Increasing the fatigue life of offshore wind turbine jacket structures using yaw stiffness and damping

In this study, an appropriate proportion of yaw stiffness and damping is proposed to greatly improve the fatigue life at the tubular joints of offshore wind turbine (OWT) jacket support structures. The fatigue analyses using the DTU 10-MW OWT jacket support structure under 1148 IEC-61400-3 loads indicated that the torsion of rotor blades under turbulent wind conditions is the most important load leading to fatigue damage to tubular joints. Other loads, such as the moments generated from rotor blades and wave loads, are less important than the torsion. A Guyan reduction two-degrees-of-freedom model and eleven full finite element models indicated that low stiffness and large damping of the yaw system can significantly increase the fatigue life of tubular joints, and the yaw angular velocity will not increase. However, it is necessary to address the restrictions in the yaw rotation and to avoid F_n3P resonance (Integer multiples of 3P) with the first natural frequency of the structural vertical rotation.