DEVELOPMENT OF A NOVEL PROCEDURE FOR MAXIMUM-PRINCIPAL-STRESS-BASED FATIGUE PREDICTION OF MOORING CHAIN CONSIDERING IN-PLANE AND OUT-OF-PLANE BENDING EFFECT

초록

It is known that In-plane and out-of-plane bending effect are causative of fatigue damage, because of friction restraint and excessive relative angle between the mooring chain link which is used to moor floating offshore structure. The procedure of established In-plane and out-of-plane bending fatigue which is using the stress concentration factor (SCF) and nominal stress have a problem that leads to the variability of the fatigue life on account of inexactitude of the SCF and the nominal stress. In order to resolve that problem, this paper proposes a principal-stress-based novel procedure which is directly using the local stress of the fatigue prediction points. The time domain hydrodynamic analyses of the OC4 floating offshore wind turbine are conducted, so as to verify a principal-stress-based novel procedure proposed in this paper. OPB and IPB fatigue life occurred chain link is calculated using tension vector history. Compared with existing SCF-based fatigue life prediction procedure, it is verified to obtain considerably mitigated fatigue life. It is predicted that a novel procedure contribute to mooring line design optimization [1].