Offshore wind turbine natural frequency evaluation for monopile and monopod foundations by centrifuge test

Abstract

Precise evaluation of the natural frequency of the offshore wind turbine is important to ensure structural safety and power generation efficiency. Analytical studies so far proved that soil stiffness and foundation types affect the natural frequency of the offshore wind turbine. However, few experimental works on this subject have been done to complement and calibrate the results to meet actual site requirements. The purpose of this research is to investigate the influence of soil-foundation-structure interaction (SFSI) on the natural frequency of a wind turbine using geotechnical centrifuge experiment and to verify results with analytical methods based on existing codes. The natural frequency of the offshore wind turbine was evaluated under a fixed-base condition as well as SFSI condition using monopile and monopod foundations. Natural frequency reduction due to SFSI was experimentally obtained for both types of foundations. The test results were compared with theoretical analysis for cross-verification. The results demonstrated the specific effect of the soil stiffness and foundation type on the natural frequency of the offshore wind turbine.