Experimental and numerical study on several crucial elements for predicting parametric roll in regular head seas

The methods for direct stability assessment of parametric roll are currently under development at the International Maritime Organization for the second generation intact stability criteria. To establish guidelines for developing accurate, but sufficiently simple prediction method, several elements required for modeling parametric roll in head waves are investigated by executing free running model experiments, partially restrained model experiments with and without surge motion and numerical simulations of uncoupled roll model, coupled surge–roll model and coupled heave–pitch–roll model for a C11 class containership. As a result, the following outcomes are obtained. First, the surge effect on parametric roll is generally small. Second, heave and pitch motions can have subharmonic components when parametric roll occurs. Third, the inclusion of the radiation and diffraction effects on restoring variation can result in more conservative prediction for parametric roll in head seas. Finally, the use of the uncoupled roll model could provide more conservative, but less time-consuming prediction for parametric roll than that of coupled heave–pitch–roll model.