| With the increasingly serious problem of energy and environment, the wind energyas a clean and renewable energy has been widely applied and concerned, and the windpower technology also obtained the fast development. As one of key components ofwind turbine, the main function of gear transmission system is to deliver the powergenerated by the wind wheel rotating to the generator and make it obtain thecorresponding speed, which performance directly determines the wind turbineperformance. As the wind turbine working in stochastic load condition, aerial erectingand repair difficulties, the higher dynamic performance and reliability of wind turbinegear transmission system are required. Therefore, research on the dynamic characteristicand the reliability design of wind turbine gear transmission system in stochastic windcondition is one of the important tasks.According to the research task of The National Natural Science Fund Project(50975294), and considering the practical operating characteristics of wind turbine instochastic wind conditions, the dynamic and the fatigue reliability problems of windturbine gear transmission system in complex load are investigated fairlycomprehensively and deeply in this dissertation. The main researches are as following:1. Stochastic wind speed model of wind turbineThe external load of wind turbine gear transmission system is researched based onthe working characteristics and the mathematical description of wind energy and windresource. The Weight Sparse Least Squares Support Vector Machines (WSLS-SVM)based on the machine learning language is used to simulate the actual wind speed.Combining with the aerodynamics theory, the torque load is obtained and be used asexternal excitation, which layings the foundation for dynamics analysis of wind turbinegear transmission system.2. Dynamic analysis of wind turbine gear transmission system coupled withbearings in stochastic wind conditionConsidering the influences such as the time-vary mesh stiffness, comprehensivemeshing error and time-varying bearing stiffness, a translational-torsional coupleddynamics model of MW level wind turbine gear system is built by usinglumped-parameter method based on the gear meshing theory and the Lagrange function,and the system’s natural frequency is calculated. The dynamic response of gear transmission system is obtained and the vibration characteristic is analysed by solvingdynamics differential equation with numerical simulation method based on thestochastic wind prediction model have been built，the change rules of system dynamicresponse with the external excitation are analyzed, the dynamic mesh force of each gearand the nonlinear bearing force of each rolling element bearing are obtained, whichprovide foundation for dynamic reliability analysis and fatigue life prediction of windturbine gear transmission system.3. Time-dependent reliability analysis of gear transmission system of wind turbinein stochastic wind conditionThe finite element method, Hertz contact theory and Quasi-static method are usedto obtain the the dynamic contact stress of each gear pairs and each rolling elementbearing on the basis of dynamic load of each gear and each bearing. The rain-flowcounting method and the mathematical statistic theory are used to obtain theprobabilistic distribution function of dynamic contact stress of each gear pair and eachbearing, and the Monte Carlo method is used to obtain the probabilistic distribution ofparts strength. Regarding the load process as random process and considering thestrength as random variable, the random process function is built, and thetime-dependent reliability and the reliability index are calculated by using first-ordersecond-moment and perturbation method. The time-dependent reliability model is builtbased on the series parallel connection between the components in gear transmissionsystem and the rules of system’s reliability changing with time are obtained. Thestatistical analysis and classification of input stochastic load of gear transmission systemare carried out and the test loading spectrum used as fatigue life test is made, thisprovides the research foundations for reliability dynamic design and fatigue lifeprediction.4. Time-dependent reliability analysis of gear transmission system of wind turbineconsidering dependent failureConsidering the factors such as the dependent failure，coupling effect between thegear and the bearing and strength degradation, using the stress strength interferencemodel at the system level, regarding the load process as random process, thetime-dependent reliability model of gear transmission system of wind turbineconsidering dependent failure is built on the basis of the statistical analysis to thedynamic contact stress of each gear pairs and each bearing in gear transmission system,the rules of system reliability varying with time are obtained, the influences of strength degenerate to system reliability are studied, and the results are compared with dynamicreliability model without considering dependent failure.5. Fatigue life prediction of wind turbine gear transmission systemThe rain-flow counting method is used to statistics cycle parameters and theworking cycle stress is converted to fatigue stress spectrum in the condition ofsymmetrical cyclic stress in the principle of equal life combining with the Goodmanformulation. Considering all kinds of factors that affect part’s fatigue strength, theP-S-N curve of part is obtained by the P-S-N curve of material, the model for predictingthe fatigue life of key parts and components is set up, and the fatigue life of each gearsand bearing of gear transmission system is estimated on the basis of Palmgren-MinerLinear accumulative damage law, this research supplies theory and method for fatiguelife prediction wind turbine gear transmission system.6. Study on the dynamic property testing and the fatigue life experiment of windturbine gear transmission systemThe wind turbine gearbox used testing is designed and manufactured based on thesimilitude theory，the test fig is set up for dynamic characteristics testing and fatigue lifetesting of wind turbine gearbox, the dynamic characteristics testing and fatigue lifetesting of wind turbine gearbox are carried out. The comparison analysis between theorycalculation and test results shows that the theory model is correct and effective. Apreliminary testing research for dynamics and reliability of wind turbine geartransmission system in random wind condition is explored and the research resultsprovide the theory and experiment foundation for design and apply of wind turbinegearbox. |
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