608 research outputs found
Classical and all-floating FETI methods for the simulation of arterial tissues
High-resolution and anatomically realistic computer models of biological soft
tissues play a significant role in the understanding of the function of
cardiovascular components in health and disease. However, the computational
effort to handle fine grids to resolve the geometries as well as sophisticated
tissue models is very challenging. One possibility to derive a strongly
scalable parallel solution algorithm is to consider finite element tearing and
interconnecting (FETI) methods. In this study we propose and investigate the
application of FETI methods to simulate the elastic behavior of biological soft
tissues. As one particular example we choose the artery which is - as most
other biological tissues - characterized by anisotropic and nonlinear material
properties. We compare two specific approaches of FETI methods, classical and
all-floating, and investigate the numerical behavior of different
preconditioning techniques. In comparison to classical FETI, the all-floating
approach has not only advantages concerning the implementation but in many
cases also concerning the convergence of the global iterative solution method.
This behavior is illustrated with numerical examples. We present results of
linear elastic simulations to show convergence rates, as expected from the
theory, and results from the more sophisticated nonlinear case where we apply a
well-known anisotropic model to the realistic geometry of an artery. Although
the FETI methods have a great applicability on artery simulations we will also
discuss some limitations concerning the dependence on material parameters.Comment: 29 page
Computational methods and software systems for dynamics and control of large space structures
Two key areas of crucial importance to the computer-based simulation of large space structures are discussed. The first area involves multibody dynamics (MBD) of flexible space structures, with applications directed to deployment, construction, and maneuvering. The second area deals with advanced software systems, with emphasis on parallel processing. The latest research thrust in the second area involves massively parallel computers
On the initial estimate of interface forces in FETI methods
The Balanced Domain Decomposition (BDD) method and the Finite Element Tearing
and Interconnecting (FETI) method are two commonly used non-overlapping domain
decomposition methods. Due to strong theoretical and numerical similarities,
these two methods are generally considered as being equivalently efficient.
However, for some particular cases, such as for structures with strong
heterogeneities, FETI requires a large number of iterations to compute the
solution compared to BDD. In this paper, the origin of the bad efficiency of
FETI in these particular cases is traced back to poor initial estimates of the
interface stresses. To improve the estimation of interface forces a novel
strategy for splitting interface forces between neighboring substructures is
proposed. The additional computational cost incurred is not significant. This
yields a new initialization for the FETI method and restores numerical
efficiency which makes FETI comparable to BDD even for problems where FETI was
performing poorly. Various simple test problems are presented to discuss the
efficiency of the proposed strategy and to illustrate the so-obtained numerical
equivalence between the BDD and FETI solvers
Coupling of boundary element regions with the boundary element tearing and interconnecting method (BETI)
The boundary integral equation for elasticity is valid for a single domain consisting of homogeneous material properties. In the case of heterogeneity the consideration of diļ¬erent material properties is possible with a coupling of boundary element regions. Of course each region is again homogeneous. Another simulation application of multiple regions is the simulation of an industrial process, where diļ¬erent subdomains of a homogenous domain are treated diļ¬erently due to a mechanical process. For instance, this is the case in tunnelling, where excavation is performed in a staged procedure. In the simulation of such an excavation process regions are deactivated step by step. As the material behaviour can be nonlinear an accurate simulation of such a staged process is a necessary requirement. Thus, the domain is decomposed into subregions which are coupled to neighbouring regions. There are diļ¬erent coupling strategies existing. In some of them stiļ¬ness matrices of subdomains are worked out which are the basis for the coupling and solution of the problem. A traditional method is the coupling of interface surfaces only [1]. In this method the stiļ¬ness matrix of a region is computed on the basis of the coupling surfaces (interfaces), whereas the coupling surface may be not identical to the complete surface of a subdomain and the size of the stiļ¬ness matrix is determined by the degrees of freedom of the coupling surface. In an application where the boundary conditions change (e.g. from interface to Neumann condition) from one calculation step to the other, the stiļ¬ness matrix has to be calculated new. A modern coupling technique is the Boundary Element Tearing and Interconnecting (BETI) method [2], similar to the method of Finite Element Tearing and Interconnecting (FETI) [3]. In this method the region stiļ¬ness matrix is worked out for the entire boundary of the region. The stiļ¬ness matrices of all regions remain the same during the whole analysis, even if the boundary conditions change during the simulation process. In setting up the equation system each subdomain is treated completely separated and independent from the others. Thus, a parallelisation of the computational work is ideally suited and implemented in the present computer code. In this work the theory of both mentioned coupling techniques are introduced brieļ¬y. The diļ¬erences of both methods are worked out and advantages/disadvantages are shown and will be demonstrated. The accuracy of the results as well as the computational performance will be shown and compared based on a realistic simulation example
Computational methods and software systems for dynamics and control of large space structures
This final report on computational methods and software systems for dynamics and control of large space structures covers progress to date, projected developments in the final months of the grant, and conclusions. Pertinent reports and papers that have not appeared in scientific journals (or have not yet appeared in final form) are enclosed. The grant has supported research in two key areas of crucial importance to the computer-based simulation of large space structure. The first area involves multibody dynamics (MBD) of flexible space structures, with applications directed to deployment, construction, and maneuvering. The second area deals with advanced software systems, with emphasis on parallel processing. The latest research thrust in the second area, as reported here, involves massively parallel computers
A scalable domain decomposition method for FEM discretizations of nonlocal equations of integrable and fractional type
Nonlocal models allow for the description of phenomena which cannot be
captured by classical partial differential equations. The availability of
efficient solvers is one of the main concerns for the use of nonlocal models in
real world engineering applications. We present a domain decomposition solver
that is inspired by substructuring methods for classical local equations. In
numerical experiments involving finite element discretizations of scalar and
vectorial nonlocal equations of integrable and fractional type, we observe
improvements in solution time of up to 14.6x compared to commonly used solver
strategies
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