Research and development about the mechanisms of a single point mooring system for offshore wind turbines

A new type of floating wind turbine, in which the floater itself can rotate from the wind is proposed in this paper. A new single point mooring system is necessary for the development of this new wind turbine. In this paper, the single point mooring system, which includes component such as catenary chains, the slip ring for the electric cable and the control cable were researched. This work will examine two different configurations of the single point mooring system that we developed. One uses a thrust bearing at the connecting points between the mooring parts and the floater parts. The other one uses not only a thrust bearing, but also an aligning bearing. Weather vane tests about the offshore wind turbine with each mooring system were conducted in an ocean basin. After performing wind tests of both configurations of the single point mooring system, it was concluded that the latter one functioned superior to the former one. This work discusses and clarifies the reason based on a physics model which focuses on the relation between the restoring yaw moment caused by the mooring chains and the static friction moment due to the bearing unit. We also performed a wind test at a real sea and verified that the bearing unit with not only the thrust bearing but also the aligning bearing could function properly.