Dynamics Analysis And Reliability Optimization Design Of Multibody Systems With Multiple Clearances

Clearances between parts,component flexibility and lubrication are often not considered in the design of mechanical systems.However,due to the influence of material deformation,wear and mechanism motion needs,the existence of clearance is inevitable.The traditional assumption of rigidity is inaccurate when analyzing high-speed,lightweight and high-precision mechanical products.Therefore,in order to predict the dynamic behavior of mechanical systems accurately,it is necessary to consider multiple clearance joints,component flexibility and lubrication conditions and other factors.At the same time,to improve the mechanical performance of multibody systems,it is also necessary to optimize the design of multibody system.Because of the uncertainty factors of dimension error,machining installation error and material inequality,the multibody systems with clearance have the deviation between the actual motion and the ideal motion.In order to prevent faults and shorten the development cycle,the reliability analysis of mechanical systems with clearances will be of great significance.In the reliability design and optimization of multibody system,the reliability sensitivity calculation can avoid the blindness of the random variable distribution parameter selection.However,the traditional reliability sensitivity calculation method based on explicit functional relation is difficult to be used in multibody systems and even flexible multibody systems with clearances.Therefore,this paper proposes a multibody system reliability sensitivity calculation method based on Kriging agent model combined with double Monte Carlo method.Considering that the optimal solution obtained by the deterministic optimization of multibody system is close to the constraint boundary and the optimization results are unreliable,this paper further introduces the parameter uncertainty into the optimization design of clearance multibody system,and put forward the reliability optimization method with clearance system.The specific research contents are as follows:(1)Dynamic analysis of multibody system considering multiple clearance joints,component flexibility and lubrication condition.Firstly,the dynamics modeling process of multibody system with planar motion is introduced in detail,then the absolute nodal coordinate equation for flexible component modeling is introduced,and then the mathematical models of the revolute joint clearance,the moving clearance model,the contact impact force model,the friction force model and the lubrication model are introduced respectively based on the absolute nodal coordinate method.At last,the crank slider mechanism considering multiple joint clearances and part flexibility and four link mechanism considering multiple clearance joints and lubrication condition are taken as the research object.The influence of the number of clearance joints,clearance joint position,lubrication joint and component flexibility on the dynamic behavior is analyzed.(2)The common mechanism wear and vibration problems in multibody system are optimized.Considering the buffer effect of harmonic drive on the gap collision,the wear performance of the rigid slider crank mechanism with harmonic drive and without harmonic drive is optimized respectively.The influence of bearing parameters on the wear performance of the two mechanisms is analyzed.The buffer effect of harmonic drive on gap collision is proved from the angle of optimization.In view of the low computational efficiency of wear optimization,the elastic foundation model considering energy dissipation(EFM)is introduced to calculate the collision pressure,and the response surface surrogate model is used to construct the functional relationship between the design variables and wear performance.In addition,the vibration optimization design of helicopter main reduction system is taken as an example.Firstly,based on the dynamic anti resonance isolation principle,the dynamic modeling of the dynamic anti resonance isolator is carried out.Then based on the Patran/Nastran finite element analysis software,the dynamic characteristics of the isolator are analyzed.Finally,the vibration isolation efficiency is evaluated based on the surrogate model.(3)The stochastic analysis and motion function reliability prediction of multibody system with different number of clearance joints are carried out.Firstly,the basic theory of stochastic analysis is introduced.Considering the high fitting accuracy of the neural network surrogate model,the BP neural network method is used to analyze the randomness of the multibody system with clearance.Then the basic theory of the motion function reliability is introduced.Aiming at the problem that the function of multibody system is an implicit function,the response surface method and the response surface method based on vector projection sampling points are adopted to predict the motion function reliability of the multibody system with clearance.(4)For the multibody system with no explicit limit state equation and uncertainty of allowable value,the reliability sensitivity calculation method of Kriging agent model combined with double Monte Carlo method is proposed.Firstly,Monte Carlo method for reliability sensitivity analysis is introduced.On this basis,a double Monte Carlo method considering uncertainty of allowable values is proposed.Then the construction process of Kriging model is introduced.Finally,the concrete steps of Kriging agent model combined with double Monte Carlo method for reliability sensitivity analysis are given.(5)Reliability optimization design for multibody systems including multibody systems with clearances is presented.Firstly,the mathematical model of reliability optimization is introduced,and then the concrete steps of reliability optimization of multibody systems based on Kriging agent model are given.On the basis of reliability sensitivity analysis,the reliability optimization design of the rotating flexible beam system and the double link flexible manipulator system is carried out.Finally,the reliability optimization design of crank slider mechanism considering two gap joints is conducted.It is proved that the reliability optimization method is more robust than the deterministic optimization method and can reduce the sensitivity of system performance to parameter variation.