Assembly Deviation Analysis And Statistical Tolerance Optimization Of All-direction Propeller

All-direction propeller has many parallel chains;and in the harsh service environment,it has high requirements about the assemble accuracy of the functional components.During the actual operation,with the alternating disturbance of load in extreme marine environment,it will cause the deformation of the mechanical structure and result in failure of the joint surface of the key components.However,the current tolerance analysis and optimization techniques rarely consider the deformation of whole machine or local structure of complex equipment in the actual service environment;on the basis of existing research,in this paper,the assembly deviation analysis and statistical tolerance optimization are studied with considering the real working condition to improve the assembly quality and service performance of all-direction propeller.In this paper,firstly,tolerance analysis model of complex assembly with partial parallel chains based on Unified Jacobian-Torsor has been established,and the assembly error calculation accuracy of spiral bevel gear pair is improved when applying to the spiral bevel gearbox of all-direction propeller.Secondly,tolerance analysis of blade bearing of alldirection propeller with considering the real working condition has been established,and the influence of the real working condition such as temperature,centrifugal force and pretension force on the assembly gap between the hub and blade foot has been analyzed.Then,the statistical tolerance optimization model based on the strategy of multiple sample testing has been constructed to improve the accuracy of statistical optimization results and reduce the computational time cost when applying to the propeller shafting components.The tolerance analysis model,service-life prediction model and tolerance-cost-service life optimization model of blade bearing of all-direction propeller are constructed.The influence of the real working condition on the service life has been analyzed,and the related assembly parameters are optimized to reduce the manufacturing cost and extend the service life.Finally,the optimization problem of blade bearing assembly parameters of all-direction propeller on the oil-drilling platform is regarded as the case study,and the results show the feasibility and reliability of the research in this paper.The research contents and innovation results are as follows:(1)Tolerance modeling and analysis of complex assembly with partial parallel chains.In order to solve the problem that the traditional tolerance analysis model could not calculate the assembly deviation of complex assembly with partial parallel chains,in this paper,the torsor parameters of parallel chains are obtained by constructing the contact points and analysis points of parallel connections and determining the position and orientation deviations of the analysis line.Then the partial parallel connections replaced by a new serial connection to calculate the final deviations of the functional requirements based on the Unified Jacobian-Torsor model.Based on this solution,more tolerance information is considered and the calculated assembly deviations would be more accurate and more in line with the actual situation.(2)Assembly deviation analysis of blade bearing based on Jacobian-Torsor model with considering the real working condition.In order to obtain the variational range of assembly deviation of complex assembly with considering the real working condition,and analyze the effect of real working conditions on assembly gap,in this paper,the tolerance analysis model of complex assembly based on Jacobian-Torsor model with considering the real working condition is constructed.Firstly,the deformed surfaces of parts are dispersed by establishing a series of concentric circles nodes,and the thermo-mechanical coupling deformations of surface of parts and the coordinates of these nodes are obtained by finite element analysis.Secondly,the assembly deviation are obtained by Unified Jacobian-Torsor model with considering the geometric tolerances,and the variational surfaces caused by assembly deviation are dispersed corresponding to the deformed surface with concentric circle nodes.Finally,the deviation with considering the real working condition can be obtained by superimposing the deformations of nodes,which have the same x,y coordinates.(3)Statistical tolerance optimization based on the strategy of multiple sample testing.Based on the Monte Carlo simulation,the statistical tolerance optimization method could simulate the probability distributions of tolerances of parts and the probability of an eligible product,but the simulation results are not stable.During the entire process of statistical tolerance optimization,it could easy to obtain the inaccurate values in many generations with large number of assembly analyses;finally,the optimization would be failed.In order to overcome this disadvantage,a strategy with multiple sample testing is proposed to obtain the high precision of fitness for the next generation,and a feasible solution that satisfies all the constraints could be obtained.Based on this strategy,the statistical tolerance optimization method can solve the statistical tolerance optimization and allocation problem well,and its optimization results are better than other traditional statistical tolerance optimization method with improving the precision of statistical tolerance optimization results largely and reducing the computational time cost.(4)Statistical tolerance optimization and allocation of blade bearing of all-direction propeller with considering the real working condition.In this paper,the assembly deviation,thermo-mechanical coupling deformations,friction and wear during service life are all considered to establish the prediction model of tolerace-sealing performance and tolerancecost-sealing performance optimization model of the blade bearing of all-direction propeller with considering the real working condition.In order to improve the accuracy of the model,we have established the relevant experimental platform about friction and wear,and at the same time in cooperation with other research institutions,the real data about hydrodynamic experiment of all-direction propeller are obtained.Based on the above prediction model and optimization model as well as the experimental platform and real data about hydrodynamic experiment,the influences of different working conditions on the sealing performance are analyzed quantitatively.At the same time,by optimizing the key assembly parameters,the sealing performance of the blade bearing is extended and the manufacturing cost of the tolerances is reduced.At last,the optimization problem of blade bearing assembly parameters of all-direction propeller on the oil-drilling platform is regarded as the case study,and based on the theory and methods in this paper,the sealing performance of blade bearing of all-direction propeller has been predicted in the actual sea condition.Then the sealing performance is regarded as the optimization object,and the optimization problem of assembly parameters under different working conditions is solved by statistical tolerance optimization method,and the optimization result is better than the initial design tolerance.In conclusion,the studies in this paper provide the new theoretical method and technical guidance for the assembly deviation analysis and optimization of all-direction propeller.