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  • 1
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 38 (1995), S. 1149-1170 
    ISSN: 0029-5981
    Keywords: material design ; structural optimization ; multiple loads ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An extension of recent work1 on the simultaneous optimization of material and structure to address the design of structures under multiple loading conditions is presented. Material properties are represented in the most general form possible, namely, as elements of the unrestricted set of positive-semi-definite constitutive tensors of a linearly elastic continuum. Existence of solutions can be shown when the objective is a weighted average of compliances and a resource constraint measured as the 2-norm or the trace of the constitutive tensors is included. The optimized material properties can be derived analytically. The optimization of the layout of the material leads to a sizing problem of structural optimization involving a non-linear, non-smooth elasticity analysis. The computational solution of this problem is discussed and illustrated with examples.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 38 (1995), S. 3483-3495 
    ISSN: 0029-5981
    Keywords: discretized Green's functions ; multiple scattering ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Discretization of boundary integral equations leads to large full systems of algebraic equations, in practice. Partitioning is a method for solving such systems by breaking them down into smaller systems. It may be viewed merely as a technique from linear algebra. However, it is profitable to view it as arising directly from partitions of the boundary; these partitions could be natural (such as two separate boundaries) but they need not be. We investigate partitioning in the context of multiple scattering of acoustic waves by two sound-hard obstacles (the ideas extend to other physical situations). Specifically, we make a connection between partitioning and the use of the exact Green's function for a single obstacle in isolation. This suggests computing the action of this Green's function once-and-for-all, storing it (perhaps on a compact disc), and then using it to solve other problems in which the second obstacle is altered. One example of this approach is computing the stress distribution around a cavity of a standard-but-complicated shape inside a structure whose shape is varied. The theoretical foundation for these ideas is given, as well as a connection with the use of generalized Born series for multiple-scattering problems. Important distinctions between the partitioning/Green's function idea in this paper and seemingly similar ideas such as substructuring, multi-zoning, and domain decomposition are made.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 687-704 
    ISSN: 0029-5981
    Keywords: boundary element methods ; Cauchy principal-value integrals ; Hadamard finite-part integrals ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Hypersingular integrals are guaranteed to exist at a point x only if the density function f in the integrand satisfies certain conditions in a neighbourhood of x. It is well known that a sufficient condition is that f has a Hölder-continuous first derivative. This is a stringent condition, especially when it is incorporated into boundary-element methods for solving hypersingular integral equations. This paper is concerned with finding weaker conditions for the existence of one-dimensional Hadamard finite-part integrals: it is shown that it is sufficient for the even part of f (with respect to x) to have a Hölder-continuous first derivative - the odd part is allowed to be discontinuous. A similar condition is obtained for Cauchy principal-value integrals. These simple results have non-trivial consequences. They are applied to the calculation of the tangential derivative of a single-layer potential and to the normal derivative of a double-layer potential. Particular attention is paid to discontinuous densities and to discontinuous boundary conditions. Also, despite the weaker sufficient conditions, it is reaffirmed that, for hypersingular integral equations, collocation at a point x at the junction between two standard conforming boundary elements is not permissible, theoretically. Various modifications to the definition of finite-part integral are explored.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 42 (1998), S. 885-906 
    ISSN: 0029-5981
    Keywords: boundary elements ; Cauchy principal-value integrals ; Hadamard finite part integrals ; Hölder continuity ; relaxed regularization ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Three stages are involved in the formulation of a typical direct boundary element method: derivation of an integral representation; taking a Limit To the Boundary (LTB) so as to obtain an integral equation; and discretization. We examine the second and third stages, focussing on strategies that are intended to permit the relaxation of standard smoothness assumptions. Two such strategies are indicated. The first is the introduction of various apparent or ‘pseudo-LTBs’. The second is ‘relaxed regularization’, in which a regularized integral equation, derived rigorously under certain smoothness assumptions, is used when less smoothness is available. Both strategies are shown to be based on inconsistent reasoning. Nevertheless, reasons are offered for having some confidence in numerical results obtained with certain strategies. Our work is done in two physical contexts, namely two-dimensional potential theory (using functions of a complex variable) and three-dimensional elastostatics. © 1998 John Wiley & Sons, Ltd.
    Type of Medium: Electronic Resource
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