A Novel Approach For Fatigue Life Prediction Of Local Hull Structures Subjected To Slamming Loads

This paper presents a novel computational technique for fatigue life assessment of hull structures subjected to repeated water slamming loads. The proposed approach combines numerical results from finite element (FE) models of a single impact event with statistical distributions of experimental peak pressures from the literature. Numerical stresses are extrapolated using Peak over Threshold (POT) analysis to simulate the effect of small variations of the angle of incidence and impact velocity in a scenario of multiple impacts. POT analysis is used to model stress exceedances above and below certain threshold levels based on a statistical distribution. In this paper, stress exceedances are assumed to follow a similar statistical distribution to that of the peak pressures. The resulting extrapolated stresses contain modified peaks and valleys which are highly dependent on the threshold levels. The stress cycles are then classified and counted using the Rainflow method. The level of structural damage associated with each cycle is computed and the individual contributions are combined using a linear damage accumulation model (Palmgren-Miner's law). In this paper, fatigue of a component in the pressure-affected zone is considered. The proposed approach predicts more damage, for a particular number of impacts, than the classical approach without stress exceedances. Damage predictions are also highly dependent on the threshold levels. A significant reduction of fatigue life is observed when small variations of the impact conditions are considered.