Research On Structural Reliability Analysis And Design Optimization Of Railway Vehicle

With the increasing complexity and lightweight of modern rail vehicle structure,higher requirements are put forward for their quality level.In the face of the increase of key and complex design requirements,it is increasingly necessary to pay more attention to the uncertainty factors such as geometric dimensions,material properties and loads in engineering practice.and accurate measurement and evaluation are carried out to reduce their impact on structural performance and ensure the reliability and safety of rail vehicle structures.However,the traditional structural analysis of rail vehicles is generally based on the determined structural parameters and load conditions,and the numerical simulation analysis and static/dynamic test are employed to verify whether it meets the standard requirements,which leads to conservative and ideal analysis results.While the uncertainty-based structural analysis in consideration of the uncertainties in engineering information,which can truly estimate the performance of structural components and predict the possibility of failure,so as to reduce the main unreliable factors and prevent accidents.Meanwhile,the structural optimization considering the uncertainty of parameters can make the analysis model in the design of rail vehicles more refined and obtain a design scheme that takes into account both reliability and excellent performance.Therefore,this paper carries out the research on the design method of rail vehicle structure from two aspects of structural reliability and optimization considering the uncertainty of parameters.The existing theoretical system of uncertainty analysis and optimization are expanded and improved,so as to provide theoretical and technical support for the reliability design of rail vehicles in the development stage.The main research contents of this paper include the following aspects.(1)The methods for structural static/fatigue strength analysis in consideration of parameters uncertainties are proposed.In order to verify the necessity of considering parameters uncertainties in structural performance analysis,the static strength of the structure under the fluctuation of design parameters is determined based on the D-optimal design of experimental and finite element analysis.The response surface surrogate model is employed to establish the functional expression between uncertainty design parameters and structural statics strength,and the influence of parameter uncertainty on structural static strength is analyzed,and then the Monte Carlo(MC)method is used to calculate the structural static strength reliability.Similarly,an evaluation model of structural fatigue strength under the influence of uncertainty is constructed based on the theory of fatigue analysis and the influence of design parameters uncertainties on structural fatigue strength is analyzed by importance sampling method.The reliability of structural fatigue strength is evaluated with the improved Goodman-Smith fatigue limit diagram.The proposed method quantitatively analyzes the influence of parameter uncertainty on structural performance,and solves the relatively conservative problem of traditional deterministic analysis.(2)The reliability analysis methods for single/multi load cases are proposed for the structural design of rail vehicles.Facing the problem of improving the structural reliability analysis accuracy under complex load cases,a piecewise function model describing interval variables is established combined 6? principle with Chebyshev's inequality.The generation strategy of interval variables and the calculation method of reliability in the new model are proposed to realize the accurate calculation of structural reliability under single load case,and reduce the dispersion of analysis results based on the assumption of probability distribution.In addition,an improved differential evolution particle swarm optimization(IDEPSO)is employed to optimize subset simulation(SS).An IDEPSO-SS-based multi load cases structural reliability analysis method is proposed by combining the improved Ditlevsen method and the optimal criterion,which reveals the influence of multi load cases and their correlation on structural reliability.The optimal failure sequence of the structure under multi load cases is finally determined.This method broadens the application scope of reliability analysis methods and overcomes the deficiency of existing models in the performance analysis of rail vehicle structure under various combined load cases.(3)The time-variant reliability analysis methods for static/fatigue strength of rail vehicle structure based on stochastic process are proposed.Considering the time-variant and dynamic characteristics of structural reliability caused by load,Poisson stochastic process and probability distribution characteristics are used to describe the number and magnitude of load respectively and gamma stochastic processes is used to describe the degradation of material strength.The influence of parameters uncertaintis and time on the static strength reliability of structure is analyzed with the time-variant reliability model which is established under the condition of considering parameters uncertaintis.On this basis,the continuous time model and Ito lemma are used to establish the time-variant equivalent stress and fatigue strength model based on the equivalent stress calculated by the line test data and fatigue damage theory,and then the equivalent time-variant dynamic stress-strength interference model of the rail vehicle structure is proposed to analyze the relationship between structural service life and fatigue reliability.The model directly reflects the effect of service life(time)on equivalent stress and fatigue strength,and is suitable for fatigue reliability analysis of welded structures based on dynamic stress at any service life(time).(4)A fuzzy design optimization method based on multi-level response surface surrogate model is proposed.Aiming at the multi-variable optimization problem of implicit structure,the Monte Carlo method is employed to analyze the sensitivity of structural design parameters and the classification is made.The fuzzy theory is used to deal with the uncertainty of the boundary constraints of the design parameters.Combined with the polynomial response surface surrogate model,the multi-level response surface fuzzy optimization model of the structure is established in turn,and it is solved by genetic algorithm(GA)and nonlinear programming(NP).Compared with the single-level response surface surrogate model,the proposed method has higher calculation accuracy and efficiency,and the problems of poor fitting accuracy and low optimization efficiency under the condition of multiple optimization variables are solved.(5)A multi-objective time-variant reliability fuzzy design optimization method is proposed.In order to characterize the effect of time on the comprehensive performance of the explicit structure,the time-variant stiffness model and the time-variant strength reliability model are established based on the theoretical derivation of the performance index by combining the continuous time model and Ito lemma.At the same time,the fuzzy theory is used to quantify the uncertainty of the structure design parameters,and the physical programming method is applied to improve the designers' preference for the optimization objectives.A multi-objective fuzzy design optimization model with time-variant stiffness constraints and time-variant strength reliability constraints is established,and a hybrid optimization solution strategy combining DoE sampling is developed.The necessity of considering time-variant reliability and fuzziness of optimization variables is verified by comparing the fuzzy/non-fuzzy optimal design with three hybrid optimization strategies.This method not only improves the accuracy and reliability of the optimization results,but also solves the problem that the optimization results tend to be dangerous due to ignoring the time factor in structural design.