Fatigue Damage Assessment for Drillship Structure based on Stochastic Method

TOI drillship, first drillship of DSME, was designed to have more than 25 years' fatigue life against given environmental conditions. Fatigue damage in hull and hull-topside interface structures was assessed based on stochastic method. D-SAFS, developed by DSME, generates stress RAO based on 'Component Based Method'. Structural analyses were carried out for each load component. Resultant stress was combined with wave load analysis results. Whole ship FE models having fine mesh in fatigue sensitive area were used in structural analysis. According to the agreement with Owner the vessel is assumed to spend 20% of her life in North Atlantic and 80% in On-site (Gulf of Mexico or Shetland in Summer Season). Some hot spots did not satisfy design fatigue life of 25 years for given sea states. Through geometry modification, structural reinforcement or improving fabrication method such as grinding, all structural details could satisfy design fatigue life of 25 years.