Solvers for large-displacement fluid–structure interaction problems: segregated versus monolithic approaches

We compare the relative performance of monolithic and segregated (partitioned) solvers for largedisplacement fluid–structure interaction (FSI) problems within the framework of oomphlib, the object-oriented multi-physics finite-element library, available as open-source software at http://www.oomph-lib.org. Monolithic solvers are widely acknowledged to be more robust than their segregated counterparts, but are believed to be too expensive for use in large-scale problems. We demonstrate that monolithic solvers are competitive even for problems in which the fluid–solid coupling is weak and, hence, the segregated solvers converge within a moderate number of iterations. The efficient monolithic solution of large-scale FSI problems requires the development of preconditioners for the iterative solution of the linear systems that arise during the solution of the monolithically coupled fluid and solid equations by Newton’s method. We demonstrate that recent improvements to oomphlib’s FSI preconditioner result in mesh-independent convergence rates under uniform and non-uniform (adaptive) mesh refinement, and explore its performance in a number of twoand three-dimensional test problems involving the interaction of finite-Reynolds-number flows with shell and beam structures, as well as finite-thickness solids.