Fatigue damage mitigation of monopile offshore wind turbines utilizing a rotational inertia double tuned mass damper (RIDTMD) under realistic wind-wave conditions

Offshore wind turbines present undesirable vibrations under cyclic environmental loadings, which induces long-term fatigue damage and even failure issue. Monopile offshore wind turbine (MOWT) is widest utilization in engineering fields. This study presents fatigue mitigation assessment of MOWT by utilizing a rotational inertia double tuned mass damper (RIDTMD), aiming to prolong the structural fatigue life and suppress vibration. An analytical model of MOWT with RIDTMD is established using Euler-Lagrangian equation and dynamic responses are solved by the finite element method. To predict metocean condition, a statistical analysis is conducted for deriving realistic wind-wave loadings. The RIDTMD parameters are optimized by simultaneously considering the maximum of fatigue life and the minimum of damper's stroke. The fatigue damage is estimated based on rain-flow cycle counting method and Miner's rule. The results show that an RIDTMD can prolong the MOWT fatigue life compared with uncontrolled system; the maximum and RMS displacement of tower top are also greatly reduced by comparison with a traditional TMD. It is demonstrated that RIDTMD can decrease MOWT's fatigue damage by using a lighter damper, which is significant for the space limitation in practical.