In conducting fatigue analysis of the mooring system of floating offshore wind turbine, there was uncertainty in determining the range of sea conditions, so it was necessary to clarify this.

In recent years, there has been increasing interest in floating wind turbines, but no country has yet seen commercial operation. In Japan, demonstration tests using prototype floating wind turbines in Fukushima and Kitakyushu have clarified the issues for practical use. The development of safety guidelines is one of the issues for the practical application of floating wind turbines. It is necessary to make it easier for power generation companies to enter the floating wind turbine business by making the safety guidelines more concrete and simple.

The safety evaluation method for land-based wind power generation facilities has been developed mainly by the International Electrotechnical Commission (IEC). On the other hand, the safety evaluation method of the floating wind turbine, especially the mooring system, is said to conform to the oil and gas field method, and it is considered that there is a lack of consistency.

In this paper, we consider the method of fatigue life analysis for mooring systems. In the oil and gas field, fatigue life analysis of mooring system is performed using the full long-term distribution of metocean parameters in the site where the floating structure is installed, and IEC suggests same method, but IEC sets a design load case (DLC) to exclude severe sea conditions from fatigue analysis. We will clarify the impact of this exclusion on a simulation basis.


Floating offshore wind turbines have wind turbines installed on moored floats. This is a fusion of floater technology and wind turbine technology. Each technology has its own history, its own safety evaluation method exists, and the safety evaluation method of floating offshore wind turbines is also a fusion of each. This creates ambiguity. In this paper, we discuss the ambiguity in the safety evaluation method of mooring systems.

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