The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
Anastasios S Lyrintzis - One of the best experts on this subject based on the ideXlab platform.
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surface integral methods in computational aeroAcoustics from the cfd near Field to the Acoustic Far Field
International Journal of Aeroacoustics, 2003Co-Authors: Anastasios S LyrintzisAbstract:A review of recent advances in the use of surface integral methods in Computational AeroAcoustics (CAA) for the extension of near-Field CFD results to the Acoustic Far-Field is given. These integral formulations (i.e. Kirchhoff's method, permeable (porous) surface FfowcsWilliams Hawkings (FW-H) equation) allow the radiating sound to be evaluated based on quantities on an arbitrary control surface if the wave equation is assumed outside. Thus only surface integrals are needed for the calculation of the Far-Field sound, instead of the volume integrals required by the traditional Acoustic analogy method (i.e. Lighthill, rigid body FW-H equation). A numerical CFD method is used for the evaluation of the flow-Field solution in the near Field and thus on the control surface. Diffusion and dispersion errors associated with wave propagation in the Far-Field are avoided. The surface integrals and the first derivatives needed can be easily evaluated from the near-Field CFD data. Both methods can be extended in orde...
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Surface integral methods in computational aeroAcoustics—From the (CFD) near-Field to the (Acoustic) Far-Field
International Journal of Aeroacoustics, 2003Co-Authors: Anastasios S LyrintzisAbstract:A review of recent advances in the use of surface integral methods in Computational AeroAcoustics (CAA) for the extension of near-Field CFD results to the Acoustic Far-Field is given. These integral formulations (i.e. Kirchhoff's method, permeable (porous) surface FfowcsWilliams Hawkings (FW-H) equation) allow the radiating sound to be evaluated based on quantities on an arbitrary control surface if the wave equation is assumed outside. Thus only surface integrals are needed for the calculation of the Far-Field sound, instead of the volume integrals required by the traditional Acoustic analogy method (i.e. Lighthill, rigid body FW-H equation). A numerical CFD method is used for the evaluation of the flow-Field solution in the near Field and thus on the control surface. Diffusion and dispersion errors associated with wave propagation in the Far-Field are avoided. The surface integrals and the first derivatives needed can be easily evaluated from the near-Field CFD data. Both methods can be extended in orde...
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Rotorcraft impulsive noise prediction using a rotating Kirchhoff formulation
Journal of Aircraft, 1996Co-Authors: Anastasios S Lyrintzis, Evangelos K. KoutsavdisAbstract:Rotorcraft impulsive [i.e., high-speed impulsive (HSI) and blade-vortex interaction (BVI)] noise for an advancing rotor is studied numerically. The unsteady transonic full-potential rotor code is used for the simulation of the near-Field flow. A rotating Kirchhoff's method is used for the extension to the Acoustic Far Field. The formulation is extended for an advancing rotor and an observer fixed relative to the rotor, and thus, moving relative to the freestream, and allows a direct comparison with experiments. Results for both HSI and BVI noise are presented and compared with experimental results. Various noise parameters are identified and investigated. The rotating Kirchhoff noise appears to be a very valuable tool for helicopter impulsive noise prediction.
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Rotating Kirchhoff method for three-dimensional transonic blade-vortex interaction hover noise
AIAA Journal, 1994Co-Authors: Anastasios S LyrintzisAbstract:The unsteady transonic full-potential rotor (FPR) code is used for the simulation of the transonic blade vortex interaction (BVI) near-Field flow. The rotating Kirchhoff method is used for the extension to the Acoustic Far Field. Two rotating Kirchhoff formulations are developed for the three-dimensional BVI Far-Field noise prediction. The first formulation (Morino's method) is for an observer rotating with the blade. This allows the direct comparison with computational fluid dynamics results. The second formulation (Farassat's method) is for a stationary observer and allows a direct comparison with Acoustic experiments
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Transonic blade-vortex interactions - Noise reduction
Journal of Aircraft, 1993Co-Authors: Anastasios S LyrintzisAbstract:Several ideas for the reduction of transonic blade-vortex interaction (BVI) noise are proposed and tested. Noise due to transonic BVI is analyzed using a finite difference code; the numerically calculated 2D near-Field aerodynamic results are extended to 3D linear Acoustic Far Field using the Kirchhoff method. It is shown that the noise can be significantly reduced by splitting the vortex in two. BVI noise is also substantially reduced by reducing the vortex strength and by increasing the angle of attack.
Theodore B. Norris - One of the best experts on this subject based on the ideXlab platform.
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Nanoscale coherent Acoustic phonon imaging
Ultrafast Phenomena in Semiconductors and Nanostructure Materials X, 2006Co-Authors: B. C. Daly, Theodore B. Norris, Julien Klein, Donald Milan Tennant, Joseph Ashley Taylor, J.e. BowerAbstract:An ultrafast optical pump and probe technique known as picosecond ultrasonics is used to generate and detect coherent Acoustic phonon pulses in nanostructured films grown on Si wafers. By detecting the phonons after they have diffracted across a millimeter thick wafer, it is possible to measure the scattered phonons in the Acoustic Far Field. Numerical backpropagation algorithms can then be used in order to reconstruct the object which scattered the Acoustic phonon pulses. We describe measurements and simulations of experiments performed on surface and sub-surface nanostructures. Results with ~500 nm image resolution are shown, and plans for improving that resolution by an order of magnitude will be described.
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Gouy phase shift of single-cycle picosecond Acoustic pulses
Applied Physics Letters, 2003Co-Authors: N. C. R. Holme, B. C. Daly, M.t. Myaing, Theodore B. NorrisAbstract:Ultrafast laser pulses are used to generate single-cycle picosecond Acoustic pulses in thin metal films on silicon. For small initial excitation spot sizes, propagation of the Acoustic pulses across a 485-μm Si crystal leads to significant diffraction effects. The temporal reshaping of the Acoustic wave form due to diffraction is investigated, and we demonstrate that the Acoustic Far Field can be reached.
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Gouy phase shift of single-cycle picosecond Acoustic pulses
The Thirteenth International Conference on Ultrafast Phenomena, 2002Co-Authors: N. C. R. Holme, B. C. Daly, M.t. Myaing, Theodore B. NorrisAbstract:Ultrafast laser pulses are used to generate single-cycle picosecond Acoustic pulses in thin metal films on silicon. For small initial excitation spot sizes, propagation of the Acoustic pulses across a 485-mm Si crystal leads to significant diffraction effects. The temporal reshaping of the Acoustic wave form due to diffraction is investigated, and we demonstrate that the Acoustic Far Field can be reached. © 2003 American Institute of Physics. @DOI: 10.1063/1.1590405#
Leonhard Kleiser - One of the best experts on this subject based on the ideXlab platform.
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Linear stability and Acoustic characteristics of compressible, viscous, subsonic coaxial jet flow
Physics of Fluids, 2013Co-Authors: Michael Gloor, Dominik Obrist, Leonhard KleiserAbstract:This study explores the parameter influence on the linear stability characteristics of viscous compressible coaxial jet flow at subsonic flow velocities. We study the impact of parameters on the disturbance development, such as the Reynolds number, Mach number, momentum thickness, temperature and velocity ratio between bypass flow and core stream as well as the influence of the azimuthal wavenumber. In addition to the discussion on the unstable modes, we also investigate the properties of Acoustic (radiating) modes which are relevant for sound propagation to the Acoustic Far-Field. By analyzing the eigenfunction profiles of the Acoustic modes, we identify a possible interaction mechanism between the shear layer and the Acoustic modes.
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Localization of Acoustic sources in subsonic jets
Pamm, 2008Co-Authors: Dominik Obrist, Leonhard KleiserAbstract:The sound in the Acoustic Far-Field of a round jet is generated by a multitude of unsteady flow structures with different len gth and time scales. Most likely, different components of the noise spectrum are created by different structures in the jet w hich emit sound in different directions. Based on Lighthill’s ac oustic analogy, we present a method for relating flow structu res of the jet with Far-Field noise spectra and their associated dir ectivity patterns. The method allows to determine what kind of noise (with respect to frequency and emission direction) is generated at a given streamwise location. We illustrate the method with numerical results for a round isothermal jet. Copyright line will be provided by the publisher
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an euler solver for the Acoustic Far Field prediction of compressible jet flow
Pamm, 2007Co-Authors: Felix Keiderling, Dominik Obrist, S B Muller, Leonhard KleiserAbstract:We report on a highly accurate Euler solver for predicting Far-Field jet noise. The solver is based on a framework for Direct Numerical Simulation (DNS) / Large-Eddy Simulation (LES) that provides the time-dependent, noise-generating flow Field and the Acoustic near-Field. The corresponding Far-Field is then computed by solving the inviscid Euler equations in a conservative formulation which is discretized with compact finite differences. Numerical stability can be guaranteed by a spectrally selective filtering procedure developed in the context of subgrid-scale modeling which is active only in the high wavenumber regime. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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An Euler solver for the Acoustic Far‐Field prediction of compressible jet flow
Pamm, 2007Co-Authors: Felix Keiderling, Dominik Obrist, S B Muller, Leonhard KleiserAbstract:We report on a highly accurate Euler solver for predicting Far-Field jet noise. The solver is based on a framework for Direct Numerical Simulation (DNS) / Large-Eddy Simulation (LES) that provides the time-dependent, noise-generating flow Field and the Acoustic near-Field. The corresponding Far-Field is then computed by solving the inviscid Euler equations in a conservative formulation which is discretized with compact finite differences. Numerical stability can be guaranteed by a spectrally selective filtering procedure developed in the context of subgrid-scale modeling which is active only in the high wavenumber regime. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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Computation of Acoustic Far-Fields with the Spectral Lighthill Method
Pamm, 2006Co-Authors: Dominik Obrist, Felix Keiderling, Leonhard KleiserAbstract:Based on Lighthill's Acoustic analogy we formulate the Spectral Lighthill Method (SLM). SLM is a method for the computation of Acoustic Far-Fields. It uses a spatio-temporal Fourier transform of the Lighthill stress tensor. We show that SLM is a straightforward tool for the computation of Acoustic Far-Fields that enhances our physical understanding of sound generation and is useful in the numerical analysis of Acoustic Far-Field solvers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Rabia Djellouli - One of the best experts on this subject based on the ideXlab platform.
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On the Solution of Inverse Obstacle Acoustic Scattering Problems with a Limited Aperture
Mathematical and Numerical Aspects of Wave Propagation WAVES 2003, 2020Co-Authors: Rabia Djellouli, Radek Tezaur, Charbel FarhatAbstract:We present a computational methodology for retrieving the shape of a rigid obstacle from the knowledge of some Acoustic Far-Field patterns. This methodology is based on the well-known regularized Newton algorithm, but distinguishes itself from similar optimization procedures by using (a) the Far Field pattern in a limited aperture, (b) a sensitivity-based and frequency-aware multi-stage solution strategy, (c) a computationally efficient usage of the exact sensitivities of the Far-Field pattern to the specified shape parameters, and (d) a numerically scalable domain decomposition method for the fast solution in a frequency band of direct Acoustic scattering problems.
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a multi step procedure for enriching limited two dimensional Acoustic Far Field pattern measurements
Journal of Inverse and Ill-posed Problems, 2010Co-Authors: Helene Barucq, Chokri Bekkey, Rabia DjellouliAbstract:We propose a three-step solution methodology to increase the discrete set of Acoustic Far-Field pattern (FFP) measurements, available in a small range of observation angles (small aperture). The first two steps of the proposed procedure allow the extension of the data to an aperture larger than $\pi/2$. They use a regularized Newton algorithm where the {\it total variation} of the FFP is incorporated as a regularization term. The third step consists in applying the standard Tikhonov regularization technique to recover the {\it full} aperture of the FFP from the previously extended Field. Numerical results obtained using synthetic data illustrate the potential of the proposed procedure for reconstructing the full aperture of the FFP from data given in an aperture as small as backscattering measurements.
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On the solution of three-dimensional inverse obstacle Acoustic scattering problems by a regularized Newton method
Inverse Problems, 2002Co-Authors: Charbel Farhat, Radek Tezaur, Rabia DjellouliAbstract:We present a computational methodology for retrieving the shape of an impenetrable obstacle from the knowledge of some Acoustic Far-Field patterns. This methodology is based on the well known regularized Newton algorithm, but distinguishes itself from similar optimization procedures by (a) a frequency-aware multi-stage solution strategy, (b) a computationally efficient usage of the exact sensitivities of the Far-Field pattern to the specified shape parameters, and (c) a numerically scalable domain decomposition method for the fast solution of three-dimensional direct Acoustic scattering problems. We illustrate the salient features and highlight the performance characteristics of the proposed computational methodology with the solution on a parallel processor of various inverse mockup submarine problems.
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An Iterative Method for the Solution of Three-Dimensional Inverse Acoustic Scattering Problems
Noise Control and Acoustics, 2002Co-Authors: Charbel Farhat, Radek Tezaur, Rabia DjellouliAbstract:We present a computational methodology for retrieving the shape of an impenetrable obstacle from the knowledge of some Acoustic Far-Field patterns. This methodology is based on the well-known regularized Newton algorithm, but distinguishes itself from similar optimization procedures by (a) a frequency-aware multi-stage solution strategy, (b) a computationally efficient usage of the exact sensitivities of the Far-Field pattern to the specified shape parameters, and (c) a numerically scalable domain decomposition method for the fast solution of three-dimensional direct Acoustic scattering problems. We illustrate the salient features and highlight the performance characteristics of the proposed computational methodology with the solution on a parallel processor of various inverse mockup submarine problems.Copyright © 2002 by ASME
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On the solution of three‐dimensional inverse Acoustic scattering problems
Journal of the Acoustical Society of America, 2001Co-Authors: Charbel Farhat, Radek Tezaur, Rabia DjellouliAbstract:A computational methodology for retrieving the shape of an obstacle from the knowledge in a limited aperture of its Acoustic Far‐Field pattern is presented. This methodology, which features a reconstruction algorithm for the Far‐Field pattern, also distinguishes itself from existing iterative Newton‐type procedures by (a) the usage of exact Jacobian matrices for formulating the linearized problems rather than approximate ones (i.e., based on finite differences), (b) a fast numerical procedure for computing these Jacobian matrices, and (c) a fast and numerically scalable fictitious domain decomposition method for high‐frequency Acoustic scattering problems. The salient features of this computational methodology are illustrated with several submarine applications. [Work supported by ONR.]
Andrea V Bragas - One of the best experts on this subject based on the ideXlab platform.
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Acoustic Far Field hypersonic surface wave detection with single plasmonic nanoantennas
Physical Review Letters, 2018Co-Authors: Rodrigo Berte, Fabricio Della Picca, Martin Poblet, Yi Li, Emiliano Cortes, R V Craster, Stefan A Maier, Andrea V BragasAbstract:The optical properties of small metallic particles allow us to bridge the gap between the myriad of subdiffraction local phenomena and macroscopic optical elements. The optomechanical coupling between mechanical vibrations of Au nanoparticles and their optical response due to collective electronic oscillations leads to the emission and the detection of surface Acoustic waves (SAWs) by single metallic nanoantennas. We take two Au nanoparticles, one acting as a source and the other as a receptor of SAWs and, even though these antennas are separated by distances orders of magnitude larger than the characteristic subnanometric displacements of vibrations, we probe the frequency content, wave speed, and amplitude decay of SAWs originating from the damping of coherent mechanical modes of the source. Two-color pump-probe experiments and numerical methods reveal the characteristic Rayleigh wave behavior of emitted SAWs, and show that the SAW-induced optical modulation of the receptor antenna allows us to accurately probe the frequency of the source, even when the eigenmodes of source and receptor are detuned.
