This paper describes the whole ship and fatigue analyses of a 170 k Ice class LNGC, first ice class vessel of DSME. This paper includes determination of design load, global strength and fatigue strength. This subject vessel was designed to have more than 40 years’ fatigue life against given environmental conditions and fatigue damage was assessed based on stochastic method. Whole ship FE analysis was also carried out to verify the structural adequacy of global strength based on direct wave load analysis. In stochastic fatigue analysis, fatigue damage was calculated based on direct wave load analysis. D-SAFS, developed by DSME, was used in stress RAO generation and fatigue damage assessment. Stress RAOs were made based on ‘Component Based Method’. In this method, structural analyses were carried out for each unit load case and then resultant stress was combined with wave load analysis results to generate stress RAOs. D-SFAS defines unit load cases automatically and generated stress RAO from motion analysis results. Whole ship FE models having fine mesh in fatigue sensitive area were used in structural analysis. Different steel density was also assigned along ship length for mass adjustment within hull structure. Some hot spots were found not to satisfy the design fatigue life of 40 years in initial design stage. Through geometry modification, structural reinforcement or improving fabrication method such as grinding, all structural details could satisfy design fatigue life of 40 years. According to the results of whole ship analysis, there were some high stresses at local area. Conclusively, additional strengthening of the hull was required compared to standard class rule requirements, with respect to yield and buckling and fatigue strength, leading to a more robust vessel.
Collapse load analysis for circumferentially cracked cylinder
subjected to combined torsion and bending moments
