Abstract
In order to further understand the coupled aero-hydrodynamic performance of the floating offshore wind turbine (FOWT) in realistic ocean environment, it is necessary to investigate the interference effects between the unsteady aerodynamics of the wind turbine and different degree-of-freedom (DOF) platform motions under combined wind-wave excitation. In this paper, a validated CFD analysis tool FOWT-UALM-SJTU with modified actuator line model is applied for the coupled aero-hydrodynamic simulations of a spar-type FOWT system. The aero-hydrodynamic characteristics of the FOWT with various platform motion modes and different wind turbine states are compared and analyzed to explore the influence of the interference effects between the wind turbine and the floating platform on the performance of the FOWT. The dynamic responses of local relative wind speed and local attack angle at the blade section and wind-wave forces acting on the floating platform are discussed in detail to reveal the interaction mechanism between the aerodynamic loads and different DOF platform motions. It is shown that the surge motion and the pitch motion of the floating platform both significantly alter the local attack angle, while only the platform pitch motion have significant impacts on the local relative wind speed experienced by the rotating blades. Besides, the shaft tilt and the pro-cone angle of the wind turbine and the height-dependent wind speed all contribute to the variation of the local attack angle. The coupling between the platform motions along different DOFs is obviously amplified by the aerodynamic forces derived from the wind turbine. In addition, the wake deflection phenomenon is clearly observed in the near wake region when platform pitch motion is considered. The dynamic pitch motion of the floating platform also contributes to the severe wake velocity deficit and the increased wake width.
Highlights
Limited by the space availability, noise restriction, visual pollution and regular problems, the exploration of wind energy is advancing from the land to the offshore area and further to the deep sea [1]
Considering that the cost of offshore wind turbines mounted on the bottom-fixed structures increases sharply with water depth, the offshore wind turbines supported by the floating structures, known as the floating offshore wind turbines (FOWTs), are believed to be the most economical choice in deep waters [2,3]
The coupled aero-hydrodynamic performance of a spar-type FOWT composed of the National Renewable Energy Laboratory (NREL) 5-MW wind turbine and the OC3-Hywind spar platform is investigated by the validated computational fluid dynamics (CFD) analysis tool FOWT-unsteady actuator line model (UALM)-SJTU
Summary
Limited by the space availability, noise restriction, visual pollution and regular problems, the exploration of wind energy is advancing from the land to the offshore area and further to the deep sea [1]. It is known that there are strong interactions between the wind turbine and the floating support platform when the FOWT is in operation [4]. The aerodynamic forces derived from the wind turbine will act on the floating platform and greatly change the motion responses. The six-degree-of-freedom (6DOF) platform motions affect the rotating blades and significantly alter the aerodynamic performance. The interference effects between the wind turbine and the floating platform make the coupled aero-hydrodynamic characteristics more complicated and lead to increased instability of the FOWT system. In order to better understand the coupling phenomena and contribute to the realization of the dynamic stability of the FOWT, it is necessary to investigate the interference effects between the wind turbine aerodynamics and different degree-of-freedom (DOF) platform motions
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