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  • Open Access


    A Variational Formulation of a Stabilized Unsplit Convolutional Perfectly Matched Layer for The Isotropic or Anisotropic Seismic Wave Equation

    R. Martin1, D. Komatitsch1,2, S. D. Gedney3

    CMES-Computer Modeling in Engineering & Sciences, Vol.37, No.3, pp. 274-304, 2008, DOI:10.3970/cmes.2008.037.274

    Abstract In the context of the numerical simulation of seismic wave propagation, the perfectly matched layer (PML) absorbing boundary condition has proven to be efficient to absorb surface waves as well as body waves with non grazing incidence. But unfortunately the classical discrete PML generates spurious modes traveling and growing along the absorbing layers in the case of waves impinging the boundary at grazing incidence. This is significant in the case of thin mesh slices, or in the case of sources located close to the absorbing boundaries or receivers located at large offset. In previous work… More >

  • Open Access


    Scattering of flexural wave in thin plate with multiple holes by using the null-field integral equation approach

    Wei-Ming Lee1, Jeng-Tzong Chen2,3

    CMES-Computer Modeling in Engineering & Sciences, Vol.37, No.3, pp. 243-273, 2008, DOI:10.3970/cmes.2008.037.243

    Abstract In this paper, a semi-analytical approach is proposed to solve the scattering problem of flexural waves and to determine dynamic moment concentration factors (DMCFs) in an infinite thin plate with multiple circular holes. The null-field integral formulation is employed in conjunction with degenerate kernels, tensor transformation and Fourier series. In the proposed direct formulation, all dynamic kernels of plate are expanded into degenerate forms and further the rotated degenerate kernels have been derived for the general exterior problem. By uniformly collocating points on the real boundary, a linear algebraic system is constructed. The results of… More >

  • Open Access


    Stable MFS Solution to Singular Direct and Inverse Problems Associated with the Laplace Equation Subjected to Noisy Data

    LiviuMarin 1

    CMES-Computer Modeling in Engineering & Sciences, Vol.37, No.3, pp. 203-242, 2008, DOI:10.3970/cmes.2008.037.203

    Abstract In this paper, a meshless method for the stable solution of direct and inverse problems associated with the two-dimensional Laplace equation in the presence of boundary singularities and noisy boundary data is proposed. The governing equation and boundary conditions are discretized by the method of fundamental solutions (MFS), whilst the existence of the boundary singularity is taken into account by subtracting from the original MFS solution the corresponding singular solutions, as given by the asymptotic expansion of the solution near the singular point. However, even in the case when the boundary singularity is accounted for, More >

  • Open Access


    Topological Shape Optimization of Electromagnetic Problems using Level Set Method and Radial Basis Function

    Hokyung Shim1, Vinh Thuy Tran Ho1,,Semyung Wang1,2, Daniel A. Tortorelli3

    CMES-Computer Modeling in Engineering & Sciences, Vol.37, No.2, pp. 175-202, 2008, DOI:10.3970/cmes.2008.037.175

    Abstract This paper presents a topological shape optimization technique for electromagnetic problems using a level set method and radial basis functions. The proposed technique is a level set (LS) based optimization dealing with geometrical shape derivatives and topological design. The shape derivative is computed by an adjoint variable method to avoid numerous sensitivity evaluations. A level set model embedded into the scalar function of higher dimensions is propagated to represent the design boundary of a domain. The level set function interpolated into a fixed initial domain is evolved by using the Hamilton-Jacobi equation. The moving free… More >

  • Open Access


    Numerical Simulation of Graphite Properties Using X-ray Tomography and Fast Multipole Boundary Element Method

    H. T. Wang, G. Hall, S. Y. Yu, Z. H. Yao

    CMES-Computer Modeling in Engineering & Sciences, Vol.37, No.2, pp. 153-174, 2008, DOI:10.3970/cmes.2008.037.153

    Abstract Graphite materials are widely used in gas-cooled nuclear reactors as both moderators and reflectors. The graphite properties change when the microstructure damage occurs due to the in-core radiation and oxidation, thereby having a strong impact on the service life of graphite. In this paper, the X-ray tomography and the boundary element method (BEM) are introduced to the microstructure modeling and numerical simulations of both the mechanical and thermal property changes of nuclear graphite due to radiolytic oxidation. The model is established by the three-dimensional X-ray scan on the isotropic nuclear graphite Gilsocarbon, which is used… More >

  • Open Access


    Inverse Sensitivity Analysis of Singular Solutions of FRF matrix in Structural System Identification

    S. Venkatesha1, R. Rajender2, C. S. Manohar3

    CMES-Computer Modeling in Engineering & Sciences, Vol.37, No.2, pp. 113-152, 2008, DOI:10.3970/cmes.2008.037.113

    Abstract The problem of structural damage detection based on measured frequency response functions of the structure in its damaged and undamaged states is considered. A novel procedure that is based on inverse sensitivity of the singular solutions of the system FRF matrix is proposed. The treatment of possibly ill-conditioned set of equations via regularization scheme and questions on spatial incompleteness of measurements are considered. The application of the method in dealing with systems with repeated natural frequencies and (or) packets of closely spaced modes is demonstrated. The relationship between the proposed method and the methods based More >

  • Open Access


    A Study of Boundary Conditions in the Meshless Local Petrov-Galerkin (MLPG) Method for Electromagnetic Field Computations

    Meiling Zhao1, Yufeng Nie2

    CMES-Computer Modeling in Engineering & Sciences, Vol.37, No.2, pp. 97-112, 2008, DOI:10.3970/cmes.2008.037.097

    Abstract Meshless local Petrov-Galerkin (MLPG) method is successfully applied for electromagnetic field computations. The moving least square technique is used to interpolate the trial and test functions. More attention is paid to imposing the essential boundary conditions of electromagnetic equations. A new coupled meshless local Petrov-Galerkin and finite element (MLPG-FE) method is presented to enforce the essential boundary conditions. Unlike the conventional coupled technique, this approach can ensure the smooth blending of the potential variables as well as their derivatives in the transition region between the meshless and finite element domains. Then the boundary singular weight More >

  • Open Access


    Analytical Solution for Estimation of Temperature-Dependent Material Properties of Metals Using Modified Morse Potential

    Kuo-Ning Chiang1, Chan-Yen Chou2, Chung-Jung Wu2,Chao-Jen Huang2, Ming-Chih Yew2

    CMES-Computer Modeling in Engineering & Sciences, Vol.37, No.1, pp. 85-96, 2008, DOI:10.3970/cmes.2008.037.085

    Abstract An atomic-level analytical solution, together with a modified Morse potential, has been developed to estimate temperature-dependent thermal expansion coefficients (CTE) and elastic characteristics of bulk metals. In this study, inter-atomic forces are considered as a set of anharmonic oscillator networks which can be described by Morse potential, while the material properties can be defined by these inter-atomic forces; when temperature increases, the vibration of the anharmonic oscillator causes the phenomenon of temperature-dependent material properties. The results of analysis showed that the original Morse potential can give a reasonable prediction of the thermal expansion coefficients and More >

  • Open Access


    Steady-state Response of the Wave Propagation in a Magneto-Electro-Elastic Square Column

    Jianping Wei1, Xianyue Su1,2

    CMES-Computer Modeling in Engineering & Sciences, Vol.37, No.1, pp. 65-84, 2008, DOI:10.3970/cmes.2008.037.065

    Abstract The steady-state response of the wave propagation in a magneto-electro-elastic square column (MEESC) was studied. Some new characteristics were discovered: the guided waves are classified in the forms of the Quasi-P, Quasi-SV and Quasi-SH waves and ordered by the standing wave number, and the three type guided waves are corresponding to the extension, twist and shear modes of the body vibration; the induced electric and magnetic fields can be aroused by the propagating stress wave. We proposed a self-adjoint method, by which the guided-wave restriction condition was derived. After finding the corresponding orthogonal sets, the More >

  • Open Access


    Efficient Numerical Solution of the 3-D Semiconductor Poisson Equation for Monte Carlo Device Simulation

    Z. Aksamija1,2, U. Ravaioli3

    CMES-Computer Modeling in Engineering & Sciences, Vol.37, No.1, pp. 45-64, 2008, DOI:10.3970/cmes.2008.037.045

    Abstract Finding the scalar potential from the Poisson equation is a common, yet challenging problem in semiconductor modeling. One of the central problems in traditional mesh-based methods is the assignment of charge to the regular mesh imposed for the discretisation. In order to avoid this problem, we create a mesh-free algorithm which starts by assigning each mesh point to each particle present in the problem. This algorithm is based on a Fourier series expansion coupled with point matching. An efficient algorithm for repeatedly solving the Poisson problem for moving charge distributions is presented. We demonstate that More >

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