Dynamic Reliability Method On Mechanical System And Its Application In The Power Transmission System Of Shearer

The mechanical power transmission system is widely applied to the large-scale equipments of industry,such as wind turbine,tunnel boring machine and shearer loader.The developing and applying levels of complex mechanical system reflect the scientific ability and technological capacity in energy,mine,transportation,chemical engineering and other key fields.Meanwhile,the reliability of mechanical system contributes directly to the security,accuracy,efficiency and maintainability of industrial production.It also has a significant influence on the personnel life safety and economic benefit.Mechanical dynamic system almost always remains in the coupled condition of heavy load,variable speed and high-frequency vibration.The mechanical reliability not only pays attention to random factors in the system but also focuses on the dynamic characteristics.Hence,the dynamic reliability should consider the mechanical performance in random conditions and dynamic characteristics during the operation process.The traction unit of MG300/700-WD shearer loader is taken as the research object in the thesis.The analytical method is proposed to analyze the reliability and reliability-based sensitivity for the mechanical power transmission system.The main content of thesis includes the following aspects:(1)The speed-varying dynamic model of power transmission system is established toanalyze the dynamic responses of traction unit in the condition of heavy and variable load.The model under fluctuation load is employed to calculate the dynamic displacements of traction unit in shearer load.The results are analyzed and compared with the experimental data from "National Coal Energy and Mining Equipment Research Center".The stochastic iterative method is proposed to analyze the statistical moments of mechanical power transmission system with nonlinear factor under deterministic and stochastic excitements.The mathematical expectation and covariance are calculated for the traction unit in shearer loader.(2)The analytical method is proposed for the dynamic reliability and reliability-based sensitivity of mechanical transmission system based on saddle-point approximation method.The distribution range and expression of saddle point are both proposed for the arbitrary distribution parameter in the system.The stress-strength interference model of traction unit is established to analyze the system reliability.The structural,environmental and material parameters are taken into consideration to calculate the reliability-based sensitivity.Meanwhile,the optimal reliability model and minimum space model are utilized to optimize the traction unit in shearer loader.(3)The improved saddle-point approximation method is proposed to analyze the dynamic reliability and reliability-based sensitivity of mechanical power transmission system with arbitrary distribution parameters.Both the improved method and stress-strength interference model are taken into consideration to analyze dynamic reliability of mechanical system.The computational efficiency and calculation error are analyzed on the improved reliability method.The approximate model is utilized to analyze the dynamic reliability and reliability-based sensitivity of traction unit in shearer loader.In the various material strengths,the reliability-based sensitivity index is discussed with times of load action.(4)The high-order stochastic response surface method is improved and employed to analyze reliability and reliability-based sensitivity of mechanical system.The influences of parameters in the method are analyzed on high order,total number of terms and mechanical reliability.The reasonable selective criterions are proposed for the power transmission system.The kinematic accuracy reliability model is established for the complex transmission system of traction unit.Meanwhile,the optimal reliability model and minimum space model are proposed on the basis of kinematic accuracy model in shearer loader.(5)The fractional polynomial response surface method is proposed,in which the nonlinear factor and non-positive integer order are taken into consideration.The range and constraint condition are derived for the factional order.The selective method of samples is discussed and the establishment of independent and cross terms is defined in the method.The fractional polynomial response surface method and improved reliability method are utilized for the coupled system of dynamic stress-strength interference model and kinematic accuracy model.The dynamic reliability and reliability-based sensitivity are analyzed for the traction unit in shearer loader.