Conditional reliability of bulk carriers damaged by ship collisions

Abstract

Time-variant reliability analysis of a bulk carrier in damage conditions, after a collision event, is performed by Monte Carlo simulation. Two different collision models are applied, the former based on the deterministic format actually embodied in the Harmonized Common Structural Rules for Oil Tankers and Bulk Carriers, the latter based on a probabilistic format, derived by the recently developed GOALDS database statistics for collision and grounding events. A modified incremental-iterative method is applied, to account for instantaneous neutral axis rotation, due to asymmetrically damaged cross-sections, as for collision events. Time-variant residual strength statistical properties are preliminarily determined by Monte Carlo simulation, up to 25-year ship lifetime, accounting for corrosion wastages of all structural members contributing to hull girder strength, welding residual stresses and material properties randomness. Finally, time-variant reliability analysis is performed, to investigate the incidence of the applied collision damage models on hull girder annual failure probabilities in sagging and hogging conditions. Reliability analysis is performed for the Capesize single side bulk carrier, benchmarked in the 2012 ISSC report and assumed as reference ship in current analysis. Obtained results are fully investigated and discussed.