Kenneth R. Podolak^*, Vihan A.W. Wickramasinghe, Gareth A. Mansfield, Alex M. Tuller

Sound & Vibration, Vol.55, No.3, pp. 235-240, 2021, DOI:10.32604/sv.2021.015008

Abstract Ernst Chladni is called the father of acoustics for his work, which includes investigating patterns formed by vibrating plates. Understanding these patterns helps research involving standing waves and other harmonic behaviors, including studies of single electron orbits in atoms. Our experiment vibrates circular plates which result in well-known patterns. Alternatively to traditional experiments that used sand or salt, we use magnetic materials, namely iron filings and nickel powder. We then manipulate the patterns by applying a localized external magnetic field to one of the rings that moves a segment of the magnetic material in that ring to the next inner… More >

Jie Wang, Fuhang Jiang, Wenchang Zhao, Haibo Chen^*

CMES-Computer Modeling in Engineering & Sciences, Vol.127, No.2, pp. 645-681, 2021, DOI:10.32604/cmes.2021.015894

Abstract A combined shape and topology optimization algorithm based on isogeometric boundary element method for 3D acoustics is developed in this study. The key treatment involves using adjoint variable method in shape sensitivity analysis with respect to non-uniform rational basis splines control points, and in topology sensitivity analysis with respect to the artificial densities of sound absorption material. OpenMP tool in Fortran code is adopted to improve the efficiency of analysis. To consider the features and efficiencies of the two types of optimization methods, this study adopts a combined iteration scheme for the optimization process to investigate the simultaneous change of… More >

Jiali Liu¹, Mengge Yu^{2, *}, Dawei Chen¹, Zhigang Yang³

FDMP-Fluid Dynamics & Materials Processing, Vol.16, No.1, pp. 21-30, 2020, DOI:10.32604/fdmp.2020.07658

Abstract In order to investigate how the aerodynamic drag and noise produced by the roof air conditioner of a high-speed train can be reduced, the related unsteady flow in the near-field was computed using the method of large eddy simulation. In this way, the aerodynamic source for noise generation has initially been determined. Then, the far-field aerodynamic noise has been computed in the framework of the Lighthill’s acoustics analogy theory. The propulsion height and flow-guide angle of the roof air conditioner were set as the design variables. According to the computational results, a lower propulsion height or flow-guide angle is beneficial… More >

Chunyu Ren, Zhihai Xiang, Zhangzhi Cen

The International Conference on Computational & Experimental Engineering and Sciences, Vol.16, No.4, pp. 121-122, 2011, DOI:10.3970/icces.2011.016.121

Abstract Recently, many interesting conceptual devices have been proposed to manipulate the propagation of acoustic waves at will. This is mostly achieved through acoustic metamaterials designed by the coordinate transformation method [1]. However, such materials are usually required to be anisotropic and inhomogeneous, which hampers their realization in practice.

In this talk, we are going to introduce conformal mapping based transformation acoustics for 2D cases [2]. In this way, the resultant metamaterial parameters are isotropic, which greatly facilitates their implementation. More >

D. Brunner¹, M. Junge¹, P. Rapp¹, M. Bebendorf², L. Gaul¹

CMES-Computer Modeling in Engineering & Sciences, Vol.58, No.2, pp. 131-160, 2010, DOI:10.3970/cmes.2010.058.131

Abstract The simulation of the hydroacoustic sound radiation of ship-like structures has an ever-growing importance due to legal regulations. Using the boundary element method, the overall dimension of the problem is reduced and only integrals over surfaces have to be considered. Additionally, the Sommerfeld radiation condition is automatically satisfied by proper choice of the fundamental solution. However, the resulting matrices are fully populated and the set-up time and memory consumption scale quadratically with respect to the degrees of freedom. Different fast boundary element methods have been introduced for the Helmholtz equation, resulting in a quasilinear complexity. Two of these methods are… More >

B. Pluymers¹, W. Desmet¹, D. Vandepitte¹, P. Sas¹

CMES-Computer Modeling in Engineering & Sciences, Vol.7, No.2, pp. 173-184, 2005, DOI:10.3970/cmes.2005.007.173

Abstract Conventional element based methods for modelling structural-acoustic radiation problems are limited to low-frequency applications. Recently, a novel prediction technique has been developed based on the indirect Trefftz approach. This new wave based method is computationally more efficient than the element based methods and, as a consequence, can tackle problems also at higher frequencies. This paper discusses the basic principles of the new method and illustrates its performance for the two-dimensional radiation analysis of a bass-reflex loudspeaker. More >

Zai You Yan^1,2, Fang Sen Cui², Kin Chew Hung²

CMES-Computer Modeling in Engineering & Sciences, Vol.7, No.1, pp. 97-106, 2005, DOI:10.3970/cmes.2005.007.097

Abstract Taking the normal derivative of solid angles on the surface into account, a modified Burton and Miller's formulation is derived. From which, a more reasonable expression of the hypersingular operator is obtained. To overcome the hypersingular integral, the regularization scheme developed recently is employed. Plane acoustic wave scattering from a rigid sphere is computed to show the correctness of the modified formulation with the regularization scheme. In the computation, eight-nodded isoparametric element is applied. More >

S. Callsen¹, O. von Estorff¹, O. Zaleski²

CMES-Computer Modeling in Engineering & Sciences, Vol.6, No.5, pp. 421-430, 2004, DOI:10.3970/cmes.2004.006.421

Abstract In standard boundary element formulations, singular integrals need to be solved as soon as the considered sources coincide with the collocation points at the boundary. Using a desingularized boundary element approach, the sources are distributed on a surface outside the acoustic domain which means that they are never located at the boundary. Consequently, all the resulting kernels are nonsingular which reduces the complexity of the numerical treatment of the boundary integral equations considerably. In the current contribution a desingularized formulation is given for both, the direct and the indirect boundary element method used to solve acoustical problems. Three basic examples… 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 inclusion of the dispersive properties… More >

L. Godinho¹, D. Soares Jr.²

CMES-Computer Modeling in Engineering & Sciences, Vol.87, No.4, pp. 327-354, 2012, DOI:10.3970/cmes.2012.087.327

Abstract In this work, a coupling strategy between the Method of Fundamental Solutions (MFS) and the Kansa's Method (KM) for the analysis of fluid-solid interaction problems in the frequency domain is proposed. In this approach, the MFS is used to model the acoustic fluid medium, while KM accounts for the elastodynamic solid medium. The coupling between the two methods is performed iteratively, with independent discretizations being used for the two methods, without requiring matching between the boundary nodes along the solid-fluid interface. Two application examples, with single and multiple solid sub-domains, are presented, illustrating the behavior of the proposed approach. More >