This study considers the nonlinear motion responses of sea-going vessels in waves. Radiation and diffraction disturbances are treated on incident wave surface and the exactly wetted body surface, according to the weak-scatterer hypothesis introduced by Pawlowski (1992). Nonlinear hydrostatic and Froude-Krylov forces are evaluated on the exactly wetted surface. As a method of solution, a three-dimensional Rankine panel method based on B-spline basis function is applied. At every time step, computational grids are distributed on the exact body surface and incident wave surface, and the corresponding boundary value problem is solved. Numerical computations are carried out for popular ship hulls including Series 60 (CB=0.7) hull and S175 containership. The computational results are validated by comparing with experimental data and other computational results on wave excitation force, hydrodynamic coefficients, and motion responses. In this paper, some technical issues for applying weak-scatterer approach is also introduced.
Linear analysis on ship motion problem has been typical approach for a long time. Recently the demand of nonlinear analysis is very high, particularly due to the design of ships faster and larger than ever before. As the ship length becomes larger, the nonlinear effects play a significant role in ship motion and global hull-girder loads. The nonlinearity on ship motion problem can be separated to two main parts. The first one is free-surface nonlinearity, naturally comes from the nonlinear free-surface boundary condition. There are furthermore violent and strong nonlinear phenomena, such as slamming, sloshing and green water, etc. There are some trials to consider the free-surface nonlinearity by solving the nonlinear free-surface boundary condition; however the consideration of nonlinear free-surface boundary condition including the strong nonlinear phenomena is not an easy problem yet. The second one is body nonlinearity, induced by the nonlinear geometrical change of hull shape. The consideration of body nonlinearity is relatively easier and the computational burden is low.
