Comparisons of dynamical characteristics of a 5 MW floating wind turbine supported by a spar-buoy and a semi-submersible using model testing methods

Development of floating offshore wind turbine technology is in need of more scaled model tests to investigate its dynamical characteristics. This paper presents the model testing investigations of a spar-buoy and semi-submersible floating wind turbines, and conducts a series of comparisons on the experimental results of the two floating wind turbines. It is found that the spar-buoy floating wind turbine is more sensitive to wind loading and has larger amplitudes of platform motion in wind only cases, especially for the yaw motion. By contrast, the semi-submersible floating wind turbine is more sensitive to wave loading, especially for the second order difference-frequency wave loading. In addition, the dynamic responses of the two floating wind turbines are both influenced by the current flow. Compared to the semi-submersible floating wind turbine, the more regular “figure-eight” surge-sway trajectory is observed in the spar-buoy floating wind turbines, showing the influence from vortex-induced-motion. This paper provides more valuable experimental details and results to the scientific community with regard to the spar-buoy and semi-submersible floating wind turbines. Moreover, the comparison of the dynamic behaviours of the two floating wind turbines in various conditions helps to understand the characteristics and mechanism about the floating wind turbine technology.