Japan has lagged behind European countries in advancing wind turbine technologies in part due to the occurrence of frequent severe earthquakes. Therefore we conducted a 1/55 scale model test to clarify vibration characteristics of an offshore wind turbine structure during earthquake conditions (actual frequencies from 3 to 1 Hz), by using shaking table together with wind action. The test was also carried out in wind tunnel generating low frequency oscillations (0.27-0.67Hz) correspondent with the first natural period of the structure. Furthermore by fixing isolation rubbers onto the foundation of the model, we also examine the effect of seismic isolation in order to diminish vibrations caused by ground motion. The measured strains in tower and acceleration of a nacelle were compared with results of dynamic analyses by using finite element analysis. We concluded that while rubber isolators are valid for wide frequencies, the fluctuating wind forces acting on rotational blades also decrease the motion of tower as aerodynamic damper.
