SEISMIC ANALYSIS OF JACKET FOUNDATION FOR OFFSHORE WIND TURBINE -VERIFICATION OF RADIATION DAMPING EFFECT-

Abstract

In offshore wind power in Japan, the seismic response in the event of an extremely rare earthquake may become dominant in the design of support structures. To reduce the seismic response, it is desirable to consider the radiation damping of the soil as much as possible. In this study, we verify the simple method that can easily consider the radiation damping only in the second mode and higher for jacket foundations for offshore wind turbines. Specifically, we performed free damped vibration analysis for a second mode with and without radiation damping to find that the increment of the second mode damping due to the radiation damping effect and add to the second mode damping rate of the Rayleigh damping. As results of verification, we confirmed that almost the same damping effect was obtained by the models using the Gazetas formula with radiation damping, the thin layer element method and the simple method for jacket foundations. For monopile foundations, we should use the simple method because other methods overestimate the radiation damping for the first mode.