Identification of Incoherent Noise Sources

2001 ◽  
Author(s):  
S. T. Raveendra ◽  
S. Sureshkumar
Keyword(s):  
Boundary Element ◽  
Sound Pressure ◽  
Partial Coherence ◽  
Noise Sources ◽  
Reconstruction Procedure ◽  
Pressure Fields ◽  
Acoustical Holography ◽  
Nearfield Acoustical Holography ◽  
Source Geometry ◽  
Incoherent Noise

Abstract A Nearfield Acoustical Holography (NAH) technique that is applicable to the identification of multiple, incoherent noise sources from measured sound pressure fields are described. Initially, a partial coherence approach is adopted to decouple an incoherent acoustic field into a set of fully coherent, mutually incoherent partial fields. Subsequently, NAH is applied individually to each coherent partial field to reconstruct the corresponding source field. A boundary element based NAH reconstruction procedure is utilized so that the technique is valid for arbitrary source geometry. The process is validated by identifying the sources in a two-speaker system that was driven by independent signal generators.

scholarly journals Experimental noise source identification in a fuselage test environment based on nearfield acoustical holography

2021 ◽  
Author(s):  
S. Ungnad ◽  
D. Sachau ◽  
M. Wandel ◽  
C. Thomas
Keyword(s):  
Sound Pressure ◽  
Noise Exposure ◽  
Transmission Loss ◽  
Measurement Data ◽  
Sound Field ◽  
Sound Intensity ◽  
Measurement Procedure ◽  
Test Environment ◽  
Acoustical Holography ◽  
Nearfield Acoustical Holography

AbstractA major challenge in the subject of noise exposure in airplanes is to achieve a desired transmission loss of lightweight structures in the low-frequency range. To make use of appropriate noise reduction methods, identification of dominant acoustic sources is required. It is possible to determine noise sources by measuring the sound field quantity, sound pressure, as well as its gradient and calculating sound intensity by post-processing. Since such a measurement procedure entails a large amount of resources, alternatives need to be established. With nearfield acoustical holography in the 1980s, a method came into play which enabled engineers to inversely determine sources of sound by just measuring sound pressures at easily accessible locations in the hydrodynamic nearfield of sound-emitting structures. This article presents an application of nearfield acoustical holography in the aircraft fuselage model Acoustic Flight-Lab at the Center of Applied Aeronautical Research in Hamburg, Germany. The necessary sound pressure measurement takes one hour approximately and is carried out by a self-moving microphone frame. In result, one gets a complete picture of active sound intensity at cavity boundaries up to a frequency of 300 Hz. Results are compared to measurement data.

scholarly journals Dense U-Net for Limited Angle Tomography of Sound Pressure Fields

2021 ◽  
Vol 11 (10) ◽  
pp. 4570
Author(s):  
Oliver Rothkamm ◽  
Johannes Gürtler ◽  
Jürgen Czarske ◽  
Robert Kuschmierz
Keyword(s):  
Measurement Errors ◽  
Sound Pressure ◽  
Tomographic Reconstruction ◽  
Synthetic Data ◽  
Projection Data ◽  
Quantitative Measurements ◽  
Pressure Fields ◽  
The Neural Network ◽  
Bias Flow ◽  
3D Information

Tomographic reconstruction allows for the recovery of 3D information from 2D projection data. This commonly requires a full angular scan of the specimen. Angular restrictions that exist, especially in technical processes, result in reconstruction artifacts and unknown systematic measurement errors. We investigate the use of neural networks for extrapolating the missing projection data from holographic sound pressure measurements. A bias flow liner was studied for active sound dampening in aviation. We employed a dense U-Net trained on synthetic data and compared reconstructions of simulated and measured data with and without extrapolation. In both cases, the neural network based approach decreases the mean and maximum measurement deviations by a factor of two. These findings can enable quantitative measurements in other applications suffering from limited angular access as well.

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