Installation: numerical investigation

Lummer, Markus

doi:10.1007/s13272-019-00382-5

Cited by 10 publications

(6 citation statements)

References 52 publications

(75 reference statements)

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“…For the purpose of analysing acoustic shielding effects at realistic aircraft configurations DLR's inhouse computer code FMCAS (Fast Multipole Code for Acoustic Shielding) [6,7] is used, which implements a Fast Multipole Boundary Element Method (FM-BEM) solving the Helmholtz equation for the pressure or the acoustic velocity potential. Some brief information about the theoretical background as well as the code will be given.…”

Section: Solution Of the Wave Equationmentioning

confidence: 99%

“…Then, the Fourier transformed wave equation (Helmholtz equation) can efficiently be solved by boundary element methods (BEM). Low Mach number potential mean flow fields can be taken into account by a so-called Taylor transformation [7,8], where the acoustic velocity potential is multiplied by an appropriate flow dependent phase factor. The BEM is obtained by discretization of the Kirchhoff integral solution of the Helmholtz equation.…”

Section: Solution Of the Wave Equationmentioning

confidence: 99%

See 1 more Smart Citation

Computation and Validation of Acoustic Shielding at Realistic Aircraft Configurations

Lummer

Mößner

Delfs

2018

2018 AIAA/CEAS Aeroacoustics Conference

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Acoustic shielding calculations were performed for a generic test object (NACA 0012) and two realistic aircraft configurations, an Unmanned Aerial Vehicle (UAV) and a Hybrid Wing Body (HWB), and compared with experimental data, where the monopole sound source was realized using laser pulses. The agreement between calculation and experiment is good. Due to wind tunnel size limits experimental data are often restricted to the acoustic nearfield and its usability for farfield shielding predictions must be assessed numerically. In the present paper, shielding patterns were defined and its evolution with increasing distance from the geometry was studied using a simple shifting and scaling procedure. For higher frequencies, a linear scaling of the patterns with increasing distance could be established.

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Section: Solution Of the Wave Equationmentioning

confidence: 99%

Section: Solution Of the Wave Equationmentioning

confidence: 99%

Computation and Validation of Acoustic Shielding at Realistic Aircraft Configurations

Lummer

Mößner

Delfs

2018

2018 AIAA/CEAS Aeroacoustics Conference

View full text Add to dashboard Cite

show abstract

“…The Green's functions are computed numerically with the Fast Multipole-Boundary Element Method (FM-BEM) code FMCAS [25,26]. FMCAS solves the Helmholtz equation using a boundary integral equation discretized on a triangulated surface.…”

Section: Simulation Setupmentioning

confidence: 99%

Beamforming for measurements under disturbed propagation conditions using numerically calculated Green’s functions

Lehmann

Ernst

Schneider

et al. 2022

Journal of Sound and Vibration

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Beamforming methods for sound source localization are usually based on free-field Green's functions to model the sound propagation between source and microphones. This assumption is known to be incorrect for many industrial applications and the beamforming results can suffer from this inconsistency regarding both, main lobe width and dynamic range. The aim of this paper is to investigate whether the use of numerically calculated Green's functions, which include the diffraction and reflection of the sound path between source and microphones, can improve the results of beamforming measurements.The current test cases of numerical and experimental investigations consist of a source placed in a short rectangular duct. The measurements are performed outside the duct in a semi-anechoic chamber. A typical example for this kind of installation is a fan with a heat exchanger.The Green's functions for this test case are calculated numerically using the boundary element method. These tailored Green's functions are used to calculate the corresponding beamforming steering vectors.Beamforming measurements are performed in this paper using a loudspeaker mounted in a disc as a reference source in the heat exchanger duct. The measurements are performed both with stationary and rotating disc. The stationary measurements are evaluated in the frequency domain. For the evaluation of the rotating measurements, a new beamforming method in the time domain is presented. This method also uses the stationary Green's functions, which were calculated numerically in the frequency domain. It is also shown how the weighting of these tailored Green's functions can be done for time domain beamforming.By means of different validation criteria it can be shown that the results with the numerical calculated Green's functions are improved compared to free field beamforming. This is true both in the stationary and rotating case.

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“…The Green's functions are computed numerically with the Fast Multipole-Boundary Element Method (FM-BEM) code FMCAS [24,25]. FMCAS solves the Helmholtz equation using a boundary integral equation discretized on a triangulated surface.…”

Section: Simulation Setupmentioning

confidence: 99%

Beamforming for measurements under disturbed propagation conditions using numerically calculated Green's functions

Lehmann¹,

Ernst²,

Schneider³

et al. 2020

Preprint

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Beamforming methods for sound source localization are usually based on free-field Green's functions to model the sound propagation between source and microphone. This assumption is known to be incorrect for many industrial applications and the beamforming results can suffer from this inconsistency regarding both, accuracy of source power estimation, and accuracy of source localisation. The aim of this paper is to investigate whether the use of numerically calculated Green's functions can improve the results of beamforming measurements.The current test cases of numerical and experimental investigations consists of sources placed in a short rectangular duct. The measurement is performed outside the duct in a semi-anechoic chamber. A typical example for this kind of installation is a fan with a heat exchanger.The Green's functions for this test case are calculated numerically using the boundary element method. These tailored Green's functions are used to calculate the corresponding beamforming steering vectors. The weighting of the Green's functions in the steering vectors has a decisive influence on the beamforming results. A generalization of the common steering vector formulations is given based on two scalars. It is shown that arbitrary differentiable Green's functions can be used to find the correct source position or source power level by using the appropriate steering vector formulations.Beamforming measurements are performed using a loudspeaker as a reference source at different positions in the heat exchanger duct. The measurements are evaluated in the frequency domain and by means of different validation criteria it can be shown that the results with the numerical calculated Green's function are improved compared to free field beamforming especially at low frequencies.

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Installation: numerical investigation

Cited by 10 publications

References 52 publications

Computation and Validation of Acoustic Shielding at Realistic Aircraft Configurations

Computation and Validation of Acoustic Shielding at Realistic Aircraft Configurations

Beamforming for measurements under disturbed propagation conditions using numerically calculated Green’s functions

Beamforming for measurements under disturbed propagation conditions using numerically calculated Green's functions

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