Commun. Comput. Phys., 14 (2013), pp. 1103-1119.


On Direct and Semi-Direct Inverse of Stokes, Helmholtz and Laplacian Operators in View of Time-Stepper-Based Newton and Arnoldi Solvers in Incompressible CFD

H. Vitoshkin 1*, A. Yu. Gelfgat 1

1 School of Mechanical Engineering, Faculty of Engineering, Tel-Aviv University, Ramat Aviv 69978, Tel-Aviv, Israel.

Received 30 April 2012; Accepted (in revised version) 1 February 2013
Available online 27 May 2013
doi:10.4208/cicp.300412.010213a

Abstract

Factorization of the incompressible Stokes operator linking pressure and velocity is revisited. The main purpose is to use the inverse of the Stokes operator with a large time step as a preconditioner for Newton and Arnoldi iterations applied to computation of steady three-dimensional flows and study of their stability. It is shown that the Stokes operator can be inversed within an acceptable computational effort. This inverse includes fast direct inverses of several Helmholtz operators and iterative inverse of the pressure matrix. It is shown, additionally, that fast direct solvers can be attractive for the inverse of the Helmholtz and Laplace operators on fine grids and at large Reynolds numbers, as well as for other problems where convergence of iterative methods slows down. Implementation of the Stokes operator inverse to time-stepping-based formulation of the Newton and Arnoldi iterations is discussed.

AMS subject classifications: 76D05

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Key words: CFD, Newton iteration, Arnoldi iteration, Stokes operator.

*Corresponding author.
Email: gelfgat@tau.ac.il (A. Yu. Gelfgat)
 

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