Title: An Abstract Nonlinear Solver Point of View on Strong Partitioned Fluid Structure Interaction Coupling Algorithms

Speaker: Michael W. Gee, Chair for Numerical Mechanics, Technical University of Munich

Date/Time: Monday, August 13, 2007 10:30 - 11:30 am

Location: CSRI Building/Room 95 (NM)

Brief Abstract: Fluid-structure interaction (FSI) simulations are a persistent matter of interest in science and engineering both for their numerous applications and computational challenges. In particular the interaction of incompressible fluids with flexible structures that undergo large deformations is in demand. The FSI problem consists of fluid and structural parts and their interaction with each other. The interaction occurs at the coupling interface, so FSI constitutes an interface coupled problem with deforming domains.

To solve the FSI problem various solution approaches have been proposed. Ideas range from melting existing structural and fluid solvers to obtain a fully monolithic FSI solver to loose couplings by once in a time step exchange of coupling information.
The former approach is obviously highly demanding in terms of solver knowledge and requires a big implementational effort. Furthermore monolithic solvers for FSI problems rely on vastly ill-conditioned linear systems of equations. The explicit coupling on the other hand is not appropriate for structures closely coupled with incompressible fluid. Iteratively coupled schemes try to combine advantages of both approaches. The iterative coupling allows to solve each field on its own, not touching the field solvers, and still the converged solution is reached in every time step. The price to pay is an extra level of iterations that can substantially increase the computational costs.

The key to a fast solution of the highly nonlinear coupled problem is an accelerated coupling iteration. Unbiased comparisons of techniques are rare since the implementation of an elaborated coupling scheme is a non-trivial task and codes that support a sufficient range of coupling schemes are still hard to find. The advent of freely available general purpose nonlinear solvers promises a remedy. The application of such a package is straight forward once the FSI problem is formulated in terms of interface degrees of freedom. In the presented study, the Trilinos library NOX as well as some extension made to it by the authors are used to discuss and compare several solution approaches to the fluid structure interface problem.

CSRI POC: David Day, (505) 844-1868