D. Soares Jr.^1,2, W.J. Mansur¹, D.L. Lima³

CMES-Computer Modeling in Engineering & Sciences, Vol.17, No.1, pp. 19-34, 2007, DOI:10.3970/cmes.2007.017.019

Abstract The present paper discussion is concerned with the development of robust and efficient algorithms to model propagation of interacting acoustic and elastic waves. The paper considers acoustic-elastic, acoustic-acoustic and elastic-elastic partitioned analyses of coupled systems; however, the focus here is the acoustic-elastic coupling considering finite elements and the acoustic-acoustic coupling considering finite elements and finite differences (other coupling procedures can be implemented analogously). One important feature of the algorithms presented is that they allow considering different time-steps for different sub-domains; so it is possible to substantially improve efficiency, accuracy and stability of the central difference time integration algorithm employed here.… More >

T. Fujimoto¹ and T. Nishioka¹

CMES-Computer Modeling in Engineering & Sciences, Vol.11, No.2, pp. 91-102, 2006, DOI:10.3970/cmes.2006.011.091

Abstract In the dynamic fracture of metallic material, some cracks propagate with the incidence of plastic deformation, and distinct plastic strain remains near the post-propagation area. In order to elucidate these dynamic nonlinear fracture processes, the moving finite element method is developed for nonlinear crack propagation. The T* integral is used as the parameter to estimate crack tip condition. First, the effect of material viscosity and crack propagation velocity have been discussed based on the numerical results for fracture under pure mode I high speed loading. Under mixed mode loading, numerical simulations for fracture path prediction are demonstrated for various crack… More >

George F. Carrier¹, Harry Yeh²

CMES-Computer Modeling in Engineering & Sciences, Vol.10, No.2, pp. 113-122, 2005, DOI:10.3970/cmes.2005.010.113

Abstract Sea-bottom displacements associated with seismic events are confined largely to strips of large but finite aspect ratio. We analyze waves that are initiated on such a strip and that propagate across a region of finite depth. We invoke the classical shallow-water-wave theory to obtain rather comprehensive descriptions of the non-dispersive aspects of the waves. The directivity of the energy radiation and the domain of pulse persistence are discussed. 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 >

L. G. Zhou¹, L. M. Hsiung², Hanchen Huang¹

CMES-Computer Modeling in Engineering & Sciences, Vol.6, No.3, pp. 245-252, 2004, DOI:10.3970/cmes.2004.006.245

Abstract Using molecular dynamics simulations, we study the deformation of polysynthetically twinned (PST) TiAl at room temperature. The simulation cell is pre-strained and thermodynamically relaxed to zero stress, so that no dislocations pre-exist in γ−α₂ interfaces. A uniaxial compression is then applied along one 1/6<112] direction. Our results show that interfacial dislocation pairs nucleate at the γ−α₂ interface under the compression. The glide and agglomeration of these dislocations lead to the nucleation of deformation twins from the interface. Based on our studies, twins may nucleate without pre-existing interfacial dislocations. Further we have monitored the propagation of the deformation twin, specifically its… More >

E. Ferretti¹

CMES-Computer Modeling in Engineering & Sciences, Vol.4, No.1, pp. 51-72, 2003, DOI:10.3970/cmes.2003.004.051

Abstract A numerical code for modeling crack propagation using the cell method is proposed. The Mohr-Coulomb criterion is used to compute the direction of crack propagation, and the new crack geometry is realized by an intra-element propagation technique. Automatic remeshing is then activated. Applications in Mode I and Mixed Mode are presented to illustrate the robustness of the implementation. More >

W. C. Liu, S. Q. Shi, C. H. Woo, Hanchen Huang¹

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 213-218, 2002, DOI:10.3970/cmes.2002.003.213

Abstract Using molecular dynamics method, we study the nucleation of dislocations and their subsequent propagation during the deposition of tungsten thin films under tension. Aiming to reveal the generic mechanisms of dislocation nucleation during the deposition of polycrystalline thin films, the case of tungsten on a substrate of the same material is considered. The substrate is under uniaxial tension along the [111] direction, with the thermodynamically favored (01^ˉˉ1) surface being horizontal. The simulation results indicate that the nucleation starts with a surface step, where a surface atom is pressed into the film along the [111^ˉˉ] direction. This process leads… 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 >

K. Nishimura¹, N. Miyazaki²

CMES-Computer Modeling in Engineering & Sciences, Vol.2, No.2, pp. 143-154, 2001, DOI:10.3970/cmes.2001.002.143

Abstract In this paper, we present a classical molecular dynamics algorithm and its implementation on Cray C90 and Fujitsu VPP700. The characters of this algorithm consist in a grid based on the block division of the atomic system and a neighbor list based on the use of a short range potential. The computer program is used for large scale simulations on a Cray C90 and a 32-node VPP700, and measurements of computational performance are reported. Then, we examine the interaction between a crack propagating and a tilt grain boundary under uniaxial tension using this computer program. The Johnson potential for α-Fe… 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 >