Wind turbines in regions of active seismicity are under a potential threat caused by the joint action of a strong earthquake and a moderate wave condition. Taking NREL-5MW monopile foundation as the prototype, a series of shake table model tests with scale 1:30 have been carried out by the world unique Earthquake, Wave and Current Joint Simulation System to investigate the structural response in dry flume, low and high calm water levels, with and without regular or random waves. Particular interest has been in the nacelle acceleration subjected to strong ground motions as well as random waves. The experimental results of nacelle peak accelerations and structural dynamic magnification factors show that the joint earthquake and wave action is important for the proper evaluation of structural response. Ignoring the effect of wave action in seismic analysis will underestimate structural response, particularly for a structure dynamically sensitive to the given ground motion input. Coupling of earthquake and wave actions is sourced not only from the relative velocity of vibration but also from the initial condition subject to waves. It has been also derived that the peak structural response excited by a moderate sea condition is comparable to that by a moderate earthquake.
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