An analytical model for dynamic responses of one operating offshore wind turbine structure supported by bucket foundation

Abstract

Recently, the bucket foundation has gained prominence in offshore wind farm (OWF) due to their superior bearing capacity and lower costs. However, higher towers and larger blades may pose significant vibration safety issues to offshore wind turbine (OWT) structures when OWFs continue developing towards deep-sea areas. It is increasingly crucial to accurately simulate the dynamic response of OWT supported by bucket foundation with the current challenges, including the need to corroborate finite element simulations with actual measurement data and the consideration of bucket-soil interaction and dynamic stiffness. In this research, a analytical model of dynamic responses for one operating OWT supported by bucket foundation was firstly established based on the multi-degree-of-freedom vibration theory. In response to the limitations of existing models, a novel bucket-soil interaction model was introduced considering the dynamic changes in foundation stiffness under external excitation and the influence of soil inside the bucket. The global model simulated wind loads, operational loads, and aerodynamic damping, and the Crayfish Optimization Algorithm (COA) was applied to correction formula of aerodynamic damping based on the measurement data. Furthermore, its accuracy was validated in both shutdown and operating modes by comparing the displacement and acceleration responses at the tower top. Finally, the structural responses were studied under extreme conditions such as earthquakes, wind, waves, and typhoons. It is concluded that the observed response growth trends of the tower-top displacement and acceleration of the established model are consistent with the actual trends observed in the prototype under the operating and shutdown conditions. In operating mode, the average deviations of the displacement and acceleration between the analytical model and the actual OWT structure are 7.18 % and 4.14 %, respectively. The model is suitable for OWT response analysis under seismic intensities below 0.3 g and typhoon of return period of 20 year. It is indicated that the proposed analysis model has good engineering application value for the vibration response simulation of actual OWT.