Experimental study on vortex-induced motion of spar-type floating offshore wind turbine based on image processing technology

Abstract

Most floating wind turbine foundations consist of single or multiple columns, which are prone to vortex-induced motion (VIM) under the action of uniform flow. VIM is the main reason causing fatigue damage to mooring structures. Exploring the motion response of VIM of the spar-type wind turbine structure, the spar wind turbine foundation was designed as a prototype, and the model was simplified to a cylinder. In this paper, we conducted an experimental study of its model in the circulating water tank based on Matlab image processing technology. The VIM characteristics of the model were discussed by capturing its optical measurement points, and then the structural response amplitude was obtained by using the target tracking method. The study showed that the optical measurement method could effectively monitor the motion response of the structure, and the binary method could better obtain the VIM characteristics of the structure. Meanwhile, it was found that the response amplitude of the cylindrical VIM presents four stages: initial excitation branch, upper branch, lower branch, and desynchronization. It was also revealed that the maximum amplitude was reached in the upper branch, and the locking phenomenon was shown at the reduced velocity 4.96 ≤ Ur ≤ 7.11.