The full exploitation of offshore wind resources can essentially satisfy the massive energy demand. The realization and application of ultra-high-power offshore wind turbines are crucial to achieving full use of deep-sea wind energy and reducing the cost of wind power. For the VolturnUS-S semi-submersible floating foundation of a 15 megawatt (MW) offshore wind turbine, the effect of structural parameters on hydrodynamic performance was investigated by controlling the variables described in this paper. Accordingly, the floating foundation was optimized and coupled to the 15 MW offshore wind turbine. The dynamic performance of the integrated 15 MW offshore wind turbine was analyzed under different operating conditions, by applying the aero-hydro-servo-elastic coupled method. The results show that for a wave in a 0-degree direction, a 5% increase of column spacing will reduce the peak value of the pitch transfer function by 33.61%, and that a 5% decrease of the outer column diameter will further reduce the peak value by 26.27%. The standard deviation of the time-domain surge responses was reduced by 19.78% for the optimized offshore wind turbine, and the maximum value of the mooring line tension was reduced by 13.55% under normal operating conditions.

Mooring system design of a floating offshore structure in the arctic region is considered to be extremely important. This paper aims at investigating an optimal mooring system for the Kulluk platform operating in the Beaufort Sea, which has ice-free and ice-covered conditions during the whole year time. In order to complete the layout design of the mooring system to satisfy the year-round operation, both the effect of wave loads and ice loads should be considered. The research establishes a coupled numerical production system composed of the Kulluk platform and mooring system. Wave load is solved by potential flow theory. The slender finite element method is used to compute the tension of the mooring system. The nonlinear finite element method, discrete element method, and empirical formula are compared to analyze ice load. Finally, the discrete element method is selected for the analysis of the Kulluk, and the simulated results are compared reasonably with the field data. When studying the mooring line configurations, quantitative time-domain analysis is carried out, including tension of mooring lines and the motions of the platform under different working conditions. The research work in this paper will provide a reference for the optimal design of the mooring system of the platform operating in the Arctic Sea.

Floating offshore wind turbines (FOWTs) suffer from continuous platform motions due to ocean environmental loads, which induces dynamic wake characteristics and affects the power performance of downstream turbines. Understanding these impacts is crucial for wind farm efficiency improvement. This study investigates the middle-to-far wake characteristics of a FOWT under harmonic surge motion, a significant degree of freedom with substantial aerodynamic consequences. By applying the Dynamic Wake Meandering (DWM) model in FAST.Farm, the wake velocity recovery, turbulence intensity (TI), and wake center positions of the NREL 5 MW wind turbine are analyzed at downstream distances of 5D, 7D, and 9D. The study systematically studies the effects of surge amplitude and frequency on these factors. The results indicate that larger surge amplitudes can lead to a pronounced increase in TI and shifting of the wake center and higher surge frequencies can promote wake recovery but have a diminishing effect on TI and velocity fluctuations in the far-wake region (≥7D). Under a typical surge motion of 8 m amplitude and 0.125 Hz frequency, the TI at 7D increases to 3.90%, and wake velocity recovery improves by 21% compared with the fixed-bottom case. Substantially, increased amplitude and frequency of the upstream turbine can lead to a higher mean power output for the downstream turbine but also introduce more significant power fluctuations. This work provides quantitative insights into the physical mechanisms of the impact of surge motion on FOWT wake evolution and its consequences for wind farm performance, which provides valuable guidance for the layout optimization of floating offshore wind farms.