Abstract
Excessive roll motion in realistic seas is one of the main reasons leading to ship capsizing. However, ship capsizing is a rare event for most of the sea states and prediction of ship capsizing probability is still a challenge. In this work, excessive roll motion for the cases of the dead ship condition and the parametric rolling are studied. Specifically, ship roll response in random seas is calculated by numerical analysis, and a stochastic process, X(t), is defined as the absolute value of the roll motion because the capsizing event can be caused by exceedance of the maximum angle at either side. Two different methods, i.e. the traditional Gumbel method and the average conditional exceedance rate (ACER) method are applied in order to predict the extreme values of the stochastic process X(t). The exceedance probability for X(t) corresponding to the critical levels, such as the flooding angle, can then be employed as an equivalent measure of the ship capsizing probability for a given sea state. The relative merits of the ACER method and the Gumbel method will be compared with Monte Carlo simulation. The studies in this work are intend to promote the understanding of ship capsizing in random seas.
