Parametric roll resonance of modern containerships was predicted at initial design phase using numerical simulations and model scale experiments in a deep towing tank. Dynamic instabilities of modern containerships vulnerable to large but bounded roll motions when either floating or advancing in certain frequencies of wave encounter were successfully simulated using three-dimensional time-domain seakeeping computations based on Rankine source panel method. In the hydrodynamic computations geometric nonlinearity was accounted for in Froude-Krylov and restoring forces using simple wave corrections over exact wet hull surface of the containerships. The numerical simulations in the present work were compared with the calculations based on a classification society in-house code specially designed to assess parametric roll motions of commercial vessels. The computations for a mid-size and an ultra-large size containerships were validated through four degree-of-freedom model scale seakeeping experiments in regular head waves at the deep towing tank of Hyundai Heavy Industries.
In general, the roll response is a matter of no great importance for the ship in head seas. However many shipping agents have reported excessive roll motions when containerships, whose ship shape and size are modern and large, were operating in head seas of the harsh ocean environments. The abrupt accident of the large containership as well as Panamax or post-Panamax class is well known (William et al., 2003; Riberiro e Silva et al., 2004). Recently, the concern for the roll resonance due to the parametric excitation in the head sea and following seas tends to increase with the size of the containership, which is now exceeding 10,000 TEU class. The parametric resonance of the roll motion occurs suddenly in head seas or following seas and causes the roll motions to grow rapidly to an excessive roll angle of 40 degrees.
