A numerical model has been developed to study the large-amplitude motions of a catamaran subjected to severe wave conditions. In this paper, emphasis is placed on the description of the theoretical aspects. The nonlinear equations of motion concerning the rigid hulls and flexible beams are developed, including large rotations between bodies. The fluid-structure interaction model satisfies exactly the body boundary condition on the instantaneous surface of the moving body, defined as the part under the incident wave profile, while the free surface boundary conditions are linearized. The problem is solved using a transient free-surface Green function singularity distribution method.
The simulation of a nonlinear global behavior of a catamaran in following waves has been obtained and it illustrates the importance of nonlinear effects associated with the changing wetted hull.