Research On Dynamic Modeling And Simulation Of 2.5MW Wind Turbine Gearbox With Crack Damage

Wind turbine gearbox is an important part in the whole wind turbine drive system which can increase the growth rate and transmit power.The stability of its operation state has an influence on the wind turbine.Planetary gear train is widely used in wind turbine owing to their advantages,such as small volume required,large ratio of transmission and high efficiency.Because it often works in a sandy,moisture or low-speed and heavy-duty situation,which easily leads to the failure of tooth root fracture,fatigue cracks in some important parts of planetary gear train.This will cause huge losses.The undefined fault mechanics is one of the main reasons why it’s hard to find out the initial damage of planetary gearboxes.Therefore,it is essential to analyze the dynamic responses of the faulty planetary gear set.Combined with the damage of some important parts form its dynamic model,a vibration characteristic analysis can be conducted under a damage stimulation.Furthermore,the damage evolution mechanics can be revealed.It can provide the necessary theoretical basis for wind turbine gearbox fault diagnosis.Consequently,in this paper,the power-split planetary gear train of two-stage is taken as the research object.After analyzing the fault generation and evolution mechanism,the dynamic model of the planetary gear train with cracks is established by building the quantitative relationship between the damage parameters and the model parameters.Based on the model simulation,the influence caused by different damage levels on the dynamic response of planetary gear train is studied.The main work of the thesis includes the following aspects:(1)The status of dynamic model of planetary gear train and model-based fault diagnosis techniques are described.After that,the existing problems in current research are summarized.(2)The configuration,kinematic characteristics and meshing characteristics of the powersplit planetary gear set are analyzed based on the multi-body dynamic model.Furthermore,a pure torsional dynamic model for two-stage power-split planetary train is established.The time-varying mesh stiffness,damping and mesh phase relation are taken into consideration.The relative displacement between two components are derived,and then overall equations of motion in a matrix form for the system are established,which lays a solid foundation for the analysis of nonlinear dynamics of system.(3)The time-varying meshing stiffness of planetary gear train is analyzed.Firstly,the gear tooth is treated as a cantilever beam on the root circle.Based on the modified potential energy method of evaluating the mesh stiffness of the planetary gear set,a cantilever beam model is used to represent the external gear tooth and derive the analytical equations of the stiffness.Next,the matlab programs are used to obtain the curves of sun-planet mesh stiffness and ring-planet mesh stiffness.Then,build a software,which can be used to calculate the meshing stiffness of planetary gear trains with different structures.Finally,the numerical analysis method is used to solve the equation of the free motion,and the inherent characteristics of the system are analyzed.The influence of time-varying meshing stiffness and mesh phase differences on the natural frequency of the system is analyzed.(4)Aiming at the diagnosis and fault features extraction of incipient crack damage,the crack model is established and the effects of crack evolution of sun gear on time-vary mesh stiffness of the planetary gear set are researched.First,the time-vary mesh stiffness analytical equations for the cracked gear is derived.Then the effects of the crack propagation on time-vary mesh stiffness are studied.It can provide a theoretical basis for establishing dynamic model with cracked damage.(5)The vibration signal components of the gear system with localized fault are analyzed.Then,through the model simulation,the system vibration response including the damage information of the sun gear is obtained.Furthermore,transient impact characteristics,sideband spectral structures and fault characteristic frequency caused by the damage of sun gear tooth are obtained.Finally,eight characteristic indicators are selected to evaluate the crack growth,which provide the necessary theoretical support for the fault diagnosis of complex planetary gear trains.