Study of asynchronicity in the fluid-structure interaction domain

With the objective of studying fluid-structure interaction (FSI) applications with sophisticated structural behavior, this work studies an approach that makes room for the use of complex structural models without penalizing the global computational time. The proposed approach is based on an algorithm that, simultaneously solving two subdomains, allows an asynchronous update of the boundary conditions at the interface according to the computational time spent by each of the solvers. The implementation of this algorithm revealed the appearance of numerical instabilities related to the parallel operation, and the independent evolution of the local solution in each subdomain. To overcome these stability problems, this work proposes a two-part stabilization strategy, both based on the use of a modal approach, as well as the adjustment of the formulation of the Jacobian of the fluid at the interface. The first part consists of a predictor-corrector method for the parallel operation and the second in an auxiliary coupling to assist the solution of the fluid domain. The impact of parameters such as the amount of correction, the number of modes and under-relaxation are studied. The use of the proposed asynchronous algorithm shows a positive impact when used for the solution of weakly coupled FSI applications (mass ratio m(F)/m(S) = 0.001). However, for applications with a larger or equivalent mass ratio, m(F)/m(S) = 0.1or m(F)/m(S) = 1, greater difficulty in stabilizing remain. Even though it is found that the proposed approach requires to be improved to ensure a robust solution, the encountered results represent an advance towards the use of an innovative algorithm in the FSI domain, one that could naturally offer an intermediary algorithm between the implicit external algorithm and the implicit internal algorithm.