Analysis Of Acoustic Radiation Research Articles

A three-dimensional sono-elastic method of ships in finite depth water with experimental validation

In order to conduct the comprehensive analysis of fluid-structure interactions, acoustic radiation and acoustic propagation, a three-dimensional sono-elastic method in the frequency domain is proposed in this paper. In this method, the three-dimensional hydroelasticity theory of floating structures is incorporated with the hydro-acoustic propagation theory by introducing frequency domain Green's functions appropriate to the ocean hydro-acoustic waveguide environment. The simple source boundary integral approach is adopted to obtain the sono-elastic response in the frequency domain. In order to deal with the irregular frequency problem in this approach, a Closed Virtual Impedance Surface (CVIS) method is put forward. At last, the sono-elastic method is validated by calculating the acoustic radiation of a floating elastic spherical shell and an experiment of the underwater acoustic radiation of two ring-stiffened cylindrical shell models.

Исследование электромагнитного и акустического излучения беспилотных летательных аппаратов в области низких частот

Исследование электромагнитного и акустического излучения беспилотных летательных аппаратов в области низких частот

Application of FEM/IBEM combined with PEM for acoustic radiation and sensitivity analysis of a randomly excited structure

The application of finite element method (FEM)/indirect boundary element method (IBEM) combined with pseudo excitation method (PEM) for acoustic radiation and sensitivity analysis of a random excited structure is investigated in this work. FEM and IBEM are used to calculate the dynamic and acoustic responses of a structure, respectively, and PEMis used to determine the stochastic acoustic responses for the acoustic radiation problems via transforming the random responses into the structuralacoustic harmonic ones. Using the PEM, acoustic radiation sensitivities of the structure are developed in the context of the transformed harmonic sensitivity analyses, and they are validated by comparingwith the results predicted using the finite difference method (FDM). Numerical examples are given to demonstrate the effectiveness of the methods proposed in this article.

Acoustic radiation analysis for a control domain based on Green's function

The acoustic radiation problem in the control domain with complex boundaries is investigated. Acoustic Green's function for acoustic point sources in the control domain was obtained by using conformal transformation theory. The expression of the acoustic radiation function for the control domain was derived. The acoustic radiation characteristics of a pulsating sphere in a quarter-infinite domain and numerical simulations were compared to illustrate the effects of the boundary characteristic, location, and radiation frequency on acoustic radiation power and acoustic directivity. This study provides a new method to analyze the acoustic radiation problem with complex boundaries.

Acoustic radiation analysis of topographically optimized structure using the direct boundary element method

A technique for controlling the noise radiation of folded plate structures is developed in this article. In this technique, the topography optimization method is introduced and an artificial parameter called [Formula: see text] is proposed as the objective function. The parameter [Formula: see text] is the upper bound of the surface velocity. The purpose of the optimization is to minimize [Formula: see text] while taking the surface velocities less than [Formula: see text] as the constraints. The infinite element method was applied to calculate the acoustic radiation pressure level. A numerical example of reducing the radiated noise of a folded plate structure using the proposed optimization technique is given. This article introduces the conjunction between the direct boundary element method and the infinite boundary method for acoustic radiation analysis of structures. The optimization results are quite encouraging and indicate that the design optimization technique developed in this article is pretty effective.

Acoustic radiation analysis based on essential solution of Green’s function

The principle objective of the paper is to study the acoustic radiation problem of the 3D space domain with control boundary. By using the conformal transformation theory, the Green’s function for acoustic point source in the control domain space is obtained. With it, the expression of acoustic radiation function of the control domain is formed. Discussion about the acoustic radiation of pulsating sphere in right-angle space is drawn in the end, including the acoustic radiation directivity effect by the boundary characteristics, acoustic radiation frequency and acoustic source location. Numerical results show that: for the lower frequency radiation, the infection of free surface is significant; for the high frequency radiation, the infection of location is significant on the contrary. The research provides a new method for boundary characteristic problem of the structural-acoustic acoustic.

Analysis of Acoustic Radiation of Submerged Damped Cylindrical Shell Combined with Thin Shell Theory and Elasticity Theory

The acoustic radiation of submerged damped cylindrical shell is investigated by combining with thin shell theory and elasticity theory. The classical integral transform technique is used to derive the solutions of coupled equations. Numerical computations show the correctness of the proposed method, and also conclude the influence of thickness of inner shell and coated layer to acoustic radiation. The conclusions may be valuable to the application of damping material on noise and vibration control of underwater pipes.

Analysis of acoustic radiation of circular piezoelectric plates with complex shapes in a flat rigid shield

Acoustic radiation from circular piezoelectric plates with complex shapes in a flat rigid shield is analyzed on the basis of a combined numerical-analytical method. It is shown that such piezoelectric plates of the first-type ceramics ((ЦТБC-3) provide a higher sensitivity in the transmission mode in comparison to a standard plate. In addition, piezoelectric plates of this type have a lower level of the side lobes of the directivity characteristic because of a more uniform distribution of the normal displacement on a flat radiating surface.

Near-field acoustic holography of acoustic radiation from structures

There are some difficulties for conventional Near-field Acoustic Holography (NAH) to analyze acoustic radiation from a large scale structure. To solve the problem, a method for NAH of large scale structures was presented. In the method, the normal velocities or sound pressure at a few points on the surface of the structure are measured by transducers, and that at other position on the surface of the structure are calculated by means of the radiation mode theory, then the radiated acoustic field may be analyzed by NAH. Since complex coupling terms no longer appear in the radiation modes, and only a few orders of modes are required to describe the acoustic field at low-to-mid frequencies, the accuracy of NAH analysis may be ensured. Moreover, according to the nesting property of radiation modes, the radiation modes at other frequencies can be replaced by that at maximum frequency, consequently the calculating procedure may be simplified and the calculating speed quicken. Finally, NAH analysis of acoustic radiation from large scale structures was illustrated using a 1m×1m simply supported steel plate. The results show that the radiated acoustic field can be reconstructed accurately under the circumstances of a few measurement points.

Numerical Analysis of Structure Acoustic Radiation Based on Wave Superposition Method

To overcome the non-uniqueness of solution at eigenfrequencies in the boundary integral equation method for structural acoustic radiation, wave superposition method is introduced to study the acoustics characteristics including acoustic field reconstruction and sound power calculation. The numerical method is implemented by using the acoustic field from a series of virtual sources which are collocated near the boundary surface to replace the acoustic field of the radiator, namely the principle of equivalent. How to collocate these equivalent sources is not indicated definitely. Once wave superposition method is applied to sound power calculation, it is necessary to evaluate its accuracy and impact factors. In the paper, the basic principle of wave superposition method is described, and then the integral equation is discretized. Also, the impact factors including element numbers, frequency limitation, and distance between virtual source and integral surface are analyzed in the process of calculate the acoustic radiation from the simply supported thin plate under concentrated force. The extensive measures of acoustic field at the thin plate are compared with results obtain using different numerical methods. The results show that: (a) The agreement between the results from the above numerical methods is excellent. The wave superposition method requires fewer elements and hence is faster. But the extensive numerical modeling suggests that as long as the volume velocity matching yields more than adequate accuracy. (b) The equivalent sources should be collocated inside the radiator. And the accuracy of a given Gauss integration formula will decrease as the source approaches the boundary surface. (c) The numerical method is applicable to the acoustic radiation of structure with complicated shape. (d) The method described in this paper can be used to perform effectively sound power calculation, and its application range can be extended on the basis of these conclusions.

Acoustic Simulation for the Gearing Engagement System

This paper concentrates on modeling the gear transmission system using a three-dimensional finite-element approach for the acoustic radiation analysis and control. The combination of dynamic analysis and vibration response calculation for the gear engagement system can contribute to evaluate acoustic radiation. A case study of for gear engagement system internally excited with gear mesh fluctuation is presented in this research. Acoustic radiation quantity investigation has been carried out by Virtual.Lab Acoustics software. It can be concluded that numerical simulation is very important during gear system design and noise control.

Analysis of acoustic radiation of circular piezoelectric plates enclosed in a flat rigid shield

Acoustic radiation of circular piezoelectric plates encased in a flat rigid shield is analyzed on the basis of a combined numerical-analytical method. It is shown that a plate made of piezoelectric ceramics of the second type with a higher dynamic coefficient of electromechanical coupling ensures a higher sensitivity in the transmission mode and a wider band of radiated frequencies. In addition, a plate of this type of piezoceramics has a lower level of side lobes of the directivity characteristic because of the more uniform normal-displacement distribution on its flat surface.

Borehole breakout evolution through acoustic emission location analysis

A series of thick-wall cylinder tests were performed on Bentheim sandstone to investigate the nucleation and propagation of borehole breakouts. Isotropic compression tests showed a significant decrease of the critical pressure required to nucleate breakouts with increasing borehole diameter. Advanced analysis of acoustic emission radiation and optical microstructures indicate a three stage process of breakout nucleation and growth. Relatively few acoustic emissions are observed during the elastic loading stage of the specimens. Once breakout nucleation has occurred at the borehole wall a drastic increase of acoustic emission activity is observed. A close spatial correspondence between located acoustic events and the breakout indicates formation of two symmetric cusp-shaped breakouts on opposite sides of the borehole. With increasing isotropic pressure the breakouts grow forming parallel-sided slots that are surrounded by a process zone revealing grain crushing and pore collapse as typically observed in experimentally produced compaction bands. We apply a simple fracture mechanics approach to predict the observed size effect of the critical pressure required to initiate breakouts.

군집행동 알고리즘을 이용한 판넬구조물의 방사소음저감에 관한 연구

In this paper, the author proposes a new method for acoustic radiation optimum design to minimize noise from a vibrating panel-like structure using a collaborative population-based search method called the particle swarm optimization algorithm(PSOA). The PSOA is a parallel evolutionary computation technique initially developed by Kennedy and Eberhart. The acoustic radiation optimization method based on the PSOA consists of two processes. In the first process, the acoustic radiation analysis by an integrated p-version FEM/BEM, which was developed by using MATLAB, is performed to evaluate the exterior acoustic radiation field of the panel. The second process is to search the optimum design variables: 1) Shape of Bezier curves and 2) Shape and position of ribs, to minimize noise from the panel using the PSOA. The optimization method based on the PSOA is compared to that based on the steady state genetic algorithm(SSGA) in order to verify the effectiveness and validity of the optimal solution by PSOA. Finally, it is shown that the optimal designs of the panel obtained by using the PSOA can achieve effective reductions in radiated sound power.

Midfrequency acoustic radiation analysis.

Boundary, finite, and infinite element methods have proven useful for solving the 3-D acoustic wave equation at low frequencies. For high frequency, localized formulations such as plane-wave and ray-tracing methods have been applied successfully. These methods are impractical, inaccurate, or both for treating midfrequency problems. Low-frequency methods make very large demands on computer processing while high-frequency methods account only for local effects. Full-spectrum methods have been developed which apply interpolation between the low and high ends of the frequency range to estimate the response in the midfrequency. While these methods have provided some insight to trends as one moves toward the midfrequency range, it is not well established that they can reliably solve problems well away from their established limits. For surfaces with features having dimensions close to midfrequency wavelengths, the physics is distinct from those that govern low and high frequencies, and is not merely a linear combination of the two. This presentation reports on research to develop a midfrequency analysis tool that directly addresses the midfrequency physics. The author will identify the challenges in a physics-based method, discuss an approach to address them, and report on simulations exercising the approach.

Decomposition of the Lighthill source term and analysis of acoustic radiation from mixing layers

Acoustic radiation from jet flow has been studied extensively by means of theoretical, experimental and numerical approaches over the past decades. Unfortunately, the mechanisms responsible for the production of sound by unbounded turbulence in subsonic flows remain unclear. For advancing our fundamental understanding of these mechanisms, the development of specific analysis tools is needed. Our study is based on a decomposition of the Lighthill source term, which is known to contain all the existing links between the fluid flow and the acoustic field. Ten subterms are written with the help of physically meaningful quantities such as velocity, density, dilatation and vorticity. The methodology is tested through the two‐dimensional compressible mixing layer flow in spatial development, at a Reynolds number of 400 and a Mach number of 0.25. A direct numerical simulation of the flow and its acoustic radiation is performed and used as a reference solution. Acoustic field generated by each source terms is predicted computing the integral solution of Lighthill's equation. Effect of the compressibility on the balance between the contribution of major subterms is of key importance. Directivity and convective effects are identified as well.

Transparent boundary condition for acoustic propagation in lined guide with mean flow

A finite element analysis of acoustic radiation in an infinite lined guide with mean flow is studied. In order to bound the domain, transparent boundary conditions are introduced by means of a Dirichlet to Neumann (DtN) operator based on a modal decomposition. This decomposition is easy to carry out in a hard‐walled guide. With absorbant lining, many difficulties occur even without mean flow. Since the eigenvalue problem is no longer selfadjoint, acoustic modes are not orthogonal with respect to the L2‐scalar product. However, an orthogonality relation exists which permits writing the modal decomposition. For a lined guide with uniform mean flow, modes are no longer orthogonal but a new scalar product allows us to define the DtN operator. We consider first the case of an infinite rectangular two‐dimensional lined guide with uniform mean flow in order to present the methodology. Then, some extensions will be presented: non‐uniform two‐dimensional geometries by calculating potential mean flow, and cylindrical axisymmetric three‐dimensional problems with uniform mean flow.

A novel modelling approach for sound propagation analysis in a multiple scatterer environment

In the past decades element‐based numerical modelling techniques have become a commonly used and invaluable tool for the analysis of acoustic radiation and scattering problems. However, the pollution errors associated with the element discretisation inherent to these methods increase with the increasing size of the problem domain. As a result, the applicability of these methods for radiation and scattering problems in which the source and receiver positions are located far from each other is often prohibited. The Wave Based Method (WBM) is an alternative deterministic prediction method for the analysis of steady‐state acoustic problems. It is based on an indirect Trefftz approach in that wave functions, which are exact solutions of the underlying differential equation, are used to describe the dynamic response. The enhanced computational efficiency of the WBM as compared to the element based methods has been shown already for the analysis of both finite and (semi‐)infinite acoustic problems. This paper introduces a novel WBM‐based methodology to model the acoustic source‐receiver transfer path functions in a multiple scatterer environment. A sound propagation validation case illustrates the potential of the proposed approach.

Optimization of Sound Pressure from Vibrating Laminated Rectangular Plates

Composite materials are frequently used in automobile and other moving vehicle structures. External and internal sounds sometimes cause unpleasant effects on the users and environment, and reduction of such sound is one of the key engineering problems. This study presents an acoustic radiation analysis from forced vibration of laminated rectangular plates and proposes a design approach to reduce the sound pressure from the plates. In the analysis the sound pressure at an arbitrary point over the plate is derived and is used as an object function in the optimization. A set of the fiber orientation angles is used as the design variable, and is optimized to minimize the sound pressure at the designated point. It is shown in numerical examples that the optimum design for sound pressure reduction is possible by the present approach.

736 床衝撃音のアクティブ遮音パネルシステム : 簡易モデルにおける音響放射パワーの解析

736 床衝撃音のアクティブ遮音パネルシステム : 簡易モデルにおける音響放射パワーの解析