The development of mooring system in shallow water environment needs to adapt to the objective environmental conditions such as small water depth, large tidal range and high flow rate. The combination of mooring components such as buoy and clump weight with mooring lines can achieve the purpose of reasonably allocating mooring stiffness and reducing mooring tension, thereby reducing the strength requirements for mooring lines. In this paper, for OC4-DeepCwind semi-submersible floating wind turbine, Sima module in Sesam software are used for frequency domain and time domain analysis to study the motion response of floating wind turbine. By comparing the motion response of mooring system with and without accessories under the same working condition, the influence of the use of buoy and clump weight on the motion response of mooring system is analyzed, and the optimal mooring configuration is selected. The results show that the hydrodynamic characteristics of mooring accessories and their combination with mooring lines will significantly change the overall dynamic characteristics of the floating system and affect the safety and cost of the system. Reasonable use can optimize the floating wind turbine mooring system.
As the fastest growing green energy, wind energy is paid more and more attention by the world, and the development of wind power industry is also getting faster and faster. Compared with the fixed land wind turbine, floating offshore wind turbine not only solves the problems of noise and vision, but also offshore wind resources are abundant and more stable. Wind energy has gradually become an important part of China ‘s energy strategy development, and support for the development of offshore wind power is also growing. By the end of 2020, China ‘s offshore wind power installed capacity will exceed 5000 MW. The continental shelf in China has a long distance and the offshore water depth changes little. The offshore water depth is generally less than 60 m. At present, most of the offshore wind power in China is in the shallow water below 30 m, and the fixed wind turbine is mainly used. However, when the water depth exceeds 30 m, the fixed wind opportunity makes the cost increase linearly, so it is necessary to develop the floating wind turbine under the condition of shallow water (Liu,2016, Hu, 2016). Mooring system is the fundamental to ensure the safety and stability of floating wind turbines at sea. How to optimize the mooring system is one of the difficulties in the development of floating wind turbines. The object of this study is OC4-DeepCWind 5 MW floating wind turbine located at 40 m water depth in the Bohai Sea of China. The combination of mooring components such as buoy and clump weight with mooring cables can reduce the motion response of floating wind turbine, reasonably allocate the mooring stiffness and reduce the mooring tension, thereby reducing the strength requirements for mooring cables and reducing the cost. The hydrodynamic characteristics of mooring components (hydrostatic recovery stiffness, viscosity, inertia and other effects) and their combination with mooring cables will significantly change the overall dynamic characteristics of the floating system and affect the safety and cost of the system. How to use the combination of mooring parts such as clump weight and buoy with mooring cable is a breakthrough to solve the mooring problem under shallow water conditions. It provides a theoretical basis for the conceptual design of offshore floating wind turbine mooring system in the future offshore area, and has an important reference role.
