Gear Micro-Pitting Simulation Of Wind Turbine Gearbox Based On Extended Finite Element Method

As the most common source of energy,the reserves of oil and coal are limited and will lead to environmental pollution and other issues.The development of new energy sources is an inevitable trend in the future.Wind energy,as a recyclable and clean energy source,has drawn the attention of all countries in the world.As of 2016,our country occupied the top of the world in the wind power field.The cumulative installed capacity of wind turbines has reached 169 million kilowatts,and the wind power market in China will continue to grow with broad prospects.Wind turbines are often installed in poor working environment,such as high mountains,wilderness and sea.It is difficult to repair and high cost.With the increasing power of wind turbines,higher requirements are put forward for their reliability.According to the statistics,in the various components of the wind turbine,the failure rate of the wind turbine gearbox is higher and its downtime is longer,and the failure of the gear occupies the largest proportion.Therefore,it is necessary to study the failure mechanism of the gear of the wind turbine gear box.The thesis regards the power split type 2.5MW wind turbine gearbox as object,carries on the FMECA analysis to determine the weak link and the main failure mode.The contact pressure distribution of gear is calculated by using the theory of the elastohydrodynamic lubrication.Then,it simulates the formation of micro-pitting under different initial cracks based on the extended finite element method.The main contents of the paper are as follows:Firstly,the background and significance of the paper are outlined,and the current situation of wind power generation at home and abroad is reviewed.Based on the summary and analysis of the pitting mechanism at home and abroad,the main contents of the paper are presented.Secondly,the structure and working conditions of power split type 2.5MW wind turbine gearbox is analyzed.stress analysis of the gear by using the finite element software,combined with the failure of the finite element analysis results and the gear box,has carried on the FMECA analysis,determine the main failure mode is gear pitting and broken teeth,weak link one or two and three from the sun gear wheel.The force of each part of the gearbox is analyzed by finite element software.Combined with the analysis results and the failure conditions of similar gearboxes in similar environment,FMECA analysis is carried out and the main failure mode is gear pitting and gear broken.The weak links are the first sun gear,the second sun gear and the third driven gear.Thirdly,there is a greater Hertzian contact stress at the pitch line,which is a high incidence area of pitting corrosion.Therefore,the related parameters of the first sun gear,the second sun gear are calculated and the third driven gear,including the radius of curvature of the section line,the contact load,the sliding speed and so on.Based on the six basic equations of isotherm contact elastohydrodynamic lubrication and the meshing parameters of gear of 2.5MW wind turbine gear,the iterative method was used to calculate the contact pressure distribution of the first sun gear,the second sun gear and the third driven gear in the state which considering elastohydrodynamic lubrication.Laid the foundation for the simulation of gear micro-pitting based on the extended finite element method.Fourth,the mechanism of the initial crack propagation to micro pitting is analyzed by using the related knowledge of fracture mechanics.Gear meshing simplifies the contact between an equivalent cylinder and infinitely long plane.In the ABAQUS software,a pitting model of the first sun gear,the second sun gear and the third driven gear is established.Based on the maximum energy release rate theory,the extended finite element method was used to simulate the formation of micro-pitting at different initial cracks(5?m,10?m,15?m,20?m)under the condition of EHL.Based on the simulation data,the stress intensity factor of the crack tip is calculated.The relationship between the crack propagation length and the number of stress cycles is established by the Paris formula.The crack propagation characteristics under different initial crack lengths are analyzed.Finally,the research work of this thesis was summarized and some shortcomings and several directions to be studied are put forward.