Application of Contour Line Method to Estimate Extreme Ship Hull Loads Considering Operational Restrictions

Abstract

This paper is concerned with estimating the response value corresponding to a return period, say 100 years. In principle, this response needs to be obtained by combining the response in all the sea states. The response for a given sea state, specified by the significant wave height, Hs, and the peak period, Tp, can be obtained in the frequency domain for the linear response. Time domain simulation is required to obtain the nonlinear response, and long time series are required to limit the statistical uncertainty in the simulations. Especially in the latter case, it is crucial to introduce ways to improve the efficiency in the calculation. A method to determine the long-term extremes by considering only a few short-term sea states is outlined. The sea states have a certain probability of occurrence and are identified by a contour line in the (Hs TJ-plane. This will make possible practical estimation of the extreme loads the vessels are exposed to.