In 2017, the MHI Vestas released a 9.5-MW offshore wind turbine. It is also actively researching and developing a 10-MW offshore wind turbine. As the capacity of a wind turbine increases, the sizes of all its system components, including length and weight, correspondingly increase. Consequently, as a wind turbine becomes larger, it becomes necessary to analyze the fatigue load applied to its entire system. The first reason for such an analysis is to achieve a safe but not overly designed large wind turbine. Second, most wind turbine accidents involve aging turbines and are related to fatigue analysis.

Accordingly, the purpose of fatigue analysis is to safely design a wind turbine that sustains repeated loads within its design life. In this study, the blades and loads for the fatigue analysis of a 12-MW floating offshore wind turbine are calculated based on the National Renewable Energy Laboratory (NREL) 5-MW wind turbine blades. The calculated loads are applied to the Markov matrix through a preprocessing, such as the cycle counting method. Finally, the equivalent fatigue load is estimated based on both mean and range.

In this study, only the equivalent fatigue load on the turbine blade is calculated. However, if fatigue analysis is to be performed for all parts using equivalent loads, it is possible to design the wind turbine to fully withstand such loads throughout its design life, and prevent the overdesign of each part as well.

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