The fully coupled aero-hydrodynamic analysis of a floating offshore wind turbine (FOWT) is investigated. This is a complex study because it needs to predict the aerodynamics of wind turbine, hydrodynamics of floating platform, and their interactions accurately, especially in the extreme sea states. The hybrid model qaleFoam, combines the fully nonlinear potential theory (FNPT) and the two-phase Navier-Stokes (NS) model, is applied. An example with a focused wave and uniform wind is considered to represent the extreme condition. The coupled effect on the aerodynamic loads of turbine blades, hydrodynamic behaviors of the supporting platform and the detailed flow field information in the wake region is analyzed. The results show that this hybrid model works well in the modeling of the FOWT coupled analysis.
In recent year, the wind turbines are installed from onshore to offshore, from fixed to floating. It is an important significance that making sure the fine working status of the floating offshore wind turbine (FOWT) in the ocean. However, it is a big challenge how to accurate predict the performance of an FOWT system especially in the extreme sea situation. For this fully coupled system, the aerodynamics of wind turbine due to incoming wind, the hydrodynamics of the floating platform because of the wave and current and the tension loads from the mooring system interact with each other. This interaction increases the complexity and the difficulty of the numerical simulation.
There are mainly two solutions to overcome this problem. The first one is the simplified method, in which the linear potential flow theory combined with Morrison's equations and Blade Element Momentum (BEM) are used. This approach has high efficiency and usually used in the design of FOWT systems (Jonkman, 2009; Robertson, 2014). Nevertheless, the highly nonlinear problems and the coupled effect between the turbine blade and its wake are not considered, which could not satisfy the research target (Nematbakhsh, 2013; Sebastian, 2012). The other is the Computational Fluid Dynamics (CFD) method that resolves the simplified method problems and thus can get more accurate tendency. Therefore, a number of studies are carried out about FOWT systems with CFD tools , e.g. Tran and Kim (2016) used the STAR-CCM+ to compare the FOWT under regular wave with FAST; Liu et al. (2017) developed a fully coupled tool based on OpenFOAM and analyzed the interaction of aerodynamics and hydrodynamics; Cheng et al. (2019) introduced the unsteady actuator line method into the naoe-FOAM-SJTU solver to simulate similar case with Tran and Kim. However, it can be found that their computational domain is very large, which is caused by the large-scale wave need enough space and time to generate and absorb completely.
