Dynamics And Vibration Control Of A Horizontal Axis Wind Turbine Blade And Rotor

A wind turbine is capable of converting the wind energy to electrical energy in a way of low carbon generating.A wind turbine blade is a key component responsible for absorbing energy from flowing air.It has the characteristics of large aspect ratio,dense modes and is subjected to complex excitation forces.With the combination of the environmental conditions,a blade can be resonance or experiences self-excited vibrations which may lead to the structural broken.Therefore,the dynamics of the wind turbine rotor receives increasing attention in recent years.The relevant researches focus on the rotory dynamic of the rotor-blade-structure,flutter analysis and the structure optimization.By studying the dynamics of a wind turbine rotor,the wind turbine’s load level will be calculated accurately and the safty level of a wind turbine is improved.The research is significant and become an important topic to investigate when designing a flexible wind turbine blade.This paper focuses on studying the dynamic behaviours of a wind turbine rotor and the pitch controller.The simplified blade model,whirling of the rotor,stall induced vibration and the close loop induced vibration are investigated individually.The main research contents are as follows:(1)The dynamics of bending-torsion effect of a thin-walled beam are studied.The equations of motion are established by applying Hamilton’s principle.The transferred differential transformation method(TDTM)is invented inheriting the ideas of transfer matrix method(TMM)and the differential transformation method(DTM).Both the free and the forced vibration of a uniformed beam and a non-uniformed beam are studied individually.The calculation results are compared with the experiment and the efficiency of the TDTM are analyzed.The effect of the shear centre and the warping deformation are discussed.(2)Based on the theory of the bending-torsion effect of a thin-walled beam,the wind turbine blade is simplified as a non-uniformed beam featuring bending-bending-twist coupled effect.The equations of motion and the associated boundary conditions are obtained by Hamilton’s principle.The tension force,centrifugal force and the Coriolis force due to the rotary effect are investigated in a way of contributions to the natural frequencies.Besides,the different phases between the bending and torsion,and the mode veering phenomenon are found.The calculation results are validated with experiment and the commercial codes.(3)The deformed state aerodynamic properties of a wind turbine blade are calculated based on blade element momentum theory.The aero-dampings of the blade are evaluated in different working conditions.The possible unstable boundary conditions of the stall induced vibration are studied.The variables which influence the unstable range such as wind speed,yawing deviation angles and structural damping are discussed respectively.(4)The equations of motion of a three-blade-rotor are established.The transformation of the blade root,rotating hub and the nacelle coordinate system are introduced individually.The modal analysis is made by TDTM.The progressive and regressive whirling mode are studied and classified by employing Alembert’s principle.The out-of-plane whirling modes are investigated using simplified elastic support model.Both aero-damping of the rotor at the operating state and the idling state are calculated and the unstable range of the deviation angle is obtained.For a stall induced vibration,the influence of the azimuth angle is discussed and a possible solution addressing the problem is proposed.(5)The torque and pitch control loop are studied individually.The influence of the time lag on the stability is investigated.The non-linear aerodynamic forces are linearized at the equilibrium points near the different operating conditions.The non-linear gain schedule method is applied to regulate the rotor speed.The aero-elastic-control coupled model of the pitch actuator is made.The self-excited vibration phenomenon of the pitch system is produced numerically.The robustness of the controller with a blade large deformed state is analyzed.