Framework for dynamic response analysis of monopile supported offshore wind turbine excited by combined wind-wave-earthquake loading

Abstract

This study develops a framework to perform integrated analysis for the seismic response of offshore wind turbines (OWTs). The ground motions are introduced in the analysis as depth-varying excitations that are obtained from free-field site response analysis involving equivalent linearization approach. The calculated accelerations at different elevations are used in a beam on nonlinear Winkler foundation model, which is then used to simulate the pile-soil interaction (PSI). These models are combined with the FAST code to develop an integrated seismic response analysis framework (SRAF) for the system consisting of OWT, along with one-dimensional site response analysis and PSI elements. Considering the NREL 5 MW OWT as an example, the reliability of SRAF is validated by comparisons with simulation results obtained from GL-Bladed and ADINA software. Subsequently, the validated model was used to investigate the influence of three earthquake excitation models on the seismic response of OWTs. We found that the uniform earthquake excitation method significantly underestimates the seismic response of OWT. In addition, the validated model was used to evaluate the seismic responses of OWTs under different operational conditions. The results indicate that the seismic responses of OWTs differ significantly under running, parked and emergency shutdown states.