Design strategy for resonance avoidance to improve the performance of tension leg platform-type floating offshore wind turbines

Abstract

The objective of this study is to determine the effect of elasticity of the tower and blades of a large tension leg platform (TLP)-type FOWT on the eigenmodes of the entire system and suggest reference directions to be implemented in the conceptual design stage. Typically, TLP-type FOWTs are connected by a mooring system with strong tension and exhibit an extremely short natural period of motion compared with a semi-submersible platform. Furthermore, the wind turbine tower mounted on the floating platform is flexible in the fore-aft and side-to-side directions, forming a vibrating system in itself; therefore, it is coupled with the motion of the floating platform. In particular, the tower elasticity is known to influence the roll and pitch motions of the platform. In this study, the motion response characteristics of the platform were investigated according to the changes in the tower design parameter (bending stiffness). The influence of blade elasticity was also confirmed, verifying that the physical characteristics of both the tower and blade significantly affect the motion of the TLP. Additionally, the degree of influence based on environmental loads was identified to suggest a design direction for FOWTs while avoiding resonance.