D. Soares Jr.¹, M. P. Vinagre²

CMES-Computer Modeling in Engineering & Sciences, Vol.25, No.1, pp. 1-8, 2008, DOI:10.3970/cmes.2008.025.001

Abstract This work presents an alternative procedure to compute time-domain electromagnetic fields. The Boundary Element Method is here adopted to numerically analyze wave propagation problems, computing just a so-called primary field (either the electric or the magnetic field can be selected as primary field; the complementary field is here named secondary field). The secondary field is obtained following Maxwell's equations, i.e., considering space derivatives of the primary field (computed by the Complex Variable Method) and time integration procedures. This methodology is more efficient and flexible since fewer systems of equations must be solved at each time-step. At the end of the… More >

Shamsh Tabrez, Mira Mitra, S. Gopalakrishnan¹

CMES-Computer Modeling in Engineering & Sciences, Vol.22, No.1, pp. 77-90, 2007, DOI:10.3970/cmes.2007.022.077

Abstract In this paper, wave propagation is studied in degraded composite beam due to moisture absorption. The obtained wave responses are then used for diagnosis of the degraded zone. Moisture absorption causes an irreversible hygrothermal deterioration of the material. The change in temperature and moisture absorption changes the mechanical properties. Thus this affects the structure in dimensional stability as well as material degradation due to reduction in mechanical properties. Here, the composite beam is modeled as Timoshenko beam using wavelet based spectral finite element (WSFE) method. The WSFE technique is especially tailored for simulation of wave propagation. It involves Daubechies scaling… More >

H.B. Chen¹, D.J. Fu¹, P.Q. Zhang¹

CMES-Computer Modeling in Engineering & Sciences, Vol.20, No.2, pp. 85-98, 2007, DOI:10.3970/cmes.2007.020.085

Abstract Researches today show that, both approximation and dispersion errors are encountered by classical Galerkin FEM solutions for Helmholtz equation governing the harmonic wave propagation, which leads to numerical inaccuracies especially for high wave number cases. In this paper, Local Boundary Integral Equation Method (LBIEM) is firstly implemented to solve the boundary value problem of Helmholtz equation. Then the regularized LBIE is proposed to overcome the singularities of the boundary integrals in the LBIEM. Owing to the advantages of the Moving Least Square Approximation (MLSA), the frequency-dependent basis functions modified by the harmonic wave propagation solutions are easily adopted instead of… More >

Ivan Christov¹, C.I. Christov², P.M. Jordan³

CMES-Computer Modeling in Engineering & Sciences, Vol.17, No.1, pp. 47-54, 2007, DOI:10.3970/cmes.2007.017.047

Abstract Two widely-used weakly-nonlinear models of acoustic wave propagation --- the inviscid Kuznetsov equation (IKE) and the Lighthill--Westervelt equation (LWE) --- are investigated numerically using a Godunov-type finite-difference scheme. A reformulation of the models as conservation laws is proposed, making it possible to use the numerical tools developed for the Euler equations to study the IKE and LWE, even after the time of shock-formation. It is shown that while the IKE is, without qualification, in very good agreement with the Euler equations, even near the time of shock formation, the same cannot generally be said for the LWE. More >

J. Bielak¹, O. Ghattas², E.-J. Kim³

CMES-Computer Modeling in Engineering & Sciences, Vol.10, No.2, pp. 99-112, 2005, DOI:10.3970/cmes.2005.010.099

Abstract We present a parallel octree-based finite element method for large-scale earthquake ground motion simulation in realistic basins. The octree representation combines the low memory per node and good cache performance of finite difference methods with the spatial adaptivity to local seismic wavelengths characteristic of unstructured finite element methods. Several tests are provided to verify the numerical performance of the method against Green's function solutions for homogeneous and piecewise homogeneous media, both with and without anelastic attenuation. A comparison is also provided against a finite difference code and an unstructured tetrahedral finite element code for a simulation of the 1994 Northridge… More >

S.G. Bardenhagen¹, J.E. Guilkey², K.M. Roessig³, J.U. Brackbill⁴, W.M. Witzel⁵, J.C.Foster⁶

CMES-Computer Modeling in Engineering & Sciences, Vol.2, No.4, pp. 509-522, 2001, DOI:10.3970/cmes.2001.002.509

Abstract Contact between deformable bodies is a difficult problem in the analysis of engineering systems. A new approach to contact has been implemented using the Material Point Method for solid mechanics, Bardenhagen, Brackbill, and Sulsky (2000a). Here two improvements to the algorithm are described. The first is to include the normal traction in the contact logic to more appropriately determine the free separation criterion. The second is to provide numerical stability by scaling the contact impulse when computational grid information is suspect, a condition which can be expected to occur occasionally as material bodies move through the computational grid. The modifications… More >

António Tadeu, Andreia Pereira, Luís Godinho¹

CMES-Computer Modeling in Engineering & Sciences, Vol.2, No.1, pp. 49-62, 2001, DOI:10.3970/cmes.2001.002.049

Abstract The Boundary Element Method (BEM) is used to compute the three-dimensional variation pressure field generated by a point pressure source inside a flat waveguide channel filled with a homogeneous fluid, in the presence of infinite rigid circular pipelines. The problem is solved in the frequency domain, using boundary elements to model the pipeline and an appropriate Green's function to simulate the free surface and the rigid floor of the channel. Because of the 2 ---1/2 ---D geometry of the problem, the separation of variables has been used, and the solution at each frequency is expressed in terms of waves with… More >

SamiaM.Said¹

CMC-Computers, Materials & Continua, Vol.52, No.1, pp. 1-24, 2016, DOI:10.3970/cmc.2016.052.001

Abstract The present paper is concerned with the wave propagation in a micropolar thermoelastic solid with distinct two temperatures under the effect of the magnetic field in the presence of the gravity field and an internal heat source. The formulation of the problem is applied in the context of the three-phase-lag model and Green-Naghdi theory without dissipation. The medium is a homogeneous isotropic thermoelastic in the half-space. The exact expressions of the considered variables are obtained by using normal mode analysis. Comparisons are made with the results in the two theories in the absence and presence of the magnetic field as… More >

B. Srivathsa¹, N. Ramakrishnan²

CMC-Computers, Materials & Continua, Vol.7, No.1, pp. 9-24, 2008, DOI:10.3970/cmc.2008.007.009

Abstract An analytical model, describing an explosive compaction process performed axially on a powder assembly of cylindrical geometry, is discussed. The powder is encapsulated in a cylindrical metal container surrounded by an explosive pad, which is detonated parallel to the major axis of the compact. The pressure generated in the powder is a function of the nature and the thickness of the explosive material as well as the powder characteristics. The model is based on the principle of shock propagation in powder aggregate and, the detonation as well as the refraction wave characteristics of the explosives. For the purpose of validation… More >

L. Godinho A. ¹, A. Tadeu¹, P. Amado Mendes¹

CMC-Computers, Materials & Continua, Vol.5, No.2, pp. 117-128, 2007, DOI:10.3970/cmc.2007.005.117

Abstract This paper presents a strategy for using the Method of Fundamental Solutions (MFS) to model the propagation of elastic waves around thin structures, like empty cracks or thin rigid screens, located in a homogeneous elastic medium. The authors make use of a simple approach for modeling these propagation conditions using the MFS together with decomposition of the domain into distinct regions. This approach makes it possible to avoid the undetermined system of equations that arises from imposing boundary conditions at both sides of a thin structure. The numerical implementation of the MFS is performed in the frequency domain, making use… More >