Simulation Research On Stability Of Semi-submersible Floating Offshore Wind Turbine Platform

With the increasing demand for energy,wind energy has received more and more attention due to its clean,renewable and pollution-free characteristics.The development and utilization of wind energy has become a research hotspot.Compared with onshore wind energy,offshore wind speed is larger and more stable.So the development potential of offshore wind energy utilization is huge.Nowadays,the main way to develop and utilize offshore wind power is using floating wind turbine foundations,while the semi-submersible wind turbine foundation is the most widely used.Due to the deep waters and complex sea conditions around China,typhoons occur frequently,so the traditional form of semisubmersible foundation is difficult to work normally for a long time.Therefore,a semisubmersible foundation suitable for the complex seas of China is designed to improve the stability of the semi-submersible wind turbine system.Based on the coupling theory of impeller aerodynamics,marine engineering hydrodynamics,and mooring system,this paper uses numerical simulation methods to analyze the hydrodynamic performance characteristics of offshore floating wind turbine systems,and calculates the motion response of floating platform under the combined action of wind and waves.Then based on the OC4 semi-submersible wind turbine model which was proposed by the National Renewable Energy Laboratory(NREL),three improvement methods to the model are proposed,namely multi-segmented catenary mooring system,inclined pontoon platform and tensioned mooring system.Various improved models were modeled with FAST,and the motion response of the improved model in 6 directions of freedom of the platform was calculated under six complex conditions.We researched the influence of the length of the multi-segmented catenary,the tilt angle of the pontoon,and the position of the tension mooring line on the motion response of the wind turbine platform.The results show that the multi-segmented catenary mooring system can reduce the surge displacement of the platform.As the length of the upper bifurcated catenary decreases,the surge displacement is smaller.The tilting pontoon platform model can reduce the platform heave displacement.As the tilt angle of the pontoon increases,the heave displacement decreases.Combining catenary and tension mooring models can reduce the platform’s surge,heave,and pitch displacements.As the distance between the tensioned mooring lines and the platform center increases,the pitch displacement becomes smaller.Combining the three model improvement methods can greatly reduce the platform’s surge,heave and pitch displacement,and improve the stability of the wind turbine system.