A numerical method for evaluating the earthquake response of a 5 MW OC4 semi-submersible FOWT under multidirectional excitations

In this study, the earthquake behavior of the 5 MW OC4 semi-submersible floating offshore wind turbine (FOWT) under multidirectional earthquakes was analyzed using finite element computer program ABAQUS. Considering the lateral displacement of the superstructure, settlement, and bending moment of the tower and shear stress, a comparison between the earthquake behavior of the FOWT under the earthquake was performed. Firstly, the dynamic response of the structure was evaluated under the unidirectional and multidirectional excitation corresponding to the earthquake. The effects of vertical and horizontal earthquake components on the dynamic response of the FOWT are discussed separately. Then, the effects of different earthquake types, intensities and multidirectional earthquakes on the dynamic response of FOWT are investigated separately. Finally, the influence of the parameters such as the added mass, the drag force of the mooring and hydrodynamic pressure due to vertical earthquakes on the FOWT system was analyzed. The results show that the long period ground motion with concentrated energy can cause a large response, while the short-period ground motion with more dispersed energy can cause a relatively small response. Meanwhile, under the influence of vertical excitation, a significant acceleration amplification effect is generated at the nacelle.