S.-W. Na¹, L.F. Kallivokas²

CMES-Computer Modeling in Engineering & Sciences, Vol.35, No.1, pp. 73-90, 2008, DOI:10.3970/cmes.2008.035.073

Abstract We discuss simple numerical schemes, termed continuation schemes, for detecting the location and shape of a scatterer embedded in a host acoustic medium, when considering scant measurements of the scattered acoustic pressure in the vicinity (near- or far-field) of the obstacle. The detection is based on incomplete information, i.e., the measurement stations are distributed in the backscatter region and do not circumscribe the sought scatterer. We consider sound-hard scatterers, and use boundary integral equations for the underlying numerical scheme. We favor amplitude-based misfit functionals, and use frequency- and directionality-continuation schemes to resolve the scatterer's location More >

B. Chandrasekhar¹

CMES-Computer Modeling in Engineering & Sciences, Vol.33, No.3, pp. 243-268, 2008, DOI:10.3970/cmes.2008.033.243

Abstract In this work, a novel numerical technique, based on method of moments solution, is presented to solve the Combined layer formulation (CLF) to insure unique solution to the exterior acoustic scattering problem at all frequencies. A new set of basis functions, namely, Node based basis functions are used to represent the source distribution on the surface of rigid body and the same functions are used as testing functions as well. Combined layer formulation (CLF) is defined by linearly combining the Single layer formulation (SLF) and Double layer formulation (DLF) with complex coupling parameter. The matrix More >

B. Chrasekhar¹, Sadasiva. M. Rao²

CMES-Computer Modeling in Engineering & Sciences, Vol.33, No.2, pp. 199-214, 2008, DOI:10.3970/cmes.2008.033.199

Abstract In this work, the acoustic scattering problem based on double layer formulation is solved with a novel numerical technique using method of moment's solution. A new set of basis functions, namely, Edge based Adaptive Basis Functions (EABF) are defined in the method of moment's solution procedure. The geometry of the body is divided into triangular patches and basis functions are defined on the edges. Since the double layer formulation involves the evaluation of the hyper-singular integral, the edge based adaptive basis functions are used to make the solution faster. The matrix equations are derived for More >

A.I. Abreu¹, W.J. Mansur¹, D. Soares Jr^1,2, J.A.M. Carrer³

CMES-Computer Modeling in Engineering & Sciences, Vol.30, No.3, pp. 123-132, 2008, DOI:10.3970/cmes.2008.030.123

Abstract This paper is concerned with the numerical computation of space derivatives of a time-domain (TD-) Boundary Element Method (BEM) formulation for the analysis of scalar wave propagation problems. In the present formulation, the Convolution Quadrature Method (CQM) is adopted, i.e., the basic integral equation of the TD-BEM is numerically substituted by a quadrature formula, whose weights are computed using the Laplace transform of the fundamental solution and a linear multi-step method. In order to numerically compute space derivatives, the present work properly transforms the quadrature weights of the CQM-BEM, adopting the so-called Complex-Variable-Differentiation Method (CVDM). More >

D. Kourounis¹, L.N. Gergidis¹, A. Charalambopoulos¹

CMES-Computer Modeling in Engineering & Sciences, Vol.28, No.3, pp. 185-202, 2008, DOI:10.3970/cmes.2008.028.185

Abstract The sensitivity of analytical solutions of the direct acoustic scattering problem in prolate spheroidal geometry on the wavenumber and shape, is extensively investigated in this work. Using the well known Vekua transformation and the complete set of radiating "outwards'' eigensolutions of the Helmholtz equation, introduced in our previous work ([Charalambopoulos and Dassios(2002)], [Gergidis, Kourounis, Mavratzas, and Charalambopoulos (2007)]), the scattered field is expanded in terms of it, detouring so the standard spheroidal wave functions along with their inherent numerical deficiencies. An approach is employed for the determination of the expansion coefficients, which is optimal in… More >

T. Kar, M.L. Munjal¹

CMES-Computer Modeling in Engineering & Sciences, Vol.27, No.1&2, pp. 37-48, 2008, DOI:10.3970/cmes.2008.027.037

Abstract In the present work, a wedge structure made of absorbing panels has been analyzed by making use of the matrizant analysis with the help of the Boundary-Condition-Transfer (BCT) algorithm. The rectangular panel wedge, as it is called in this manuscript, is simple in geometry. The theoretical model, based on the plane wave acoustical coupling between multiple interacting ducts of variable cross sectional area, is applied to predict the pressure reflection coefficient of the present wedge configuration. Bulk reaction and hence wave propagation in the wedge material has been assumed in the proposed model. An asymptotic More >

Aleš Belšak¹, Jurij Prezelj²

Structural Durability & Health Monitoring, Vol.3, No.4, pp. 239-246, 2007, DOI:10.3970/sdhm.2007.003.239

Abstract Noise source vizualization represents an important tool in the field of technical acoustics. There are many different techniques of noise source visualization. Most of them, however, are intended for a specific noise source in a specific type of acoustic environment. Consequently, a certain visualization method can be used only for certain types of noise sources in a specific acoustic environment and in a restricted frequency area. This paper presents a new visualization method of complex noise sources on the basis of the use of an acoustic camera. A new algorithm has been used, which makes More >

J. António¹ , A. Tadeu¹, L. Godinho

The International Conference on Computational & Experimental Engineering and Sciences, Vol.3, No.3, pp. 157-162, 2007, DOI:10.3970/icces.2007.003.157

Abstract A frequency dependent formulation based on the Method of Fundamental Solutions (MFS) is used to simulate the sound wave propagation in a 3D acoustic space. This solution is approximated by a linear combination of fundamental solutions generated by virtual sources placed outside the domain in order to avoid singularities. The coating materials can be assumed to be absorbent. This is achieved in the model prescribing the impedance that is defined as a function of the absorption coefficient. The model is first verified against analytical solutions, provided by the image source technique for a parallelepiped room More >

G.V. Norton^*, J.C. Novarini^†

Molecular & Cellular Biomechanics, Vol.4, No.2, pp. 75-86, 2007, DOI:10.3970/mcb.2007.004.075

Abstract Ultrasonic imaging in medical applications involves propagation and scattering of acoustic waves within and by biological tissues that are intrinsically dispersive. Analytical approaches for modeling propagation and scattering in inhomogeneous media are difficult and often require extremely simplifying approximations in order to achieve a solution. To avoid such approximations, the direct numerical solution of the wave equation via the method of finite differences offers the most direct tool, which takes into account diffraction and refraction. It also allows for detailed modeling of the real anatomic structure and combination/layering of tissues. In all cases the correct… More >

Ya Yan Lu¹, Jianxin Zhu²

CMES-Computer Modeling in Engineering & Sciences, Vol.22, No.3, pp. 235-248, 2007, DOI:10.3970/cmes.2007.022.235

Abstract The perfectly matched layer (PML) is a widely used technique for truncating unbounded domains in numerical simulations of wave propagation problems. In this paper, the PML technique is used with a standard one-way model to solve a benchmark problem for underwater acoustics modeling. Accurate solutions are obtained with a PML layer with a thickness of only a quarter of the wavelength. The effect of a PML is analyzed in a perturbation analysis for waveguides. More >