Dynamic Response Analysis And Shutdown Strategy Investigation Of Floating Offshore Wind Turbine With Mooring Line Breakage

Energy and the environment are the foundation of the development of human civilization.In order to implement the sustainable development strategy and promote the energy transition,it is the best choice to use the huge,widely distributed,and pollution-free wind energy to generate electricity.Relying on floating foundations and mooring positioning systems to establish floating wind turbines on the sea have broad development prospects and are currently research hotspots.It has the advantages of getting rid of water depth restrictions,large singleunit installations,high wind speeds and stable working conditions,and closing to economically developed areas,etc.However,it is also faced with challenges such as the difficulty of accurately simulating the dynamic response of its complex multi-system coupling structure and the complex and diversified environmental loads,especially the extreme gusts that are unpredictable.Therefore,it is necessary to study the mooring breakage mechanism of floating wind turbines,and to formulate shutdown strategies in accordance with its dynamic response law to ensure the safety of floating wind turbines under complex and severe extreme gusty sea conditions.Based on the flexible multi-body dynamics theory,the finite element method is used to establish a full-system coupling model,and the New Mark-β and Wilson-θ numerical methods are used to solve the nonlinear finite dynamic problem.Comparing the numerical results with the model test results,the accuracy of the numerical tools used to simulate the coupling response of the floating wind turbine was verified.Based on the design background of the once-in-ahundred-year working conditions in my country’s 50 m water depth and combined with existing design schemes,a mooring scheme that considers both cost and manufacturing feasibility was designed.Aiming at the problem of mooring breakage of floating wind turbines induced by extreme operating gusts,the OC4-Deep Cwind semi-submersible coupling model with self-designed mooring scheme is taken as the research object.By analyzing the characteristics of extreme operating gusts and the influence of the superposition of extreme operating gusts and waves on floating wind turbines,it is found that the superposition of extreme operating gusts and average wave drift force under a certain characteristic parameter will induce the mooring snap tension of floating wind turbines and cause mooring line breakage,and there is a certain delay between the moment when the mooring tension appears extreme and when the extreme operating gust occurs.Considering the influence factors such as the pitch angle rate and wind conditions of the floating wind turbine when its shutdown,by analyzing the dynamic response of the floating wind turbine in different shutdown periods under the mooring breakage condition,summarized the shutdown period and shutdown method that can effectively avoid the risk of mooring breakage.Aiming at the dynamic response and shutdown strategy of the floating wind turbine after mooring breakage,by analyzing the dynamic response after one or two mooring line breakage whether shutdown or not,it is found that shutdown the floating wind turbine immediately after a mooring line breakage can slow down the drastically drifting speed and prevents other mooring lines breakage,but the risk of collision with other structures and damage to the grid system still exists;shut down immediately after the two mooring lines breakage,and the response of the third mooring line has no obvious change,but the pitch,roll,and yaw response of the floating offshore wind turbine increased,and the stability decreased.