| Wind power brake is an important component of wind turbine, and the spindlebrake has great effects on the normal operation of whole wind turbine. The brakingprocess of brake involves complex multi-physical field coupling problems. On theanalysis of thermo-mechanical coupling of brake, not only the braking process can berevealed, but the technical basis for the development of domestic industrial brakebrand can be provided. In this paper, a large three-dimensional finite element modelof main shaft brake of wind turbine is built based on the finite element softwareANSYS, then the temperature field and stress field of brake are simulated andanalyzed with using the theory of thermo mechanical coupling. And the braketemperature distribution, temperature gradient, the mechanical stress, thermal stress,thermal deformation are studied, the modal analysis of noise problems of brake is alsoachieved.The main researches are listed as follow.Firstly, the domestic and foreign research situations of the thermo-mechanicalcoupling analysis on brake are summarized. The theories related tothermo-mechanical coupling analysis, such as friction theory, the establishment oftransient heat conduction equation, coupling method, are introduced. And thevibration theory is briefly introduced.Secondly, the three-dimensional transient finite element model of the brakefriction has been established based on ANSYS software. The relevant parameters andboundary conditions have been determined. With considering the influence of changeof material parameters, the temperature fields of disc and brake are simulated undernormal condition and emergency condition through the method of loading heat flux offixed displacement. The results show that the temperature distribution of disc isinhomogeneous and high temperature mainly concentrates on the surface, and frictiontemperature appears jagged fluctuations which results in thermal shock. The highesttemperature of friction area on disc surface occurs in the3/5braking process. Thetemperature of friction pad does not fluctuate, and the temperature is much highercompared with the temperature of disc. The surface temperature distribution isrelatively uniform, and the surface temperature difference is less than100. In thedirection of thickness, there is a phenomenon of temperature lag. The temperature of disc and pad under two conditions is similar while the temperature of emergencycondition is relatively higher. Then the bench test under normal condition has beenachieved. The maximum temperature is lower about15℃than analog value in thetest results, which basically verifies the correctness of numerical simulation.Thirdly, three-dimensional finite element model is built according to thecomplete model of brake. The influence of mechanical stress on brake underemergency condition is studied. The results show that mechanical stress field issymmetrical distribution about the middle interface. Ignoring sharp stress of modeland the phenomenon of local distortion, the equivalent stresses of brake are below30MPa which is far less than the material yield limits. The thermal stress field resultsare got and solved by the method of indirect coupling using the results of emergencytemperature field as body load of stress field. Results show that thermal stress issimilar to the temperature distribution which is increased sharply then slowly decline,and equivalent stress is moving gradually towards inner radius and middle sectionwith braking time increased. Distribution of thermal stress in the friction region isbasically uniform and stress gradient is smaller. The hoop stresses and radial stressesin friction region are tensile stress while stresses in non friction region arecompressive stress and the value of hoop stress is always larger than radial stress.Therefore the heat cracks are most likely to occur in the friction surface of disc and itis most likely radial cracks. The deformation produced by thermal stress is up to4.5mm and the deformation increases as the radius increasing. The deformation on themedium-term braking is the maximum.Finally, the actual finite element models of spindle disc and pad have been built.Then modal analyses are carried on separately to study the problems of chatter noiseof brake. The results show that from sixth to tenth order modal frequency of discbelongs to the chatter noise range, however, the natural frequency of pad which is inthe range of frequency of scream is much higher than the range of chatter noise.The studies in this paper have reference value for the choice of spindle brakematerial and the structural optimization design. The analysis results can providetheoretical research related to the direct coupling analysis of the spindle brake andimprovement of the structure of wind turbine brake. The results of modal analysis ofbrake and pad also can provide a basic research on noise study. |
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