| Wind power is developing from land to offshore and from shallow waters to deep waters.In order to exploit the wind power resources of the sea area of which the water depth is deeper than 50 meters,offshore floating wind power technology has become an important area and hot spot of current wind power technology research.The feasibility of implementing offshore floating wind power technology has been proved by field test and theoretical research.However,the existed field offshore floating wind turbine(OFWT)are obtained by installing the offshore wind turbine on a floating platform directly.The Levelized Cost of Energy(LCOE)of Floating wind turbine like this configuration is very high because of low operation efficiency,high maintenance cost,and unassured design life.In the last decade,a lot of work about offshore floating wind power has been done in order to reduce LCOE through increasing unit capacity,optimizing structure,and implementing vibration control.But because of the inherent complexity of offshore floating wind power technology,the coupling dynamics behavior of OFWT is still poorly understood.So this results in lack of theoretical basis in terms of increment of the unit capacity,the structure optimization,and the implement of advanced vibration control system for OFWT.Therefore,the key problem at this stage is to establish a fully coupled dynamics calculating model of OFWT and do research on dynamic behavior,which is significant meaningful in both engineering and economic.For the complete machine of OFWT,the fully coupled dynamics model is established,as well as the dynamic excitation mechanism and characteristic is studied in this paper.The obtained conclusions can provide theoretical guidance for increment of the unit capacity,the structure optimization,and the implement of advanced vibration control system for OFWT.So the LCOE of OFWT can be cut down.The main research contents are as below.(1)Aiming at enhancing the unsteady aerodynamic capturing capability of the existing wind turbine aerodynamic models,the aerodynamic force combination model of OFWT is constructed based on Generalized dynamic wake(GDW),blade element momentum(BEM)and Beddoes-Leishman(B-L)dynamic stall model.The rotor aerodynamic force in the middle and high wind speed is calculated by using GDW combining B-L model.Consequently,two main aerodynamic unsteady effects of OFWT including dynamic inflow and airfoil stall are considered at the same time.One disadvantage existed in GDW is that the numerical calculation is unsteady in low wind speed.In order to solve that problem,BEM is combined with B-L model for the aerodynamic computation in low wind speed.The combined model is proposed based on the improvement of GDW,BEM and B-L model.Thus,a engineering reference model is provided to calculate the aerodynamic force of OFWT.(2)Concentrated on the structural features and operation state of the floating platform of OFWT,the disadvantages existed in current commonly used hydrodynamic model are considered.Based on linear wave kinematics,linear potential flow theory and Morrison viscosity term,the hydrodynamic force combination model of OFWT is constructed.Based on solving the first-order hydrodynamic force,the calculation method for second-order hydrodynamic force is proposed.The hydrostatic recovery,diffraction and irradiation effect,the viscosity effect of the small scale structures and the second-order hydrodynamic force generated by the first-order linear motion coupling of wind turbine floating platform are all considered in the hydrodynamic force combination model,which can provide a engineering reference model for the hydrodynamic calculation of OFWT.The feasibility of hydrodynamic force combination model is testified by using literatures test data of the OC4 DeepCwind wind turbine.Then the excitation characteristic of the first-order and second-order hydrodynamic force to the floating platform is studied by the fully coupled dynamics calculation of OFWT,which can provide theoretical guidance for the structure design of wind turbine floating platform.(3)Compared with the simply and commonly used quasi static mooring model,dynamic mooring model is more consistent with the actual situation.To simulate the dynamic mooring force more accurately,dynamic mooring model is constructed by applying lumped mass method.In the model,the cable segments are uniformly discrete and connected by joints,and the mass of cable segment is centralized in the joints.The underwater drag force and the force caused by contact between seabed and cable segments are also considered in joints besides the gravity,buoyancy,the axial tensile force and the axial damping force.By comparing the results of model calculation and experimenal test,it can be concluded that dynamic mooring model constructed in this paper is obviously superior to static mooring model.Thus an engineering reference model is provided for the mooring system of OFWT.(4)As it is lack of the fully coupled dynamics integrated model of the complete machine of OFWT,the rigid-flexible hybrid multi-body dynamics model of OFWT is constructed based on Kane method and mode superposition principle.Incorporated with the rotor aerodynamic force combined model,floating platform hydrodynamic force combined model,dynamic mooring model,variable speed and variable pitch control strategy which are constructed in this paper,and through the variable coupling between modules,the air-structure-servo-water fully coupled dynamics model of the complete machine of OFWT is constructed.OC4 DeepCwind wind turbine is taken as the research object,and the response computation and characteristic research of wind-wave joint excitations are carried out.The accuracy of the fully coupled dynamics model of the complete machine is verified by comparing the calculation results of FAST developed by NREL(National Renewable Energy Laboratory).Experimental test and fully coupled dynamics calculation of the complete machine of a 2kW small semi-submersible floating wind motor and its corresponding onshore wind turbines are done.Then comparisons are made between the testing results and calculation results,by which the accuracy of the fully coupled dynamics model of the complete machine of OFWT is validated again.Theoretical support is provided for the dynamic behavioral research of OFWT by the fully coupled dynamics model of the complete machine constructed in this paper.(5)The dynamic excitation mechanism and characteristics of OFWT are studied,and an analysis method for the dynamic characteristics of OFWT is proposed based on response spectrum.To the OC4 DeepCwind wind turbine,through analyzing the fully coupled calculation results and theoretical derivation,the dynamic excitation mechanism and characteristics of wave,dynamic wind,flexible blade and shear wind is studied based on the air-structure-servo-water fully coupled model of OFWT.Furthermore,research on the dynamic coupling mechanism and dynamic excitation characteristic in the situation that multiple dynamic incentive sources are existed simultaneously is also done,which can provide theoretical basis for the unit capacity increment,structure optimization and vibration control of OFWT... |
PDF Full Text Request