A comparative linear and nonlinear ship motion study using 3-D time domain methods

This paper reports on 3D time domain seakeeping computations at different level of modeling of nonlinear effects. Four successively improved levels of computations are considered: (i) a linear computation, (ii) Froude-Krylov nonlinear computation, (iii) body nonlinear computation where the perturbation potential is computed based on the instantaneous hull under the mean free-surface, and finally (iv) the body-exact nonlinear computation, where the perturbation potential is determined based on the wetted hull under the incident wave profile after suitable mapping of the hull into a computational domain. Computations are carried out for a Wigley hull (having less ‘geometric’ nonlinearity due to vertical sides), and a S175 hull at different forward speeds. The results are obtained for both regular and irregular waves.