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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Structural optimization 16 (1998), S. 162-175 
    ISSN: 0934-4373
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Single and multiple flaw identification problems are considered. Static and steady-state dynamic analysis of structures with flaw(s) is performed by the boundary element method. Inverse problems are formulated as output (i.e. measurement) error minimization problems and they are solved by numerical optimization techniques. As it is shown in this paper by means of numerical experiments, for elastostatic cases, an appropriate modelling of the structural analysis problem, a good choice of the error measure, and the use of established numerical optimization software are usually sufficient for the solution of the problem. Even multiple flaw identification is possible. Elastodynamic loadings lead to nonconvex problems which are solved here by means of global, genetic optimization algorithms.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Computing 9 (1972), S. 203-209 
    ISSN: 1436-5057
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Summary Schoenhage [4] gives the remainder term of then-dimensional Romberg-integration for the sequenceh k =21−k ,k=1,2, ... Here this results are extended to the monotonically decreasing sequencesh k =m 1−k ,k=1,2, ....
    Notes: Zusammenfassung Es wird hier eine Verallgemeinerung der vonSchoenhage [4] fürh k =21−k ,k=1,2, ..., bewiesenen Resultate, insbesondere der Restglieduntersuchungen auf die monoton abnehmenden Schrittweitenfolgenh k =m 1−k ,k=1,2, ..., gegeben.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Computing 9 (1972), S. 45-52 
    ISSN: 1436-5057
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Summary TheRomberg-method of numerical integration is extended to fourdimensional integration. This brings a formula of arbitrary high degree, which needs not more function values in the whole domain than other formulas of the same degree. Moreover practical sure bounds for the exact value are given.
    Notes: Zusammenfassung Es wird nach der Methode vonRomberg mit Hilfe von Trapezsummen eine Formel beliebig hoher Fehlerordnung zur Berechnung vierfacher Integrale mit konstanten Grenzen aufgebaut. Dazu werden praktisch sichere Schranken für den exakten Wert erprobt. Das benützteFortran-Programm wird angegeben.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Acta mechanica 90 (1991), S. 125-137 
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary In this paper, a direct boundary element approach for solving three-dimensional problems of dynamic poroelasticity in the time domain is developed. Based on Biot's theory of wave propagation in poroelastic media, and on Cleary's reciprocal theorem, the complete set of necessary time-dependent fundamental solutions has been derived. Then, after an analytical time integration, a time stepping Boundary Element procedure for the numerical solution of wave propagation problems is established.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Computational mechanics 20 (1997), S. 452-459 
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The usual time domain Boundary Element Method (BEM) contains fundamental solutions which are convoluted with time-dependent boundary data and integrated over the boundary surface. If the fundamental solution is known, e.g., in Elastodynamics, the temporal convolution can be performed analytically when the boundary data are approximated by polynomial shape functions in time and in the boundary elements. This formulation is well known, but the resulting time-stepping BEM procedure produces instabilities and high numerical damping, when the time step size is chosen too small and too large, respectively. Moreover, in case of viscoelastic or poroelastic domains, the fundamental solution is known only in the frequency domain such that the time history of a response can only be obtained by an inverse transformation of the frequency domain results. Here, a new approach for the evaluation of the convolution integrals, the so-called “Operational Quadrature Methods” developed by LUBICH, is presented. In this formulation, the convolution integral is numerically approximated by a quadrature formula whose weights are determined by the Laplace transform of the fundamental solution and a linear multistep method. Hence, the frequency domain fundamental solution can be used without the need of an inverse transformation. Therefore, the extension to viscoelastic problems succeeds using the elastic-viscoelastic correspondence principle.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Computational mechanics 20 (1997), S. 439-451 
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An inverse problem in nonlinear elastostatics is considered which concerns the identification of unilateral contact cracks by means of boundary measurements for given static loadings. Highly nonlinear structural behaviour like closed cracks can hardly be identified. In this case, the analysis of more than one loading cases is proposed and tested in this paper. The direct problem is modelled by using a direct multiregion boundary element formulation. The arising linear complementarity problem is solved explicitly by a pivoting (Lemke) technique. In view of the complexity of the inverse problem, a neural network based identification approach is adopted which uses feed-forward multilayer neural networks trained by back-propagation, error-driven supervised training. The applicability of the method is demonstrated by some numerical examples.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Computational mechanics 6 (1990), S. 47-53 
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In this paper, it is shown that the boundary element method leads to correct results regardless the convexity of the actual domain, if the discretisations are sufficiently refined, and enough elements have been used to approximate infinite boundary geometries. The examples, drawn from acoustic wave propagations in 2-D domains, are presented in order to demonstrate this fact.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 59 (1989), S. 17-31 
    ISSN: 1432-0681
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Summary By using Graffi's reciprocal theorem a time-dependent integro-differential equation and therefrom a time step boundary element method is derived. It is applicable to arbitrary compressible but non-viscous fluids (acoustic media), especially suitable for determining transient pressure waves in infinite or semi-infinite domains. As an application of the method, a reservoir-dam system is analyzed, especially considering the influence of the topography and of the dynamic interaction with the soil.
    Notes: Übersicht Unter Benutzung des Reziprozitätssatzes von Graffi wird eine zeitabhängige Integro-Differen-tialgleichung und daraus eine Zeitschritt-Randelementmethode hergeleitet. Sie ist bei beliebigen kompressiblen, nicht-viskosen Flüssigkeiten (akustischen Medien) anwendbar und besonders zur Ermittlung transienter Druckwellen in unendlichen oder halb-unendlichen Gebieten geeignet. Als Anwendung wird das Staudammproblem, dabei vor allem der Einfluß der Topographie und der dynamischen Interaktion mit dem Untergrund untersucht.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 45 (1976), S. 99-114 
    ISSN: 1432-0681
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Summary Starting from known fundamental solutions of plates the construction of singular basic estimate functions is shown. These are necessary in finite approximation methods basing on the functionals of ‘total energy’ or ‘complementary energy’. The proceeding is explained in detail in a cylindrical shell analysis.
    Notes: Übersicht Ausgehend von bekannten Fundamentallösungen für Platten bzw. Scheiben wird die Erstellung singulärer Ansatzfunktionen gezeigt, wie sie für finite Näherungsverfahren benötigt werden, die von den Funktionalen der ‚totalen Energie’ bzw. der ‚komplementären Energie’ ausgehen. Das Vorgehen wird eingehend an Kreiszylinderschalen erläutert.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Meccanica 32 (1997), S. 179-186 
    ISSN: 1572-9648
    Keywords: BEM ; Time domain ; Multistep method ; Transform methods ; Solid mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The usual time domain Boundary Element Method (BEM) contains fundamentalsolutions which are convoluted with time-dependent boundary data andintegrated over the boundary surface. Here, a new approach for theevaluation of the convolution integrals, the so-called ’OperationalQuadrature Methods‘ developed by Lubich, is presented. In thisformulation, the convolution integral is numerically approximated by aquadrature formula whose weights are determined using the Laplacetransform of the fundamental solution and a linear multisep method. Tostudy the behaviour of the method, the numerical convolution of afundamental solution with a unit step function is compared with theanalytical result. Then, a time domain Boundary Element formulationapplying the ’Operational Quadrature Methods‘ is derived. For thisformulation only the fundamental solutions in Laplace domain arenecessary. The properties of the new formulation are studied with anumerical example.
    Type of Medium: Electronic Resource
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