In this study, time-domain fatigue analyses of multi-planar tubular joints for a jacket-type substructure of offshore wind turbines designed for Taiwan's local environmental conditions are performed. The potential design load cases could affect the overall calculation procedure. A series of fatigue loads from the IEC 61400-3 standard were calculated to investigate the dominant design load cases and to improve the load calculation efficiency. The stress distributions of tubular joints are computed by finite element analysis to determine the stress concentration factors. The results show that the fatigue damage caused by the power production design scenario accounts for the total cumulative fatigue damage up to 90%. This work, in addition to more efficient load calculation procedure, will be helpful for cost assessment and could accelerate the development of offshore wind farms in Taiwan.

INTRODUCTION

Because of global warming and climate change, using renewable energy has become an inevitable substitute for fossil fuel and coal power. Wind power is one of the most promising renewable energy utilizations, providing an essential contribution to a clean, robust, and diversified energy portfolio. In Taiwan, the government's reiteration of the target is that 20% of the country's electricity will come from renewable energy by 2025, with wind power generation accounting for 15% of the renewable energy. In 2017, the first two offshore wind turbines of the 128 MW Formosa 1 Project, each a 4 MW machine, were installed, and the total installed capacity for offshore wind is predicted to reach 5.5 GW by 2025.

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