Practical Performances of Non-linear Algorithms for Partitioned Iterative Method of Fluid-Structure Interaction Problems

Recently, tightly coupled partitioned iterative methods have drawn a great deal of attentions due to easy implementation and encapsulation features, and several nonlinear algorithms have been proposed so far. However, their practical performances have not been well understood yet. This paper describes the intensive parametric study on convergence and stability performances of four nonlinear algorithms and their relaxed variations for partitioned iterative methods of steady / unsteady fluid-structure interaction (FSI) problems. Here we choose three typical FSI problems as test problems, i.e. (1) Collapsible channel as a steady problem, (2) Cavity with flexible bottom membrane and (3) Channel with flexible wall as unsteady problems. Efficiency and robustness dependency of those nonlinear algorithms on physical parameters such as degree of nonlinearity, added mass effect, time step, and on control parameters peculiar to each algorithm are clarified. Through those tests, we demonstrate that Broyden method is the fastest algorithm for easy FSI problems such as weakly coupling and Line Search method has robustness even for difficult FSI problems such as strongly coupling.