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.

Simulation and experimental investigations for the patch near-field acoustical holography

2008 ◽  
Vol 222 (6) ◽  
pp. 945-953 ◽  
Author(s):  
C Yang ◽  
J Chen ◽  
J Q Li ◽  
W F Xue
Keyword(s):  
Fourier Transform ◽  
Sound Pressure ◽  
Near Field ◽  
Sound Field ◽  
Experimental Investigations ◽  
Regularization Methods ◽  
Aperture Size ◽  
Measurement Surface ◽  
Physical Necessity ◽  
Acoustical Holography

In order to reconstruct the sound field, the fast Fourier transform (FFT)-based near-field acoustical holography (NAH) demands that the measurement surface must extend to a region where the sound pressure decreases to a low level. This method is unfit for reconstructing the partial sound field in which the measurement aperture size is limited either by physical necessity or as a way of reducing the measurement cost. Statistically optimal NAH (SONAH) performs plane-to-plane calculations directly in the spatial domain, avoids all errors occurred in the FFT-based NAH and significantly increases the accuracy of the reconstruction of the partial sound field. In the present work, combined with the different regularization methods, SONAH is performed for reconstructing the partial sound field. The errors over the central and the peripheral sections of the reconstruction area are researched separately. Simulations and experiments show that SONAH is successful in reconstructing the partial sound field and the errors over the central sections are smaller than that over the peripheral sections. Experiments demonstrate that Tikhonov regularization in conjunction with Engl's criterion is suitable for the reconstruction of the practical sound field.

Sound Power Measurements in the Near Field of Transformers

2012 ◽  
Author(s):  
Michael Ertl ◽  
Hermann Landes
Keyword(s):  
Sound Pressure ◽  
Power Level ◽  
Near Field ◽  
Sound Field ◽  
Sound Intensity ◽  
Sound Level ◽  
Numerical Analyses ◽  
Sound Power ◽  
3D Fem ◽  
Sound Power Level

The international standard for the determination of the sound power level of transformers allows both the sound pressure and the sound intensity measurement method. Since the sound measurements take place in the reactive near-field next to the vibrating transformer tank walls, local disturbances influence the sound field characteristics at the measurement positions. As a result, the measured mean sound power level differs commonly up to 6dB at comparative measurements with both methods. Beyond these near field effects, the influence of an industrial measurement environment (background sound sources, hard-reflecting floor, semi-reverberant walls, and standing waves) to the sound pressure and sound intensity field characteristics is investigated. Hereby, numerical analyses based on 3D-FEM with consideration of the fluid-structure-coupling are used. The measured sound level differences can be re-produced and clarified in numerical analyses.

scholarly journals Sound field measurement and evaluation research for radiated acoustic fields in amplitude-variable sonochemical systems

2019 ◽  
Vol 52 (9-10) ◽  
pp. 1499-1507
Author(s):  
Yaguang Kong ◽  
Xuyang Tao ◽  
Zhangpin Chen
Keyword(s):  
Sound Pressure ◽  
Evaluation Research ◽  
Sound Field ◽  
Sound Intensity ◽  
Longitudinal Distribution ◽  
Average Intensity ◽  
Ultrasonic Frequency ◽  
Threshold Method ◽  
Cavitation Intensity ◽  
Filter Noise

The content of this study is based on the background of sonochemistry processes. First, the hydrophone is used to measure the sound pressure in the reactor (the experimental ultrasonic frequency range is 20 ± 1 kHz). The sound pressure signals are processed by threshold method, Kalman filter algorithm, and five-point three-time smoothing method. These methods eliminate singular items in the sound pressure signal, filter noise, smooth burrs, and so on. In addition, the sound intensity value is calculated by dual hydrophone method. In this paper, the average intensity of ultrasonic cavitation is studied. The radial distribution and longitudinal distribution of cavitation intensity of the same tool head are studied, and the effects of different power and different tool heads on cavitation intensity are also discussed in this paper. The experimental results show that the instrument designed in this paper can effectively measure the distribution of ultrasonic sound field and evaluate the performance of the tool head. We can infer from the experiments that the performance of the diamond tool head is better than that of the nine-section whip and the dumbbell tool head.

Acoustic Parts in Vehicle Sound Transmission Loss Test Method Research

2013 ◽  
Vol 380-384 ◽  
pp. 73-76
Author(s):  
Xiu Feng Wang ◽  
Jie Shi
Keyword(s):  
Sound Pressure ◽  
Transmission Loss ◽  
Sound Transmission ◽  
Sound Intensity ◽  
Pressure Level ◽  
Test Method ◽  
Intensity Level ◽  
Sound Transmission Loss ◽  
Passenger Compartment ◽  
Exterior Panel

The sound transmission loss (STL) of the acoustic parts in the vehicle was proposed to be computed using the Sound Pressure Level measured at the several locations inside the vehicle and the transmitted Sound Intensity Level on the vehicles exterior panel, which the acoustic treated vehicle passenger compartment is assumed as a small reverberation room. The necessary parts retrofits and acoustic treatments for Sound transmission loss tests of the acoustic parts in the vehicle were listed. The values of the appropriate number and positions of the loud speakers, microphones and sound intensity probes for Sound transmission loss of the acoustic parts in the vehicle were recommended. The in vehicle sound transmission loss tests of the acoustic parts such as the doors, carpets, wheel house etc. were achieved in the semi-anechoic room. Based on the door system, the correlation work has been done among the methods of the proposed in vehicle STL test, the reverberation - semi-anechoic chamber buck STL test and SEA analysis.

scholarly journals Sound Transmission Prediction of Sandwich Plates With Honeycomb and Foam Cores and an Emphatic Discussion on Radiation Terms

2021 ◽  
Vol 26 (1) ◽  
pp. 70-79
Author(s):  
Tong Zhang ◽  
Ludi Kang ◽  
Xin Li ◽  
Hongbo Zhang ◽  
Bilong Liu
Keyword(s):  
Sound Pressure ◽  
Transmission Loss ◽  
Measurement Data ◽  
Sound Radiation ◽  
Sound Transmission ◽  
Flexural Vibration ◽  
Summation Method ◽  
Theoretical Formula ◽  
Sandwich Plates ◽  
Modal Summation

When applying the modal summation method to the sound transmission loss (STL) prediction of various plates, the assumption of the blocked sound pressure, or alternatively speaking, ignoring sound radiation terms, has obvious simplicity and is sometimes used for the single-layered panels, rib-stiffened plates or heavily damped sandwich plates. For light-weighted sandwich plates with honeycomb and foam cores, however, this assumption is somewhat in doubt and worth examining. Based on sixth-order differential equations governing the flexural vibration of sandwich plates, the prediction formula of STL is derived by the modal summation approach. Theoretical predictions were validated by measurement data. Next, the theoretical formula of STL under the assumption of the blocked sound pressure was examined. The STL discrepancies of sandwich plates caused by sound radiation terms are illustrated. It was found that the STL discrepancies of sandwich plates were closely related to frequency, reached their peak value at the coincidence frequency region. The results indicate that the sound radiation terms, or the couplings between the radiated sound pressure and the plate response, should not be ignored for the prediction of STL for sandwich plates with honeycomb and foam cores.

Observations on the Systematic Deviations between Two Methods of Measuring Sound Transmission Loss

1996 ◽  
Vol 3 (1) ◽  
pp. 1-11 ◽  
Author(s):  
F. Jacobsen ◽  
H. Ding
Keyword(s):  
Measurement Errors ◽  
Transmission Loss ◽  
Sound Transmission ◽  
Sound Field ◽  
Sound Intensity ◽  
Field Method ◽  
Sound Transmission Loss ◽  
Careful Measurement ◽  
Linear Decay ◽  
Comparable Size

The paper examines and discusses possible explanations of the systematic deviations between conventional and intensity-based sound transmission loss measurements frequently reported in the literature. Both the conventional diffuse-field method and the method based on the sound intensity technique are subject to several systematic errors of comparable size. The sources of error include non-linear decay functions, the absorption of the partition itself, and intensity measurement errors, which are aggravated by the fact that the sound field conditions are usually fairly difficult. It is concluded that with very careful measurement procedures there are no systematic deviations.

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 3D Acoustic Field Intensity Probe Design and Measurements

2016 ◽  
Vol 41 (4) ◽  
pp. 701-711 ◽  
Author(s):  
Józef Kotus ◽  
Andrzej Czyżewski ◽  
Bożena Kostek
Keyword(s):  
Acoustic Field ◽  
Field Intensity ◽  
Research Study ◽  
Sound Field ◽  
Sound Intensity ◽  
Calibration Procedure ◽  
Measurement Procedure ◽  
Probe Design ◽  
Intensity Measurements ◽  
Probe Measurements

Abstract The aim of this paper is two-fold. First, some basic notions on acoustic field intensity and its measurement are shortly recalled. Then, the equipment and the measurement procedure used in the sound intensity in the performed research study are described. The second goal is to present details of the design of the engineered 3D intensity probe, as well as the algorithms developed and applied for that purpose. Results of the intensity probe measurements along with the calibration procedure are then contained and discussed. Comparison between the engineered and the reference commercial probe confirms that the designed construction is applicable to the sound field intensity measurements with a sufficient effectiveness.

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