Floating wind turbine technology has become mature in recent years, it tends to be large-scale and deep-water deployment. Nowadays floating wind turbines are mainly semi-submersible platforms that are sensitive to the change of water depth and are mostly designed in deep water over 100 meters. However, the water depth in the South China Sea tends to be shallower than the North-sea in Europe, which should result in different mooring and platform dynamic response characteristics. So, the adaptability of a large floating wind turbine to the middle and shallow waters of the South China Sea has attracted much attention in China. In this paper, the DTU10MW wind turbine designed by the Technical University of Denmark and the OO-STAR platform proposed by the University of Stuttgart are taken as the research objects. The hydrodynamic model is established by AQWA. Based on the potential flow theory, the hydrodynamic coefficients of the OO-STAR platform in three different water depths are compared and further imported into OPENFAST for fully coupled time-domain simulation. Firstly, mooring schemes of different water depths are designed based on the bottom anchor uplift. Then various natural periods of OO-STAR are evaluated (mainly including platform motion and pitch vibration of the tower), Finally, based on the power spectral density method, the tower-base fore-aft bending moments, platform motion, and mooring response characteristics are analyzed under the low-frequency excitation load of turbulence wind and different water depth, and the excitation action of the 1P effect to the structural response is also considered. It provides a reference for the design of super large floating wind turbines in a medium and shallow seas in China.
Over decades of development in renewable industry, offshore wind energy has become renewable energy indispensably. The total global installed base of the floating offshore wind turbines (FOWT) is 35.3GW until 2020 (GWEC 2021). China ranks second in the world with 9.88GW offshore installed. Without a doubt that FOWT will flourish in China. The world has entered the operational stage of 5MW FOWT with the completion of the world's first floating wind farm (H. R. 2015). At the same time, the Kincardine offshore wind farm under construction marks the exploration of the 10MW level of floating wind turbines. The large-scale FOWT has deepened its deployment depth. However, The South China Sea has a vast sea area as the depth of 50 meters (Hsiao et al., 2016). The bottom-fixed substructure can no longer be used at deeper water depths(>50m) due to the high cost (Han et al., 2017), Therefore, it is of great significance to study the mooring and platform dynamic characteristics of ultra-large floating wind turbines in different water depths.
