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  • Numerical Methods and Modeling  (170)
  • Wiley-Blackwell  (170)
  • EDP Sciences
  • Springer Science + Business Media
  • 1
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 139-151 
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The response of a p-i-n photodetector made from gallium arsenide to both steady-state and transient illumination has been modelled. Both an ensemble Monte-Carlo model and a drift-diffusion model were used, the latter with the choice of two different mobility models. The effects of high intensity steady-state illumination on the field and carrier distributions in the photodetector were calculated, and a comparative study of the models made. The transient response to pulsed illumination has also been calculated and the different results obtained from the models explained. The effect of high illumination on the response speed of the detector has been demonstrated. In addition, an expression for obtaining the photocurrent from the Monte-Carlo simulation, with much reduced statistical noise over the conventional estimate, has been derived and successfully tested. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 14 (1998), S. 731-749 
    ISSN: 1069-8299
    Keywords: superconvergence ; corrected conjoint polynomial ; weight functions ; element patch ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A superconvergent element patch based stress extraction strategy is proposed for general FE postprocessing and/or error estimation procedures in adaptive finite element analysis. Generalized weight functions are proposed for discrete least-square functionals, and a corrected conjoint polynomial fitting procedure is presented to ensure accurate stress extraction from the element domain once the primary level stress parameters have been evaluated. A numerical example is presented to fix the parameters of the weight functions. Several plane stress examples are solved using QUAD4 elements, and results are compared to those of the node patch based extraction method using the conventional conjoint polynomial method. It is shown that the proposed technique yields more accurate results with enhanced local convergence. Although the method may be applied to higher-order elements too, only QUAD4 elements are chosen for the present examples since the present secondary refitting strategy assumes superconvergent points only to be at element centroids. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 24 (1997), S. 1433-1448 
    ISSN: 0271-2091
    Keywords: flow simulation ; moving mechanical components ; fluid-structure interactions ; two-fluid interfaces ; 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: The application of a stabilized space-time finite element formulation to problems involving fluid-structure interactions and two-fluid interfaces is discussed. Two sample problems are presented and the method is validated by comparison with a test problem. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 10 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 25 (1997), S. 205-223 
    ISSN: 0271-2091
    Keywords: optimal control ; Navier-Stokes equations ; finite element method ; 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: We study the numerical solution of optimal control problems associated with two-dimensional viscous incompressible thermally convective flows. Although the techniques apply to more general settings, the presentation is confined to the objectives of minimizing the vorticity in the steady state case and tracking the velocity field in the non-stationary case with boundary temperature controls. In the steady state case we develop a systematic way to use the Lagrange multiplier rules to derive an optimality system of equations from which an optimal solution can be computed; finite element methods are used to find approximate solutions for the optimality system of equations. In the time-dependent case a piecewise-in-time optimal control approach is proposed and the fully discrete approximation algorithm for solving the piecewise optimal control problem is defined. Numerical results are presented for both the steady state and time-dependent optimal control problems. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 2 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 25 (1997), S. 599-610 
    ISSN: 0271-2091
    Keywords: axisymmetric nozzles ; two-dimensional nozzles ; Navier-Stokes solver ; internal flows ; 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: MacCormack's explicit time-marching scheme is used to solve the full Navier-Stokes unsteady, compressible equations for internal flows. The requirement of a very fine grid to capture shock as well as separated flows is circumvented by employing grid clustering. The numerical scheme is applied for axisymmetric as well as two-dimensional flows. Numerical predictions are compared with experimental data and the qualitative as well as the quantitative agreement is found to be quite satisfactory. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 18 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 24 (1997), S. 1417-1432 
    ISSN: 0271-2091
    Keywords: parallel computing methods ; compressible flows ; missile aerodynamics ; 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 flow simulation tool, developed by the authors at the Army HPC Research Center, for compressible flows governed by the Navier-Stokes equations is used to study missile aerodynamics at supersonic speeds, high angles of attack and for large Reynolds numbers. The goal of this study is the evaluation of this Navier-Stokes computational technique for the prediction of separated flow fields around high-length-to-diameter (L/D) bodies. In particular, this paper addresses two issues: (i) turbulence modelling with a finite element computational technique and (ii) efficient performance of the computational technique on two different multiprocessor mainframes, the Thinking Machines CM-5 and CRAY T3D. The paper first provides a discussion of the Navier-Stokes computational technique and the algorithm issues for achieving efficient performance on the CM-5 and T3D. Next, comparisons are shown between the computation and experiment for supersonic ramp flow to evaluate the suitability of the turbulence model. Following that, results of the computations for missile flow fields are shown for laminar and turbulent viscous effects. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 13 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 293-328 
    ISSN: 0029-5981
    Keywords: structural synthesis ; optimization ; topology optimization ; discrete variable optimization ; Mixed-Integer Non-linear Programming ; MINLP ; the Modified OA/ER algorithm ; MINLP strategy ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Part II describes the Mixed-Integer Non-linear Programming (MINLP) approach to structural synthesis where standard dimensions are added to simultaneous topology and parameter optimization. For this purpose, the mechanical superstructure has been enhanced and a special MINLP-MS model formulation for mechanical superstructures from Part I adapted to standard dimension alternatives, which give rise to complex MINLP problems that are difficult to solve. A Linked Two-Phase MINLP Strategy has been developed to efficiently accelerate the solutions of highly combinatorial MINLP problems, performed by the Modified OA/ER algorithm. In the first phase, the strategy uses only continuous dimensions making it easier to find an optimal topology. Based on the obtained global linear approximation of the superstructure, the proposed strategy in the second phase continues to perform an overall simultaneous optimization, where standard dimensions are added as additional discrete optimization alternatives. Thus, simultaneous topology, parameter and standard dimension optimization is now performed in the second phase. The synthesis of a multiple cantilever beam, introduced in Part I, was performed in accordance with the steps proposed by the MINLP optimization approach. This approach enables the obtaining of additional savings when compared to the one in Part I. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 1 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 507-532 
    ISSN: 0029-5981
    Keywords: adaptivity ; finite element method ; interior error estimates ; a posteriori error estimators ; hybrid interior error estimators ; pollution errors ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A hybrid error estimator using a priori interior region estimates in an a posteriori framework is presented for linear elastostatics problems in FEA. It is shown that local rates of convergence are augmented by this technique and global rates are not adversely affected. The effects of pollution for this estimator are explained and a pollution error estimator is derived using the concept of error loads. It is shown that pollution error estimation can improve the performance of both the conventional a posteriori and the hybrid techniques. A series of numerical results are presented which demonstrate the superior performance of the proposed method over previously published interior error estimation techniques. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 8 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. 829-846 
    ISSN: 0029-5981
    Keywords: fuzzy analysis ; linear equations ; numerical solution ; fuzzy systems ; search-based algorithms ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A computational methodology is presented for the solution of simultaneous linear equations that arise in the analysis of engineering systems involving fuzzy input parameters. In addition to a discussion on the existence of solution to the problem, the numerical solution to the fuzzy linear systems is defined and formalized. The framework of the proposed methodology consists of three major aspects involving (1) computerized selection of fuzziness, (2) implementation of fuzzy operations and (3) development and execution of a search-based algorithm. Two numerical examples are presented to illustrate the computational aspects of the proposed methodology. The present results are compared with those given by the combinatorial approach. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 6 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 42 (1998), S. 1343-1390 
    ISSN: 0029-5981
    Keywords: optimal design ; design sensitivity ; direct differentiation method ; non-isothermal ; metal forming ; finite element method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new approach to process optimal design in non-isothermal, non-steady-state metal forming is presented. In this approach, the optimal design problem is formulated on the basis of the integrated thermo-mechanical finite element process model so as to cover diverse objective functions and design variables, and a derivative-based approach is adopted for conducting optimization. The process model, the formulation for process optimal design, and the schemes for the evaluation of the design sensitivity, and an iterative procedure for optimization are described in detail. The validity of the schemes for the evaluation of the design sensitivity is examined by performing a series of numerical tests. The capability of the proposed approach to deal with diverse process parameters and objective functions is demonstrated through applications to some selected process design problems. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 23 Ill.
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