Hydrodynamic characteristics of a novel towerless floating wind turbine integrated with wave energy converters

Abstract

A novel towerless floating wind turbine (TFW) is proposed in this study and integrated with three wave energy converters (WECs) by the hinge joint to further increase the stability of the system. This aims to reduce large pitch accelerations for the nacelle and excessive stresses at the tower base when encountering large amplitude waves. Based on the numerical tests performed with the viscous corrected panel method, it is revealed that the in-phase wave excitation forces acting on three columns can result in the largest mooring tension in short-period waves and the high-frequency tension oscillation appeared under specific conditions is attributed to the triple-frequency components. The pitch motion of the novel TFW platform can be largely suppressed by mitigating the adverse effect induced by the superstructure. Hit by the abnormal wave, the floating wind turbine exhibits a significant hysteresis phenomenon in the maximum pitch response due to the multi-system coupling effect. Compared with the traditional DeepCwind platform, the survivability of the novel TFW platform in extreme sea states is greatly improved, considering that the maximum motion responses and the snap loads have been largely reduced at the transient stage, and that the durations of the heave and pitch become much shortened at the decaying stage. The stability of TFW can be further enhanced by integrating with the hinged WECs under the condition of a larger power-takeoff damping force but at the expense of decreasing the wave energy capture efficiency.