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  • 1
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 13 (1997), S. 83-94 
    ISSN: 1069-8299
    Keywords: boundary elements ; dual reciprocity ; body forces ; approximation functions ; elasticity ; hybrid functions ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The dual reciprocity boundary element method traditionally uses the linear radial basis function r for interpolation. Recently, however, the use of the r function has been questioned both in relation to accuracy and in relation to the number and position of internal nodes required to obtain satisfactory solutions. Much research has been done in an attempt to fix criteria for choosing which approximation function should be used. One of the alternatives recently suggested is the augmented thin plate spline function, which consists of a thin plate spline function, r2 log(r), augmented with the first three terms of a Pascal triangle expansion. In this paper families of similar functions are obtained by augmenting radial basis functions with appropriate global expansions: these functions will be called hybrid approximate functions. It will be shown that using an appropriate hybrid function accurate results can be obtained for many body forces or pseudo body forces in elasticity without the need for internal nodes.© 1997 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 40 (1997), S. 1687-1700 
    ISSN: 0029-5981
    Keywords: soil amplification ; elastodynamics ; boundary truncation ; infinite domains ; layered domains ; boundary elements ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A method is described in this article to correct for the error that arises with the discretization of domains that include boundaries that extend to infinity. Typically when open domains are discretized, part of the boundary is excluded from the calculation resulting in a truncated region. Of particular interest in this article are earthquake wave amplification problems through zoned media. In these type of problems, the boundary element discretization scheme typically results in truncated regions. Correction for truncation in anti-plane wave problems has already been addressed in a previous article by Heymsfield. In this article, truncation correction for in-plane body waves in a damped material will be discussed. To prove the validity of the proposed technique, the method is checked by calculating the soil amplification of a unit in-plane SV wave through a soil layer resting on a rock half-space. Since an analytic solution exists for this problem, the problem serves as a good basis to compare results with and without the corrections for truncation. Results for this particular problem compare the analytic solution with the numerical solution considering (1) no truncation correction, (2) only layer correction, and (3) both layer and half-space corrections. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 10 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. 2913-2931 
    ISSN: 0029-5981
    Keywords: boundary elements ; symmetric Galerkin ; multi-zone ; condensation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The recent development of the symmetric Galerkin approach to boundary element analysis (BEA) has been demonstrated to be superior to the collocation method for medium to large problems. This fact has been shown in both heat conduction and elasticity. Accounts of collocation multi-zone analysis techniques have also been prevalent in the literature, dealing with multiple boundary integral relations associated with portions of overall objects. This technique results in overall system matrices with a blocked, sparse, but unsymmetric character. It has been shown that multi-zone techniques can produce smaller solution times than a single zone analysis for large problems. These techniques are useful for multi-material problems as well. This paper presents an approach for combining the benefits of both techniques resulting in a Galerkin multi-zone method, that is overall unsymmetric but contains a significant amount of block symmetry. A condensation technique in the multi-zone solver is shown to exploit the symmetry of the Galerkin formulation as well as the blocked sparsity of the multi-zone technique. This method is compared to collocation multi-zone on two elasticity problems from the literature. It is concluded that an appropriate implementation of the symmetric Galerkin multi-zone BEA indeed has the potential to be superior to the collocation based multi-zone BEA, for medium to large-scale elasticity problems. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 40 (1997), S. 637-654 
    ISSN: 0029-5981
    Keywords: design sensitivity ; shape design ; boundary integral ; boundary elements ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A general shape design sensitivity analysis approach, different from traditional sensitivity methods is developed for three-dimensional elastostatic problems. The boundary integral design sensitivity formulation is given in order to obtain traction, displacement and equivalent stress sensitivities which are required for design optimization. Those integral equations are derived analytically by differentiation with respect to the normal to the surface at design variable points. Subdivision of boundary elements into sub-elements and rigid body translation methods are employed to deal with singularities that occur during the numerical discretization of the domain. Four different examples are demonstrated to show the accuracy of the method. The boundary integral sensitivity results are compared with the finite difference sensitivity results. Excellent agreement is achieved between the two methods. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 8 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 40 (1997), S. 2227-2236 
    ISSN: 0029-5981
    Keywords: boundary elements ; integral equations ; elastostatics ; iterative solvers ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The GMRES (Generalized Minimal RESidual) iterative method is receiving increased attention as a solver for the large dense and unstructured matrices generated by boundary element elastostatic analyses. Existing published results are predominantly for two-dimensional problems, of only medium size. When these methods are applied to large three-dimensional problems, which actually do require efficient iterative methods for practical solution, they fail. This failure is exacerbated by the use of the pre-conditioning otherwise desirable in such problems. The cause of the failure is identified as being in the orthogonalization process, and is demonstrated by the divergence of the ‘true’ residual, and the residual calculated during the GMRES algorithm. It is shown that double precision arithmetic is required for only the small fraction of the work comprising the orthogonalization process, and exploitation of this largely removes the penalties associated with the use of double precision. Additionally, it is shown that full re-orthogonalization can be employed to overcome the lack of convergence, extending the applicability of the GMRES to significantly larger problems. The approach is demonstrated by solving three-dimensional problems comprising ∼4000 and ∼5000 equations. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 40 (1997), S. 319-342 
    ISSN: 0029-5981
    Keywords: numerical instability ; elastodynamics ; boundary elements ; dynamic fracture ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the literature there is growing evidence of instabilities in standard time-stepping schemes to solve boundary integral elastodynamic models. However, there has been no theory to support scientists and engineers in assessing the stability of their boundary element algorithms or to help them with the design of new, more stable algorithms. In this paper we present a general framework for the analysis of the stability of any time-domain boundary element model. We illustrate how the stability theory can be used to assess the stability of existing boundary element models and how the insight gained from this analysis can be used to design more stable time-stepping schemes. In particular, we describe a new time-stepping procedure that we have developed, which has substantially enhanced stability characteristics and greater accuracy for the same computational effort. The new scheme, which we have called ‘the half-step scheme’, is shown to have substantially improved performance for the displacement discontinuity boundary element method commonly used to model dynamic fracture interaction and propagation. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 15 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 40 (1997), S. 953-964 
    ISSN: 0029-5981
    Keywords: soil amplification ; boundary truncation ; boundary elements ; infinite domains ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A method is described in this article to correct for the error that arises with the discretization of domains that include boundaries that extend to infinity. Typically, when these types of domains are discretized, part of the boundary is excluded from the calculation resulting in a truncated region. Of particular interest are seismic wave problems through zoned media since these types of problems typically have discretization schemes which result in truncated regions. In this article, the correction for incident SH waves is addressed. The correction for layer truncation has been investigated previously by Hadley et al. for SH waves in an elastic material and here it is extended to damped materials. For the truncation of the half-space, an alternative approach to the enclosing element method proposed by Ahmad and Banerjee is described here. The solution for the half-space correction described in this article is primarily analytic and therefore is a simple implementation. To prove the validity of the proposed technique, the method is checked by calculating the soil amplification of a unit SH wave through a soil layer on a rock half-space. Since an analytic solution exists for this particular problem, the problem serves as a good basis to compare results with and without the truncation corrections. Numerical solutions for this problem are included considering (1) neither layer nor half-space correction, (2) layer correction, but excluding the half-space correction, and (3) both the layer and half-space corrections. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
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