Based on the I EC 61400-3 offshore wind turbine(OWT)design guidelines.The NREL 5MW wind turbine with Taiwan domestic jacket support structure in 18 meters water depth was selected to perform the fatigue strength calculation for the support structure.Commercial software Bladed and SACS are used to perform the required structural responses and fatigue strength calculations.The stress concentration factors(SCF)and S-N curves for the stress calculations of tubular joints are adopted based on the recommendation of DNV GL guidelines.The magnitude of the stress variation range and the corresponding number of counts are obtained by the rainflow counting algorithm.Finally under the assumption of Palmgren-Miner linear cumulative damage rule,the cumulative damage of the structure component can be calculated and then the fatigue life can be estimated.The numerical evaluation results can also be available for the further reference on the determination of sensor locations for the structural monitor system.
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