Introduction Offshre wind turbine support structure is under large stochastic loads within the whole design life, thus fatigue design is an important subject. The Equivalent Fatigue Static Load Method (EFSLM) is widely used in calculating the cumulative fatigue damage, while this method is questionable and is studied in this research. Method After a short review of EFSLM, its application scope was analysed theothetically. Based on NREL 5 MW wind turbine model and pseudo survey data, the quasi-dynamic method and EFSLM were used in calculating the cumulative fatigue damamge of a joint.
Result EFSLM is accurate only if the 1st principle stress is linear proportion to loads. Numerical simulation results indicate that EFSLM over estimates the cumulative fatigue damage.
Conclusion EFSLM over estimates the cumulative fatigue damage and the quasi-dynamic method is an alternative method, while, the accuracy of which needs further studies.
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