The effect of forward speed on the nonlinear ship motions

Time-domain nonlinear vertical motion response of the S-175 containership advancing in head sea condition in large amplitude waves are analysed and compared with the experimental results provided in the literature. The boundary value problem is solved by linear 3D Rankine source panel method with sources distributed on the ship surface, free surface and control surfaces. Nonlinear fluid forces, which arise from nonlinear restoring and Froude-Kylov forces, are calculated over the instantaneous wetted portion of the ship hull. Radiation forces are kept as linear and presented in terms of impulse response functions using convolution integrals. In large amplitude waves, nonlinear motion responses are identified and presented in terms of transfer functions. The numerical results are well agreed with the experimental results and show a significant increase in non-dimensional amplitudes with the increase in the ship speed. Validation of the in-house developed code is performed and showed good agreement with the experimental results in the large amplitude waves.