It is strongly desired to develop a cost-effective wind turbine system of floating-type in order to gain the renewable energy resources. In this study, the SPAR-type floating foundations using reinforced concrete are examined. The regular and irregular wave experiments are performed for 1/100 scale models of the prototypes. Three models are examined, that is, a uniform cylinder moored at the gravity center, a uniform cylinder moored at the upper position and a stepped-type floating cylinder moored at the upper position. The experimental results are compared with numerical predictions using potential theory and Morison's equation. The stepped-type floating cylinder moored at the upper position has shown smaller motions than the uniform cylinders.
Several concepts for Floating Offshore Wind Turbine (FOWT) have been proposed and under research in Japan (e.g., Fukumoto, et al., 2006; Ishihara, et al., 2006; Kitamura, et al., 2006; Ohkawa, et al., 2006; Sukegawa, et al., 2006; Yago et al., 2007). On the other hand, Blue H Technologies BV (2007) implemented a TLP-type FOWT mounting 80kW-class wind turbine in 108 meters waters offshore in Southern Italy. StatoilHydro (2008) announced to build a full scale SPAR-type FOWT, Hywind, offshore in Norway. Nielsen, et al. (2006) and Skaare, et al. (2007) examined the dynamic response of the SPARtype FOWT, Hywind, under the action of winds and waves by experiment and numerical simulations. They have shown the importance of the effect of pitch-angle control of blades on the dynamic response of FOWT in the region of the wind speed above the rated wind speed. In this research, attention is paid to a SPAR-type FOWT made of concrete because of its possible cost-effectiveness. Main objectives of the research are to examine the wave-motion characteristics by wave tank experiment, and to develop and validate a wave motion simulation program using Morison's equation for wave force evaluation. In a past study (Moriya, et al., 2007), a stepped-type SPAR has been examined for its dynamic motion induced by wind, wave and current.
