Sound field of normal modes in a stratified medium with a plane-parallel stream

1996 ◽  
Vol 38 (1-2) ◽  
pp. 81-84
Author(s):  
N. K. Vdovicheva ◽  
I. A. Shereshevsky
Keyword(s):  
Normal Modes ◽  
Sound Field ◽  
Stratified Medium ◽  
Plane Parallel ◽  
Parallel Stream

Optimization of the Sound Source Position for Shaping Acoustically-Structurally Coupled Cavities

2001 ◽  
Author(s):  
Arzu Gonenc Sorguc ◽  
Ichiro Hagiwara ◽  
Qinzhong Shi ◽  
Haldun Akagunduz
Keyword(s):  
Sound Source ◽  
Sequential Quadratic Programming ◽  
Normal Modes ◽  
Sound Field ◽  
Source Strength ◽  
Source Position ◽  
Sound Sources ◽  
Coupled Cavities ◽  
Structural Loading ◽  
Initial Starting

Abstract In this study, sound field inside acoustically-structurally coupled rectangular cavity excited by structural loading and sound sources is shaped by optimizing the position of the sound source. In the optimization, Most Probable Optimal Design (MPOD) based on Holographic Neural Network is employed and the results are compared with Sequential Quadratic Programming (SQP). It is shown that source position, rather than source strength, is more effective in acoustically controlled modes. The nodal positions for in-vacuo acoustical normal modes are good candidates for initial starting points.

scholarly journals Improving the Performance of Mode-Based Sound Propagation Models by Using Perturbation Formulae for Eigenvalues and Eigenfunctions

2021 ◽  
Vol 9 (9) ◽  
pp. 934
Author(s):  
Alena Zakharenko ◽  
Mikhail Trofimov ◽  
Pavel Petrov
Keyword(s):  
Sound Propagation ◽  
Underwater Acoustics ◽  
Computational Cost ◽  
Normal Modes ◽  
Sound Field ◽  
Field Calculation ◽  
Combined Model ◽  
Eigenvalues And Eigenfunctions ◽  
Propagation Models ◽  
Area Of Interest

Numerous sound propagation models in underwater acoustics are based on the representation of a sound field in the form of a decomposition over normal modes. In the framework of such models, the calculation of the field in a range-dependent waveguide (as well as in the case of 3D problems) requires the computation of normal modes for every point within the area of interest (that is, for each pair of horizontal coordinates x,y). This procedure is often responsible for the lion’s share of total computational cost of the field simulation. In this study, we present formulae for perturbation of eigenvalues and eigenfunctions of normal modes under the water depth variations in a shallow-water waveguide. These formulae can reduce the total number of mode computation instances required for a field calculation by a factor of 5–10. We also discuss how these formulae can be used in a combination with a wide-angle mode parabolic equation. The accuracy of such combined model is validated in a series of numerical examples.

scholarly journals Transverse horizontal spatial coherence in shallow water

2019 ◽  
Vol 283 ◽  
pp. 02001
Author(s):  
Bo Zhang ◽  
Fenghua Li ◽  
Zhenglin Li ◽  
Yanjun Zhang ◽  
Jingyan Wang
Keyword(s):  
Shallow Water ◽  
Acoustical Society ◽  
Coherence Length ◽  
Environmental Variability ◽  
Northern South China Sea ◽  
Spatial Coherence ◽  
Normal Modes ◽  
Sound Field ◽  
Acoustic Frequency ◽  
Field Correlation

Since the advent of large-aperture array processing, more and more attention has been paid to the sound field correlation, which has fundamental limit to the array gain of spatial coherent signal processing. The two dominant mechanisms that degrade the spatial coherence are normal modes (or multi-paths) interference and the environmental variability caused by several relevant oceanographic processes. In the present study, the transverse horizontal spatial coherence of explosive signals has been studied experimentally by a bottom-mounted array in the Northern South China Sea. And the effects of normal mode interference on the transverse horizontal spatial coherence have been analyzed numerically. Expressed in terms of wavelengths, the coherence length is shown to be larger than 170λ/185λ at acoustic frequency 508-640Hz/80-101Hz in shallow water. It is much greater than Carey’s shallow-water result 30λ estimated from array signal gain after assuming a specific functional form for the coherence (The Journal of the Acoustical Society of America 104, 831 (1998)). It, however, is consistent with Rouseff’s modelling result of a coherence length larger than 100λ (The Journal of the Acoustical Society of America 138, 2256 (2015)). Both Carey and Rouseff argue that the transverse horizontal spatial coherence length depends only weakly on range, in direct. In the present study, however, the coherence length is shown to depend highly on source-receiver range, and it fluctuates synchronously with the sound-field intensity while range varies.

scholarly journals Three-Dimensional Enclosures

2020 ◽  
pp. 621-672
Author(s):  
Steven L. Garrett
Keyword(s):  
Separation Of Variables ◽  
Three Dimensional ◽  
Normal Modes ◽  
Sound Field ◽  
Statistical Energy Analysis ◽  
Link Type ◽  
Wave Solutions ◽  
Different Shapes ◽  
The Individual ◽  
Degenerate Modes

Abstract In this chapter, solutions to the wave equation that satisfies the boundary conditions within three-dimensional enclosures of different shapes are derived. This treatment is very similar to the two-dimensional solutions for waves on a membrane of Chap. 10.1007/978-3-030-44787-8_6. Many of the concepts introduced in Sect. 10.1007/978-3-030-44787-8_6#Sec1 for rectangular membranes and Sect. 10.1007/978-3-030-44787-8_6#Sec5 for circular membranes are repeated here with only slight modifications. These concepts include separation of variables, normal modes, modal degeneracy, and density of modes, as well as adiabatic invariance and the splitting of degenerate modes by perturbations. Throughout this chapter, familiarity with the results of Chap. 10.1007/978-3-030-44787-8_6 will be assumed. The similarities between the standing-wave solutions within enclosures of different shapes are stressed. At high enough frequencies, where the individual modes overlap, statistical energy analysis will be introduced to describe the diffuse (reverberant) sound field.

Noise and Vibration Analysis of an Impact Forming Machine

1974 ◽  
Vol 96 (1) ◽  
pp. 233-240 ◽  
Author(s):  
A. E. M. Osman ◽  
M. M. Sadek ◽  
W. A. Knight
Keyword(s):  
Normal Modes ◽  
Sound Field ◽  
Input Energy ◽  
Constant Input ◽  
Noise And Vibration ◽  
Lumped Parameter ◽  
Modes Of Vibration ◽  
Impact Area ◽  
Noise Vibration ◽  
The Impact

The mechanism of noise and vibration generation in an impact forming machine is investigated using Fourier Transform methods. Noise, vibration, and load measurements have been correlated for a fixed input energy and the sound field around the machine investigated. The measured results are compared with those predicted by a lumped parameter computer model for determining the normal modes of vibration of the machine structure and the moving platen. It is found that the major proportion of the noise energy is generated in the impact area and the dominant source of noise is the free vibration of the structure. Further contributions are observed due to the excitation of the structure by the impact force. For a constant input energy the noise and vibration levels increase as the billet height for simple upsetting is reduced.

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