Low-cycle fatigue of ship hull damaged in collision

Abstract This work aims to extend the conventional post-accidental structural safety assessment by investigating the possibility of damage propagation in a damaged ship during the salvage period as a low-cycle high-stress fatigue process caused by fluctuating wave loads. Low-cycle loading can cause high-amplitude stresses at the edge of the damage opening, which consequently lead to high-stress concentrations. In the present study, a finite element model is created for an intact ship and 50 random damage scenarios for which the stress concentration factors are calculated. Random damage scenarios are generated using damage parameters obtained from historical data on ship accidents. The number of constant-amplitude wave load cycles to initiate a fatigue crack is calculated using the strain-life method defined according to Det Norske Veritas classification notes. Accumulated low-cycle fatigue damage is then estimated by Monte Carlo simulation, where individual vertical wave bending moment amplitudes are drawn as random numbers according to Weibull distribution. Parametric analysis is also performed in order to investigate the influence of cyclic material properties, sea environment and the number of towing days on the overall low-cycle fatigue damage accumulation. Realistic sea state scenarios are selected in order to investigate the influence of low-cycle fatigue damage accumulation during some specific constant sea states, enabling to determine marginal sea conditions for a safe rescue operation.