In this study, a series of physical model tests were carried out in a three-dimensional wave basin to investigate the motion response characteristics and stability of a semi-submersible wind turbine foundation under different waves, current and wind conditions. When the waves and wind loads are superimposed, the maximum inclination of the wind turbine foundation is slightly lower than that of the wave load alone. When the wave, current and wind loads are combined, the maximum inclination of the wind turbine foundation is basically the same as that of the wave load alone.
In the deep sea areas far from the mainland, there are many high-quality wind resources that can be developed and utilized. To develop these offshore wind farms with a water depth of more than 50 m, floating-type foundations are often applied. The semi-submersible foundation is one of the typical floating foundations for offshore wind turbines. At present, many countries are actively developing the foundations for offshore floating wind turbines, especially the semi-submersible foundations for wind turbines, and have made certain progress in conceptual design, and researches on stability and hydrodynamic performances.
In terms of conceptual design, Bulder, et al. (2002) proposed a variety of conceptual design schemes for floating foundations such as truncated cone-shaped floating body, triangular platform and quadrilateral platform. They comprehensively studied the feasibility of these schemes in the water depth over 50 m from different aspects such as the stability, motion response characteristics, the usage amount of steel, maintainability, etc., which turns out that the triangular platform is the optimal scheme. Zambrano, et al. (2006) installed three sets of wind turbines on the semi-submersible platform MiniFloat, and used the time domain analysis to study the motion response of the platform under different working conditions. The result showed that the average pitch angle was less than 5° and the amplitude was less than ±15°, indicating that the platform has good motion performance. Ishihara, et al. (2007) designed a semi-submersible wind turbine platform that can carry three sets of wind turbine towers, and studied its motion response characteristics under wave and wind loads through numerical simulation and scale-model tests. Tang, et al. (2014) designed a triangular semi-submersible floating foundation for 5 MW wind turbine and studied its hydrodynamic performance under different working conditions. Deng, et al. (2016) proposed a conceptual design scheme of a semi-submersible wind turbine platform based on a reinforced concrete structure and carried out a performance analysis through numerical simulation, proving the feasibility of the scheme.
