An experimental investigation of parametric rolling in head waves

In this paper, the possibility of excitation of parametric rolling on a shi p advancing in head sea condition is studied on an experimental basis. The excitation of parametric rolling was effectively observed in the experiment al tests, together with some case of capsizing. The parametric rolling exhi bited the typical subharmonic behavior The use of classical Mathieu equatio n theory, coupled with hydrostatic calculations in longitudinal waves, acco unting for both vertical motions and wave effect an stability, allows a sat isfactory explanation of the observed phenomena. In addition, the problem o f determination of roll damping dependence on ship speed was solved by usin g roll decay tests in calm water with forward speed A simplified nonlinear modeling was proposed to account for the roll motion amplitude above thresh old. The comparison with the experimental results is reasonably good.