A floating offshore wind turbine (FOWT) is always subjected to the combined action of nonlinear waves and winds in the realistic operating conditions. It is important to explore the high-order hydrodynamic loads and the motion responses of the offshore floating wind turbine. Based on the nonlinear potential flow theory and the perturbative expansion technique, the time-domain higher-order boundary element method (HOBEM) is used to model the hydrodynamics of an offshore floating wind turbine in the present study. In addition, the Blade Element Momentum Theory (BEMT) is applied to the aerodynamics. The present methodology is verified by comparing with the FAST code. It is found that the nonlinear effect is significant. This study can provide a reference for the design of an offshore wind turbine system.
The offshore wind turbine is widely applied to the utilization of wind power in the ocean engineering. Compared to land-based wind turbines, floating wind turbines are located in deep-sea, bringing more challenges in the cost management. However, the economic advantage of offshore wind turbines are apparent, in terms of a more stable year-round wind speed, a higher proportion of high-quality wind energy, greater turbine power, less wind farm development space limitations, and less visual pollution, etc. (Barthelmie et al., 2010; Breton and Moe, 2009).
Offshore wind turbine foundation is mainly divided into two forms: fixed foundation and floating foundation. The fixed foundations are typically applied in the shallow water regions (Musial et al., 2006). On the one hand, with the continuous development of the wind power technology, onshore wind power in the future will not be able to meet the needs of renewable energy developments. On the other hand, the global deep-sea resources are abundant, the future development of offshore wind power will be gradually expanded from shallow to deep sea. In deep-sea (over 60m water depth), the traditional fixed foundations are not practically feasible due to the high cost and the unguaranteed stability. Therefore, the development of floating offshore wind turbines (FOWTs) has been a research focus of both industrial and academic institutions (Butterfield et al., 2007).
