Numerical Solutions for Large-Amplitude Ship Motions in the Time Domain

A three-dimensional time domain approach is used to study the large-amplitude motions and loads of a ship in a seaway. In this approach, the exact body boundary condition is satisfied on the instantaneous wetted surface of the moving body while the free-surface boundary conditions are linearised. The problem is solved using a transient free-surface Green function source distribution on the submerged hull. Extensive results are presented which validate and demonstrate the efficacy of the method. These results include linear and large-amplitude motion coefficients and diffraction forces with and without forward speed, calm-water resistance and added-resistance with waves and motions, the large-amplitude motion history of a ship advancing in an irregular seaway, as well as load distributions on the changing submerged hull. Most of the large-amplitude results we obtained are new and illustrate the importance of nonlinear effects associated with the changing wetted hull. Of special significance are the dramatic changes of the added mass, the steady resistance, and sinkage and trim forces as the motion amplitudes increase.