In order to ensure the safety of the offshore wind turbines (OWTs), the fatigue damage assessment is a key factor at the design and maintenance stages. To evaluate the fatigue damage accurately, the coupled effects of wind-wave loads should be taken into account seriously. The purpose of this paper is to investigate the influences of the coupled wind-wave loads on the fatigue assessment. Both of a fixed tripod-type OWT and a floating OWT are chosen as the target structures. To study the coupled effects, 3 load cases are performed, which are wind load only; wave load only and combined wind and wave loads. The dynamic response under 3 loads cases are calculated respectively. The time histories of responses at failure-critical locations are also derived. The fatigue damages are assessed with the rain-flow counting method and Palmgren–Miner rule in time domain. Finally, by comparing the results of uncoupled and coupled load cases, the coupled effects of wind and wave loads on the fatigue damage are concluded.
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