Multi-stage hybrid damper: Experimental validation and application in monopile offshore wind turbines

To enhance the seismic performance of monopile offshore wind turbines (MOWT), an innovative multi-stage hybrid damper (MSHD) was proposed. The MSHD was composed of a prismatic strip device (PSD) and variable friction devices (VFDs). Following the conceptual introduction of the MSHD, experimental investigations on six proof-of-concept specimens were performed to examine the hysteretic behaviour. Experimental results indicated that the MSHD exhibited multi-stage energy dissipation mechanisms, with a stable and high energy dissipation capacity. The shape of the hysteretic curve was proven to be adjusted by modifying the width and height-to-width ratio of the steel strips. The theoretical hysteretic model and simplified numerical model for predicting the hysteretic behaviour of the MSHD were developed, and the predictions were in good agreement with the test results. Finally, the MOWT equipped with the MSHD (MOWT-MSHD) was proposed, and the seismic performance was evaluated by the nonlinear static analyses and nonlinear dynamic analyses. Results confirmed that the MOWT-MSHD exhibited greater energy dissipation capacity and superior ductility compared with conventional MOWT.