Efficient response analysis of the cable of offshore wind turbine at static state: Hybrid of perturbation method and grey wolf optimization

The mooring cable system is an important component of the offshore floating wind turbine. The mooring system mainly consists of several cables to be used to connect the floating body and seabed. The efficiency of dynamic response analysis of the mooring cable under flow current is generally low and thus complicates the optimal analysis of offshore floating wind turbines. As the determination of the dynamic response of cables highly relies on the static state, the static state response analysis of cables is important. To achieve the static state response analysis of cables, the mooring cable is simplified as a two-point boundary-valued model, which considers the hydrodynamic effect of flow current. Specifically, the perturbation method is first used to linearize the highly nonlinear equations of motion of a cable into the partial differential equations with a constant coefficient for easing the solution of equations. Then, to obtain the undetermined parameters of functions after linearization and reduce the computational cost, the grey wolf optimization algorithm is adopted. Lastly, three examples considering different currents are presented to demonstrate the responses of the mooring cable. Results show that the proposed algorithm can significantly improve the calculation efficiency. To better understand the effects of main parameters on the static response and mooring force of cable, a parametric analysis is carried out under the zero current velocity, considering the cable's stiffness, mass, and diameter as well as the number of nodes. The parametric analysis results indicate that the stiffness influences the response of cables, while the effects from mass and diameter can be ignored.