FUNDAMENTAL WIND TUNNEL EXPERIMENTS ON WIND DRAG FORCES AND DAMPINGS OF AN OFFSHORE WIND TURBINE STRUCTURE

Since an offshore wind turbine may be designed considering the effects caused by fluctuating wind and wave loadings as well as forces by rotation of blades, it is necessaryt o make clear dynamic characteristics such as damping and drag force coefficients of the blades and a tower-like-structure. Therefore we conducted a 1/55 scale model test for a rotor-nacelle-tower-foundation structure of 1500kW wind generator at top. The foundation corresponding to several kinds of structure was modeled as columns having different flexural rigidity. The wind force measurements were done for a sole tower and a tower with rotating and non-rotatingt hree-blades to obtain the drag coefficients of the tower and blades respectively. While the damping constants were measured by free oscillation tests without w ind during non-operation, the ones with wind during both operation and non-operation condition were also determined by half power point method for response spectra of strains and accelerations induced in the tower. The paper also describes a comparison with the measured and calculated response of the model.