Improvement of the ship emergency response procedure in case of collision accident considering crack propagation during salvage period

Abstract

Specialized procedures to help in the emergency response situations following ship accidents have been under development by the Classification Societies. Such procedures consider the hull-girder collapse as the most important failure mode, without the possibility of crack propagation caused by fluctuating wave loads. In the present study, the fatigue crack propagation in the main deck of the oil tanker damaged in collision during salvage is investigated. The shape and size of the damage are modelled using the realistic bow shape of the striking ship and historical data of ship accidents. The stress intensity factor (SIF) across the main deck of the struck ship is calculated numerically and by the method based on the available experimental results of the crack propagation in the stiffened panel. Fluctuating wave–induced stresses in short-term sea conditions during salvage are obtained by Monte Carlo simulation (MC) based on Rayleigh distribution. Cycle-by-cycle crack propagation is calculated using Paris law. Many salvage simulations are performed to cover different possible time-histories of the fatigue loading. Results of the analysis are presented as histogram of the crack increase during salvage. Parametric analysis is performed to investigate the influence of the sea state severity, initial crack size, and towing duration on the final crack size. The proposed procedure can be considered as a part of a software tool for emergency response action during salvage of damaged ship.