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  • Open Access

    ARTICLE

    A Dual BEM Genetic Algorithm Scheme for the Identification of Polarization Curves of Buried Slender Structures

    L.A. de Lacerda1, J. M. da Silva1

    CMES-Computer Modeling in Engineering & Sciences, Vol.14, No.3, pp. 153-160, 2006, DOI:10.3970/cmes.2006.014.153

    Abstract A two-dimensional boundary element formulation is presented and coupled to a genetic algorithm to identify polarization curves of buried slender structures. The dual boundary element method is implemented to model the cathodic protection of the metallic body and the genetic algorithm is employed to deal with the inverse problem of determining the non-linear polarization curve, which describes the relation between current density and electrochemical potential at the soil metal interface. In this work, this non-linear relation resulting from anodic and cathodic reactions is represented by a classical seven parameters expression. Stratified soil resistivity is modeled with a piece-wise homogeneous domain.… More >

  • Open Access

    ARTICLE

    Meshless Local Petrov-Galerkin (MLPG) Mixed Collocation Method For Elasticity Problems

    S. N. Atluri1, H. T. Liu2, Z. D. Han2

    CMES-Computer Modeling in Engineering & Sciences, Vol.14, No.3, pp. 141-152, 2006, DOI:10.3970/cmes.2006.014.141

    Abstract The Meshless Local Petrov-Galerkin (MLPG) mixed collocation method is proposed in this paper, for solving elasticity problems. In the present MLPG approach, the mixed scheme is applied to interpolate the displacements and stresses independently, as in the MLPG finite volume method. To improve the efficiency, the local weak form is established at the nodal points, for the stresses, by using the collocation method. The traction boundary conditions are also imposed into the stress equations directly. It becomes very simple and straightforward to impose various boundary conditions, especially for the high-order PDEs. Numerical examples show that the proposed MLPG mixed collocation… More >

  • Open Access

    ARTICLE

    Sequential Limit Analysis of Rotating Hollow Cylinders of Nonlinear Isotropic Hardening

    S.-Y. Leu1, J.T. Chen2

    CMES-Computer Modeling in Engineering & Sciences, Vol.14, No.2, pp. 129-140, 2006, DOI:10.3970/cmes.2006.014.129

    Abstract Plastic limit angular velocity of rotating hollow cylinders made of the von Mises materials with nonlinear isotropic hardening is investigated numerically and analytically in the paper. The paper applies sequential limit analysis to deal with the rotating problems involving hardening material property and weakening behavior resulted from the widening deformation. By sequential limit analysis, the paper treats the plasticity problems as a sequence of limit analysis problems stated in the upper bound formulation. Rigorous upper bounds are acquired iteratively through a computational optimization procedure with the angular velocity factor as the objective function. Especially, rigorous validation was conducted by numerical… More >

  • Open Access

    ARTICLE

    The Applications of Meshless Local Petrov-Galerkin (MLPG) Approaches in High-Speed Impact, Penetration and Perforation Problems

    Z. D. Han1, H. T. Liu1, A. M. Rajendran2, S. N. Atluri3

    CMES-Computer Modeling in Engineering & Sciences, Vol.14, No.2, pp. 119-128, 2006, DOI:10.3970/cmes.2006.014.119

    Abstract This paper presents the implementation of a three-dimensional dynamic code, for contact, impact, and penetration mechanics, based on the Meshless Local Petrov-Galerkin (MLPG) approach. In the current implementation, both velocities and velocity-gradients are interpolated independently, and their compatibility is enforced only at nodal points. As a result, the time consuming differentiations of the shape functions at all integration points is avoided, and therefore, the numerical process becomes more stable and efficient. The ability of the MLPG code for solving high-speed contact, impact and penetration problems with large deformations and rotations is demonstrated through several computational simulations, including the Taylor impact… More >

  • Open Access

    ARTICLE

    Multiscale Simulation Using Generalized Interpolation Material Point (GIMP) Method and Molecular Dynamics (MD)1

    J. Ma2, H. Lu2, B. Wang2, R. Hornung3, A. Wissink3, R. Komanduri2,*

    CMES-Computer Modeling in Engineering & Sciences, Vol.14, No.2, pp. 101-118, 2006, DOI:10.3970/cmes.2006.014.101

    Abstract A new method for multiscale simulation bridging two scales, namely, the continuum scale using the generalized interpolation material point (GIMP) method and the atomistic scale using the molecular dynamics (MD), is presented and verified in 2D. The atomistic strain from the molecular dynamics simulation is determined through interpolation of the displacement field into an Eulerian background grid using the same generalized interpolation functions as that in the GIMP method. The atomistic strain is consistent with that determined from the virial theorem for interior points but provides more accurate values at the boundary of the MD region and in the transition… More >

  • Open Access

    ARTICLE

    A lattice-based cell model for calculating thermal capacity and expansion of single wall carbon nanotubes

    Xianwu Ling1, S.N. Atluri

    CMES-Computer Modeling in Engineering & Sciences, Vol.14, No.2, pp. 91-100, 2006, DOI:10.3970/cmes.2006.014.091

    Abstract In this paper, a lattice-based cell model is proposed for single wall carbon nanotubes (SWNTs). The finite temperature effect is accounted for via the local harmonic approach. The equilibrium SWNT configurations are obtained by minimizing the Helmholtz free energy with respect to seven primary coordinate variables that are subjected to a chirality constraint. The calculated specific heats agree well with the experimental data, and at low temperature depend on the tube radii with small tubes having much lower values. Our calculated coefficients of thermal expansion (CTEs) are universally positive for all the radial, axial and circumferential directions, and increase with… More >

  • Open Access

    ARTICLE

    An Efficient Simultaneous Estimation of Temperature-Dependent Thermophysical Properties

    Chein-Shan Liu1

    CMES-Computer Modeling in Engineering & Sciences, Vol.14, No.2, pp. 77-90, 2006, DOI:10.3970/cmes.2006.014.077

    Abstract In this paper we derive the first-order and second-order one-step GPS applied to the estimation of thermophysical properties. Solving the resultant algebraic equations, which usually converges within ten iterations, it is not difficult to estimate the unknown temperature-dependent thermal conductivity and heat capacity simultaneously, if some supplemented data of measured temperature at a time T is provided. When the measured temperature in the conducting slab is contaminated by noise, our estimated results are also good. The new method does not require any prior information on the functional forms of thermal conductivity and heat capacity. Numerical examples are examined to show… More >

  • Open Access

    ARTICLE

    Parallel iterative procedures for a computational electromagnetic modeling based on a nonconforming mixed finite element method

    Taeyoung Ha1, Sangwon Seo2, Dongwoo Sheen3

    CMES-Computer Modeling in Engineering & Sciences, Vol.14, No.1, pp. 57-76, 2006, DOI:10.3970/cmes.2006.014.057

    Abstract We present nonoverlapping domain decomposition methods for the approximation of both electromagnetic fields in a three-dimensional bounded domain satisfying absorbing boundary conditions. A Seidel-type domain decomposition iterative method is introduced based on a hybridization of a nonconforming mixed finite element method. Convergence results for the numerical procedure are proved by introducing a suitable pseudo-energy. The spectral radius of the iterative procedure is estimated and a method for choosing an optimal matching parameter is given. A red-black Seidel-type method which is readily parallelizable is also introduced and analyzed. Numerical experiments confirm that the presented algorithms are faster than the conventional Jacobi-type… More >

  • Open Access

    ARTICLE

    A Parallel Multi-block Method for the Unsteady Vorticity-velocity Equations

    A. Grimaldi1, G. Pascazio2, M. Napolitano3

    CMES-Computer Modeling in Engineering & Sciences, Vol.14, No.1, pp. 45-56, 2006, DOI:10.3970/cmes.2006.014.045

    Abstract This paper provides a numerical method for solving two- and three-dimensional unsteady incompressible flows. The vorticity-velocity formulation of the Navier--Stokes equations is considered, employing the vorticity transport equation and a second-order Poisson equation for the velocity. Second-order-accurate centred finite differences on a staggered grid are used for the space discretization. The vorticity equation is discretized in time using a fully implicit three-level scheme. At each physical time level, a dual-time stepping technique is used to solve the coupled system of non linear algebraic equations by various efficient relaxation schemes. Steady flows are computed by dropping the physical time derivative and… More >

  • Open Access

    ARTICLE

    Optimal Tetrahedralization for Small Polyhedron: A New Local Transformation Strategy for 3-D Mesh Generation and Mesh Improvement

    Liu Jianfei1,2, Sun Shuli1,3, Wang Dachuan1

    CMES-Computer Modeling in Engineering & Sciences, Vol.14, No.1, pp. 31-44, 2006, DOI:10.3970/cmes.2006.014.031

    Abstract Local transformation, or topological re-connection, is one of effective procedures of mesh improvement method, especially in three-dimensional situation. The commonly used local transformations for tetrahedral mesh involve changing in mesh topology (i.e. node-element connectivity relationship) within a relatively small region composed of several tetrahedra, such as 2-3 flip, 3-2 flip, 2-2 flip, 4-4 flip, etc. Although these local transformations are easy to implement and effective in removing poorly-shaped tetrahedra, it is still possible to improve the quality of mesh further by expanding the space of transformation region. In this paper, the concept of optimal tetrahedralization for small polyhedron and corresponding… More >

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