Development of geotechnical centrifuge experiment technique for dynamic evaluation of offshore wind turbine

Abstract

Understanding of dynamic response of offshore wind turbine is important to reduce vibration of offshore wind turbine induced by structural and environmental loadings. Although dynamic characteristics of offshore wind turbine such as natural frequency and seismic behavior are affected by foundation and soil conditions, conventional analytic methods focused mainly on structural aspect of tower with less consideration about soil-foundation-structure interaction (SFSI). The goal of this study is to evaluate the natural frequency and seismic behavior of offshore wind turbine considering SFSI. Geotechnical centrifuge tests in fixed-based and SFSI condition were performed to measure natural frequency in each case. Results were compared with theoretical calculation result based on conventional analytical method. Also, series of seismic loadings with different intensities are applied to observe seismic behavior of offshore wind turbine during the earthquake, and permanent changes after the earthquake. Established centrifuge experiment technique was put into the test by evaluating actual field offshore wind turbine natural frequency. Study shows apparent natural frequency reduction in SFSI condition compared to fixed-based condition. Natural frequency evaluation result using geotechnical centrifuge showed promising match with that of actual field offshore wind turbine. Seismic test result showed nonlinear changes in dynamic response during series of earthquakes, and permanent changes occurred in natural frequency and rotational displacement after earthquakes.