DECIV - Departamento de Engenharia Civil

URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/496

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Autor: search.filters.author.Araújo, Francisco Célio deData final: 2009

Resultados da Pesquisa

Agora exibindo 1 - 7 de 7
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    Analysis of thin-walled structural elements via 3D standard BEM with generic substructuring.
    (2008) Araújo, Francisco Célio de; Gray, Leonard J.
    This paper is concerned with the application of standard 3DBoundary Element Methods to solve thin-walled structural elements (needle-like/shell-like solids). A subregion- by-subregion data structure, incorporating iterative solvers and discontinuous boundary elements, is presented. To efficiently and accurately evaluate the quasi-singular integrals, special quadrature methods are applied. In addition, structured matrix-vector products, designed to avoid the excessive number of conditional tests during solver iterations, are proposed. Numerical results for complex thinwalled BE models are validated by comparison with FEM calculations and previously published BEM analyses.
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    Application of a generic domain-decomposition strategy to solve shell-like problems through 3D BE models.
    (2007) Araújo, Francisco Célio de; Silva, Kátia Inácio da; Telles, José Cláudio de Faria
    Efficient integration algorithms and solvers specially devised for boundary-element procedures have been established over the last two decades. A good deal of quadrature techniques for singular and quasisingular boundary-element integrals have been developed and reliable Krylov solvers have proven to be advantageous when compared to direct ones, also in case of non-Hermitian matrices. The former has implied in CPU-time reduction during the assembling of the system of equations and the latter in its faster solution. Here, a triangular polar co-ordinate transformation and the Telles co-ordinate transformation are employed separately and combined to develop the matrix-assembly routines (integration routines). In addition, the Jacobi-preconditioned Biconjugate Gradient solver (J-BiCG) is used along with a generic substructuring boundary element algorithm. Thus, solution CPU time and computer memory can be considerably reduced. Discontinuous boundary elements are also included to simplify the coupling of the BE models (substructures). Numerical experiments involving 3D thin-walled domains (shell-like structural elements) are carried out to show the performance of the computer code with respect to accuracy and efficiency of the system solution. Precision, CPU-time and potential applications of the BE code developed are commented upon.
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    Generic domain decomposition and iterative solvers for 3D BEM problems.
    (2006) Araújo, Francisco Célio de; Silva, Kátia Inácio da; Telles, José Cláudio de Faria
    In the past two decades, considerable improvements concerning integration algorithms and solvers involved in boundary-element formulations have been obtained. First, a great deal of efficient techniques for evaluating singular and quasi-singular boundary-element integrals have been, definitely, established, and second, iterative Krylov solvers have proven to be advantageous when compared to direct ones also including non-Hermitian matrices. The former fact has implied in CPU-time reduction during the assembling of the system of equations and the latter fact in its faster solution. In this paper, a triangle-polar-co-ordinate transformation and the Telles co-ordinate transformation, applied in previous works independently for evaluating singular and quasi-singular integrals, are combined to increase the efficiency of the integration algorithms, and so, to improve the performance of the matrixassembly routines. In addition, the Jacobi-preconditioned biconjugate gradient (J-BiCG) solver is used to develop a generic substructuring boundary-element algorithm. In this way, it is not only the system solution accelerated but also the computer memory optimized. Discontinuous boundary elements are implemented to simplify the coupling algorithm for a generic number of subregions. Several numerical experiments are carried out to show the performance of the computer code with regard to matrix assembly and the system solving. In the discussion of results, expressed in terms of accuracy and CPU time, advantages and potential applications of the BE code developed are highlighted.
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    An efficient BE iterative-solver-based substructuring algorithm for 3D time-harmonic problems in elastodynamics.
    (2001) Araújo, Francisco Célio de; Martins, Cláudio José; Mansur, Webe João
    This work is concerned with the development of an efficient and general algorithm to solve frequency-domain problems modelled by the boundary element method based on a sub-region technique. A specific feature of the algorithm discussed here is that the global sparse matrix of the coupled system is implicitly considered, i.e. problem quantities are not condensed into interface variables. The proposed algorithm requires that only the block matrices with non-zero complex-valued coefficients be stored and manipulated during the analysis process. In addition, the efficiency of the technique presented is improved by using iterative solvers. The good performance of pre-conditioned iterative solvers for systems of equations having real-valued coefficients, well demonstrated in the literature, is confirmed for the present case where the system matrix coefficients are complex. The efficiency of the algorithm described here is verified by analysing a soil–machine foundation interaction problem. CPU time and accuracy are the parameters used for estimating the computational efficiency.
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    New developments on BE/BE multi-zone algorithms based on krylov solvers - applications to 3D frequency-dependent problems.
    (2004) Araújo, Francisco Célio de; Mansur, Webe João; Dors, Cleberson; Martins, Cláudio José
    In this paper, new developments concerning the use of BE/BE coupling algorithms for solving 3D time-harmonic problems are reported. The algorithms are derived by considering different iterative solvers. Their chief idea is to work with the global sparse matrix of the coupled system, however without considering the many zero blocks associated with the non-coupled nodes of different subregions. The use of iterative solvers makes it possible to store and manipulate only the block matrices with non-zero coefficients. Preconditioned iterative solvers based on the Lanczos, bi-conjugate gradient, and GMRES (generalized minimal residual) methods are used to derive the BE/BE coupling algorithms. A description of the formulation of these solvers, which are completely general and can be applied to any non-singular, non-hermitian systems of equations, is provided. The performance of the algorithms is verified by solving some foundation-soil interaction problems. Important parameters for estimating the efficiency of the algorithms as required CPU times, matrix sparsity, and accuracy of the obtained responses are presented in the results of the paper.
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    Analysis of 3D time-dependent acoustic problems via a generic BE substructuring algorithm based on iterative solvers.
    (2003) Araújo, Francisco Célio de; Alberto, Denival Rogério; Dors, Cleberson
    In this paper, a generic BE/BE coupling algorithm based on iterative solvers is applied to solve 3D time-dependent acoustic problems. As regards the treatment of the time-dependence, a direct time-marching scheme is considered. Several types of boundary elements and cells are available in the code for the spatial description of the involved variables. Concerning the BE/BE coupling technique, its chief idea is to completely avoid storing and manipulating the zero blocks appearing in the coupled system by the use of iterative solvers. The global system matrix is not explicitly assembled; instead the algebraic subsystems (associated with the substructures of the model) are manipulated as they were independent of each other. An insight into the coupling strategy and the used iterative solver (Jacobi-preconditioned bi-conjugate gradient method) is given. Analyses of sound barriers are carried out for verifying the performance of the respective computational code modules.
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    On the use of pseudo-forces to consider initial conditions in 3D time- and frequency-domain acoustic analysis.
    (2006) Martins, Cláudio José; Carrer, José Antonio Marques; Mansur, Webe João; Araújo, Francisco Célio de
    This work is mainly concerned with a general strategy, based on well known concepts of classical mechanics, for taking into account initial conditions in frequency-domain (FD) and time-domain (TD) analyses. A general approach, extended here to three-dimensional applications, is presented. Special problems associated with analyses through Discrete-Fourier-Transform (DFT) algorithms, as those occurring in consequence of a non-correct choice of extended period or those connected with aliasing phenomenon, are also discussed. Furthermore, an alternative starting procedure for time-marching schemes (in TD analyses) is proposed. At the end of the paper, to validate the proposed techniques and to demonstrate their generality, two- and three-dimensional problems with non-homogeneous initial conditions are solved through frequency- and time-domain approaches by employing the Finite Element Method (FEM). Numerical results are compared with existing analytical solutions.