A study on the dynamic response of a semisubmersible floating offshore wind turbine system Part 1: water tank test with considering the effect of wind load

ABSTRACT: A new semi-submersible floating structure was proposed on which three wind turbine towers would be installed. This paper presented the dynamic behaviors of the 1/150 scaled rigid model experiments in a water tank. A free vibration test was conducted in still water to obtain the natural pe-riods for verifying the numerical model and modeling the damping ratio of the vertical motion in the part 2 of this study. To evaluate the dynamic behavior of the floater, regular wave tests were conducted with the wave heights 2,4,8cm, wave periods range 0.6~3.0s and the responses of floater were meas-ured by using an optical system. The observed surges varied linearly with the wave height in the ranges of periods far from the natural period. However, the surges normalized by wave height had peaks around the natural period, and decreased significantly when wave heights increased. To investigate the effect of the wind turbines to the floater, collinear wave and wind tests were also conducted in the same wave condition, wind speed was set at 2 and 4m/s corresponding the operating and survival case of wind turbine, respectively. The observed surges showed that the peak responses of the floater decrease in the operating condition due to the aerodynamic damping from wind turbine, but there was little ef-fect in the survival condition