Physical Modeling of the Dynamic Response of Offshore Wind Turbines Founded on Monopiles

An experimental study of the dynamic response of model offshore wind turbines founded on monopiles is presented. This exploratory set of dynamic experiments on modeled monopile foundations were analyzed by comparing the physical model test results to an analytical solution. Studied parameters included pile foundation material, water level, turbine mass, and load application. The response to free vibration decay was monitored using a vertical array of MEMS accelerometers, and the collected data were processed using Fourier analysis to assess the natural frequency of the structures. Physical model results were compared to closed form approximations using the Rayleigh energy method. Good prediction of natural frequency was achieved for turbines founded in concrete and stiff sandy soil conditions, however, the natural frequency of turbines founded in soft clays was overpredicted by up to 40%. These results highlight the importance of the sediment-structure interaction in the evaluation of the dynamic performance of offshore wind turbines.