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Abstract The floating offshore wind turbines (FOWTs) had started activities as commercial floating wind farms in Europe. Japanese Government released the future plan, which is called “Green Innovation Fund Project (GI)”, to install and operate several FOWTs with large scale wind turbines in some areas around Japanese coast. However, further LCOE (Levelized Cost of Energy) saving, such as the building cost of substructures or operation & maintenance cost, is needed to expand the commercial use of FOWTs. The application of synthetic fiber ropes to FOWTs mooring is expected to contribute to the cost reduction. The light weight is one of the properties of synthetic fiber ropes. It also will be an advantageous aspect at the viewpoint of the harbor protection or the burden reduction of the pier ability. On the other hand, there are many kinds of materials for synthetic fiber ropes and the characteristics or the descriptions in safety guidelines have wide variety depending on the rope materials. Furthermore, the water depth of the installation site has a large effect on the selection of rope materials. Therefore, many conditions must be considered at the early stage of the FOWTs projects. The authors carried out the initial design of mooring systems of FOWTs with multiple kinds of rope materials in several water depths. The semisubmersible floater with 15 MW wind turbine was applied to this study. The polyester, nylon and HMPE (High Modulus Polyethylene) ropes were applied in this study. The maximum value of floater offset and the safety factor were considered as design conditions. We clarified the differences of mooring system specifications and the characteristics of mooring systems and floater offset through the numerical simulations. Furthermore, the differences in the physical quantities of mooring components were revealed in many kinds of mooring conditions which have large effect on the procurement costs.
Chujo et al. (Sun,) studied this question.