This study investigates the influence of second-order wave forces on the dynamic response of a semi-submersible floating wind turbines, using the "Guoneng Sharing" as a case study. A comparative analysis of the differences between far-field and near-field methods for calculating the second-order mean wave force transfer functions （QTFs） is presented. A coupled time-domain model of aerodynamic, hydrodynamic, structural, and servo dynamics was established to analyze the dynamic responses of the floating wind turbine under four scenarios： neglecting second-order wave forces, considering second-order mean wave forces, considering second-order difference wave forces, and considering both second-order difference and sum wave forces. The results indicate that the QTFs calculated by the far-field and near-field methods are nearly identical when the angular frequency is less than 1.1 rad/s. However, as the angular frequency increases, the far-field method generally yields larger values than that of the near-field method. The second-order wave forces significantly impact the motion response of the semi-submersible platform, with the primary contributing components being the second-order mean wave forces or second-order difference wave forces, while the second-order sum wave forces exhibit negligible influence. Notably, the second-order difference frequency and sum frequency wave forces significantly affect the acceleration of the semi-submersible platform and the load at the top of the tower, whereas the second-order mean wave forces have no discernible effect on either. The high-frequency response of the tower top load is excited under the influence of second-order difference and sum frequency wave forces and must be taken into account in calculations. Furthermore, second-order wave forces markedly affect the tension and fatigue life of the mooring anchor chains, not only increasing the fatigue damage but also influencing the location of maximum fatigue damage occurrence.

offshore wind power  /  floating wind turbines  /  second-order wave force  /  dynamic response  /  second-order difference frequency  /  second-order sum frequency