A frequency-time domain method for ship fatigue damage assessment

Abstract

Ships in ocean waves are suffered from cyclic wave loads which can cause fatigue damage to ship structures. Classification societies require owners to carry out fatigue assessment for ship structure for its potential great loss caused by fatigue failure. Currently there are many fatigue assessment methods including simplified method, deterministic method, spectral-based method and time domain method. But none of them predict fatigue life precisely and effectively. Based on linear superposition theory and the assumption that a linear relationship occurred between waves and ship structural response, some scholars proposed the hybrid frequency-time domain method. This method avoids the imprecise narrow band approximation in spectral-based method and adopts rainflow counting instead. However, the hybrid method is not applied extensively on ship fatigue assessment because relevant research is insufficient. In this paper, aiming to validate the hybrid method, a segmented ship model test is carried out, and the short-term fatigue damages of a 4600TEU container forecasted by hybrid method and traditional methods are compared. Results shows that the hybrid method forecasts the closest fatigue damage prediction to time domain analysis and owns enough efficiency. But in some area located at midship, hybrid method may predict lower fatigue damage than time domain method.