LAUSR

Abstract Monopile offshore wind turbines (MOWT) are inserted into sea water and sea bed soil. As the piles are usually embedded into the soil as deep as about 40 m, dynamic pile-water and pile-soil interactions, as well as seismic excitation non-uniformity, often occur under earthquake. In this paper, the response spectrum method (RSM) is developed to calculate the maximum response of MOWT considering the pile-water and pile-soil interactions subjected to the non-uniform seismic excitation. The tower and pile are modeled by Timoshenko beam elements, with both nacelle and rotor including hub and blades integrated as a lumped mass at the top of the tower. The pile-water and pile-soil interactions are considered by added mass and soil spring at their interfaces, respectively. The non-uniform seismic excitation is obtained by the site transfer function from the horizontal earthquake motions or design response spectrum at the water-soil interface. The seismic analysis model is solved by using a multiple-support RSM under design response spectrum. Seismic responses of a case of 5-MW MOWT on two types of soil sites are analyzed. The results indicate that the pile-water and pile-soil interactions and seismic excitation non-uniformity should be considered in analyzing such seismic problems of MOWT, while the RSM can be an effective tool.