Fatigue Strength Analysis For 308,000 DWT VLCC

VLCC(Very Large Crude Oil Carrier) is the main ship for the oil carrying. All over the world, there are about 440 vessels; about 17% of which have been served for more than 20 years. In the last 10 years, the demands for VLCC are hold on the high level. So we need to develop a new type of vessel, which will fit the newest requirements.The research is based on the 308,000t VLCC. This thesis tries to find out the factor for fatigue and the potential fatigue crack position. It should be noted that every welded joint and attachment or other form of stress concentration is potentially a source of fatigue cracking and should be individually considered.Fatigue analysis may be carried out by methods based on fatigue tests (S-N data) and estimation of cumulative damage (Palmgrens-Miner rule). Where the loading or geometry is too complex, a finite element (FEM) analysis of the details is to be carried out to determine the fatigue stress of that detail. So, the finite element analysis to determine hot spot stress that should be used for weld toe locations that are typically at welded hopper knuckle connection in way of transverse primary support members.The aim of the fatigue control is to ensure that all parts of the hull structure subjected to fatigue (dynamic) loading have an adequate fatigue life. Calculated fatigue lives, calibrated with the relevant fatigue damage data, may give the basis for the structure design of VLCC. Furthermore, we can form the basis for efficient inspection programs during fabrication and throughout the design life of the vessel.