The occurrence of parametric rolling will threaten the ship safety. The bilge keel is selected as the device of stabilization and suppression of the parametric rolling for an ONR tumblehome ship. The influence of the installation angle and breadth of the bilge keel on the roll damping is calculated based on the viscous CFD method. A new retractable bilge keel stabilizer is designed to improve the stabilization effect. The rolling characteristics of the ONR tumblehome ship in regular head seas with different bilge keel schemes are analyzed by using the three-dimensional potential flow method. The simulation results show that the bilge keel can effectively suppressthe parametric rolling and stabilize the ONR tumblehome ship.In particular, the designed retractable bilge keel can obviously suppressthe parametric rolling.

The accurate numerical prediction of large-amplitude nonlinear ship motions is quite important for the safe navigation of ships under rough sea conditions. A weakly nonlinear ship motion model is proposed to analyze the vertical ship motion in the wave. In the numerical model, the radiation force and the diffraction force are estimated by using the impulse response function, and the ship slamming force is introduced according to the momentum impact theory. The incident wave forces (Froude-Krylov forces (F-K)) and hydrostatic forces on the instantaneous wetted ship surface are calculated for ship under the incident wave profile. One of the unique features is that the fully nonlinear stream function wave theory is introduced to estimate the incident wave kinematics, dynamic pressure and the F-K fluid loads, where the detailed numerical results are presented and discussed. The proposed numerical model is used to estimate the vertical nonlinear ship motions of a S175 container ship sailing in regular waves. It is found that the vertical FK forces and the heave motions based on the stream function wave theory are slightly larger than those of the linear wave theory especially when the incident wave steepness is relatively large. Another feature is that the momentum impact theory is used to estimate the section slamming forces. The results show that at a relatively high speed, the slamming force greatly impact the ship vertical motion, and the inclusion of the slamming force contributes evidently to the reduction of the motion amplitude.