Prediction of parametric rolling in waves with a time domain non-linear strip theory model

A time-domain non-linear strip theory model of ship′s motions in six degrees-of-freedom is described and is validated by comparing numerical predictions with experimental results of parametric rolling of a containership. The calculation of the time variations of the restoring force is made using a pressure integration technique over the instantaneous submerged hull. Hydrodynamic effects are based on a potential flow strip theory using Frank′s Close fit method. A semi-empirical formulation is adopted for the surge motion. Different models for roll damping have been introduced so far in the governing equations but in the present case roll damping is determined directly from experimental data that includes roll decay tests with different forward speed, which allows the assessment of the effect of ship speed on roll damping. Comparisons between numerical and experimental results demonstrate the usefulness and accuracy of the method proposed.