Wave drift forces on two ships in close proximity

Numerical calculation methods are studied for evaluating the wave drift forces and moments on two ships located in close proximity. Hydrodynamic interactions are taken into account by solving the integral equation for the first-order velocity potentials on the whole wetted surface of both ships with a higher-order boundary-element method. The second-order steady forces on each ship are computed by the near-field method and a new far-field method applying the momentum-conservation principle in a fluid region encompassing only either ship. Good numerical accuracy is confirmed by computations for two identical ellipsoids. Computed results are also compared with measured ones for the side-by-side arrangement of a modified Wigley model and a rectangular barge model, and good agreement is found.