To improve the reliability of a mooring system of a floating wind turbine under extreme sea conditions, a constant tension mooring system is proposed in this paper. In extreme sea conditions, when the mooring force reaches the set value, the mooring system automatically releases the weights stored on the floating platform, and the floating platform moves along the waves with a basically constant mooring force. Through coupled time-domain simulations, the dynamic responses of the 5-MW-CSC, a semisubmersible wind turbine developed at the Centre for Ships and Ocean Structures with a constant tension mooring system, were studied under the extreme conditions with 50-year return period.
Offshore floating wind power is maturing and has significantly reduced costs over the past few years. Compared with fixed offshore wind power, floating wind power is still in the stage of small-scale development. With the rapid maturity of technology and the continuous emergence of demonstration projects, it is expected to realize large-scale commercial development by 2030. According to the prediction of the European Wind Energy Association (now WindEurope), the global installed capacity of floating wind power will reach 15 GW by the end of 2030 (Corbetta et al., 2015). WindEurope conservatively estimates that the cost of floating units will decrease by 38% by 2050 (WindEurope Floating Wind Task Force, 2017). At that time, 150 GW of offshore floating wind power will be developed in Europe, which means that one-third of offshore wind power will be floating wind power in deep sea.