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Search Results (22)
  • Open Access

    ARTICLE

    Assessment and Computational Improvement of Thermal Lattice Boltzmann Models Based Benchmark Computations

    R. Djebali1, M. El Ganaoui2

    CMES-Computer Modeling in Engineering & Sciences, Vol.71, No.3, pp. 179-202, 2011, DOI:10.3970/cmes.2011.071.179

    Abstract The Lattice Boltzmann method (LBM) became, today, a powerful tool for simulating fluid flows. Its improvements for different applications and configurations offers more flexibility and results in several schemes such as in presence of external/internal forcing term. However, we look for the suitable model that gives correct informations, matches the hydrodynamic equations and preserves some features like coding easily, preserving computational cost, stability and accuracy. In the present work, high order incompressible models and equilibrium distribution functions for the advection-diffusion equations are analyzed. Boundary conditions, acceleration, stability and preconditioning with initial fields are underlined which… More >

  • Open Access

    ARTICLE

    A Simple OpenMP Scheme for Parallel Iteration Solvers in Finite Element Analysis

    S.H. Ju1

    CMES-Computer Modeling in Engineering & Sciences, Vol.64, No.1, pp. 91-109, 2010, DOI:10.3970/cmes.2010.064.091

    Abstract This study develops an OpenMP scheme to parallel the preconditioned conjugate gradient methods (PCG) in shared memory computers. The proposed method is simple and systematic, so a minor change in traditional PCG methods may produce effective parallelism. At first, the global stiffness matrix is re-numbered in order to produce a parallel three-line form matrix, and a subroutine only needs to be called once in the finite element analysis. Several basic OpenMP commands are then added into the traditional incomplete Cholesky factorization (ILU) and symmetric successive over-relaxation (SSOR) codes to make the procedures of matrix multiplication, More >

  • Open Access

    ABSTRACT

    Influence of thrust vectoring on radiative heat flux from plume flow

    S.N. Lee1, S.W. Baek1, K.M. Kim2, M.J. Yu3

    The International Conference on Computational & Experimental Engineering and Sciences, Vol.15, No.1, pp. 1-8, 2010, DOI:10.3970/icces.2010.015.001

    Abstract A finite volume method with nongray gases is applied to examine the radiative base heating due to plume which is changed by mechanical deflection. Numerical approaches are made to predict the effect of TVC. The radiative properties within plume flow are modeled with the weighted sum of 4 gray gases. The exhaust plume is considered as an absorbing and emitting medium with no scattering. Flow field is molded with using Preconditioned Navier-Stokes(N-S) algorithms with multi-block. The Geometric Conservation Law(GCL) is considered to compute the nozzle moving mechanism. The radiative base heating is changed by the More >

  • Open Access

    ABSTRACT

    A simple and effective preconditioner for integrated-RBF-based Cartesian-grid schemes

    N. Mai-Duy1, T. Tran-Cong1

    The International Conference on Computational & Experimental Engineering and Sciences, Vol.14, No.2, pp. 51-56, 2010, DOI:10.3970/icces.2010.014.051

    Abstract This paper presents a preconditioning scheme to improve the condition number of integrated radial-basis-function (RBF) matrices in solving large-scale 2D elliptic problems. The problem domain is discretised using a Cartesian grid, over which integrated RBF networks are employed to represent the field variable. The present preconditioner is constructed from 1D integrated RBF networks along grid lines. Test problems defined on rectangular and non-rectangular domains are employed to study the performance of the scheme. More >

  • Open Access

    ARTICLE

    A Preconditioned JFNK Algorithm Applied to Unsteady Incompressible Flow and Fluid Structure Interaction Problems

    Peter Lucas1, Alexander H. van Zuijlen1, Hester Bijl1

    CMES-Computer Modeling in Engineering & Sciences, Vol.59, No.1, pp. 79-106, 2010, DOI:10.3970/cmes.2010.059.079

    Abstract Despite the advances in computer power and numerical algorithms over the last decades, solutions to unsteady flow problems remain computing time intensive.
    In previous work [Lucas, P.,Bijl, H., and Zuijlen, A.H. van(2010)], we have shown that a Jacobian-free Newton-Krylov (JFNK) algorithm, preconditioned with an approximate factorization of the Jacobian which approximately matches the target residual operator, enables a speed up of a factor of 10 compared to nonlinear multigrid (NMG) for two-dimensional, large Reynolds number, unsteady flow computations. Furthermore, in [Lucas, P., Zuijlen, A.H. van, and Bijl, H. (2010)] we show that this algorithm also greatly… More >

  • Open Access

    ABSTRACT

    Preconditioners for finite element consolidation

    G. Gambolati1, M. Ferronato1, C. Janna1

    The International Conference on Computational & Experimental Engineering and Sciences, Vol.9, No.2, pp. 99-106, 2009, DOI:10.3970/icces.2009.009.099

    Abstract The Finite Element (FE) solution to consolidation equations in large geological settings raises a few numerical issues depending on the actual process addressed by the analysis. There are two basic problems where the solver efficiency plays a crucial role: 1- fully coupled consolidation, and 2- non-linear faulted (uncoupled) consolidation. Using a proper nodal numbering the FE matrices exhibit a block (or multilevel) structure. Krylov subspace solvers are attracting a growing attention, provided that a relatively inexpensive and effective preconditioner is available. For both problems possible preconditioners include the Diagonal Scaling (DS), the Incomplete Triangular Factorization More >

  • Open Access

    ARTICLE

    An Efficient Parallel MLPG Method for Poroelastic Models

    Luca Bergamaschi1,2, ,Ángeles Martínez2, Giorgio Pini2

    CMES-Computer Modeling in Engineering & Sciences, Vol.49, No.3, pp. 191-216, 2009, DOI:10.3970/cmes.2009.049.191

    Abstract A meshless model, based on the Meshless Local Petrov-Galerkin (MLPG) approach, is developed and implemented in parallel for the solution of axi-symmetric poroelastic problems. The parallel code is based on a concurrent construction of the stiffness matrix by the processors and on a parallel preconditioned iterative method of Krylov type for the solution of the resulting linear system. The performance of the code is investigated on a realistic application concerning the prediction of land subsidence above a deep compacting reservoir. The overall code is shown to obtain a very high parallel efficiency (larger than 78% More >

  • Open Access

    ARTICLE

    Preconditioned Conjugate Gradient Method Enhanced by Deflation of Rigid Body Modes Applied to Composite Materials

    T.B Jönsthövel1, M.B. van Gijzen2, C.Vuik2, C. Kasbergen1, A. Scarpas1

    CMES-Computer Modeling in Engineering & Sciences, Vol.47, No.2, pp. 97-118, 2009, DOI:10.3970/cmes.2009.047.097

    Abstract The introduction of computed x-ray tomography allows for the construction of high quality, material-per-element based 3D meshes in the field of structural mechanics. The use of these meshes enables a shift from meso to micro scale analysis of composite materials like cement concrete, rocks and asphalt concrete. Unfortunately, because of the extremely long execution time, memory and storage space demands, the majority of commercially available finite element packages are not capable of handling efficiently the most computationally demanding operation of the finite element solution process, that is, the inversion of the structural stiffness matrix. To More >

  • Open Access

    ARTICLE

    Fast Parallel Finite Element Approximate Inverses

    G.A. Gravvanis, K.M. Giannoutakis1

    CMES-Computer Modeling in Engineering & Sciences, Vol.32, No.1, pp. 35-44, 2008, DOI:10.3970/cmes.2008.032.035

    Abstract A new parallel normalized optimized approximate inverse algorithm, based on the concept of the ``fish bone'' computational approach with cyclic distribution of the processors satisfying an antidiagonal data dependency, for computing classes of explicit approximate inverses, is introduced for symmetric multiprocessor systems. The parallel normalized explicit approximate inverses are used in conjunction with parallel normalized explicit preconditioned conjugate gradient square schemes, for the efficient solution of finite element sparse linear systems. The parallel design and implementation issues of the new proposed algorithms are discussed and the parallel performance is presented, using OpenMP. More >

  • Open Access

    ABSTRACT

    H-matrix preconditioners for saddle-point systems from meshfree discretization 1

    Suely Oliveira2, Fang Yang2

    The International Conference on Computational & Experimental Engineering and Sciences, Vol.3, No.2, pp. 113-120, 2007, DOI:10.3970/icces.2007.003.113

    Abstract In this paper we describe and compare preconditioners for saddle-point systems obtained from meshfree discretizations, using the concepts of hierarchical (or H-)matrices. Previous work by the authors using this approach did not use H-matrix techniques throughout, as is done here. Comparison shows the method described here to be better than the author's previous method, an AMG method adapted to saddle point systems, and conventional iterative methods such as JOR. More >

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