Finite Element Tearing And Interconnecting Method Research Articles

An Iteration-Free Domain Decomposition Method for the Fast Finite Element Analysis of Electromagnetic Problems

An iteration-free finite element domain decomposition method (DDM) is proposed for the simulation of 3-D electromagnetic problems. The finite element tearing and interconnecting (FETI) with Robin-type transmission condition is introduced to construct a domain decomposition framework. Based on hierarchical ( $\mathcal {H}$ -) matrix algorithm, the numerical Green’s function of each subdomain can be represented by a data-sparse matrix form. Subsequently, the original 3-D problem is reduced to a 2-D problem on the skeleton. Derived from the finite element discretization of pseudo-differential operator, the skeleton matrix can also be efficiently approximated with an $\mathcal {H}$ -matrix by assembling all the numerical Green’s functions of subdomains. Based on $\mathcal {H}$ -LU factorization algorithm, the computational complexity and memory requirement for the direct solution of the skeleton equation can be reduced to be logarithmic linear. The resulting direct FETI (D-FETI) method completely depends on direct method without any iterative process. Hence, it does not suffer from the issue of convergence rate, and avoids redundant computations for multiple right-hand side problems. Numerical examples demonstrate the effectiveness of the proposed method.

Parallel computation for three-dimensional shell analysis of curved configuration based on domain decomposition method

In this paper, a parallel computational algorithm is developed based on finite element tearing and interconnecting (FETI) method, specifically, localized Lagrange multipliers. The proposed FETI method decomposes large-size structures into non-overlapping subdomains via localized Lagrange multipliers. To consider the curved configuration of large-size structures, a facet shell element created by combining an optimal triangle membrane and discrete Kirchhoff triangle bending plate (OPT-DKT) is suggested and used by introducing rotational operators. Moreover, practical performance of the present OPT-DKT facet shell element is evaluated through static and dynamic analysis. Finally, parallel computation is implemented for the proposed approach using message passing interface (MPI).

Finite Element Tearing and Interconnecting Method and its Algorithms for Parallel Solution of Magnetic Field Problems

Abstract Because of the exponential increase of computational resource requirement for numerical field simulations of more and more complex physical phenomena and more and more complex large problems in science and engineering practice, parallel processing appears to be an essential tool to handle the resulting large-scale numerical problems. One way of parallelization of sequential (singleprocessor) finite element simulations is the use of domain decomposition methods. Domain decomposition methods (DDMs) for parallel solution of linear systems of equations are based on the partitioning of the analyzed domain into sub-domains which are calculated in parallel while doing appropriate data exchange between those sub-domains. In this case, the non-overlapping domain decomposition method is the Lagrange multiplier based Finite Element Tearing and Interconnecting (FETI) method. This paper describes one direct solver and two parallel solution algorithms of FETI method. Finally, comparative numerical tests demonstrate the differences in the parallel running performance of the solvers of FETI method. We use a single-phase transformer and a three-phase induction motor as twodimensional static magnetic field test problems to compare the solvers

The nsBETI method: an extension of the FETI method to non‐symmetrical BEM‐FEM coupled problems

SUMMARYThe finite element tearing and interconnecting (FETI) method is recognized as an effective domain decomposition tool to achieve scalability in the solution of partitioned second‐order elasticity problems. In the boundary element tearing and interconnecting (BETI) method, a direct extension of the FETI algorithm to the BEM, the symmetric Galerkin BEM formulation, is used to obtain symmetric system matrices, making possible to apply the same FETI conjugate gradient solver. In this work, we propose a new BETI variant labeled nsBETI that allows to couple substructures modeled with the FEM and/or non‐symmetrical BEM formulations. The method connects non‐matching BEM and FEM subdomains using localized Lagrange multipliers and solves the associated non‐symmetrical flexibility equations with a Bi‐CGstab iterative algorithm. Scalability issues of nsBETI in BEM–BEM and combined BEM–FEM coupled problems are also investigated. Copyright © 2012 John Wiley & Sons, Ltd.

Highly scalable parallel domain decomposition methods with an application to biomechanics

AbstractHighly scalable parallel domain decomposition methods for elliptic partial differential equations are considered with a special emphasis on problems arising in elasticity. The focus of this survey article is on Finite Element Tearing and Interconnecting (FETI) methods, a family of nonoverlapping domain decomposition methods where the continuity between the subdomains, in principle, is enforced by the use of Lagrange multipliers. Exact onelevel and dual‐primal FETI methods as well as related inexact dual‐primal variants are described and theoretical convergence estimates are presented together with numerical results confirming the parallel scalability properties of these methods. New aspects such as a hybrid onelevel FETI/FETI‐DP approach and the behavior of FETI‐DP for anisotropic elasticity problems are presented. Parallel and numerical scalability of the methods for more than 65 000 processor cores of the JUGENE supercomputer is shown. An application of a dual‐primal FETI method to a nontrivial biomechanical problem from nonlinear elasticity, modeling arterial wall stress, is given, showing the robustness of our domain decomposition methods for such problems.

Preconditioning the FETI Method for Accelerating the Solution of Large EM Scattering Problems

This letter addresses the convergence rate of the Finite Element Tearing and Interconnecting (FETI) algorithm when applied to the solution of large electromagnetic scattering problems formulated via the finite element method (FEM). The FETI-H formulation is applied to derive a preconditioner for the scalar Helmholtz operator with inhomogeneous media. Examples are presented which show increased speedup over the nonpreconditioned FETI method as well as dramatic speedup as compared to a traditional diagonally preconditioned BiConjugate Gradient Method (BiCGM) solver

FETI Domain Decomposition Methods for Second Order Elliptic Partial Differential Equations

AbstractA survey on certain Finite Element Tearing and Interconnecting (FETI) methods for second order elliptic partial differential equations is given. FETI methods are nonoverlapping domain decomposition algorithms where continuity across subdomain boundaries is treated, sometimes only in parts, by Lagrange multipliers. The family of FETI algorithms is among the best known and most severely tested domain decomposition methods for elliptic partial differential equations. In this article, an overview is given of the classical one‐level FETI method and the more recent dual‐primal FETI methods; both type of algorithms are considered for scalar, second order, elliptic equations and the system of linear elasticity, and are illustrated by some computational results. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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 poor efficiency of FETI in these particular cases is traced back to bad 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.

An additive Schwarz preconditioner for the FETI method

A new additive Schwarz preconditioner for the Finite Element Tearing and Interconnecting (FETI) method is analyzed in this paper. This preconditioner has the unique feature that the coefficient matrix of its ``coarse grid'' problem is mesh independent. For a model second order heterogeneous elliptic boundary value problem in two dimensions, the condition number of the preconditioned system is shown to be bounded by C[1+ln(H/h)]2, where h is the mesh size, H is the typical diameter of the subdomains, and the constant C is independent of h, H, the number of subdomains and the coefficients of the boundary value problem.

Extended preconditioners for the FETI method applied to constrained problems

AbstractAn efficient and simple approach for handling linear multipoint constraints in a class of substructure‐based solvers, namely the finite element tearing and interconnecting (FETI) method, is proposed. Previously, it was argued that multipoint constraints should be handled in FETI by adding a second level iteration on a coarse grid such that the FETI iterates satisfy the multipoint constraints exactly. The procedure presented here does not require an additional coarse grid but instead takes account of the multipoint constraints in the preconditioning step. The preconditioning strategy is shown to be mechanically consistent and to incur only a small additional computational cost. This strategy is simpler and computationally less expensive than the two‐level FETI procedure. Its numerical scalability even for highly heterogeneous problems is demonstrated in several test examples. Copyright © 2002 John Wiley & Sons, Ltd.

A two-level domain decomposition method for the iterative solution of high frequency exterior Helmholtz problems

Summary. We present a Lagrange multiplier based two-level domain decomposition method for solving iteratively large-scale systems of equations arising from the finite element discretization of high-frequency exterior Helmholtz problems. The proposed method is essentially an extension of the regularized FETI (Finite Element Tearing and Interconnecting) method to indefinite problems. Its two key ingredients are the regularization of each subdomain matrix by a complex interface lumped mass matrix, and the preconditioning of the interface problem by an auxiliary coarse problem constructed to enforce at each iteration the orthogonality of the residual to a set of carefully chosen planar waves. We show numerically that the proposed method is scalable with respect to the mesh size, the subdomain size, and the wavenumber. We report performance results for a submarine application that highlight the efficiency of the proposed method for the solution of high frequency acoustic scattering problems discretized by finite elements.

Two-level domain decomposition methods with Lagrange multipliers for the fast iterative solution of acoustic scattering problems

We present two different but related Lagrange multiplier based domain decomposition (DD) methods for solving iteratively large-scale systems of equations arising from the finite element discretization of high-frequency exterior Helmholtz problems. The proposed methods are essentially two distinct extensions of the regularized finite element tearing and interconnecting (FETI) method to indefinite or complex problems. The first method employs a single Lagrange multiplier field to glue the local solutions at the subdomain interface boundaries. The second method employs two Lagrange multiplier fields for that purpose. The key ingredients of both of these FETI methods are the regularization of each subdomain matrix by a complex lumped mass matrix defined on the subdomain interface boundary, and the preconditioning of the global interface problem by a coarse second-level problem constructed with planar waves. We show numerically that both methods are scalable with respect to the mesh size, the subdomain size, and the wavenumber, but that the FETI method with a single Lagrange multiplier field – labeled FETI-H (H for Helmholtz) in this paper – delivers superior computational performances. We apply the FETI-H method to the parallel solution on a 24-processor Origin 2000 of an acoustic scattering problem with a submarine shaped obstacle, and report performance results that highlight the unique efficiency of this DD method for the solution of high frequency acoustic scattering problems.

A transient FETI methodology for large‐scale parallel implicit computations in structural mechanics

AbstractWe present a domain decomposition method for implicit schemes that requires significantly less storage than factorization algorithms, that is several times faster than other popular direct and iterative methods, that can be easily implemented on both shared and local memory parallel processors, and that is both computationally and communication‐wise efficient. The proposed transient domain decomposition method is an extension of the method of Finite Element Tearing and Interconnecting (FETI) developed by Farhat and Roux for the solution of static problems. Serial and parallel performance results on the CRAY Y‐MP/8 and the iPSC‐860/128 systems are reported and analyzed for realistic structural dynamics problems. These results establish the superiority of the FETI method over both the serial/parallel conjugate gradient algorithm with diagonal scaling and the serial/parallel direct method, and contrast the computational power of the iPSC‐860/128 parallel processor with that of the CRAY Y‐MP/8 system.

Optimal convergence properties of the FETI domain decomposition method

Abstract The Finite Element Tearing and Interconnecting (FETI) method is a practical and efficient domain decomposition (DD) algorithm for the solution of self-adjoint elliptic partial differential equations. For large-scale structural problems discretized with shell and beam elements, this method was found to outperform popular iterative algorithms and direct solvers on both serial and parallel computers, and to compare favorably with leading DD methods. In this paper, we discuss some numerical properties of the FETI method that were not addressed before. In particular, we show that the mathematical treatment of the floating subdomains and the specific conjugate projected gradient algorithm that characterize the FETI method are equivalent to the construction and solution of a coarse problem that propagates the error globally, accelerates convergence, and ensures a performance that is independent of the number of subdomains. We also show that when the interface problem is optimally preconditioned and the mesh is partitioned into well structured subdomains with good aspect ratios, the performance of the FETI method is also independent of the mesh size. However, we also argue that the FETI and other leading DD methods for unstructured problems lose in practice these scalability properties when the mesh contains junctures with rotational degrees of freedom, or the decomposition is irregular and characterized by arbitrary subdomain aspect ratios. Finally, we report that for realistic problems, optimal preconditioners are not necessarily computationally efficient and can be outperformed by non-optimal ones.