Combination of HOSM and FORM for extreme wave-induced response prediction of a ship in nonlinear waves

Abstract

This paper proposes a method for predicting the extreme values of linear and nonlinear wave-induced responses of a ship in nonlinear waves. The method is based on a combination of the Higher Order Spectrum Method (HOSM) and First Order Reliability Method (FORM), allowing the most-probable wave episodes for extreme values of interest to be efficiently calculated. The proposed HOSM + FORM approach is first applied to extreme wave crest prediction, and the results are validated through comparisons against Monte Carlo simulations. The HOSM + FORM approach is then used to predict the extreme wave-induced vertical bending moment (VBM) distribution in a container ship. The wave-induced VBM is assumed to be linear with respect to the incident wave profile by leveraging pre-computed VBM transfer functions. Finally, the extreme value distribution of nonlinear roll motion in beam seas is investigated. The proposed HOSM + FORM approach is shown to predict the extreme linear and nonlinear wave-induced responses efficiently and accurately. The effect of wave nonlinearity is found to be significant under circumstances where the VBM is sensitive to high-frequency waves or large roll angles are excited by the wave crests.