A novelty floating wind turbine concept, which utilizes a newly developed triple-column spar platform to support the NREL 5MW baseline wind turbine, is proposed in this research. A modified environmental counter method is proposed to estimate the long-term extreme response of the novelty concept. Aero-hydro-servo-elastic coupled simulations are performed. Numerical simulations demonstrate that the triple-column Spar floating wind turbine has a better dynamic performance compared with a single-column concept, in terms of platform motion, tower base structural loads and mooring line tension. The critical environmental condition is identified with the modified environmental contour method, and it is shown that the 50-year return period extreme tower base structural load is reduced with the application of the three-column Spar platform. Nevertheless, the extreme mooring line tension which is dominated by the wind load, is not reduced. The present research reveals the prospect of the three-column Spar concept in the offshore wind energy application.


Powered by the increasing global pursuit of sustainable energy, the traditional wind industry is moving to deeper water to exploit the high-quality offshore wind resource. Since the proposal of the Hywind demo (Equinor, 2017), the world's first full scale offshore floating wind turbine, various floating structures have been developed for offshore floating wind turbine application. The WindFloat (Principle Power, 2015) is a semisubmersible floating wind turbine, which utilizes three columns with heaving plates to produce buoyancy force. Three floating platforms are proposed in the OC4 DeepCwind project (Koo et al., 2014). Goupee et al. (2014) conducted an experimental comparison of floating wind turbine with three supporting platforms. Li et al. (2018) numerically simulated the dynamic response a Spar-type floating wind turbine integrated with a wave energy converter (WEC) and two tidal turbines. While the short-term investigation (assuming that the stochastic environmental condition is fixed) on floating wind turbine has been fully conducted, the effort spared on long-term performance is insufficient.

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