rotor voltages and currents are derived. The model, thus obtained, is assumed to be valid, since the resulting relationships between mechanical power and active volt-amperes agrees with the results of others. In addition, the model allows for a new interpretation of the power flow in the doubly-fed generator.
Twin-Rotor Patrol Airship Flying Model Design Rationale
1981-06-01
MONITORING AGENCY NAME & ’ADORES(f d•llffewent from Contriollin# Ofifer) IS, SECURITY CL.ASS. (at this ve .0d6 ) Unclassified TDiCL.A-SsIPrlCA1ION...experimental data on the controllability of tilt-rotor airships operating near neutral buoyancy, a 32-foot long 1/10 scale flying model is bein...foot long 1/10 scale flying model is being developed using two cuntrarotating tilt-rotors representing those on the NASA/Bell XV-15 research aircraft
Advance finite element modeling of rotor blade aeroelasticity
NASA Technical Reports Server (NTRS)
Straub, F. K.; Sangha, K. B.; Panda, B.
1994-01-01
An advanced beam finite element has been developed for modeling rotor blade dynamics and aeroelasticity. This element is part of the Element Library of the Second Generation Comprehensive Helicopter Analysis System (2GCHAS). The element allows modeling of arbitrary rotor systems, including bearingless rotors. It accounts for moderately large elastic deflections, anisotropic properties, large frame motion for maneuver simulation, and allows for variable order shape functions. The effects of gravity, mechanically applied and aerodynamic loads are included. All kinematic quantities required to compute airloads are provided. In this paper, the fundamental assumptions and derivation of the element matrices are presented. Numerical results are shown to verify the formulation and illustrate several features of the element.
A new dynamic model of rotor-blade systems
NASA Astrophysics Data System (ADS)
Ma, Hui; Lu, Yang; Wu, Zhiyuan; Tai, Xingyu; Li, Hui; Wen, Bangchun
2015-11-01
A new dynamic model of rotor-blade systems is developed in this paper considering the lateral and torsional deformations of the shaft, gyroscopic effects of the rotor which consists of shaft and disk, and the centrifugal stiffening, spin softening and Coriolis force of the blades. In this model, the rotating flexible blades are represented by Timoshenko beams. The shaft and rigid disk are described by multiple lumped mass points (LMPs), and these points are connected by massless springs which have both lateral and torsional stiffness. LMPs are represented by the corresponding masses and mass moments of inertia in lateral and rotational directions, where each point has five degrees of freedom (dofs) excluding axial dof. Equations of motion of the rotor-blade system are derived using Hamilton's principle in conjunction with the assumed modes method to describe blade deformation. The proposed model is compared with both finite element (FE) model and real experiments. The proposed model is first validated by comparing the model natural frequencies and vibration responses with those obtained from an FE model. A further verification of the model is then performed by comparing the model natural frequencies at zero rotational speed with those obtained from experimental studies. The results shown a good agreement between the model predicted system characteristics and those obtained from the FE model and experimental tests. Moreover, the following interesting phenomena have been revealed from the new model based analysis: The torsional natural frequency of the system decreases with the increase of rotational speed, and the frequency veering phenomenon has been observed at high rotational speed; The complicated coupling modes, such as the blade-blade coupling mode (BB), the coupling mode between the rotor lateral vibration and blade bending (RBL), and the coupling mode between the rotor torsional vibration and blade bending (RBT), have also been observed when the number of
Hover tests of a model H-force rotor
NASA Technical Reports Server (NTRS)
Velkoff, H. R.
1981-01-01
The potential of using tip vanes at the ends of helicopter rotor blades to obtain a controllable H-force is considered. The addition of vanes placed perpendicular to the blade tips can be used to obtain an inplane force. By varying the angle of the vanes, a radial force can be created which can be controllable in azimuth position. Such a force could be used to provide translational motion of the rotor and aircraft without the requirement for rotor tilting. In addition, an H-force generated at high flight speed could be used as a propulsive force in a matter similar to a propeller. The force generated by the vanes could also affect the aircraft's stability characteristics. The H-force could also modify rotor performance in hovering since they could be thought to act as a virtual shroud. Tests were run with a model rotor which has a 6 foot diameter with a 3 inch chord blade. Test data are presented on the effects of various tip-vane configurations on the hovering figure of merit. The extreme sensitivity of the performance to vane arrangement is shown.
Wake model for helicopter rotors in high speed flight
NASA Technical Reports Server (NTRS)
Johnson, Wayne R.
1988-01-01
Two alternative approaches are developed to calculate blade-vortex interaction airloads on helicopter rotors: second order lifting-line theory, and a lifting surface theory correction. The common approach of using a larger vortex core radius to account for lifting-surface effects is quantified. The second order lifting-line theory also improves the modeling of yawed flow and swept tips. Calculated results are compared with wind tunnel measurements of lateral flapping, and with flight test measurements of blade section lift on SA349/2 and H-34 helicopter rotors. The tip vortex core radius required for good correlation with the flight test data is about 20 percent chord, which is within the range of measured viscous core sizes for helicopter rotors.
Modeling and simulation of coaxial helicopter rotor aerodynamics
NASA Astrophysics Data System (ADS)
Gecgel, Murat
A framework is developed for the computational fluid dynamics (CFD) analyses of a series of helicopter rotor flowfields in hover and in forward flight. The methodology is based on the unsteady solutions of the three-dimensional, compressible Navier-Stokes equations recast in a rotating frame of reference. The simulations are carried out by solving the developed mathematical model on hybrid meshes that aim to optimally exploit the benefits of both the structured and the unstructured grids around complex configurations. The computer code is prepared for parallel processing with distributed memory utilization in order to significantly reduce the computational time and the memory requirements. The developed model and the simulation methodology are validated for single-rotor-in-hover flowfields by comparing the present results with the published experimental data. The predictive merit of different turbulence models for complex helicopter aerodynamics are tested extensively. All but the kappa-o and LES results demonstrate acceptable agreement with the experimental data. It was deemed best to use the one-equation Spalart-Allmaras turbulence model for the subsequent rotor flowfield computations. First, the flowfield around a single rotor in forward flight is simulated. These time---accurate computations help to analyze an adverse effect of increasing the forward flight speed. A dissymmetry of the lift on the advancing and the retreating blades is observed for six different advance ratios. Since the coaxial rotor is proposed to mitigate the dissymmetry, it is selected as the next logical step of the present investigation. The time---accurate simulations are successfully obtained for the flowfields generated by first a hovering then a forward-flying coaxial rotor. The results for the coaxial rotor in forward flight verify the aerodynamic balance proposed by the previously published advancing blade concept. The final set of analyses aims to investigate if the gap between the
A numerical model for dynamic wave rotor analysis
NASA Technical Reports Server (NTRS)
Paxson, D. E.
1995-01-01
A numerical model has been developed which can predict the dynamic (and steady state) performance of a wave rotor, given the geometry and time dependent boundary conditions. The one-dimensional, perfect gas, CFD based code tracks the gasdynamics in each of the wave rotor passages as they rotate past the various ducts. The model can operate both on and off-design, allowing dynamic behavior to be studied throughout the operating range of the wave rotor. The model accounts for several major loss mechanisms including finite passage opening time, fluid friction, heat transfer to and from the passage walls, and leakage to and from the passage ends. In addition, it can calculate the amount of work transferred to and from the fluid when the flow in the ducts is not aligned with the passages such as occurs in off-design operation. Since it is one-dimensional, the model runs reasonably fast on a typical workstation. This paper will describe the model and present the results of some transient calculations for a conceptual four port wave rotor designed as a topping cycle for a small gas turbine engine.
Modelling and control of a rotor supported by magnetic bearings
NASA Technical Reports Server (NTRS)
Gurumoorthy, R.; Pradeep, A. K.
1994-01-01
In this paper we develop a dynamical model of a rotor and the active magnetic bearings used to support the rotor. We use this model to develop a stable state feedback control of the magnetic bearing system. We present the development of a rigid body model of the rotor, utilizing both Rotation Matrices (Euler Angles) and Euler Parameters (Quaternions). In the latter half of the paper we develop a stable state feedback control of the actively controlled magnetic bearing to control the rotor position under inbalances. The control law developed takes into account the variation of the model with rotational speed. We show stability over the whole operating range of speeds for the magnetic bearing system. Simulation results are presented to demonstrate the closed loop system performance. We develop the model of the magnetic bearing, and present two schemes for the excitation of the poles of the actively controlled magnetic bearing. We also present a scheme for averaging multiple sensor measurements and splitting the actuation forces amongst redundant actuators.
Modeling of a rotor speed transient response with radial rubbing
NASA Astrophysics Data System (ADS)
Roques, S.; Legrand, M.; Cartraud, P.; Stoisser, C.; Pierre, C.
2010-03-01
A rotor-stator model of a turbogenerator is introduced in order to investigate speed transients with rotor-to-stator rubbing caused by an accidental blade-off imbalance. In order to assess the angular deceleration of the rotor due to rubbing, the angular position of its cross-section is considered as an unknown of the problem. Displacement fields are discretized through a finite element formulation. The highly nonlinear equations due to contact conditions are solved through an explicit prediction-correction time-marching procedure combined with the Lagrange multiplier approach dealing with a node-to-line contact strategy. The developed numerical tool is suitable for analyzing rotor-stator interactions in turbomachines as the system passes through critical speeds during an accidental shutdown. The sensitivity of the system response to modeling, physical and numerical parameters is investigated. The results highlight the significant role of the friction coefficient together with the diaphragm modeling, from rigid to fully flexible, in the interaction phenomenon. Rigid models have the advantage of simplicity and provide reasonable estimations of the overall response of the turbine. A flexible model, however, may be more computationally intensive but is more appropriate in order to accurately capture quantities of interest such as shaft eccentricity and bearing loads.
Using a collision model to design safer wind turbine rotors for birds
Tucker, V.A.
1996-11-01
A mathematical model for collisions between birds and propeller-type turbine rotors identifies the variables that can be manipulated to reduce the probability that birds will collide with the rotor. This study defines a safety index--the clearance power density--that allows rotors of different sizes and designs to be compared in terms of the amount of wind energy converted to electrical energy per bird collision. The collision model accounts for variations in wind speed during the year and shows that for model rotors with simple, one-dimensional blades, the safety index increases in proportion to rotor diameter, and variable speed rotors have higher safety indexes than constant speed rotors. The safety index can also be increased by enlarging the region near the center of the rotor hub where the blades move slowly enough for birds to avoid them. Painting the blades to make them more visible might have this effect. Model rotors with practical designs can have safety indexes an order of magnitude higher than those for model rotors typical of the constant speeds rotors in common use today. This finding suggests that redesigned rotors could have collision rates with birds perhaps an order of magnitude lower than today`s rotors, with no reduction in the production of wind power. The empirical data that exist for collisions between raptors, such as hawks and eagles, and rotors are consistent with the model: the numbers of raptor carcasses found beneath large variable speed rotors, relative to the numbers found under small constant speed rotors, are in the proportions predicted by the collision model rather than in proportion to the areas swept by the rotor blades. However, uncontrolled variables associated with these data prevent a stronger claim of support for the model.
Flow Measurements of an Isolated Model Tilt Rotor
1999-05-01
Murashige , A., Kobiki, N., Tsuchihashi, A., Nakamura, H., Inagaki, K., Yamakawa, E., “ATIC Aeroacoustic Model Rotor Test at DNW,” AHS International...Meeting on Advanced Rotorcraft Technology and Disaster Relief, Gifu, Japan, April 1998. 25. Murashige , A., Tsuchihashi, A., Tsujiuchi, T., Yamakawa, E
A 3D finite element model for the vibration analysis of asymmetric rotating machines
NASA Astrophysics Data System (ADS)
Lazarus, A.; Prabel, B.; Combescure, D.
2010-08-01
This paper suggests a 3D finite element method based on the modal theory in order to analyse linear periodically time-varying systems. Presentation of the method is given through the particular case of asymmetric rotating machines. First, Hill governing equations of asymmetric rotating oscillators with two degrees of freedom are investigated. These differential equations with periodic coefficients are solved with classic Floquet theory leading to parametric quasimodes. These mathematical entities are found to have the same fundamental properties as classic eigenmodes, but contain several harmonics possibly responsible for parametric instabilities. Extension to the vibration analysis (stability, frequency spectrum) of asymmetric rotating machines with multiple degrees of freedom is achieved with a fully 3D finite element model including stator and rotor coupling. Due to Hill expansion, the usual degrees of freedom are duplicated and associated with the relevant harmonic of the Floquet solutions in the frequency domain. Parametric quasimodes as well as steady-state response of the whole system are ingeniously computed with a component-mode synthesis method. Finally, experimental investigations are performed on a test rig composed of an asymmetric rotor running on nonisotropic supports. Numerical and experimental results are compared to highlight the potential of the numerical method.
NASA Technical Reports Server (NTRS)
Harendra, P. B.; Joglekar, M. J.; Gaffey, T. M.; Marr, R. L.
1973-01-01
A mathematical model for real-time flight simulation of a tilt rotor research aircraft was developed. The mathematical model was used to support the aircraft design, pilot training, and proof-of-concept aspects of the development program. The structure of the mathematical model is indicated by a block diagram. The mathematical model differs from that for a conventional fixed wing aircraft principally in the added requirement to represent the dynamics and aerodynamics of the rotors, the interaction of the rotor wake with the airframe, and the rotor control and drive systems. The constraints imposed on the mathematical model are defined.
NASA Technical Reports Server (NTRS)
Rosenstein, H.; Mcveigh, M. A.; Mollenkof, P. A.
1973-01-01
A mathematical model for a real time simulation of a tilt rotor aircraft was developed. The mathematical model is used for evaluating aircraft performance and handling qualities. The model is based on an eleven degree of freedom total force representation. The rotor is treated as a point source of forces and moments with appropriate response time lags and actuator dynamics. The aerodynamics of the wing, tail, rotors, landing gear, and fuselage are included.
Symmetry of asymmetric quantum Rabi models
NASA Astrophysics Data System (ADS)
Wakayama, Masato
2017-04-01
The aim of this paper is a better understanding for the eigenstates of the asymmetric quantum Rabi model by Lie algebra representations of sl2 . We define a second order element of the universal enveloping algebra U(sl_2) of sl_2({R}) , which, through the action of a certain infinite dimensional representation of sl_2({R}) , provides a picture of the asymmetric quantum Rabi model equivalent to the one drawn by confluent Heun ordinary differential equations. Using this description, we prove the existence of level crossings in the spectral graph of the asymmetric quantum Rabi model when the symmetry-breaking parameter ɛ is equal to \\frac12 , and conjecture a formula that ensures likewise the presence of level crossings for general ε \\in \\frac12{Z} . This result on level crossings was demonstrated numerically by Li and Batchelor in 2015, investigating an earlier empirical observation by Braak (2011). The first analysis of the degenerate spectrum was given for the symmetric quantum Rabi model by Kuś in 1985. In our picture, we find a certain reciprocity (or {Z}2 -symmetry) for ε \\in \\frac12{Z} if the spectrum is described by representations of sl2 . We further discuss briefly the non-degenerate part of the exceptional spectrum from the viewpoint of infinite dimensional representations of sl_2({R}) having lowest weight vectors.
Asymmetric dark matter models in SO(10)
NASA Astrophysics Data System (ADS)
Nagata, Natsumi; Olive, Keith A.; Zheng, Jiaming
2017-02-01
We systematically study the possibilities for asymmetric dark matter in the context of non-supersymmetric SO(10) models of grand unification. Dark matter stability in SO(10) is guaranteed by a remnant Z2 symmetry which is preserved when the intermediate scale gauge subgroup of SO(10) is broken by a {126} dimensional representation. The asymmetry in the dark matter states is directly generated through the out-of-equilibrium decay of particles around the intermediate scale, or transferred from the baryon/lepton asymmetry generated in the Standard Model sector by leptogenesis. We systematically classify possible asymmetric dark matter candidates in terms of their quantum numbers, and derive the conditions for each case that the observed dark matter density is (mostly) explained by the asymmetry of dark matter particles.
General model and control of an n rotor helicopter
NASA Astrophysics Data System (ADS)
Sidea, A. G.; Yding Brogaard, R.; Andersen, N. A.; Ravn, O.
2014-12-01
The purpose of this study was to create a dynamic, nonlinear mathematical model of a multirotor that would be valid for different numbers of rotors. Furthermore, a set of Single Input Single Output (SISO) controllers were implemented for attitude control. Both model and controllers were tested experimentally on a quadcopter. Using the combined model and controllers, simple system simulation and control is possible, by replacing the physical values for the individual systems.
Acoustical properties of a model rotor in nonaxial flight. [wind tunnel model noise measurements
NASA Technical Reports Server (NTRS)
Hinterkeuser, E. G.
1973-01-01
Wind tunnel measurements on model rotor blade loads and acoustical noise were correlated to a theoretical formulation of the rotational noise of a rotor in non-axial flight. Good correlation between theory and data was achieved using actual measured rotor blade pressure harmonic decay levels and lift, drag and radial force magnitudes. Both pressure and acoustic data exhibited considerable scatter in hover and low speed forward flight which resulted in a fairly wide latitude in the noise level prediction at higher harmonics.
An investigation of rotor harmonic noise by the use of small scale wind tunnel models
NASA Technical Reports Server (NTRS)
Sternfeld, H., Jr.; Schaffer, E. G.
1982-01-01
Noise measurements of small scale helicopter rotor models were compared with noise measurements of full scale helicopters to determine what information about the full scale helicopters could be derived from noise measurements of small scale helicopter models. Comparisons were made of the discrete frequency (rotational) noise for 4 pairs of tests. Areas covered were tip speed effects, isolated rotor, tandem rotor, and main rotor/tail rotor interaction. Results show good comparison of noise trends with configuration and test condition changes, and good comparison of absolute noise measurements with the corrections used except for the isolated rotor case. Noise measurements of the isolated rotor show a great deal of scatter reflecting the fact that the rotor in hover is basically unstable.
Wind tunnel investigation of helicopter-rotor wake effects on three helicopter fuselage models
NASA Technical Reports Server (NTRS)
Wilson, J. C.; Mineck, R. E.
1975-01-01
The effects of rotor wake on helicopter fuselage aerodynamic characteristics were investigated in the Langley V/STOL tunnel. Force, moment, and pressure data were obtained on three fuselage models at various combinations of windspeed, sideslip angle, and pitch angle. The data show that the influence of rotor wake on the helicopter fuselage yawing moment imposes a significant additional thrust requirement on the tail rotor of a single-rotor helicopter at high sideslip angles.
Correlation of full-scale helicopter rotor performance in air with model-scale Freon data
NASA Technical Reports Server (NTRS)
Yeager, W. T., Jr.; Mantay, W. R.
1976-01-01
An investigation was conducted in a transonic dynamics tunnel to measure the performance of a 1/5 scale model helicopter rotor in a Freon atmosphere. Comparisons were made between these data and full scale data obtained in air. Both the model and full scale tests were conducted at advance ratios between 0.30 and 0.40 and advancing tip Mach numbers between 0.79 and 0.95. Results show that correlation of model scale rotor performance data obtained in Freon with full scale rotor performance data in air is good with regard to data trends. Mach number effects were found to be essentially the same for the model rotor performance data obtained in Freon and the full scale rotor performance data obtained in air. It was determined that Reynolds number effects may be of the same magnitude or smaller than rotor solidity effects or blade elastic modeling in rotor aerodynamic performance testing.
Modelling pressure rolling of asymmetric rolling process
NASA Astrophysics Data System (ADS)
Alexa, V.; Ratiu, S. A.; Kiss, I.; Cioata, V. G.
2017-05-01
The paper presents a comparative analysis between experimental results and modelling in order to interpret the value of the contact pressure on the asymmetric longitudinal rolling. It is also intended action and the different behaviour of upper cylinder compared to the lower cylinder action in situations when both are driven, or only one operates. In the modelling will be presented on the basis of boundary conditions imposed rolling pressure variation in the degree of reduction and also re size arc length of contact. Determining a curve is also important to determine the locus of points which characterize symmetry conditions partial rolling process between unequal diameters cylinders.
A mathematical model of bird collisions with wind turbine rotors
Tucker, V.A.
1996-11-01
When a bird flies through the disk swept out by the blades of a wind turbine rotor, the probability of collision depends on the motions and dimensions of the bird and the blades. The collision model in this paper predicts the probability for birds that glide upwind, downwind, an across the wind past simple one-dimensional blades represented by straight lines, and upwind and downwind past more realistic three-dimensional blades with chord and twist. Probabilities vary over the surface of the disk, and in most cases, the tip of the blade is less likely to collide with a bird than parts of the blade nearer the hub. The mean probability may be found by integration over the disk area. The collision model identifies the rotor characteristics that could be altered to make turbines safer for birds.
Rotor stability estimation with competing tilting pad bearing models
NASA Astrophysics Data System (ADS)
Cloud, C. Hunter; Maslen, Eric H.; Barrett, Lloyd E.
2012-05-01
When predicting the stability of rotors supported by tilting pad journal bearings, it is currently debated whether or not the bearings should be represented with frequency dependent dynamics. Using an experimental apparatus, measurements of pad temperatures, unbalance response and stability are compared with modeling predictions for two tilting pad bearing designs. Predictions based on frequency dependent tilting pad bearing dynamics exhibited significantly better correlation with the stability measurements than those assuming frequency independent dynamics.
Centrifuge Rotor Models: A Comparison of the Euler-Lagrange and the Bond Graph Modeling Approach
NASA Technical Reports Server (NTRS)
Granda, Jose J.; Ramakrishnan, Jayant; Nguyen, Louis H.
2006-01-01
A viewgraph presentation on centrifuge rotor models with a comparison using Euler-Lagrange and bond graph methods is shown. The topics include: 1) Objectives; 2) MOdeling Approach Comparisons; 3) Model Structures; and 4) Application.
Preliminary Study of a Model Rotor in Descent
NASA Technical Reports Server (NTRS)
McAlister, K. W.; Tung, C.; Sharpe, D. L.; Huang, S.; Hendley, E. M.
2000-01-01
Within a program designed to develop experimental techniques for measuring the trajectory and structure of vortices trailing from the tips of rotor blades, the present preliminary study focuses on a method for quantifying the trajectory of the trailing vortex during descent flight conditions. This study also presents rotor loads and blade surface pressures for a range of tip-path plane angles and Mach numbers. Blade pressures near the leading edge and along the outer radius are compared with data obtained on the same model rotor, but in open jet facilities. A triangulation procedure based on two directable laser-light sheets, each containing an embedded reference, proved effective in defining the spatial coordinates of the trailing vortex. When interrogating a cross section of the flow that contains several trailing vortices, the greatest clarity was found to result when the flow is uniformly seeded. Surface pressure responses during blade-vortex interactions appeared equally sensitive near the leading edge and along the outer portion of the blade, but diminished rapidly as the distance along the blade chord increased. The pressure response was virtually independent of whether the tip-path plane angle was obtained through shaft tilt or cyclic pitch. Although the shape and frequency of the pressure perturbations on the advancing blade during blade-vortex interaction are similar to those obtained in open-jet facilities, the angle of the tip-path plane may need to be lower than the range covered in this study.
Analytical model of rotor wake aerodynamics in ground effect
NASA Technical Reports Server (NTRS)
Saberi, H. A.
1983-01-01
The model and the computer program developed provides the velocity, location, and circulation of the tip vortices of a two-blade helicopter in and out of the ground effect. Comparison of the theoretical results with some experimental measurements for the location of the wake indicate that there is excellent accuracy in the vicinity of the rotor and fair amount of accuracy far from it. Having the location of the wake at all times enables us to compute the history of the velocity and the location of any point in the flow. The main goal of out study, induced velocity at the rotor, can also be calculated in addition to stream lines and streak lines. Since the wake location close to the rotor is known more accurately than at other places, the calculated induced velocity over the disc should be a good estimate of the real induced velocity, with the exception of the blade location, because each blade was replaced only by a vortex line. Because no experimental measurements of the wake close to the ground were available to us, quantitative evaluation of the theoretical wake was not possible. But qualitatively we have been able to show excellent agreement. Comparison of flow visualization with out results has indicated the location of the ground vortex is estimated excellently. Also the flow field in hover is well represented.
Model helicopter rotor high-speed impulsive noise: Measured acoustics and blade pressures
NASA Technical Reports Server (NTRS)
Boxwell, D. A.; Schmitz, F. H.; Splettstoesser, W. R.; Schultz, K. J.
1983-01-01
A 1/17-scale research model of the AH-1 series helicopter main rotor was tested. Model-rotor acoustic and simultaneous blade pressure data were recorded at high speeds where full-scale helicopter high-speed impulsive noise levels are known to be dominant. Model-rotor measurements of the peak acoustic pressure levels, waveform shapes, and directively patterns are directly compared with full-scale investigations, using an equivalent in-flight technique. Model acoustic data are shown to scale remarkably well in shape and in amplitude with full-scale results. Model rotor-blade pressures are presented for rotor operating conditions both with and without shock-like discontinuities in the radiated acoustic waveform. Acoustically, both model and full-scale measurements support current evidence that above certain high subsonic advancing-tip Mach numbers, local shock waves that exist on the rotor blades ""delocalize'' and radiate to the acoustic far-field.
An Incidence Loss Model for Wave Rotors with Axially Aligned Passages
NASA Technical Reports Server (NTRS)
Paxson, Daniel E.
1998-01-01
A simple mathematical model is described to account for the losses incurred when the flow in the duct (port) of a wave rotor is not aligned with the passages. The model, specifically for wave rotors with axially aligned passages, describes a loss mechanism which is sensitive to incident flow angle and Mach number. Implementation of the model in a one-dimensional CFD based wave rotor simulation is presented. Comparisons with limited experimental results are consistent with the model. Sensitivity studies are presented which highlight the significance of the incidence loss relative to other loss mechanisms in the wave rotor.
Wind-tunnel acoustic results of two rotor models with several tip designs
NASA Technical Reports Server (NTRS)
Martin, R. M.; Connor, A. B.
1986-01-01
A three-phase research program has been undertaken to study the acoustic signals due to the aerodynamic interaction of rotorcraft main rotors and tail rotors. During the first phase, two different rotor models with several interchangeable tips were tested in the Langley 4- by 7-Meter Tunnel on the U.S. Army rotor model system. An extensive acoustic data base was acquired, with special emphasis on blade-vortex interaction (BVI) noise. The details of the experimental procedure, acoustic data acquisition, and reduction are documented. The overall sound pressure level (OASPL) of the high-twist rotor systems is relatively insensitive to flight speed but generally increases with rotor tip-path-plane angle. The OASPL of the high-twist rotors is dominated by acoustic energy in the low-frequency harmonics. The OASPL of the low-twist rotor systems shows more dependence on flight speed than the high-twist rotors, in addition to being quite sensitive to tip-path-plane angle. An integrated band-limited sound pressure level, limited by 500 to 3000 Hz, is a useful metric to quantify the occurrence of BVI noise. The OASPL of the low-twist rotors is strongly influenced by the band-limited sound levels, indicating that the blade-vortex impulsive noise is a dominant noise source for this rotor design. The midfrequency acoustic levels for both rotors show a very strong dependence on rotor tip-path-plane angle. The tip-path-plane angle at which the maximum midfrequency sound level occurs consistently decreases with increasing flight speed. The maximum midfrequency sound level measured at a given location is constant regardless of the flight speed.
Flap motion of helicopter rotors with novel, dynamic stall model
NASA Astrophysics Data System (ADS)
Han, Wei; Liu, Jie; Liu, Chun; Chen, Lei; Su, Xichao; Zhao, Peng
2016-01-01
In this paper, a nonlinear flapping equation for large inflow angles and flap angles is established by analyzing the aerodynamics of helicopter blade elements. In order to obtain a generalized flap equation, the Snel stall model was first applied to determine the lift coefficient of the helicopter rotor. A simulation experiment for specific airfoils was then conducted to verify the effectiveness of the Snel stall model as it applies to helicopters. Results show that the model requires no extraneous parameters compared to the traditional stall model and is highly accurate and practically applicable. Based on the model, the relationship between the flapping angle and the angle of attack was analyzed, as well as the advance ratio under the dynamic stall state.
An advanced stochastic model for threshold crossing studies of rotor blade vibrations.
NASA Technical Reports Server (NTRS)
Gaonkar, G. H.; Hohenemser, K. H.
1972-01-01
A stochastic model to analyze turbulence-excited rotor blade vibrations, previously described by Gaonkar et al. (1971), is generalized to include nonuniformity of the atmospheric turbulence velocity across the rotor disk in the longitudinal direction. The results of the presented analysis suggest that the nonuniformity of the vertical turbulence over the rotor disk is of little influence on the random blade flapping response, at least as far as longitudinal nonuniformity is concerned.
Stability Analysis of a Spinning and Precessing Viscoelastic Rotor Model
NASA Astrophysics Data System (ADS)
Bose, S.; Nandi, A.; Neogy, S.
2013-10-01
The present work deals with stability analysis of a spinning and precessing gyroscopic systems, where the spin axis and precession axis intersect at right angle. The nutation speed is zero, the spin and precession speeds are considered to be uniform and the precession axis is located at one end of the shaft. The properties of the shaft material correspond to a four element type linear viscoelastic model. The shaft disk system is assumed to be axially and torsionally stiff. For analysis, a simple rotor has been considered with the rigid disk placed on a massless viscoelastic shaft at specified locations from one end of the shaft. The governing parametric equations for such a rotor are derived in the simultaneously spinning and precessing frame. A stability analysis is performed considering both two- and four-degree of freedom models. The stability borderlines are computed considering spin and precession speeds as parameters. It is shown that though viscoelastic material may appear attractive for its large material damping, for gyroscopic systems it may lead to unstable vibrations.
Modeling Disk Cracks in Rotors by Utilizing Speed Dependent Eccentricity
NASA Astrophysics Data System (ADS)
Gyekenyesi, Andrew L.; Sawicki, Jerzy T.; Haase, Wayne C.
2010-03-01
This paper discusses the feasibility of vibration-based structural health monitoring for detecting disk cracks in rotor systems. The approach of interest assumes that a crack located on a rotating disk causes a minute change in the system’s center of mass due to the centrifugal force induced opening of the crack. The center of mass shift is expected to reveal itself in the vibration vector (i.e., whirl response; plotted as amplitude and phase versus speed) gathered during a spin-up and/or spin-down test. Here, analysis is accomplished by modeling a Jeffcott rotor that is characterized by analytical, numerical, and experimental data. The model, which has speed dependent eccentricity, is employed in order to better understand the sensitivity of the approach. For the experimental set-up emulated here (i.e., a single disk located mid-span on a flexible shaft), it appears that a rather sizable flaw in the form of a through-thickness notch could be detected by monitoring the damage-induced shift in center of mass. Although, identifying actual disk cracks in complex “real world” environments, where noncritical crack lengths are small and excessive mechanical and/or electrical noise are present, would prove to be rather challenging. Further research is needed in this regard.
Acoustic characteristics of 1/20-scale model helicopter rotors
NASA Technical Reports Server (NTRS)
Shenoy, Rajarama K.; Kohlhepp, Fred W.; Leighton, Kenneth P.
1986-01-01
A wind tunnel test to study the effects of geometric scale on acoustics and to investigate the applicability of very small scale models for the study of acoustic characteristics of helicopter rotors was conducted in the United Technologies Research Center Acoustic Research Tunnel. The results show that the Reynolds number effects significantly alter the Blade-Vortex-Interaction (BVI) Noise characteristics by enhancing the lower frequency content and suppressing the higher frequency content. In the time domain this is observed as an inverted thickness noise impulse rather than the typical positive-negative impulse of BVI noise. At higher advance ratio conditions, in the absence of BVI, the 1/20 scale model acoustic trends with Mach number follow those of larger scale models. However, the 1/20 scale model acoustic trends appear to indicate stall at higher thrust and advance ratio conditions.
a Uqp(u2) Rotor Model for Rotational Bands of Superdeformed Nuclei
NASA Astrophysics Data System (ADS)
Barbier, R.; Meyer, J.; Kibler, M.
A nonrigid rotor model is developed from the two-parameter quantum algebra Uqp(u2). (This model presents the Uqp(u2) symmetry and shall be refered to as the qp-rotor model.) A rotational energy formula as well as a qp-deformation of E2 reduced transition probabilities are derived. The qp-rotor model is applied (through fitting procedures) to twenty rotational bands of superdeformed nuclei in the A~130, 150, and 190 mass regions. Systematic comparisons between the qp-rotor model and the q-rotor model of Raychev, Roussev, and Smirnov, on one hand, and a basic three-parameter model, on the other, are performed on energy spectra, on dynamical moments of inertia and on B(E2) values. The physical significance of the deformation parameters q and p is discussed.
Gonzales, Matthew J.; Vincent, Kevin P.; Rappel, Wouter-Jan; Narayan, Sanjiv M.; McCulloch, Andrew D.
2014-01-01
Aims The aim of this study was to investigate structural contributions to the maintenance of rotors in human atrial fibrillation (AF) and possible mechanisms of termination. Methods and results A three-dimensional human biatrial finite element model based on patient-derived computed tomography and arrhythmia observed at electrophysiology study was used to study AF. With normal physiological electrical conductivity and effective refractory periods (ERPs), wave break failed to sustain reentrant activity or electrical rotors. With depressed excitability, decreased conduction anisotropy, and shorter ERP characteristic of AF, reentrant rotors were readily maintained. Rotors were transiently or permanently trapped by fibre discontinuities on the lateral wall of the right atrium near the tricuspid valve orifice and adjacent to the crista terminalis, both known sites of right atrial arrhythmias. Modelling inexcitable regions near the rotor tip to simulate fibrosis anchored the rotors, converting the arrhythmia to macro-reentry. Accordingly, increasing the spatial core of inexcitable tissue decreased the frequency of rotation, widened the excitable gap, and enabled an external wave to impinge on the rotor core and displace the source. Conclusion These model findings highlight the importance of structural features in rotor dynamics and suggest that regions of fibrosis may anchor fibrillatory rotors. Increasing extent of fibrosis and scar may eventually convert fibrillation to excitable gap reentry. Such macro-reentry can then be eliminated by extending the obstacle or by external stimuli that penetrate the excitable gap. PMID:25362167
Asymmetric Subductions in an Asymmetric Earth: Geodynamics and Numerical Modeling
NASA Astrophysics Data System (ADS)
Dal Zilio, L.; Ficini, E.; Doglioni, C.; Gerya, T.
2016-12-01
The driving mechanism of plate tectonics is still controversial. Moreover, mantle kinematics is still poorly constrained due to the limited information available on its composition, thermal state, and physical parameters. The net rotation of the lithosphere, or so-called W-ward drift, however, indicates a decoupling of the plates relative to the underlying asthenosphere at about 100-200 km depth in the Low-Velocity Zone and a relative "E-ward" mantle counterflow. This mantle flow can account for a number of tectonic asymmetries on subduction dynamics such as steep versus shallow slab dip, diverging versus converging subduction hinge, low versus high topography of mountain belts, etc. This asymmetry is generally interpreted to reflect the age-dependent negative buoyancy of the subducting lithosphere. However, slab dip is insensitive to the age of the lithosphere. Here we investigate the role of mantle flow in controlling subduction dynamics using a high-resolution rheologically consistent two-dimensional numerical modeling. Results show the evolution of a subducting oceanic plate beneath a continent: when the subducting plate is dipping in opposite direction with respect to the mantle flow, the slab is sub-vertically deflected by the mantle flow, thus leading the coeval development of a back-arc basin. In contrast, agreement between mantle flow and dipping of the subducting slab relieves shallow dipping subduction zone, which in turn controls the development of a pronounced topography. Moreover, this study confirms that the age of the subducting oceanic lithosphere (i.e. its negative buoyancy) has a second order effect on the dip angle of the slab and, more generally, on subduction dynamics. Our numerical experiments show strong similarities to the observed evolution of subduction zone worldwide and demonstrate that the possibility of a horizontal mantle flow is universally valid.
Experimentally determined flutter from two- and three-bladed model bearingless rotors in hover
NASA Technical Reports Server (NTRS)
Bousman, W. G.; Dawson, S.
1985-01-01
A series of experiments was performed on a 1.8-m-diam model rotor in hover for the principal purpose of investigating the lead-lag stability of isolated bearingless rotors. Incidental to those tests, at least three types of pitch-flap flutter were encountered. Type 1 flutter occurred approximately at the second flap-mode frequency on both two-and three-bladed rotors for both small and large pitch angles and appeared to be a classic pitch-flap flutter. Type 2 flutter showed mostly torsional motion and was seen on both two- and three-bladed rotors. Type 3 flutter was a regressing flap flutter that occurred for only the three-bladed rotor configurations and appears to be a wake excited flutter. Although flutter occurred on a number of different configurations, no rotor parameters were identified that were clearly stabilizing or destabilizing.
Reduction of high-speed impulsive noise by blade planform modification of a model helicopter rotor
NASA Technical Reports Server (NTRS)
Conner, D. A.; Hoad, D. R.
1982-01-01
The reduction of high speed impulsive noise for the UH-1H helicopter was investigated by using an advanced main rotor system. The advanced rotor system had a tapered blade planform compared with the rectangular planform of the standard rotor system. Models of both the advanced main rotor system and the UH-1H standard main rotor system were tested at 1/4 scale in the 4 by 7 Meter Tunnel. In plane acoustic measurements of the high speed impulsive noise demonstrated that the advanced rotor system on the UH-1H helicopter reduced the high speed impulsive noise by up to 20 dB, with a reduction in overall sound pressure level of up to 5 dB.
NASA Technical Reports Server (NTRS)
Marr, R. L.; Sambell, K. W.; Neal, G. T.
1973-01-01
Stability and control tests of a scale model of a tilt rotor research aircraft were conducted. The characteristics of the model for hover, low speed, and conversion flight were analyzed. Hover tests were conducted in a rotor whirl cage. Helicopter and conversion tests were conducted in a low speed wind tunnel. Data obtained from the tests are presented as tables and graphs. Diagrams and illustrations of the test equipment are provided.
Rigid rotor as a toy model for Hodge theory
NASA Astrophysics Data System (ADS)
Gupta, Saurabh; Malik, R. P.
2010-07-01
We apply the superfield approach to the toy model of a rigid rotor and show the existence of the nilpotent and absolutely anticommuting Becchi-Rouet-Stora-Tyutin (BRST) and anti-BRST symmetry transformations, under which, the kinetic term and the action remain invariant. Furthermore, we also derive the off-shell nilpotent and absolutely anticommuting (anti-) co-BRST symmetry transformations, under which, the gauge-fixing term and the Lagrangian remain invariant. The anticommutator of the above nilpotent symmetry transformations leads to the derivation of a bosonic symmetry transformation, under which, the ghost terms and the action remain invariant. Together, the above transformations (and their corresponding generators) respect an algebra that turns out to be a physical realization of the algebra obeyed by the de Rham cohomological operators of differential geometry. Thus, our present model is a toy model for the Hodge theory.
Symmetry in the Generalized Rotor Model for Extremely Floppy Molecules
NASA Astrophysics Data System (ADS)
Schmiedt, Hanno; Jensen, Per; Schlemmer, Stephan
2016-06-01
Protonated methane CH_5^+ is unique: It is an extremely fluxional molecule. All attempts to assign quantum numbers to the high-resolution transitions obtained over the last 20 years have failed because molecular rotation and vibration cannot be separated in the conventional way. The first step towards a theoretical description is to include internal rotational degrees of freedom into the overall ones, which can be used to formulate a fundamentally new zero order approximation for the (now) generalized rotational states and energies. Predictions from this simple five-dimensional rotor model compare very favorably with the combination differences of protonated methane found in recent low temperature experiments. This talk will focus on symmetry aspects and implications of permutation symmetry for the generalized rotational states. Furthermore, refinements of the theory will be discussed, ranging from the generalization to even higher-dimensional rotors to explicit symmetry breaking and corresponding energy splittings. The latter includes the link to well-known theories of internal rotation dynamics and will show the general validity of the presented theory. Schmiedt, H., et al.; J. Chem. Phys. 143 (15), 154302 (2015) Wodraszka, R. et al.; J. Phys. Chem. Lett. 6, 4229-4232 (2015) Asvany, O. et al.; Science, 347, (6228), 1346-1349 (2015)
Numerical Modeling of Dependence of Separative Power of the Gas Centrifuge on the Length of Rotor
NASA Astrophysics Data System (ADS)
Bogovalov, S. V.; Borisevich, V. D.; Borman, V. D.; Tronin, I. V.; Tronin, V. N.
Numerical modelling and optimization of the gas flow and isotope separation in the Iguasu gas centrifuge (GC) for uranium enrichment have been performed for different lengths of the rotor. The calculations show that the specific separative power of the GC reduces with the length of the rotor. We show that the reduction of the specific separative power is connected with the growth of the pressure in the optimal regime and corresponding growth of temperature to prevent the working gas sublimation. The specific separative power remains constant with the growth of the rotor length provided that the temperature of the rotor is taken to be constant.
Theory and Modeling of Asymmetric Catalytic Reactions.
Lam, Yu-Hong; Grayson, Matthew N; Holland, Mareike C; Simon, Adam; Houk, K N
2016-04-19
Modern density functional theory and powerful contemporary computers have made it possible to explore complex reactions of value in organic synthesis. We describe recent explorations of mechanisms and origins of stereoselectivities with density functional theory calculations. The specific functionals and basis sets that are routinely used in computational studies of stereoselectivities of organic and organometallic reactions in our group are described, followed by our recent studies that uncovered the origins of stereocontrol in reactions catalyzed by (1) vicinal diamines, including cinchona alkaloid-derived primary amines, (2) vicinal amidophosphines, and (3) organo-transition-metal complexes. Two common cyclic models account for the stereoselectivity of aldol reactions of metal enolates (Zimmerman-Traxler) or those catalyzed by the organocatalyst proline (Houk-List). Three other models were derived from computational studies described in this Account. Cinchona alkaloid-derived primary amines and other vicinal diamines are venerable asymmetric organocatalysts. For α-fluorinations and a variety of aldol reactions, vicinal diamines form enamines at one terminal amine and activate electrophilically with NH(+) or NF(+) at the other. We found that the stereocontrolling transition states are cyclic and that their conformational preferences are responsible for the observed stereoselectivity. In fluorinations, the chair seven-membered cyclic transition states is highly favored, just as the Zimmerman-Traxler chair six-membered aldol transition state controls stereoselectivity. In aldol reactions with vicinal diamine catalysts, the crown transition states are favored, both in the prototype and in an experimental example, shown in the graphic. We found that low-energy conformations of cyclic transition states occur and control stereoselectivities in these reactions. Another class of bifunctional organocatalysts, the vicinal amidophosphines, catalyzes the (3 + 2) annulation
Model rotor high-speed impulsive noise - Parametric variations and full-scale comparisons
NASA Astrophysics Data System (ADS)
Splettstoesser, W. R.; Schultz, K. J.; Schmitz, F. H.; Boxwell, D. A.
1983-05-01
The results of a 1/7-scale model of the AH-1 series helicopter main rotor test in the German-Dutch anechoic wind tunnel are discussed, with emphasis given on exploring the important scaling parameters of helicopter-rotor high-speed impulsive noise. Nondimensional parameters are derived from the governing equations and employed to compare the model rotor measurements with full-scale investigations, using an equivalent in-flight technique. The peak acoustic pressure, impulsive noise directivity, and acoustic waveform of the model are found to scale well in shape and in amplitude with full-scale results. Parametric variations of the model-rotor acoustic measurements, such as the change of the high-speed impulsive noise level over a range of advancing-tip Mach numbers at constant advance ratio or constant velocity, are presented. It is concluded that model-scale rotors can be used to explore potential acoustic design innovations on full-scale helicopters.
Vibration model of rolling element bearings in a rotor-bearing system for fault diagnosis
NASA Astrophysics Data System (ADS)
Cong, Feiyun; Chen, Jin; Dong, Guangming; Pecht, Michael
2013-04-01
Rolling element bearing faults are among the main causes of breakdown in rotating machines. In this paper, a rolling bearing fault model is proposed based on the dynamic load analysis of a rotor-bearing system. The rotor impact factor is taken into consideration in the rolling bearing fault signal model. The defect load on the surface of the bearing is divided into two parts, the alternate load and the determinate load. The vibration response of the proposed fault signal model is investigated and the fault signal calculating equation is derived through dynamic and kinematic analysis. Outer race and inner race fault simulations are realized in the paper. The simulation process includes consideration of several parameters, such as the gravity of the rotor-bearing system, the imbalance of the rotor, and the location of the defect on the surface. The simulation results show that different amplitude contributions of the alternate load and determinate load will cause different envelope spectrum expressions. The rotating frequency sidebands will occur in the envelope spectrum in addition to the fault characteristic frequency. This appearance of sidebands will increase the difficulty of fault recognition in intelligent fault diagnosis. The experiments given in the paper have successfully verified the proposed signal model simulation results. The test rig design of the rotor bearing system simulated several operating conditions: (1) rotor bearing only; (2) rotor bearing with loader added; (3) rotor bearing with loader and rotor disk; and (4) bearing fault simulation without rotor influence. The results of the experiments have verified that the proposed rolling bearing signal model is important to the rolling bearing fault diagnosis of rotor-bearing systems.
NASA Technical Reports Server (NTRS)
Jambunathan, V.; Murthy, V. R.
1993-01-01
A generic mathematical model that is capable of accurately modeling the multiple load path bearingless rotor blade is developed. A comprehensive, finite element based solution for the natural vibration of the rotor blade is developed. An iterative scheme based on harmonic balance is used to evaluate the nonlinear response of the rotor to control inputs and a Newton-Raphson procedure is employed to evaluate the trim of rotorcraft. Linearized perturbation model of the nonlinear system are presented. The model is validated by comparing with existing whirl tower, wind tunnel and flight test results of BMR/BO-105 helicopter. Frequencies of two bearingless rotor blades compare well with results from experiments. Nonlinear response and trim results are presented for the bearingless BMR/BO-105 rotor. Aeroelastic stability in forward flight, evaluated using floquet theory agrees with test data in general.
Development of Motor Model of Rotor Slot Harmonics for Speed Sensorless Control of Induction Motor
NASA Astrophysics Data System (ADS)
Okubo, Tatsuya; Ishida, Muneaki; Doki, Shinji
This paper proposes a novel mathematical dynamic model to represent steady-state and transient-state characteristics of rotor slot harmonics of an induction motor for sensorless control. Although it is well known that the rotor slot harmonics originate from the mechanical structure of the induction motor, a mathematical model that describes the relationship between stator/rotor currents of the induction motor and the slot harmonics has not yet been proposed. Therefore, in this paper, a three-phase model of the induction motor that depicts the rotor slot harmonics is developed by taking into consideration the magnetomotive force harmonics and the change in the magnetic air gap caused by the rotor slots. Moreover, the validity of the proposed model is verified by comparing the experimental results and the calculated values.
Aerodynamic characteristics of a 1/6-scale powered model of the rotor systems research aircraft
NASA Technical Reports Server (NTRS)
Mineck, R. E.; Freeman, C. E.
1977-01-01
A wind-tunnel investigation was conducted to determine the effects of the main-rotor wake on the aerodynamic characteristics of the rotor systems research aircraft (RSRA). For the investigation, a 1/6-scale model with a four-blade articulated main rotor was used. Tests were conducted with and without the main rotor. Both the helicopter and the compound helicopter were tested. The latter configuration included the auxiliary thrust engines and the variable-incidence wing. Data were obtained over ranges of angle of attack, angle of sideslip, and main-rotor collective pitch angle at several main-rotor advance ratios. Results are presented for the total loads on the airframe as well as the loads on the rotor, the wing, and the tail. The results indicated that without the effect of the rotor wake, the RSRA had static longitudinal and directional stability and positive effective dihedral. With the effect of the main rotor and its wake, the RSRA exhibited longitudinal instability but retained static directional stability and positive effective dihedral.
Computation of rotor aerodynamic loads with a constant vorticity contour free wake model
NASA Technical Reports Server (NTRS)
Quackenbush, Todd R.; Wachspress, Daniel A.; Boschitsch, Alexander H.
1991-01-01
An analytical method is presented which facilitates the study of isolated rotors with an improved approach to wake simulation. Vortex filaments are simulated along contours of constant sheet strength for the sheet of vorticity resulting from each rotor blade. Curved vortex elements comprise the filaments which can be distorted by the local velocity field. Called the Constant Vorticity Contour wake model, the approach permits the simulation of the blades' wakes corresponding to the full span of the rotor blade. The discretization of the wake of the rotor blade produces spacing and structure that are consistent with the spatial and temporal variations in the loading. A vortex-lattice aerodynamic model of the blade is also included which introduces a finite-element structural model of the blade and consideration of the force and moment trim analysis. Results of the present version of the simulation, called RotorCRAFT, are found to correlate well with H-34 flight-test data.
NASA Technical Reports Server (NTRS)
Korkan, K. D.; Cross, E. J., Jr.; Cornell, C. C.
1984-01-01
An experimental study utilizing a remote controlled model helicopter has been conducted to measure the performance degradation due to simulated ice accretion on the leading edge of the main rotor for hover and forward flight. The 53.375 inch diameter main rotor incorporates a NACA 0012 airfoil with a generic ice shape corresponding to a specified natural ice condition. Thrust coefficients and torque coefficients about the main rotor were measured as a function of velocity, main rotor RPM, angle-of-incidence of the fuselage, collective pitch angle, and extent of spanwise ice accretion. An experimental airfoil data bank has been determined using a two-dimensional twenty-one inch NACA 0012 airfoil with scaled ice accretion shapes identical to that used on the model helicopter main rotor. The corresponding experimental data are discussed with emphasis on Reynolds number effects and ice accretion scale model testing.
NASA Technical Reports Server (NTRS)
Korkan, K. D.; Cross, E. J., Jr.; Cornell, C. C.
1984-01-01
An experimental study utilizing a remote controlled model helicopter has been conducted to measure the performance degradation due to simulated ice accretion on the leading edge of the main rotor for hover and forward flight. The 53.375 inch diameter main rotor incorporates a NACA 0012 airfoil with a generic ice shape corresponding to a specified natural ice condition. Thrust coefficients and torque coefficients about the main rotor were measured as a function of velocity, main rotor RPM, angle-of-incidence of the fuselage, collective pitch angle, and extent of spanwise ice accretion. An experimental airfoil data bank has been determined using a two-dimensional twenty-one inch NACA 0012 airfoil with scaled ice accretion shapes identical to that used on the model helicopter main rotor. The corresponding experimental data are discussed with emphasis on Reynolds number effects and ice accretion scale model testing.
NASA Technical Reports Server (NTRS)
Fisher, R. K., Jr.; Tompkins, J. E.; Bobo, C. J.; Child, R. F.
1971-01-01
A wind tunnel test program was conducted on an eight foot diameter model rotor system to determine blade element airloads characteristics in the unstalled and stalled flight regimes. The fully articulated model rotor system utilized three blades with a Vertol 23010-1.58 airfoil section, the blades being 1/7.5 scale models of the Ch-47C rotor blades. Instrumentation was incorporated at the blade 75% radial station to measure pressure and skin friction distributions, surface streamline directions and local angle of attack. The test program was conducted in three phases; non-rotating, hover and forward flight at advance ratios of 0.15, 0.35 and 0.60. Test data were analyzed with respect to providing insight to the mechanisms affecting blade stall, particularly retreating blade stall during forward flight conditions. From such data, an assessment was made as to the applicability of current theoretical analyses used for the prediction of blade element airloads in the stall regime.
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.
An Evolving Asymmetric Game for Modeling Interdictor-Smuggler Problems
2016-06-01
ASYMMETRIC GAME FOR MODELING INTERDICTOR-SMUGGLER PROBLEMS by Richard J. Allain June 2016 Thesis Advisor: David L. Alderson Second Reader: W...DATES COVERED Master’s thesis 4. TITLE AND SUBTITLE AN EVOLVING ASYMMETRIC GAME FOR MODELING INTERDICTOR- SMUGGLER PROBLEMS 5. FUNDING NUMBERS 6...is unlimited 12b. DISTRIBUTION CODE A 13. ABSTRACT (maximum 200 words) We propose a novel network interdiction model that reconciles many
Model rotor icing tests in the NASA Lewis icing research tunnel
NASA Technical Reports Server (NTRS)
Flemming, Robert J.; Britton, Randall K.; Bond, Thomas H.
1991-01-01
Tests of a lightly instrumented two-bladed teetering rotor and a heavily instrumented sub-scale articulated main rotor were conducted in the NASA Lewis Research Center Icing Research Tunnel (IRT) in August 1988 and September and November 1989. The first was an OH-58 tail rotor which had a diameter of 1.575 m and a blade chord of 0.133 m, and was mounted on a NASA designed test rig. The second, a four bladed articulated rotor, had a diameter of 1.83 m with 0.124 m chord blades specially fabricated for the experiment. This rotor was mounted on a Sikorsky Aircraft Powered Force Model, which enclosed a rotor balance and other measurement systems. The models were exposed to variations in temperature, liquid water content, and medium droplet diameter, and were operated over ranges of advance ratio, shaft angle, tip Mach number (rotor speed), and weight coefficient to determine the effect of these parameters on ice accretion. In addition to strain gage and balance data, the test was documented with still, video, and high speed photography, ice profile tracing, and ice molds. Presented here are the sensitivity of the model rotors to the test parameters and a comparison of the results to theoretical predictions.
NASA Technical Reports Server (NTRS)
Bousman, William G.
1988-01-01
Three cases were selected for correlation from an experiment that examined the aeromechanical stability of a small-scale model of a hingeless rotor and fuselage in hover. The first case examined the stability of a configuration with 0 degree blade pitch so that coupling between dynamic modes was minimized. The second case was identical to the first except the blade pitch was set to 9 degrees which provides flap-lag coupling of the rotor modes. The third case had 9 degrees of blade pitch and also included negative pitch-lag coupling, and therefore was the most highly coupled configuration. Analytical calculations were made by Bell Helicopter Textron, Boeing Vertol, Hughes Helicopters, Sikorsky Aircraft, the U.S. Army Aeromechanics Laboratory, and NASA Ames Research Center and compared to some or all of the experimental cases. Overall, the correlation ranged from very poor-to-poor to good.
Analysis of the wind tunnel test of a tilt rotor power force model
NASA Technical Reports Server (NTRS)
Marr, R. L.; Ford, D. G.; Ferguson, S. W.
1974-01-01
Two series of wind tunnel tests were made to determine performance, stability and control, and rotor wake interaction on the airframe, using a one-tenth scale powered force model of a tilt rotor aircraft. Testing covered hover (IGE/OCE), helicopter, conversion, and airplane flight configurations. Forces and moments were recorded for the model from predetermined trim attitudes. Control positions were adjusted to trim flight (one-g lift, pitching moment and drag zero) within the uncorrected test data balance accuracy. Pitch and yaw sweeps were made about the trim attitudes with the control held at the trimmed settings to determine the static stability characteristics. Tail on, tail off, rotors on, and rotors off configurations were testes to determine the rotor wake effects on the empennage. Results are presented and discussed.
Vibratory Loads Data from a Wind-Tunnel Test of Structurally Tailored Model Helicopter Rotors
NASA Technical Reports Server (NTRS)
Yeager, William T., Jr.; Hamouda, M-Nabil H.; Idol, Robert F.; Mirick, Paul H.; Singleton, Jeffrey D.; Wilbur, Matthew L.
1991-01-01
An experimental study was conducted in the Langley Transonic Dynamics Tunnel to investigate the use of a Bell Helicopter Textron (BHT) rotor structural tailoring concept, known as rotor nodalization, in conjunction with advanced blade aerodynamics as well as to evaluate rotor blade aerodynamic design methodologies. A 1/5-size, four-bladed bearingless hub, three sets of Mach-scaled model rotor blades were tested in forward flight from transition up to an advance ratio of 0.35. The data presented pertain only to the evaluation of the structural tailoring concept and consist of fixed-system and rotating system vibratory loads. These data will be useful for evaluating the effects of tailoring blade structural properties on fixed-system vibratory loads, as well as validating analyses used in the design of advanced rotor systems.
Takeoff/approach noise for a model counterrotation propeller with a forward-swept upstream rotor
NASA Technical Reports Server (NTRS)
Woodward, Richard P.; Hall, David G.; Podboy, Gary G.; Jeracki, Robert J.
1993-01-01
A scale model of a counterrotating propeller with forward-swept blades in the forward rotor and aft-swept blades in the aft rotor (designated F39/A31) has been tested in the NASA Lewis 9- by 15-Foot Anechoic Wind Tunnel. This paper presents aeroacoustic results at a takeoff/approach condition of Mach 0.20. Laser Doppler Velocimeter results taken in a plane between the two rotors are also included to quantify the interaction flow field. The intention of the forward-swept design is to reduce the magnitude of the forward rotor tip vortex and/or wakes which impinge on the aft rotor, thus lowering the interaction tone levels.
NASA Astrophysics Data System (ADS)
Laiho, Antti; Holopainen, Timo P.; Klinge, Paul; Arkkio, Antero
2007-05-01
In this work the effects of the electromechanical interaction on rotordynamics and vibration characteristics of cage rotor electrical machines were considered. An eccentric rotor motion distorts the electromagnetic field in the air-gap between the stator and rotor inducing a total force, the unbalanced magnetic pull, exerted on the rotor. In this paper a low-order parametric model for the unbalanced magnetic pull is coupled with a three-dimensional finite element structural model of the electrical machine. The main contribution of the work is to present a computationally efficient electromechanical model for vibration analysis of cage rotor machines. In this model, the interaction between the mechanical and electromagnetic systems is distributed over the air gap of the machine. This enables the inclusion of rotor and stator deflections into the analysis and, thus, yields more realistic prediction for the effects of electromechanical interaction. The model was tested by implementing it for two electrical machines with nominal speeds close to one of the rotor bending critical speeds. Rated machine data was used in order to predict the effects of the electromechanical interaction on vibration characteristics of the example machines.
CAA modeling of helicopter main rotor in hover
NASA Astrophysics Data System (ADS)
Kusyumov, Alexander N.; Mikhailov, Sergey A.; Batrakov, Andrey S.; Kusyumov, Sergey A.; Barakos, George
In this work rotor aeroacoustics in hover is considered. Farfield observers are used and the nearfield flow parameters are obtained using the in house HMB and commercial Fluent CFD codes (identical hexa-grids are used for both solvers). Farfield noise at a remote observer position is calculated at post processing stage using FW-H solver implemented in Fluent and HMB. The main rotor of the UH-1H helicopter is considered as a test case for comparison to experimental data. The sound pressure level is estimated for different rotor blade collectives and observation angles.
Effects of Different Rub Models on Simulated Rotor Dynamics
1984-02-01
disks were overhung thermal mismatch, rotor imbalance, high "g" maneuver and the third was centered with respect to the bearing loads, aerodynamic...system Aas assumed to be balanced prior to It is known that rotor rubs can have an important blade loss and operating at 160 Hz (9550 rpm). The blade...that can drive a rotor 130 -Mmn (5-mil) mass eccentricity in only one of the to whiI in a direction opposite to the direction of overhung disks. Each
Performance of Gas Turbine Engines Using Wave Rotors Modeled
NASA Technical Reports Server (NTRS)
1997-01-01
A wave rotor is a device that can boost the pressure and temperature of an airflow. When used as part of the core of a gas turbine engine, a wave rotor can significantly improve the thrust or shaft horsepower by boosting the flow pressure without raising the turbine inlet temperature. The NASA Lewis Research Center's Aeropropulsion Analysis Office, which is identifying technologies and research opportunities that will enhance the technical and economic competitiveness of the U.S. aeronautics industry, is evaluating the wave rotor to quantify the potential benefits of this device. Preliminary studies such as these are critical to identifying technologies that have high payoffs.
Ugarte, Juan P; Orozco-Duque, Andrés; Tobón, Catalina; Kremen, Vaclav; Novak, Daniel; Saiz, Javier; Oesterlein, Tobias; Schmitt, Clauss; Luik, Armin; Bustamante, John
2014-01-01
There is evidence that rotors could be drivers that maintain atrial fibrillation. Complex fractionated atrial electrograms have been located in rotor tip areas. However, the concept of electrogram fractionation, defined using time intervals, is still controversial as a tool for locating target sites for ablation. We hypothesize that the fractionation phenomenon is better described using non-linear dynamic measures, such as approximate entropy, and that this tool could be used for locating the rotor tip. The aim of this work has been to determine the relationship between approximate entropy and fractionated electrograms, and to develop a new tool for rotor mapping based on fractionation levels. Two episodes of chronic atrial fibrillation were simulated in a 3D human atrial model, in which rotors were observed. Dynamic approximate entropy maps were calculated using unipolar electrogram signals generated over the whole surface of the 3D atrial model. In addition, we optimized the approximate entropy calculation using two real multi-center databases of fractionated electrogram signals, labeled in 4 levels of fractionation. We found that the values of approximate entropy and the levels of fractionation are positively correlated. This allows the dynamic approximate entropy maps to localize the tips from stable and meandering rotors. Furthermore, we assessed the optimized approximate entropy using bipolar electrograms generated over a vicinity enclosing a rotor, achieving rotor detection. Our results suggest that high approximate entropy values are able to detect a high level of fractionation and to locate rotor tips in simulated atrial fibrillation episodes. We suggest that dynamic approximate entropy maps could become a tool for atrial fibrillation rotor mapping.
Attraction of Rotors to the Pulmonary Veins in Paroxysmal Atrial Fibrillation: A Modeling Study
Calvo, Conrado J.; Deo, Makarand; Zlochiver, Sharon; Millet, José; Berenfeld, Omer
2014-01-01
Maintenance of paroxysmal atrial fibrillation (AF) by fast rotors in the left atrium (LA) or at the pulmonary veins (PVs) is not fully understood. To gain insight into this dynamic and complex process, we studied the role of the heterogeneous distribution of transmembrane currents in the PVs and LA junction (PV-LAJ) in the localization of rotors in the PVs. We also investigated whether simple pacing protocols could be used to predict rotor drift in the PV-LAJ. Experimentally observed heterogeneities in IK1, IKs, IKr, Ito, and ICaL in the PV-LAJ were incorporated into two- and pseudo three-dimensional models of Courtemanche-Ramirez-Nattel-Kneller human atrial kinetics to simulate various conditions and investigate rotor drifting mechanisms. Spatial gradients in the currents resulted in shorter action potential duration, minimum diastolic potential that was less negative, and slower upstroke and conduction velocity for rotors in the PV region than in the LA. Rotors under such conditions drifted toward the PV and stabilized at the shortest action potential duration and less-excitable region, consistent with drift direction under intercellular coupling heterogeneities and regardless of the geometrical constraint in the PVs. Simulations with various IK1 gradient conditions and current-voltage relationships substantiated its major role in the rotor drift. In our 1:1 pacing protocol, we found that among various action potential properties, only the minimum diastolic potential gradient was a rate-independent predictor of rotor drift direction. Consistent with experimental and clinical AF studies, simulations in an electrophysiologically heterogeneous model of the PV-LAJ showed rotor attraction toward the PV. Our simulations suggest that IK1 heterogeneity is dominant compared to other currents in determining the drift direction through its impact on the excitability gradient. These results provide a believed novel framework for understanding the complex dynamics of rotors
NASA Astrophysics Data System (ADS)
Chou, Y. C.; Hsiao, Yi-Feng; Hwang, Gwo-Jen; To, Kiwing
2016-02-01
The rotation of the γ subunit of F1-ATPase is stochastic, processive, unidirectional, reversible through an external torque, and stepwise with a slow rotation. We propose a mechanism that can explain these properties of the rotary molecular motor, and that can determine the direction of rotation. The asymmetric structures of the γ subunit, both at the tip of the shaft (C and N termini) and at the part (ɛ subunit) protruding from the α3β3 subunits, are critical. The torque required for stochastic rotation is generated from the impulsive reactive force due to the random collisions between the γ subunit and the quasihexagonal α3β3 subunits. The rotation is the result of the random motion of the confined asymmetric γ subunit. The steps originate from the chemical reactions of the γ subunit and physical interaction between the γ subunit and the flexible protrusions of the α3β3 subunits. An external torque as well as a configurational modification in the γ subunit (the central rotor) can reverse the rotational direction. We demonstrate the applicability of the mechanism to a macroscopic simulation system, which has the essential ingredients of the F1-ATPase structure, by reproducing the dynamic properties of the rotation.
Chou, Y C; Hsiao, Yi-Feng; Hwang, Gwo-Jen; To, Kiwing
2016-02-01
The rotation of the γ subunit of F(1)-ATPase is stochastic, processive, unidirectional, reversible through an external torque, and stepwise with a slow rotation. We propose a mechanism that can explain these properties of the rotary molecular motor, and that can determine the direction of rotation. The asymmetric structures of the γ subunit, both at the tip of the shaft (C and N termini) and at the part (ε subunit) protruding from the α(3)β(3) subunits, are critical. The torque required for stochastic rotation is generated from the impulsive reactive force due to the random collisions between the γ subunit and the quasihexagonal α(3)β(3) subunits. The rotation is the result of the random motion of the confined asymmetric γ subunit. The steps originate from the chemical reactions of the γ subunit and physical interaction between the γ subunit and the flexible protrusions of the α(3)β(3) subunits. An external torque as well as a configurational modification in the γ subunit (the central rotor) can reverse the rotational direction. We demonstrate the applicability of the mechanism to a macroscopic simulation system, which has the essential ingredients of the F(1)-ATPase structure, by reproducing the dynamic properties of the rotation.
Aerodynamic and acoustic test of a United Technologies model scale rotor at DNW
NASA Technical Reports Server (NTRS)
Yu, Yung H.; Liu, Sandy R.; Jordan, Dave E.; Landgrebe, Anton J.; Lorber, Peter F.; Pollack, Michael J.; Martin, Ruth M.
1990-01-01
The UTC model scale rotors, the DNW wind tunnel, the AFDD rotary wing test stand, the UTRC and AFDD aerodynamic and acoustic data acquisition systems, and the scope of test matrices are discussed and an introduction to the test results is provided. It is pointed out that a comprehensive aero/acoustic database of several configurations of the UTC scaled model rotor has been created. The data is expected to improve understanding of rotor aerodynamics, acoustics, and dynamics, and lead to enhanced analytical methodology and design capabilities for the next generation of rotorcraft.
Nonlinear dynamic modeling of a simple flexible rotor system subjected to time-variable base motions
NASA Astrophysics Data System (ADS)
Chen, Liqiang; Wang, Jianjun; Han, Qinkai; Chu, Fulei
2017-09-01
Rotor systems carried in transportation system or under seismic excitations are considered to have a moving base. To study the dynamic behavior of flexible rotor systems subjected to time-variable base motions, a general model is developed based on finite element method and Lagrange's equation. Two groups of Euler angles are defined to describe the rotation of the rotor with respect to the base and that of the base with respect to the ground. It is found that the base rotations would cause nonlinearities in the model. To verify the proposed model, a novel test rig which could simulate the base angular-movement is designed. Dynamic experiments on a flexible rotor-bearing system with base angular motions are carried out. Based upon these, numerical simulations are conducted to further study the dynamic response of the flexible rotor under harmonic angular base motions. The effects of base angular amplitude, rotating speed and base frequency on response behaviors are discussed by means of FFT, waterfall, frequency response curve and orbits of the rotor. The FFT and waterfall plots of the disk horizontal and vertical vibrations are marked with multiplications of the base frequency and sum and difference tones of the rotating frequency and the base frequency. Their amplitudes will increase remarkably when they meet the whirling frequencies of the rotor system.
Model updating of rotor systems by using Nonlinear least square optimization
NASA Astrophysics Data System (ADS)
Jha, A. K.; Dewangan, P.; Sarangi, M.
2016-07-01
Mathematical models of structure or machineries are always different from the existing physical system, because the approach of numerical predictions to the behavior of a physical system is limited by the assumptions used in the development of the mathematical model. Model updating is, therefore necessary so that updated model should replicate the physical system. This work focuses on the model updating of rotor systems at various speeds as well as at different modes of vibration. Support bearing characteristics severely influence the dynamics of rotor systems like turbines, compressors, pumps, electrical machines, machine tool spindles etc. Therefore bearing parameters (stiffness and damping) are considered to be updating parameters. A finite element model of rotor systems is developed using Timoshenko beam element. Unbalance response in time domain and frequency response function have been calculated by numerical techniques, and compared with the experimental data to update the FE-model of rotor systems. An algorithm, based on unbalance response in time domain is proposed for updating the rotor systems at different running speeds of rotor. An attempt has been made to define Unbalance response assurance criterion (URAC) to check the degree of correlation between updated FE model and physical model.
NASA Technical Reports Server (NTRS)
Hohenemser, K. H.; Crews, S. T.
1972-01-01
A two bladed 16-inch hingeless rotor model was built and tested outside and inside a 24 by 24 inch wind tunnel test section at collective pitch settings up to 5 deg and rotor advance ratios up to .4. The rotor model has a simple eccentric mechanism to provide progressing or regressing cyclic pitch excitation. The flapping responses were compared to analytically determined responses which included flap-bending elasticity but excluded rotor wake effects. Substantial systematic deviations of the measured responses from the computed responses were found, which were interpreted as the effects of interaction of the blades with a rotating asymmetrical wake.
CFD modeling and analysis of rotor wake in hover interacting with a ground plane
NASA Astrophysics Data System (ADS)
Kalra, Tarandeep Singh
The action of the rotor wake on loose sediment on the ground is primarily responsible for inducing the rotorcraft brownout phenomenon. Therefore, any simulation of brownout must be capable of accurately predicting the velocity field induced by the rotor when it is operating in ground effect. This work attempts to use a compressible, structured, overset Reynolds-Averaged Navier-Stokes (RANS) based solver to simulate hovering rotors in ground effect (IGE) to demonstrate the capability of the code to provide accurate tip vortex flow field predictions, and provide a good understanding of the ground-wake interactions. The computations are performed for a micro-scale rotor (0.086m radius, aspect ratio of 4.387 operating at a tip Mach number of 0.08 and Reynolds number of 32,500) and a sub-scale rotor (0.408m radius, aspect ratio of 9.132 operating at a tip Mach number of 0.24 and Reynolds number of 250,000) in order to compare to experimental measurements. The micro-scale rotor has a rectangular tip shape and is simulated three rotor heights: 1.5R, 1.0R and 0.5R above ground (R = Rotor radius). The sub-scale rotor is simulated at one particular rotor height (i.e. 1R) but with four different tip shapes: rectangular, swept, BERP-like and slotted tip. Various mesh placement strategies are devised to efficiently capture the path of the tip vortices for both regimes. The micro-scale rotor simulations are performed using the Spalart Allmaras (S-A) turbulence model. The examination of the IGE tip vortex flow field suggests high degree of instabilities close to the ground. In addition, the induced velocities arising from the proximity of the rotor tip vortices causes flow separation at the ground. The sub-scale rotor simulations show a smeared out flow field even at early wake ages due to excessive turbulence levels. The distance function in the S-A turbulence model is modified using the Delayed Detached Eddy Simulation (DDES) approach and a correction to length scaling is
On determining the acoustic properties of main helicopter rotor models on an open test bench
NASA Astrophysics Data System (ADS)
Kop'ev, V. F.; Zaitsev, M. Yu.; Ostrikov, N. N.; Denisov, S. L.; Makashov, S. Yu.; Anikin, V. A.; Gromov, V. V.
2016-11-01
The paper presents the results of experimental studies on developing a technique to determine the acoustic properties of models of main helicopter rotors on an open test bench. The method of maximum length sequences is used to choose the optimum arrangement of microphones for an open test bench that would minimize the influence of parasitic echo. The results of processing the data of an acoustic experiment with a model rotor are detailed.
Numerical Study of a Jeffcott Rotor Model with a Snubber Ring
NASA Astrophysics Data System (ADS)
Páez Chávez, J.; Wiercigroch, M.; Demrdash, H.
2012-08-01
In this article we study a two-degrees-of-freedom model of a rotor system with a bearing clearance. During operation the rotor makes intermittent contact with an outer snubber ring, which results in complex dynamical behaviour. Specifically, the system will be analyzed numerically by a path following method, where we will use the toolbox TC-HAT, which is a module for modeling non-smooth systems by AUTO 97.
Matrix product states and the non-Abelian rotor model
NASA Astrophysics Data System (ADS)
Milsted, Ashley
2016-04-01
We use uniform matrix product states to study the (1 +1 )D O (2 ) and O (4 ) rotor models, which are equivalent to the Kogut-Susskind formulation of matter-free non-Abelian lattice gauge theory on a "Hawaiian earring" graph for U (1 ) and S U (2 ), respectively. Applying tangent space methods to obtain ground states and determine the mass gap and the β function, we find excellent agreement with known results, locating the Berezinskii-Kosterlitz-Thouless transition for O (2 ) and successfully entering the asymptotic weak-coupling regime for O (4 ). To obtain a finite local Hilbert space, we truncate in the space of generalized Fourier modes of the gauge group, comparing the effects of different cutoff values. We find that higher modes become important in the crossover and weak-coupling regimes of the non-Abelian theory, where entanglement also suddenly increases. This could have important consequences for tensor network state studies of Yang-Mills on higher-dimensional graphs.
Influence of Reynolds number on performance modeling of horizontal axis wind rotors
Musial, W.D.; Cromack, D.E.
1988-05-01
This paper investigates the influence of Reynolds number on performance modeling of horizontal axis wind rotors. A procedure for accounting for Reynolds number effects on airfoil section models was developed and implemented for NACA 0012 and NACA 4415 profiles; both of these models is valid through angles of attack up to 90 deg and for Reynolds numbers ranging from 4 x 10/sup 4/ to 3 x 10/sup 6/. These models were incorporated into both a lifting line computer code, LL200R, adapted for this report. This enabled greater uncertainty to be obtained in evaluating theoretical performance codes with respect to actual data, as well as providing a means by which a parametric analysis of the relative effects of Re changes on rotor performance to be performed. The use of low Reynolds number section data was found to significantly lower the predicted values of power coefficient, particularly at off-design tip speed-ratios. For symmetrical airfoils, this effect on performance was only significant for low tip-speed- ratios, while cambered airfoils were affected more uniformly at all operating conditions. Changes in performance were induced by parametric variations of wind speed, rotor scale, and rotor generating mode using the Reynolds number dependent section models. Results show that wind speed variations are more significant for smaller rotors at lower wind-speeds, and section models represented at only a single Reynolds number are more suitable for the analysis of constant RPM rotors.
NASA Astrophysics Data System (ADS)
Roy, H.; Chandraker, S.; Dutt, J. K.; Roy, T.
2016-05-01
Inherent material damping plays a very significant role on dynamic behaviour of rotors. The material damping in a spinning rotor produces a tangential force along the whirl direction and its magnitude being proportional to spin speed. After certain value of spin speed, decided by the characteristic of the system, the tangential force becomes strong enough to throw the rotor centre out of the whirl orbit by inflating it progressively. This leads to destabilization of the system and corresponding speed is known as stability limit of spin speed. Stability limit of spin speed for Jeffcott rotor, by using viscous form of material damping model is straight forward and has been reported by several researchers, however the same analysis for viscoelastic material characteristics is not reported much. This analysis is very relevant for industrial requirements to replace bulky and heavy metal rotor by light but strong rotors. This is achieved either by reinforcing fibre or multi layering arrangements. Both of which are represented by viscoelastic constitutive behaviour. This paper gives mathematical derivation of equations of motion for multi-disc, multi-layered rotor-shaft-system. Both lumped mass and discretized approach (finite element) are presented here mathematically and numerical simulation results are compared. The lumped mass approach gives a concise yet acceptable accuracy of the results.
Applying dynamic wake models to induced power calculations for an optimum rotor
NASA Astrophysics Data System (ADS)
Garcia-Duffy, Cristina
Recent studies have pointed out that conventional lifting rotors in forward flight have efficiencies far lower than the optimum efficiencies predicted by theory. This dissertation explains how a closed-form optimization of induced power with finite-state models is expanded to successfully reproduce the results for the optimization of induced power given by classical theories for axial flow and for a rotor in forward flight. Results for induced power change in forward flight and for different conditions will help the determination of what produces the efficiency in real rotors to be inferior to the predicted values by theoretical calculations. Mainly three factors contribute to the decreased efficiency for real rotors: a finite number of blades, the effect of lift tilt and the lift distribution. The ultimate goals of the present research effort are to: (1) develop a complete and comprehensive inflow model, and (2) determine which of these contribute to the drastic increase in induced power.
Noise of a model helicopter rotor due to ingestion of turbulence
NASA Technical Reports Server (NTRS)
Paterson, R. W.; Amiet, R. K.
1979-01-01
A theoretical and experimental investigation of the noise of a model helicoper rotor due to ingestion of turbulence was conducted. Experiments were performed with a 0.76 m dia, articulated model rotor for a range of inflow turbulence and rotor operating conditions. Inflow turbulence levels varied from approximately 2 to 19 percent and tip Mach number was varied from 0.3 to 0.52. Test conditions included ingestion of a atmospheric turbulence in outdoor hover as well as ingestion of grid generated isotropic turbulence in the wind tunnel airstream. In wind tunnel testing, both forward flight and vertical ascent (climb) were simulated. Far field noise spectra and directivity were measured in addition to incident turbulence intensities, length scales, and spectra. Results indicate that ingestion of atmospheric turbulence is the dominant helicopter rotor hover noise mechanism at the moderate to high frequencies which determine perceived noise level.
Evaluation of a load cell model for dynamic calibration of the rotor systems research aircraft
NASA Technical Reports Server (NTRS)
Duval, R. W.; Bahrami, H.; Wellman, B.
1985-01-01
The Rotor Systems Research Aircraft uses load cells to isolate the rotor/transmission system from the fuselage. An analytical model of the relationship between applied rotor loads and the resulting load cell measurements is derived by applying a force-and-moment balance to the isolated rotor/transmission system. The model is then used to estimate the applied loads from measured load cell data, as obtained from a ground-based shake test. Using nominal design values for the parameters, the estimation errors, for the case of lateral forcing, were shown to be on the order of the sensor measurement noise in all but the roll axis. An unmodeled external load appears to be the source of the error in this axis.
Effect of advanced rotorcraft airfoil sections on the hover performance of a small-scale rotor model
NASA Technical Reports Server (NTRS)
Althoff, Susan L.
1988-01-01
A hover test was conducted on a small scale rotor model for two sets of tapered rotor blades. The baseline rotor blade set used a NACA 0012 airfoil section, whereas the second rotor blade set had advanced rotorcraft airfoils distributed along the radius. The experiment was conducted for a range of thrust coefficients and tip speeds, and the data were compared to the predictions of three analytical methods. The data show the advantage of the advanced airfoils at the higher rotor thrust levels; two of the analyses predicted the correct data trends.
Wieland, Birgit; Ropte, Sven
2017-10-05
The production of rotor blades for wind turbines is still a predominantly manual process. Process simulation is an adequate way of improving blade quality without a significant increase in production costs. This paper introduces a module for tolerance simulation for rotor-blade production processes. The investigation focuses on the simulation of temperature distribution for one-sided, self-heated tooling and thick laminates. Experimental data from rotor-blade production and down-scaled laboratory tests are presented. Based on influencing factors that are identified, a physical model is created and implemented as a simulation. This provides an opportunity to simulate temperature and cure-degree distribution for two-dimensional cross sections. The aim of this simulation is to support production processes. Hence, it is modelled as an in situ simulation with direct input of temperature data and real-time capability. A monolithic part of the rotor blade, the main girder, is used as an example for presenting the results.
NASA Astrophysics Data System (ADS)
Vorotnikov, V. I.; Martyshenko, Yu. G.
2013-09-01
The nonlinear game problem of the three-axis reorientation of an asymmetric solid body with three flywheels (rotors) has been solved. Acceptable levels of uncontrollable noise depending on given constraints of control moments have been estimated.
Elastoplastic viscous model of rotor-stator impact interaction without separation
NASA Astrophysics Data System (ADS)
Nikiforov, A. N.; Shokhin, A. E.
2016-06-01
The impact interaction without separation between a flexible rotor and a rigid stator is analyzed in the framework of the plane model based on the equations of motion in Cartesian coordinates and the Hertz, Rivin, and Gerstner relations. It is shown that there are critical values of the system parameters at which the so-called asynchronous rolling of the rotor on the stator arises.
Microscopic modeling of exciton spectra in asymmetric quantum wells
Grigoryev, P. S. Kurdiubov, A. S.; Kuznetsova, M. S.; Ignatiev, I. V.; Efimov, Yu. P.; Eliseev, S. A.; Petrov, V. V.; Lovtcius, V. A.; Shapochkin, P. Yu.
2016-06-17
A theoretical model of reflectance spectra is applied to the analysis of spectra of the two high-quality structures with asymmetric InGaAs/GaAs quantum wells. The analysis allows to quantitatively describe the exciton resonances related to the lowest quantum-confined exciton states. Main parameters of the quantum well potential profiles are obtained in the modeling.
A synchronous strobed laser light sheet for helicopter model rotor flow visualization
NASA Technical Reports Server (NTRS)
Leighty, Bradley D.; Rhodes, David B.; Jones, Stephen B.; Franke, John M.
1990-01-01
A synchronous, strobed laser light sheet has been developed for use in flow visualization of a helicopter rotor model. The light sheet strobe circuit included selectable blade position, strobe duration, and multiple pulses per revolution for rotors having 2 to 9 blades. The flow was seeded with propylene glycol. Between runs, a calibration grid board was placed in the plane of the laser sheet and recorded with the video camera at the position used to record the flow field. A slip-sync mode permitted slow motion visualization of the flow field over complete rotations of the rotor. The system was used to make two-dimensional flow field cuts of a four-bladed rotor operating at advance ratio of 0.37 at wind tunnel speeds up to 79.25 meters per second (260 feet per second).
NASA Technical Reports Server (NTRS)
Sadler, S. G.
1971-01-01
Rotor wake geometries are predicted by a process similar to the startup of a rotor in a free stream. An array of discrete trailing and shed vortices is generated with vortex strengths corresponding to stepwise radial and azimuthal blade circulations. The array of shed and trailing vortices is limited to an arbitrary number of azimuthal steps behind each blade. The remainder of the wake model of each blade is an arbitrary number of trailing vortices. Vortex element end points were allowed to be transported by the resultant velocity of the free stream and vortex-induced velocities. Wake geometry, wake flow, and wake-induced velocity influence coefficients are generated by this program for use in the blade loads portion of the calculations. Blade loads computations include the effects of nonuniform inflow due to a free wake, nonlinear airfoil characteristics, and response of flexible blades to the applied loads. Computed wake flows and blade loads are compared with experimentally measured data. Predicted blade loads, response and shears and moments are obtained for a model rotor system having two independent rotors. The effects of advance ratio, vertical separation of rotors, different blade radius ratios, and different azimuthal spacing of the blades of one rotor with respect to the other are investigated.
Takeoff/approach noise for a model counterrotation propeller with a forward-swept upstream rotor
NASA Technical Reports Server (NTRS)
Woodward, Richard P.; Hall, David G.; Podboy, Gary G.; Jeracki, Robert J.
1993-01-01
A scale model of a counterrotating propeller with forward-swept blades in the forward rotor and aft-swept blades in the aft rotor (designated F39/A31) has been tested in the NASA Lewis 9- by 15-Foot Anechoic Wind Tunnel. This paper presents aeroacoustic results at a takeoff/approach condition of Mach 0.20. Laser Doppler velocimeter results taken in a plane between the two rotors are also included to quantify the interaction flow field. The intention of the forward-swept design is to reduce the magnitude of the forward rotor tip vortex and/or wakes which impinge on the aft rotor, thus lowering the interaction tone levels. A reference model propeller (designated F31/A31), having aft-swept blades in both rotors, was also tested. Aeroelastic performance of the F39/A31 propeller was disappointing. The forward rotor tip region tended to untwist toward higher effective blade angles under load. The forward rotor also exhibited steady state blade flutter at speeds and loadings well below the design condition. The noise results, based on sideline acoustic data, show that the interaction tone levels were up to 8 dB higher with the forward-swept design compared to those for the reference propeller at similar operating conditions, with these tone level differences extending down to lower propeller speeds where flutter did not occur. These acoustic results are for a poorly-performing forward-swept propeller. It is quite possible that a properly-designed forward-swept propeller would exhibit substantial interaction tone level reductions.
Calculation of the Aerodynamic Behavior of the Tilt Rotor Aeroacoustic Model (TRAM) in the DNW
NASA Technical Reports Server (NTRS)
Johnson, Wayne
2001-01-01
Comparisons of measured and calculated aerodynamic behavior of a tiltrotor model are presented. The test of the Tilt Rotor Aeroacoustic Model (TRAM) with a single, 1/4-scale V- 22 rotor in the German-Dutch Wind Tunnel (DNW) provides an extensive set of aeroacoustic, performance, and structural loads data. The calculations were performed using the rotorcraft comprehensive analysis CAMRAD II. Presented are comparisons of measured and calculated performance and airloads for helicopter mode operation, as well as calculated induced and profile power. An aerodynamic and wake model and calculation procedure that reflects the unique geometry and phenomena of tiltrotors has been developed. There are major differences between this model and the corresponding aerodynamic and wake model that has been established for helicopter rotors. In general, good correlation between measured and calculated performance and airloads behavior has been shown. Two aspects of the analysis that clearly need improvement are the stall delay model and the trailed vortex formation model.
A hybrid approach for modelling dynamic behaviours of a rotor-foundation system
NASA Astrophysics Data System (ADS)
Zhang, Z. G.; Zhang, Z. Y.; Jing, B.; Hua, H. X.
2016-09-01
A new hybrid approach is presented to study the dynamic behaviour of a rotor- foundation system, in which a shaft coupled with various discontinuities are connected to a flexible foundation via discrete spring subunits. By modelling the rotor with the modified transfer matrix method and describing the flexible foundation through the appropriate modal model, the proposed technique facilitates a computationally efficient modelling approach where a mixture of theoretical, numerical or experimental models can be incorporated into one overall numerical model. Particularly, the present model enables one to conveniently consider both the free and forced vibrations as well as effects of various combinations of discontinuities encountered in the rotor. Some results are compared with available results in previous publications and those from the finite element method to validate the model. Parametric studies are also performed to demonstrate the accuracy and versatility of the developed method for substructure coupling analysis.
A flight-dynamic helicopter mathematical model with a single flap-lag-torsion main rotor
NASA Technical Reports Server (NTRS)
Takahashi, Marc D.
1990-01-01
A mathematical model of a helicopter system with a single main rotor that includes rigid, hinge-restrained rotor blades with flap, lag, and torsion degrees of freedom is described. The model allows several hinge sequences and two offsets in the hinges. Quasi-steady Greenberg theory is used to calculate the blade-section aerodynamic forces, and inflow effects are accounted for by using three-state nonlinear dynamic inflow model. The motion of the rigid fuselage is defined by six degrees of freedom, and an optional rotor rpm degree of freedom is available. Empennage surfaces and the tail rotor are modeled, and the effect of main-rotor downwash on these elements is included. Model trim linearization, and time-integration operations are described and can be applied to a subset of the model in the rotating or nonrotating coordinate frame. A preliminary validation of the model is made by comparing its results with those of other analytical and experimental studies. This publication presents the results of research compiled in November 1989.
A mathematical simulation model of a 1985-era tilt-rotor passenger aircraft
NASA Technical Reports Server (NTRS)
Mcveigh, M. A.; Widdison, C. A.
1976-01-01
A mathematical model for use in real-time piloted simulation of a 1985-era tilt rotor passenger aircraft is presented. The model comprises the basic six degrees-of-freedom equations of motion, and a large angle of attack representation of the airframe and rotor aerodynamics, together with equations and functions used to model turbine engine performance, aircraft control system and stability augmentation system. A complete derivation of the primary equations is given together with a description of the modeling techniques used. Data for the model is included in an appendix.
Thermal Modeling of Disc Brake Rotor in Frictional Contact
NASA Astrophysics Data System (ADS)
Ali, Belhocine; Ghazaly, Nouby Mahdi
2013-01-01
Safety aspect in automotive engineering has been considered as a number one priority in development of new vehicle. Each single system has been studied and developed in order to meet safety requirement. Instead of having air bag, good suspension systems, good handling and safe cornering, there is one most critical system in the vehicle which is brake systems. The objective of this work is to investigate and analyze the temperature distribution of rotor disc during braking operation using ANSYS Multiphysics. The work uses the finite element analysis techniques to predict the temperature distribution on the full and ventilated brake disc and to identify the critical temperature of the rotor. The analysis also gives us, the heat flux distribution for the two discs.
Tilt Rotor Aeroacoustic Model (TRAM): A New Rotorcraft Research Facility
1998-04-01
Lautenschlager (U.S. Army), Mike Derby, Jeff Johnson, A lexand ra Swanson, Stephen S w a n s o n (Sterling Software), Ken Su l l ivan , Scott Ralston...a 0.658-Scale V-22 Rotor and Wing, NASA TM 89419 , April 1987. 11. F. Felker, P. Shinoda , R. Heffernan, and H. S h e e h y , Wing Force and S
Totally Asymmetric Limit for Models of Heat Conduction
NASA Astrophysics Data System (ADS)
De Carlo, Leonardo; Gabrielli, Davide
2017-08-01
We consider one dimensional weakly asymmetric boundary driven models of heat conduction. In the cases of a constant diffusion coefficient and of a quadratic mobility we compute the quasi-potential that is a non local functional obtained by the solution of a variational problem. This is done using the dynamic variational approach of the macroscopic fluctuation theory (Bertini et al. in Rev Mod Phys 87:593, 2015). The case of a concave mobility corresponds essentially to the exclusion model that has been discussed in Bertini et al. (J Stat Mech L11001, 2010; Pure Appl Math 64(5):649-696, 2011; Commun Math Phys 289(1):311-334, 2009) and Enaud and Derrida (J Stat Phys 114:537-562, 2004). We consider here the convex case that includes for example the Kipnis-Marchioro-Presutti (KMP) model and its dual (KMPd) (Kipnis et al. in J Stat Phys 27:6574, 1982). This extends to the weakly asymmetric regime the computations in Bertini et al. (J Stat Phys 121(5/6):843-885, 2005). We consider then, both microscopically and macroscopically, the limit of large externalfields. Microscopically we discuss some possible totally asymmetric limits of the KMP model. In one case the totally asymmetric dynamics has a product invariant measure. Another possible limit dynamics has instead a non trivial invariant measure for which we give a duality representation. Macroscopically we show that the quasi-potentials of KMP and KMPd, which are non local for any value of the external field, become local in the limit. Moreover the dependence on one of the external reservoirs disappears. For models having strictly positive quadratic mobilities we obtain instead in the limit a non local functional having a structure similar to the one of the boundary driven asymmetric exclusion process.
Development of an Open Rotor Cycle Model in NPSS Using a Multi-Design Point Approach
NASA Technical Reports Server (NTRS)
Hendricks, Eric S.
2011-01-01
NASA's Environmentally Responsible Aviation Project and Subsonic Fixed Wing Project are focused on developing concepts and technologies which may enable dramatic reductions to the environmental impact of future generation subsonic aircraft (Refs. 1 and 2). The open rotor concept (also referred to as the Unducted Fan or advanced turboprop) may allow the achievement of this objective by reducing engine emissions and fuel consumption. To evaluate its potential impact, an open rotor cycle modeling capability is needed. This paper presents the initial development of an open rotor cycle model in the Numerical Propulsion System Simulation (NPSS) computer program which can then be used to evaluate the potential benefit of this engine. The development of this open rotor model necessitated addressing two modeling needs within NPSS. First, a method for evaluating the performance of counter-rotating propellers was needed. Therefore, a new counter-rotating propeller NPSS component was created. This component uses propeller performance maps developed from historic counter-rotating propeller experiments to determine the thrust delivered and power required. Second, several methods for modeling a counter-rotating power turbine within NPSS were explored. These techniques used several combinations of turbine components within NPSS to provide the necessary power to the propellers. Ultimately, a single turbine component with a conventional turbine map was selected. Using these modeling enhancements, an open rotor cycle model was developed in NPSS using a multi-design point approach. The multi-design point (MDP) approach improves the engine cycle analysis process by making it easier to properly size the engine to meet a variety of thrust targets throughout the flight envelope. A number of design points are considered including an aerodynamic design point, sea-level static, takeoff and top of climb. The development of this MDP model was also enabled by the selection of a simple power
NASA Technical Reports Server (NTRS)
Boxwell, D. A.; Schmitz, F. H.; Splettstoesser, W. R.; Schultz, K. J.; Lewy, S.; Caplot, M.
1986-01-01
Two aeroacoustic facilities--the CEPRA 19 in France and the DNW in the Netherlands--are compared. The two facilities have unique acoustic characteristics that make them appropriate for acoustic testing of model-scale helicopter rotors. An identical pressure-instrumented model-scale rotor was tested in each facility and acoustic test results are compared with full-scale-rotor test results. Blade surface pressures measured in both tunnels were used to correlated nominal rotor operating conditions in each tunnel, and also used to assess the steadiness of the rotor in each tunnel's flow. In-the-flow rotor acoustic signatures at moderate forward speeds (35-50 m/sec) are presented for each facility and discussed in relation to the differences in tunnel geometries and aeroacoustic characteristics. Both reports are presented in appendices to this paper. ;.);
FEM Modeling and Experimental Verification of a Rotor System with an Open Crack
NASA Astrophysics Data System (ADS)
Inoue, Tsuyoshi; Kato, Masato; Nagata, Nobuhiro; Ishida, Yukio
Continuous operation of rotating machinery with a rotor crack is a risk condition since the rotor crack grows rapidly and may fail causing a catastrophic accident. This paper develops the finite element model of the rotating shaft with an open crack. The analytical method for the calculation of the natural frequencies of such a rotor system with an open crack is investigated, and the modeling of the open crack element is discussed. The natural frequency of the experimental system is measured for various cases of positions and depths of the open crack. By comparing both the theoretical and experimental results of the natural frequencies, the accuracy of the developed finite element model of the rotating shaft with an open crack is clarified.
Modeling and Design of a Full-Scale Rotor Blade with Embedded Piezocomposite Actuators
NASA Astrophysics Data System (ADS)
Kovalovs, A.; Barkanov, E.; Ruchevskis, S.; Wesolowski, M.
2017-05-01
An optimization methodology for the design of a full-scale rotor blade with an active twist in order to enhance its ability to reduce vibrations and noise is presented. It is based on a 3D finite-element model, the planning of experiments, and the response surface technique to obtain high piezoelectric actuation forces and displacements with a minimum actuator weight and energy applied. To investigate an active twist of the helicopter rotor blade, a structural static analysis using a 3D finite-element model was carried out. Optimum results were obtained at two possible applications of macrofiber composite actuators. The torsion angle found from the finite-element simulation of helicopter rotor blades was successfully validated by its experimental values, which confirmed the modeling accuracy.
Simplified rotor load models and fatigue damage estimates for offshore wind turbines.
Muskulus, M
2015-02-28
The aim of rotor load models is to characterize and generate the thrust loads acting on an offshore wind turbine. Ideally, the rotor simulation can be replaced by time series from a model with a few parameters and state variables only. Such models are used extensively in control system design and, as a potentially new application area, structural optimization of support structures. Different rotor load models are here evaluated for a jacket support structure in terms of fatigue lifetimes of relevant structural variables. All models were found to be lacking in accuracy, with differences of more than 20% in fatigue load estimates. The most accurate models were the use of an effective thrust coefficient determined from a regression analysis of dynamic thrust loads, and a novel stochastic model in state-space form. The stochastic model explicitly models the quasi-periodic components obtained from rotational sampling of turbulent fluctuations. Its state variables follow a mean-reverting Ornstein-Uhlenbeck process. Although promising, more work is needed on how to determine the parameters of the stochastic model and before accurate lifetime predictions can be obtained without comprehensive rotor simulations. © 2015 The Author(s) Published by the Royal Society. All rights reserved.
An overview of a model rotor icing test in the NASA Lewis Icing Research Tunnel
NASA Technical Reports Server (NTRS)
Britton, Randall K.; Bond, Thomas H.; Flemming, Robert J.
1994-01-01
During two entries in late 1989, a heavily instrumented sub-scale model of a helicopter main rotor was tested in the NASA LeRC Icing Research Tunnel (IRT). The results of this series of tunnel tests were published previously. After studying the results from the 1989 test and comparing them to predictions, it became clear that certain test conditions still needed investigation. Therefore, a re-entry of the Sikorsky Aircraft Powered Force Model (PFM) in the IRT was instituted in order to expand upon the current rotor craft sub-scale model experimental database. The major areas of interest included expansion of the test matrix to include a larger number of points in the FAA AC 29-2 icing envelope, inclusion of a number of high power rotor performance points, close examination of warm temperature operations, operation of the model in constant lift mode, and testing for conditions for icing test points in the full scale helicopter database. The expanded database will allow further and more detailed examination and comparison with analytical models. Participants in the test were NASA LeRC, the U.S. Army Vehicle Propulsion Directorate based at LeRC, and Sikorsky Aircraft. The model rotor was exposed to a range of icing conditions (temperature, liquid water content, median droplet diameter) and was operated over ranges of shaft angle, rotor tip speed, advance ratio, and rotor lift. The data taken included blade strain gage and balance data, as well as still photography, video, ice profile tracings, and ice molds. A discussion of the details of the test is given herein. Also, a brief examination of a subset of the data taken is also given.
Helicopter main-rotor noise: Determination of source contributions using scaled model data
NASA Astrophysics Data System (ADS)
Brooks, Thomas F.; Jolly, J. Ralph, Jr.; Marcolini, Michael A.
1988-08-01
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 noise contributions from different rotor noise sources. Key results include a component breakdown of the noise contributions, in terms of noise criteria calculations of a weighted sound pressure level (dBA) and perceived noise 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) noise is the dominant contributor to the noise. In level flight and mild climb, broadband blade-turbulent wake interaction (BWI) noise is dominant due to the absence of BVI activity. At high climb angles, BWI is reduced and self-noise from blade boundary-layer turbulence becomes the most prominent.
Helicopter main-rotor noise: Determination of source contributions using scaled model data
NASA Technical Reports Server (NTRS)
Brooks, Thomas F.; Jolly, J. Ralph, Jr.; Marcolini, Michael A.
1988-01-01
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 noise contributions from different rotor noise sources. Key results include a component breakdown of the noise contributions, in terms of noise criteria calculations of a weighted sound pressure level (dBA) and perceived noise 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) noise is the dominant contributor to the noise. In level flight and mild climb, broadband blade-turbulent wake interaction (BWI) noise is dominant due to the absence of BVI activity. At high climb angles, BWI is reduced and self-noise from blade boundary-layer turbulence becomes the most prominent.
Wind tunnel investigation of helicopter rotor wake effects on three helicopter fuselage models
NASA Technical Reports Server (NTRS)
Wilson, J. C.; Mineck, R. E.
1974-01-01
The effects of rotor downwash on helicopter fuselage aerodynamic characteristics were investigated. A rotor model for generating the downwash was mounted close to each of three fuselage models. The main report presents the force and moment data in both graphical and tabular form and the pressure data in graphical form. This supplement presents the pressure data in tabular form. Each run or parameter sweep is identified by a unique run number. The data points in each run are identified by a point number. The pressure data can be matched to the force data by matching the run and point number.
A comparison of model helicopter rotor Primary and Secondary blade/vortex interaction blade slap
NASA Technical Reports Server (NTRS)
Hubbard, J. E., Jr.; Leighton, K. P.
1983-01-01
A study of the relative importance of blade/vortex interactions which occur on the retreating side of a model helicopter rotor disk is described. Some of the salient characteristics of this phenomenon are presented and discussed. It is shown that the resulting Secondary blade slap may be of equal or greater intensity than the advancing side (Primary) blade slap. Instrumented model helicopter rotor data is presented which reveals the nature of the retreating blade/vortex interaction. The importance of Secondary blade slap as it applies to predictive techniques or approaches is discussed. When Secondary blade slap occurs it acts to enlarge the window of operating conditions for which blade slap exists.
Rotating Shake Test and Modal Analysis of a Model Helicopter Rotor Blade
NASA Technical Reports Server (NTRS)
Wilkie, W. Keats; Mirick, Paul H.; Langston, Chester W.
1997-01-01
Rotating blade frequencies for a model generic helicopter rotor blade mounted on an articulated hub were experimentally determined. Testing was conducted using the Aeroelastic Rotor Experimental System (ARES) testbed in the Helicopter Hover Facility (HBF) at Langley Research Center. The measured data were compared to pretest analytical predictions of the rotating blade frequencies made using the MSC/NASTRAN finite-element computer code. The MSC/NASTRAN solution sequences used to analyze the model were modified to account for differential stiffening effects caused by the centrifugal force acting on the blade and rotating system dynamic effects. The correlation of the MSC/NASTRAN-derived frequencies with the experimental data is, in general, very good although discrepancies in the blade torsional frequency trends and magnitudes were observed. The procedures necessary to perform a rotating system modal analysis of a helicopter rotor blade with MSC/NASTRAN are outlined, and complete sample data deck listings are provided.
NASA Technical Reports Server (NTRS)
Free, April M.; Flowers, George T.; Trent, Victor S.
1993-01-01
Auxiliary bearings are a critical feature of any magnetic bearing system. They protect the soft iron core of the magnetic bearing during an overload or failure. An auxiliary bearing typically consists of a rolling element bearing or bushing with a clearance gap between the rotor and the inner race of the support. The dynamics of such systems can be quite complex. It is desired to develop a rotor-dynamic model and assess the dynamic behavior of a magnetic bearing rotor system which includes the effects of auxiliary bearings. Of particular interest is the effects of introducing sideloading into such a system during failure of the magnetic bearing. A model is developed from an experimental test facility and a number of simulation studies are performed. These results are presented and discussed.
Modeling and design strategies for the vibration response of turbine engine rotors
NASA Astrophysics Data System (ADS)
Baik, Sanghum
Efficient, novel design and analysis methods are presented for improving the structural performance of turbine engine rotors with respect to blade vibration response. For a bladed disk, the blades are intended to be identical; however, blade-to-blade structural irregularities, known as blade mistuning, in practice are unavoidable due to manufacturing tolerances and in-service wear. Even small levels of blade mistuning may cause severe increases in blade vibration amplitudes relative to those computed for the ideal, tuned rotor. Thus, the sensitivity of bladed disks to mistuning is a serious safety, readiness, and maintenance concern for turbine engines. Hereby, the effects of blade mistuning are systematically accounted for in searching for a reliable, robust rotor design; that is, a bladed disk less sensitive to mistuning. To this end, design analysis tools are developed for bladed disks. First, as an efficient tool for accurately predicting the vibration response of mistuned rotors, a previously developed reduced-order vibration modeling technique is extended to handle the case of mass mistuning. Even when mass mistuning occurs in small geometric regions of the blades, the enhanced technique can precisely capture free and forced vibration response of the mistuned rotors. Second, as a fast tool for approximately assessing mistuning sensitivity of rotors, a power flow analysis method is proposed. This approach enables the systematic estimation of vibration energy flow within a nominal rotor for excitation cases of interest. This dynamic information is then used to evaluate the robustness of the rotor design with respect to blade mistuning. These tools are incorporated into the design problem of finding an optimal disk geometry to achieve minimum weight while ensuring that blade stress levels of mistuned rotors are kept below a specified safety limit. In doing so, an optimum candidate satisfying the design constraints in an approximate sense is calculated quickly
NASA Technical Reports Server (NTRS)
Martin, R. M.; Elliott, J. W.; Hoad, D. R.
1984-01-01
Helicopter blade-vortex interaction (BVI) noise is studied using a model scale rotor acoustic data base and an analytical rotor wake prediction method. The variation of BVI acoustic levels with vehicle flight conditions (forward speed and disk attitude) is presented. Calculations of probable BVI locations on the rotor disk are made for a range of operating conditions using the measured acoustic signals and an acoustic ray tracing technique. Analytical predictions of possible BVI locations on the rotor disk are made using a generalized distorted wake analysis program. Comparisons of the interaction locations are made with the results of both the analytic approach and the acoustic ray tracing technique.
An analytic modeling and system identification study of rotor/fuselage dynamics at hover
NASA Technical Reports Server (NTRS)
Hong, Steven W.; Curtiss, H. C., Jr.
1993-01-01
A combination of analytic modeling and system identification methods have been used to develop an improved dynamic model describing the response of articulated rotor helicopters to control inputs. A high-order linearized model of coupled rotor/body dynamics including flap and lag degrees of freedom and inflow dynamics with literal coefficients is compared to flight test data from single rotor helicopters in the near hover trim condition. The identification problem was formulated using the maximum likelihood function in the time domain. The dynamic model with literal coefficients was used to generate the model states, and the model was parametrized in terms of physical constants of the aircraft rather than the stability derivatives, resulting in a significant reduction in the number of quantities to be identified. The likelihood function was optimized using the genetic algorithm approach. This method proved highly effective in producing an estimated model from flight test data which included coupled fuselage/rotor dynamics. Using this approach it has been shown that blade flexibility is a significant contributing factor to the discrepancies between theory and experiment shown in previous studies. Addition of flexible modes, properly incorporating the constraint due to the lag dampers, results in excellent agreement between flight test and theory, especially in the high frequency range.
An analytic modeling and system identification study of rotor/fuselage dynamics at hover
NASA Technical Reports Server (NTRS)
Hong, Steven W.; Curtiss, H. C., Jr.
1993-01-01
A combination of analytic modeling and system identification methods have been used to develop an improved dynamic model describing the response of articulated rotor helicopters to control inputs. A high-order linearized model of coupled rotor/body dynamics including flap and lag degrees of freedom and inflow dynamics with literal coefficients is compared to flight test data from single rotor helicopters in the near hover trim condition. The identification problem was formulated using the maximum likelihood function in the time domain. The dynamic model with literal coefficients was used to generate the model states, and the model was parametrized in terms of physical constants of the aircraft rather than the stability derivatives resulting in a significant reduction in the number of quantities to be identified. The likelihood function was optimized using the genetic algorithm approach. This method proved highly effective in producing an estimated model from flight test data which included coupled fuselage/rotor dynamics. Using this approach it has been shown that blade flexibility is a significant contributing factor to the discrepancies between theory and experiment shown in previous studies. Addition of flexible modes, properly incorporating the constraint due to the lag dampers, results in excellent agreement between flight test and theory, especially in the high frequency range.
Asymmetric dark matter models and the LHC diphoton excess
Frandsen, Mads T.; Shoemaker, Ian M.
2016-05-31
The existence of dark matter (DM) and the origin of the baryon asymmetry are persistent indications that the SM is incomplete. More recently, the ATLAS and CMS experiments have observed an excess of diphoton events with invariant mass of about 750 GeV. One interpretation of this excess is decays of a new spin-0 particle with a sizable diphoton partial width, e.g. induced by new heavy weakly charged particles. These are also key ingredients in models cogenerating asymmetric DM and baryons via sphaleron interactions and an initial particle asymmetry. We explore what consequences the new scalar may have for models of asymmetric DM that attempt to account for the similarity of the dark and visible matter abundances.
Exact results for the one dimensional asymmetric exclusion model
NASA Astrophysics Data System (ADS)
Derrida, B.; Evans, M. R.; Hakim, V.; Pasquier, V.
1993-11-01
The asymmetric exclusion model describes a system of particles hopping in a preferred direction with hard core repulsion. These particles can be thought of as charged particles in a field, as steps of an interface, as cars in a queue. Several exact results concerning the steady state of this system have been obtained recently. The solution consists of representing the weights of the configurations in the steady state as products of non-commuting matrices.
Loads and Performance Data from a Wind-Tunnel Test of Generic Model Helicopter Rotor Blades
NASA Technical Reports Server (NTRS)
Yeager, William T., Jr.; Wilbur, Matthew L.
2005-01-01
An investigation was conducted in the NASA Langley Transonic Dynamics Tunnel to acquire data for use in assessing the ability of current and future comprehensive analyses to predict helicopter rotating-system and fixed-system vibratory loads. The investigation was conducted with a generic model helicopter rotor system using blades with rectangular planform, no built-in twist, uniform radial distribution of mass and stiffnesses, and a NACA 0012 airfoil section. Rotor performance data, as well as mean and vibratory components of blade bending and torsion moments, fixed-system forces and moments, and pitch link loads were obtained at advance ratios up to 0.35 for various combinations of rotor shaft angle-of-attack and collective pitch. The data are presented without analysis.
Wake Geometry Measurements and Analytical Calculations on a Small-Scale Rotor Model
NASA Technical Reports Server (NTRS)
Ghee, Terence A.; Berry, John D.; Zori, Laith A. J.; Elliott, Joe W.
1996-01-01
An experimental investigation was conducted in the Langley 14- by 22-Foot Subsonic Tunnel to quantify the rotor wake behind a scale model helicopter rotor in forward level flight at one thrust level. The rotor system in this test consisted of a four-bladed fully articulated hub with blades of rectangular planform and an NACA 0012 airfoil section. A laser light sheet, seeded with propylene glycol smoke, was used to visualize the vortex geometry in the flow in planes parallel and perpendicular to the free-stream flow. Quantitative measurements of wake geometric proper- ties, such as vortex location, vertical skew angle, and vortex particle void radius, were obtained as well as convective velocities for blade tip vortices. Comparisons were made between experimental data and four computational method predictions of experimental tip vortex locations, vortex vertical skew angles, and wake geometries. The results of these comparisons highlight difficulties of accurate wake geometry predictions.
Bifurcation analysis of periodic orbits of a non-smooth Jeffcott rotor model
NASA Astrophysics Data System (ADS)
Páez Chávez, Joseph; Wiercigroch, Marian
2013-09-01
We investigate complex dynamics occurring in a non-smooth model of a Jeffcott rotor with a bearing clearance. A bifurcation analysis of the rotor system is carried out by means of the software TC-HAT [25], a toolbox of AUTO 97 [6] allowing path-following and detection of bifurcations of periodic trajectories of non-smooth dynamical systems. The study reveals a rich variety of dynamics, which includes grazing-induced fold and period-doubling bifurcations, as well as hysteresis loops produced by a cusp singularity. Furthermore, an analytical expression predicting grazing incidences is derived.
A Linear City Model with Asymmetric Consumer Distribution
Azar, Ofer H.
2015-01-01
The article analyzes a linear-city model where the consumer distribution can be asymmetric, which is important because in real markets this distribution is often asymmetric. The model yields equilibrium price differences, even though the firms’ costs are equal and their locations are symmetric (at the two endpoints of the city). The equilibrium price difference is proportional to the transportation cost parameter and does not depend on the good's cost. The firms' markups are also proportional to the transportation cost. The two firms’ prices will be equal in equilibrium if and only if half of the consumers are located to the left of the city’s midpoint, even if other characteristics of the consumer distribution are highly asymmetric. An extension analyzes what happens when the firms have different costs and how the two sources of asymmetry – the consumer distribution and the cost per unit – interact together. The model can be useful as a tool for further development by other researchers interested in applying this simple yet flexible framework for the analysis of various topics. PMID:26034984
A linear city model with asymmetric consumer distribution.
Azar, Ofer H
2015-01-01
The article analyzes a linear-city model where the consumer distribution can be asymmetric, which is important because in real markets this distribution is often asymmetric. The model yields equilibrium price differences, even though the firms' costs are equal and their locations are symmetric (at the two endpoints of the city). The equilibrium price difference is proportional to the transportation cost parameter and does not depend on the good's cost. The firms' markups are also proportional to the transportation cost. The two firms' prices will be equal in equilibrium if and only if half of the consumers are located to the left of the city's midpoint, even if other characteristics of the consumer distribution are highly asymmetric. An extension analyzes what happens when the firms have different costs and how the two sources of asymmetry - the consumer distribution and the cost per unit - interact together. The model can be useful as a tool for further development by other researchers interested in applying this simple yet flexible framework for the analysis of various topics.
A theoretical model of asymmetric wave ripples
Blondeaux, P.; Foti, E.; Vittori, G.
2015-01-01
The time development of ripples under sea waves is investigated by means of the weakly nonlinear stability analysis of a flat sandy bottom subjected to the viscous oscillatory flow that is present in the boundary layer at the bottom of propagating sea waves. Second-order effects in the wave steepness are considered, to take into account the presence of the steady drift generated by the surface waves. Hence, the work of Vittori & Blondeaux (1990 J. Fluid Mech. 218, 19–39 (doi:10.1017/S002211209000091X)) is extended by considering steeper waves and/or less deep waters. As shown by the linear analysis of Blondeaux et al. (2000 Eur. J. Mech. B 19, 285–301 (doi:10.1016/S0997-7546(90)00106-I)), because of the presence of a steady velocity component in the direction of wave propagation, ripples migrate at a constant rate that depends on sediment and wave characteristics. The weakly nonlinear analysis shows that the ripple profile is no longer symmetric with respect to ripple crests and troughs and the symmetry index is computed as a function of the parameters of the problem. In particular, a relationship is determined between the symmetry index and the strength of the steady drift. A fair agreement between model results and laboratory data is obtained, albeit further data and analyses are necessary to determine the behaviour of vortex ripples and to be conclusive. PMID:25512587
A theoretical model of asymmetric wave ripples.
Blondeaux, P; Foti, E; Vittori, G
2015-01-28
The time development of ripples under sea waves is investigated by means of the weakly nonlinear stability analysis of a flat sandy bottom subjected to the viscous oscillatory flow that is present in the boundary layer at the bottom of propagating sea waves. Second-order effects in the wave steepness are considered, to take into account the presence of the steady drift generated by the surface waves. Hence, the work of Vittori & Blondeaux (1990 J. Fluid Mech. 218, 19-39 (doi:10.1017/S002211209000091X)) is extended by considering steeper waves and/or less deep waters. As shown by the linear analysis of Blondeaux et al. (2000 Eur. J. Mech. B 19, 285-301 (doi:10.1016/S0997-7546(90)00106-I)), because of the presence of a steady velocity component in the direction of wave propagation, ripples migrate at a constant rate that depends on sediment and wave characteristics. The weakly nonlinear analysis shows that the ripple profile is no longer symmetric with respect to ripple crests and troughs and the symmetry index is computed as a function of the parameters of the problem. In particular, a relationship is determined between the symmetry index and the strength of the steady drift. A fair agreement between model results and laboratory data is obtained, albeit further data and analyses are necessary to determine the behaviour of vortex ripples and to be conclusive.
NASA Technical Reports Server (NTRS)
Chou, S.-T.; George, A. R.
1986-01-01
A study was made of helicopter tail rotor noise, particularly that due to interactions with the main rotor tip vortices, and with the fuselage separation mean wake. The tail rotor blade-main rotor tip vortex interaction is modelled as an airfoil of infinite span cutting through a moving vortex. The vortex and the geometry information required by the analyses are obtained through a free wake geometry analysis of the main rotor. The acoustic pressure-time histories for the tail rotor blade-vortex interactions are then calculated. These acoustic results are compared to tail rotor loading and thickness noise, and are found to be significant to the overall tail rotor noise generation. Under most helicopter operating conditions, large acoustic pressure fluctuations can be generated due to a series of skewed main rotor tip vortices passing through the tail rotor disk. The noise generation depends strongly upon the helicopter operating conditions and the location of the tail rotor relative to the main rotor.
The Role of Flow Diagnostic Techniques in Fan and Open Rotor Noise Modeling
NASA Technical Reports Server (NTRS)
Envia, Edmane
2016-01-01
A principal source of turbomachinery noise is the interaction of the rotating and stationary blade rows with the perturbations in the airstream through the engine. As such, a lot of research has been devoted to the study of the turbomachinery noise generation mechanisms. This is particularly true of fan and open rotors, both of which are the major contributors to the overall noise output of modern aircraft engines. Much of the research in fan and open rotor noise has been focused on developing theoretical models for predicting their noise characteristics. These models, which run the gamut from the semi-empirical to fully computational ones, are, in one form or another, informed by the description of the unsteady flow-field in which the propulsors (i.e., the fan and open rotors) operate. Not surprisingly, the fidelity of the theoretical models is dependent, to a large extent, on capturing the nuances of the unsteady flowfield that have a direct role in the noise generation process. As such, flow diagnostic techniques have proven to be indispensible in identifying the shortcoming of theoretical models and in helping to improve them. This presentation will provide a few examples of the role of flow diagnostic techniques in assessing the fidelity and robustness of the fan and open rotor noise prediction models.
Housing flexibility effects on rotor stability
NASA Technical Reports Server (NTRS)
Davis, L. B.; Wolfe, E. A.; Beatty, R. F.
1985-01-01
Preliminary rotordynamic evaluations are performed with a housing stiffness assumption that is typically determined only after the hardware is built. In addressing rotor stability, a rigid housing assumption was shown to predict an instability at a lower spin speed than a comparable flexible housing analysis. This rigid housing assumption therefore provides a conservative estimate of the stability threshold speed. A flexible housing appears to act as an energy absorber and dissipated some of the destabilizing force. The fact that a flexible housing is usually asymmetric and considerably heavier than the rotor was related to this apparent increase in rotor stability. Rigid housing analysis is proposed as a valuable screening criteria and may save time and money in construction of elaborate housing finite element models for linear stability analyses.
Interference resistance of pentamaran ship model with asymmetric outrigger configurations
NASA Astrophysics Data System (ADS)
Yanuar; Ibadurrahman; Waskito, Kurniawan T.; Karim, S.; Ichsan, M.
2017-01-01
An experimental investigation is performed to assess the relation of interference performance on the total resistance of a pentamaran model advancing in calm water. For this motivation, the total drag of the ship is performed for several values of asymmetric outrigger configuration and hull separation, altering the Froude number in the range 0.3-0.9. Our results indicate that remarkable changes in resistance require notable changes in transverse distance values (hull separation) when wave interference may occur. In addition, there is no single configuration that consistently outperforms the other configurations across the entire speed range and the optimum interference factor -0.2 appears at a Froude number of 0.45 in S/L=0.33 with the outrigger outer position: asymmetric outboard for A3 configuration.
Interference resistance of pentamaran ship model with asymmetric outrigger configurations
NASA Astrophysics Data System (ADS)
Yanuar; Ibadurrahman; Waskito, Kurniawan T.; Karim, S.; Ichsan, M.
2017-03-01
An experimental investigation is performed to assess the relation of interference performance on the total resistance of a pentamaran model advancing in calm water. For this motivation, the total drag of the ship is performed for several values of asymmetric outrigger configuration and hull separation, altering the Froude number in the range 0.3-0.9. Our results indicate that remarkable changes in resistance require notable changes in transverse distance values (hull separation) when wave interference may occur. In addition, there is no single configuration that consistently outperforms the other configurations across the entire speed range and the optimum interference factor -0.2 appears at a Froude number of 0.45 in S/L=0.33 with the outrigger outer position: asymmetric outboard for A3 configuration.
A Model for Cell Population Size Control Using Asymmetric Division
Hamidi, Mani; Emberly, Eldon
2013-01-01
In multicellular organisms one can find examples where a growing tissue divides up until some final fixed cell number. Asymmetric division plays a prevalent feature in tissue differentiation in these organisms, where the daughters of each asymmetric division inherit unequal amounts of a fate determining molecule and as a result follow different developmental fates. In some tissues the accumulation or decrease of cell cycle regulators acts as an intrinsic timing mechanism governing proliferation. Here we present a minimal model based on asymmetric division and dilution of a cell-cycle regulator that can generate any final population size that might be needed. We show that within the model there are a variety of growth mechanisms from linear to non-linear that can lead to the same final cell count. Interestingly, when we include noise at division we find that there are special final cell population sizes that can be generated with high confidence that are flanked by population sizes that are less robust to division noise. When we include further perturbations in the division process we find that these special populations can remain relatively stable and in some cases even improve in their fidelity. PMID:24040230
Stress analysis of 27% scale model of AH-64 main rotor hub
NASA Technical Reports Server (NTRS)
Hodges, R. V.
1985-01-01
Stress analysis of an AH-64 27% scale model rotor hub was performed. Component loads and stresses were calculated based upon blade root loads and motions. The static and fatigue analysis indicates positive margins of safety in all components checked. Using the format developed here, the hub can be stress checked for future application.
NASA Technical Reports Server (NTRS)
Friedmann, P. P.; Venkatesan, C.
1988-01-01
The results of an analytical study aimed at predicting the aeromechanical stability of a helicopter in ground resonance, with the inclusion of aerodynamic forces are presented. The theoretical results are found to be in good agreement with the experimental results, available in literature, indicating that the coupled rotor/fuselage system can be represented by a reasonably simple mathematical model.
NASA Technical Reports Server (NTRS)
Mchugh, F. J.; Eason, W.; Alexander, H. R.; Mutter, H.
1973-01-01
Wind tunnel test data obtained from a 1/4.622 Froude scale Boeing Model 222 with a full span, two prop, tilt rotor, powered model in the Boeing V/STOL wind tunnel are reported. Data were taken in transition and cruise flight conditions and include performance, stability and control and blade loads information. The effects of the rotors, tail surfaces and airframe on the performance and stability are isolated as are the effects of the airframe on the rotors.
NASA Technical Reports Server (NTRS)
Ghee, Terence A.; Elliott, Joe W.
1992-01-01
An experimental investigation was conducted in the 14 by 22 ft subsonic tunnel at NASA Langley Research Center to quantify the rotor wake behind a scale model helicopter rotor in forward flight (mu = 0.15 and 0.23) at one thrust level (C sub T = 0.0064). The rotor system used in the present test consisted of a four-bladed, fully articulated hub and utilized blades of rectangular planform with a NACA-0012 airfoil section. A laser light sheet, seeded with propylene glycol smoke, was used to visualize the flow in planes parallel and perpendicular to the freestream flow. Quantitative measurements of vortex location, vertical skew angle, and vortex particle void radius were obtained for vortices in the flow; convective velocities were obtained for blade tip vortices. Comparisons were made between the experimental results and the wake geometry generated by computational predictions. The results of these comparisons show that the interaction between wake vortex structures is an important consideration for correctly predicting the wake geometry.
Dynamic modelling and analysis of a magnetically suspended flexible rotor. M.S. Thesis, 1988
NASA Technical Reports Server (NTRS)
Mccallum, Duncan C.
1991-01-01
A 12-state lumped-element model is presented for a flexible rotor supported by two attractive force electromagnetic journal bearings. The rotor is modeled as a rigid disk with radial mass unbalance mounted on a flexible, massless shaft with internal damping (Jeffcott rotor). The disk is offset axially from the midspan of the shaft. Bearing dynamics in each radial direction are modeled as a parallel combination of a negative (unstable) spring and a linear current-to-force actuator. The model includes translation and rotation of the rigid mass and the first and second bending models of the flexible shaft, and it simultaneously includes internal shaft damping, gyroscopic effects, and the unstable nature of the attractive force magnetic bearings. The model is used to analyze the dependence of the system transmission zeros and open-loop poles on system parameters. The dominant open-loop poles occur in stable/unstable pairs with bandwidth dependent on the ratios of bearing (unstable) stiffnesses to rotor mass and damping dependent on the shaft spin rate. The zeros occur in complex conjugate pairs with bandwidth dependent on the ratios of shaft stiffness to rotor mass and damping dependent on the shaft spin rate. Some of the transmission zeros are non-minimum phase when the spin rate exceeds the shaft critical speed. The transmission zeros and open-loop poles impact the design of magnetic bearing control systems. The minimum loop cross-over frequency of the closed-loop system is the speed of the unstable open-loop poles. For the supercritical shaft spin rates, the presence of non-minimum phase zeros limits the distribution rejection achievable at frequencies near or above the shaft critical speed. Since non-minimum phase transmission zeros can only be changed by changing the system inputs and/or outputs, closed-loop performance is limited for supercritical spin rates unless additional force or torque actuators are added.
Unified continuum damage model for matrix cracking in composite rotor blades
Pollayi, Hemaraju; Harursampath, Dineshkumar
2015-03-10
This paper deals with modeling of the first damage mode, matrix micro-cracking, in helicopter rotor/wind turbine blades and how this effects the overall cross-sectional stiffness. The helicopter/wind turbine rotor system operates in a highly dynamic and unsteady environment leading to severe vibratory loads present in the system. Repeated exposure to this loading condition can induce damage in the composite rotor blades. These rotor/turbine blades are generally made of fiber-reinforced laminated composites and exhibit various competing modes of damage such as matrix micro-cracking, delamination, and fiber breakage. There is a need to study the behavior of the composite rotor system under various key damage modes in composite materials for developing Structural Health Monitoring (SHM) system. Each blade is modeled as a beam based on geometrically non-linear 3-D elasticity theory. Each blade thus splits into 2-D analyzes of cross-sections and non-linear 1-D analyzes along the beam reference curves. Two different tools are used here for complete 3-D analysis: VABS for 2-D cross-sectional analysis and GEBT for 1-D beam analysis. The physically-based failure models for matrix in compression and tension loading are used in the present work. Matrix cracking is detected using two failure criterion: Matrix Failure in Compression and Matrix Failure in Tension which are based on the recovered field. A strain variable is set which drives the damage variable for matrix cracking and this damage variable is used to estimate the reduced cross-sectional stiffness. The matrix micro-cracking is performed in two different approaches: (i) Element-wise, and (ii) Node-wise. The procedure presented in this paper is implemented in VABS as matrix micro-cracking modeling module. Three examples are presented to investigate the matrix failure model which illustrate the effect of matrix cracking on cross-sectional stiffness by varying the applied cyclic load.
The asymmetric quantum Rabi model in the polaron picture
NASA Astrophysics Data System (ADS)
Liu, Maoxin; Ying, Zu-Jian; An, Jun-Hong; Luo, Hong-Gang; Lin, Hai-Qin
2017-02-01
The concept of the polaron in condensed matter physics has been extended to the Rabi model, where polarons resulting from the coupling between a two-level system and single-mode photons represent two oppositely displaced oscillators. Interestingly, tunneling between these two displaced oscillators can induce an anti-polaron, which has not been systematically explored in the literature, especially in the presence of an asymmetric term. In this paper, we present a systematic analysis of the competition between the polaron and anti-polaron under the interplay of the coupling strength and the asymmetric term. While intuitively the anti-polaron should be secondary owing to its higher potential energy, we find that, under certain conditions, the minor anti-polaron may gain a reversal in the weight over the major polaron. If the asymmetric amplitude ɛ is smaller than the harmonic frequency ω, such an overweighted anti-polaron can occur beyond a critical value of the coupling strength g; if ɛ is larger, the anti-polaron can even be always overweighted at any g. We propose that the explicit occurrence of the overweighted anti-polaron can be monitored by a displacement transition from negative to positive values. This displacement is an experimentally accessible observable, which can be measured by quantum optical methods, such as balanced Homodyne detection.
NASA Technical Reports Server (NTRS)
Hohenemser, K. H.; Banerjee, D.
1977-01-01
An introduction to aircraft state and parameter identification methods is presented. A simplified form of the maximum likelihood method is selected to extract analytical aeroelastic rotor models from simulated and dynamic wind tunnel test results for accelerated cyclic pitch stirring excitation. The dynamic inflow characteristics for forward flight conditions from the blade flapping responses without direct inflow measurements were examined. The rotor blades are essentially rigid for inplane bending and for torsion within the frequency range of study, but flexible in out-of-plane bending. Reverse flow effects are considered for high rotor advance ratios. Two inflow models are studied; the first is based on an equivalent blade Lock number, the second is based on a time delayed momentum inflow. In addition to the inflow parameters, basic rotor parameters like the blade natural frequency and the actual blade Lock number are identified together with measurement bias values. The effect of the theoretical dynamic inflow on the rotor eigenvalues is evaluated.
Application of a High-Fidelity Icing Analysis Method to a Model-Scale Rotor in Forward Flight
NASA Technical Reports Server (NTRS)
Narducci, Robert; Orr, Stanley; Kreeger, Richard E.
2012-01-01
An icing analysis process involving the loose coupling of OVERFLOW-RCAS for rotor performance prediction and with LEWICE3D for thermal analysis and ice accretion is applied to a model-scale rotor for validation. The process offers high-fidelity rotor analysis for the noniced and iced rotor performance evaluation that accounts for the interaction of nonlinear aerodynamics with blade elastic deformations. Ice accumulation prediction also involves loosely coupled data exchanges between OVERFLOW and LEWICE3D to produce accurate ice shapes. Validation of the process uses data collected in the 1993 icing test involving Sikorsky's Powered Force Model. Non-iced and iced rotor performance predictions are compared to experimental measurements as are predicted ice shapes.
A Comparison Between Numerically Modelled and Experimentally Measured Loss Mechanisms in Wave Rotors
NASA Technical Reports Server (NTRS)
Paxson, Daniel E.
1993-01-01
A numerical model has been developed which is capable of predicting the performance of a wave rotor (pressure exchanger) of specified geometry over a wide range of operating conditions. The model can account for the major loss mechanisms of leakage from the tube ends, fluid viscosity, heat transfer to the tube walls, finite tube opening time, shock waves, and non-uniform port flows. It is a one dimensional flow model which follows a single tube as it rotates past the various stationary ports. Since the model is relatively simple (i.e. one dimensional) it uses little computer time. This makes it suitable for design as well as analytical purposes. This paper will present a brief description of the model then discuss a comparison between the model predictions and several wave rotor experiments.
Ice accretion modeling for wind turbine rotor blades
Chocron, D.; Brahimi, T.; Paraschivoiu, I.; Bombardier, J.A.
1997-12-31
The increasing application of wind energy in northern climates implies operation of wind turbines under severe atmospheric icing conditions. Such conditions are well known in the Scandinavian countries, Canada and most of Eastern European countries. An extensive study to develop a procedure for the prediction of ice accretion on wind turbines rotor blades appears to be essential for the safe and economic operation of wind turbines in these cold regions. The objective of the present paper is to develop a computer code capable of simulating the shape and amount of ice which may accumulate on horizontal axis wind turbine blades when operating in icing conditions. The resulting code is capable to predict and simulate the formation of ice in rime and glaze conditions, calculate the flow field and particle trajectories and to perform thermodynamic analysis. It also gives the possibility of studying the effect of different parameters that influence ice formation such as temperature, liquid water content, droplet diameter and accretion time. The analysis has been conducted on different typical airfoils as well as on NASA/DOE Mod-0 wind turbine. Results showed that ice accretion on wind turbines may reduce the power output by more than 20%.
MRAC Control with Prior Model Knowledge for Asymmetric Damaged Aircraft
Zhang, Jing
2015-01-01
This paper develops a novel state-tracking multivariable model reference adaptive control (MRAC) technique utilizing prior knowledge of plant models to recover control performance of an asymmetric structural damaged aircraft. A modification of linear model representation is given. With prior knowledge on structural damage, a polytope linear parameter varying (LPV) model is derived to cover all concerned damage conditions. An MRAC method is developed for the polytope model, of which the stability and asymptotic error convergence are theoretically proved. The proposed technique reduces the number of parameters to be adapted and thus decreases computational cost and requires less input information. The method is validated by simulations on NASA generic transport model (GTM) with damage. PMID:26180839
Some issues on modeling atmospheric turbulence experienced by helicopter rotor blades
NASA Technical Reports Server (NTRS)
Costello, Mark; Gaonkar, G. H.; Prasad, J. V. R.; Schrage, D. P.
1992-01-01
The atmospheric turbulence velocities seen by nonrotating aircraft components and rotating blades can be substantially different. The differences are due to the spatial motion of the rotor blades, which move fore and aft through the gust waves. Body-fixed atmospheric turbulence refers to the actual atmospheric turbulence experienced by a point fixed on a nonrotating aircraft component such as the aircraft's center of gravity or the rotor hub, while blade-fixed atmospheric turbulence refers to the atmospheric turbulence experienced by an element of the rotating rotor blade. An example is presented, which, though overly simplified, shows important differences between blade- and body-fixed rotorcraft atmospheric turbulence models. All of the information necessary to develop the dynamic equations describing the atmospheric turbulence velocity field experienced by an aircraft is contained in the atmospheric turbulence velocity correlation matrix. It is for this reason that a generalized formulation of the correlation matrix describing atmospheric turbulence that a rotating blade encounters is developed. From this correlation matrix, earlier treated cases restricted to a rotor flying straight and level directly into the mean wind can be recovered as special cases.
Tone and Broadband Noise Separation from Acoustic Data of a Scale-Model Counter-Rotating Open Rotor
NASA Technical Reports Server (NTRS)
Sree, David; Stephens, David B.
2014-01-01
Renewed interest in contra-rotating open rotor technology for aircraft propulsion application has prompted the development of advanced diagnostic tools for better design and improved acoustical performance. In particular, the determination of tonal and broadband components of open rotor acoustic spectra is essential for properly assessing the noise control parameters and also for validating the open rotor noise simulation codes. The technique of phase averaging has been employed to separate the tone and broadband components from a single rotor, but this method does not work for the two-shaft contra-rotating open rotor. A new signal processing technique was recently developed to process the contra-rotating open rotor acoustic data. The technique was first tested using acoustic data taken of a hobby aircraft open rotor propeller, and reported previously. The intent of the present work is to verify and validate the applicability of the new technique to a realistic one-fifth scale open rotor model which has 12 forward and 10 aft contra-rotating blades operating at realistic forward flight Mach numbers and tip speeds. The results and discussions of that study are presented in this paper.
Tone and Broadband Noise Separation from Acoustic Data of a Scale-Model Contra-Rotating Open Rotor
NASA Technical Reports Server (NTRS)
Sree, Dave; Stephens, David B.
2014-01-01
Renewed interest in contra-rotating open rotor technology for aircraft propulsion application has prompted the development of advanced diagnostic tools for better design and improved acoustical performance. In particular, the determination of tonal and broadband components of open rotor acoustic spectra is essential for properly assessing the noise control parameters and also for validating the open rotor noise simulation codes. The technique of phase averaging has been employed to separate the tone and broadband components from a single rotor, but this method does not work for the two-shaft contra-rotating open rotor. A new signal processing technique was recently developed to process the contra-rotating open rotor acoustic data. The technique was first tested using acoustic data taken of a hobby aircraft open rotor propeller, and reported previously. The intent of the present work is to verify and validate the applicability of the new technique to a realistic one-fifth scale open rotor model which has 12 forward and 10 aft contra-rotating blades operating at realistic forward flight Mach numbers and tip speeds. The results and discussions of that study are presented in this paper.
Noise Benefits of Rotor Trailing Edge Blowing for a Model Turbofan
NASA Technical Reports Server (NTRS)
Woodward, Richard P.; Fite, E. Brian; Podboy, Gary G.
2007-01-01
An advanced model turbofan was tested in the NASA Glenn 9- by 15-Foot Low Speed Wind Tunnel (9x15 LSWT) to explore far field acoustic effects associated with rotor Trailing-Edge-Blowing (TEB) for a modern, 1.294 stage pressure ratio turbofan model. The TEB rotor (Fan9) was designed to be aerodynamically similar to the previously tested Fan1, and used the same stator and nacelle hardware. Fan9 was designed with trailing edge blowing slots using an external air supply directed through the rotor hub. The TEB flow was heated to approximate the average fan exit temperature at each fan test speed. Rotor root blockage inserts were used to block TEB to all but the outer 40 and 20% span in addition to full-span blowing. A configuration with full-span TEB on alternate rotor blades was also tested. Far field acoustic data were taken at takeoff/approach conditions at 0.10 tunnel Mach. Far-field acoustic results showed that full-span blowing near 2.0% of the total flow could reduce the overall sound power level by about 2 dB. This noise reduction was observed in both the rotor-stator interaction tones and for the spectral broadband noise levels. Blowing only the outer span region was not very effective for lowering noise, and actually increased the far field noise level in some instances. Full-span blowing of alternate blades at 1.0% of the overall flow rate (equivalent to full-span blowing of all blades at 2.0% flow) showed a more modest noise decrease relative to full-span blowing of all blades. Detailed hot film measurements of the TEB rotor wake at 2.0% flow showed that TEB was not every effective for filling in the wake defect at approach fan speed toward the tip region, but did result in overfilling the wake toward the hub. Downstream turbulence measurements supported this finding, and support the observed reduction in spectral broadband noise.
Modeling and control of a flexible rotor system with AMB-based sustentation.
Arredondo, I; Jugo, J; Etxebarria, V
2008-01-01
In this work the modeling and basic control design process of a rotary flexible spindle hovered by Active Magnetic Bearings (AMB) whose good capabilities for machine-tool industry extensively treated in the literature is presented. The modeling takes into account the three main behavioral characteristics of such magnetically-levitated rotor: the rigid dynamics, the flexible dynamics and the rotating unbalanced motion. Besides, the gyroscopic coupling is also studied proving that in this case, its effects are not significant and can be neglected. Using this model, a stabilizing controller based on symmetry properties is successfully designed for the system and a complete experimental analysis of its performance is carried out. Also, the predictions of the model are compared with the actual measured experimental results on a laboratory set-up based on the MBC500 Rotor Dynamics. Afterwards, a brief study about some nonlinear behavior observed in the system and its effect over the system stability at the critical speed is included.
Development of a comprehensive analysis for rotorcraft. I - Rotor model and wake analysis
NASA Technical Reports Server (NTRS)
Johnson, W.
1981-01-01
The development of a comprehensive analytical model of rotorcraft aerodynamics and dynamics is described. Particular emphasis is given to describing the reasons behind the choices and decisions involved in constructing the model. The analysis is designed to calculate rotor performance, loads and noise; helicopter vibration and gust response; flight dynamics and handling qualities; and system aeroelastic stability. It is intended for use in the design, testing and evaluation of a wide class of rotors and rotorcraft, and to be the basis for further development of rotary wing theories. The general characteristics of the geometric, structural, inertial, and aerodynamic models used for the rotorcraft components are described, including the assumptions introduced by the chosen models and the resulting capabilities and limitations. Finally, some examples from recent applications of the analysis are given.
Asymmetric adaptive modeling of central tarsal bones in racing greyhounds.
Johnson, K A; Muir, P; Nicoll, R G; Roush, J K
2000-08-01
Fatigue fracture of the cuboidal bones of the foot, especially the navicular tarsal bone, is common in athletes and dancers. The racing greyhound is a naturally occurring animal model of this injury because both microcracking and complete fracture occur in the right central (navicular) tarsal bone (CTB). The right limb is on the outside when racing in a counter-clockwise direction on circular tracks, and is subjected to asymmetric cyclic compressive loading. We wished to study in more detail adaptive modeling in the right CTB in racing greyhounds. We hypothesized that cyclic asymmetric loading of a cuboidal bone induced by racing on a circular track would induce site-specific bone adaptation. We also hypothesized that such an adaptive response would be attenuated in greyhounds that were retired from racing and no longer subjected to cyclic asymmetric loading. Central tarsal bones from racing greyhounds (racing group, n = 6) and retired greyhounds being used for breeding (nonracing group, n = 4) were examined using quantitative computed tomography (CT). Bone mineral density (BMD) was determined in a 3-mm diameter region-of-interest (ROI) in six contiguous 1-mm-thick sagittal CT slices of each CTB. Bones were subsequently examined histomorphometrically and percentage bone area (B.Ar./T.Ar., %) was determined in 10 ROI from dorsal to plantar in a transverse plane, mid-way between the proximal and distal articular surfaces. The BMD of the right CTB was greater than the left in all greyhounds (p < 0. 001). In comparing ipsilateral limbs between groups, BMD of the racing group was greater than the nonracing group for each side (p < 0.005). In sagittal plane histologic sections, bone in the dorsal region of the right CTB had undergone adaptive modeling, through thickening and compaction of trabeculae. B.Ar./T.Ar., % in the right CTB of the racing group was greater than in the contralateral CTB (p < 0.001), and the ipsilateral CTB of the nonracing group (p < 0.001). In the
Rotor Wake Development During the First Revolution
NASA Technical Reports Server (NTRS)
McAlister, Kenneth W.
2003-01-01
The wake behind a two-bladed model rotor in light climb was measured using particle image velocimetry, with particular emphasis on the development of the trailing vortex during the first revolution of the rotor. The distribution of vorticity was distinguished from the slightly elliptical swirl pattern. Peculiar dynamics within the void region may explain why the peak vorticity appeared to shift away from the center as the vortex aged, suggesting the onset of instability. The swirl and axial velocities (which reached 44 and 12 percent of the rotor-tip speed, respectively) were found to be asymmetric relative to the vortex center. In particular, the axial flow was composed of two concentrated zones moving in opposite directions. The radial distribution of the circulation rapidly increased in magnitude until reaching a point just beyond the core radius, after which the rate of growth decreased significantly. The core-radius circulation increased slightly with wake age, but the large-radius circulation appeared to remain relatively constant. The radial distributions of swirl velocity and vorticity exhibit self-similar behaviors, especially within the core. The diameter of the vortex core was initially about 10 percent of the rotor-blade chord, but more than doubled its size after one revolution of the rotor. According to vortex models that approximate the measured data, the core-radius circulation was about 79 percent of the large-radius circulation, and the large-radius circulation was about 67 percent of the maximum bound circulation on the rotor blade. On average, about 53 percent of the maximum bound circulation resides within the vortex core during the first revolution of the rotor.
Estimation of rotor effective wind speeds using autoregressive models on Lidar data
NASA Astrophysics Data System (ADS)
Giyanani, A.; Bierbooms, W. A. A. M.; van Bussel, G. J. W.
2016-09-01
Lidars have become increasingly useful for providing accurate wind speed measurements in front of the wind turbine. The wind field measured at distant meteorological masts changes its structure or was too distorted before it reaches the turbine. Thus, one cannot simply apply Taylor's frozen turbulence for representing this distant flow field at the rotor. Wind turbine controllers can optimize the energy output and reduce the loads significantly, if the wind speed estimates were known in advance with high accuracy and low uncertainty. The current method to derive wind speed estimations from aerodynamic torque, pitch angle and tip speed ratio after the wind field flows past the turbine and have their limitations, e.g. in predicting gusts. Therefore, an estimation model coupled with the measuring capability of nacelle based Lidars was necessary for detecting extreme events and for estimating accurate wind speeds at the rotor disc. Nacelle-mounted Lidars measure the oncoming wind field from utpo 400m(5D) in front of the turbine and appropriate models could be used for deriving the rotor effective wind speed from these measurements. This article proposes an auto-regressive model combined with a method to include the blockage factor in order to estimate the wind speeds accurately using Lidar measurements. An Armax model was used to determine the transfer function that models the physical evolution of wind towards the wind turbine, incorporating the effect of surface roughness, wind shear and wind variability at the site. The model could incorporate local as well as global effects and was able to predict the rotor effective wind speeds with adequate accuracy for wind turbine control actions. A high correlation of 0.86 was achieved as the Armax modelled signal was compared to a reference signal. The model could also be extended to estimate the damage potential during high wind speeds, gusts or abrupt change in wind directions, allowing the controller to act appropriately
Rotordynamic Modelling and Response Characteristics of an Active Magnetic Bearing Rotor System
NASA Technical Reports Server (NTRS)
Free, April M.; Flowers, George T.; Trent, Victor S.
1996-01-01
Auxiliary bearings are a critical feature of any magnetic bearing system. They protect the soft iron core of the magnetic bearing during an overload or failure. An auxiliary bearing typically consists of a rolling element bearing or bushing with a clearance gap between the rotor and the inner race of the support. The dynamics of such systems can be quite complex. It is desired to develop a rotordynamic model which describes the dynamic behavior of a flexible rotor system with magnetic bearings including auxiliary bearings. The model is based upon an experimental test facility. Some simulation studies are presented to illustrate the behavior of the model. In particular, the effects of introducing sideloading from the magnetic bearing when one coil fails is studied. These results are presented and discussed.
NASA Technical Reports Server (NTRS)
Free, April M.; Flowers, George T.; Trent, Victor S.
1995-01-01
Auxiliary bearings are a critical feature of any magnetic bearing system. They protect the soft iron core of the magnetic bearing during an overload or failure. An auxiliary bearing typically consists of a rolling element bearing or bushing with a clearance gap between the rotor and the inner race of the support. The dynamics of such systems can be quite complex. It is desired to develop a rotordynamic model which describes the dynamic behavior of a flexible rotor system with magnetic bearings including auxiliary bearings. The model is based upon an experimental test facility. Some simulation studies are presented to illustrate the behavior of the model. In particular, the effects of introducing sideloading from the magnetic bearing when one coil fails is studied.
Unsteady separation experiments on 2-D airfoils, 3-D wings, and model helicopter rotors
NASA Technical Reports Server (NTRS)
Lorber, Peter F.; Carta, Franklin O.
1992-01-01
Information on unsteady separation and dynamic stall is being obtained from two experimental programs that have been underway at United Technologies Research Center since 1984. The first program is designed to obtain detailed surface pressure and boundary layer condition information during high amplitude pitching oscillations of a large (17.3 in. chord) model wing in a wind tunnel. The second program involves the construction and testing of a pressure-instrumented model helicopter rotor. This presentation describes some of the results of these experiments, and in particular compares the detailed dynamic stall inception information obtained from the oscillating wing with the unsteady separation and reverse flow results measured on the retreating blade side of the model rotor during wind tunnel testing.
Rotordynamic Modelling and Response Characteristics of an Active Magnetic Bearing Rotor System
NASA Technical Reports Server (NTRS)
Free, April M.; Flowers, George T.; Trent, Victor S.
1996-01-01
Auxiliary bearings are a critical feature of any magnetic bearing system. They protect the soft iron core of the magnetic bearing during an overload or failure. An auxiliary bearing typically consists of a rolling element bearing or bushing with a clearance gap between the rotor and the inner race of the support. The dynamics of such systems can be quite complex. It is desired to develop a rotordynamic model which describes the dynamic behavior of a flexible rotor system with magnetic bearings including auxiliary bearings. The model is based upon an experimental test facility. Some simulation studies are presented to illustrate the behavior of the model. In particular, the effects of introducing sideloading from the magnetic bearing when one coil fails is studied. These results are presented and discussed.
Mutual information in a dilute, asymmetric neural network model
NASA Astrophysics Data System (ADS)
Greenfield, Elliot
We study the computational properties of a neural network consisting of binary neurons with dilute asymmetric synaptic connections. This simple model allows us to simulate large networks which can reflect more of the architecture and dynamics of real neural networks. Our main goal is to determine the dynamical behavior that maximizes the network's ability to perform computations. To this end, we apply information theory, measuring the average mutual information between pairs of pre- and post-synaptic neurons. Communication of information between neurons is an essential requirement for collective computation. Previous workers have demonstrated that neural networks with asymmetric connections undergo a transition from ordered to chaotic behavior as certain network parameters, such as the connectivity, are changed. We find that the average mutual information has a peak near the order-chaos transition, implying that the network can most efficiently communicate information between cells in this region. The mutual information peak becomes increasingly pronounced when the basic model is extended to incorporate more biologically realistic features, such as a variable threshold and nonlinear summation of inputs. We find that the peak in mutual information near the phase transition is a robust feature of the system for a wide range of assumptions about post-synaptic integration.
Tilt Rotor Aircraft Aeroacoustics
NASA Technical Reports Server (NTRS)
George, Albert R.
1996-01-01
A fleet of civil tilt rotor transports offers a means of reducing airport congestion and point-to-point travel time. The speed, range, and fuel economy of these aircraft, along with their efficient use of vertiport area, make them good candidates for short-to-medium range civil transport. However, to be successfully integrated into the civilian community, the tilt rotor must be perceived as a quiet, safe, and economical mode of transportation that does not harm the environment. In particular, noise impact has been identified as a possible barrier to the civil tilt rotor. Along with rotor conversion-mode flight, and blade-vortex interaction noise during descent, hover mode is a noise problem for tilt rotor operations. In the present research, tilt rotor hover aeroacoustics have been studied analytically, experimentally, and computationally. Various papers on the subject were published as noted in the list of publications. More recently, experimental measurements were made on a 1/12.5 scale model of the XV-15 in hover and analyses of this data and extrapolations to full scale were also carried out. A dimensional analysis showed that the model was a good aeroacoustic approximation to the full-scale aircraft, and scale factors were derived to extrapolate the model measurements to the full-scale XV-15. The experimental measurements included helium bubble flow visualization, silk tuft flow visualization, 2-component hot wire anemometry, 7-hole pressure probe measurements, vorticity measurements, and outdoor far field acoustic measurements. The hot wire measurements were used to estimate the turbulence statistics of the flow field into the rotors, such as length scales, velocity scales, dissipation, and turbulence intermittency. Several different configurations of the model were tested: (1) standard configurations (single isolated rotor, two rotors without the aircraft, standard tilt rotor configuration); (2) flow control devices (the 'plate', the 'diagonal fences'); (3
Measurement and Modelling of Multicopter UAS Rotor Blades in Hover
NASA Technical Reports Server (NTRS)
Nowicki, Nathalie
2016-01-01
Multicopters are becoming one of the more common and popular type of unmanned aircraft systems (UAS) which have both civilian and military applications. One example being the concept of drone deliveries proposed by the distribution company Amazon [1]. The electrical propulsion is considered to have both faster and easier deliveries and also environmental benefits compared to other vehicles that still use fossil fuel. Other examples include surveillance and just simple entertainment. The reason behind their success is often said to be due to their small size, relatively low cost, simple structure and finally simple usage. With an increase in the UAS market comes challenges in terms of security, as both people and other aircrafts could be harmed if not used correctly. Therefore further studies and regulations are needed to ensure that future use of drones, especially in the civilian and public sectors, are safe and efficient. Thorough research has been done on full scale, man or cargo transporting, helicopters so that most parts of flight and performance are fairly well understood. Yet not much of it have been verified for small multicopters. Until today many studies and research projects have been done on the control systems, navigation and aerodynamics of multicopters. Many of the methods used today for building multicopters involve a process of trial an error of what will work well together, and once that is accomplished some structural analysis of the multicopter bodies might be done to verify that the product will be strong enough and have a decent aerodynamic performance. However, not much has been done on the research of the rotor blades, especially in terms of structural stress analyses and ways to ensure that the commonly used parts are indeed safe and follow safety measures. Some producers claim that their propellers indeed have been tested, but again that usually tends towards simple fluid dynamic analyses and even simpler stress analyses. There is no real
An asymmetric inhibition model of hemispheric differences in emotional processing
Grimshaw, Gina M.; Carmel, David
2014-01-01
Two relatively independent lines of research have addressed the role of the prefrontal cortex in emotional processing. The first examines hemispheric asymmetries in frontal function; the second focuses on prefrontal interactions between cognition and emotion. We briefly review each perspective and highlight inconsistencies between them. We go on to describe an alternative model that integrates approaches by focusing on hemispheric asymmetry in inhibitory executive control processes. The asymmetric inhibition model proposes that right-lateralized executive control inhibits processing of positive or approach-related distractors, and left-lateralized control inhibits negative or withdrawal-related distractors. These complementary processes allow us to maintain and achieve current goals in the face of emotional distraction. We conclude with a research agenda that uses the model to generate novel experiments that will advance our understanding of both hemispheric asymmetries and cognition-emotion interactions. PMID:24904502
Modeling and Control for an Asymmetric Hydraulic Active Suspension System
NASA Astrophysics Data System (ADS)
Kim, Wanil; Won, Sangchul
In this paper we present a model for an automotive active suspension system which includes the dynamics of an asymmetric hydraulic actuator. In this model the force exerted by a single-rod cylinder is regarded as an internal state, and the sum of the oil flow rates through the orifice of a servo valve as the control input. We obtain a linear time-invariant (LTI) state state equation and propose a force-tracking-free one-step control method which can accept various linear control techniques. An optimal state-feedback control is applied as an example. Quarter car test rig experiment results show the effectiveness of the proposed approach in modeling and control.
Simulation and experimental validation of the dynamical model of a dual-rotor vibrotactor
NASA Astrophysics Data System (ADS)
Miklós, Á.; Szabó, Z.
2015-01-01
In this work, a novel design for small vibrotactors called the Dual Excenter is presented, which makes it possible to produce vibrations with independently adjustable frequency and amplitude. This feature has been realized using two coaxially aligned eccentric rotors, which are driven by DC motors independently. The prototype of the device has been built, where mechanical components are integrated on a frame with two optical sensors for the measurement of angular velocity and phase angle. The system is equipped with a digital controller. Simulations confirm the results of analytical investigations and they allow us to model the sampling method of the signals of the angular velocity and the phase angle between the rotors. Furthermore, we model the discrete behavior of the controller, which is a PI controller for the angular velocities and a PID controller for the phase angle. Finally, simulation results are compared to experimental ones, which show that the Dual Excenter concept is feasible.
NASA Technical Reports Server (NTRS)
Bousman, William G.
1988-01-01
Two cases were selected for correlation from an experiment that examined the aeromechanical stability of a small-scale model rotor that used tantalum rods instead of blades to simulate vacuum conditions. The first case involved body roll freedom only while the second case included body pitch and roll degrees of freedom together. Analyses from Hughes Helicopters and the U.S. Army Aeromechanics Laboratory were compared with the data and the correlations ranged from poor to good.
Experimental and analytical studies of a model helicopter rotor in hover
NASA Technical Reports Server (NTRS)
Caradonna, F. X.; Tung, C.
1981-01-01
A benchmark test to aid the development of various rotor performance codes was conducted. Simultaneous blade pressure measurements and tip vortex surveys were made for a wide range of tip Mach numbers including the transonic flow regime. The measured tip vortex strength and geometry permit effective blade loading predictions when used as input to a prescribed wake lifting surface code. It is also shown that with proper inflow and boundary layer modeling, the supercritical flow regime can be accurately predicted.
Multidisciplinary Optimization of Tilt Rotor Blades Using Comprehensive Composite Modeling Technique
NASA Technical Reports Server (NTRS)
Chattopadhyay, Aditi; McCarthy, Thomas R.; Rajadas, John N.
1997-01-01
An optimization procedure is developed for addressing the design of composite tilt rotor blades. A comprehensive technique, based on a higher-order laminate theory, is developed for the analysis of the thick composite load-carrying sections, modeled as box beams, in the blade. The theory, which is based on a refined displacement field, is a three-dimensional model which approximates the elasticity solution so that the beam cross-sectional properties are not reduced to one-dimensional beam parameters. Both inplane and out-of-plane warping are included automatically in the formulation. The model can accurately capture the transverse shear stresses through the thickness of each wall while satisfying stress free boundary conditions on the inner and outer surfaces of the beam. The aerodynamic loads on the blade are calculated using the classical blade element momentum theory. Analytical expressions for the lift and drag are obtained based on the blade planform with corrections for the high lift capability of rotor blades. The aerodynamic analysis is coupled with the structural model to formulate the complete coupled equations of motion for aeroelastic analyses. Finally, a multidisciplinary optimization procedure is developed to improve the aerodynamic, structural and aeroelastic performance of the tilt rotor aircraft. The objective functions include the figure of merit in hover and the high speed cruise propulsive efficiency. Structural, aerodynamic and aeroelastic stability criteria are imposed as constraints on the problem. The Kreisselmeier-Steinhauser function is used to formulate the multiobjective function problem. The search direction is determined by the Broyden-Fletcher-Goldfarb-Shanno algorithm. The optimum results are compared with the baseline values and show significant improvements in the overall performance of the tilt rotor blade.
Strong coupling and quasispinor representations of the SU(3) rotor model
NASA Astrophysics Data System (ADS)
Rowe, D. J.; de Guise, H.
1992-06-01
We define a coupling scheme, in close parallel to the coupling scheme of Elliott and Wilsdon, in which nucleonic intrinsic spins are strongly coupled to SU(3) spatial wave functions. The scheme is proposed for shell-model calculations in strongly deformed nuclei and for semimicroscopic analyses of rotations in odd-mass nuclei and other nuclei for which the spin-orbit interaction is believed to play an important role. The coupling scheme extends the domain of utility of the SU(3) model, and the symplectic model, to heavy nuclei and odd-mass nuclei. It is based on the observation that the low angular-momentum states of an SU(3) irrep have properties that mimic those of a corresponding irrep of the rotor algebra. Thus, we show that strongly coupled spin-SU(3) bands behave like strongly coupled rotor bands with properties that approach those of irreducible representations of the rigid-rotor algebra in the limit of large SU(3) quantum numbers. Moreover, we determine that the low angular-momentum states of a strongly coupled band of states of half-odd integer angular momentum behave to a high degree of accuracy as if they belonged to an SU(3) irrep. These are the quasispinor SU(3) irreps referred to in the title.
Bogovalov, S. V.; Borisevich, V. D.; Borman, V. D.; Tronin, I. V.; Tronin, V. N.
2016-06-08
Numerical modelling and optimization of the gas flow and isotope separation in the Iguasu gas centrifuge (GC) for uranium enrichment have been performed for different lengths of the rotor. The calculations show that the specific separative power of the GC reduces with the length of the rotor. We show that the reduction of the specific separative power is connected with the growth of the pressure in the optimal regime and corresponding growth of temperature to prevent the working gas sublimation. The specific separative power remains constant with the growth of the rotor length provided that the temperature of the gas is taken to be constant.
NASA Astrophysics Data System (ADS)
Bogovalov, S. V.; Borisevich, V. D.; Borman, V. D.; Tronin, I. V.; Tronin, V. N.
2016-06-01
Numerical modelling and optimization of the gas flow and isotope separation in the Iguasu gas centrifuge (GC) for uranium enrichment have been performed for different lengths of the rotor. The calculations show that the specific separative power of the GC reduces with the length of the rotor. We show that the reduction of the specific separative power is connected with the growth of the pressure in the optimal regime and corresponding growth of temperature to prevent the working gas sublimation. The specific separative power remains constant with the growth of the rotor length provided that the temperature of the gas is taken to be constant.
The Effects of Ambient Conditions on Helicopter Rotor Source Noise Modeling
NASA Technical Reports Server (NTRS)
Schmitz, Frederic H.; Greenwood, Eric
2011-01-01
A new physics-based method called Fundamental Rotorcraft Acoustic Modeling from Experiments (FRAME) is used to demonstrate the change in rotor harmonic noise 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 noise is used together with parameter identification techniques to develop a model of helicopter external noise that is a hybrid between theory and experiment. The FRAME method is used to evaluate the main rotor harmonic noise of a Bell 206B3 helicopter operating at different altitudes. The variation with altitude of Blade-Vortex Interaction (BVI) noise, 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 noise levels. Results also show that thickness noise 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 noise source models may give incorrect noise estimates when they are used at conditions where data were not measured and may need to be corrected for mission land-use planning purposes.
Pulsatile flow in a compliant stenosed asymmetric model
NASA Astrophysics Data System (ADS)
Usmani, Abdullah Y.; Muralidhar, K.
2016-12-01
Time-varying velocity field in an asymmetric constricted tube is experimentally studied using a two-dimensional particle image velocimetry system. The geometry resembles a vascular disease which is characterized by arterial narrowing due to plaque deposition. The present study compares the nature of flow patterns in rigid and compliant asymmetric constricted tubes for a range of dimensionless parameters appearing in a human artery. A blood analogue fluid is employed along with a pump that mimics cardioflow conditions. The peak Reynolds number range is Re 300-800, while the Womersley number range considered in experiments is Wo 6-8. These values are based on the peak velocity in a straight rigid tube connected to the model, over a pulsation frequency range of 1.2-2.4 Hz. The medial-plane velocity distribution is used to investigate the nature of flow patterns. Temporal distribution of stream traces and hemodynamic factors including WSS, TAWSS and OSI at important phases of the pulsation cycle are discussed. The flow patterns obtained from PIV are compared to a limited extent against numerical simulation. Results show that the region downstream of the constriction is characterized by a high-velocity jet at the throat, while a recirculation zone, attached to the wall, evolves in time. Compliant models reveal large flow disturbances upstream during the retrograde flow. Wall shear stress values are lower in a compliant model as compared to the rigid. Cross-plane flow structures normal to the main flow direction are visible at select phases of the cycle. Positive values of largest Lyapunov exponent are realized for wall movement and are indicative of chaotic motion transferred from the flow to the wall. These exponents increase with Reynolds number as well as compliance. Period doubling is observed in wall displacement of highly compliant models, indicating possible triggering of hemodynamic events in a real artery that may cause fissure in the plaque deposits.
NASA Astrophysics Data System (ADS)
Stringer, David Blake
The overarching objective in this research is the development of a robust, rotor dynamic, physics based model of a helicopter drive train as a foundation for the prognostic modeling for rotary-wing transmissions. Rotorcrafts rely on the integrity of their drive trains for their airworthiness. Drive trains rely on gear technology for their integrity and function. Gears alter the vibration characteristics of a mechanical system and significantly contribute to noise, component fatigue, and personal discomfort prevalent in rotorcraft. This research effort develops methodologies for generating a rotor dynamic model of a rotary-wing transmission based on first principles, through (i) development of a three-dimensional gear-mesh stiffness model for helical and spur gears and integration of this model in a finite element rotor dynamic model, (ii) linear and nonlinear analyses of a geared system for comparison and validation of the gear-mesh model, (iii) development of a modal synthesis technique for potentially providing model reduction and faster analysis capabilities for geared systems, and (iv) extension of the gear-mesh model to bevel and epicyclic configurations. In addition to model construction and validation, faults indigenous to geared systems are presented and discussed. Two faults are selected for analysis and seeded into the transmission model. Diagnostic vibration parameters are presented and used as damage indicators in the analysis. The fault models produce results consistent with damage experienced during experimental testing. The results of this research demonstrate the robustness of the physics-based approach in simulating multiple normal and abnormal conditions. The advantages of this physics-based approach, when combined with contemporary probabilistic and time-series techniques, provide a useful method for improving health monitoring technologies in mechanical systems.
Generic icing effects on forward flight performance of a model helicopter rotor
NASA Technical Reports Server (NTRS)
Tinetti, Ana F.; Korkan, Kenneth D.
1989-01-01
An experimental program using a commercially available model helicopter has been conducted in the TAMU 7 ft x 10 ft Subsonic Wind Tunnel to investigate main rotor performance degradation due to generic ice adhesion. Base and iced performance data were gathered as functions of fuselage incidence, blade collective pitch, main rotor rotational velocity, and freestream velocity. The experimental values have shown that, in general, the presence of generic ice introduces decrements in performance caused by leading edge separation regions and increased surface roughness. In addition to the expected changes in aerodynamic forces caused by variations in test Reynolds number, forward flight data seemed to be influenced by changes in freestream and rotational velocity. The dependence of the data upon such velocity variations was apparently enhanced by increases in blade chord.
Surface pressure measurements at two tips of a model helicopter rotor in hover
NASA Technical Reports Server (NTRS)
Gray, R. B.; Mcmahon, H. M.; Shenoy, K. R.; Hammer, M. L.
1980-01-01
Surface pressures were measured near the tip of a hovering single-bladed model helicopter rotor with two tip shapes. The rotor had a constant-chord, untwisted blade with a square, flat tip which could be modified to a body-of-revolution tip. Pressure measurements were made on the blade surface along the chordwise direction at six radial stations outboard of the 94 percent blade radius. Data for each blade tip configuration were taken at blade collective pitch angles of 0, 6.18 and 11.4 degrees at a Reynolds number of 736,000 and a Mach number of 0.25 both based on tip speed. Chordwise pressure distributions and constant surface pressure contours are presented and discussed.
A model for asymmetric magnetoimpedance effect in multilayered bimagnetic films
NASA Astrophysics Data System (ADS)
Buznikov, N. A.; Antonov, A. S.
2016-12-01
The magnetoimpedance in three-layered bimagnetic film structure is studied theoretically. The structure consists of the soft and hard magnetic films separated by highly conductive non-magnetic layer. A model to describe the magnetoimpedance effect in the film structure based on a simultaneous solution of linearized Maxwell equations and Landau-Lifshitz equation is proposed. It is shown that magnetostatic coupling between the magnetic layers results in the asymmetry in the field dependence of the film impedance. The magnetostatic coupling is described in terms of an effective bias field appearing in the soft magnetic layer. The calculated field and frequency dependences of the film impedance are shown to be in a qualitative agreement with previous results of experimental studies of the asymmetric magnetoimpedance in NiFe/Cu/Co film structures. The results obtained may be useful for development of weak magnetic-field sensors.
Flight dynamics and control modelling of damaged asymmetric aircraft
NASA Astrophysics Data System (ADS)
Ogunwa, T. T.; Abdullah, E. J.
2016-10-01
This research investigates the use of a Linear Quadratic Regulator (LQR) controller to assist commercial Boeing 747-200 aircraft regains its stability in the event of damage. Damages cause an aircraft to become asymmetric and in the case of damage to a fraction (33%) of its left wing or complete loss of its vertical stabilizer, the loss of stability may lead to a fatal crash. In this study, aircraft models for the two damage scenarios previously mentioned are constructed using stability derivatives. LQR controller is used as a direct adaptive control design technique for the observable and controllable system. Dynamic stability analysis is conducted in the time domain for all systems in this study.
A Control System for the Wind Tunnel Model of a Reverse-Blowing Circulation Control Rotor (RB-CCR)
1976-05-01
for possible application, e.g., (1) sleeve valves , (2) cam driver poppet valves , (3) on-off (bang-bang) type valves , (4) cam nozzle valves , and (5...Identify by block number) Circulation Control Rotors Control System for High Speed Circulation Control Rotor Model Pneumatic Valving System, Dual Receiver...Continued on reverse side) 20. A STRACT (Continue on reverse side if neceesary iand IdjntIty by block number) A pneumatic valving system has been
Modeling the Asymmetric Wind of Massive LBV Binary MWC 314
NASA Astrophysics Data System (ADS)
Lobel, A.; Groh, J.; Torres Dozinel, K.; Gorlova, N.; Martayan, C.; Raskin, G.; Van Winckel, H.; Prins, S.; Pessemier, W.; Waelkens, C.; Frémat, Y.; Hensberge, H.; Dummortier, L.; Jorissen, A.; Van Eck, S.; Lehmann, H.
2012-12-01
Spectroscopic monitoring with Mercator-HERMES over the past two years reveals that MWC 314 is a massive binary system composed of an early B-type primary LBV star and a less-luminous supergiant companion. We determine an orbital period Porb of 60.85 d from optical S II and Ne I absorption lines observed in this single-lined spectroscopic binary. We find an orbital eccentricity of e = 0.26, and a large amplitude of the radial velocity curve of 80.6 km s-1. The ASAS V light-curve during our spectroscopic monitoring reveals two brightness minima (ΔV = 0.1 mag) over the orbital period due to partial eclipses at an orbital inclination angle of ˜ 70°. We find a clear correlation between the orbital phases and the detailed shapes of optical and near-IR P Cygni-type line profiles of He I, Si II, and double- or triple-peaked stationary cores of prominent Fe II emission lines. A preliminary 3-D radiative transfer model computed with Wind3D shows that the periodic P Cygni line profile variability results from an asymmetric common-envelope wind with enhanced density (or line opacity) in the vicinity of the LBV primary. The variable orientation of the inner LBV wind region due to the orbital motion produces variable P Cygni line profiles (with wind velocities of ˜ 200 km s-1) between orbital phases φ = 0.65 to 0.85, while weak inverse P Cygni profiles are observed half an orbital period later around φ = 0.15 to 0.35. We do not observe optical or near-IR He II, C III, and Si III lines, signaling that the LBV's spectral type is later than B0. Detailed modeling of the asymmetrical wind properties of massive binary MWC 314 provides important new physical information about the most luminous hot (binary) stars such as η Carinae.
Compressible cell gas models for asymmetric fluid criticality
NASA Astrophysics Data System (ADS)
Cerdeiriña, Claudio A.; Orkoulas, Gerassimos
2017-03-01
We thoroughly describe a class of models recently presented by Fisher and coworkers [Phys. Rev. Lett. 116, 040601 (2016)], 10.1103/PhysRevLett.116.040601. The crucial feature of such models, termed compressible cell gases (CCGs), is that the individual cell volumes of a lattice gas are allowed to fluctuate. They are studied via the seldom-used (μ , p , T ) ensemble, which leads to their exact mapping onto the Ising model. Remarkably, CCGs obey complete scaling, a formulation for the thermodynamic behavior of fluids near the gas-liquid critical point that accommodates features inherent to the asymmetric nature of this phase transition like the Yang-Yang (YY) and singular coexistence-curve diameter anomalies. The CCG0 models generated when volumes vary freely reveal local free volume fluctuations as the origin of these phenomena. Local energy-volume coupling is found to be another relevant microscopic factor. Furthermore, the CCG class is greatly extended by using the decoration transformation, with an interesting example being the Sastry-Debenedetti-Sciortino-Stanley model for hydrogen bonding in low-temperature water. The magnitude of anomalies is characterized by a single parameter, the YY ratio, which for the models so far considered here ranges from -∞ to 1/2 .
Measured Boundary Layer Transition and Rotor Hover Performance at Model Scale
NASA Technical Reports Server (NTRS)
Overmeyer, Austin D.; Martin, Preston B.
2017-01-01
An experiment involving a Mach-scaled, 11:08 f t: diameter rotor was performed in hover during the summer of 2016 at NASA Langley Research Center. The experiment investigated the hover performance as a function of the laminar to turbulent transition state of the boundary layer, including both natural and fixed transition cases. The boundary layer transition locations were measured on both the upper and lower aerodynamic surfaces simultaneously. The measurements were enabled by recent advances in infrared sensor sensitivity and stability. The infrared thermography measurement technique was enhanced by a paintable blade surface heater, as well as a new high-sensitivity long wave infrared camera. The measured transition locations showed extensive amounts, x=c>0:90, of laminar flow on the lower surface at moderate to high thrust (CT=s > 0:068) for the full blade radius. The upper surface showed large amounts, x=c > 0:50, of laminar flow at the blade tip for low thrust (CT=s < 0:045). The objective of this paper is to provide an experimental data set for comparisons to newly developed and implemented rotor boundary layer transition models in CFD and rotor design tools. The data is expected to be used as part of the AIAA Rotorcraft SimulationWorking Group
An integrated airloads-inflow model for use in rotor aeroelasticity and control analysis
NASA Technical Reports Server (NTRS)
Peters, David A.; Su, AY
1991-01-01
The airloads-inflow model presented is ideally suited for rotor aeroelasticity and control analysis, especially where eigenvalues are sought. The model, which is derived from thin-airfoil theory with an extension that allows for other airfoil effects, is of hierarchical-lift type and may be simplified to any degree desired; the inflow is also expanded in shape functions which may be truncated to any desired texture. Both models are written in closed-form, state-variable equations without hidden states and without integrals over the wake.
Identification of a linear model of rotor-fuselage dynamics from nonlinear simulation data
NASA Technical Reports Server (NTRS)
Duval, R. W.; Mackie, D. B.
1980-01-01
Linear regression techniques are used to obtain 9- and 12-degree-of-freedom linear rotorcraft models from the input-output data generated by a nonlinear, blade-element rotorcraft simulation in hover. The resulting models are used to evaluate the coupling of the fuselage modes with the rotor flapping and lead-lag modes at various frequencies. New techniques are proposed and evaluated to improve the identification process, including a method of verifying the assumed model structure by using data sets generated at different input frequencies.
Vortex modeling for rotor aerodynamics - The 1991 Alexander A. Nikolsky Lecture
NASA Technical Reports Server (NTRS)
Gray, Robin B.
1992-01-01
The efforts toward realistic vortex modeling for rotary wings which began under the guidance of professor A. A. Nikolsky of Princeton University in 1955-1956 are discussed. Attention is given to Nikolsky's flow-visualization studies and major theoretical considerations for vortex modeling. More recent efforts by other researchers have led to models of increasing complexity. The neglect of compressibility and viscous effects in the classical approach is noted to be a major limiting factor in full-scale rotor applications of the classical vortex theory; it has nevertheless been valuable for the delineation of problem areas and the guiding of both experimental and theoretical investigations.
NASA Astrophysics Data System (ADS)
Jiang, Kejian; Zhu, Changsheng; Chen, Liangliang; Qiao, Xiaoli
2015-08-01
To represent the support characteristic of active magnetic bearings (AMB), the commonly used parameters are the equivalent stiffness and the equivalent damping, which inherit the parameters of the stiffness and the damping from traditional mechanical bearings. First, by analyzing the diversity and the similarity between traditional mechanical bearing and AMB, the prior condition for applying the parametric representation of equivalent stiffness and equivalent damping to AMB is illuminated. Then, a method for measuring the equivalent stiffness and the equivalent damping of AMB-rotor system is proposed with multi-frequency excitation. One of its outstanding features is that the proposed method is based on the multi-degree of freedom (DOF) rotor model, not the single- DOF model, because the single DOF model cannot be suitably applied to the multi-DOF AMB-rotor systems. Otherwise, in order to decrease the identification error, the multi-frequency excitation can achieve the lowest peak value by means of appropriate selection for the relative phasing of each component, so that the possibility of the rotor displacement exceeding clearances of AMB and the magnetic force reaching saturation is minimized. Finally, the experiments, which are carried out on an AMB-rotor test rig with a vertical shaft, indicate that the proposed method can efficiently reduce the peak value for the superimposed multi-frequency excitation and correctly identify the equivalent stiffness and equivalent damping of AMB-rotor system.
Metallic Rotor Sizing and Performance Model for Flywheel Systems
NASA Technical Reports Server (NTRS)
Moore, Camille J.; Kraft, Thomas G.
2012-01-01
The NASA Glenn Research Center (GRC) is developing flywheel system requirements and designs for terrestrial and spacecraft applications. Several generations of flywheels have been designed and tested at GRC using in-house expertise in motors, magnetic bearings, controls, materials and power electronics. The maturation of a flywheel system from the concept phase to the preliminary design phase is accompanied by maturation of the Integrated Systems Performance model, where estimating relationships are replaced by physics based analytical techniques. The modeling can incorporate results from engineering model testing and emerging detail from the design process.
Rotor-vortex interaction noise
NASA Technical Reports Server (NTRS)
Schlinker, R. H.; Amiet, R. K.
1983-01-01
A theoretical and experimental study was conducted to develop a validated first principles analysis for predicting noise generated by helicopter main-rotor shed vortices interacting with the tail rotor. The generalized prediction procedure requires a knowledge of the incident vortex velocity field, rotor geometry, and rotor operating conditions. The analysis includes compressibility effects, chordwise and spanwise noncompactness, and treats oblique intersections with the blade planform. Assessment of the theory involved conducting a model rotor experiment which isolated the blade-vortex interaction noise from other rotor noise mechanisms. An isolated tip vortex, generated by an upstream semispan airfoil, was convected into the model tail rotor. Acoustic spectra, pressure signatures, and directivity were measured. Since assessment of the acoustic prediction required a knowledge of the vortex properties, blade-vortes intersection angle, intersection station, vortex stength, and vortex core radius were documented. Ingestion of the vortex by the rotor was experimentally observed to generate harmonic noise and impulsive waveforms.
Generic phase coexistence in the totally asymmetric kinetic Ising model
NASA Astrophysics Data System (ADS)
Godrèche, Claude; Luck, Jean-Marc
2017-07-01
The physical analysis of generic phase coexistence in the North-East-Center Toom model was originally given by Bennett and Grinstein. The gist of their argument relies on the dynamics of interfaces and droplets. We revisit the same question for a specific totally asymmetric kinetic Ising model on the square lattice. This nonequilibrium model possesses the remarkable property that its stationary-state measure in the absence of a magnetic field coincides with that of the usual ferromagnetic Ising model. We use both analytical arguments and numerical simulations in order to make progress in the quantitative understanding of the phenomenon of generic phase coexistence. At zero temperature a mapping onto the TASEP allows an exact determination of the time-dependent shape of the ballistic interface sweeping a large square minority droplet of up or down spins. At finite temperature, measuring the mean lifetime of such a droplet allows an accurate measurement of its shrinking velocity v, which depends on temperature T and magnetic field h. In the absence of a magnetic field, v vanishes with an exponent Δ_v≈2.5+/-0.2 as the critical temperature T c is approached. At fixed temperature in the ordered phase, v vanishes at the phase-boundary fields +/- h_b(T) which mark the limits of the coexistence region. The latter fields vanish with an exponent Δ_h≈3.2+/-0.3 as T c is approached.
Parameterized reduced order modeling of misaligned stacked disks rotor assemblies
NASA Astrophysics Data System (ADS)
Ganine, Vladislav; Laxalde, Denis; Michalska, Hannah; Pierre, Christophe
2011-01-01
Light and flexible rotating parts of modern turbine engines operating at supercritical speeds necessitate application of more accurate but rather computationally expensive 3D FE modeling techniques. Stacked disks misalignment due to manufacturing variability in the geometry of individual components constitutes a particularly important aspect to be included in the analysis because of its impact on system dynamics. A new parametric model order reduction algorithm is presented to achieve this goal at affordable computational costs. It is shown that the disks misalignment leads to significant changes in nominal system properties that manifest themselves as additional blocks coupling neighboring spatial harmonics in Fourier space. Consequently, the misalignment effects can no longer be accurately modeled as equivalent forces applied to a nominal unperturbed system. The fact that the mode shapes become heavily distorted by extra harmonic content renders the nominal modal projection-based methods inaccurate and thus numerically ineffective in the context of repeated analysis of multiple misalignment realizations. The significant numerical bottleneck is removed by employing an orthogonal projection onto the subspace spanned by first few Fourier harmonic basis vectors. The projected highly sparse systems are shown to accurately approximate the specific misalignment effects, to be inexpensive to solve using direct sparse methods and easy to parameterize with a small set of measurable eccentricity and tilt angle parameters. Selected numerical examples on an industrial scale model are presented to illustrate the accuracy and efficiency of the algorithm implementation.
Quantum rotor description of the Mott-insulator transition in the Bose-Hubbard model
Polak, T. P.; Kopec, T. K.
2007-09-01
We present an approach to the Bose-Hubbard model using the U(1) quantum rotor description. The effective action formalism allows us to formulate a problem in the phase only action and obtain analytical formulas for the critical lines. We show that the nontrivial U(1) phase field configurations have an impact on the phase diagrams. The topological character of the quantum field is governed by terms of the integer charges--winding numbers. The comparison of presented results to recently obtained quantum Monte Carlo numerical calculations suggests that the competition between quantum effects in strongly interacting boson systems is correctly captured by our model.
Dynamic modelling and experimental study of asymmetric optothermal microactuator
NASA Astrophysics Data System (ADS)
Wang, Shuying; Chun, Qin; You, Qingyang; Wang, Yingda; Zhang, Haijun
2017-01-01
This paper reports the dynamic modelling and experimental study of an asymmetric optothermal microactuator (OTMA). According to the principle of thermal flux, a theoretical model for instantaneous temperature distribution of an expansion arm is established and the expression of expansion increment is derived. Dynamic expansion properties of the arm under laser pulse irradiation are theoretically analyzed indicating that both of the maximum expansion and expansion amplitude decrease with the pulse frequency increasing. Experiments have been further carried out on an OTMA fabricated by using an excimer laser micromachining system. It is shown that the OTMA deflects periodically with the same frequency of laser pulse irradiation. Experimental results also prove that both OTMA's maximum deflection and deflection amplitude (related to maximum expansion and expansion amplitude of the arm) decrease as frequency increases, matching with the theoretical model quite well. Even though the OTMA's deflection decrease at higher frequency, it is still capable of generating 8.2 μm maximum deflection and 4.2 μm deflection amplitude under 17 Hz/2 mW laser pulse irradiation. This work improves the potential applications of optothermal microactuators in micro-opto-electro-mechanical system (MOEMS) and micro/nano-technology fields.
Nearfield Unsteady Pressures at Cruise Mach Numbers for a Model Scale Counter-Rotation Open Rotor
NASA Technical Reports Server (NTRS)
Stephens, David B.
2012-01-01
An open rotor experiment was conducted at cruise Mach numbers and the unsteady pressure in the nearfield was measured. The system included extensive performance measurements, which can help provide insight into the noise generating mechanisms in the absence of flow measurements. A set of data acquired at a constant blade pitch angle but various rotor speeds was examined. The tone levels generated by the front and rear rotor were found to be nearly equal when the thrust was evenly balanced between rotors.
Nonlinear dynamic modeling of rotor system supported by angular contact ball bearings
NASA Astrophysics Data System (ADS)
Wang, Hong; Han, Qinkai; Zhou, Daning
2017-02-01
In current bearing dynamic models, the displacement coordinate relations are usually utilized to approximately obtain the contact deformations between the rolling element and raceways, and then the nonlinear restoring forces of the rolling bearing could be calculated accordingly. Although the calculation efficiency is relatively higher, the accuracy is lower as the contact deformations should be solved through iterative analysis. Thus, an improved nonlinear dynamic model is presented in this paper. Considering the preload condition, surface waviness, Hertz contact and elastohydrodynamic lubrication, load distribution analysis is solved iteratively to more accurately obtain the contact deformations and angles between the rolling balls and raceways. The bearing restoring forces are then obtained through iteratively solving the load distribution equations at every time step. Dynamic tests upon a typical rotor system supported by two angular contact ball bearings are conducted to verify the model. Through comparisons, the differences between the nonlinear dynamic model and current models are also pointed out. The effects of axial preload, rotor eccentricity and inner/outer waviness amplitudes on the dynamic response are discussed in detail.
Casimir force in the rotor model with twisted boundary conditions.
Bergknoff, Jonathan; Dantchev, Daniel; Rudnick, Joseph
2011-10-01
We investigate the three-dimensional lattice XY model with nearest neighbor interaction. The vector order parameter of this system lies on the vertices of a cubic lattice, which is embedded in a system with a film geometry. The orientations of the vectors are fixed at the two opposite sides of the film. The angle between the vectors at the two boundaries is α where 0≤α≤π. We make use of the mean field approximation to study the mean length and orientation of the vector order parameter throughout the film--and the Casimir force it generates--as a function of the temperature T, the angle α, and the thickness L of the system. Among the results of that calculation are a Casimir force that depends in a continuous way on both the parameter α and the temperature and that can be attractive or repulsive. In particular, by varying α and/or T one controls both the sign and the magnitude of the Casimir force in a reversible way. Furthermore, for the case α=π, we discover an additional phase transition occurring only in the finite system associated with the variation of the orientations of the vectors.
Statistics of a neuron model driven by asymmetric colored noise.
Müller-Hansen, Finn; Droste, Felix; Lindner, Benjamin
2015-02-01
Irregular firing of neurons can be modeled as a stochastic process. Here we study the perfect integrate-and-fire neuron driven by dichotomous noise, a Markovian process that jumps between two states (i.e., possesses a non-Gaussian statistics) and exhibits nonvanishing temporal correlations (i.e., represents a colored noise). Specifically, we consider asymmetric dichotomous noise with two different transition rates. Using a first-passage-time formulation, we derive exact expressions for the probability density and the serial correlation coefficient of the interspike interval (time interval between two subsequent neural action potentials) and the power spectrum of the spike train. Furthermore, we extend the model by including additional Gaussian white noise, and we give approximations for the interspike interval (ISI) statistics in this case. Numerical simulations are used to validate the exact analytical results for pure dichotomous noise, and to test the approximations of the ISI statistics when Gaussian white noise is included. The results may help to understand how correlations and asymmetry of noise and signals in nerve cells shape neuronal firing statistics.
Rotor Dynamic Inflow Derivatives and Time Constants from Various Inflow Models.
1980-12-01
DEGREES Angle of the (3,1) is$ Element of COMPLEX LINV(3,1) Inverted Complex L(K) Matrix for a Sweep (Corrected P sk ,’ Pressure) HA S E A NC L E -So...66. Banerjee , D., Crews, S . T., Hohenemser, K. H., and Yin, S . K., "State and Parameter Identification Applied to Rotor Model Dynamic Test Results...34, Journal of the American Helicopter Society, April 1977. 67. Banerjee , D., Crews, S . T., and Hohenemser, K. H., "Parameter Identification Applied to
Vortex Wake Geometry of a Model Tilt Rotor in Forward Flight
NASA Technical Reports Server (NTRS)
Yamauchi, G. K.; Johnson, W.; Wadcock, A. J.
2002-01-01
The vortex wake trajectory from one rotor of a 0.25-scale V-22 tiltrotor model was measured for four test conditions in the NASA Ames 40- by 80-Foot Wind Tunnel. Vortex wake images were acquired using a laser light sheet and video camera. Wake trajectories were constructed by extracting vortex positions from the video images. Wake trajectories were also calculated using the comprehensive analysis CAMRAD II. Measured and calculated wake geometries exhibit similar trends when advance ratio is varied at fixed thrust or when thrust is varied at fixed advance ratio.
Vortex Wake Geometry of a Model Tilt Rotor in Forward Flight
NASA Technical Reports Server (NTRS)
Yamauchi, G. K.; Johnson, W.; Wadcock, A. J.
2002-01-01
The vortex wake trajectory from one rotor of a 0.25-scale V-22 tiltrotor model was measured for four test conditions in the NASA Ames 40- by 80-Foot Wind Tunnel. Vortex wake images were acquired using a laser light sheet and video camera. Wake trajectories were constructed by extracting vortex positions from the video images. Wake trajectories were also calculated using the comprehensive analysis CAMRAD II. Measured and calculated wake geometries exhibit similar trends when advance ratio is varied at fixed thrust or when thrust is varied at fixed advance ratio.
Dynamic behavior of dissymmetric rotor bearings modelled with a periodic coefficient large system
NASA Technical Reports Server (NTRS)
Guilhen, P. M.; Berthier, P.; Ferraris, G.; Lalanne, M.
1987-01-01
The instability and unbalance response of dissymmetric rotor-bearing systems containing periodic coefficients when modeling produces matrices with a large number of degrees of freedom are discussed. It is important to solve the equations and then predict the dynamic behavior of the system. This can be done knowing the instability areas and the unbalance response in the stable areas. One deals here with a large number of equations and a reduction of the number of degrees of freedom of the system is achieved through a pseudo modal method. This method is shown to give satisfactory results.
Modelling crystal growth: Convection in an asymmetrically heated ampoule
NASA Technical Reports Server (NTRS)
Alexander, J. Iwan D.; Rosenberger, Franz; Pulicani, J. P.; Krukowski, S.; Ouazzani, Jalil
1990-01-01
The objective was to develop and implement a numerical method capable of solving the nonlinear partial differential equations governing heat, mass, and momentum transfer in a 3-D cylindrical geometry in order to examine the character of convection in an asymmetrically heated cylindrical ampoule. The details of the numerical method, including verification tests involving comparison with results obtained from other methods, are presented. The results of the study of 3-D convection in an asymmetrically heated cylinder are described.
NASA Technical Reports Server (NTRS)
Castles, Walter, Jr; Gray, Robin B
1951-01-01
The empirical relation between the induced velocity, thrust, and rate of vertical descent of a helicopter rotor was calculated from wind tunnel force tests on four model rotors by the application of blade-element theory to the measured values of the thrust, torque, blade angle, and equivalent free-stream rate of descent. The model tests covered the useful range of C(sub t)/sigma(sub e) (where C(sub t) is the thrust coefficient and sigma(sub e) is the effective solidity) and the range of vertical descent from hovering to descent velocities slightly greater than those for autorotation. The three bladed models, each of which had an effective solidity of 0.05 and NACA 0015 blade airfoil sections, were as follows: (1) constant-chord, untwisted blades of 3-ft radius; (2) untwisted blades of 3-ft radius having a 3/1 taper; (3) constant-chord blades of 3-ft radius having a linear twist of 12 degrees (washout) from axis of rotation to tip; and (4) constant-chord, untwisted blades of 2-ft radius. Because of the incorporation of a correction for blade dynamic twist and the use of a method of measuring the approximate equivalent free-stream velocity, it is believed that the data obtained from this program are more applicable to free-flight calculations than the data from previous model tests.
NASA Technical Reports Server (NTRS)
Castles, Walter, Jr.; Gray, Robin B.
1951-01-01
The empirical relation between the induced velocity, thrust, and rate of vertical descent of a helicopter rotor was calculated from wind tunnel force tests on four model rotors by the application of blade-element theory to the measured values of the thrust, torque, blade angle, and equivalent free-stream rate of descent. The model tests covered the useful range of C(sub t)/sigma(sub e) (where C(sub t) is the thrust coefficient and sigma(sub e) is the effective solidity) and the range of vertical descent from hovering to descent velocities slightly greater than those for autorotation. The three bladed models, each of which had an effective solidity of 0.05 and NACA 0015 blade airfoil sections, were as follows: (1) constant-chord, untwisted blades of 3-ft radius; (2) untwisted blades of 3-ft radius having a 3/1 taper; (3) constant-chord blades of 3-ft radius having a linear twist of 12 degrees (washout) from axis of rotation to tip; and (4) constant-chord, untwisted blades of 2-ft radius. Because of the incorporation of a correction for blade dynamic twist and the use of a method of measuring the approximate equivalent free-stream velocity, it is believed that the data obtained from this program are more applicable to free-flight calculations than the data from previous model tests.
Lifetime Measurements of ^170Hf and a test of the Confined Beta Soft Rotor Model
NASA Astrophysics Data System (ADS)
Smith, M. K.; Werner, V.; Heinz, A.; Terry, J. R.; Qian, J.; Winkler, R.; Casperson, R.; Williams, E.; Berant, Z.; L"Uttke, R.; Shoraka, B.; Henning, G.
2009-10-01
Significant deviations from rigid rotor model energy level predictions have been known to occur in rare earth nuclei. Recently, it was shown these deviations may be caused by centrifugal stretching effects within the nucleus [1]. New geometrical models have been proposed that account for centrifugal stretching, such as the confined beta soft model (CBS). We present the results from a high precision lifetime experiment performed with the New Yale Plunger Device at WNSL, Yale University. The ground state band of ^170Hf was measured through the J=12^+ level using the Recoil Distance Doppler Shift method. Excited states were populated in the ^124Sn(^50Ti,γ)^170Hf fusion evaporation reaction. Using the lifetimes, the B(E2) values and the quadrupole deformation parameter are determined. Centrifugal stretching is observed as an increased deviation in energy at higher spins in 170Hf. These results are compared to theoretical predictions from the CBS rotor model. Supported by grant DE-FG02-91ER40609.[4pt] [1] Costin et al, Phys.Rev. C 79, 024307 (2009)
NASA Astrophysics Data System (ADS)
Toni Liong, Rugerri; Proppe, Carsten
2013-04-01
The breathing mechanism of a transversely cracked rotor and its influence on a rotor system that appears due to shaft weight and inertia forces is studied. A method is proposed for the evaluation of the stiffness losses in the cross-section that contains the crack. This method is based on a cohesive zone model (CZM) instead of linear elastic fracture mechanics (LEFM). The CZM is developed for mode-I plane strain conditions and accounts explicitly for triaxiality of the stress state by using constitutive relations. The breathing crack is modelled by a parabolic shape. As long as the relative crack depth is small, a crack closure straight line model may be used, while the crack closure parabolic line should be used in the case of a deep crack. The CZM is also implemented in a one-dimensional continuum rotor model by means of finite element (FE) discretisation in order to predict and to analyse the dynamic behavior of a cracked rotor. The proposed method provides a useful tool for the analysis of rotor systems containing cracks.
NASA Technical Reports Server (NTRS)
Splettstoesser, W. R.; Schultz, K. J.; Boxwell, D. A.; Schmitz, F. H.
1984-01-01
Acoustic data taken in the anechoic Deutsch-Niederlaendischer Windkanal (DNW) have documented the blade vortex interaction (BVI) impulsive noise radiated from a 1/7-scale model main rotor of the AH-1 series helicopter. Averaged model scale data were compared with averaged full scale, inflight acoustic data under similar nondimensional test conditions. At low advance ratios (mu = 0.164 to 0.194), the data scale remarkable well in level and waveform shape, and also duplicate the directivity pattern of BVI impulsive noise. At moderate advance ratios (mu = 0.224 to 0.270), the scaling deteriorates, suggesting that the model scale rotor is not adequately simulating the full scale BVI noise; presently, no proved explanation of this discrepancy exists. Carefully performed parametric variations over a complete matrix of testing conditions have shown that all of the four governing nondimensional parameters - tip Mach number at hover, advance ratio, local inflow ratio, and thrust coefficient - are highly sensitive to BVI noise radiation.
Triaxial rotor model description of E2 properties in {sup 186,188,190,192}Os
Allmond, J. M.; Zaballa, R.; Oros-Peusquens, A. M.; Kulp, W. D.; Wood, J. L.
2008-07-15
The triaxial rotor model with independent inertia and electric quadrupole tensors is applied to the description of the extensive set of E2 matrix elements available for {sup 186,188,190,192}Os. Most large and medium transition E2 matrix elements can be reproduced to within {approx}10%, and most diagonal elements to within {approx}30%. Most small transition matrix elements can be reproduced to within {approx}30%, and they support the interference effect exhibited by the model between the inertia and E2 tensors: this is a new feature of quantum rotor models. The diagonal E2 matrix elements at higher spins in the K=2 band are extremely sensitive to admixtures of higher K values: the low experimental values in {sup 190,192}Os indicate significant admixtures of K=4 components. Attention is given to the K{sup {pi}}=4{sup +} bands in these nuclei and the controversial issue of whether they are of quadrupole or hexadecapole nature.
Helicopter tail rotor noise analyses
NASA Technical Reports Server (NTRS)
George, A. R.; Chou, S. T.
1986-01-01
A study was made of helicopter tail rotor noise, particularly that due to interactions with the main rotor tip vortices, and with the fuselage separation mean wake. The tail rotor blade-main rotor tip vortex interaction is modelled as an airfoil of infinite span cutting through a moving vortex. The vortex and the geometry information required by the analyses are obtained through a free wake geometry analysis of the main rotor. The acoustic pressure-time histories for the tail rotor blade-vortex interactions are then calculated. These acoustic results are compared to tail rotor loading and thickness noise, and are found to be significant to the overall tail rotor noise generation. Under most helicopter operating conditions, large acoustic pressure fluctuations can be generated due to a series of skewed main rotor tip vortices passing through the tail rotor disk. The noise generation depends strongly upon the helicopter operating conditions and the location of the tail rotor relative to the main rotor.
NASA Technical Reports Server (NTRS)
Kelley, Henry L.
1990-01-01
Performance of a 27 percent scale model rotor designed for the AH-64 helicopter (alternate rotor) was measured in hover and forward flight and compared against and AH-64 baseline rotor model. Thrust, rotor tip Mach number, advance ratio, and ground proximity were varied. In hover, at a nominal thrust coefficient of 0.0064, the power savings was about 6.4 percent for the alternate rotor compared to the baseline. The corresponding thrust increase at this condition was approx. 4.5 percent which represents an equivalent full scale increase in lift capability of about 660 lbs. Comparable results were noted in forward flight except for the high thrust, high speed cases investigated where the baseline rotor was slightly superior. Reduced performance at the higher thrusts and speeds was likely due to Reynolds number effects and blade elasticity differences.
NASA Technical Reports Server (NTRS)
Mineck, Raymond E.; Gorton, Susan A.
2000-01-01
A wind tunnel test of a generic helicopter fuselage model with an independently mounted rotor has been conducted to obtain steady and periodic pressure data on the helicopter body. The model was tested at four advance ratios and three thrust coefficients. The periodic unsteady pressure coefficients are marked by four peaks associated with the passage of the four rotor blades. Blade passage effects are largest on the nose and tail boom of the model. The magnitude of the pulse increases with rotor thrust coefficient. Tabular listings of the unsteady pressure data are included to permit independent analysis. A CD-rom containing the steady and unsteady pressure data presented in the report is available from the authors.
An Update on Phased Array Results Obtained on the GE Counter-Rotating Open Rotor Model
NASA Technical Reports Server (NTRS)
Podboy, Gary; Horvath, Csaba; Envia, Edmane
2013-01-01
Beamform maps have been generated from 1) simulated data generated by the LINPROP code and 2) actual experimental phased array data obtained on the GE Counter-rotating open rotor model. The beamform maps show that many of the tones in the experimental data come from their corresponding Mach radius. If the phased array points to the Mach radius associated with a tone then it is likely that the tone is a result of the loading and thickness noise on the blades. In this case, the phased array correctly points to where the noise is coming from and indicates the axial location of the loudest source in the image but not necessarily the correct vertical location. If the phased array does not point to the Mach radius associated with a tone then some mechanism other than loading and thickness noise may control the amplitude of the tone. In this case, the phased array may or may not point to the actual source. If the source is not rotating it is likely that the phased array points to the source. If the source is rotating it is likely that the phased array indicates the axial location of the loudest source but not necessarily the correct vertical location. These results indicate that you have to be careful in how you interpret phased array data obtained on an open rotor since they may show the tones coming from a location other than the source location. With a subsonic tip speed open rotor the tones can come form locations outboard of the blade tips. This has implications regarding noise shielding.
NASA Technical Reports Server (NTRS)
Hill, Gary; Du Val, Ronald W.; Green, John A.; Huynh, Loc C.
1990-01-01
A piloted comparison of rigid and aeroelastic blade-element rotor models was conducted at the Crew Station Research and Development Facility (CSRDF) at Ames Research Center. FLIGHTLAB, a new simulation development and analysis tool, was used to implement these models in real time using parallel processing technology. Pilot comments and quantitative analysis performed both on-line and off-line confirmed that elastic degrees of freedom significantly affect perceived handling qualities. Trim comparisons show improved correlation with flight test data when elastic modes are modeled. The results demonstrate the efficiency with which the mathematical modeling sophistication of existing simulation facilities can be upgraded using parallel processing, and the importance of these upgrades to simulation fidelity.
NASA Technical Reports Server (NTRS)
Holms, A. G.
1977-01-01
A statistical decision procedure called chain pooling had been developed for model selection in fitting the results of a two-level fixed-effects full or fractional factorial experiment not having replication. The basic strategy included the use of one nominal level of significance for a preliminary test and a second nominal level of significance for the final test. The subject has been reexamined from the point of view of using as many as three successive statistical model deletion procedures in fitting the results of a single experiment. The investigation consisted of random number studies intended to simulate the results of a proposed aircraft turbine-engine rotor-burst-protection experiment. As a conservative approach, population model coefficients were chosen to represent a saturated 2 to the 4th power experiment with a distribution of parameter values unfavorable to the decision procedures. Three model selection strategies were developed.
NASA Astrophysics Data System (ADS)
Sasi, Ahmed Y. Ben; Gu, Fengshou; Li, Yuhua; Ball, Andrew D.
2006-10-01
Instantaneous angular speed (IAS)-based condition monitoring is an area in which significant progress has been achieved over the recent years. This condition monitoring technique is less known compared to the existing conventional methods. This paper presents model-predicted simulation and experimental results of broken rotor bar faults in a three-phase induction motor using IAS variations. The simulation was performed under normal, and a broken rotor bar fault. The present paper evaluates through simulating and measuring the IAS of an induction motor at broken rotor bar faults in both time and frequency domains. Experimental results show a good agreement with the model-predicted simulation results. Three vital key features were extracted from the angular speed variations. One feature is the modulating contour of pole pass frequency periods in time domain. The other two features are in frequency domain. The primary feature is the presence of the pole pass frequency component at the low-frequency region of the IAS spectrum. The secondary feature which are the multiple of pole pass frequency sideband components around the rotor speed frequency component. Experimental results confirm the validity of the simulation results for the proposed method. The IAS has demonstrated more sensitivity than current signature analysis in detecting the fault. This research also shows the power of angular speed features as a useful tool to detect broken rotor bar deteriorations using any economical transducer such as low-resolution rotary shaft encoders; which may well be already installed for process control purposes.
Shen, Chen
2014-04-01
The goal of this project is to model creep-fatigue-environment interactions in steam turbine rotor materials for advanced ultra-supercritical (A-USC) coal power Alloy 282 plants, to develop and demonstrate computational algorithms for alloy property predictions, and to determine and model key mechanisms that contribute to the damages caused by creep-fatigue-environment interactions.
NASA Technical Reports Server (NTRS)
Johnson, W.
1976-01-01
A mathematical model is developed for the dynamics of a wind tunnel support system consisting of a balance frame, struts, and an aircraft or test module. Data are given for several rotor test modules in the Ames 40 by 80 ft wind tunnel. A model for ground resonance calculations is also described.
Tilt rotor hover aeroacoustics
NASA Technical Reports Server (NTRS)
Coffen, Charles David
1992-01-01
The methodology, results, and conclusions of a study of tilt rotor hover aeroacoustics and aerodynamics are presented. Flow visualization and hot wire velocity measurement were performed on a 1/12-scale model of the XV-15 Tilt Rotor Aircraft in hover. The wing and fuselage below the rotor cause a complex recirculating flow. Results indicate the physical dimensions and details of the flow including the relative unsteadiness and turbulence characteristics of the flow. Discrete frequency harmonic thickness and the loading noise mechanism were predicted using WOPWOP for the standard metal blades and the Advanced Technology Blades. The recirculating flow created by the wing below the rotor is a primary sound mechanism for a hovering tilt rotor. The effects of dynamic blade response should be included for fountain flow conditions which produce impulsive blade loading. Broadband noise mechanisms were studied using Amiet's method with azimuthally varying turbulence characteristics derived from the measurements. The recirculating fountain flow with high turbulence levels in the recirculating zone is the dominant source of broadband noise for a hovering rotor. It is shown that tilt rotor hover aeroacoustic noise mechanisms are now understood. Noise predictions can be made based on reasonably accurate aerodynamic models developed here.
A quasi-three-dimensional model for intra-stator transport of rotor wakes
NASA Astrophysics Data System (ADS)
Ng, W. F.; Epstein, A. H.
The time-resolved flowfield in a high thru-flow compressor stage has been studied using a higher frequency response angle probe and a newly developed time-resolved total temperature and pressure probe. The investigation revealed the presence of large gapwise nonuniformity (20C) in stagnation temperature at the stator exit. A quasi-three-dimensional wake transport model, modified from that developed by Kerrebrock and Mikolajczak, was used to investigate the transport of the wake fluid within the stator passage. The present model accounts for three-dimensional effect by including the radial velocity in the wake. In addition, the relative flow angle is not assumed to be uniform across the wake and the inviscid core. The model compares favorably with measurements taken at the stator exit plane. The loss associated with the recirculation of the rotor wake within the stator passage is also calculated.
Modeling XV-15 tilt-rotor aircraft dynamics by frequency and time-domain identification techniques
NASA Technical Reports Server (NTRS)
Tischler, Mark B.; Kaletka, Juergen
1987-01-01
Models of the open-loop hover dynamics of the XV-15 Tilt-Rotor Aircraft are extracted from flight data using two approaches: frequency domain and time-domain identification. Both approaches are reviewed and the identification results are presented and compared in detail. The extracted models are compared favorably, with the differences associated mostly with the inherent weighing of each technique. Step responses are used to show that the predictive capability of the models from both techniques is excellent. Based on the results of this study, the relative strengths and weaknesses of the frequency and time-domain techniques are summarized and a proposal for a coordinated parameter identification approach is presented.
Modeling XV-15 tilt-rotor aircraft dynamics by frequency and time-domain identification techniques
NASA Technical Reports Server (NTRS)
Tischler, Mark B.; Kaletka, Juergen
1986-01-01
Models of the open-loop hover dynamics of the XV-15 Tilt-Rotor Aircraft are extracted from flight data using two approaches: frequency-domain and time-domain identification. Both approaches are reviewed and the identification results are presented and compared in detail. The extracted models compare favorable, with the differences associated mostly with the inherent weighting of each technique. Step responses are used to show that the predictive capability of the models from both techniques is excellent. Based on the results of this study, the relative strengths and weaknesses of the frequency- and time-domain techniques are summarized, and a proposal for a coordinated parameter identification approach is presented.
A review of ice accretion data from a model rotor icing test and comparison with theory
NASA Technical Reports Server (NTRS)
Britton, Randall K.; Bond, Thomas H.
1991-01-01
An experiment was conducted by the Helicopter Icing Consortium (HIC) in the NASA Lewis Icing Research Tunnel (IRT) in which a 1/6 scale fuselage model of a UH-60A Black Hawk helicopter with a generic rotor was subjected to a wide range of icing conditions. The HIC consists of members from NASA, Bell Helicopter, Boeing Helicopter, McDonnell Douglas Helicopters, Sikorsky Aircraft, and Texas A&M University. Data was taken in the form of rotor torque, internal force balance measurements, blade strain gage loading, and two dimensional ice shape tracings. A review of the ice shape data is performed with special attention given to repeatability and correctness of trends in terms of radial variation, rotational speed, icing time, temperature, liquid water content, and volumetric median droplet size. Moreover, an indepth comparison between the experimental data and the analysis of NASA's ice accretion code LEWICE is given. Finally, conclusions are drawn as to the quality of the ice accretion data and the predictability of the data base as a whole. Recommendations are also given for improving data taking technique as well as potential future work.
A review of ice accretion data from a model rotor icing test and comparison with theory
NASA Technical Reports Server (NTRS)
Britton, Randall K.; Bond, Thomas H.
1991-01-01
An experiment was conducted by the Helicopter Icing Consortium (HIC) in the NASA Lewis Icing Research Tunnel (IRT) in which a 1/6 scale fuselage model of a UH-60A Black Hawk helicopter with a generic rotor was subjected to a wide range of icing conditions. The HIC consists of members from NASA, Bell Helicopter, Boeing Helicopter, McDonnell Douglas Helicopters, Sikorsky Aircraft, and Texas A&M University. Data was taken in the form of rotor torque, internal force balance measurements, blade strain gage loading, and two dimensional ice shape tracings. A review of the ice shape data is performed with special attention given to repeatability and correctness of trends in terms of radial variation, rotational speed, icing time, temperature, liquid water content, and volumetric median droplet size. Moreover, an indepth comparison between the experimental data and the analysis of NASA's ice accretion code LEWICE is given. Finally, conclusions are shown as to the quality of the ice accretion data and the predictability of the data base as a whole. Recommendations are also given for improving data taking technique as well as potential future work.
Unsteady Velocity Measurements Taken Behind a Model Helicopter Rotor Hub in Forward Flight
NASA Technical Reports Server (NTRS)
Berry, John D.
1997-01-01
Drag caused by separated flow behind the hub of a helicopter has an adverse effect on aerodynamic performance of the aircraft. To determine the effect of separated flow on a configuration used extensively for helicopter aerodynamic investigations, an experiment was conducted using a laser velocimeter to measure velocities in the wake of a model helicopter hub operating at Mach-scaled conditions in forward flight. Velocity measurements were taken using a laser velocimeter with components in the vertical and downstream directions. Measurements were taken at 13 stations downstream from the rotor hub. At each station, measurements were taken in both a horizontal and vertical row of locations. These measurements were analyzed for harmonic content based on the rotor period of revolution. After accounting for these periodic velocities, the remaining unsteady velocities were treated as turbulence. Turbulence intensity distributions are presented. Average turbulent intensities ranged from approximately 2 percent of free stream to over 15 percent of free stream at specific locations and azimuths. The maximum average value of turbulence was located near the rear-facing region of the fuselage.
NASA Technical Reports Server (NTRS)
Martin, R. M.; Splettstoesser, W. R.; Elliott, J. W.; Schultz, K.-J.
1988-01-01
Acoustic data are presented from a 40 percent scale model of the four-bladed BO-105 helicopter main rotor, tested in a large aerodynamic wind tunnel. Rotor blade-vortex interaction (BVI) noise data in the low-speed flight range were acquired using a traversing in-flow microphone array. Acoustic results presented are used to assess the acoustic far field of BVI noise, to map the directivity and temporal characteristics of BVI impulsive noise, and to show the existence of retreating-side BVI signals. The characterics of the acoustic radiation patterns, which can often be strongly focused, are found to be very dependent on rotor operating condition. The acoustic signals exhibit multiple blade-vortex interactions per blade with broad impulsive content at lower speeds, while at higher speeds, they exhibit fewer interactions per blade, with much sharper, higher amplitude acoustic signals. Moderate-amplitude BVI acoustic signals measured under the aft retreating quadrant of the rotor are shown to originate from the retreating side of the rotor.
Backward whirl in a simple rotor supported on hydrodynamic bearings
NASA Technical Reports Server (NTRS)
Subbiah, R.; Rhat, R. B.; Sankar, T. S.; Rao, J. S.
1985-01-01
The asymmetric nature of the fluid film stiffness and damping properties in rotors supported on fluid film bearings causes a forward or a backward whirl depending on the bearing parameters and the speed of the rotor. A rotor was designed to exhibit backward synchronous whirl. The rotor-bearing system exhibited split criticals, and a backward whirl was observed between the split criticals. The orbital diagrams show the whirl pattern.
Research investigation of helicopter main rotor/tail rotor interaction noise
NASA Technical Reports Server (NTRS)
Fitzgerald, J.; Kohlhepp, F.
1988-01-01
Acoustic measurements were obtained in a Langley 14 x 22 foot Subsonic Wind Tunnel to study the aeroacoustic interaction of 1/5th scale main rotor, tail rotor, and fuselage models. An extensive aeroacoustic data base was acquired for main rotor, tail rotor, fuselage aerodynamic interaction for moderate forward speed flight conditions. The details of the rotor models, experimental design and procedure, aerodynamic and acoustic data acquisition and reduction are presented. The model was initially operated in trim for selected fuselage angle of attack, main rotor tip-path-plane angle, and main rotor thrust combinations. The effects of repositioning the tail rotor in the main rotor wake and the corresponding tail rotor countertorque requirements were determined. Each rotor was subsequently tested in isolation at the thrust and angle of attack combinations for trim. The acoustic data indicated that the noise was primarily dominated by the main rotor, especially for moderate speed main rotor blade-vortex interaction conditions. The tail rotor noise increased when the main rotor was removed indicating that tail rotor inflow was improved with the main rotor present.
Comparison of calculated and measured pressures on straight and swept-tip model rotor blades
NASA Technical Reports Server (NTRS)
Tauber, M. E.; Chang, I. C.; Caughey, D. A.; Phillipe, J. J.
1983-01-01
Using the quasi-steady, full potential code, ROT22, pressures were calculated on straight and swept tip model helicopter rotor blades at advance ratios of 0.40 and 0.45, and into the transonic tip speed range. The calculated pressures were compared with values measured in the tip regions of the model blades. Good agreement was found over a wide range of azimuth angles when the shocks on the blade were not too strong. However, strong shocks persisted longer than predicted by ROT22 when the blade was in the second quadrant. Since the unsteady flow effects present at high advance ratios primarily affect shock waves, the underprediction of shock strengths is attributed to the simplifying, quasi-steady, assumption made in ROT22.
NASA Technical Reports Server (NTRS)
Pegg, R. J.; Shidler, P. A.
1978-01-01
Approaches to minimizing the noise generated by the interaction of the tail rotor blades with the wake of the main rotor considered include repositioning of the tail rotor with respect to the main rotor, changes in the rotational direction of the tail rotor, and modification of the main rotor tip vortex. A variable geometry model was built which had the capability of varying tail rotor position relative to the main rotor as well as direction of tail rotor rotation. Acoustic data taken from the model in the Langley anechoic noise facility indicates interaction effects due to both main rotor shed vortex and the main rotor turbulence.
A guide to the use of the pressure disk rotor model as implemented in INS3D-UP
NASA Technical Reports Server (NTRS)
Chaffin, Mark S.
1995-01-01
This is a guide for the use of the pressure disk rotor model that has been placed in the incompressible Navier-Stokes code INS3D-UP. The pressure disk rotor model approximates a helicopter rotor or propeller in a time averaged manner and is intended to simulate the effect of a rotor in forward flight on the fuselage or the effect of a propeller on other aerodynamic components. The model uses a modified actuator disk that allows the pressure jump across the disk to vary with radius and azimuth. The cyclic and collective blade pitch angles needed to achieve a specified thrust coefficient and zero moment about the hub are predicted. The method has been validated with experimentally measured mean induced inflow velocities as well as surface pressures on a generic fuselage. Overset grids, sometimes referred to as Chimera grids, are used to simplify the grid generation process. The pressure disk model is applied to a cylindrical grid which is embedded in the grid or grids used for the rest of the configuration. This document will outline the development of the method, and present input and results for a sample case.
NASA Technical Reports Server (NTRS)
Nguyen, Louis H.; Ramakrishnan, Jayant; Granda, Jose J.
2006-01-01
The assembly and operation of the International Space Station (ISS) require extensive testing and engineering analysis to verify that the Space Station system of systems would work together without any adverse interactions. Since the dynamic behavior of an entire Space Station cannot be tested on earth, math models of the Space Station structures and mechanical systems have to be built and integrated in computer simulations and analysis tools to analyze and predict what will happen in space. The ISS Centrifuge Rotor (CR) is one of many mechanical systems that need to be modeled and analyzed to verify the ISS integrated system performance on-orbit. This study investigates using Bond Graph modeling techniques as quick and simplified ways to generate models of the ISS Centrifuge Rotor. This paper outlines the steps used to generate simple and more complex models of the CR using Bond Graph Computer Aided Modeling Program with Graphical Input (CAMP-G). Comparisons of the Bond Graph CR models with those derived from Euler-Lagrange equations in MATLAB and those developed using multibody dynamic simulation at the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC) are presented to demonstrate the usefulness of the Bond Graph modeling approach for aeronautics and space applications.
NASA Technical Reports Server (NTRS)
Tangler, J. L.; Wohlfeld, R. M.; Miley, S. J.
1973-01-01
Schlieren methods of flow visualization and hot-wire anemometry for velocity measurements were used to investigate the wakes generated by hovering model propellers and rotors. The research program was directed toward investigating (1) the stability of the tip vortex, (2) the effects produced by various tip shapes on performance and tip vortex characteristics, and (3) the shock formation and noise characteristics associated with various tip shapes. A free-wake analysis was also conducted for comparison with the vortex stability experimental results. Schlieren photographs showing wake asymmetry, interaction, and instability are presented along with a discussion of the effects produced by the number of blades, collective pitch, and tip speed. Two hot-wire anemometer techniques, used to measure the maximum circumferential velocity in the tip vortex, are discussed.
Rotor-to-stator Partial Rubbing and Its Effects on Rotor Dynamic Response
NASA Technical Reports Server (NTRS)
Muszynska, Agnes; Franklin, Wesley D.; Hayashida, Robert D.
1991-01-01
Results from experimental and analytical studies on rotor to stationary element partial rubbings at several locations and their effects on rotor dynamic responses are presented. The mathematical model of a rubbing rotor is given. The computer program provides numerical results which agree with experimentally obtained rotor responses.
Stochastic modeling of cell growth with symmetric or asymmetric division
NASA Astrophysics Data System (ADS)
Marantan, Andrew; Amir, Ariel
2016-07-01
We consider a class of biologically motivated stochastic processes in which a unicellular organism divides its resources (volume or damaged proteins, in particular) symmetrically or asymmetrically between its progeny. Assuming the final amount of the resource is controlled by a growth policy and subject to additive and multiplicative noise, we derive the recursive integral equation describing the evolution of the resource distribution over subsequent generations and use it to study the properties of stable resource distributions. We find conditions under which a unique stable resource distribution exists and calculate its moments for the class of affine linear growth policies. Moreover, we apply an asymptotic analysis to elucidate the conditions under which the stable distribution (when it exists) has a power-law tail. Finally, we use the results of this asymptotic analysis along with the moment equations to draw a stability phase diagram for the system that reveals the counterintuitive result that asymmetry serves to increase stability while at the same time widening the stable distribution. We also briefly discuss how cells can divide damaged proteins asymmetrically between their progeny as a form of damage control. In the appendixes, motivated by the asymmetric division of cell volume in Saccharomyces cerevisiae, we extend our results to the case wherein mother and daughter cells follow different growth policies.
NASA Astrophysics Data System (ADS)
Zhang, Xuening; Han, Qinkai; Peng, Zhike; Chu, Fulei
2016-03-01
In this paper, a comprehensive dynamic model is proposed to analyze the dynamic behaviors of the rotor-bearing system. Three types of excitation including the bearing waviness, the unbalanced force and the finite number of balls (varying compliance effect) are considered. Based on the extended Jones-Harris model with five degrees of freedom, the load distribution and then the stiffness of the angular contact ball bearing are obtained theoretically. After introducing the three types of excitation into the model, the bearing stiffness matrix becomes time-varying and many parametric frequencies are found due to the multiple excitations. Then, the stability problems of the parametrically excited rotor-bearing system are investigated utilizing the discrete state transition matrix method (DSTM). The simple instability regions arising from the translational and the angular motions are analyzed respectively. The effects of the amplitude and the initial phase angle of the bearing waviness, the rotor eccentricity, the bearing preload and the damping of the rotating system on the instability regions are discussed thoroughly. It is shown that the waviness amplitudes have significant influences on the instability regions, while the initial phase angles of the waviness almost have no effect on the instability regions. The rotor eccentricity just affects the widths of the instability regions. The increasing of the bearing preload only shifts the positions of the instability regions. Damping could reduce the instability regions but it could not diminish the regions completely.
Modeling of asymmetric pulsed phenomena in dielectric-barrier atmospheric-pressure glow discharges
Ha Yan; Wang Huijuan; Wang Xiaofei
2012-01-15
Asymmetric current pulses in dielectric-barrier atmospheric-pressure glow discharges are investigated by a self-consistent, one-dimensional fluid model. It is found that the glow mode and Townsend mode can coexist in the asymmetric discharge even though the gas gap is rather large. The reason for this phenomenon is that the residual space charge plays the role of anode and reduces the gap width, resulting in the formation of a Townsend discharge.
Chen, J.E.
1995-12-31
This paper describes non-linear models of a 2-phase permanent magnet synchronous motor drive in brushless DC and microstepping modes. The models account for everything from the main power bus up to and including the mechanical load and velocity feedback loop. In particular, the models include the power electronics for each phase complete with their internal feedback loops. Classical state space averaged power electronics models are transformed to the rotor reference frame along with the usual electromechanical variables. Since SPICE linearizes the rotor reference frame model about shaft velocity, instead of shaft angle, frequency domain methods apply. The frequency domain analysis detects unstable interactions between torque angle and deliberate feedback within the drives. Time domain simulations using stator reference frame models confirm the results. All models are SPICE-compatible but were developed on Cadence`s Analog Workbench.
NASA Astrophysics Data System (ADS)
Zhang, Xuening; Han, Qinkai; Peng, Zhike; Chu, Fulei
2015-05-01
A great deal of research work has been done on the dynamic behaviors of the rotor-bearing system. However, the important effects of load and variation of contact angle on the bearing performance have not been focused on sufficiently. In this paper, a five-degree-of-freedom load distribution model is set up considering the bearing preload and the loads due to the rotor imbalance. Utilizing this model, the variation of the bearing contact angle is investigated thoroughly. The comparisons of the obtained contact angle against the results from literature validate that the proposed load distribution model is effective. With this model, the static ball deformations are obtained considering variation of the contact angle. Through resolving the dynamic displacements of the rotor, the dynamic ball deformations could also be obtained. Then the total restoring forces and moments of the bearings could be formulated. By introducing these nonlinear forces and moments into the rotating system, a new dynamic model considering the preload and the variation of contact angle is set up. The present analyses indicate that the bearing contact angle will be changed remarkably with the effect of bearing load. The deflection vibration of the rotor-bearing system will be underestimated without considering the varying contact angle. With the effect of varying contact angle, the ball passage frequency and its combinations with the shaft rotating frequency become more noticeable. The main resonance regions for the rotor-bearing system shift to the lower speed ranges when the variation of contact angle is taken into account.
NASA Technical Reports Server (NTRS)
DeSmidt, Hans A.; Smith, Edward C.; Bill, Robert C.; Wang, Kon-Well
2013-01-01
This project develops comprehensive modeling and simulation tools for analysis of variable rotor speed helicopter propulsion system dynamics. The Comprehensive Variable-Speed Rotorcraft Propulsion Modeling (CVSRPM) tool developed in this research is used to investigate coupled rotor/engine/fuel control/gearbox/shaft/clutch/flight control system dynamic interactions for several variable rotor speed mission scenarios. In this investigation, a prototypical two-speed Dual-Clutch Transmission (DCT) is proposed and designed to achieve 50 percent rotor speed variation. The comprehensive modeling tool developed in this study is utilized to analyze the two-speed shift response of both a conventional single rotor helicopter and a tiltrotor drive system. In the tiltrotor system, both a Parallel Shift Control (PSC) strategy and a Sequential Shift Control (SSC) strategy for constant and variable forward speed mission profiles are analyzed. Under the PSC strategy, selecting clutch shift-rate results in a design tradeoff between transient engine surge margins and clutch frictional power dissipation. In the case of SSC, clutch power dissipation is drastically reduced in exchange for the necessity to disengage one engine at a time which requires a multi-DCT drive system topology. In addition to comprehensive simulations, several sections are dedicated to detailed analysis of driveline subsystem components under variable speed operation. In particular an aeroelastic simulation of a stiff in-plane rotor using nonlinear quasi-steady blade element theory was conducted to investigate variable speed rotor dynamics. It was found that 2/rev and 4/rev flap and lag vibrations were significant during resonance crossings with 4/rev lagwise loads being directly transferred into drive-system torque disturbances. To capture the clutch engagement dynamics, a nonlinear stick-slip clutch torque model is developed. Also, a transient gas-turbine engine model based on first principles mean
Sensitivity of Hingeless Rotor Blade Flap-lag Stability in Hover to Analytical Modelling Assumptions
NASA Technical Reports Server (NTRS)
Curtiss, H. C., Jr.
1975-01-01
Prediction of flap-lag stability using a single bending mode for each degree-of-freedom is examined in the case in which the bending modes are assumed to be the same in the flap and lag directions and are independent of pitch angle and stiffness distribution. It is shown that this model gives results analogous to those obtained by Ormiston employing a rigid blade model with the blade and hub stiffness represented by springs in the limiting cases of the elastic coupling parameter R = 0 and 1. For intermediate values of R the results are shown to be quite different. The mode shape assumptions are shown to result in what is referred to as the parallel spring model in contrast to Ormiston's model which is referred to as a series spring model. The similarities and differences between these two models are developed in some details. The differences between these two models are examined for various typical rotor blade characteristics. Other aspects of the sensitivity of this problem are also considered.
Wind Tunnel Testing of a 120th Scale Large Civil Tilt-Rotor Model in Airplane and Helicopter Modes
NASA Technical Reports Server (NTRS)
Theodore, Colin R.; Willink, Gina C.; Russell, Carl R.; Amy, Alexander R.; Pete, Ashley E.
2014-01-01
In April 2012 and October 2013, NASA and the U.S. Army jointly conducted a wind tunnel test program examining two notional large tilt rotor designs: NASA's Large Civil Tilt Rotor and the Army's High Efficiency Tilt Rotor. The approximately 6%-scale airframe models (unpowered) were tested without rotors in the U.S. Army 7- by 10-foot wind tunnel at NASA Ames Research Center. Measurements of all six forces and moments acting on the airframe were taken using the wind tunnel scale system. In addition to force and moment measurements, flow visualization using tufts, infrared thermography and oil flow were used to identify flow trajectories, boundary layer transition and areas of flow separation. The purpose of this test was to collect data for the validation of computational fluid dynamics tools, for the development of flight dynamics simulation models, and to validate performance predictions made during conceptual design. This paper focuses on the results for the Large Civil Tilt Rotor model in an airplane mode configuration up to 200 knots of wind tunnel speed. Results are presented with the full airframe model with various wing tip and nacelle configurations, and for a wing-only case also with various wing tip and nacelle configurations. Key results show that the addition of a wing extension outboard of the nacelles produces a significant increase in the lift-to-drag ratio, and interestingly decreases the drag compared to the case where the wing extension is not present. The drag decrease is likely due to complex aerodynamic interactions between the nacelle and wing extension that results in a significant drag benefit.
NASA Technical Reports Server (NTRS)
Splettstoesser, Wolf R.; Schultz, KLAUS-J.; Kube, Roland; Brooks, Thomas F.; Booth, Earl R., Jr.; Niesl, Georg; Streby, Olivier
1991-01-01
Results are presented of a model rotor acoustics test performed to examine the benefit of higher harmonic control (HHC) of blade pitch to reduce blade-vortex interaction (BVI) impulsive noise. A dynamically scaled, four-bladed, rigid rotor model, a 40-percent replica of the B0-105 main rotor, was tested in the German Dutch Wind Tunnel. Noise characteristics and noise directivity patterns as well as vibratory loads were measured and used to demonstrate the changes when different HHC schedules were applied. Dramatic changes of the acoustic signatures and the noise radiation directivity with the HHC phase variations are found. Compared to the baseline conditions (without HHC), significant mid-frequency noise reductions of locally 6 dB are obtained for low-speed descent conditions where GVI is most intense. For other rotor operating conditions with less intense BVI there is less or no benefit from the use of HHC. LF noise and vibratory loads, especially at optimum noise reduction control settings, are found to increase.
Exact solution of the asymmetric exclusion model with particles of arbitrary size.
Alcaraz, F C; Bariev, R Z
1999-07-01
A generalization of the simple exclusion asymmetric model is introduced. In this model an arbitrary mixture of molecules with distinct sizes s=0,1,2, ..., in units of lattice space, diffuses asymmetrically on the lattice. A related surface growth model is also presented. Variations of the distribution of the molecules sizes may change the excluded volume almost continuously. We solve the model exactly through the Bethe ansatz and the dynamical critical exponent z is calculated from the finite-size corrections of the mass gap of the related quantum chain. Our results show that for an arbitrary distribution of molecules, the dynamical critical behavior is on the Kardar-Parizi-Zhang universality.
NASA Astrophysics Data System (ADS)
Pavlenko, I. V.; Simonovskiy, V. I.; Demianenko, M. M.
2017-08-01
This research paper is aimed to investigating rotor dynamics of multistage centrifugal machines with ball bearings by using the computer programs “Critical frequencies of the rotor” and “Forced oscillations of the rotor,” which are implemented the mathematical model based on the use of beam finite elements. Free and forces oscillations of the rotor for the multistage centrifugal oil pump NPS 200-700 are observed by taking into account the analytical dependence of bearing stiffness on rotor speed, which is previously defined on the basis of results’ approximation for the numerical simulation in ANSYS by applying 3D finite elements. The calculations found that characteristic and constrained oscillations of rotor and corresponded to them forms of vibrations, as well as the form of constrained oscillation on the actual frequency for acceptable residual unbalance are determined.
Modeling the Overalternating Bias with an Asymmetric Entropy Measure
Gronchi, Giorgio; Raglianti, Marco; Noventa, Stefano; Lazzeri, Alessandro; Guazzini, Andrea
2016-01-01
Psychological research has found that human perception of randomness is biased. In particular, people consistently show the overalternating bias: they rate binary sequences of symbols (such as Heads and Tails in coin flipping) with an excess of alternation as more random than prescribed by the normative criteria of Shannon's entropy. Within data mining for medical applications, Marcellin proposed an asymmetric measure of entropy that can be ideal to account for such bias and to quantify subjective randomness. We fitted Marcellin's entropy and Renyi's entropy (a generalized form of uncertainty measure comprising many different kinds of entropies) to experimental data found in the literature with the Differential Evolution algorithm. We observed a better fit for Marcellin's entropy compared to Renyi's entropy. The fitted asymmetric entropy measure also showed good predictive properties when applied to different datasets of randomness-related tasks. We concluded that Marcellin's entropy can be a parsimonious and effective measure of subjective randomness that can be useful in psychological research about randomness perception. PMID:27458418
2006-10-31
Molecular Dipolar Rotors on Insulating Surfaces," Salamanca , Spain. Trends in Nanotechnology Conference. September 5-9, 2003 [86] Laura I. Clarke, Mary Beth...Horansky at the Trends in Nanotechnology Conference, Salamanca , Spain (September 5-9, 2003). [145] Michl, J. “Unusual Molecules: Artificial Surface...temperature and frequency for difluorophenylene rotor crystal. Figure JP6. Monte Carlo results for the local potential asymmetry at
Machado, Tiago Henrique; Cavalca, Katia L
2016-01-01
The present work gives continuity in the analysis of the wear influence on cylindrical hydrodynamic bearings by presenting an experimental validation of the wear model previously proposed by the authors. This validation is carried on using the frequency response of the rotor-bearings system in directional coordinates. For this purpose, a test rig was assembled in order to evaluate the behavior of the rotating system when supported by hydrodynamic bearings with different wear patterns. The experimental measurements are used to validate the wear model, comparing the anisotropy influence on the experimental and numerical responses. The simulated directional frequency responses showed a good agreement with the experimental ones, demonstrating the potential of the proposed wear model in satisfactorily represent its influence on the rotor-bearings system response in the frequency range where the numerical model was validated.
NASA Astrophysics Data System (ADS)
Reinisch, Guillaume; Leyssale, Jean-Marc; Vignoles, Gérard L.
2010-10-01
We present an extension of some popular hindered rotor (HR) models, namely, the one-dimensional HR (1DHR) and the degenerated two-dimensional HR (d2DHR) models, allowing for a simple and accurate treatment of internal rotations. This extension, based on the use of a variable kinetic function in the Hamiltonian instead of a constant reduced moment of inertia, is extremely suitable in the case of rocking/wagging motions involved in dissociation or atom transfer reactions. The variable kinetic function is first introduced in the framework of a classical 1DHR model. Then, an effective temperature and potential dependent constant is proposed in the cases of quantum 1DHR and classical d2DHR models. These methods are finally applied to the atom transfer reaction SiCl3+BCl3→SiCl4+BCl2. We show, for this particular case, that a proper accounting of internal rotations greatly improves the accuracy of thermodynamic and kinetic predictions. Moreover, our results confirm (i) that using a suitably defined kinetic function appears to be very adapted to such problems; (ii) that the separability assumption of independent rotations seems justified; and (iii) that a quantum mechanical treatment is not a substantial improvement with respect to a classical one.
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.
NASA Astrophysics Data System (ADS)
Zaslavsky, M.
1996-06-01
The phenomena of dynamical localization, both classical and quantum, are studied in the Fermi accelerator model. The model consists of two vertical oscillating walls and a ball bouncing between them. The classical localization boundary is calculated in the case of ``sinusoidal velocity transfer'' [A. J. Lichtenberg and M. A. Lieberman, Regular and Stochastic Motion (Springer-Verlag, Berlin, 1983)] on the basis of the analysis of resonances. In the case of the ``sawtooth'' wall velocity we show that the quantum localization is determined by the analytical properties of the canonical transformations to the action and angle coordinates of the unperturbed Hamiltonian, while the existence of the classical localization is determined by the number of continuous derivatives of the distance between the walls with respect to time.
Short-channel drain current model for asymmetric heavily / lightly doped DG MOSFETs
NASA Astrophysics Data System (ADS)
Dutta, Pradipta; Syamal, Binit; Koley, Kalyan; Dutta, Arka; Sarkar, C. K.
2017-08-01
The paper presents a drain current model for double gate metal oxide semiconductor field effect transistors (DG MOSFETs) based on a new velocity saturation model that accounts for short-channel velocity saturation effect independently in the front and the back gate controlled channels under asymmetric front and back gate bias and oxide thickness. To determine the front and the back-channel velocity saturation, drain-induced barrier lowering is evaluated by effective gate voltages at the front and back gates obtained from surface potential at the threshold condition after considering symmetric and asymmetric front and back oxide thickness. The model also incorporates surface roughness scattering and ionized impurity scattering to estimate drain current for heavily / lightly doped channel for short-channel asymmetric DG MOSFET and a good agreement has been achieved with TCAD simulations, with a relative error of around 3-7%.
A mathematical model for the doubly-fed wound rotor generator, part 2
NASA Technical Reports Server (NTRS)
Brady, F. J.
1984-01-01
A mathematical analysis of a doubly-fed wound rotor generator is presented. The constraints of constant stator voltage and frequency to the circuit equations were applied and expressions for the currents and voltages in the machine obtained. The derived variables are redefined as direct and quadrature components. In addition, the apparent (complex) power for both the rotor and the stator are derived in terms of these redefined components.
A mathematical model for the doubly-fed wound rotor generator. II
NASA Technical Reports Server (NTRS)
Brady, F. J.
1986-01-01
A mathematical analysis of a doubly-fed wound rotor generator is presented. The constraints of constant stator voltage and frequency to the circuit equations were applied and expressions for the currents and voltages in the machine obtained. The derived variables are redefined as direct and quadrature components. In addition, the apparent (complex) power for both the rotor and the stator are derived in terms of these redefined components.
Modeling Non-Stationary Asymmetric Lens Blur by Normal Sinh-Arcsinh Model.
Jang, Jinhyeok; Yun, Joo Dong; Yang, Seungjoon
2016-05-01
Images acquired by a camera show lens blur due to imperfection in the optical system even when images are properly focused. Lens blur is non-stationary in a sense that the amount of blur depends on pixel locations in a sensor. Lens blur is also asymmetric in a sense that the amount of blur is different in the radial and tangential directions, and also in the inward and outward radial directions. This paper presents parametric blur kernel models based on the normal sinh-arcsinh distribution function. The proposed models can provide flexible shapes of blur kernels with a different symmetry and skewness to model complicated lens blur due to optical aberration in a properly focused images accurately. Blur of single focal length lenses is estimated, and the accuracy of the models is compared with the existing parametric blur models. An advantage of the proposed models is demonstrated through deblurring experiments.
Modeling Non-Stationary Asymmetric Lens Blur By Normal Sinh-Arcsinh Model.
Jang, Jinhyeok; Yun, Joo Dong; Yang, Seungjoon
2016-03-08
Images acquired by a camera show lens blur due to imperfection in the optical system even when images are properly focused. Lens blur is non-stationary in a sense the amount of blur depends on pixel locations in a sensor. Lens blur is also asymmetric in a sense the amount of blur is different in the radial and tangential directions, and also in the inward and outward radial directions. This paper presents parametric blur kernel models based on the normal sinh-arcsinh distribution function. The proposed models can provide flexible shapes of blur kernels with different symmetry and skewness to model complicated lens blur due to optical aberration in a properly focused images accurately. Blur of single focal length lenses is estimated and the accuracy of the models is compared with existing parametric blur models. Advantage of the proposed models is demonstrated through deblurring experiments.
Vortex Wake Geometry of a Model Tilt Rotor in Forward Flight
NASA Technical Reports Server (NTRS)
Wadcock, Alan J.; Yamauchi, Gloria K.; Rutkowski, Michael (Technical Monitor)
2001-01-01
A full-span 0.25-scale V-22 tiltrotor was tested in the NASA Ames 40-by 80-Foot Wind Tunnel in November 2000. The main objective of the test was to acquire a comprehensive database to validate tiltrotor analyses. Figure 1 shows the model installed in the Ames 40- by 80-Foot Wind Tunnel. Rotor and vehicle performance measurements were taken in addition to wing pressures, acoustics, and flow visualization. A dual acoustic traverse system was installed to measure blade-vortex interaction (BVI) noise levels and directivity. Test conditions included hover and forward flight in helicopter mode. Angle-of-attack and thrust sweeps for three tunnel speeds were acquired before model problems caused the premature conclusion of the test. The test will resume in the Ames 80- by 120-Foot Wind Tunnel in late 2001. This paper will focus on the wake geometry measurements that were acquired during the test. The wake geometry measurements were a small subset of a larger matrix of planned measurements designed to study the development and structure of the dual vortex system generated during BVI conditions. The present paper will provide wake geometry data for four test conditions. In addition, the data will be compared with previously acquired wake measurements from an isolated tiltrotor
Tunneling of electrons via rotor-stator molecular interfaces: Combined ab initio and model study
NASA Astrophysics Data System (ADS)
Petreska, Irina; Ohanesjan, Vladimir; Pejov, Ljupčo; Kocarev, Ljupčo
2016-07-01
Tunneling of electrons through rotor-stator anthracene aldehyde molecular interfaces is studied with a combined ab initio and model approach. Molecular electronic structure calculated from first principles is utilized to model different shapes of tunneling barriers. Together with a rectangular barrier, we also consider a sinusoidal shape that captures the effects of the molecular internal structure more realistically. Quasiclassical approach with the Simmons' formula for current density is implemented. Special attention is paid on conformational dependence of the tunneling current. Our results confirm that the presence of the side aldehyde group enhances the interesting electronic properties of the pure anthracene molecule, making it a bistable system with geometry dependent transport properties. We also investigate the transition voltage and we show that conformation-dependent field emission could be observed in these molecular interfaces at realistically low voltages. The present study accompanies our previous work where we investigated the coherent transport via strongly coupled delocalized orbital by application of Non-equilibrium Green's Function Formalism.
NASA Astrophysics Data System (ADS)
Teixeira, Miguel A. C.
2017-04-01
A linear model is used to diagnose the onset of rotors in flow over 2D ridges, for atmospheres that are neutrally stratified near the surface and stably stratified aloft, with a sharp temperature inversion in between, where trapped lee waves may propagate. This is achieved by coupling an inviscid two-layer mountain-wave model with a bulk boundary-layer model. The full model shows some ability to detect flow stagnation as a function of key input parameters, such as the Froude number and the height of the inversion, by comparison with results from numerical simulations and laboratory experiments carried out by previous authors. The effect of a boundary layer is essential to correctly predict flow stagnation, as the inviscid version of the model severely overestimates the dimensionless critical mountain height necessary for stagnation to occur. An improved model that includes only the effects of mean flow deceleration and amplification of the velocity perturbation within the boundary layer predicts flow stagnation much better in the most non-hydrostatic cases treated here, where waves appear to be directly forced by the orography. However, in the most hydrostatic case, only the full model, taking into account the feedback of the boundary layer on the inviscid flow, satisfactorily predicts flow stagnation, although the corresponding stagnation condition is unable to discriminate between rotors and hydraulic jumps. This is due to the fact that the trapped lee waves associated with the rotors are not forced directly by the orography in this case, but rather seem to be generated indirectly by nonlinear processes. This mechanism is, to a certain extent, mimicked by the modified surface boundary condition adopted in the full model, where an "effective orography" that differs from the real one forces the trapped lee waves. Versions of the model not including this feedback severely underestimate the amplitude of the trapped lee waves in the most hydrostatic case, partly
NASA Astrophysics Data System (ADS)
Li, Hai-Bin; Nie, Qing-Miao; Xin, Xiao-Tian
2009-07-01
The heat conduction in a one-dimensional (1D) hard-point model with mass gradient is studied. Using numerical simulation, we find an asymmetric heat conduction in this model with greater heat current in the direction of mass increase. The increase of temperature gradient, mass gradient and system size are found to enhance the asymmetric heat conduction. Based on the collision dynamic of a hard-point particle, we give a qualitative explanation for the underlying mechanism of asymmetric effect.
NASA Technical Reports Server (NTRS)
Kazin, S. B.; Paas, J. E.; Minzner, W. R.
1973-01-01
A scale model of the bypass flow region of a 1.5 pressure ratio, single stage, low tip speed fan was tested with a serrated rotor leading edge to determine its effects on noise generation. The serrated rotor was produced by cutting teeth into the leading edge of the nominal rotor blades. The effects of speed and exhaust nozzle area on the scale models noise characteristics were investigated with both the nominal rotor and serrated rotor. Acoustic results indicate the serrations reduced front quadrant PNL's at takeoff power. In particular, the 200 foot (61.0 m) sideline noise was reduced from 3 to 4 PNdb at 40 deg for nominal and large nozzle operation. However, the rear quadrant maximum sideline PNL's were increased 1.5 to 3 PNdb at approach thust and up to 2 PNdb at takeoff thust with these serrated rotor blades. The configuration with the serrated rotor produced the lowest maximum 200 foot (61.0 m) sideline PNL for any given thust when the large nozzle (116% of design area) was employed.
Effects of asymmetrical damping on a 2 DOF quarter-car model under harmonic excitation
NASA Astrophysics Data System (ADS)
Silveira, M.; Wahi, P.; Fernandes, J. C. M.
2017-02-01
The objective of this work is to study the dynamical behavior of vehicle suspension systems employing asymmetrical viscous damping, with a focus on improving passenger comfort. Previous studies have shown that the use of asymmetrical dampers in these types of systems can be advantageous with regard to comfort of the passengers. The modeling and the behavior of a quarter-car model with asymmetrical viscous damping under harmonic excitation is presented. The response is obtained with an analytical approximation via the method of Harmonic Balance. The choice of the asymmetry ratio diminishes the effects that the uneven road causes on the displacement and acceleration of the sprung mass. Although current systems usually adopt larger damping during the expansion phase, it is shown in this work that, for lower frequencies, smaller damping in this phase results in better comfort.
NASA Astrophysics Data System (ADS)
An, Taeyang; Cha, Min-Chul
2013-03-01
We study the superfluid-insulator quantum phase transition in a disordered two-dimensional quantum rotor model with random on-site interactions in the presence of particle-hole symmetry. Via worm-algorithm Monte Carlo calculations of superfluid density and compressibility, we find the dynamical critical exponent z ~ 1 . 13 (2) and the correlation length critical exponent 1 / ν ~ 1 . 1 (1) . These exponents suggest that the insulating phase is a incompressible Mott glass rather than a Bose glass.
1986-03-01
Aerodynamic 5. Kocurek, J. David; Berkowitz, Lenard F.; and Harris , Characteristics of Three Helicopter Airfoil Sections at Franklin D.: Hover... Rotorcraft and Investigation of Helicopter Rotor Hover Performance and Powered Lift Aircraft Forum (Aix-en-Province, France), Wake Geometry Characteristics...Technology for Advanced Surface Pressure Measurements of a Helicopter Wind- Rotorcraft -Part 1. J. American Helicopter Soc., vol. 22, Tunnel Model With a 8.15
Rotor/Wing Interactions in Hover
NASA Technical Reports Server (NTRS)
Young, Larry A.; Derby, Michael R.
2002-01-01
Hover predictions of tiltrotor aircraft are hampered by the lack of accurate and computationally efficient models for rotor/wing interactional aerodynamics. This paper summarizes the development of an approximate, potential flow solution for the rotor-on-rotor and wing-on-rotor interactions. This analysis is based on actuator disk and vortex theory and the method of images. The analysis is applicable for out-of-ground-effect predictions. The analysis is particularly suited for aircraft preliminary design studies. Flow field predictions from this simple analytical model are validated against experimental data from previous studies. The paper concludes with an analytical assessment of the influence of rotor-on-rotor and wing-on-rotor interactions. This assessment examines the effect of rotor-to-wing offset distance, wing sweep, wing span, and flaperon incidence angle on tiltrotor inflow and performance.
Semenov, Alexander; Dubernet, Marie-Lise; Babikov, Dmitri
2014-09-21
The mixed quantum/classical theory (MQCT) for inelastic molecule-atom scattering developed recently [A. Semenov and D. Babikov, J. Chem. Phys. 139, 174108 (2013)] is extended to treat a general case of an asymmetric-top-rotor molecule in the body-fixed reference frame. This complements a similar theory formulated in the space-fixed reference-frame [M. Ivanov, M.-L. Dubernet, and D. Babikov, J. Chem. Phys. 140, 134301 (2014)]. Here, the goal was to develop an approximate computationally affordable treatment of the rotationally inelastic scattering and apply it to H{sub 2}O + He. We found that MQCT is somewhat less accurate at lower scattering energies. For example, below E = 1000 cm{sup −1} the typical errors in the values of inelastic scattering cross sections are on the order of 10%. However, at higher scattering energies MQCT method appears to be rather accurate. Thus, at scattering energies above 2000 cm{sup −1} the errors are consistently in the range of 1%–2%, which is basically our convergence criterion with respect to the number of trajectories. At these conditions our MQCT method remains computationally affordable. We found that computational cost of the fully-coupled MQCT calculations scales as n{sup 2}, where n is the number of channels. This is more favorable than the full-quantum inelastic scattering calculations that scale as n{sup 3}. Our conclusion is that for complex systems (heavy collision partners with many internal states) and at higher scattering energies MQCT may offer significant computational advantages.
Simulating asymmetric colloidal mixture with adhesive hard sphere model.
Jamnik, A
2008-06-21
Monte Carlo simulation and Percus-Yevick (PY) theory are used to investigate the structural properties of a two-component system of the Baxter adhesive fluids with the size asymmetry of the particles of both components mimicking an asymmetric binary colloidal mixture. The radial distribution functions for all possible species pairs, g(11)(r), g(22)(r), and g(12)(r), exhibit discontinuities at the interparticle distances corresponding to certain combinations of n and m values (n and m being integers) in the sum nsigma(1)+msigma(2) (sigma(1) and sigma(2) being the hard-core diameters of individual components) as a consequence of the impulse character of 1-1, 2-2, and 1-2 attractive interactions. In contrast to the PY theory, which predicts the delta function peaks in the shape of g(ij)(r) only at the distances which are the multiple of the molecular sizes corresponding to different linear structures of successively connected particles, the simulation results reveal additional peaks at intermediate distances originating from the formation of rigid clusters of various geometries.
NASA Astrophysics Data System (ADS)
Svinin, Mikhail; Morinaga, Akihiro; Yamamoto, Motoji
2013-01-01
The paper deals with the dynamics of a spherical rolling robot actuated by internal rotors that are placed on orthogonal axes. The driving principle for such a robot exploits nonholonomic constraints to propel the rolling carrier. A full mathematical model as well as its reduced version are derived, and the inverse dynamics are addressed. It is shown that if the rotors are mounted on three orthogonal axes, any feasible kinematic trajectory of the rolling robot is dynamically realizable. For the case of only two rotors the conditions of controllability and dynamic realizability are established. It is shown that in moving the robot by tracing straight lines and circles in the contact plane the dynamically realizable trajectories are not represented by the circles on the sphere, which is a feature of the kinematic model of pure rolling. The implication of this fact to motion planning is explored under a case study. It is shown there that in maneuvering the robot by tracing circles on the sphere the dynamically realizable trajectories are essentially different from those resulted from kinematic models. The dynamic motion planning problem is then formulated in the optimal control settings, and properties of the optimal trajectories are illustrated under simulation.
A preliminary investigation of finite-element modeling for composite rotor blades
NASA Technical Reports Server (NTRS)
Lake, Renee C.; Nixon, Mark W.
1988-01-01
The results from an initial phase of an in-house study aimed at improving the dynamic and aerodynamic characteristics of composite rotor blades through the use of elastic couplings are presented. Large degree of freedom shell finite element models of an extension twist coupled composite tube were developed and analyzed using MSC/NASTRAN. An analysis employing a simplified beam finite element representation of the specimen with the equivalent engineering stiffness was additionally performed. Results from the shell finite element normal modes and frequency analysis were compared to those obtained experimentally, showing an agreement within 13 percent. There was appreciable degradation in the frequency prediction for the torsional mode, which is elastically coupled. This was due to the absence of off-diagonal coupling terms in the formulation of the equivalent engineering stiffness. Parametric studies of frequency variation due to small changes in ply orientation angle and ply thickness were also performed. Results showed linear frequency variations less than 2 percent per 1 degree variation in the ply orientation angle, and 1 percent per 0.0001 inch variation in the ply thickness.
The triaxial particle plus rotor model and wobbling mode: A semiclassical view
NASA Astrophysics Data System (ADS)
Gupta, Rajiv; Malik, S. S.; Jain, A. K.; Jain, S. R.
2010-11-01
A systematic analysis of the triaxial particle rotor model with single-j shell configuration is carried out to explain the prominent features of observed wobbling excitations in odd A nuclei. The equations of motion for the angular momentum vectors I↻ and j↻ generate two types of equilibrium (i.e., (i) the axes aligned and (ii) the planar) states. The planar equilibrium states involve mainly the orientation degree of freedom γ and their Jacobian matrix J gives purely imaginary eigenvalues in conjugate pairs. Also, our dynamical results show a substantial projection of angular momentum vectors on all the three principal axes, which implies that the resultant angular momentum lies outside the planes of three axes. Both these signatures confirm the spontaneous breakdown of time reversal (T) plus rotation by 180° (Rπ) i.e., RπT symmetry and as a result nearly two identical bands consisting of even and odd spins emerge. We have tested our dynamical formalism for the wobbling mode observed in 163Lu.
The triaxial particle plus rotor model and wobbling mode: A semiclassical view
Gupta, Rajiv; Malik, S. S.; Jain, A. K.; Jain, S. R.
2010-11-24
A systematic analysis of the triaxial particle rotor model with single-j shell configuration is carried out to explain the prominent features of observed wobbling excitations in odd A nuclei. The equations of motion for the angular momentum vectors I-vector and j-vector generate two types of equilibrium (i.e., (i) the axes aligned and (ii) the planar) states. The planar equilibrium states involve mainly the orientation degree of freedom {gamma} and their Jacobian matrix J gives purely imaginary eigenvalues in conjugate pairs. Also, our dynamical results show a substantial projection of angular momentum vectors on all the three principal axes, which implies that the resultant angular momentum lies outside the planes of three axes. Both these signatures confirm the spontaneous breakdown of time reversal (T) plus rotation by 180 deg. (R{sub {pi}}) i.e., R{sub {pi}T} symmetry and as a result nearly two identical bands consisting of even and odd spins emerge. We have tested our dynamical formalism for the wobbling mode observed in {sup 163}Lu.
A numerical strategy for finite element modeling of frictionless asymmetric vocal fold collision.
Granados, Alba; Misztal, Marek Krzysztof; Brunskog, Jonas; Visseq, Vincent; Erleben, Kenny
2017-02-01
Analysis of voice pathologies may require vocal fold models that include relevant features such as vocal fold asymmetric collision. The present study numerically addresses the problem of frictionless asymmetric collision in a self-sustained three-dimensional continuum model of the vocal folds. Theoretical background and numerical analysis of the finite-element position-based contact model are presented, along with validation. A novel contact detection mechanism capable to detect collision in asymmetric oscillations is developed. The effect of inexact contact constraint enforcement on vocal fold dynamics is examined by different variational methods for inequality constrained minimization problems, namely, the Lagrange multiplier method and the penalty method. In contrast to the penalty solution, which is related to classical spring-like contact forces, numerical examples show that the parameter-independent Lagrange multiplier solution is more robust and accurate in the estimation of dynamical and mechanical features at vocal fold contact. Furthermore, special attention is paid to the temporal integration schemes in relation to the contact problem, the results suggesting an advantage of highly diffusive schemes. Finally, vocal fold contact enforcement is shown to affect asymmetric oscillations. The present model may be adapted to existing vocal fold models, which may contribute to a better understanding of the effect of the nonlinear contact phenomenon on phonation. Copyright © 2016 John Wiley & Sons, Ltd.
NASA Technical Reports Server (NTRS)
Woodward, Richard P.; Gordon, Eliott B.
1988-01-01
A model high-speed advanced counterrotation propeller, F7/A3, was tested in the NASA Lewis Research Center 9 by 15 foot Anechoic Wind Tunnel at simulated takeoff/approach conditions of 0.2 Mach number. Acoustic measurements were taken with an axially translating microphone probe, and with a polar microphone probe which was fixed to the propeller nacelle and could take both sideline and circumferential acoustic surveys. Aerodynamic measurements were also made to establish propeller operating conditions. The propeller was run at two setting angles (front angle/rear angle) of 36.4/43.5 and 41.1/46.4 degrees, forward rotor tip speeds from 165 to 259 m/sec, rotor spacings from 8.48 to 14.99 cm based on pitch change axis separation, and angles of attack to 16 degrees. The aft rotor diameter was 85 percent of the forward rotor diameter to reduce tip vortex-aft rotor interaction as a major interaction noise source. Results are compared with equal diameter F7/A7 data which was previously obtained under similar operating conditions. The aft rotor-alone tone was 7 dB lower for the reduced diameter aft rotor, due to reduced tip speed at constant rpm. Interaction tone levels for the F7/A3 propeller were higher at minimum row spacing and lower at maximum spacing.
Investigation of rotor blade element airloads for a teetering rotor in the blade stall regime
NASA Technical Reports Server (NTRS)
Dadone, L. U.; Fukushima, T.
1974-01-01
A model of a teetering rotor was tested in a low speed wind tunnel. Blade element airloads measured on an articulated model rotor were compared with the teetering rotor and showed that the teetering rotor is subjected to less extensive flow separation. Retreating blade stall was studied. Results show that stall, under the influence of unsteady aerodynamic effects, consists of four separate stall events, each associated with a vortex shed from the leading edge and sweeping over the upper surface of the rotor blade. Current rotor performance prediction methodology was evaluated through computer simulation.
A Petal-type Chiral NADH Model: Design, Synthesis and its Asymmetric Reduction
Bai, Cui-Bing; Wang, Nai-Xing; Wang, Yan-Jing; Xing, Yalan; Zhang, Wei; Lan, Xing-Wang
2015-01-01
A new type of NADH model compound has been synthesized by an efficient and convenient method. This model compound exhibits high reactivity and enantioselectivity in asymmetric reduction reactions. The results show that chiral NADH model S could be effectively combined with Mg2+ to form ternary complexes. This novel C3 symmetrical NADH model is capable of fluorescence emission at 460 nm when excited at 377 nm. PMID:26648413
NASA Technical Reports Server (NTRS)
Dawson, Seth
1988-01-01
Three cases were selected for correlation from an experiment that examined the aeroelastic stability of a small-scale bearingless motor rotor in hover. The 1.8 m diameter model rotor included flap, lead-lag, and torsional degrees of freedom, but no body degrees of freedom. The first case looked at a configuration with a single pitch link on the leading edge, the second case examined a configuration with a single pitch link on the trailing edge, and the third case examined a configuration with pitch links on the leading and trailing edges to simulate a pitch link with shear restraint. Analyses from Bell Helicopter Textron, Boeing Vertol, Hughes Helicopters, Sikorsky Aircraft, and the U.S. Army Aeromechanics Laboratory were compared with the data, and the correlation ranged from poor to fair.
Exact diffusion constant for the one-dimensional partially asymmetric exclusion model
NASA Astrophysics Data System (ADS)
Derrida, B.; Mallick, K.
1997-02-01
We calculate exactly the diffusion constant associated with the fluctuations of the current for the partial asymmetric exclusion model on a ring with an arbitrary number of particles and holes. We also give the diffusion constant of a tagged particle on that ring. Our approach extends, using the deformed harmonic oscillator algebra, a result already known for the fully asymmetric case. In the limit of weak asymmetry, we extract from our exact expression the crossover between the Edwards - Wilkinson and the Kardar - Parisi - Zhang equations in (1 + 1) dimensions.
Asymmetric magnetic reconnection with out-of-plane shear flows in a two dimensional hybrid model
Wang, Lin; Wang, Xiao-Gang; Wang, Xian-Qu; Liu, Yue
2015-05-15
Effects of out-of-plane shear flows on asymmetric magnetic reconnect are investigated in a two-dimensional (2D) hybrid model with an initial Harris sheet equilibrium. It is found that the out-of-plane flow with an in-plane shear can significantly change the asymmetric reconnection process as well as the related geometry. The magnetic flux, out-of-plane magnetic field, in-plane flow vorticity, plasma density, and the reconnection rate are discussed in detail. The results are in comparison with the cases without the shear flows to further understand the effect.
Improving Atomic Force Microscopy Imaging by a Direct Inverse Asymmetric PI Hysteresis Model
Wang, Dong; Yu, Peng; Wang, Feifei; Chan, Ho-Yin; Zhou, Lei; Dong, Zaili; Liu, Lianqing; Li, Wen Jung
2015-01-01
A modified Prandtl–Ishlinskii (PI) model, referred to as a direct inverse asymmetric PI (DIAPI) model in this paper, was implemented to reduce the displacement error between a predicted model and the actual trajectory of a piezoelectric actuator which is commonly found in AFM systems. Due to the nonlinearity of the piezoelectric actuator, the standard symmetric PI model cannot precisely describe the asymmetric motion of the actuator. In order to improve the accuracy of AFM scans, two series of slope parameters were introduced in the PI model to describe both the voltage-increase-loop (trace) and voltage-decrease-loop (retrace). A feedforward controller based on the DIAPI model was implemented to compensate hysteresis. Performance of the DIAPI model and the feedforward controller were validated by scanning micro-lenses and standard silicon grating using a custom-built AFM. PMID:25654719
Improving atomic force microscopy imaging by a direct inverse asymmetric PI hysteresis model.
Wang, Dong; Yu, Peng; Wang, Feifei; Chan, Ho-Yin; Zhou, Lei; Dong, Zaili; Liu, Lianqing; Li, Wen Jung
2015-02-03
A modified Prandtl-Ishlinskii (PI) model, referred to as a direct inverse asymmetric PI (DIAPI) model in this paper, was implemented to reduce the displacement error between a predicted model and the actual trajectory of a piezoelectric actuator which is commonly found in AFM systems. Due to the nonlinearity of the piezoelectric actuator, the standard symmetric PI model cannot precisely describe the asymmetric motion of the actuator. In order to improve the accuracy of AFM scans, two series of slope parameters were introduced in the PI model to describe both the voltage-increase-loop (trace) and voltage-decrease-loop (retrace). A feedforward controller based on the DIAPI model was implemented to compensate hysteresis. Performance of the DIAPI model and the feedforward controller were validated by scanning micro-lenses and standard silicon grating using a custom-built AFM.
NASA Technical Reports Server (NTRS)
Gray, Robin B.
1960-01-01
Hovering and steady low-speed forward-flight tests were run on a 4-foot-diameter rotor at a ground height of 1 rotor radius. The two blades had a 2 to 1 taper ratio and were mounted in a see-saw hub. The solidity ratio was 0.05. Measurements were made of the rotor rpm, collective pitch, and forward-flight velocity. Smoke was introduced into the tip vortex and the resulting vortex pattern was photographed from two positions. Using the data obtained from these photographs, wire models of the tip vortex configurations were constructed and the distribution of the normal component of induced velocity at the blade feathering axis that is associated with these tip vortex configurations was experimentally determined at 450 increments in azimuth position from this electromagnetic analog. Three steady-state conditions were analyzed. The first was hovering flight; the second, a flight velocity just under the wake "tuck under" speed; and the third, a flight velocity just above this speed. These corresponded to advance ratios of 0, 0.022, and 0.030 (or ratios of forward velocity to calculated hovering induced velocity of approximately 0, 0.48, and 0.65), respectively, for the model test rotor. Cross sections of the wake at 450 intervals in azimuth angle as determined from the path of the tip vortex are presented graphically for all three cases. The nondimensional normal component of the induced velocity that is associated with the tip vortex as determined by an electromagnetic analog at 450 increments in azimuth position and at the blade feathering axis is presented graphically. It is shown that the mean value of this component of the induced velocity is appreciably less after tuck-under than before. It is concluded that this method yields results of engineering accuracy and is a very useful means of studying vortex fields.
NASA Technical Reports Server (NTRS)
Blanchard, U. J.
1977-01-01
Vibration investigations of a model of the asymmetric multielement space shuttle were made. The influence on overall motions of local deformation in the vicinity of element interfaces, high modal density, low structural damping, and high responsiveness in the crew cabin are included in the findings. Mode frequencies generally increase with decreasing propellant masses and staging of elements.
A general model for metabolic scaling in self-similar asymmetric networks
Savage, Van M.; Enquist, Brian J.
2017-01-01
How a particular attribute of an organism changes or scales with its body size is known as an allometry. Biological allometries, such as metabolic scaling, have been hypothesized to result from selection to maximize how vascular networks fill space yet minimize internal transport distances and resistances. The West, Brown, Enquist (WBE) model argues that these two principles (space-filling and energy minimization) are (i) general principles underlying the evolution of the diversity of biological networks across plants and animals and (ii) can be used to predict how the resulting geometry of biological networks then governs their allometric scaling. Perhaps the most central biological allometry is how metabolic rate scales with body size. A core assumption of the WBE model is that networks are symmetric with respect to their geometric properties. That is, any two given branches within the same generation in the network are assumed to have identical lengths and radii. However, biological networks are rarely if ever symmetric. An open question is: Does incorporating asymmetric branching change or influence the predictions of the WBE model? We derive a general network model that relaxes the symmetric assumption and define two classes of asymmetrically bifurcating networks. We show that asymmetric branching can be incorporated into the WBE model. This asymmetric version of the WBE model results in several theoretical predictions for the structure, physiology, and metabolism of organisms, specifically in the case for the cardiovascular system. We show how network asymmetry can now be incorporated in the many allometric scaling relationships via total network volume. Most importantly, we show that the 3/4 metabolic scaling exponent from Kleiber’s Law can still be attained within many asymmetric networks. PMID:28319153
A general model for metabolic scaling in self-similar asymmetric networks.
Brummer, Alexander Byers; Savage, Van M; Enquist, Brian J
2017-03-01
How a particular attribute of an organism changes or scales with its body size is known as an allometry. Biological allometries, such as metabolic scaling, have been hypothesized to result from selection to maximize how vascular networks fill space yet minimize internal transport distances and resistances. The West, Brown, Enquist (WBE) model argues that these two principles (space-filling and energy minimization) are (i) general principles underlying the evolution of the diversity of biological networks across plants and animals and (ii) can be used to predict how the resulting geometry of biological networks then governs their allometric scaling. Perhaps the most central biological allometry is how metabolic rate scales with body size. A core assumption of the WBE model is that networks are symmetric with respect to their geometric properties. That is, any two given branches within the same generation in the network are assumed to have identical lengths and radii. However, biological networks are rarely if ever symmetric. An open question is: Does incorporating asymmetric branching change or influence the predictions of the WBE model? We derive a general network model that relaxes the symmetric assumption and define two classes of asymmetrically bifurcating networks. We show that asymmetric branching can be incorporated into the WBE model. This asymmetric version of the WBE model results in several theoretical predictions for the structure, physiology, and metabolism of organisms, specifically in the case for the cardiovascular system. We show how network asymmetry can now be incorporated in the many allometric scaling relationships via total network volume. Most importantly, we show that the 3/4 metabolic scaling exponent from Kleiber's Law can still be attained within many asymmetric networks.
Comparison of Asymmetric and Ice-cream Cone Models for Halo Coronal Mass Ejections
NASA Astrophysics Data System (ADS)
Na, H.; Moon, Y.
2011-12-01
Halo coronal mass ejections (HCMEs) are major cause of the geomagnetic storms. To minimize the projection effect by coronagraph observation, several cone models have been suggested: an ice-cream cone model, an asymmetric cone model etc. These models allow us to determine the three dimensional parameters of HCMEs such as radial speed, angular width, and the angle between sky plane and central axis of the cone. In this study, we compare these parameters obtained from different models using 48 well-observed HCMEs from 2001 to 2002. And we obtain the root mean square error (RMS error) between measured projection speeds and calculated projection speeds for both cone models. As a result, we find that the radial speeds obtained from the models are well correlated with each other (R = 0.86), and the correlation coefficient of angular width is 0.6. The correlation coefficient of the angle between sky plane and central axis of the cone is 0.31, which is much smaller than expected. The reason may be due to the fact that the source locations of the asymmetric cone model are distributed near the center, while those of the ice-cream cone model are located in a wide range. The average RMS error of the asymmetric cone model (85.6km/s) is slightly smaller than that of the ice-cream cone model (87.8km/s).
Acoustic Shielding for a Model Scale Counter-rotation Open Rotor
NASA Technical Reports Server (NTRS)
Stephens, David B.; Edmane, Envia
2012-01-01
The noise shielding benefit of installing an open rotor above a simplified wing or tail is explored experimentally. The test results provide both a benchmark data set for validating shielding prediction tools and an opportunity for a system level evaluation of the noise reduction potential of propulsion noise shielding by an airframe component. A short barrier near the open rotor was found to provide up to 8.5 dB of attenuation at some directivity angles, with tonal sound particularly well shielded. Predictions from two simple shielding theories were found to overestimate the shielding benefit.
A comparison of theory and experiment for aeroelastic stability of a hingeless rotor model in hover
NASA Technical Reports Server (NTRS)
Sharpe, David L.
1988-01-01
Theoretical predictions of aeroelastic stability are compared with experimental, isolated, hingeless-rotor data. The six cases selected represent a torsionally soft rotor having either a stiff or soft pitch-control system in combination with zero precone and droop, 5 degree precone, or -5 degree droop. Analyses from Bell Helicopter Textron, Boeing Vertol, Hughes Helicopters, Sikorsky Aircraft, the National Aeronautics and Space Administration, and the U.S. Army Aeromechanics Laboratory were compared with the experimental data. The correlation ranged from poor to fair.
Separators for flywheel rotors
Bender, Donald A.; Kuklo, Thomas C.
1998-01-01
A separator forms a connection between the rotors of a concentric rotor assembly. This separator allows for the relatively free expansion of outer rotors away from inner rotors while providing a connection between the rotors that is strong enough to prevent disassembly. The rotor assembly includes at least two rotors referred to as inner and outer flywheel rings or rotors. This combination of inner flywheel ring, separator, and outer flywheel ring may be nested to include an arbitrary number of concentric rings. The separator may be a segmented or continuous ring that abuts the ends of the inner rotor and the inner bore of the outer rotor. It is supported against centrifugal loads by the outer rotor and is affixed to the outer rotor. The separator is allowed to slide with respect to the inner rotor. It is made of a material that has a modulus of elasticity that is lower than that of the rotors.
Separators for flywheel rotors
Bender, D.A.; Kuklo, T.C.
1998-07-07
A separator forms a connection between the rotors of a concentric rotor assembly. This separator allows for the relatively free expansion of outer rotors away from inner rotors while providing a connection between the rotors that is strong enough to prevent disassembly. The rotor assembly includes at least two rotors referred to as inner and outer flywheel rings or rotors. This combination of inner flywheel ring, separator, and outer flywheel ring may be nested to include an arbitrary number of concentric rings. The separator may be a segmented or continuous ring that abuts the ends of the inner rotor and the inner bore of the outer rotor. It is supported against centrifugal loads by the outer rotor and is affixed to the outer rotor. The separator is allowed to slide with respect to the inner rotor. It is made of a material that has a modulus of elasticity that is lower than that of the rotors. 10 figs.
Coupled escape probability for an asymmetric spherical case: Modeling optically thick comets
Gersch, Alan M.; A'Hearn, Michael F.
2014-05-20
We have adapted Coupled Escape Probability, a new exact method of solving radiative transfer problems, for use in asymmetrical spherical situations. Our model is intended specifically for use in modeling optically thick cometary comae, although not limited to such use. This method enables the accurate modeling of comets' spectra even in the potentially optically thick regions nearest the nucleus, such as those seen in Deep Impact observations of 9P/Tempel 1 and EPOXI observations of 103P/Hartley 2.
Kumar, Jason
2014-06-24
We review the theoretical framework underlying models of asymmetric dark matter, describe astrophysical constraints which arise from observations of neutron stars, and discuss the prospects for detecting asymmetric dark matter.
Cui, Peiling; Yan, Ning
2012-12-12
The magnetically suspended Control Moment Gyroscope (CMG) has the advantages of long-life, micro-vibration and being non-lubricating, and is the ideal actuator for agile maneuver satellite attitude control. However, the stability of the rotor in magnetic bearing and the precision of the output torque of a magnetically suspended CMG are affected by the rapid maneuvers of satellites. In this paper, a dynamic model of the agile satellite including a magnetically suspended single gimbal control moment gyroscope is built and the equivalent disturbance torque effected on the rotor is obtained. The feedforward compensation control method is used to depress the disturbance on the rotor. Simulation results are given to show that the rotor displacement is obviously reduced.
Cui, Peiling; Yan, Ning
2012-01-01
The magnetically suspended Control Moment Gyroscope (CMG) has the advantages of long-life, micro-vibration and being non-lubricating, and is the ideal actuator for agile maneuver satellite attitude control. However, the stability of the rotor in magnetic bearing and the precision of the output torque of a magnetically suspended CMG are affected by the rapid maneuvers of satellites. In this paper, a dynamic model of the agile satellite including a magnetically suspended single gimbal control moment gyroscope is built and the equivalent disturbance torque effected on the rotor is obtained. The feedforward compensation control method is used to depress the disturbance on the rotor. Simulation results are given to show that the rotor displacement is obviously reduced. PMID:23235442
NASA Technical Reports Server (NTRS)
Rosenstein, H.; Mcveigh, M. A.; Mollenkof, P. A.
1973-01-01
The results of a real time piloted simulation to investigate the handling qualities and performance of a tilting rotor aircraft design are presented. The aerodynamic configuration of the aircraft is described. The procedures for conducting the simulator evaluation are reported. Pilot comments of the aircraft handling qualities under various simulated flight conditions are included. The time histories of selected pilot maneuvers are shown.
Flight Acoustic Testing and Data Acquisition For the Rotor Noise Model (RNM)
NASA Technical Reports Server (NTRS)
Conner, David A.; Burley, Casey L.; Smith, Charles D.
2006-01-01
Two acoustic flight tests have been conducted on a remote test range at Eglin Air Force Base in the panhandle of Florida. The first was the Acoustics Week flight test conducted in September 2003. The second was the NASA Heavy Lift Rotorcraft Acoustics Flight Test conducted in October-November 2005. Benchmark acoustic databases were obtained for a number of rotorcraft and limited fixed wing vehicles for a variety of flight conditions. The databases are important for validation of acoustic prediction programs such as the Rotorcraft Noise Model (RNM), as well as for the development of low noise flight procedures and for environmental impact assessments. An overview of RNM capabilities and a detailed description of the RNM/ART (Acoustic Repropagation Technique) process are presented. The RNM/ART process is demonstrated using measured acoustic data for the MD600N. The RNM predictions for a level flyover speed sweep show the highest SEL noise levels on the flight track centerline occurred at the slowest vehicle speeds. At these slower speeds, broadband noise content is elevated compared to noise levels obtained at the higher speeds. A descent angle sweep shows that, in general, ground noise levels increased with increasing descent rates. Vehicle orientation in addition to vehicle position was found to significantly affect the RNM/ART creation of source noise semi-spheres for vehicles with highly directional noise characteristics and only mildly affect those with weak acoustic directionality. Based on these findings, modifications are proposed for RNM/ART to more accurately define vehicle and rotor orientation.
Evaluation of an asymmetric anterior glottic web in an excised canine larynx model.
Pulvermacher, Allyson C; Xue, Chao; Leggon, Robert; Mills, Randal; Jiang, Jack J
2017-03-01
The main objective of the study is to model asymmetry within anterior glottic webs in excised larynges using sutures and apply aerodynamic and acoustic analyses. Anterior glottic webs (AGW) were modeled in eight excised larynges using sutures secured at the level of the glottis to mimic the scar tissue of the web. Each of the eight larynges were tested under three different pressure increments for each of the three models of AGW: symmetric, vertically asymmetric, and laterally asymmetric. Phonation threshold pressure (PTP) and flow (PTF) differed significantly across AGW conditions (p = 0.006 and p = 0.005, respectively). Additionally, vocal efficiency was significantly different among conditions (p = 0.005) as well as significantly lower in the asymmetric groups (p = 0.015 and p = 0.007). Perturbation measures were not significantly different across conditions. Correlation dimension (D2) was significantly different at PTP, 1.25 × PTP, and 1.5 × PTP (p = 0.003, p = 0.010, and p < 0.001, respectively) as well as significantly higher in the asymmetric groups at each pressure increment. The increased PTP, PTF, and D2 values as well as decreased vocal efficiency among the asymmetric conditions indicates a significant decrease in vocal function, and thus represents that asymmetries could be a contributing factor to the pathological symptoms associated with glottic webs.
An asymmetric approach to modeling ion channels using finite element analysis.
Siksik, M; Krishnamurthy, V
2009-01-01
Biological ion channels are water filled pores in the cell membrane. They regulate the flow of ions in and out of the cell. Modeling the dynamics of these channels and relating their structure to functionality is crucial in understanding the mechanisms by which they conduct. This paper proposes a novel Finite Element Method (FEM) based simulation framework for modeling of ion channels that does not assume channel symmetry. This is the first framework that allows the use of multiple dielectric constants inside such channels without assuming geometrical symmetry thus providing a more realistic model of the channel. Due to the run-time complexity of the problem, lookup tables must be constructed in memory to store pre-calculated electric potential information. The large number of elements involved in FEM and channel resolution requirements can potentially result in very large lookup tables leading to a performance "bottleneck". This paper answers the following question: Does the accuracy introduced by using an asymmetric model outweigh the inaccuracy caused by having to reduce the size and resolution of electric-field look-up tables? This paper compares the memory footprint of an ion channel simulator that assumes a symmetric channel model versus an asymmetric model. We show that currently available personal computers are sufficient for attaining reasonable levels of accuracy for both. Our results show diminishing returns in accuracy with tables sized greater than 8.5 GB for the asymmetric model.
AN ASYMMETRICAL SYNCHROTRON MODEL FOR KNOTS IN THE 3C 273 JET
Liu, Wen-Po; Chen, Y. J.; Wang, Chun-Cheng
2015-06-20
To interpret the emission of knots in the 3C 273 jet from radio to X-rays, we propose a synchrotron model in which, owing to the shock compression effect, the injection spectra from a shock into the upstream and downstream emission regions are asymmetric. Our model could well explain the spectral energy distributions of knots in the 3C 273 jet, and predictions regarding the knots’ spectra could be tested by future observations.
Quantum Molecular Interaction Field Models of Substrate Enantioselection in Asymmetric Processes
Kozlowski, Marisa C.; Ianni, James C.
2010-01-01
Computational models correlating substrate structure to enantioselection with asymmetric catalysts using the QMQSAR program are described. In addition to rapidly providing predictions that could be used to facilitate the screening of catalysts for novel substrates, the QMQSAR program identifies the portions of the substrate that most directly influence the enantioselectivity. The lack underlying relationship between all the substrates in one case, requires two quantitative structure selectivity relationships (QSSR) models to describe all of the experimental results. PMID:20676382
Rotor for a line start permanent magnet machine
Melfi, Mike; Schiferl, Rich; Umans, Stephen
2017-07-11
A rotor comprises laminations with a plurality of rotor bar slots with an asymmetric arrangement about the rotor. The laminations also have magnet slots equiangularly spaced about the rotor. The magnet slots extend near to the rotor outer diameter and have permanent magnets disposed in the magnet slots creating magnetic poles. The magnet slots may be formed longer than the permanent magnets disposed in the magnets slots and define one or more magnet slot apertures. The permanent magnets define a number of poles and a pole pitch. The rotor bar slots are spaced from adjacent magnet slots by a distance that is at least 4% of the pole pitch. Conductive material is disposed in the rotor bar slots, and in some embodiments, may be disposed in the magnet slot apertures.
Blade tip, finite aspect ratio, and dynamic stall effects on the Darrieus rotor
Paraschivoiu, I.; Desy, P.; Masson, C.
1988-02-01
The objective of the work described in this paper was to apply the Boeing-Vertol dynamic stall model in an asymmetric manner to account for the asymmetry of the flow between the left and right sides of the rotor. This phenomenon has been observed by the flow visualization of a two-straight-bladed Darrieus rotor in the IMST water tunnel. Also introduced into the aerodynamic model are the effects of the blade tip and finite aspect ratio on the aerodynamic performance of the Darrieus wind turbine. These improvements are compatible with the double-multiple-streamtube model and have been included in the CARDAAV computer code for predicting the aerodynamic performance. Very good agreement has been observed between the test data (Sandia 17 m) and theoretical predictions; a significant improvement over the previous dynamic stall model was obtained for the rotor power at low tip speed ratios, while the inclusion of the finite aspect ratio effects enhances the prediction of the rotor power for high tip speed ratios. The tip losses and finite aspect ratio effects were also calculated for a small-scale vertical-axis wind turbine, with a two-straight-bladed (NACA 0015) rotor. 15 references.
Behavior of Bilayer Leaflets in Asymmetric Model Membranes: Atomistic Simulation Studies
Tian, Jianhui; Nickels, Jonathan; Katsaras, John; Cheng, Xiaolin
2016-04-27
Spatial organization within lipid bilayers is an important feature for a range of biological processes. Leaflet compositional asymmetry and lateral lipid organization are just two of the ways in which membrane structure appears to be more complex than initially postulated by the fluid mosaic model. This raises the question of how the phase behavior in one bilayer leaflet may affect the apposing leaflet and how one begins to construct asymmetric model systems to investigate these interleaflet interactions. In this paper, we report on all-atom molecular dynamics simulations (a total of 4.1 μs) of symmetric and asymmetric bilayer systems composed of liquid-ordered (Lo) or liquid-disordered (Ld) leaflets, based on the nanodomain-forming POPC/DSPC/cholesterol system. We begin by analyzing an asymmetric bilayer with leaflets derived from simulations of symmetric Lo and Ld bilayers. In this system, we observe that the properties of the Lo and Ld leaflets are similar to those of the Lo and Ld leaflets in corresponding symmetric systems. However, it is not obvious that mixing the equilibrium structures of their symmetric counterparts is the most appropriate way to construct asymmetric bilayers nor that these structures will manifest interleaflet couplings that lead to domain registry/antiregistry. We therefore constructed and simulated four additional asymmetric bilayer systems by systematically adding or removing lipids in the Ld leaflet to mimic potential density fluctuations. We find that the number of lipids in the Ld leaflet affects its own properties, as well as those of the apposing Lo leaflet. Collectively, the simulations reveal the presence of weak acyl chain interdigitation across bilayer leaflets, suggesting that interdigitation alone does not contribute significantly to the interleaflet coupling in nonphase-separated bilayers of this chemical composition. Finally, however, the properties of both leaflets appear to be sensitive to changes in in-plane lipid
Behavior of Bilayer Leaflets in Asymmetric Model Membranes: Atomistic Simulation Studies
Tian, Jianhui; Nickels, Jonathan; Katsaras, John; Cheng, Xiaolin
2016-04-27
Spatial organization within lipid bilayers is an important feature for a range of biological processes. Leaflet compositional asymmetry and lateral lipid organization are just two of the ways in which membrane structure appears to be more complex than initially postulated by the fluid mosaic model. This raises the question of how the phase behavior in one bilayer leaflet may affect the apposing leaflet and how one begins to construct asymmetric model systems to investigate these interleaflet interactions. In this paper, we report on all-atom molecular dynamics simulations (a total of 4.1 μs) of symmetric and asymmetric bilayer systems composed of liquid-ordered (Lo) or liquid-disordered (Ld) leaflets, based on the nanodomain-forming POPC/DSPC/cholesterol system. We begin by analyzing an asymmetric bilayer with leaflets derived from simulations of symmetric Lo and Ld bilayers. In this system, we observe that the properties of the Lo and Ld leaflets are similar to those of the Lo and Ld leaflets in corresponding symmetric systems. However, it is not obvious that mixing the equilibrium structures of their symmetric counterparts is the most appropriate way to construct asymmetric bilayers nor that these structures will manifest interleaflet couplings that lead to domain registry/antiregistry. We therefore constructed and simulated four additional asymmetric bilayer systems by systematically adding or removing lipids in the Ld leaflet to mimic potential density fluctuations. We find that the number of lipids in the Ld leaflet affects its own properties, as well as those of the apposing Lo leaflet. Collectively, the simulations reveal the presence of weak acyl chain interdigitation across bilayer leaflets, suggesting that interdigitation alone does not contribute significantly to the interleaflet coupling in nonphase-separated bilayers of this chemical composition. Finally, however, the properties of both leaflets appear to be sensitive to changes in in-plane lipid
Influence of an asymmetric ring on the modeling of an orthogonally stiffened cylindrical shell
NASA Technical Reports Server (NTRS)
Rastogi, Naveen; Johnson, Eric R.
1994-01-01
Structural models are examined for the influence of a ring with an asymmetrical cross section on the linear elastic response of an orthogonally stiffened cylindrical shell subjected to internal pressure. The first structural model employs classical theory for the shell and stiffeners. The second model employs transverse shear deformation theories for the shell and stringer and classical theory for the ring. Closed-end pressure vessel effects are included. Interacting line load intensities are computed in the stiffener-to-skin joints for an example problem having the dimensions of the fuselage of a large transport aircraft. Classical structural theory is found to exaggerate the asymmetric response compared to the transverse shear deformation theory.
A simple model of asymmetric quasi-species: network sustained by emergent high mutation rates
NASA Astrophysics Data System (ADS)
Iwasaki, Yuishi; Yonezawa, Fumiko
1999-02-01
A simple model of adaptive mutation rates is studied to understand asymmetric adaptive systems. In the model, two sources of asymmetries are introduced. One is a spin-glass-type energy function and gives an asymmetry of the fitness landscape. The other is the variable mutation rate associated with each gene and gives an asymmetry of the transition probabilities. A control parameter is a selection pressure rather than a mutation rate. We find that the model shows three results: (i) High mutation rates emerge in the iterative Darwinian selection process. (ii) Detailed balance is satisfied in the diverse system sustained by the emergent high mutation rates. (iii) A transition from the positive Darwinian selection (ordered state) to the nearly neutral selection (disordered state) takes place as the selection pressure decreases. Based on these results, we study the asymmetric network sustained by emergent high mutation rates.
Large eddy simulation of high frequency oscillating flow in an asymmetric branching airway model.
Nagels, Martin A; Cater, John E
2009-11-01
The implementation of artificial ventilation schemes is necessary when respiration fails. One approach involves the application of high frequency oscillatory ventilation (HFOV) to the respiratory system. Oscillatory airflow in the upper bronchial tree can be characterized by Reynolds numbers as high as 10(4), hence, the flow presents turbulent features. In this study, transitional and turbulent flow within an asymmetric bifurcating model of the upper airway during HFOV are studied using large eddy simulation (LES) methods. The flow, characterized by a peak Reynolds number of 8132, is analysed using a validated LES model of a three-dimensional branching geometry. The pressures, velocities, and vorticity within the flow are presented and compared with prior models for branching flow systems. The results demonstrate how pendelluft occurs at asymmetric branches within the respiratory system. These results may be useful in optimising treatments using HFOV methods.
Ko, Young-Rae; Hwang, Yoonkyu; Chae, Minji; Kim, Tae-Hyoung
2017-09-01
In this study, we present an identification-based direct construction of the inverse generalized Prandtl-Ishlinskii (P-I) model to facilitate inverse model-based feedforward compensation of asymmetric hysteresis nonlinearities. Compared with the derivation of the inverse model analytically from a generalized P-I model, this direct modeling approach has the following advantages. First, direct inverse model identification is formulated as a nonlinear optimization problem, which is not subject to the constraint condition on the generalized P-I model's threshold and density functions, where this is indispensable for the analytical model inversion procedure. Second, this approach may be a simple and attractive alternative when the identification precision of a generalized P-I model is limited by the constraint condition, which necessarily results in insufficient hysteresis compensation functionality for the analytically derived inverse model. Finally, direct inverse model identification can overcome the drawbacks of the analytical inversion method, including the accumulation of parameter estimation errors in an analytical inverse model because these parameters are computed from the generalized P-I model's parameters in a recursive manner. Our experimental results demonstrated that the implementation of open-loop control with the directly identified inverse generalized P-I model as a feedforward compensator achieved precise compensation for the asymmetric hysteresis nonlinearities of a piezoelectric stack actuator. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.
TH-C-BRD-02: Analytical Modeling and Dose Calculation Method for Asymmetric Proton Pencil Beams
Gelover, E; Wang, D; Hill, P; Flynn, R; Hyer, D
2014-06-15
Purpose: A dynamic collimation system (DCS), which consists of two pairs of orthogonal trimmer blades driven by linear motors has been proposed to decrease the lateral penumbra in pencil beam scanning proton therapy. The DCS reduces lateral penumbra by intercepting the proton pencil beam near the lateral boundary of the target in the beam's eye view. The resultant trimmed pencil beams are asymmetric and laterally shifted, and therefore existing pencil beam dose calculation algorithms are not capable of trimmed beam dose calculations. This work develops a method to model and compute dose from trimmed pencil beams when using the DCS. Methods: MCNPX simulations were used to determine the dose distributions expected from various trimmer configurations using the DCS. Using these data, the lateral distribution for individual beamlets was modeled with a 2D asymmetric Gaussian function. The integral depth dose (IDD) of each configuration was also modeled by combining the IDD of an untrimmed pencil beam with a linear correction factor. The convolution of these two terms, along with the Highland approximation to account for lateral growth of the beam along the depth direction, allows a trimmed pencil beam dose distribution to be analytically generated. The algorithm was validated by computing dose for a single energy layer 5×5 cm{sup 2} treatment field, defined by the trimmers, using both the proposed method and MCNPX beamlets. Results: The Gaussian modeled asymmetric lateral profiles along the principal axes match the MCNPX data very well (R{sup 2}≥0.95 at the depth of the Bragg peak). For the 5×5 cm{sup 2} treatment plan created with both the modeled and MCNPX pencil beams, the passing rate of the 3D gamma test was 98% using a standard threshold of 3%/3 mm. Conclusion: An analytical method capable of accurately computing asymmetric pencil beam dose when using the DCS has been developed.
The results of a wind tunnel investigation of a model rotor with a free tip
NASA Technical Reports Server (NTRS)
Stroub, Robert H.; Young, Larry A.
1985-01-01
The results of a wind-tunnel test of the free tip rotor are presented. The free tip extended over the outer 10% of the rotor blade and included a simple, passive controller mechanism. Wind-tunnel test hardware is described. The free-tip assembly, which includes the controller, functioned flawlessly throughout the test. The tip pitched freely and responded to airflow perturbation in a sharp, quick, and stable manner. Tip pitch-angle responses are presented for an advance ratio range of 0.1 to 0.397 and for a thrust coefficient range of 0.038 to 0.092. The free tip reduced power requirements, loads going into the control system, and some flatwise blade-bending moments. Chordwise loads were not reduced by the free tip.
Dynamic response characteristics of a circulation control rotor model pneumatic system
NASA Technical Reports Server (NTRS)
Watkins, C. B.; Reader, K. R.; Dutta, S. K.
1985-01-01
Numerical and experimental simulation of unsteady airflow through the control valve and slotted air duct of a circulation control rotor is described. The numerical analysis involves the solution of the quasi-one-dimensional compressible fluid-dynamic equations in the blade air duct together with the coupled isentropic flow equations for flow into the blade through the valve and out of the blade through the Coanda slot. Numerical solutions are compared with basic experimental results obtained for a mockup of a circulation control rotor and its pneumatic valving system. The pneumodynamic phenomena that were observed are discussed with particular emphasis on the characteristic system time lags associated with the response of the flow variables to transient and periodic control valve inputs.
Roback, R.J.; Dring, R.P. )
1992-01-01
Experimental documentation and analytical correlations demonstrating the effects of hot streak accumulation and phantom cooling on turbine rotor airfoil surface temperature are presented. Results are shown which quantify the impact of a nonuniform temperature profile at the entrance of a turbine due to combustor-generated hot and cold streaks, and cooling air discharged from the trailing edge of the upstream stator. Experimental results are shown for a range of controlling variables to identify where streak accumulation and phantom cooling were most likely to be strongest. These variables include streak-to-free stream density ratio, streak injection location, and coolant-to-free stream density and velocity ratios. Experimental results are shown for the combined effects of hot streak and stator coolant on the adiabatic recovery temperature of the rotor. 2 refs.
NASA Technical Reports Server (NTRS)
Roback, Richard J.; Dring, Robert P.
1992-01-01
Experimental documentation and analytical correlations demonstrating the effects of hot streak accumulation and phantom cooling on turbine rotor airfoil surface temperature are presented. Results are shown which quantify the impact of a nonuniform temperature profile at the entrance of a turbine due to combustor-generated hot and cold streaks, and cooling air discharged from the trailing edge of the upstream stator. Experimental results are shown for a range of controlling variables to identify where streak accumulation and phantom cooling were most likely to be strongest. These variables include streak-to-free stream density ratio, streak injection location, and coolant-to-free stream density and velocity ratios. Experimental results are shown for the combined effects of hot streak and stator coolant on the adiabatic recovery temperature of the rotor.
Modeling bee swarming behavior through diffusion adaptation with asymmetric information sharing
NASA Astrophysics Data System (ADS)
Li, Jinchao; Sayed, Ali H.
2012-12-01
Honeybees swarm when they move to a new site for their hive. During the process of swarming, their behavior can be analyzed by classifying them as informed bees or uninformed bees, where the informed bees have some information about the destination while the uninformed bees follow the informed bees. The swarm's movement can be viewed as a network of mobile nodes with asymmetric information exchange about their destination. In these networks, adaptive and mobile agents share information on the fly and adapt their estimates in response to local measurements and data shared with neighbors. Diffusion adaptation is used to model the adaptation process in the presence of asymmetric nodes and noisy data. The simulations indicate that the models are able to emulate the swarming behavior of bees under varied conditions such as a small number of informed bees, sharing of target location, sharing of target direction, and noisy measurements.
Partial SUSY breaking for asymmetric Gepner models and non-geometric flux vacua
NASA Astrophysics Data System (ADS)
Blumenhagen, Ralph; Fuchs, Michael; Plauschinn, Erik
2017-01-01
Using the method of simple current extensions, asymmetric Gepner models of Type IIB with N = 1 space-time supersymmetry are constructed. The combinatorics of the massless vector fields suggests that these classical Minkowski string vacua provide fully backreacted solutions corresponding to N = 1 minima of N = 2 gauged supergravity. The latter contain abelian gaugings along the axionic isometries in the hypermultiplet moduli space, and can be considered as Type IIB flux compactifications on Calabi-Yau manifolds equipped with (non-)geometric fluxes. For a particular class of asymmetric Gepner models, we are able to explicitly specify the underlying CICYs and to check necessary conditions for a GSUGRA interpretation. If this conjecture is correct, there exists a large class of exactly solvable non-geometric flux compactifications on CY threefolds.
The asymmetric Hubbard model with a confining potential: The partial filling case
NASA Astrophysics Data System (ADS)
Silva-Valencia, J.; Franco, R.; Figueira, M. S.
We investigate the one-dimensional asymmetric Hubbard model with a confining potential, which may describe the ground state of two species of fermionic atoms trapped in a one-dimensional optical lattice. We use White's density matrix renormalization group and the global electronic density considered is n=0.8. The fermion density profiles and their variance were computed. We observe coexistence of insulating and metallic regions in the system. The effective confinement region is different for each kind of fermionic atom.
NASA Astrophysics Data System (ADS)
Shahverdi, H.; Nobari, A. S.; Behbahani-Nejad, M.; Haddadpour, H.
2009-11-01
This paper presents a coupled flap-lag-torsion aeroelastic stability analysis and response of a hingeless helicopter blade in the hovering flight condition. The boundary element method based on the wake eigenvalues is used for the prediction of unsteady airloads of the rotor blade. The aeroelastic equations of motion of the rotor blade are derived by Galerkin's method. To obtain the aeroelastic stability and response, the governing nonlinear equations of motion are linearized about the nonlinear steady equilibrium positions using small perturbation theory. The equilibrium deflections are calculated through the iterative Newton-Raphson method. Numerical results comprising steady equilibrium state deflections, aeroelastic eigenvalues and time history response about these states for a two-bladed rotor are presented, and some of them are compared with those obtained from a two-dimensional quasi-steady strip aerodynamic theory. Also, the effect of the number of aerodynamic eigenmodes is investigated. The results show that the three-dimensional aerodynamic formulation has considerable impact on the determination of both the equilibrium condition and lead-lag instability.
Computer considerations for real time simulation of a generalized rotor model
NASA Technical Reports Server (NTRS)
Howe, R. M.; Fogarty, L. E.
1977-01-01
Scaled equations were developed to meet requirements for real time computer simulation of the rotor system research aircraft. These equations form the basis for consideration of both digital and hybrid mechanization for real time simulation. For all digital simulation estimates of the required speed in terms of equivalent operations per second are developed based on the complexity of the equations and the required intergration frame rates. For both conventional hybrid simulation and hybrid simulation using time-shared analog elements the amount of required equipment is estimated along with a consideration of the dynamic errors. Conventional hybrid mechanization using analog simulation of those rotor equations which involve rotor-spin frequencies (this consititutes the bulk of the equations) requires too much analog equipment. Hybrid simulation using time-sharing techniques for the analog elements appears possible with a reasonable amount of analog equipment. All-digital simulation with affordable general-purpose computers is not possible because of speed limitations, but specially configured digital computers do have the required speed and consitute the recommended approach.
Broadband rotor noise analyses
NASA Technical Reports Server (NTRS)
George, A. R.; Chou, S. T.
1984-01-01
The various mechanisms which generate broadband noise on a range of rotors studied include load fluctuations due to inflow turbulence, due to turbulent boundary layers passing the blades' trailing edges, and due to tip vortex formation. Existing analyses are used and extensions to them are developed to make more accurate predictions of rotor noise spectra and to determine which mechanisms are important in which circumstances. Calculations based on the various prediction methods in existing experiments were compared. The present analyses are adequate to predict the spectra from a wide variety of experiments on fans, full scale and model scale helicopter rotors, wind turbines, and propellers to within about 5 to 10 dB. Better knowledge of the inflow turbulence improves the accuracy of the predictions. Results indicate that inflow turbulence noise depends strongly on ambient conditions and dominates at low frequencies. Trailing edge noise and tip vortex noise are important at higher frequencies if inflow turbulence is weak. Boundary layer trailing edge noise, important, for large sized rotors, increases slowly with angle of attack but not as rapidly as tip vortex noise.
Advances in tilt rotor noise prediction
NASA Technical Reports Server (NTRS)
George, A. R.; Coffen, C. D.; Ringler, T. D.
1992-01-01
The two most serious tilt rotor external noise problems, hover noise and blade-vortex interaction noise, 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 noise mechanisms in hover are examined by first modeling tilt rotor hover aerodynamics and then applying various noise 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 source for hover.
Fuselage upwash effects on RSRA rotor systems
NASA Technical Reports Server (NTRS)
Cowan, J.; Dadone, L.
1985-01-01
The effects of RSRA fuselage configurations on rotor performance and loads have been quantified analytically by means of currently available potential flow and rotor analysis. Four configurations of the Rotor Systems Research Aircraft (RSRA) were considered in this study. They were: (1) fuselage alone (conventional helicopter); (2) fuselage with auxiliary propulsion; (3) fuselage with wings (auxiliary lift); and (4) fuselage with both auxiliary lift propulsion. The rotor system investigated was identical to a CH-47D front rotor except that it had four instead of three blades. Two scaled-down versions of the same rotor were also analyzed to determine the effect of rotor scale on the fuselage upwash effects. The flight conditions considered for the upwash study are discussed. The potential flow models for the RSRA configuration, with and without the wings and the auxiliary propulsion system, are presented. The results of fuselage/wing/propulsion system upwash on performance and loads are also presented.
Advances in tilt rotor noise prediction
NASA Technical Reports Server (NTRS)
George, A. R.; Coffen, C. D.; Ringler, T. D.
1992-01-01
The two most serious tilt rotor external noise problems, hover noise and blade-vortex interaction noise, 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 noise mechanisms in hover are examined by first modeling tilt rotor hover aerodynamics and then applying various noise 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 source for hover.
Active patterning and asymmetric transport in a model actomyosin network
Wang, Shenshen; Wolynes, Peter G.
2013-12-21
Cytoskeletal networks, which are essentially motor-filament assemblies, play a major role in many developmental processes involving structural remodeling and shape changes. These are achieved by nonequilibrium self-organization processes that generate functional patterns and drive intracellular transport. We construct a minimal physical model that incorporates the coupling between nonlinear elastic responses of individual filaments and force-dependent motor action. By performing stochastic simulations we show that the interplay of motor processes, described as driving anti-correlated motion of the network vertices, and the network connectivity, which determines the percolation character of the structure, can indeed capture the dynamical and structural cooperativity which gives rise to diverse patterns observed experimentally. The buckling instability of individual filaments is found to play a key role in localizing collapse events due to local force imbalance. Motor-driven buckling-induced node aggregation provides a dynamic mechanism that stabilizes the two-dimensional patterns below the apparent static percolation limit. Coordinated motor action is also shown to suppress random thermal noise on large time scales, the two-dimensional configuration that the system starts with thus remaining planar during the structural development. By carrying out similar simulations on a three-dimensional anchored network, we find that the myosin-driven isotropic contraction of a well-connected actin network, when combined with mechanical anchoring that confers directionality to the collective motion, may represent a novel mechanism of intracellular transport, as revealed by chromosome translocation in the starfish oocyte.
Active patterning and asymmetric transport in a model actomyosin network
NASA Astrophysics Data System (ADS)
Wang, Shenshen; Wolynes, Peter G.
2013-12-01
Cytoskeletal networks, which are essentially motor-filament assemblies, play a major role in many developmental processes involving structural remodeling and shape changes. These are achieved by nonequilibrium self-organization processes that generate functional patterns and drive intracellular transport. We construct a minimal physical model that incorporates the coupling between nonlinear elastic responses of individual filaments and force-dependent motor action. By performing stochastic simulations we show that the interplay of motor processes, described as driving anti-correlated motion of the network vertices, and the network connectivity, which determines the percolation character of the structure, can indeed capture the dynamical and structural cooperativity which gives rise to diverse patterns observed experimentally. The buckling instability of individual filaments is found to play a key role in localizing collapse events due to local force imbalance. Motor-driven buckling-induced node aggregation provides a dynamic mechanism that stabilizes the two-dimensional patterns below the apparent static percolation limit. Coordinated motor action is also shown to suppress random thermal noise on large time scales, the two-dimensional configuration that the system starts with thus remaining planar during the structural development. By carrying out similar simulations on a three-dimensional anchored network, we find that the myosin-driven isotropic contraction of a well-connected actin network, when combined with mechanical anchoring that confers directionality to the collective motion, may represent a novel mechanism of intracellular transport, as revealed by chromosome translocation in the starfish oocyte.
Modeling asymmetric cavity collapse with plasma equations of state
NASA Astrophysics Data System (ADS)
Tully, Brett; Hawker, Nicholas; Ventikos, Yiannis
2016-05-01
We explore the effect that equation of state (EOS) thermodynamics has on shock-driven cavity-collapse processes. We account for full, multidimensional, unsteady hydrodynamics and incorporate a range of relevant EOSs (polytropic, QEOS-type, and SESAME). In doing so, we show that simplified analytic EOSs, like ideal gas, capture certain critical parameters of the collapse such as velocity of the main transverse jet and pressure at jet strike, while also providing a good representation of overall trends. However, more sophisticated EOSs yield different and more relevant estimates of temperature and density, especially for higher incident shock strengths. We model incident shocks ranging from 0.1 to 1000 GPa, the latter being of interest in investigating the warm dense matter regime for which experimental and theoretical EOS data are difficult to obtain. At certain shock strengths, there is a factor of two difference in predicted density between QEOS-type and SESAME EOS, indicating cavity collapse as an experimental method for exploring EOS in this range.
Modeling asymmetric cavity collapse with plasma equations of state.
Tully, Brett; Hawker, Nicholas; Ventikos, Yiannis
2016-05-01
We explore the effect that equation of state (EOS) thermodynamics has on shock-driven cavity-collapse processes. We account for full, multidimensional, unsteady hydrodynamics and incorporate a range of relevant EOSs (polytropic, QEOS-type, and SESAME). In doing so, we show that simplified analytic EOSs, like ideal gas, capture certain critical parameters of the collapse such as velocity of the main transverse jet and pressure at jet strike, while also providing a good representation of overall trends. However, more sophisticated EOSs yield different and more relevant estimates of temperature and density, especially for higher incident shock strengths. We model incident shocks ranging from 0.1 to 1000 GPa, the latter being of interest in investigating the warm dense matter regime for which experimental and theoretical EOS data are difficult to obtain. At certain shock strengths, there is a factor of two difference in predicted density between QEOS-type and SESAME EOS, indicating cavity collapse as an experimental method for exploring EOS in this range.
Richardson, Robin A; Papachristos, Konstantinos; Read, Daniel J; Harlen, Oliver G; Harrison, Michael; Paci, Emanuele; Muench, Stephen P; Harris, Sarah A
2014-12-01
Advances in structural biology, such as cryo-electron microscopy (cryo-EM) have allowed for a number of sophisticated protein complexes to be characterized. However, often only a static snapshot of a protein complex is visualized despite the fact that conformational change is frequently inherent to biological function, as is the case for molecular motors. Computer simulations provide valuable insights into the different conformations available to a particular system that are not accessible using conventional structural techniques. For larger proteins and protein complexes, where a fully atomistic description would be computationally prohibitive, coarse-grained simulation techniques such as Elastic Network Modeling (ENM) are often employed, whereby each atom or group of atoms is linked by a set of springs whose properties can be customized according to the system of interest. Here we compare ENM with a recently proposed continuum model known as Fluctuating Finite Element Analysis (FFEA), which represents the biomolecule as a viscoelastic solid subject to thermal fluctuations. These two complementary computational techniques are used to answer a critical question in the rotary ATPase family; implicit within these motors is the need for a rotor axle and proton pump to rotate freely of the motor domain and stator structures. However, current single particle cryo-EM reconstructions have shown an apparent connection between the stators and rotor axle or pump region, hindering rotation. Both modeling approaches show a possible role for this connection and how it would significantly constrain the mobility of the rotary ATPase family.
NASA Technical Reports Server (NTRS)
Muszynska, Agnes; Bently, Donald E.
1991-01-01
Perturbation techniques used for identification of rotating system dynamic characteristics are described. A comparison between two periodic frequency-swept perturbation methods applied in identification of fluid forces of rotating machines is presented. The description of the fluid force model identified by inputting circular periodic frequency-swept force is given. This model is based on the existence and strength of the circumferential flow, most often generated by the shaft rotation. The application of the fluid force model in rotor dynamic analysis is presented. It is shown that the rotor stability is an entire rotating system property. Some areas for further research are discussed.
The asymmetric effect of coal price on the China's macro economy using NARDL model
NASA Astrophysics Data System (ADS)
Hou, J. C.; Yang, M. C.
2016-08-01
The present work endeavors to explore the asymmetric effect of coal price on the China's macro economy by applying nonlinear autoregressive distributed lag (NARDL) model for the period of January 2005 to June 2015. The obtained results indicate that the coal price has a strong asymmetric effect on China's macro economy in the long-run. Namely one percent increase in coal price leads to 0.6194 percent of the China's macro economy increase; and while the coal price is reduces by 1 percent, the China's macro economy will decrease by 0.008 percent. These data indicate that when coal price rises, the effect on China's macro economy is far greater than the price decline. In the short-run, coal price fluctuation has a positive effect on the China's macro economy.
Asymmetric primitive-model electrolytes: Debye-Hückel theory, criticality, and energy bounds.
Zuckerman, D M; Fisher, M E; Bekiranov, S
2001-07-01
Debye-Hückel (DH) theory is extended to treat two-component size- and charge-asymmetric primitive models, focusing primarily on the 1:1 additive hard-sphere electrolyte with, say, negative ion diameters a(--) larger than the positive ion diameters a(++). The treatment highlights the crucial importance of the charge-unbalanced "border zones" around each ion into which other ions of only one species may penetrate. Extensions of the DH approach that describe the border zones in a physically reasonable way are exact at high T and low density rho and, furthermore, are also in substantial agreement with recent simulation predictions for trends in the critical parameters, T(c) and rho(c), with increasing size asymmetry. Conversely, the simplest linear asymmetric DH description, which fails to account for physically expected behavior in the border zones at low T, can violate a new lower bound on the energy (which applies generally to models asymmetric in both charge and size). Other theories, including those based on the mean spherical approximation, predict trends in the critical parameters quite opposite to those established by the simulations.
Asymmetric dark matter and CP violating scatterings in a UV complete model
Baldes, Iason; Bell, Nicole F.; Millar, Alexander J.; Volkas, Raymond R. E-mail: n.bell@unimelb.edu.au E-mail: raymondv@unimelb.edu.au
2015-10-01
We explore possible asymmetric dark matter models using CP violating scatterings to generate an asymmetry. In particular, we introduce a new model, based on DM fields coupling to the SM Higgs and lepton doublets, a neutrino portal, and explore its UV completions. We study the CP violation and asymmetry formation of this model, to demonstrate that it is capable of producing the correct abundance of dark matter and the observed matter-antimatter asymmetry. Crucial to achieving this is the introduction of interactions which violate CP with a T{sup 2} dependence.
Asymmetric dark matter and CP violating scatterings in a UV complete model
Baldes, Iason; Bell, Nicole F.; Millar, Alexander J.; Volkas, Raymond R.
2015-10-21
We explore possible asymmetric dark matter models using CP violating scatterings to generate an asymmetry. In particular, we introduce a new model, based on DM fields coupling to the SM Higgs and lepton doublets, a neutrino portal, and explore its UV completions. We study the CP violation and asymmetry formation of this model, to demonstrate that it is capable of producing the correct abundance of dark matter and the observed matter-antimatter asymmetry. Crucial to achieving this is the introduction of interactions which violate CP with a T{sup 2} dependence.
Heberle, Frederick A.; Marquardt, Drew; Doktorova, Milka; ...
2016-04-29
Cell membranes possess a complex three-dimensional architecture, including nonrandom lipid lateral organization within the plane of a bilayer leaflet, and compositional asymmetry between the two leaflets. As a result, delineating the membrane structure–function relationship has been a highly challenging task. Even in simplified model systems, the interactions between bilayer leaflets are poorly understood, due in part to the difficulty of preparing asymmetric model membranes that are free from the effects of residual organic solvent or osmotic stress. To address these problems, we have modified a technique for preparing asymmetric large unilamellar vesicles (aLUVs) via cyclodextrin-mediated lipid exchange in order tomore » produce tensionless, solvent-free aLUVs suitable for a range of biophysical studies. Leaflet composition and structure were characterized using isotopic labeling strategies, which allowed us to avoid the use of bulky labels. NMR and gas chromatography provided precise quantification of the extent of lipid exchange and bilayer asymmetry, while small-angle neutron scattering (SANS) was used to resolve bilayer structural features with subnanometer resolution. Isotopically asymmetric POPC vesicles were found to have the same bilayer thickness and area per lipid as symmetric POPC vesicles, demonstrating that the modified exchange protocol preserves native bilayer structure. Partial exchange of DPPC into the outer leaflet of POPC vesicles produced chemically asymmetric vesicles with a gel/fluid phase-separated outer leaflet and a uniform, POPC-rich inner leaflet. SANS was able to separately resolve the thicknesses and areas per lipid of coexisting domains, revealing reduced lipid packing density of the outer leaflet DPPC-rich phase compared to typical gel phases. Lastly, our finding that a disordered inner leaflet can partially fluidize ordered outer leaflet domains indicates some degree of interleaflet coupling, and invites speculation on a role
NASA Technical Reports Server (NTRS)
Hill, Gary; Duval, Ronald W.; Green, John A.; Huynh, Loc C.
1991-01-01
A piloted comparison of rigid and aeroelastic blade-element rotor models was conducted at the Crew Station Research and Development Facility (CSRDF) at Ames Research Center. A simulation development and analysis tool, FLIGHTLAB, was used to implement these models in real time using parallel processing technology. Pilot comments and quantitative analysis performed both on-line and off-line confirmed that elastic degrees of freedom significantly affect perceived handling qualities. Trim comparisons show improved correlation with flight test data when elastic modes are modeled. The results demonstrate the efficiency with which the mathematical modeling sophistication of existing simulation facilities can be upgraded using parallel processing, and the importance of these upgrades to simulation fidelity.
NASA Technical Reports Server (NTRS)
Hill, Gary; Du Val, Ronald W.; Green, John A.; Huynh, Loc C.
1991-01-01
A piloted comparison of rigid and aeroelastic blade-element rotor models was conducted at the Crew Station Research and Development Facility (CSRDF) at Ames Research Center. A simulation development and analysis tool, FLIGHTLAB, was used to implement these models in real time using parallel processing technology. Pilot comments and qualitative analysis performed both on-line and off-line confirmed that elastic degrees of freedom significantly affect perceived handling qualities. Trim comparisons show improved correlation with flight test data when elastic modes are modeled. The results demonstrate the efficiency with which the mathematical modeling sophistication of existing simulation facilities can be upgraded using parallel processing, and the importance of these upgrades to simulation fidelity.
Modelling of asymmetrical interconnect T-tree laminated on flexible substrate
NASA Astrophysics Data System (ADS)
Ravelo, Blaise
2015-11-01
A fast and accurate behavioral modelling of asymmetrical microstrip tree printed on plastic substrate is investigated. The methodology for extracting the asymmetrical tree transfer responses based on the ABCD-matrix analysis is presented. The elements of the interconnect T-tree are constituted by transmission lines (TLs) defined by their characteristic impedance and physical length. The distributed tree network can be assumed as a single input multiple output (SIMO) topology. By considering the circuit equivalent between the electrical path from the tree input and output, the single input single output (SISO) simplified circuit can be established. In order to determine the frequency response of the interconnect tree system, the elementary TLs constituting the tree branches are modelled with their equivalent frequency dependent RLCG network. The novelty of the present paper is the application of the model to the microstrip structure printed on the plastic substrate by analyzing the influence of the metallization conductivity. As proof of concept (POC), a single input and three output distributed interconnect T-tree having branches presented physical lengths from 3 cm to 20 cm was designed. The POC was printed on the Cu metal deposited plastic Kapton substrate. Then, the frequency dependent per unit length resistance, inductance, capacitance and conductance of the elementary branches of the T-tree from DC to 10 GHz were extracted. By implementing the behavioral model of the circuit, the frequency- and time-domain responses of the proposed asymmetrical T-tree are computed. Then, the analyses of the asymmetrical T-tree responses in function of the thin film conductivity of the microstrip interconnect lines were discussed. In addition, time domain analysis enabling to predict the influence of the deposited metallic ink conductivity on the signal integrity is realized by considering a mixed signal corresponding to the digital data "010110000" having 0.5 Gbps rate
Inertial dynamics of a general purpose rotor
NASA Technical Reports Server (NTRS)
Duval, R. W.
1979-01-01
The inertial dynamics of a fully articulated stiff rotor blade are derived with emphasis on equations that facilitate an organized programming approach for simulation applications. The model for the derivation includes hinge offset and six degrees of freedom for the rotor shaft. Results are compared with the flapping and lead-lag equations currently used in the Rotor Systems Research Aircraft simulation model and differences are analyzed.
NASA Astrophysics Data System (ADS)
Wang, Shuai; Wang, Yu; Zi, Yanyang; Li, Bing; He, Zhengjia
2015-10-01
A novel reduced-order modeling method is presented in this paper for dynamics analysis of rotating impeller-shaft-bearing assembly with cracked impellers. Based on three-dimensional finite element model, the complex component mode synthesis (CMS) method is employed to generate an efficient reduced-order model (ROM) for studying the effects of crack on the global vibration of the rotating assembly. First, a modeling framework for impeller-shaft-bearing systems in rotating frame is presented. Rotational effects, including Coriolis matrix and centrifugal softening, have been taken into account. Then, the governing equation of motion of the damped gyroscopic system is reduced by the complex CMS method. Finally, the obtained ROM is employed to study the effects of crack on assembly's vibration. During the steady-state response analysis, external excitations on the impeller due to rotor-stator interactions have been taken into account, which was however neglected in previous investigations on rotordynamics. Numerical results show that the lower-order eigenvalues and the unbalance response of the assembly are not sensitive to the local crack on impeller. Nevertheless, the flexible coupling between impeller and shaft becomes more complex when the air flow-induced excitations are considered. Under EO1 traveling wave excitations, a crack leads to slight changes in the assembly's response. In contrast, the effect of crack becomes significant when the assembly is excited by EO2 and higher EO excitations. Moreover, the nonlinear crack breathing effects affect the assembly's response obviously. Finally, a potential technique for detecting the crack on impeller during operation is discussed.
Complex double-mass dynamic model of rotor on thrust foil gas dynamic bearings
NASA Astrophysics Data System (ADS)
Sytin, A.; Babin, A.; Vasin, S.
2017-08-01
The present paper considers simulation of a rotor’s dynamics behaviour on thrust foil gas dynamic bearings based on simultaneous solution of gas dynamics differential equations, equations of theory of elasticity, motion equations and some additional equations. A double-mass dynamic system was considered during the rotor’s motion simulation which allows not only evaluation of rotor’s dynamic behaviour, but also to evaluate the influence of operational and load parameters on the dynamics of the rotor-bearing system.
Flight Simulation of the Model 347 Advanced Tandem-Rotor Helicopter
1974-11-01
the influence of rotor downwash on the fuselage and for steady wind or gust velocity. The total linear aerodynamic velocities associated with... influence on the growth and steady-state magnitude of the limit cycle. The shape could not be defined precisely because of the inaccuracy of the test...F*oo, d CTB. P* Ol,Oi LtPT AlftCHAFT Mv>f>t 1. F’iOO.Ol CT*. (OOC’O^ S4I5 LOAD MOOC I LOAD Moot l FSOO^« ti&HT F
A method for modeling laterally asymmetric proton beamlets resulting from collimation
Gelover, Edgar; Wang, Dongxu; Hill, Patrick M.; Flynn, Ryan T.; Gao, Mingcheng; Laub, Steve; Pankuch, Mark; Hyer, Daniel E.
2015-01-01
Purpose: To introduce a method to model the 3D dose distribution of laterally asymmetric proton beamlets resulting from collimation. The model enables rapid beamlet calculation for spot scanning (SS) delivery using a novel penumbra-reducing dynamic collimation system (DCS) with two pairs of trimmers oriented perpendicular to each other. Methods: Trimmed beamlet dose distributions in water were simulated with MCNPX and the collimating effects noted in the simulations were validated by experimental measurement. The simulated beamlets were modeled analytically using integral depth dose curves along with an asymmetric Gaussian function to represent fluence in the beam’s eye view (BEV). The BEV parameters consisted of Gaussian standard deviations (sigmas) along each primary axis (σx1,σx2,σy1,σy2) together with the spatial location of the maximum dose (μx,μy). Percent depth dose variation with trimmer position was accounted for with a depth-dependent correction function. Beamlet growth with depth was accounted for by combining the in-air divergence with Hong’s fit of the Highland approximation along each axis in the BEV. Results: The beamlet model showed excellent agreement with the Monte Carlo simulation data used as a benchmark. The overall passing rate for a 3D gamma test with 3%/3 mm passing criteria was 96.1% between the analytical model and Monte Carlo data in an example treatment plan. Conclusions: The analytical model is capable of accurately representing individual asymmetric beamlets resulting from use of the DCS. This method enables integration of the DCS into a treatment planning system to perform dose computation in patient datasets. The method could be generalized for use with any SS collimation system in which blades, leaves, or trimmers are used to laterally sharpen beamlets. PMID:25735287
A method for modeling laterally asymmetric proton beamlets resulting from collimation
Gelover, Edgar; Wang, Dongxu; Flynn, Ryan T.; Hyer, Daniel E.; Hill, Patrick M.; Gao, Mingcheng; Laub, Steve; Pankuch, Mark
2015-03-15
Purpose: To introduce a method to model the 3D dose distribution of laterally asymmetric proton beamlets resulting from collimation. The model enables rapid beamlet calculation for spot scanning (SS) delivery using a novel penumbra-reducing dynamic collimation system (DCS) with two pairs of trimmers oriented perpendicular to each other. Methods: Trimmed beamlet dose distributions in water were simulated with MCNPX and the collimating effects noted in the simulations were validated by experimental measurement. The simulated beamlets were modeled analytically using integral depth dose curves along with an asymmetric Gaussian function to represent fluence in the beam’s eye view (BEV). The BEV parameters consisted of Gaussian standard deviations (sigmas) along each primary axis (σ{sub x1},σ{sub x2},σ{sub y1},σ{sub y2}) together with the spatial location of the maximum dose (μ{sub x},μ{sub y}). Percent depth dose variation with trimmer position was accounted for with a depth-dependent correction function. Beamlet growth with depth was accounted for by combining the in-air divergence with Hong’s fit of the Highland approximation along each axis in the BEV. Results: The beamlet model showed excellent agreement with the Monte Carlo simulation data used as a benchmark. The overall passing rate for a 3D gamma test with 3%/3 mm passing criteria was 96.1% between the analytical model and Monte Carlo data in an example treatment plan. Conclusions: The analytical model is capable of accurately representing individual asymmetric beamlets resulting from use of the DCS. This method enables integration of the DCS into a treatment planning system to perform dose computation in patient datasets. The method could be generalized for use with any SS collimation system in which blades, leaves, or trimmers are used to laterally sharpen beamlets.
NASA Astrophysics Data System (ADS)
Cuevas Cely, C. J.; Acevedo, C. H.; Torres Moreno, Y.
2017-01-01
This work shows experimental and theoretical results of the characterization of a nematic liquid-crystal spatial light modulator Sony model LCX038ARA for the parameters angle of molecular rotation, the birefringence and angle of the molecular axis, using the retarder-rotor model without electric field applied in the amplitude regime-coupled.
Alternating carrier models of asymmetric glucose transport violate the energy conservation laws.
Naftalin, Richard J
2008-11-01
Alternating access transporters with high-affinity externally facing sites and low-affinity internal sites relate substrate transit directly to the unliganded asymmetric "carrier" (Ci) distribution. When both bathing solutions contain equimolar concentrations of ligand, zero net flow of the substrate-carrier complex requires a higher proportion of unliganded low-affinity inside sites (proportional, variant 1/KD(in)) and slower unliganded "free" carrier transit from inside to outside than in the reverse direction. However, asymmetric rates of unliganded carrier movement, kij, imply that an energy source, DeltaGcarrier = RT ln (koi/kio) = RT ln (Cin/Cout) = RT ln (KD(in)/KD(out)), where R is the universal gas constant (8.314 Joules/M/K degrees), and T is the temperature, assumed here to be 300 K degrees , sustains the asymmetry. Without this invalid assumption, the constraints of carrier path cyclicity, combined with asymmetric ligand affinities and equimolarity at equilibrium, are irreconcilable, and any passive asymmetric uniporter or cotransporter model system, e.g., Na-glucose cotransporters, espousing this fundamental error is untenable. With glucose transport via GLUT1, the higher maximal rate and Km of net ligand exit compared to net ligand entry is only properly simulated if ligand transit occurs by serial dissociation-association reactions between external high-affinity and internal low-affinity immobile sites. Faster intersite transit rates occur from lower-affinity sites than from higher-affinity sites and require no other energy source to maintain equilibrium. Similar constraints must apply to cotransport.
Measurements of the Early Development of Trailing Vorticity from a Rotor
NASA Technical Reports Server (NTRS)
McAlister, Kenneth W.; Heineck, James T.
2002-01-01
The wake behind a two-bladed model rotor in light climb was measured using particle image velocimetry, with particular emphasis on the development of the trailing vortex during the first revolution of the rotor. The distribution of vorticity was distinguished from the slightly elliptical swirl pattern. Peculiar dynamics within the "void" region may explain why the peak vorticity appeared to shift away from the center as the vortex aged, suggesting the onset of instability. The swirl and axial velocities (which reached 44% and 12% of the rotor tip speed, respectively) were found to be asymmetric relative to the vortex center. In particular, the axial flow was composed of two concentrated zones moving in opposite directions. The radial distribution of the circulation rapidly increased in magnitude until reaching a point just beyond the core radius, after which the rate of growth decreased significantly. The core-radius circulation increased slightly with wake age, but the large-radius circulation appeared to remain relatively constant. The radial distributions of swirl velocity and vorticity exhibit self-similar behaviors, especially within the core. The diameter of the vortex core was initially about 10% of the rotor-blade chord, but more than doubled its size after one revolution of the rotor.
NASA Astrophysics Data System (ADS)
Aunai, N.; Hesse, M.; Kuznetsova, M. M.; Lavraud, B.
2014-12-01
The mechanisms controlling collisionless magnetic reconnection at electron scales are still poorly understood and the canonical symmetric 2D antiparallel reconnection configuration is quite limited in front of the great diversity of upstream plasma and field configurations reconnection can encounter. Therefore, efficient comparison between numerical simulations and in situ observations requires to look at features as generic as possible and to understand what can limit their generality. In this context, we will discuss the signatures of electron nongyrotropy, the impact of non kinetic equilibrium as an initial condition of asymmetric reconnection models, and of the orientation of the reconnection plane with respect to the upstream field in 2D models.
Two-Dimensional Wang-Landau Sampling of AN Asymmetric Ising Model
NASA Astrophysics Data System (ADS)
Tsai, Shan-Ho; Wang, Fugao; Landau, D. P.
We study the critical endpoint behavior of an asymmetric Ising model with two- and three-body interactions on a triangular lattice, in the presence of an external field. We use a two-dimensional Wang-Landau sampling method to determine the density of states for this model. An accurate density of states allowed us to map out the phase diagram accurately and observe a clear divergence of the curvature of the spectator phase boundary and of the derivative of the magnetization coexistence diameter near the critical endpoint, in agreement with previous theoretical predictions.
The ``Asymmetric-lift'' Model of Saturn's Magnetosphere Revisited: Observations Through the Equinox
NASA Astrophysics Data System (ADS)
Khurana, K. K.; Dougherty, M. K.; Russell, C. T.
2010-12-01
Magnetic field and particle observations from Saturn’s magnetosphere show that a rotating partial ring current exists between the radial distance of 8 and 13 RS. Khurana et al. (2009) showed that this rotating partial ring current has profound effects on the structure of the magnetosphere. In the outer magnetosphere, the partial ring current imposes a sinusoidal variation of the magnetic field in the lobe region. The resulting asymmetric distribution of magnetic flux in Saturn’s magnetosphere leads to an asymmetric lift of the magnetosphere by the solar wind which tilts the planet’s current sheet even when the internal field is completely axisymmetric. The current sheet tilt (in the rotating frame) generates out-of-phase periodicities in which the particle fluxes and the magnetic field strength are anti-correlated. The original model examined Cassini data from the period of 2004-2006, when the solar elevation angle was > 14 degrees. The model has specific predictions for the state of the magnetosphere during equinox. The model posits that during equinox when the solar elevation angle is close to zero, the solar wind would not be able to lift the current sheet out of Saturn’s equatorial plane and the current sheet tilt should disappear. Thus, during equinox no periodic current sheet crossings are expected. Now, by examining the magnetic field data through the equinox (July 2009), we show that this indeed is the case. We show that the current sheet tilt is governed largely by the solar elevation angle. We present a new quantitative model of the current sheet tilt which is consistent with the asymmetric-lift model of Saturn’s magnetosphere.
Feng, Yuan; Lee, Chung-Hao; Sun, Lining; Ji, Songbai; Zhao, Xuefeng
2017-01-01
Characterizing the mechanical properties of white matter is important to understand and model brain development and injury. With embedded aligned axonal fibers, white matter is typically modeled as a transversely isotropic material. However, most studies characterize the white matter tissue using models with a single anisotropic invariant or in a small-strain regime. In this study, we combined a single experimental procedure - asymmetric indentation - with inverse finite element (FE) modeling to estimate the nearly incompressible transversely isotropic material parameters of white matter. A minimal form comprising three parameters was employed to simulate indentation responses in the large-strain regime. The parameters were estimated using a global optimization procedure based on a genetic algorithm (GA). Experimental data from two indentation configurations of porcine white matter, parallel and perpendicular to the axonal fiber direction, were utilized to estimate model parameters. Results in this study confirmed a strong mechanical anisotropy of white matter in large strain. Further, our results suggested that both indentation configurations are needed to estimate the parameters with sufficient accuracy, and that the indenter-sample friction is important. Finally, we also showed that the estimated parameters were consistent with those previously obtained via a trial-and-error forward FE method in the small-strain regime. These findings are useful in modeling and parameterization of white matter, especially under large deformation, and demonstrate the potential of the proposed asymmetric indentation technique to characterize other soft biological tissues with transversely isotropic properties.
Behavior of Bilayer Leaflets in Asymmetric Model Membranes: Atomistic Simulation Studies
Tian, Jianhui; Nickels, Jonathan; Katsaras, John; ...
2016-04-27
Spatial organization within lipid bilayers is an important feature for a range of biological processes. Leaflet compositional asymmetry and lateral lipid organization are just two of the ways in which membrane structure appears to be more complex than initially postulated by the fluid mosaic model. This raises the question of how the phase behavior in one bilayer leaflet may affect the apposing leaflet and how one begins to construct asymmetric model systems to investigate these interleaflet interactions. In this paper, we report on all-atom molecular dynamics simulations (a total of 4.1 μs) of symmetric and asymmetric bilayer systems composed ofmore » liquid-ordered (Lo) or liquid-disordered (Ld) leaflets, based on the nanodomain-forming POPC/DSPC/cholesterol system. We begin by analyzing an asymmetric bilayer with leaflets derived from simulations of symmetric Lo and Ld bilayers. In this system, we observe that the properties of the Lo and Ld leaflets are similar to those of the Lo and Ld leaflets in corresponding symmetric systems. However, it is not obvious that mixing the equilibrium structures of their symmetric counterparts is the most appropriate way to construct asymmetric bilayers nor that these structures will manifest interleaflet couplings that lead to domain registry/antiregistry. We therefore constructed and simulated four additional asymmetric bilayer systems by systematically adding or removing lipids in the Ld leaflet to mimic potential density fluctuations. We find that the number of lipids in the Ld leaflet affects its own properties, as well as those of the apposing Lo leaflet. Collectively, the simulations reveal the presence of weak acyl chain interdigitation across bilayer leaflets, suggesting that interdigitation alone does not contribute significantly to the interleaflet coupling in nonphase-separated bilayers of this chemical composition. Finally, however, the properties of both leaflets appear to be sensitive to changes in in
The strain energy release approach for modeling cracks in rotors: A state of the art review
NASA Astrophysics Data System (ADS)
Papadopoulos, Chris A.
2008-05-01
The strain energy release rate (SERR) theory, combined with Linear Fracture Mechanics and Rotordynamics theories, has been widely used over the last three decades in order to calculate the compliance that causes a transverse surface crack in a rotating shaft. In this paper, the basic theory of this approach is presented, along with some extensions and limitations of its usage. The SERR theory is applied to a rotating crack and gives good results. The linear or nonlinear cracked rotor behavior depends on the mechanism of opening and closure of the crack during the shaft rotation. A brief history of the SERR theory is presented. In the 1970s, this theory met with rotordynamics as a result of research conducted on the causes of rotor failures in power industries. The main goal of this research was to give the engineer an early warning about the cracked situation of the rotor—in other words, to make the identification of the crack possible. Different methods of crack identification are presented here as well as those for multi-crack identification.
Finite Element Stability Analysis for Coupled Rotor and Support Systems
NASA Technical Reports Server (NTRS)
Hohenemser, K. H.; Yin, S. K.
1977-01-01
The effects of fuselage motions on stability and random response were analytically assessed. The feasibility of adequate perturbation models from non-linear trim conditions was studied by computer and hardware experiments. Rotor wake-blade interactions were assessed by using a 4-bladed rotor model with the capability of progressing and regressing blade pitch excitation (cyclic pitch stirring), by using a 4-bladed rotor model with hub tilt stirring, and by testing rotor models in sinusoidal up or side flow.
Analysis of rotor vibratory loads using higher harmonic pitch control
NASA Technical Reports Server (NTRS)
Quackenbush, Todd R.; Bliss, Donald B.; Boschitsch, Alexander H.; Wachspress, Daniel A.
1992-01-01
Experimental studies of isolated rotors in forward flight have indicated that higher harmonic pitch control can reduce rotor noise. These tests also show that such pitch inputs can generate substantial vibratory loads. The modification is summarized of the RotorCRAFT (Computation of Rotor Aerodynamics in Forward flighT) analysis of isolated rotors to study the vibratory loading generated by high frequency pitch inputs. The original RotorCRAFT code was developed for use in the computation of such loading, and uses a highly refined rotor wake model to facilitate this task. The extended version of RotorCRAFT incorporates a variety of new features including: arbitrary periodic root pitch control; computation of blade stresses and hub loads; improved modeling of near wake unsteady effects; and preliminary implementation of a coupled prediction of rotor airloads and noise. Correlation studies are carried out with existing blade stress and vibratory hub load data to assess the performance of the extended code.
NASA Technical Reports Server (NTRS)
Callahan, Cynthia B.; Bassett, Duane E.
1988-01-01
A model of the AH-64A helicopter was generated in a Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics (CAMRAD) in an effort to validate its analytical capabilities for modeling a current advanced Army helicopter. The initial phase of the effort involved the generation of CAMRAD input files necessary for the complete aerodynamic, structural, and dynamic definition of the production AH-64A helicopter. The input files were checked by making comparisons of CAMRAD full helicopter trim and main rotor blade natural frequency predictions with those of full helicopter trim program, Blade Element Trim (BETRIM), and dynamic analysis code, Dynamic Analysis Research Tool (DART), respectively. The main thrust concerned the application of the AH-64A CAMRAD model thus developed and verified for main rotor blade structural loads predictions and comparison with DART analytical results. The investigation provided insight not only into the usefulness of CAMRAD for the AH-64A performance and dynamics prediction, but also into the limitations of the program for modeling advanced rotor and fuselage systems. The model development effort is discussed, the results of the CAMRAD correlation studies presented, and some general conclusions are offered on the applicability of CAMRAD for rotor aeroelastic loads prediction for current and future rotorcraft configurations.
Pickup, B.A.; Thomson, S.L.
2012-01-01
The influence of asymmetric vocal fold stiffness on voice production was evaluated using life-sized, self-oscillating vocal fold models with an idealized geometry based on the human vocal folds. The models were fabricated using flexible, materially-linear silicone compounds with Young’s modulus values comparable to that of vocal fold tissue. The models included a two-layer design to simulate the vocal fold layered structure. The respective Young’s moduli of elasticity of the “left” and “right” vocal fold models were varied to create asymmetric conditions. High-speed videokymography was used to measure maximum vocal fold excursion, vibration frequency, and left-right phase shift, all of which were significantly influenced by asymmetry. Onset pressure, a measure of vocal effort, increased with asymmetry. Particle image velocimetry (PIV) analysis showed significantly greater skewing of the glottal jet in the direction of the stiffer vocal fold model. Potential applications to various clinical conditions are mentioned, and suggestions for future related studies are presented. PMID:19664777
NASA Technical Reports Server (NTRS)
Leighton, K. P.; Harris, W. L.
1984-01-01
An investigation of blade slap due to blade vortex interaction (BVI) has been conducted. This investigation consisted of an examination of BVI blade slap for two, three, and four-bladed model rotors at tip Mach numbers ranging from 0.20 to 0.50. Blade slap contours have been obtained for each configuration tested. Differences in blade slap contours, peak sound pressure level, and directivity for each configuration tested are noted. Additional fundamental differences, such as multiple interaction BVI, are observed and occur for only specific rotor blade configurations. The effect of increasing the Mach number on the BVI blade slap for various rotor blade combinations has been quantified. A peak blade slap Mach number scaling law is proposed. Comparison of measured BVI blade slap with theory is made.
NASA Technical Reports Server (NTRS)
Leighton, K. P.; Harris, W. L.
1984-01-01
An investigation of blade slap due to blade vortex interaction (BVI) has been conducted. This investigation consisted of an examination of BVI blade slap for two, three, and four-bladed model rotors at tip Mach numbers ranging from 0.20 to 0.50. Blade slap contours have been obtained for each configuration tested. Differences in blade slap contours, peak sound pressure level, and directivity for each configuration tested are noted. Additional fundamental differences, such as multiple interaction BVI, are observed and occur for only specific rotor blade configurations. The effect of increasing the Mach number on the BVI blade slap for various rotor blade combinations has been quantified. A peak blade slap Mach number scaling law is proposed. Comparison of measured BVI blade slap with theory is made.
Aeroelastic considerations for torsionally soft rotors
NASA Technical Reports Server (NTRS)
Mantay, W. R.; Yeager, W. T., Jr.
1986-01-01
A research study was initiated to systematically determine the impact of selected blade tip geometric parameters on conformable rotor performance and loads characteristics. The model articulated rotors included baseline and torsionally soft blades with interchangeable tips. Seven blade tip designs were evaluated on the baseline rotor and six tip designs were tested on the torsionally soft blades. The designs incorporated a systemmatic variation in geometric parameters including sweep, taper, and anhedral. The rotors were evaluated in the NASA Langley Transonic Dynamics Tunnel at several advance ratios, lift and propulsive force values, and tip Mach numbers. A track sensitivity study was also conducted at several advance ratios for both rotors. Based on the test results, tip parameter variations generated significant rotor performance and loads differences for both baseline and torsionally soft blades. Azimuthal variation of elastic twist generated by variations in the tip parameters strongly correlated with rotor performance and loads, but the magnitude of advancing blade elastic twist did not. In addition, fixed system vibratory loads and rotor track for potential conformable rotor candidates appears very sensitive to parametric rotor changes.
NASA Technical Reports Server (NTRS)
Bielawa, Richard L.
1988-01-01
In response to a systematic methodology assessment program directed to the aeroelastic stability of hingeless helicopter rotor blades, improved basic aeroelastic reformulations and new formulations relating to structural sweep were achieved. Correlational results are presented showing the substantially improved performance of the G400 aeroelastic analysis incorporating these new formulations. The formulations pertain partly to sundry solutions to classic problem areas, relating to dynamic inflow with vortex-ring state operation and basic blade kinematics, but mostly to improved physical modeling of elastic axis offset (structural sweep) in the presence of nonlinear structural twist. Specific issues addressed are an alternate modeling of the delta EI torsional excitation due to compound bending using a force integration approach, and the detailed kinematic representation of an elastically deflected point mass of a beam with both structural sweep and nonlinear twist.
Study of the Standard k-ɛ Model for Tip Leakage Flow in an Axial Compressor Rotor
NASA Astrophysics Data System (ADS)
Gao, Yanfei; Liu, Yangwei; Zhong, Luyang; Hou, Jiexuan; Lu, Lipeng
2016-12-01
The standard k-ɛ model (SKE) and the Reynolds stress model (RSM) are employed to predict the tip leakage flow (TLF) in a low-speed large-scale axial compressor rotor. Then, a new research method is adopted to "freeze" the turbulent kinetic energy and dissipation rate of the flow field derived from the RSM, and obtain the turbulent viscosity using the Boussinesq hypothesis. The Reynolds stresses and mean flow field computed on the basis of the frozen viscosity are compared with the results of the SKE and the RSM. The flow field in the tip region based on the frozen viscosity is more similar to the results of the RSM than those of the SKE, although certain differences can be observed. This finding indicates that the non-equilibrium turbulence transport nature plays an important role in predicting the TLF, as well as the turbulence anisotropy.
Wang, Hailong; Ho, Derek Y H; Lawton, Wayne; Wang, Jiao; Gong, Jiangbin
2013-11-01
Recent studies have established that, in addition to the well-known kicked-Harper model (KHM), an on-resonance double-kicked rotor (ORDKR) model also has Hofstadter's butterfly Floquet spectrum, with strong resemblance to the standard Hofstadter spectrum that is a paradigm in studies of the integer quantum Hall effect. Earlier it was shown that the quasienergy spectra of these two dynamical models (i) can exactly overlap with each other if an effective Planck constant takes irrational multiples of 2π and (ii) will be different if the same parameter takes rational multiples of 2π. This work makes detailed comparisons between these two models, with an effective Planck constant given by 2πM/N, where M and N are coprime and odd integers. It is found that the ORDKR spectrum (with two periodic kicking sequences having the same kick strength) has one flat band and N-1 nonflat bands with the largest bandwidth decaying in a power law as ~K(N+2), where K is a kick strength parameter. The existence of a flat band is strictly proven and the power-law scaling, numerically checked for a number of cases, is also analytically proven for a three-band case. By contrast, the KHM does not have any flat band and its bandwidths scale linearly with K. This is shown to result in dramatic differences in dynamical behavior, such as transient (but extremely long) dynamical localization in ORDKR, which is absent in the KHM. Finally, we show that despite these differences, there exist simple extensions of the KHM and ORDKR model (upon introducing an additional periodic phase parameter) such that the resulting extended KHM and ORDKR model are actually topologically equivalent, i.e., they yield exactly the same Floquet-band Chern numbers and display topological phase transitions at the same kick strengths. A theoretical derivation of this topological equivalence is provided. These results are also of interest to our current understanding of quantum-classical correspondence considering that
NASA Astrophysics Data System (ADS)
Wang, Hailong; Ho, Derek Y. H.; Lawton, Wayne; Wang, Jiao; Gong, Jiangbin
2013-11-01
Recent studies have established that, in addition to the well-known kicked-Harper model (KHM), an on-resonance double-kicked rotor (ORDKR) model also has Hofstadter's butterfly Floquet spectrum, with strong resemblance to the standard Hofstadter spectrum that is a paradigm in studies of the integer quantum Hall effect. Earlier it was shown that the quasienergy spectra of these two dynamical models (i) can exactly overlap with each other if an effective Planck constant takes irrational multiples of 2π and (ii) will be different if the same parameter takes rational multiples of 2π. This work makes detailed comparisons between these two models, with an effective Planck constant given by 2πM/N, where M and N are coprime and odd integers. It is found that the ORDKR spectrum (with two periodic kicking sequences having the same kick strength) has one flat band and N-1 nonflat bands with the largest bandwidth decaying in a power law as ˜KN+2, where K is a kick strength parameter. The existence of a flat band is strictly proven and the power-law scaling, numerically checked for a number of cases, is also analytically proven for a three-band case. By contrast, the KHM does not have any flat band and its bandwidths scale linearly with K. This is shown to result in dramatic differences in dynamical behavior, such as transient (but extremely long) dynamical localization in ORDKR, which is absent in the KHM. Finally, we show that despite these differences, there exist simple extensions of the KHM and ORDKR model (upon introducing an additional periodic phase parameter) such that the resulting extended KHM and ORDKR model are actually topologically equivalent, i.e., they yield exactly the same Floquet-band Chern numbers and display topological phase transitions at the same kick strengths. A theoretical derivation of this topological equivalence is provided. These results are also of interest to our current understanding of quantum-classical correspondence considering that the
Kajala, Kaisa; Ramakrishna, Priya; Fisher, Adam; C. Bergmann, Dominique; De Smet, Ive; Sozzani, Rosangela; Weijers, Dolf; Brady, Siobhan M.
2014-01-01
Background Asymmetric cell divisions are formative divisions that generate daughter cells of distinct identity. These divisions are coordinated by either extrinsic (‘niche-controlled’) or intrinsic regulatory mechanisms and are fundamentally important in plant development. Scope This review describes how asymmetric cell divisions are regulated during development and in different cell types in both the root and the shoot of plants. It further highlights ways in which omics and modelling approaches have been used to elucidate these regulatory mechanisms. For example, the regulation of embryonic asymmetric divisions is described, including the first divisions of the zygote, formative vascular divisions and divisions that give rise to the root stem cell niche. Asymmetric divisions of the root cortex endodermis initial, pericycle cells that give rise to the lateral root primordium, procambium, cambium and stomatal cells are also discussed. Finally, a perspective is provided regarding the role of other hormones or regulatory molecules in asymmetric divisions, the presence of segregated determinants and the usefulness of modelling approaches in understanding network dynamics within these very special cells. Conclusions Asymmetric cell divisions define plant development. High-throughput genomic and modelling approaches can elucidate their regulation, which in turn could enable the engineering of plant traits such as stomatal density, lateral root development and wood formation. PMID:24825294
Etchemendy, Pablo E; Eguia, Manuel C; Mesz, Bruno
2014-03-01
In this work, the overall perceived pitch (principal pitch) of pure tones modulated in frequency with an asymmetric waveform is studied. The dependence of the principal pitch on the degree of asymmetric modulation was obtained from a psychophysical experiment. The modulation waveform consisted of a flat portion of constant frequency and two linear segments forming a peak. Consistent with previous results, significant pitch shifts with respect to the time-averaged geometric mean were observed. The direction of the shifts was always toward the flat portion of the modulation. The results from the psychophysical experiment, along with those obtained from previously reported studies, were compared with the predictions of six models of pitch perception proposed in the literature. Even though no single model was able to predict accurately the perceived pitch for all experiments, there were two models that give robust predictions that are within the range of acceptable tuning of modulated tones for almost all the cases. Both models point to the existence of an underlying "stability sensitive" mechanism for the computation of pitch that gives more weight to the portion of the stimuli where the frequency is changing more slowly.
Development of Virtual Blade Model for Modelling Helicopter Rotor Downwash in OpenFOAM
2013-12-01
flow of non-Newtonian fluids in a single rotating frame pisoFoam Transient solver for incompressible flow based on PISO algorithm Compressible Flow...velocity p a reference static pressure based on the freestream condition C a coefficient in the k turbulence models HD equivalent hydraulic...distributor1. Furthermore, at Reference 1 DSTO developed in- house a separate VBM code, as an add-on to ANSYS Fluent based on Reference 2. Since early 2010
Prediction of the Aero-Acoustic Performance of Open Rotors
NASA Technical Reports Server (NTRS)
Van Zante, Dale E.; Envia, Edmane
2014-01-01
The rising cost of jet fuel has renewed interest in contrarotating open rotor propulsion systems. Contemporary design methods offer the potential to maintain the inherently high aerodynamic efficiency of open rotors while greatly reducing their noise output, something that was not feasible in the 1980's designs. The primary source mechanisms of open rotor noise generation are thought to be the front rotor wake and tip vortex interacting with the aft rotor. In this paper, advanced measurement techniques and high-fidelity prediction tools are used to gain insight into the relative importance of the contributions to the open rotor noise signature of the front rotor wake and rotor tip vortex. The measurements include three-dimensional particle image velocimetry of the intra-rotor flowfield and the acoustic field of a model-scale open rotor. The predictions provide the unsteady flowfield and the associated acoustic field. The results suggest that while the front rotor tip vortex can have a significant influence on the blade passing tone noise produced by the aft rotor, the front rotor wake plays the decisive role in the generation of the interaction noise produced as a result of the unsteady aerodynamic interaction of the two rotors. At operating conditions typical of takeoff and landing operations, the interaction noise level is easily on par with that generated by the individual rotors, and in some cases is even higher. This suggests that a comprehensive approach to reducing open rotor noise should include techniques for mitigating the wake of the front rotor as well as eliminating the interaction of the front rotor tip vortex with the aft rotor blade tip.
Phase separation and pairing regimes in the one-dimensional asymmetric Hubbard model
Barbiero, L.; Casadei, M.; Dalmonte, M.; Ercolessi, E.; Ortolani, F.
2010-06-01
We address some open questions regarding the phase diagram of the one-dimensional Hubbard model with asymmetric hopping coefficients and balanced species. In the attractive regime we present a numerical study of the passage from on-site pairing dominant correlations at small asymmetries to charge-density waves in the region with markedly different hopping coefficients. In the repulsive regime we exploit two analytical treatments in the strong- and weak-coupling regimes in order to locate the onset of phase separation at small and large asymmetries, respectively.
NASA Astrophysics Data System (ADS)
Pal, Debdatta; Mitra, Subrata Kumar
2016-10-01
This study used a quantile autoregressive distributed lag (QARDL) model to capture asymmetric impact of rainfall on food production in India. It was found that the coefficient corresponding to the rainfall in the QARDL increased till the 75th quantile and started decreasing thereafter, though it remained in the positive territory. Another interesting finding is that at the 90th quantile and above the coefficients of rainfall though remained positive was not statistically significant and therefore, the benefit of high rainfall on crop production was not conclusive. However, the impact of other determinants, such as fertilizer and pesticide consumption, is quite uniform over the whole range of the distribution of food grain production.
Parametric tip effects for conformable rotor applications
NASA Technical Reports Server (NTRS)
Mantay, W. R.; Yeager, W. T., Jr.
1983-01-01
A research study was initiated to systematically determine the impact of selected blade tip geometric parameters on aeroelasticity conformable rotor performance and loads characteristics. The model articulated rotors included baseline and torsionally soft blades with interchangeable tips. Seven blade tip designs were evaluated on the baseline rotor and three tip designs were tested on the torsionally soft blades. The designs incorporated a systematic variation in three geometric parameters: sweep, taper, and anhedral. The rotors were evaluated in the NASA Langley Transonic Dynamics Tunnel at several advance ratios, lift and propulsive force values, and tip Mach numbers. Based on the test results, tip parameter variations generated significant rotor performance and loads difference for both baseline and torsionally soft blades. Azimuthal variation of elastic twist generated by the tip parameters strongly correlated with rotor performance and loads, but the magnitude of advancing blade elastic twist did not correlate.
Self-organized criticality in asymmetric exclusion model with noise for freeway traffic
NASA Astrophysics Data System (ADS)
Nagatani, Takashi
1995-02-01
The one-dimensional asymmetric simple-exclusion model with open boundaries for parallel update is extended to take into account temporary stopping of particles. The model presents the traffic flow on a highway with temporary deceleration of cars. Introducing temporary stopping into the asymmetric simple-exclusion model drives the system asymptotically into a steady state exhibiting a self-organized criticality. In the self-organized critical state, start-stop waves (or traffic jams) appear with various sizes (or lifetimes). The typical interval < s>between consecutive jams scales as < s> ≃ Lv with v = 0.51 ± 0.05 where L is the system size. It is shown that the cumulative jam-interval distribution Ns( L) satisfies the finite-size scaling form ( Ns( L) ≃ L- vf( s/ Lv). Also, the typical lifetime
The asymmetric median tree - a new model for building consensus trees
Phillips, C.; Warnow, T.J. |
1996-12-31
Inferring the consensus of a set of different evolutionary trees for a given species set is a well-studied problems, for which several different models have been proposed. In this paper, the authors propose a new optimization problem for consensus tree construction, which they call the asymmetric median tree, or AMT. Their main theoretical result is the equivalence between the asymmetric median tree problem on {kappa} trees and the maximum independent set (MIS) problem on {kappa}-colored graphs. Although the problem is NP-hard for three or more trees, the authors have polynomial time algorithms to construct the AMT for two trees and an approximation algorithm for three or more trees. They define a measure of phylogenetic resolution and show that their algorithms (both exact and approximate) produce consensus trees that on every input are at least as resolved as the standard models (strict consensus and majority tree) in use. Finally, they show that the AMT combines desirable features of many of the standard consensus tree models in use. 23 refs.
Modified particle-rotor model and low-lying rotational bands in odd-A triaxial nuclei
NASA Astrophysics Data System (ADS)
Modi, Swati; Patial, M.; Arumugam, P.; Maglione, E.; Ferreira, L. S.
2017-09-01
The low-lying rotational bands of triaxially deformed nuclei 137Pr, 137Pm and 139Eu are studied with a modified particle-rotor model following the nonadiabatic quasiparticle approach. The matrix elements of the odd-A nucleus are obtained in terms of a coupling matrix and the rotational energies of the even-even core. The spectra of the cores 136Ce, 136Nd and 138Sm indicate a strong influence of triaxial deformation and vibrational degrees of freedom. These properties are appropriately carried forward to the calculations for the odd-A nucleus. We demonstrate that the ground and side bands of the odd-A nucleus and its core can be explained with the same set of deformation parameters ({β }2, γ). We argue that this method could be useful in studying the low-lying states in exotic nuclei also.
Anisotropy-resolving models for predicting separation in 3--D asymmetric diffusers
NASA Astrophysics Data System (ADS)
Jeyapaul, Elbert; Durbin, Paul
2011-11-01
All linear eddy-viscosity models are qualitatively incorrect in predicting separation in 3-D asymmetric diffusers. The failure to predict normal stress and shear stress anisotropy at high production-dissipation ratios is the cause. The Explicit algebraic Reynolds stress model (Wallin and Johansson, 2000) predicts the mean flow field in the diffuser accurately, but not the wall pressure and Reynolds stresses. Recalibrating the coefficients of the rapid part of pressure-strain model improves the wall pressure prediction. Including the convective, diffusive, streamline curvature effects on anisotropy has not been beneficial. The model has been tested using a family of diffusers having the same nominal streamwise pressure gradient, LES data is used as a reference. Professor
Epicardial rotors in panoramic optical maps of fibrillating swine ventricles.
Kay, Matthew W; Rogers, Jack M
2006-01-01
It has been proposed that VF waves emanate from stable periodic sources (often called "mother rotors"). Our objective was to determine if stable rotors are consistently present on the epicardial surface of hearts comparable in size to human hearts. Using new optical mapping technology, we imaged VF from nearly the entire ventricular surface of 6 isolated swine hearts. Using newly developed pattern analysis algorithms, we identified and tracked VF wavefronts and phase singularities (PS). We introduce the notion of a compound rotor in which the rotor's central PS can change and describe an algorithm for automatically identifying such patterns. This prevents rotor lifetimes from being inappropriately abbreviated by wavefront fragmentation and collision events near the PS. We found that stable epicardial rotors were not consistently present during VF: only 1 of 17 VF episodes contained a compound rotor that lasted for the entire mapped interval of 4s. However, shorter-lived rotors were common; 12.2+/-3.3 compound rotors with lifetime>200 ms were visible on the epicardium at any given instant. We conclude that epicardial mother rotors do not drive VF in this experimental model; if mother rotors do exist, they are intramural or septal. This paucity of persistent rotors suggests that individual rotors will eventually terminate by themselves and therefore the continual formation of new rotors is critical for VF maintenance.
Synthesis of rotor test data for real-time simulation
NASA Technical Reports Server (NTRS)
Mcveigh, M. A.
1979-01-01
A mathematical model of a hingeless tilting rotor is presented. The model was obtained by a systematic curve fit procedure applied to an extensive set of model scale wind tunnel data. The math model equations were used in a real time flight simulation model of a hingeless tilt rotor XV-15 to assess changes in flying qualities compared to those obtained using a previous rotor model. Extensive plots of the rotor derivatives are given. Discussions of attempts to apply multivariable linear regression technqiues to the data and the use of an analytical rotor representation are included.
NASA Technical Reports Server (NTRS)
Sree, Dave
2015-01-01
Near-field acoustic power level analysis of F31A31 open rotor model has been performed to determine its noise characteristics at simulated cruise flight conditions. The non-proprietary parts of the test data obtained from experiments in the 8x6 supersonic wind tunnel were provided by NASA-Glenn Research Center. The tone and broadband components of total noise have been separated from raw test data by using a new data analysis tool. Results in terms of sound pressure levels, acoustic power levels, and their variations with rotor speed, freestream Mach number, and input shaft power, with different blade-pitch setting angles at simulated cruise flight conditions, are presented and discussed. Empirical equations relating models acoustic power level and input shaft power have been developed. The near-field acoustic efficiency of the model at simulated cruise conditions is also determined. It is hoped that the results presented in this work will serve as a database for comparison and improvement of other open rotor blade designs and also for validating open rotor noise prediction codes.
Vansteenkiste, P; Van Neck, D; Van Speybroeck, V; Waroquier, M
2006-01-28
Large-amplitude motions, particularly internal rotations, are known to affect substantially thermodynamic functions and rate constants of reactions in which flexible molecules are involved. Up to now all methods for computing the partition functions of these motions rely on the Pitzer approximation of more than 50 years ago, in which the large-amplitude motion is treated in complete independence of the other (vibrational) degrees of freedom. In this paper an extended hindered-rotor model (EHR) is developed in which the vibrational modes, treated harmonically, are correctly separated from the large-amplitude motion and in which relaxation effects (the changes in the kinetic-energy matrix and potential curvature) are taken into account as one moves along the large-amplitude path. The model also relies on a specific coordinate system in which the Coriolis terms vanish at all times in the Hamiltonian. In this way an increased level of consistency between the various internal modes is achieved, as compared with the more usual hindered-rotor (HR) description. The method is illustrated by calculating the entropies and heat capacities on 1,3-butadiene and 1-butene (with, respectively, one and two internal rotors) and the rate constant for the addition reaction of a vinyl radical to ethene. We also discuss various variants of the one-dimensional hindered-rotor scheme existing in the literature and its relation with the EHR model. It is argued why in most cases the HR approach is already quite successful.
Agent-Based Model with Asymmetric Trading and Herding for Complex Financial Systems
Chen, Jun-Jie; Zheng, Bo; Tan, Lei
2013-01-01
Background For complex financial systems, the negative and positive return-volatility correlations, i.e., the so-called leverage and anti-leverage effects, are particularly important for the understanding of the price dynamics. However, the microscopic origination of the leverage and anti-leverage effects is still not understood, and how to produce these effects in agent-based modeling remains open. On the other hand, in constructing microscopic models, it is a promising conception to determine model parameters from empirical data rather than from statistical fitting of the results. Methods To study the microscopic origination of the return-volatility correlation in financial systems, we take into account the individual and collective behaviors of investors in real markets, and construct an agent-based model. The agents are linked with each other and trade in groups, and particularly, two novel microscopic mechanisms, i.e., investors’ asymmetric trading and herding in bull and bear markets, are introduced. Further, we propose effective methods to determine the key parameters in our model from historical market data. Results With the model parameters determined for six representative stock-market indices in the world, respectively, we obtain the corresponding leverage or anti-leverage effect from the simulation, and the effect is in agreement with the empirical one on amplitude and duration. At the same time, our model produces other features of the real markets, such as the fat-tail distribution of returns and the long-term correlation of volatilities. Conclusions We reveal that for the leverage and anti-leverage effects, both the investors’ asymmetric trading and herding are essential generation mechanisms. Among the six markets, however, the investors’ trading is approximately symmetric for the five markets which exhibit the leverage effect, thus contributing very little. These two microscopic mechanisms and the methods for the determination of the key
Agent-based model with asymmetric trading and herding for complex financial systems.
Chen, Jun-Jie; Zheng, Bo; Tan, Lei
2013-01-01
For complex financial systems, the negative and positive return-volatility correlations, i.e., the so-called leverage and anti-leverage effects, are particularly important for the understanding of the price dynamics. However, the microscopic origination of the leverage and anti-leverage effects is still not understood, and how to produce these effects in agent-based modeling remains open. On the other hand, in constructing microscopic models, it is a promising conception to determine model parameters from empirical data rather than from statistical fitting of the results. To study the microscopic origination of the return-volatility correlation in financial systems, we take into account the individual and collective behaviors of investors in real markets, and construct an agent-based model. The agents are linked with each other and trade in groups, and particularly, two novel microscopic mechanisms, i.e., investors' asymmetric trading and herding in bull and bear markets, are introduced. Further, we propose effective methods to determine the key parameters in our model from historical market data. With the model parameters determined for six representative stock-market indices in the world, respectively, we obtain the corresponding leverage or anti-leverage effect from the simulation, and the effect is in agreement with the empirical one on amplitude and duration. At the same time, our model produces other features of the real markets, such as the fat-tail distribution of returns and the long-term correlation of volatilities. We reveal that for the leverage and anti-leverage effects, both the investors' asymmetric trading and herding are essential generation mechanisms. Among the six markets, however, the investors' trading is approximately symmetric for the five markets which exhibit the leverage effect, thus contributing very little. These two microscopic mechanisms and the methods for the determination of the key parameters can be applied to other complex
Bardhan, Jaydeep P.; Knepley, Matthew G.
2014-10-07
We show that charge-sign-dependent asymmetric hydration can be modeled accurately using linear Poisson theory after replacing the standard electric-displacement boundary condition with a simple nonlinear boundary condition. Using a single multiplicative scaling factor to determine atomic radii from molecular dynamics Lennard-Jones parameters, the new model accurately reproduces MD free-energy calculations of hydration asymmetries for: (i) monatomic ions, (ii) titratable amino acids in both their protonated and unprotonated states, and (iii) the Mobley “bracelet” and “rod” test problems [D. L. Mobley, A. E. Barber II, C. J. Fennell, and K. A. Dill, “Charge asymmetries in hydration of polar solutes,” J. Phys. Chem. B 112, 2405–2414 (2008)]. Remarkably, the model also justifies the use of linear response expressions for charging free energies. Our boundary-element method implementation demonstrates the ease with which other continuum-electrostatic solvers can be extended to include asymmetry.
NASA Astrophysics Data System (ADS)
Seppäläinen, Timo; Krug, Joachim
1999-05-01
We consider a one-dimensional totally asymmetric exclusion model with quenched random jump rates associated with the particles, and an equivalent interface growth process on the square lattice. We obtain rigorous limit theorems for the shape of the interface, the motion of a tagged particle, and the macroscopic density profile on the hydrodynamic scale. The theorems are valid under almost every realization of the disordered rates. Under suitable conditions on the distribution of jump rates the model displays a disorder-dominated low-density phase where spatial inhomogeneities develop below the hydrodynamic resolution. The macroscopic signature of the phase transition is a density discontinuity at the front of the rarefaction wave moving out of an initial step-function profile. Numerical simulations of the density fluctuations ahead of the front suggest slow convergence to the predictions of a deterministic particle model on the real line, which contains only random velocities but no temporal noise.
Bardhan, Jaydeep P; Knepley, Matthew G
2014-10-07
We show that charge-sign-dependent asymmetric hydration can be modeled accurately using linear Poisson theory after replacing the standard electric-displacement boundary condition with a simple nonlinear boundary condition. Using a single multiplicative scaling factor to determine atomic radii from molecular dynamics Lennard-Jones parameters, the new model accurately reproduces MD free-energy calculations of hydration asymmetries for: (i) monatomic ions, (ii) titratable amino acids in both their protonated and unprotonated states, and (iii) the Mobley "bracelet" and "rod" test problems [D. L. Mobley, A. E. Barber II, C. J. Fennell, and K. A. Dill, "Charge asymmetries in hydration of polar solutes," J. Phys. Chem. B 112, 2405-2414 (2008)]. Remarkably, the model also justifies the use of linear response expressions for charging free energies. Our boundary-element method implementation demonstrates the ease with which other continuum-electrostatic solvers can be extended to include asymmetry.
NASA Astrophysics Data System (ADS)
Bardhan, Jaydeep P.; Knepley, Matthew G.
2014-10-01
We show that charge-sign-dependent asymmetric hydration can be modeled accurately using linear Poisson theory after replacing the standard electric-displacement boundary condition with a simple nonlinear boundary condition. Using a single multiplicative scaling factor to determine atomic radii from molecular dynamics Lennard-Jones parameters, the new model accurately reproduces MD free-energy calculations of hydration asymmetries for: (i) monatomic ions, (ii) titratable amino acids in both their protonated and unprotonated states, and (iii) the Mobley "bracelet" and "rod" test problems [D. L. Mobley, A. E. Barber II, C. J. Fennell, and K. A. Dill, "Charge asymmetries in hydration of polar solutes," J. Phys. Chem. B 112, 2405-2414 (2008)]. Remarkably, the model also justifies the use of linear response expressions for charging free energies. Our boundary-element method implementation demonstrates the ease with which other continuum-electrostatic solvers can be extended to include asymmetry.
Rectification of asymmetric surface vibrations with dry friction: An exactly solvable model
NASA Astrophysics Data System (ADS)
Baule, A.; Sollich, P.
2013-03-01
We consider a stochastic model for the directed motion of a solid object due to the rectification of asymmetric surface vibrations with Poissonian shot-noise statistics. The friction between the object and the surface is given by a piecewise-linear friction force. This models the combined effect of dynamic friction and singular dry friction. We derive an exact solution of the stationary Kolmogorov-Feller (KF) equation in the case of two-sided exponentially distributed amplitudes. The stationary density of the velocity exhibits singular features such as a discontinuity and a delta-peak singularity at zero velocity, and also contains contributions from nonintegrable solutions of the KF equation. The mean velocity in our model generally varies nonmonotonically as the strength of the dry friction is increased, indicating that transport improves for increased dissipation.
An asymmetric dimer in a periodic potential: a minimal model for friction of graphene flakes
NASA Astrophysics Data System (ADS)
Hens, Remco; Fasolino, Annalisa
2016-07-01
We discuss the friction and motion of a model of a dimer with asymmetric interactions with a substrate potential. Starting from the consideration that a rigid dimer with spacing equal to half of the period of the potential has exactly zero static friction like the infinite incommensurate Frenkel Kontorova model, we show how stick-slip behaviour and friction arise as a function of asymmetry. We argue that this model can yield a simple yet insightful description of the frictional behaviour of graphene flakes on graphite and of superlubricity. The results can also be of interest for diatomic molecules on surfaces. Supplementary material in the form of three mp4 files available from the Journal web page at http://dx.doi.org/10.1140/epjb/e2016-70273-5
NASA Astrophysics Data System (ADS)
Suarez Mullins, Astrid
Terrain-induced gravity waves and rotor circulations have been hypothesized to enhance the generation of submeso motions (i.e., nonstationary shear events with spatial and temporal scales greater than the turbulence scale and smaller than the meso-gamma scale) and to modulate low-level intermittency in the stable boundary layer (SBL). Intermittent turbulence, generated by submeso motions and/or the waves, can affect the atmospheric transport and dispersion of pollutants and hazardous materials. Thus, the study of these motions and the mechanisms through which they impact the weakly to very stable SBL is crucial for improving air quality modeling and hazard predictions. In this thesis, the effects of waves and rotor circulations on submeso and turbulence variability within the SBL is investigated over the moderate terrain of central Pennsylvania using special observations from a network deployed at Rock Springs, PA and high-resolution Weather Research and Forecasting (WRF) model forecasts. The investigation of waves and rotors over central PA is important because 1) the moderate topography of this region is common to most of the eastern US and thus the knowledge acquired from this study can be of significance to a large population, 2) there have been little evidence of complex wave structures and rotors reported for this region, and 3) little is known about the waves and rotors generated by smaller and more moderate topographies. Six case studies exhibiting an array of wave and rotor structures are analyzed. Observational evidence of the presence of complex wave structures, resembling nonstationary trapped gravity waves and downslope windstorms, and complex rotor circulations, resembling trapped and jump-type rotors, is presented. These motions and the mechanisms through which they modulate the SBL are further investigated using high-resolution WRF forecasts. First, the efficacy of the 0.444-km horizontal grid spacing WRF model to reproduce submeso and meso
NASA Astrophysics Data System (ADS)
Liu, Jing; Shao, Yimin
2017-06-01
Rotor bearing systems (RBSs) play a very valuable role for wind turbine gearboxes, aero-engines, high speed spindles, and other rotational machinery. An in-depth understanding of vibrations of the RBSs is very useful for condition monitoring and diagnosis applications of these machines. A new twelve-degree-of-freedom dynamic model for rigid RBSs with a localized defect (LOD) is proposed. This model can formulate the housing support stiffness, interfacial frictional moments including load dependent and load independent components, time-varying displacement excitation caused by a LOD, additional deformations at the sharp edges of the LOD, and lubricating oil film. The time-varying displacement model is determined by a half-sine function. A new method for calculating the additional deformations at the sharp edges of the LOD is analytical derived based on an elastic quarter-space method presented in the literature. The proposed dynamic model is utilized to analyze the influences of the housing support stiffness and LOD sizes on the vibration characteristics of the rigid RBS, which cannot be predicted by the previous dynamic models in the literature. The results show that the presented method can give a new dynamic modeling method for vibration formulation for a rigid RBS with and without the LOD on the races.
NASA Astrophysics Data System (ADS)
Liu, Shibing; Yang, Bingen
2015-08-01
Flexible multistage rotating systems that are supported or guided by long water-lubricated rubber bearings (WLRBs) have a variety of engineering applications. Vibration analysis of this type of machinery for performance and duality requires accurate modeling of WLRBs and related rotor-bearing assemblies. This work presents a new model of WLRBs, with attention given to the determination of bearing dynamic coefficients. Due to its large length-to-diameter ratio, a WLRB cannot be described by conventional pointwise bearing models with good fidelity. The bearing model proposed in this paper considers spatially distributed bearing forces. For the first time in the literature, the current study addresses the issue of mixed lubrication in the operation of WLRBs, which involves interactions of shaft vibration, elastic deformation of rubber material and fluid film pressure, and validates the WLRB model in experiments. Additionally, with the new bearing model, vibration analysis of WLRB-supported flexible multistage rotating systems is performed through use of a distributed transfer function method, which delivers accurate and closed-form analytical solutions of steady-state responses without discretization.
Meta-Boolean models of asymmetric division patterns in the C. elegans intestinal lineage
Pettersson, Sofia; Forchheimer, Robert; Larsson, Jan-Åke
2013-01-01
The intestine of Caenorhabditis elegans is derived from 20 cells that are organized into nine intestinal rings. During embryogenesis, three of the rings rotate approximately 90 degrees in a process known as intestinal twist. The underlying mechanisms for this morphological event are not fully known, but it has been demonstrated that both left-right and anterior-posterior asymmetry is required for intestinal twist to occur. We have recently presented a rule-based meta-Boolean tree model intended to describe complex lineages. In this report we apply this model to the E lineage of C. elegans, specifically targeting the asymmetric anterior-posterior division patterns within the lineage. The resulting model indicates that cells with the same factor concentration are located next to each other in the intestine regardless of lineage origin. In addition, the shift in factor concentrations coincides with the boundary for intestinal twist. When modeling lit-1 mutant data according to the same principle, the factor distributions in each cell are altered, yet the concurrence between the shift in concentration and intestinal twist remains. This pattern suggests that intestinal twist is controlled by a threshold mechanism. In the current paper we present the factor concentrations for all possible combinations of symmetric and asymmetric divisions in the E lineage and relate these to the potential threshold by studying existing data for wild-type and mutant embryos. Finally, we discuss how the resulting models can serve as a basis for experimental design in order to reveal the underlying mechanisms of intestinal twist. PMID:24058861
Tip Vortex and Wake Characteristics of a Counterrotating Open Rotor
NASA Technical Reports Server (NTRS)
VanZante, Dale E.; Wernet, Mark P.
2012-01-01
One of the primary noise sources for Open Rotor systems is the interaction of the forward rotor tip vortex and blade wake with the aft rotor. NASA has collaborated with General Electric on the testing of a new generation of low noise, counterrotating Open Rotor systems. Three-dimensional particle image velocimetry measurements were acquired in the intra-rotor gap of the Historical Baseline blade set. The velocity measurements are of sufficient resolution to characterize the tip vortex size and trajectory as well as the rotor wake decay and turbulence character. The tip clearance vortex trajectory is compared to results from previously developed models. Forward rotor wake velocity profiles are shown. Results are presented in a form as to assist numerical modeling of Open Rotor system aerodynamics and acoustics.
Prediction and reduction of rotor broadband noise
NASA Technical Reports Server (NTRS)
Hayden, R. E.; Aravamudan, K. S.
1978-01-01
Prediction techniques which can be or have been applied to subsonic rotors, and methods for designing helicopter rotors for reduced broadband noise generation are summarized. It is shown how detailed physical models of the noise source can be used to identify approaches to noise control.
Autocorrelations in the totally asymmetric simple exclusion process and Nagel-Schreckenberg model
NASA Astrophysics Data System (ADS)
de Gier, Jan; Garoni, Timothy M.; Zhou, Zongzheng
2010-08-01
We study via Monte Carlo simulation the dynamics of the Nagel-Schreckenberg model on a finite system of length L with open boundary conditions and parallel updates. We find numerically that in both the high and low density regimes the autocorrelation function of the system density behaves like 1-|t|/τ with a finite support [-τ,τ] . This is in contrast to the usual exponential decay typical of equilibrium systems. Furthermore, our results suggest that in fact τ=L/c , and in the special case of maximum velocity vmax=1 (corresponding to the totally asymmetric simple exclusion process) we can identify the exact dependence of c on the input, output and hopping rates. We also emphasize that the parameter τ corresponds to the integrated autocorrelation time, which plays a fundamental role in quantifying the statistical errors in Monte Carlo simulations of these models.
The one-dimensional asymmetric Hubbard model at partial band filling
NASA Astrophysics Data System (ADS)
Silva-Valencia, J.; Franco, R.; Figueira, M. S.
2007-09-01
We study the one-dimensional asymmetric Hubbard model (AHM) through the White's density matrix renormalization group technique at the density n=0.8. The AHM describes a correlated system where the hopping of electrons depend on their spin. The spin structure factor and the charge structure factor of heavy electrons were calculated as a function of the hopping and the repulsive on-site interaction. We found that the ground state displays phase separation for strong coupling, and a non-universal critical hopping separates the states of density wave and the phase separation. This outcome generalizes the result found one in the Falicov-Kimball model, which is a particular case of the AHM.
A new mathematical model for the equation of state of an asymmetric infinite nuclear matter
Zoghi-Foumani, N. Shojaei, M. R.
2016-04-21
In this paper, the average energy variation with respect to the density of a system of nucleons is studied. A new formula is presented for the nuclear equation of state. This formula is related to an infinite system of protons and neutrons with relatively small thermal excitations. It is shown that the proposed formulation for the nuclear equation of state reproduces the results obtained in the Skyrme-Hartree-Fock (SHF) and Relativistic Mean-Field (RMF) models of nuclear matter. It should be realized that the consistency of the obtained results for nuclear matter with the predictions of well-known SHF and RMF models for symmetric and asymmetric system of nucleons indicates the reliability of this formulation for different types of nuclear matter in large scales such as neutron stars.
NASA Astrophysics Data System (ADS)
Golinelli, Olivier; Mallick, Kirone
2006-10-01
The asymmetric simple exclusion process (ASEP) plays the role of a paradigm in non-equilibrium statistical mechanics. We review exact results for the ASEP obtained by the Bethe ansatz and put emphasis on the algebraic properties of this model. The Bethe equations for the eigenvalues of the Markov matrix of the ASEP are derived from the algebraic Bethe ansatz. Using these equations we explain how to calculate the spectral gap of the model and how global spectral properties such as the existence of multiplets can be predicted. An extension of the Bethe ansatz leads to an analytic expression for the large deviation function of the current in the ASEP that satisfies the Gallavotti-Cohen relation. Finally, we describe some variants of the ASEP that are also solvable by the Bethe ansatz.
NASA Astrophysics Data System (ADS)
Valera, J.; Negredo, A. M.; Billen, M.
2008-12-01
Recent studies provide compelling evidence for an event of removal of lithospheric mantle in southern -and possibly central- Sierra Nevada (SN) mountains, California (Zandt et al., Nature, 431, 2004). A sequential history of foundering of the ultramafic root of the Sierra Nevada batholith, with a pronounced asymmetric flow, is proposed to explain a number of geophysical and geological observations, including a fast seismic velocity in the mantle located to the west of the SN crest, a gap in the Moho, recent subsidence and tilting of the Sierra Nevada, and a change in mineralogy of the xenolith population recorded at the surface. In the present study we focus on the quantitative evaluation of this conceptual model. We apply new thermo- mechanical algorithms, developed in MATLAB code, suitable to study the temporal evolution of laterally migrating lithospheric delamination. The motion equation, formulated in terms of the stream function, and the coupled thermal equation are solved applying finite difference techniques. Our physical modeling is shown to properly reproduce the first order features of the conceptual model for lithospheric delamination in the Sierra Nevada. We investigate the evolution of a dense ultramafic root, which brings about a Rayleigh-Taylor gravitational instability. Following our preliminary results, the presence of a fluid-weakened lithosphere, located just east of Sierra Nevada, is required to reproduce the asymmetric development of this instability, as previously proposed by Zandt et al. (2004). This weak rheology zone, which is modeled by means of a reduced viscosity, is shown to enable the ascent of asthenospheric material and westward propagation of delamination. Our predictions are also consistent with the previous inference of the V-shaped cone of crust being dragged down into the downwelling mantle (i.e., the Moho gap). Present results highlight that viscous drag is also likely responsible for present-day surface subsidence.
Halbach Magnetic Rotor Development
NASA Technical Reports Server (NTRS)
Gallo, Christopher A.
2008-01-01
The NASA John H. Glenn Research Center has a wealth of experience in Halbach array technology through the Fundamental Aeronautics Program. The goals of the program include improving aircraft efficiency, reliability, and safety. The concept of a Halbach magnetically levitated electric aircraft motor will help reduce harmful emissions, reduce the Nation s dependence on fossil fuels, increase efficiency and reliability, reduce maintenance and decrease operating noise levels. Experimental hardware systems were developed in the GRC Engineering Development Division to validate the basic principles described herein and the theoretical work that was performed. A number of Halbach Magnetic rotors have been developed and tested under this program. A separate test hardware setup was developed to characterize each of the rotors. A second hardware setup was developed to test the levitation characteristics of the rotors. Each system focused around a unique Halbach array rotor. Each rotor required original design and fabrication techniques. A 4 in. diameter rotor was developed to test the radial levitation effects for use as a magnetic bearing. To show scalability from the 4 in. rotor, a 1 in. rotor was developed to also test radial levitation effects. The next rotor to be developed was 20 in. in diameter again to show scalability from the 4 in. rotor. An axial rotor was developed to determine the force that could be generated to position the rotor axially while it is rotating. With both radial and axial magnetic bearings, the rotor would be completely suspended magnetically. The purpose of this report is to document the development of a series of Halbach magnetic rotors to be used in testing. The design, fabrication and assembly of the rotors will be discussed as well as the hardware developed to test the rotors.
A multisensor evaluation of the asymmetric convective model, version 2, in southeast Texas.
Kolling, Jenna S; Pleim, Jonathan E; Jeffries, Harvey E; Vizuete, William
2013-01-01
There currently exist a number of planetary boundary layer (PBL) schemes that can represent the effects of turbulence in daytime convective conditions, although these schemes remain a large source of uncertainty in meteorology and air quality model simulations. This study evaluates a recently developed combined local and nonlocal closure PBL scheme, the Asymmetric Convective Model, version 2 (ACM2), against PBL observations taken from radar wind profilers, a ground-based lidar, and multiple daytime radiosonde balloon launches. These observations were compared against predictions of PBLs from the Weather Research and Forecasting (WRF) model version 3.1 with the ACM2 PBL scheme option, and the Fifth-Generation Meteorological Model (MM5) version 3.7.3 with the Eta PBL scheme option that is currently being used to develop ozone control strategies in southeast Texas. MM5 and WRF predictions during the regulatory modeling episode were evaluated on their ability to predict the rise and fall of the PBL during daytime convective conditions across southeastern Texas. The MM5 predicted PBLs consistently underpredicted observations, and were also less than the WRF PBL predictions. The analysis reveals that the MM5 predicted a slower rising and shallower PBL not representative of the daytime urban boundary layer. Alternatively, the WRF model predicted a more accurate PBL evolution improving the root mean square error (RMSE), both temporally and spatially. The WRF model also more accurately predicted vertical profiles of temperature and moisture in the lowest 3 km of the atmosphere. Inspection of median surface temperature and moisture time-series plots revealed higher predicted surface temperatures in WRF and more surface moisture in MM5. These could not be attributed to surface heat fluxes, and thus the differences in performance of the WRF and MM5 models are likely due to the PBL schemes. An accurate depiction of the diurnal evolution of the planetary boundary layer (PBL) is
On Cup Anemometer Rotor Aerodynamics
Pindado, Santiago; Pérez, Javier; Avila-Sanchez, Sergio
2012-01-01
The influence of anemometer rotor shape parameters, such as the cups' front area or their center rotation radius on the anemometer's performance was analyzed. This analysis was based on calibrations performed on two different anemometers (one based on magnet system output signal, and the other one based on an opto-electronic system output signal), tested with 21 different rotors. The results were compared to the ones resulting from classical analytical models. The results clearly showed a linear dependency of both calibration constants, the slope and the offset, on the cups' center rotation radius, the influence of the front area of the cups also being observed. The analytical model of Kondo et al. was proved to be accurate if it is based on precise data related to the aerodynamic behavior of a rotor's cup. PMID:22778638
On cup anemometer rotor aerodynamics.
Pindado, Santiago; Pérez, Javier; Avila-Sanchez, Sergio
2012-01-01
The influence of anemometer rotor shape parameters, such as the cups' front area or their center rotation radius on the anemometer's performance was analyzed. This analysis was based on calibrations performed on two different anemometers (one based on magnet system output signal, and the other one based on an opto-electronic system output signal), tested with 21 different rotors. The results were compared to the ones resulting from classical analytical models. The results clearly showed a linear dependency of both calibration constants, the slope and the offset, on the cups' center rotation radius, the influence of the front area of the cups also being observed. The analytical model of Kondo et al. was proved to be accurate if it is based on precise data related to the aerodynamic behavior of a rotor's cup.
NASA Astrophysics Data System (ADS)
Yamamoto, Shu; Yamaguchi, Tomonobu; Hirahara, Hideaki; Ara, Takahiro
This paper presents asymmetric circuit models and an inductance parameter measurement method for Permanent Magnet Linear Synchronous Motors (PMLSMs). The reason why the tested PMLSM with surface permanent magnet structure exhibits both asymmetry and salient pole natures is investigated. Asymmetric circuit models considering the saliency and inductance harmonic effects are discussed for PMLSM fed by three-phase three-wire power source systems. All fundamental and harmonic inductance parameters are easily determined by a standstill test using a single-phase commercial source. Experimental and simulation results on a single-sided PMLSM with a 3-phase, 4-pole and 14-slot mover demonstrate the validity of the proposed method.
Nandy, Lucy; Dutcher, Cari S
2017-08-04
Adsorption isotherm-based statistical thermodynamic models can be used to determine solute concentration and solute and solvent activities in aqueous solutions. Recently, the number of adjustable parameters in the isotherm model of Dutcher et al. J. Phys. Chem. A/C 2011, 2012, 2013 were reduced for neutral solutes as well as symmetric 1:1 electrolytes by using a Coulombic model to describe the solute - solvent energy interactions (Ohm et al. J. Phys. Chem. A 2015, Nandy et al. J. Phys. Chem. A 2016). Here, the Coulombic treatment for symmetric electrolytes is extended to establish improved isotherm model equations for asymmetric 1-2 and 1-3 electrolyte systems. The Coulombic model developed here results in prediction of activities and other thermodynamic properties in multicomponent systems containing ions of arbitrary charge. The model is found to accurately calculate osmotic coefficient over the entire solute concentration range with two model parameters, related to intermolecular solute-solute and solute-solvent spacing. The inorganic salts and acids treated here are generally considered to be fully dissociated. However, there are certain weak acids that do not dissociate completely, such as the bisulfate ion. In this work, partial dissociation of the bisulfate ion from sulfuric acid is treated as a mixture, with an additional model parameter which accounts for dissociation ratio of the dissociated ions to non-dissociated ions.
Internal rotor friction instability
NASA Technical Reports Server (NTRS)
Walton, J.; Artiles, A.; Lund, J.; Dill, J.; Zorzi, E.
1990-01-01
The analytical developments and experimental investigations performed in assessing the effect of internal friction on rotor systems dynamic performance are documented. Analytical component models for axial splines, Curvic splines, and interference fit joints commonly found in modern high speed turbomachinery were developed. Rotor systems operating above a bending critical speed were shown to exhibit unstable subsynchronous vibrations at the first natural frequency. The effect of speed, bearing stiffness, joint stiffness, external damping, torque, and coefficient of friction, was evaluated. Testing included material coefficient of friction evaluations, component joint quantity and form of damping determinations, and rotordynamic stability assessments. Under conditions similar to those in the SSME turbopumps, material interfaces experienced a coefficient of friction of approx. 0.2 for lubricated and 0.8 for unlubricated conditions. The damping observed in the component joints displayed nearly linear behavior with increasing amplitude. Thus, the measured damping, as a function of amplitude, is not represented by either linear or Coulomb friction damper models. Rotordynamic testing of an axial spline joint under 5000 in.-lb of static torque, demonstrated the presence of an extremely severe instability when the rotor was operated above its first flexible natural frequency. The presence of this instability was predicted by nonlinear rotordynamic time-transient analysis using the nonlinear component model developed under this program. Corresponding rotordynamic testing of a shaft with an interference fit joint demonstrated the presence of subsynchronous vibrations at the first natural frequency. While subsynchronous vibrations were observed, they were bounded and significantly lower in amplitude than the synchronous vibrations.
Preliminary simulation of an advanced, hingless rotor XV-15 tilt-rotor aircraft
NASA Technical Reports Server (NTRS)
Mcveigh, M. A.
1976-01-01
The feasibility of the tilt-rotor concept was verified through investigation of the performance, stability and handling qualities of the XV-15 tilt rotor. The rotors were replaced by advanced-technology fiberglass/composite hingless rotors of larger diameter, combined with an advanced integrated fly-by-wire control system. A parametric simulation model of the HRXV-15 was developed, model was used to define acceptable preliminary ranges of primary and secondary control schedules as functions of the flight parameters, to evaluate performance, flying qualities and structural loads, and to have a Boeing-Vertol pilot conduct a simulated flight test evaluation of the aircraft.
NASA Technical Reports Server (NTRS)
Van Zante, Dale E.; Rizzi, Stephen A.
2016-01-01
The ERA project executed a comprehensive test program for Open Rotor aerodynamic and acoustic performance. System studies used the data to estimate the fuel burn savings and acoustic margin for an aircraft system with open rotor propulsion. The acoustic measurements were used to produce an auralization that compares the legacy blades to the current generation of open rotor designs.
Chao, Lin; Rang, Camilla Ulla; Proenca, Audrey Menegaz; Chao, Jasper Ubirajara
2016-01-01
Non-genetic phenotypic variation is common in biological organisms. The variation is potentially beneficial if the environment is changing. If the benefit is large, selection can favor the evolution of genetic assimilation, the process by which the expression of a trait is transferred from environmental to genetic control. Genetic assimilation is an important evolutionary transition, but it is poorly understood because the fitness costs and benefits of variation are often unknown. Here we show that the partitioning of damage by a mother bacterium to its two daughters can evolve through genetic assimilation. Bacterial phenotypes are also highly variable. Because gene-regulating elements can have low copy numbers, the variation is attributed to stochastic sampling. Extant Escherichia coli partition asymmetrically and deterministically more damage to the old daughter, the one receiving the mother's old pole. By modeling in silico damage partitioning in a population, we show that deterministic asymmetry is advantageous because it increases fitness variance and hence the efficiency of natural selection. However, we find that symmetrical but stochastic partitioning can be similarly beneficial. To examine why bacteria evolved deterministic asymmetry, we modeled the effect of damage anchored to the mother's old pole. While anchored damage strengthens selection for asymmetry by creating additional fitness variance, it has the opposite effect on symmetry. The difference results because anchored damage reinforces the polarization of partitioning in asymmetric bacteria. In symmetric bacteria, it dilutes the polarization. Thus, stochasticity alone may have protected early bacteria from damage, but deterministic asymmetry has evolved to be equally important in extant bacteria. We estimate that 47% of damage partitioning is deterministic in E. coli. We suggest that the evolution of deterministic asymmetry from stochasticity offers an example of Waddington's genetic assimilation
Chao, Lin; Rang, Camilla Ulla; Proenca, Audrey Menegaz; Chao, Jasper Ubirajara
2016-01-01
Non-genetic phenotypic variation is common in biological organisms. The variation is potentially beneficial if the environment is changing. If the benefit is large, selection can favor the evolution of genetic assimilation, the process by which the expression of a trait is transferred from environmental to genetic control. Genetic assimilation is an important evolutionary transition, but it is poorly understood because the fitness costs and benefits of variation are often unknown. Here we show that the partitioning of damage by a mother bacterium to its two daughters can evolve through genetic assimilation. Bacterial phenotypes are also highly variable. Because gene-regulating elements can have low copy numbers, the variation is attributed to stochastic sampling. Extant Escherichia coli partition asymmetrically and deterministically more damage to the old daughter, the one receiving the mother’s old pole. By modeling in silico damage partitioning in a population, we show that deterministic asymmetry is advantageous because it increases fitness variance and hence the efficiency of natural selection. However, we find that symmetrical but stochastic partitioning can be similarly beneficial. To examine why bacteria evolved deterministic asymmetry, we modeled the effect of damage anchored to the mother’s old pole. While anchored damage strengthens selection for asymmetry by creating additional fitness variance, it has the opposite effect on symmetry. The difference results because anchored damage reinforces the polarization of partitioning in asymmetric bacteria. In symmetric bacteria, it dilutes the polarization. Thus, stochasticity alone may have protected early bacteria from damage, but deterministic asymmetry has evolved to be equally important in extant bacteria. We estimate that 47% of damage partitioning is deterministic in E. coli. We suggest that the evolution of deterministic asymmetry from stochasticity offers an example of Waddington’s genetic
NASA Astrophysics Data System (ADS)
Perez-Gussinye, M.; Ranero, C. R.
2010-12-01
Many continental margins of the world exhibit little evidence for magmatism during rifting, and are commonly known as ‘non-volcanic’ (NVMs). While such margins are commonly found world-wide, their tectonic evolution is still a matter of much debate. Here we use observations from pre-stack depth migrated data from the archetypical non-volcanic West Iberia-Newfoundland margins, to infer that if faulting becomes progressively sequential in time, the so-called “extension discrepancy” between horizontal extension by faulting and crustal thinning, and the asymmetric structure of conjugate margin pairs can be explained with simple Andersonian faulting. To demonstrate this we have developed a new kinematic reconstruction methodology, as commercially available balancing software require the decoupling of upper from lower crustal deformation, and cannot simulate the fault-controlled crustal-scale thinning interpreted from our data. Our balanced kinematic rift model accounts for the progressive focusing of faulting towards the basin centre, lower crustal embrittlement and the geometry of structures on seismic images. Our model differentiates two stages: A rift basin stage, where faulting is distributed across numerous disconnected, short faults with no dominant inward or outward sense of dip and a following rifted margin stage, where faulting acquires a unique sense of dip and becomes progressively sequential in time. Our model reproduces the tectonic evolution from moderately extended basins, such as the North Sea and Gulf of Suez, and Gulf of Corinth to hyper-extended, asymmetric margins like the West Iberia-Newfoundland conjugates without the need for large-scale detachment faults and/or differential extension of upper and lower crust.
NASA Astrophysics Data System (ADS)
Aksyonov, A. N.; Shabarov, A. B.
2009-12-01
A local damping of eddy viscosity depending on the ratio of the production of turbulent energy to turbulence dissipation rate is proposed at the computation of flows in transonic axial compressors. The results of the numerical modeling of flows in compressor NASA Rotor 37 are presented, and the computed distributions of the increase in the total temperature and total pressure are compared with experimental data for different rotation frequencies. An increase in the accuracy of modelling was obtained in all considered regimes.
Derikx, Loes C; Vis, Roeland; Meinders, Timo; Verdonschot, Nico; Tanck, Esther
2011-02-01
Although asymmetric yielding in bone is widely shown in experimental studies, previous case-specific non-linear finite element (FE) studies have mainly adopted material behaviour using the Von Mises yield criterion (VMYC), assuming equal bone strength in tension and compression. In this study, it was verified that asymmetric yielding in FE models can be captured using the Drucker-Prager yield criterion (DPYC), and can provide better results than simulations using the VMYC. A sensitivity analysis on parameters defining the DPYC (i.e. the degree of yield asymmetry and the yield stress settings) was performed, focusing on the effect on bone failure. In this study, the implementation of a larger degree of yield asymmetry improved the prediction of the fracture location; variations in the yield stress mainly affected the predicted failure force. We conclude that the implementation of asymmetric yielding in case-specific FE models improves the prediction of femoral bone strength.
NASA Astrophysics Data System (ADS)
Sommer, David; Erath, Byron D.; Zanartu, Matias; Peterson, Sean D.
2011-11-01
Voiced speech is produced by dynamic fluid-structure interactions in the larynx. Traditionally, reduced order models of speech have relied upon simplified inviscid flow solvers to prescribe the fluid loadings that drive vocal fold motion, neglecting viscous flow effects that occur naturally in voiced speech. Viscous phenomena, such as skewing of the intraglottal jet, have the most pronounced effect on voiced speech in cases of vocal fold paralysis where one vocal fold loses some, or all, muscular control. The impact of asymmetric intraglottal flow in pathological speech is captured in a reduced order two-mass model of speech by coupling a boundary-layer estimation of the asymmetric pressures with asymmetric tissue parameters that are representative of recurrent laryngeal nerve paralysis. Nonlinear analysis identifies the emergence of irregular and chaotic vocal fold dynamics at values representative of pathological speech conditions.
Fan, G.W. ); Nelson, H.D. ); Crouch, P.E.; Mignolet, M.P. )
1993-04-01
The complex mode and balanced realization methods are used separately to obtain reduced-order models for general linear asymmetric rotor systems. The methods are outlined and then applied to a typical rotor system represented by a 52 degree-or-freedom finite element model. The accuracy of the two methods is compared for this model and the complex model method is found to be more accurate than the balanced realization method for the desired frequency bandwidth and for models of the same reduced order. However, with some limitations, it is also shown that the balanced realization method can be applied to the reduced-order complex mode model to obtain further order reduction without loss of model accuracy. A Linear-Quadratic-Regulator-based least-squares output feedback control procedure is developed for the vibration control of rotor systems. This output feedback procedure eliminates the requirement of an observer for the use of an LQ regulator, and provides the advantage that the rotor vibration can be effectively controlled by monitoring only one single location along the rotor shaft while maintaining an acceptable performance. The procedures presented are quite general and may be applied to a large class of vibration problems including rotordynamics.
NASA Technical Reports Server (NTRS)
Chen, Robert T. N.
1992-01-01
This paper presents the results of an analytical study conducted to investigate airframe/engine interface dynamics, and the influence of rotor speed variations on the flight dynamics of the helicopter in hover, and to explore the potential benefits of using rotor states as additional feedback signals in the flight control system. The analytical investigation required the development of a parametric high-order helicopter hover model, which included heave/yaw body motion, the rotor speed degree of freedom, rotor blade motion in flapping and lead-lag, inflow dynamics, a drive train model with a flexible rotor shaft, and an engine/rpm governor. First, the model was used to gain insight into the engine/drive train/rotor system dynamics and to obtain an improved simple formula for easy estimation of the dominant first torsional mode, which is important in the dynamic integration of the engine and airframe system. Then, a linearized version of the model was used to investigate the effects of rotor speed variations and rotor state feedback on helicopter flight dynamics. Results show that, by including rotor speed variations, the effective vertical damping decreases significantly from that calculated with a constant speed assumption, thereby providing a better correlation with flight test data. Higher closed-loop bandwidths appear to be more readily achievable with rotor state feedback. The results also indicate that both aircraft and rotor flapping responses to gust disturbance are significantly attenuated when rotor state feedback is used.
Melin, Alexander M; Kisner, Roger A; Fugate, David L; Holcomb, David Eugene
2015-01-01
Embedding instrumentation and control Embedding instrumentation and control (I\\&C) at the component level in nuclear power plants can improve component performance, lifetime, and resilience by optimizing operation, reducing the constraints on physical design, and providing on-board prognostics and diagnostics. However, the extreme environments that many nuclear power plant components operate in makes embedding instrumentation and control at the component level difficult. Successfully utilizing embedded I\\&C requires developing a deep understanding of the system's dynamics and using that knowledge to overcome material and physical limitations imposed by the environment. In this paper, we will develop a coupled dynamic model of a high temperature (700 $^\\circ$C) canned rotor pump that incorporates rotordynamics, hydrodynamics, and active magnetic bearing dynamics. Then we will compare two control design methods, one that uses a simplified decoupled model of the system and another that utilizes the full coupled system model. It will be seen that utilizing all the available knowledge of the system dynamics in the controller design yield an order of magnitude improvement in the magnitude of the magnetic bearing response to disturbances at the same level of control effort, a large reduction in the settling time of the system, and a smoother control action.
Naderi, Peyman
2016-09-01
The inter-turn short fault for the Cage-Rotor-Induction-Machine (CRIM) is studied in this paper and its local saturation is taken into account. However, in order to observe the exact behavior of machine, the Magnetic-Equivalent-Circuit (MEC) and nonlinear B-H curve are proposed to provide an insight into the machine model and saturation effect respectively. The electrical machines are generally operated near to their saturation zone due to some design necessities. Hence, when the machine is exposed to a fault such as short circuit or eccentricities, it is operated within its saturation zone and thus, time and space harmonics are integrated and as a result, current and torque harmonics are generated which the phenomenon cannot be explored when saturation is dismissed. Nonetheless, inter-turn short circuit may lead to local saturation and this occurrence is studied in this paper using MEC model. In order to achieve the mentioned objectives, two and also four-pole machines are modeled as two samples and the machines performances are analyzed in healthy and faulty cases with and without saturation effect. A novel strategy is proposed to precisely detect inter-turn short circuit fault according to the stator׳s lines current signatures and the accuracy of the proposed method is verified by experimental results.
Interaction between rotors of a counter rotating propeller
NASA Technical Reports Server (NTRS)
Chung, Jin-Deog; Hough, Joseph; Nagel, Robert T.
1990-01-01
Thermal anemometer measurements were obtained from a stationary hot film probe mounted between the forward and aft rotors of a model CRP. Data were obtained at several locations between rotors. To establish the rotor-rotor interaction flow mechanism, a method of conditional sampling has been developed which effectively fixes the forward rotor position in time or space and permits averaging the mean wake at any fixed rotor angular location. By 'fixing' the position of the forward blades, one can track the disturbance of the forward rotor as the rear rotor moves by. The decay and spreading of the forward blade wakes and the upstream propagation of the rear blade disturbance are shown along with the interaction of the flow disturbances from the two sets of blades.
Exact diffusion constant of a one-dimensional asymmetric exclusion model with open boundaries
NASA Astrophysics Data System (ADS)
Derrida, B.; Evans, M. R.; Mallick, K.
1995-06-01
For the 1D fully asymmetric exclusion model with open boundary conditions, we calculate exactly the fluctuations of the current of particles. The method used is an extension of a matrix technique developed recently to describe the equatime steady-state properties for open boundary conditions and the diffusion constant for particles on a ring. We show how the fluctuations of the current are related to non-equal-time correlations. In the thermodynamic limit, our results agree with recent results of Ferrari and Fontes obtained by working directly in the infinite system. We also show that the fluctuations of the current become singular when the system undergoes a phase transition with discontinuities along the first-order transition line.
Charge Renormalization and Charge Oscillation in Asymmetric Primitive Model of Electrolytes
NASA Astrophysics Data System (ADS)
Ding, Mingnan; Liang, Yihao; Lu, Bing-Sui; Xing, Xiangjun
2016-12-01
Debye charging method is generalized to study the linear response properties of the asymmetric primitive model for electrolytes. Analytic results are obtained for the effective charge distributions of constituent ions inside the electrolyte, from which all static linear response properties of the system follow. It is found that, as the ion density increases, both the screening length and the dielectric constant receive substantial renormalization due to ionic correlations. Furthermore, the valence of larger ion is substantially renormalized upward by ionic correlations, while those of smaller ions remain approximately the same. For sufficiently high density, the system exhibits charge oscillations. The threshold ion density for charge oscillation is much lower than the corresponding values for symmetric electrolytes. Our results agree well with large-scale Monte Carlo simulations, and find good agreement in general, except for the case of small ion sizes (d = 4 Å) near the charge oscillation threshold.
Gravity perception and asymmetric growth in plants - A model derived from the grass pulvinus
NASA Technical Reports Server (NTRS)
Dayanandan, P.; Franklin, C. I.; Kaufman, P. B.
1982-01-01
It is pointed out that gravitropic responses in plants involve asymmetric growth. On the basis of the geometry of growth response in grass leaf sheath pulvinus, a general model is proposed for gravitropism in multicellular plant organs. The negative gravitropic response of a pulvinus is a result of cell elongation involving all but the uppermost region of a horizontally placed organ. Whereas the uppermost region does not grow, the lowermost region elongates maximally. The regions between elongate to intermediate extents. An expression is given relating the angle of curvature of the organ to the diameter and initial and final lengths of the organ. It is shown that the response of the individual cells can be expressed as inherent sensitivity to gravitational stimulus according to a particular equation.
Gravity perception and asymmetric growth in plants - A model derived from the grass pulvinus
NASA Technical Reports Server (NTRS)
Dayanandan, P.; Franklin, C. I.; Kaufman, P. B.
1982-01-01
It is pointed out that gravitropic responses in plants involve asymmetric growth. On the basis of the geometry of growth response in grass leaf sheath pulvinus, a general model is proposed for gravitropism in multicellular plant organs. The negative gravitropic response of a pulvinus is a result of cell elongation involving all but the uppermost region of a horizontally placed organ. Whereas the uppermost region does not grow, the lowermost region elongates maximally. The regions between elongate to intermediate extents. An expression is given relating the angle of curvature of the organ to the diameter and initial and final lengths of the organ. It is shown that the response of the individual cells can be expressed as inherent sensitivity to gravitational stimulus according to a particular equation.
Asymmetric Dispersal Can Maintain Larval Polymorphism: A Model Motivated by Streblospio benedicti
Zakas, Christina; Hall, David W.
2012-01-01
Polymorphism in traits affecting dispersal occurs in a diverse variety of taxa. Typically, the maintenance of a dispersal polymorphism is attributed to environmental heterogeneity where parental bet-hedging can be favored. There are, however, examples of dispersal polymorphisms that occur across similar environments. For example, the estuarine polychaete Streblospio benedicti has a highly heritable offspring dimorphism that affects larval dispersal potential. We use analytical models of dispersal to determine the conditions necessary for a stable dispersal polymorphism to exist. We show that in asexual haploids, sexual haploids, and in sexual diploids in the absence of overdominance, asymmetric dispersal is required in order to maintain a dispersal polymorphism when patches do not vary in intrinsic quality. Our study adds an additional factor, dispersal asymmetry, to the short list of mechanisms that can maintain polymorphism in nature. The region of the parameter space in which polymorphism is possible is limited, suggesting why dispersal polymorphisms within species are rare. PMID:22576818
Whirl and whip: Rotor/bearing stability problems
NASA Technical Reports Server (NTRS)
Muszynska, A.
1985-01-01
A mathematical model of a symmetric rotor supported by one rigid and one fluid lubricated bearing is proposed. The rotor model is represented by generalized (modal) parameters of its first bending mode. The rotational character of the bearing fluid force is taken into account. The model yields synchronous vibrations due to rotor unbalance as a particular solution of the equations of motion, rotor/bearing system natural frequencies and corresponding self-excited vibrations known as oil whirl and oil whip. The stability analysis yields rotative speed threshold of stability. The model also gives the evaluation of stability of the rotor synchronous vibrations. In the first balance resonance speed region two more thresholds of stability are yielded. The width of this stability region is directly related to the amount of rotor unbalance. The results of the analysis based on this model stand with very good agreement with field observations of rotor dynamic behavior and the experimental results.
Helicopter rotor induced velocities theory and experiment
NASA Technical Reports Server (NTRS)
Berry, John D.; Hoad, Danny R.; Elliott, Joe W.; Althoff, Susan L.
1987-01-01
An investigation has been performed to assess methods used for rotor inflow modeling. A key element of this assessment has been the recent acquisition of high quality experimental measurements of inflow velocities taken in the proximity of a lifting rotor in forward flight. Widely used rotor performance predictive methods are based on blade element strip theory coupled with an inflow model. The inflow prediction models assessed in this paper include the uniform inflow based on momentum, a skewed disk model, and two methods based on a vortex wake structure.
Wind Tunnel Evaluation of a Model Helicopter Main-Rotor Blade With Slotted Airfoils at the Tip
NASA Technical Reports Server (NTRS)
Noonan, Kevin W.; Yeager, William T., Jr.; Singleton, Jeffrey D.; Wilbur, Matthew L.; Mirick, Paul H.
2001-01-01
Data for rotors using unconventional airfoils are of interest to permit an evaluation of this technology's capability to meet the U.S. Army's need for increased helicopter mission effectiveness and improved safety and survivability. Thus, an experimental investigation was conducted in the Langley Transonic Dynamics Tunnel (TDT) to evaluate the effect of using slotted airfoils in the rotor blade tip region (85 to 100 percent radius) on rotor aerodynamic performance and loads. Four rotor configurations were tested in forward flight at advance ratios from 0.15 to 0.45 and in hover in-ground effect. The hover tip Mach number was 0.627, which is representative of a design point of 4000-ft geometric altitude and a temperature of 95 F. The baseline rotor configuration had a conventional single-element airfoil in the tip region. A second rotor configuration had a forward-slotted airfoil with a -6 deg slat, a third configuration had a forward-slotted airfoil with a -10 slat, and a fourth configuration had an aft-slotted airfoil with a 3 deg flap (trailing edge down). The results of this investigation indicate that the -6 deg slat configuration offers some performance and loads benefits over the other three configurations.
Quantum rotor in nanostructured superconductors
Lin, Shi-Hsin; Milošević, M. V.; Covaci, L.; Jankó, B.; Peeters, F. M.
2014-01-01
Despite its apparent simplicity, the idealized model of a particle constrained to move on a circle has intriguing dynamic properties and immediate experimental relevance. While a rotor is rather easy to set up classically, the quantum regime is harder to realize and investigate. Here we demonstrate that the quantum dynamics of quasiparticles in certain classes of nanostructured superconductors can be mapped onto a quantum rotor. Furthermore, we provide a straightforward experimental procedure to convert this nanoscale superconducting rotor into a regular or inverted quantum pendulum with tunable gravitational field, inertia, and drive. We detail how these novel states can be detected via scanning tunneling spectroscopy. The proposed experiments will provide insights into quantum dynamics and quantum chaos. PMID:24686241
Asymmetric impacting on the Moon and its dependence on debiased NEA models
NASA Astrophysics Data System (ADS)
Ito, T.; Malhotra, R.
2010-12-01
Recent lunar crater counting studies have revealed an asymmetric distribution of rayed craters on the lunar surface. The asymmetry is related to the synchronous rotation of the Moon, and there is a higher density of rayed craters on the leading hemisphere compared with the trailing hemisphere. Here we report the progress in our study to test the hypotheses that (i) the population of near-Earth asteroids is the source of the impactors that have made the rayed craters, and (ii) that impacts by this projectile population account quantitatively for the observed asymmetry. We carried out numerical simulations of the orbital evolution of a large number of test particles representing near-Earth asteroids in order to determine directly their impact flux on the Moon. In a previous study, we reported results based on the debiased NEA model of Bottke et al.(2002), where we found that the theoretical model yields a smaller asymmetry than is observed on the Moon. A possible reason for the discrepancy is that the population of NEAs having low relative velocity with respect to the Earth-Moon system is underestimated in the debiased NEA model. In the present work, we report results based on a second debiased NEA model (Morbidelli, 2006), and we compare these with our previous study. Our results provide possible constraints on the dynamical characteristics of the near-Earth asteroid population and may help to improve theoretical models of this population.
Aunai, Nicolas; Hesse, Michael; Kuznetsova, Maria; Black, Carrie; Evans, Rebekah; Zenitani, Seiji; Smets, Roch
2013-02-15
Magnetic reconnection occurring in collisionless environments is a multi-scale process involving both ion and electron kinetic processes. Because of their small mass, the electron scales are difficult to resolve in numerical and satellite data, it is therefore critical to know whether the overall evolution of the reconnection process is influenced by the kinetic nature of the electrons, or is unchanged when assuming a simpler, fluid, electron model. This paper investigates this issue in the general context of an asymmetric current sheet, where both the magnetic field amplitude and the density vary through the discontinuity. A comparison is made between fully kinetic and hybrid kinetic simulations of magnetic reconnection in coplanar and guide field systems. The models share the initial condition but differ in their electron modeling. It is found that the overall evolution of the system, including the reconnection rate, is very similar between both models. The best agreement is found in the guide field system, which confines particle better than the coplanar one, where the locality of the moments is violated by the electron bounce motion. It is also shown that, contrary to the common understanding, reconnection is much faster in the guide field system than in the coplanar one. Both models show this tendency, indicating that the phenomenon is driven by ion kinetic effects and not electron ones.
NASA Technical Reports Server (NTRS)
Kuczynski, W. A.; Sissingh, G. J.
1972-01-01
Wind tunnel tests to determine the dynamic characteristics of hingeless rotors with hub moment feedback controls and to acquire experimental hingeless rotor transfer functions are discussed. Rotor transfer functions were calculated from data acquired during open loop frequency response tests. The transfer functions are linear and present the rotor longitudinal and lateral frequency responses to collective pitch, longitudinal cyclic pitch, and lateral cyclic pitch. The theoretical analysis was based on the rigid blade flapping model coupled with appropriate control system and cyclic pitch actuator equations of motion.
A simulation study of an asymmetric exclusion model with open boundaries and random rates
NASA Astrophysics Data System (ADS)
Bengrine, M.; Benyoussef, A.; Ez-Zahraouy, H.; Krug, J.; Loulidi, M.; Mhirech, F.
1999-04-01
Using numerical simulations, we study the asymmetric exclusion model with open boundaries, particlewise disorder and parallel dynamics. At each time step, particles are injected at the left boundary with probability 0305-4470/32/13/005/img9, removed on the right with probability 0305-4470/32/13/005/img10, and jump in the bulk with probability 0305-4470/32/13/005/img11, where 0305-4470/32/13/005/img12 is a random rate associated with each injected particle 0305-4470/32/13/005/img13. The parameter 0305-4470/32/13/005/img14 interpolates between fully parallel 0305-4470/32/13/005/img15 and random sequential 0305-4470/32/13/005/img16 dynamics. The phase diagram in the 0305-4470/32/13/005/img17-plane displays high-density, low-density and maximum-current phases, with the first-order transition line between high- and low-density phases shifted away from the line 0305-4470/32/13/005/img18. Within the low-density phase a platoon phase transition occurs, many features of which can be explained using exact results for asymmetric exclusion with particlewise disorder on the ring. In a certain region of parameter space the disorder induces a cusp in the current-density relation at maximum flow. Our simulations indicate that this does not affect the topology of the phase diagram, nor the familiar 0305-4470/32/13/005/img19-decay of the density profile in the maximum-current phase.
Dorn, Jonas F.; Zhang, Li; Phi, Tan-Trao; Lacroix, Benjamin; Maddox, Paul S.; Liu, Jian; Maddox, Amy Shaub
2016-01-01
During cytokinesis, the cell undergoes a dramatic shape change as it divides into two daughter cells. Cell shape changes in cytokinesis are driven by a cortical ring rich in actin filaments and nonmuscle myosin II. The ring closes via actomyosin contraction coupled with actin depolymerization. Of interest, ring closure and hence the furrow ingression are nonconcentric (asymmetric) within the division plane across Metazoa. This nonconcentricity can occur and persist even without preexisting asymmetric cues, such as spindle placement or cellular adhesions. Cell-autonomous asymmetry is not explained by current models. We combined quantitative high-resolution live-cell microscopy with theoretical modeling to explore the mechanistic basis for asymmetric cytokinesis in the Caenorhabditis elegans zygote, with the goal of uncovering basic principles of ring closure. Our theoretical model suggests that feedback among membrane curvature, cytoskeletal alignment, and contractility is responsible for asymmetric cytokinetic furrowing. It also accurately predicts experimental perturbations of conserved ring proteins. The model further suggests that curvature-mediated filament alignment speeds up furrow closure while promoting energy efficiency. Collectively our work underscores the importance of membrane–cytoskeletal anchoring and suggests conserved molecular mechanisms for this activity. PMID:26912796
Computational Analysis of Multi-Rotor Flows
NASA Technical Reports Server (NTRS)
Yoon, Seokkwan; Lee, Henry C.; Pulliam, Thomas H.
2016-01-01
Interactional aerodynamics of multi-rotor flows has been studied for a quadcopter representing a generic quad tilt-rotor aircraft in hover. The objective of the present study is to investigate the effects of the separation distances between rotors, and also fuselage and wings on the performance and efficiency of multirotor systems. Three-dimensional unsteady Navier-Stokes equations are solved using a spatially 5th order accurate scheme, dual-time stepping, and the Detached Eddy Simulation turbulence model. The results show that the separation distances as well as the wings have significant effects on the vertical forces of quadroror systems in hover. Understanding interactions in multi-rotor flows would help improve the design of next generation multi-rotor drones.
Sensitivity analysis of an asymmetric Monte Carlo beam model of a Siemens Primus accelerator.
Schreiber, Eric C; Sawkey, Daren L; Faddegon, Bruce A
2012-03-08
The assumption of cylindrical symmetry in radiotherapy accelerator models can pose a challenge for precise Monte Carlo modeling. This assumption makes it difficult to account for measured asymmetries in clinical dose distributions. We have performed a sensitivity study examining the effect of varying symmetric and asymmetric beam and geometric parameters of a Monte Carlo model for a Siemens PRIMUS accelerator. The accelerator and dose output were simulated using modified versions of BEAMnrc and DOSXYZnrc that allow lateral offsets of accelerator components and lateral and angular offsets for the incident electron beam. Dose distributions were studied for 40 × 40 cm² fields. The resulting dose distributions were analyzed for changes in flatness, symmetry, and off-axis ratio (OAR). The electron beam parameters having the greatest effect on the resulting dose distributions were found to be electron energy and angle of incidence, as high as 5% for a 0.25° deflection. Electron spot size and lateral offset of the electron beam were found to have a smaller impact. Variations in photon target thickness were found to have a small effect. Small lateral offsets of the flattening filter caused significant variation to the OAR. In general, the greatest sensitivity to accelerator parameters could be observed for higher energies and off-axis ratios closer to the central axis. Lateral and angular offsets of beam and accelerator components have strong effects on dose distributions, and should be included in any high-accuracy beam model.
Point vortex modelling of the wake dynamics behind asymmetric vortex generator arrays
NASA Astrophysics Data System (ADS)
Baldacchino, D.; Ferreira, C.; Ragni, D.; van Bussel, G. J. W.
2016-09-01
In this work, we present a simple inviscid point vortex model to study the dynamics of asymmetric vortex rows, as might appear behind misaligned vortex generator vanes. Starting from the existing solution of the infinite vortex cascade, a numerical model of four base-vortices is chosen to represent two primary counter-rotating vortex pairs and their mirror plane images, introducing the vortex strength ratio as a free parameter. The resulting system of equations is also defined in terms of the vortex row separation and the qualitative features of the ensuing motion are mapped. A translating and orbiting regime are identified for different cascade separations. The latter occurs for all unequal strength vortex pairs. Thus, the motion is further classified by studying the cyclic behaviour of the orbiting regime and it is shown that for small mismatches in vortex strength, the orbiting length and time scales are sufficiently large as to appear, in the near wake, as translational (non-orbiting). However, for larger mismatches in vortex strength, the orbiting motion approaches the order of the starting height of the vortex. Comparisons between experimental data and the potential flow model show qualitative agreement whilst viscous effects account for the major discrepancies. Despite this, the model captures the orbital mode observed in the measurements and provides an impetus for considering the impact of these complex interactions on vortex generator designs.
Asymmetric nuclear matter and neutron skin in an extended relativistic mean-field model
Agrawal, B. K.
2010-03-15
The density dependence of the symmetry energy, instrumental in understanding the behavior of the asymmetric nuclear matter, is investigated within the extended relativistic mean-field (ERMF) model, which includes the contributions from the self- and mixed-interaction terms for the scalar-isoscalar ({sigma}), vector-isoscalar ({omega}), and vector-isovector ({rho}) mesons up to the quartic order. Each of the 26 different parametrizations of the ERMF model employed is compatible with the bulk properties of the finite nuclei. The behavior of the symmetry energy for several parameter sets is found to be consistent with the empirical constraints on them as extracted from the analyses of the isospin diffusion data. The neutron-skin thickness in the {sup 208}Pb nucleus for these parameter sets of the ERMF model lies in the range of {approx}0.20-0.24 fm, which is in harmony with the thickness predicted by the Skyrme Hartree-Fock model. We also investigate the role of various mixed-interaction terms that are crucial for the density dependence of the symmetry energy.
NASA Astrophysics Data System (ADS)
Jeffery, Rondo N.; Montgomery, Jerry R.
2010-10-01
The new quark-lattice model of the nucleus has been extended through heavy nuclei. Three specific issues illustrate the power of the model: (1) large thermal neutron absorption cross sections, (2) radioactive decay of K-40, and (3) asymmetric fission. Large neutron absorption cross sections occur when there are openings in the lattice into which neutrons can naturally fit. Examples are He-3, Li-6, and B-10. B-10 results in neutron-activated fission. The decay of K-40 into either Ar-40 or Ca-40 illustrates the role spin plays in determining nuclear structure. K-40 has net spin 4 whereas Ar-40 and Ca-40 both have spin 0. Zome models are used to show these structures. The fission of heavy nuclei occurs, in the lattice model, as the core of the structure separates from the loosely-packed ends. The ends are repacked into a smaller nucleus, which forms the lighter of the two daughter fragments. This explains why the lighter fragment mass increases with total mass whereas the heavier fragment mass remains relatively constant.
Application of the wide-field shadowgraph technique to rotor wake visualization
NASA Technical Reports Server (NTRS)
Norman, Thomas R.; Light, Jeffrey S.
1989-01-01
The wide field shadowgraph technique is reviewed along with its application to the visualization of rotor wakes. In particular, current experimental methods and data reduction requirements are discussed. Sample shadowgraphs are presented. These include shadowgraphs of model-scale helicopter main rotors and tilt rotors, and full scale tail rotors, both in hover and in forward flight.
2009-01-01
A Process Model for Deployment Planning of Ground-based Air Defense System Against Asymmetric Homeland Threat Ronald L. Cypert Scientific...units, along with coordination at the state and federal agency level, a dynamic process modeling capability was chosen to chart the myriad...COVERED 00-00-2009 to 00-00-2009 4. TITLE AND SUBTITLE A Process Model for Deployment Planning of Ground-based Air Defense System Against
Helicopter tail rotor blade-vortex interaction noise
NASA Technical Reports Server (NTRS)
George, Albert R.; Chou, S.-T.
1987-01-01
A study is made of helicopter tail rotor noise, particularly that due to the interactions with main rotor tip vortices. Summarized here are present analysis, the computer codes, and the results of several test cases. Amiet's unsteady thin airfoil theory is used to calculate the acoustics of blade-vortex interaction. The noise source is modelled as a force dipole resulting from an airfoil of infinite span chopping through a skewed line vortex. To analyze the interactions between helicopter tail rotor and main rotor tip vortices, we developed a two-step approach: (1) the main rotor tip vortex system is obtained through a free wake geometry calculation of the main rotor using CAMRAD code; (2) acoustic analysis takes the results from the aerodynamic interaction analysis and calculates the farfield pressure signatures for the interactions. It is found that under a wide range of helicopter flight conditions, acoustic pressure fluctuations of significant magnitude can be generated by tail rotors due to a series of interactions with main rotor tip vortices. This noise mechanism depends strongly on the helicopter flight conditions and the relative location and phasing of the main and tail rotors. fluctuations of significant magnitude can be generated by tail rotors due to a series of interactions with main rotor tip vortices. This noise mechanism depends strongly upon the helicopter flight conditions and the relative location and phasing of the main and tail rotors.
NASA Astrophysics Data System (ADS)
Erath, Byron D.; Plesniak, Michael W.
2006-11-01
Pulsatile two-dimensional flow through asymmetric static divergent models of the human vocal folds is investigated. Included glottal divergence angles are varied between 10° and 30°, with asymmetry angles between the vocal fold pairs ranging from 5° to 15°. The model glottal configurations represent asymmetries that arise during a phonatory cycle due to voice disorders. The flow is scaled to physiological values of Reynolds, Strouhal, and Euler numbers. Data are acquired in the anterior posterior mid-plane of the vocal fold models using phase-averaged Particle Image Velocimetry (PIV) acquired at ten discrete locations in a phonatory cycle. Glottal jet stability arising from the vocal fold asymmetries is investigated and compared to previously reported work for symmetric vocal fold passages. Jet stability is enhanced with an increase in the included divergence angle, and the glottal asymmetry. Concurrently, the bi-modal jet trajectory and flow unsteadiness diminishes. Consistent with previous findings, the flow attachment due to the Coanda effect occurs when the acceleration of the forcing function is zero.
A Rough Set Bounded Spatially Constrained Asymmetric Gaussian Mixture Model for Image Segmentation.
Ji, Zexuan; Huang, Yubo; Sun, Quansen; Cao, Guo; Zheng, Yuhui
2017-01-01
Accurate image segmentation is an important issue in image processing, where Gaussian mixture models play an important part and have been proven effective. However, most Gaussian mixture model (GMM) based methods suffer from one or more limitations, such as limited noise robustness, over-smoothness for segmentations, and lack of flexibility to fit data. In order to address these issues, in this paper, we propose a rough set bounded asymmetric Gaussian mixture model with spatial constraint for image segmentation. First, based on our previous work where each cluster is characterized by three automatically determined rough-fuzzy regions, we partition the target image into three rough regions with two adaptively computed thresholds. Second, a new bounded indicator function is proposed to determine the bounded support regions of the observed data. The bounded indicator and posterior probability of a pixel that belongs to each sub-region is estimated with respect to the rough region where the pixel lies. Third, to further reduce over-smoothness for segmentations, two novel prior factors are proposed that incorporate the spatial information among neighborhood pixels, which are constructed based on the prior and posterior probabilities of the within- and between-clusters, and considers the spatial direction. We compare our algorithm to state-of-the-art segmentation approaches in both synthetic and real images to demonstrate the superior performance of the proposed algorithm.
A Rough Set Bounded Spatially Constrained Asymmetric Gaussian Mixture Model for Image Segmentation
Ji, Zexuan; Huang, Yubo; Sun, Quansen; Cao, Guo; Zheng, Yuhui
2017-01-01
Accurate image segmentation is an important issue in image processing, where Gaussian mixture models play an important part and have been proven effective. However, most Gaussian mixture model (GMM) based methods suffer from one or more limitations, such as limited noise robustness, over-smoothness for segmentations, and lack of flexibility to fit data. In order to address these issues, in this paper, we propose a rough set bounded asymmetric Gaussian mixture model with spatial constraint for image segmentation. First, based on our previous work where each cluster is characterized by three automatically determined rough-fuzzy regions, we partition the target image into three rough regions with two adaptively computed thresholds. Second, a new bounded indicator function is proposed to determine the bounded support regions of the observed data. The bounded indicator and posterior probability of a pixel that belongs to each sub-region is estimated with respect to the rough region where the pixel lies. Third, to further reduce over-smoothness for segmentations, two novel prior factors are proposed that incorporate the spatial information among neighborhood pixels, which are constructed based on the prior and posterior probabilities of the within- and between-clusters, and considers the spatial direction. We compare our algorithm to state-of-the-art segmentation approaches in both synthetic and real images to demonstrate the superior performance of the proposed algorithm. PMID:28045950
Two-dimensional analytical model for asymmetric dual-gate tunnel FETs
NASA Astrophysics Data System (ADS)
Xu, Hui Fang; Dai, Yue Hua; Gui Guan, Bang; Zhang, Yong Feng
2017-01-01
An analytical model for asymmetric dual-gate (ADG) tunnel field-effect transistors (TFETs) combining a TFET with a junctionless field-effect transistor (JL FET) is presented and investigated extensively for the first time in this paper, with the aim of addressing the challenges of conventional DG TFETs. The drain current is composed of the tunneling current of TFET and the drift-diffusion current of JL FET, which leads to high drain current. The model also predicts the impacts of the lengths of the source and intrinsic regions on the potential and drain current. The results show that ADG TFET can generate optimum results (in terms of on-state current I on and on-to-off current ratio I on/I off) compared with the conventional DG TFET, higher I on of 129 µA/µm and a larger I on/I off of 2.1 × 1010 are obtained when the optimized lengths of the source and intrinsic regions are almost 14 nm. Very good agreements for both the potential and the drain current are observed between the model calculations and the simulated results.
Vortex Ring State and Asymmetric Thrust Oscillations
NASA Astrophysics Data System (ADS)
McCauley, Gregory; Savas, Omer; Caradonna, Francis
2008-11-01
When the helical vortices of a rotor are not convected away, the vortices may form a ring-like structure about the rotor disk. This vortex ring state (VRS) is most common during rapid descent and leads to thrust oscillations coupled to the formation and subsequent breakdown of the ring. Experimental observations at and near VRS were made using strobed particle image velocimetry on a three-blade rotor in a towing tank. Simultaneous strain gage readings allowed direct measurement of the rotor's thrust history in this state. Operating conditions near the cusp of VRS were investigated to offer insight into the initial evolution of this undesirable state. In addition, asymmetries in the periodic thrust histories during non-axial descent are analyzed in conjunction with corresponding vorticity evolutions. Salient features of the vortex wake structure during highly asymmetric thrust oscillations are discussed in contrast to VRS cases with nearly symmetric thrust oscillations.
On the flow field around a Savonius rotor
NASA Astrophysics Data System (ADS)
Bergeles, G.; Athanassiadis, N.
A model of a two-bucket Savonius rotor windmill was constructed and tested in a wind tunnel. The flow field around the rotor was examined visually and also quantitatively with the use of a hot wire. The flow visualization revealed an upstream influence on the flow field up to 3 rotor diameters away and a strong downwash downstream. Hot wire measurements showed a large velocity deficit behind the rotor and a quick velocity recovery downstream due to strong mixing; the latter was associated with high levels of turbulence. Energy spectra revealed that all turbulence was concentrated in a single harmonic corresponding to twice the rotational speed of the rotor.
2011-01-01
Asymmetric cell division is common in biology and plays critical roles in differentiation and development. Unicellular organisms are often used as model systems for understanding the origins and consequences of asymmetry during cell division. Although basic as compared to mammalian cells, these are already quite complex. We report complete budding and asymmetric fission of very simple nonliving model cells to produce daughter vesicles that are chemically distinct in both interior and membrane compositions. Our model cells are based on giant lipid vesicles (GVs, 10–30 μm) encapsulating a polyethylene glycol (PEG)/dextran aqueous two-phase system (ATPS) as a crowded and compartmentalized cytoplasm mimic. Ternary lipid compositions were used to provide coexisting micrometer-scale liquid disordered (Ld) and liquid ordered (Lo) domains in the membranes. ATPS-containing vesicles formed buds when sucrose was added externally to provide increased osmotic pressure, such that they became not only morphologically asymmetric but also asymmetric in both their interior and their membrane compositions. Further increases in osmolality drove formation of two chemically distinct daughter vesicles, which were in some cases connected by a lipid nanotube (complete budding), and in others were not (fission). In all cases, separation occurred at the aqueous–aqueous phase boundary, such that one daughter vesicle contained the PEG-rich aqueous phase and the other contained the dextran-rich aqueous phase. PEGylated lipids localized in the Lo domain resulted in this membrane domain preferentially coating the PEG-rich bud prior to division, and subsequently the PEG-rich daughter vesicle. Varying the mole ratio of lipids resulted in excess surface area of Lo or Ld membrane domains such that, upon division, this excess portion was inherited by one of the daughter vesicles. In some cases, a second “generation” of aqueous phase separation and budding could be induced in these daughter
NASA Astrophysics Data System (ADS)
Khouli, F.
An aeroelastic phenomenon, known as blade sailing, encountered during maritime operation of helicopters is identified as being a factor that limits the tactical flexibility of helicopter operation in some sea conditions. The hazards associated with this phenomenon and its complexity, owing to the number of factors contributing to its occurrence, led previous investigators to conclude that advanced and validated simulation tools are best suited to investigate it. A research gap is identified in terms of scaled experimental investigation of this phenomenon and practical engineering solutions to alleviate its negative impact on maritime helicopter operation. The feasibility of a proposed strategy to alleviate it required addressing a gap in modelling thin-walled composite active beams/rotor blades. The modelling is performed by extending a mathematically-consistent and asymptotic reduction strategy of the 3-D elastic problem to account for embedded active materials. The derived active cross-sectional theory is validated using 2-D finite element results for closed and open cross-sections. The geometrically-exact intrinsic formulation of active maritime rotor systems is demonstrated to yield compact and symbolic governing equations. The intrinsic feature is shown to allow a classical and proven solution scheme to be successfully applied to obtain time history solutions. A Froude-scaled experimental rotor was designed, built, and tested in a scaled ship airwake environment and representative ship motion. Based on experimental and simulations data, conclusions are drawn regarding the influence of the maritime operation environment and the rotor operation parameters on the blade sailing phenomenon. The experimental data is also used to successfully validate the developed simulation tools. The feasibility of an open-loop control strategy based on the integral active twist concept to counter blade sailing is established in a Mach-scaled maritime operation environment
The prediction of transonic loading on advancing helicopter rotors
NASA Technical Reports Server (NTRS)
Strawn, R. C.; Tung, C.
1986-01-01
Two different schemes are presented for including the effect of rotor wakes on the finie-difference prediction of rotor loads. The first formulation includes wake effects by means of a blade-surface inflow specification. This approach is sufficiently simple to permit coupling of a full-potential finite-difference rotor code to a comprehensive integral model for the rotor wake and blade motion. The coupling involves a transfer of appropriate loads and inflow data between the two computer codes. Results are compared with experimental data for two advancing rotor cases. The second rotor-wake modeling scheme is a split potential formulation for computing unsteady blade-vortex interactions. Discrete vortex fields are introduced into a three-dimensional, conservative, full-potential rotor code. Computer predictions are compared with two experimental blade-vortex interaction cases.
The prediction of transonic loading advancing helicopter rotors
NASA Technical Reports Server (NTRS)
Strawn, R.; Tung, C.
1986-01-01
Two different schemes are presented for including the effect of rotor wakes on the finite-difference prediction of rotor loads. The first formulation includes wake effects by means of a blade-surface inflow specification. This approach is sufficiently simple to permit coupling of a full-potential finite-difference rotor code to a comprehensive integral model for the rotor wake and blade motion. The coupling involves a transfer of appropriate loads and inflow data between the two computer codes. Results are compared with experimental data for two advancing rotor cases. The second rotor wake modeling scheme in this paper is a split potential formulation for computing unsteady blade-vortex interactions. Discrete vortex fields are introduced into a three-dimensional, conservative, full-potential rotor code. Computer predictions are compared with two experimental blade-vortex interaction cases.
NASA Astrophysics Data System (ADS)
Bodaghi, M.; Damanpack, A. R.; Liao, W. H.
2016-07-01
The aim of this article is to develop a robust macroscopic bi-axial model to capture self-accommodation, martensitic transformation/orientation/reorientation, normal-shear deformation coupling and asymmetric/anisotropic strain generation in polycrystalline shape memory alloys. By considering the volume fraction of martensite and its preferred direction as scalar and directional internal variables, constitutive relations are derived to describe basic mechanisms of accommodation, transformation and orientation/reorientation of martensite variants. A new definition is introduced for maximum recoverable strain, which allows the model to capture the effects of tension-compression asymmetry and transformation anisotropy. Furthermore, the coupling effects between normal and shear deformation modes are considered by merging inelastic strain components together. By introducing a calibration approach, material and kinetic parameters of the model are recast in terms of common quantities that characterize a uniaxial phase kinetic diagram. The solution algorithm of the model is presented based on an elastic-predictor inelastic-corrector return mapping process. In order to explore and demonstrate capabilities of the proposed model, theoretical predictions are first compared with existing experimental results on uniaxial tension, compression, torsion and combined tension-torsion tests. Afterwards, experimental results of uniaxial tension, compression, pure bending and buckling tests on {{NiTi}} rods and tubes are replicated by implementing a finite element method along with the Newton-Raphson and Riks techniques to trace non-linear equilibrium path. A good qualitative and quantitative correlation is observed between numerical and experimental results, which verifies the accuracy of the model and the solution procedure.
Free Wake Techniques for Rotor Aerodynamic Analylis. Volume 2: Vortex Sheet Models
NASA Technical Reports Server (NTRS)
Tanuwidjaja, A.
1982-01-01
Results of computations are presented using vortex sheets to model the wake and test the sensitivity of the solutions to various assumptions used in the development of the models. The complete codings are included.
NASA Astrophysics Data System (ADS)
Splettstoesser, W. R.; Lehmann, G.; van der Wall, B.
1989-09-01
Initial acoustic results are presented from a higher harmonic control (HHC) wind tunnel pilot experiment on helicopter rotor blade-vortex interaction (BVI) impulsive noise reduction, making use of the DFVLR 40-percent-scaled BO-105 research rotor in the DNW 6m by 8m closed test section. Considerable noise reduction (of several decibels) has been measured for particular HHC control settings, however, at the cost of increased vibration levels and vice versa. The apparently adverse results for noise and vibration reduction by HHC are explained. At optimum pitch control settings for BVI noise reduction, rotor simulation results demonstrate that blade loading at the outer tip region is decreased, vortex strength and blade vortex miss-distance are increased, resulting altogether in reduced BVI noise generation. At optimum pitch control settings for vibration reduction adverse effects on blade loading, vortex strength and blade vortex miss-distance are found.
Analytical Model of an Asymmetric Sunspot with a Steady Plasma Flow in its Penumbra
NASA Astrophysics Data System (ADS)
Solov'ev, A. A.; Kirichek, E. A.
2016-08-01
A new exact analytical solution to the stationary problem of ideal magnetohydrodynamics is derived for an unipolar asymmetric sunspot immersed in a realistic solar atmosphere. The radial and vertical profiles of pressure, plasma density, and temperature in the visible layers of the sunspot are calculated. The reduction in plasma density in the magnetic funnel of the sunspot, corresponding to the Wilson depression, is also obtained. The magnetic structure of the sunspot is given analytically in a realistic way: a part of the magnetic flux of the sunspot approaches the surrounding photosphere at the outer edge of the penumbra. The magnetic field of the sunspot is not assumed to be axially symmetric. For the first time, the angular dependence of the physical variables in this model allows us to simulate not only a deviation from the circular shape of the sunspot, but also a fine filamentary structure of the sunspot penumbra. The Alfvén Mach number (the ratio of the plasma speed to the Alfvén speed) is zero at the center of the sunspot and rises slowly toward the periphery of the sunspot; this corresponds to the structure of the Evershed flow in the penumbra. The Evershed flow in our model is mainly concentrated in dark penumbral filaments, as is observed.
Shinisha, C B; Sunoj, Raghavan B
2010-09-08
The use of chiral auxiliaries is one of the most fundamental protocols employed in asymmetric synthesis. In the present study, stereoselectivity-determining factors in a chiral auxiliary-based asymmetric aldol reaction promoted by TiCl(4) are investigated by using density functional theory methods. The aldol reaction between chiral titanium enolate [derived from Evans propionyl oxazolidinone (1a) and its variants oxazolidinethione (1b) and thiazolidinethione (1c)] and benzaldehyde is examined by using transition-state modeling. Different stereochemical possibilities for the addition of titanium enolates to aldehyde are compared. On the basis of the coordination of the carbonyl/thiocarbonyl group of the chiral auxiliary with titanium, both pathways involving nonchelated and chelated transition states (TSs) are considered. The computed relative energies of the stereoselectivity-determining C-C bond formation TSs in the nonchelated pathway, for both 1a and 1c, indicate a preference toward Evans syn aldol product. The presence of a ring carbonyl or thiocarbonyl group in the chiral auxiliary renders the formation of neutral TiCl(3)-enolate, which otherwise is energetically less favored as compared to the anionic TiCl(4)-enolate. Hence, under suitable conditions, the reaction between titanium enolate and aldehyde is expected to be viable through chelated TSs leading to the selective formation of non-Evans syn aldol product. Experimentally known high stereoselectivity toward Evans syn aldol product is effectively rationalized by using the larger energy differences between the corresponding diastereomeric TSs. In both chelated and nonchelated pathways, the attack by the less hindered face of the enolate on aldehyde through a chair-like TS with an equatorial disposition of the aldehydic substituent is identified as the preferred mode. The steric hindrance offered by the isopropyl group and the possible chelation are identified as the key reasons behind the interesting
NASA Technical Reports Server (NTRS)
Balch, D. T.; Lombardi, J.
1985-01-01
A model scale hover test was conducted in the Sikorsky Aircraft Model Rotor hover Facility to identify and quantify the impact of the tail rotor on the demonstrated advantages of advanced geometry tip configurations. The existence of mutual interference between hovering main rotor and a tail rotor was acknowledged in the test. The test was conducted using the Basic Model Test Rig and two scaled main rotor systems, one representing a 1/5.727 scale UH-60A BLACK HAWK and the others a 1/4.71 scale S-76. Eight alternate rotor tip configurations were tested, 3 on the BLACK HAWK rotor and 6 on the S-76 rotor. Four of these tips were then selected for testing in close proximity to an operating tail rotor (operating in both tractor and pusher modes) to determine if the performance advantages that could be obtained from the use of advanced geometry tips in a main rotor only environment would still exist in the more complex flow field involving a tail rotor. This volume contains the test run log and tabulated data.
NASA Technical Reports Server (NTRS)
Bradford, Michael P. (Inventor); Maciolek, Joseph R. (Inventor)
1987-01-01
A helicopter rotor control system (13) including a stop azimuth controller (32) for establishing the value of a deceleration command (15') to a deceleration controller (23), a transition azimuth predictor (41) and a position reference generator (55), which are effective during the last revolution of said rotor (14) to establish a correction indication (38) to adjust the deceleration command (15') to ensure that one of the rotor blades (27) stops at a predetermined angular position.
2012-01-01
Background If the geographical displacement of one species by another is accompanied by hybridization, mitochondrial DNA can introgress asymmetrically, from the outcompeted species into the invading species, over a large area. We explore this phenomenon using the two parapatric crested newt species, Triturus macedonicus and T. karelinii, distributed on the Balkan Peninsula in south-eastern Europe, as a model. Results We first delimit a ca. 54,000 km2 area in which T. macedonicus contains T. karelinii mitochondrial DNA. This introgression zone bisects the range of T. karelinii, cutting off a T. karelinii enclave. The high similarity of introgressed mitochondrial DNA haplotypes with those found in T. karelinii suggests a recent transfer across the species boundary. We then use ecological niche modeling to explore habitat suitability of the location of the present day introgression zone under current, mid-Holocene and Last Glacial Maximum conditions. This area was inhospitable during the Last Glacial Maximum for both species, but would have been habitable at the mid-Holocene. Since the mid-Holocene, habitat suitability generally increased for T. macedonicus, whereas it decreased for T. karelinii. Conclusion The presence of a T. karelinii enclave suggests that T. karelinii was the first to colonize the area where the present day introgression zone is positioned after the Last Glacial Maximum. Subsequently, we propose T. karelinii was outcompeted by T. macedonicus, which captured T. karelinii mitochondrial DNA via introgressive hybridization in the process. Ecological niche modeling suggests that this replacement was likely facilitated by a shift in climate since the mid-Holocene. We suggest that the northwestern part of the current introgression zone was probably never inhabited by T. karelinii itself, and that T. karelinii mitochondrial DNA spread there through T. macedonicus exclusively. Considering the spatial distribution of the introgressed mitochondrial DNA and
Wielstra, Ben; Arntzen, Jan W
2012-08-30
If the geographical displacement of one species by another is accompanied by hybridization, mitochondrial DNA can introgress asymmetrically, from the outcompeted species into the invading species, over a large area. We explore this phenomenon using the two parapatric crested newt species, Triturus macedonicus and T. karelinii, distributed on the Balkan Peninsula in south-eastern Europe, as a model. We first delimit a ca. 54,000 km(2) area in which T. macedonicus contains T. karelinii mitochondrial DNA. This introgression zone bisects the range of T. karelinii, cutting off a T. karelinii enclave. The high similarity of introgressed mitochondrial DNA haplotypes with those found in T. karelinii suggests a recent transfer across the species boundary. We then use ecological niche modeling to explore habitat suitability of the location of the present day introgression zone under current, mid-Holocene and Last Glacial Maximum conditions. This area was inhospitable during the Last Glacial Maximum for both species, but would have been habitable at the mid-Holocene. Since the mid-Holocene, habitat suitability generally increased for T. macedonicus, whereas it decreased for T. karelinii. The presence of a T. karelinii enclave suggests that T. karelinii was the first to colonize the area where the present day introgression zone is positioned after the Last Glacial Maximum. Subsequently, we propose T. karelinii was outcompeted by T. macedonicus, which captured T. karelinii mitochondrial DNA via introgressive hybridization in the process. Ecological niche modeling suggests that this replacement was likely facilitated by a shift in climate since the mid-Holocene. We suggest that the northwestern part of the current introgression zone was probably never inhabited by T. karelinii itself, and that T. karelinii mitochondrial DNA spread there through T. macedonicus exclusively. Considering the spatial distribution of the introgressed mitochondrial DNA and the signal derived from