Development and performance study of a multi-degree-of-freedom loading device for real-time hybrid model testing of floating offshore wind turbines

To address the challenges encountered in reproducing turbulent wind loads and scaling conflicts between the turbine and platform in traditional model tests for floating offshore wind turbines. This paper proposes a new real-time hybrid model test strategy with a multi-degree-of-freedom loading device. The design theories of the multi-degree-of-freedom loading device are thoroughly presented. Following this, a software-in-the-loop simulation system was constructed in MATLAB to develop simulation validation on the feasibility and load reproduction capability of the multi-degree-of-freedom loading device. This study addresses the challenges of scale conflicts and turbulent wind load reproduction in traditional model tests, providing a reference for the further development of real-time hybrid model testing techniques for floating offshore wind turbine. The results indicate that the thrust force error in the Fx direction is within 2 %, while the torque and bending moment errors in the Mx, My, and Mz directions are within 8 %. Finally, a hardware-in-the-loop testing system was established to conduct performance tests on the static and dynamic load reproduction capabilities of the multi-degree-of-freedom loading device. The dynamic load variation rate of the multi-degree-of-freedom loading device is 45 N/s, ensuring its capability for dynamic force changes at the scaled-down level. The reproducibility of aerodynamic loads on floating offshore wind turbine under steady wind and turbulent wind conditions by the multi-degree-of-freedom loading device is investigated. The maximum error in reproducing steady wind loads using the multi-degree-of-freedom loading device was found to be 3.7 %. In comparison, the maximum error in reproducing the average values of thrust force and torques in different directions under turbulent wind loads was 9.05 %. Within the 0-5 Hz frequency range, the aerodynamic loads in various directions achieved an energy recurrence rate of at least 99.2 %. It has been demonstrated that the thrust force, torque and bending moment of the floating offshore wind turbine can be effectively reproduced by the device, thereby mitigating the impact of scale effects on floating offshore wind turbine model testing.