Time domain simulation of nonlinear ship motions using an impulse response function method

In this paper, a nonlinear time domain method based on the impulse response function concept is presented. For the simulation of the six DOF nonlinear motions of a ship in seaways, the equations of motion are derived by application of the momentum conservation theorem and numerically solved in the time domain. Hydrodynamic coefficients are determined by linear potential theory, whereas certain nonlinear terms are considered in the equations of motion, such as the excitation by large amplitude waves, the exact restoring forces and moments resulting from the actual wetting of the ship hull geometry and the semi-empirical nonlinear viscous damping. Finally, nonlinear inertia terms are retained when considering large angles of motions. The validation of the developed theoretical method and computer code has been conducted by the study of well-established benchmark ship models, namely the S-175 hull, the DTC hull and the KVLCC2 hull. Good agreement has been observed between the results of the present method, other numerical codes and available experimental data, which confirm the capability of the developed numerical approach to deliver reliable predictions.