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  • 1
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 27 (1998), S. 207-227 
    ISSN: 0271-2091
    Keywords: directional solidification ; multicomponent alloys ; dendritic monocrystals ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A finite element model of dendritic solidification of multicomponent alloys is presented that includes solutal convection and is an extension of a previously developed model for solidification of binary alloys. The model is applied to simulation of the solidification of ternary and quaternary Ni-based alloys. The role of solutal convection in the macrosegregation and the formation of freckles is analysed. Calculations show the effects of geometry and material properties on the convection patterns and the attendant segregation. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 20 (1995), S. 1163-1178 
    ISSN: 0271-2091
    Keywords: electrolyte flow ; finite element method ; non-linear ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Electrical double-layer effects are unimportant in flows through porous media except when the Debye length k-1 is comparable in magnitude with the pore radius a. Under these conditions the equations governing the flow of electrolyte are those of Stokes, Nernst-Planck and Poisson. These equations are non-linear and require numerical solution. The finite element method provides a useful basis for solution and various algorithms are investigated. The numerical stability and errors of each scheme are analysed together with the development of an appropriate finite element mesh. The electro-osmotic flow of a typical electrolyte (barium chloride) through a uniformly charged cylindrical membrane pore is investigated and the ion fluxes are post-computed from the numerical solutions. The ion flux is shown to be strongly dependent on both zeta potential and pore radius, ka, indicating the effects of overlapping electrical double layers.
    Additional Material: 7 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 40 (1997), S. 887-903 
    ISSN: 0029-5981
    Keywords: multigrid ; adaptive agglomeration ; additive correction ; anisotropic grids ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the computational simulation of fluid flow and scalar transport, multigrid iterative solution techniques often fail or stall when the discrete linearized equations have strongly anisotropic coefficients. In the present work, an adaptive agglomeration algorithm for forming coarse grids is presented that allows multigrid techniques to work efficiently for equation sets with anisotropic coefficients. The adaptive agglomeration is defined by two rules and several guidelines that follow from a physical interpretation of the performance of iterative solvers like Gauss-Seidel. The effectiveness of the adaptive agglomeration algorithm is demonstrated for a wide range of test cases. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 10 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 479-492 
    ISSN: 0029-5981
    Keywords: boundary element method (BEM) ; singular value decomposition (SVD) ; L-curve method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This study investigates the numerical solution of the Laplace and biharmonic equations subjected to noisy boundary data. Since both equations are linear, they are numerically discretized using the Boundary Element Method (BEM), which does not use any solution domain discretization, to reduce the problem to solving a system of linear algebraic equations for the unspecified boundary values. It is shown that when noisy, lower-order derivatives are prescribed on the boundary, then a direct approach, e.g. Gaussian elimination, for solving the resulting discretized system of linear equations produces an unstable, i.e. unbounded and highly oscillatory, numerical solution for the unspecified higher-order boundary derivatives data. In order to overcome this difficulty, and produce a stable solution of the resulting system of linear equations, the singular value decomposition approach (SVD), truncated at an optimal level given by the L-curve method, is employed. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 8 (1995), S. 341-356 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A novel transmission-line model for the minority carrier transport through quasi-neutral arbitrarily doped layers is proposed. Based on detailed drift-diffusion equations, the novel TLEC includes the inductance that represents the influence of the relaxation-time term. Coupled with a object-orientated hybrid circuit simulator, the novel transmission-line model is implemented for the transient analysis of minority carrier transport. A substantial longer storage time of the minority carrier transient current at the collector end of ultra-narrow base is predicted owing to inclusion of the relaxation-time term.
    Additional Material: 10 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 13 (1997), S. 47-49 
    ISSN: 1069-8299
    Keywords: nonlinear structural analysis ; arc-length algorithm ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper, we have proved in theory that the sign of the current stiffness matrix provides a correct indicator for determining the sign of the loading parameter in the arc-length algorithm before the first bifurcation point is encountered, but may not be the case thereafter. © 1997 John Wiley & Sons, Ltd.
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1761-1774 
    ISSN: 0029-5981
    Keywords: optimization ; algorithms ; structural ; design ; comparative ; evaluation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Non-linear programming algorithms play an important role in structural design optimization. Fortunately, several algorithms with computer codes are available. At NASA Lewis Research Centre, a project was initiated to assess the performance of eight different optimizers through the development of a computer code CometBoards. This paper summarizes the conclusions of that research. CometBoards was employed to solve sets of small, medium and large structural problems, using the eight different optimizers on a Cray-YMP8E/8128 computer. The reliability and efficiency of the optimizers were determined from the performance of these problems. For small problems, the performance of most of the optimizers could be considered adequate. For large problems, however, three optimizers (two sequential quadratic programming routines, DNCONG of IMSL and SQP of IDESIGN, along with Sequential Unconstrained Minimizations Technique SUMT) outperformed others. At optimum, most optimizers captured an identical number of active displacement and frequency constraints but the number of active stress constraints differed among the optimizers. This discrepancy can be attributed to singularity conditions in the optimization and the alleviation of this discrepancy can improve the efficiency of optimizers.
    Additional Material: 5 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1219-1235 
    ISSN: 0029-5981
    Keywords: plasticity ; numerical integration algorithms ; consistent linearization ; finite elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a consistent algorithm, which combines the advantages of the exact time integration of Prandtl-Reuss elastoplastic models and the quadratic asymptotic convergence of Newton-Raphson iteration strategies. The consistent modulus is evaluated by a full linearization of the exact stress update procedure. Numerical tests for a thin wall tube subjected to combined loads of tension and torsion are performed to illustrate the accuracy and efficiency of the consistently linearized exact stress update algorithm described in the paper. For comparison purpose numerical results of the radial return method are also given.
    Additional Material: 6 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 42 (1998), S. 1441-1462 
    ISSN: 0029-5981
    Keywords: GMRES ; Galerkin multi-grid ; variable preconditioning scheme ; conjugate gradient method ; large-scale elasto-plastic problem ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A combination of both GMRES and multi-grid (MG) methods is presented in this paper for solving large-scale two- and three-dimensional elasto-plastic problems, in which each MG iteration cycle serves as the preconditioning step for the GMRES procedure. A particular multi-grid approach, termed the Galerkin multi-grid scheme, is considered and the main effort is devoted to the implementation aspects of the proposed algorithm. Numerical examples, characterised by large-scale (up to 82145 DOF), strong non-linearity (nearly plastic limit state, necking and localization) and severe ill-conditioned states (presence of loading limit points), and also involving symmetric and unsymmetric as well as SPD and indefinite system matrices, are provided. The numerical results illustrate that the proposed method exhibits a remarkable performance in terms of efficiency and robustness in all circumstances. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 825-843 
    ISSN: 0363-9061
    Keywords: fracture modelling ; granular materials ; numerical modelling ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper describes the computer algorithms used in a numerical simulation of the compression of an aggregate of crushable grains. It has been used in a model for the evolution of a granular medium under one-dimensional compression, in which the probability of fracture for individual particles is a function of applied stress, particle-size and co-ordination number. The information relating to the particles is represented in a compact way on the computer which allows the number of particles produced to become sufficiently large for satisfactory comparisons to be made with experimental data and which allows information, such as the positions and sizes of the particles, to be easily extracted. An algorithm based on the representation is used to locate neighbouring particles in a way which does not deteriorate unacceptably in terms of speed as the number of particles increases. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 13 Ill.
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