An experimental study on characteristics of rolling in head waves for a vessel with nonlinear GZ-curve

Abstract

In this study, the characteristics of rolling in head waves for a vessel with strong nonlinear GZ-curve, which includes parametric rolling, are investigated. Rolling is measured for systematically changed wave length and height under the same forward speed, which is service speed in heavy weather. As a result, the range of Te/Tϕ (Te and Tϕ are encounter wave period and the roll natural period of the model) when oscillatory rolling occurs is wider than that of previous results by Taguchi et al. (Model Experiment on Parametric Rolling of a Post-Panamax Containership in Head Waves. Proceedings of the Ninth International Conference on Stability of Ships and Ocean Vehicles, 2006), and the range spreads out wide area of Te/Tϕ > 0.5. Especially, in the range of Te/Tϕ > 0.5, oscillatory rolling is caused by large wave height and roll amplitude becomes larger than that at Te/T = 0.5. It is supposed that the result is caused by change of roll natural period caused by nonlinear GZ-curve. In order to confirm it, numerical simulations are carried out for several variations of GZ-curve. Additionally, roll measurements in irregular waves with Pierson-Moskowitz spectrum are also carried out.