range: 50–300 m). Along with the development of modern horizon axis wind turbine, Sathcwell [22] noted, in the Royal Aeronautical Society Conference, that it was inescapable that floating foundation would be adopted in the near future to harvest offshore wind energy in deep waters. The DTI in U.K. took the lead in subsidizing researches on floating horizon axis wind turbines [23]. In terms of conceptual design of floating wind turbines, Tong [24] investigated, from both technical and economical perspectives, the feasibility of a wind farm, composed of 9 floating wind turbines, located in the North Sea. A ring-shaped floating structure named ‘Eolomar foundation’ was proposed by Italian scholars [25] to be used for areas with water depth larger than 100 m. It should be noted that all the above-mentioned projects still remain in the conceptual stage due to the prohibitive cost.
The floating foundation under investigation can be generally classified into three mainstream configurations based on floating principles adopted to achieve static stability: a semi-submersible