Incidence of wind spectrum and turbulence intensity on the design of mooring systems for floating offshore wind turbines

The paper focuses on the incidence of wind spectrum and turbulence intensity on the design of stationkeeping systems for Floating Offshore Wind Turbines. After a brief review about the employed nonlinear time-domain hydrodynamic model, some basics about the Ultimate and Fatigue Limit State design conditions of the mooring system are provided. Subsequently, the two wind spectra, employed in the numerical simulations, are briefly introduced. The former is the NPD wind spectrum, generally applied for the design of mooring systems for typical offshore structures, employed in the oil and gas sector. The latter is the Kaimal wind spectrum, generally employed for the design of offshore wind turbines in conjunction with different turbulence models, depending on the operative scenario. The numerical investigation is performed considering the DeepCwind platform, equipped with the 5 MW NREL wind turbine, as reference support structure, deployed in the North Sea area. Three different water depths, from 200 up to 400 m, are considered. It is verified that both the wind spectrum and turbulence model play a fundamental role not only for the optimum design of the stationkeeping system, but also for the proper selection of the line scope, as well as of the leading usage factors.