Experimental study on the tower loading characteristics of a floating wind turbine based on wave basin model tests

Abstract

The tower is an essential supporting structure for a Floating Wind Turbine (FWT). Due to the complexities of system structure and the environmental excitations, FWT towers present rather complicated loading characteristics, potentially threat the system reliability. This paper aims to reveal the FWT tower dynamics in wind-wave-current environments with a dedicated experimental apparatus. A new strategy is proposed to design the FWT structure. Then, extensive tests are conducted with different offshore environments and varying rotor operating conditions. Results show that the FWT tower loading presents complicated dynamic characteristics. The frequency response mainly consists of three parts: the low-frequency component associated with floater oscillations and wind excitations, the wave-frequency component induced by the linear wave loads, and the high-frequency component resulted from the rotor-nacelle assembly (RNA) operating and vibrations. The low- and wave-frequency responses increase with the wave height, while the high-frequency response amplifies with the aerodynamic loads. Vibrations transmit between the upper RNA and the lower floating platform through the tower structure, smearing the system stability and increasing the structure fatigue damages. Optimizations should be proposed to improve the FWT tower performance to suppress or isolate these unexpected vibrations.