The limit state of a newly proposed floating wind turbine concept, in terms of ultimate structural load and fatigue damage load, is studied in the present work. This novel floating structure utilizes a triple-column spar platform to support the wind turbine. An aero-hydro-servo-elastic numerical model is developed to simulate its coupled dynamics. The probability distribution of the ultimate structural load is estimated based on the Monte-Carlo method. In order to reduce computation endeavor, a statistic model is used to extrapolate the sampled-based distribution function. The S-N curve method, a state-of-art fatigue analysis approach, is used to assess the fatigue damage load. The limit states of tower base and fairlead are investigated. It is shown that the newly proposed triplecolumn spar concept suffers less fatigue damage and the ultimate structural loads are also reduced, resulting in the enhancement of safety level of the floating wind turbine system.


Powered by the increasing global pursuit of sustainable energy, the traditional wind industry is moving to deeper water to exploit highquality offshore wind resources. Since the successful deployment of the world’s first floating wind turbine concept, Hywind demo (Equinor, 2017), various floating structures have been developed for offshore floating wind turbine application. Principle Power proposed the WindFloat (Principle Power, 2015), a semisubmersible floating wind turbine. Three types of floating wind turbine concept are designed in the OC4 DeepCwind project (Koo et al., 2014). More recently, Li and Wang (2019) investigated the long-term extreme loads of a new concept triplecolumn spar-type floating wind turbine, or TC Spar. The TC Spar is designed to be self-installed, thus no need for costly large DP crane vessels to perform offshore installation. Another advantage of the TC Spar is that the smaller diameter hull column makes it easier for efficient standardized fabrication.

In advance of the practical application of a new floating wind turbine concept, the structural integrity and reliability must be carefully investigated. Usually, the ultimate limit state and fatigue limit state are two critical parameters to assess the reliability and safety of the structure.

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