Structural Optimization Design And Characteristics Research Of Mooring System Of X30 Floating Platform For The Wind Turbines

In response to the call to peak carbon dioxide emissions by 2030 and achieve carbon neutrality by 2060,China needs to reduce the intensity of its carbon emissions,and wind energy,as a clean and renewable energy source,is crucial to achieving the "two-carbon" goal and the transition to a low-carbon energy system.Ocean wind direction changes less frequently and wind speed is higher than onshore,so the stability of wind energy and wind density of ocean wind power is higher,which results in the utilization rate of offshore wind turbines is higher than that of onshore wind turbines.At the same time,ocean wind power can save land resources to avoid occupying human activity areas,reduce the impact on the land environment,and reduce the interference with human life.These are advantages that cannot be replaced by onshore wind power.Offshore wind also has challenges that cannot be ignored.For example,the marine environment is relatively more dangerous and therefore more expensive to build and maintain,and the installation and transportation of marine wind power equipment also requires more complex technology.Therefore,in order to reach the goal of reducing the cost of offshore floating wind power,innovative support platforms with efficient structural features need to be studied,while ensuring that the platforms can be adapted to large turbines.In this thesis,according to the parent configuration of the X30 floating turbine designed by X1 wind and combined with the characteristics of the sea environment,the mooring system and platform configuration of the X30 floating turbine are optimized.Based on the 3D potential flow theory,the hydrodynamic performance of the platform is analyzed by using the fully coupled time-domain method.The kinematic response of the platform and the characteristics of the mooring system are studied by the model test method,and the numerical simulation method is verified.The main research contents include:(1)The main scale of the X30 floating turbine platform was summarized and the finite element model was established.The hydrodynamic characteristics such as added mass,radiation damping,and motion response transfer function RAOs were calculated,and the hydrodynamic characteristics of the turbine prototype were preliminarily analyzed.(2)The 1:50 scale ratio was used to carry out the floating turbine pool test.The numerical model was verified and modified from the attenuation period,mooring cable tension,and motion response by combining numerical simulation and physical test.(3)According to the characteristics of the environment,eight different mooring schemes are designed catenary mooring,semi-tensioning mooring,and tensioning mooring.The stiffness characteristics of mooring cables,the motion response of the platform,and the tension characteristics of mooring cables were analyzed by using the time-domain fully coupled analysis method,and the positioning characteristics of multi-point mooring system of floating turbine in shallow sea area were obtained by a floating turbine.A comprehensive comparison of all mooring schemes shows that,under the same design parameters such as anchor radius and preload,the motion response and mooring cable tension of an all-anchor chain mooring system in mooring scheme are better than that of an all-steel cable mooring system.Under the condition of 45° wave with meaningful wave height of 2.5m,5m and7.5m,the total mooring cable tension is only 42%,34% and 50% of the total steel mooring system.New elastic cables such as polyester cables are used in the combined mooring scheme which can effectively reduce the motion response and mooring cable tension of the floating turbine.(4)Based on the hydrodynamic characteristics and configuration characteristics of the X30 floating turbine platform,six sets of different optimal configurations of the floating turbine were optimized for the large motion response of the turbine prototype in pitch,roll,and heave.Based on the results of the research on the positioning characteristics of the mooring system,the full-anchor chain and three-stage mooring system were selected,and the fully coupled time-domain analysis method was used to carry out the numerical calculation of the motion characteristics of the optimized configuration of the X30 floating turbine platform.The drag force on the floating turbine optimized configuration was analyzed under four typical random wave conditions of wave direction.The kinematic response and mooring cable tension characteristics of the optimal configuration of the floating turbine in the full anchor chain and three-stage mooring system are analyzed.A comprehensive comparison of all optimal configurations shows that the pitch and heave motion responses of the other optimal configurations can be reduced to about 30% of that of the prototype,and the mooring cable tension can be reduced to 40%-50% of that of the prototype.Among them,the mooring cable tension of the H10D30＿D configuration is minimum when the wave downward is not 180°.To reduce the motion response of the floating turbine under the condition of self-storage and increase the stability of the floating foundation,the H10D30＿D configuration can be considered the optimal configuration of the floating turbine.(5)In conclusion,this thesis mainly studies the positioning characteristics of the multi-point mooring system of a floating turbine in a shallow sea area and the motion response and mooring cable tension characteristics of the optimal configuration of the floating turbine.The research contents will provide a theoretical basis for the future design of mooring systems and configuration optimization of the offshore floating turbine.