Session: 09-01-10 Wind Energy: Moorings 2

Paper Number: 126232

126232 - Study on the Synthetic Fiber Rope Mooring for Floating Offshore Wind Turbines Depending on the Water Depth and Materials of Ropes 

The floating offshore wind turbines (FOWTs) had started their activities as commercial floating windfarms in Europe. Japanese Government released their future plan, which is called “Green Innovation Fund Project”, 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, are needed to expand commercial use of FOWTs. The application of synthetic fiber ropes to FOWTs mooring is expected to contribute on 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 large effect on the selection of rope materials. Therefore, a lot of conditions must be considered at the early stage of the FOWTs projects. For example, because the seabed around Japanese coast is steep, the difference in water depth from one anchor to another anchor in one substructure may add to the further difficulty of the planning and the designing.

The authors carried out the initial design of mooring systems of FOWTs with multiple kinds of synthetic fiber ropes in several water depths which are considered suitable for the installation around Japanese coast and clarified the differences of mooring system specifications and the characteristics of mooring systems and floaters’ displacement through the numerical simulations. The turbine, the substructure and the maximum value of floater offset in a surge motion and environmental conditions were common, and the safety factor of mooring ropes was set to 2.5 according to the guideline of Class NK in the simulations. The IEA 15 MW reference wind turbine and Volturn US-S semisubmersible floater were applied to this study. The authors carried out the initial design and simulations for the nylon and the polyester ropes, which are major and promising materials for FOWTs mooring systems and also for a high strength material such as the HMPE (High Modulus Polyethylene). The differences in the physical quantities of mooring components in many kinds of mooring conditions which have large effect on the procurement costs and the offshore installation costs were revealed in this study.

Presenting Author: Toshiki Chujo National maritime Research Institute

Presenting Author Biography: Graduated from Graduate school of Engineering, Tokyo University on 2003.3
Worked at Shipbuilding Research Center of Japan until 2008.1
Worked as a researcher at National Maritime Research Institute Japan from 2008.2
Worked as a chief researcher at National Maritime Research Institute Japan from 2011.4
Worked as a team leader of offshore wind turbine project team at National Maritime Research Institute Japan from 2020.3

Authors:

Toshiki Chujo National maritime Research Institute
Ken Kamizawa Japan Marine United Corporation
Haruki Yoshimoto Japan Marine United Corporation