A fast, robust, and non-stiff Immersed Boundary Method

We propose a fast and non-stiff approach for the solutions of the Immersed Boundary Method, for Newtonian, incompressible flows in two or three dimensions. The proposed methodology is built on a robust semi-implicit discretization introduced by Peskin in the late 70s which is solved efficiently through the novel use of a fast, treecode strategy to compute flow-structure interactions. Optimal multipole-type expansions are performed numerically by solving a least squares problem with a new, fast iterative algorithm. The new Immersed Boundary Method is particularly well suited for three-dimensional applications and/or for problems where the number of immersed boundary points is large. We demonstrate the efficacy and superiority of the method over existing approaches with two simple but illustrative examples in 3D.