The mooring design for moderate water encounters a conundrum of combining the virtues of reliable mooring performance and a competitive cost. In this article, an innovative mooring concept specially for moderate water (30-100m) is proposed. Taking a floating offshore wind turbine (FOWT) as the moored object, a comprehensive comparison between a proposed and patented new mooring scheme and the traditional catenary mooring is carried out through static, free decay, dynamic and cost analyses. Almost all results demonstrate that the new mooring is not only superior in mooring performance but economically attractive in fabrication.
In recent years, wind energy has gained more and more attention worldwide due to its renewability, sustainability, high efficiency and low emission of carbon. Many countries consider the exploitation of wind energy as an indispensable part of their energy strategies. Compared with the onshore wind energy, several attributes of offshore wind energy provide immense potential for its development such as more stable resource, vaster in space for utilization, and of fewer impacts on environments. According to the Global Wind Energy Council (GWEC, 2022), the cumulative installed capacity of offshore wind power reached 56GW as of the end of 2021, up 60% on the previous year.
In terms of foundation patterns, the offshore wind turbines are divided into bottom-fixed wind turbines and FOWTs. The construction and installation cost of the bottom-fixed wind turbine soars when the water depth exceeds 50m (Henderson, 2010), but the FOWT quickly emerges as a strong alternative for a wide range of water depths. The last ten years have seen dozens of FOWT projects successfully commissioned in moderate water and even deep water. As the world's first commercial offshore wind farm, Hywind Scotland (Equinor, 2017) consists of five 6MW wind turbines with Spar foundation. Hywind Tampen (Equinor, 2022), the world's first FOWT project to supply power to offshore oil platforms, continues to adopt the same Spar foundation concept. Simultaneously, the semi-submersible wind turbine begins to emerge by virtue of its small draft and convenient wind turbine installation operation. The semi-submersible foundation is successfully adopted in WindFloat Atlantic (EDP Renewables, 2019) in Portugal as well as Kincardine (Principle Power, 2021) in UK. Currently, Kincardine is the largest floating wind farm in the world with a total of 50MW turbines. Its 9.5MW unit makes a key breakthrough in the development of large capacity of a single wind turbine. A detailed review of the latest FOWT projects worldwide can be referred to Yang et al. (2022).
