Running Safety Evaluation And Optimal Design Of Suspension Parameters For High-speed Freight EMU Equipped With Four Double-Axle Bogies

With the rapid development of China’s e-commerce economy and high-speed railway network,high-speed freight has become an inevitable development trend and demand of railway freight transportation.However,for the rapid transportation of extremely large and extremely heavy goods,there is still a lack of specialized high-speed rail transport vehicles in China at present.In order to fill the gap in the field of high-speed freight transportation equipment,China has developed a high-speed freight electric multiple unit(EMU)equipped with four double-axle bogies.Compared with the ordinary high-speed passenger EMU,this high-speed freight EMU has larger load-carrying capacity,and its wheel-rail dynamic interaction is more intensified under the high-speed running condition.Especially,the presence of the eccentric cargo loading extremely threatens the running safety.Therefore,revealing the dynamic characteristics of the high-speed freight EMU equipped with four double-axle bogies,assessing the running safety,and revealing the influence law of the eccentric cargo as well as optimizing the EMU vehicle suspension parameters,have important theoretical guiding significance on improving the EMU vehicle system dynamics performance,formulating scientific and reasonable scheme of loading,and ensuring the running safety of vehicle under high-speed running.Based on the structural and functional characteristics of the high-speed freight EMU equipped with four double-axle bogies,this thesis established the vehicle system dynamics model,and revealed the similarities and differences in the vibration characteristics,wheel-rail dynamic interaction and safety index results when compared with the traditional vehicle dynamics model.On this basis,the variation rule of the vehicle running safety index under the effect of the eccentric cargo is studied,and the multi-objective optimization on the vehicle suspension parameters is performed based on the surrogate modeling technique.The main research work includes:Firstly,the dynamics model of the high-speed freight EMU vehicle system is established with considering the structural and functional characteristics of the three suspensions,bogie group,traction power transmission system.Considering the wheel-rail contact,the gear mesh and other internal/external dynamic excitation characteristics,the similarities and differences between the established vehicle system dynamics model and the traditional vehicle dynamics model without considering the traction power transmission system are compared and analyzed.These work could provide theoretical support for the model selection of the dynamic performance investigation in the following chapters.Then,based on the established dynamics model of the high-speed freight EMU vehicle equipped with four double-axle bogies with considering the traction power transmission system,effects of the cargo eccentricity along the longitudinal,lateral and vertical directions on the vehicle running safety index are analyzed by changing the position of the cargo gravity center in the carbody.Then,the cargo eccentric distribution area within the limit of the vehicle running safety index is obtained.The research results can provide theoretical basis for the cargo loading.Finally,the surrogate model between the vehicle suspension parameters and the optimization objective function is established by using the approximate surrogate technology.The multi-objective optimization analysis of the vehicle suspension parameters is carried out together with using the established vehicle system dynamics model and the optimal solution set of three double objective optimization combinations consisting of the nonlinear critical speed and wheel unloading rate,overturning coefficient and wear index is obtained.The obtained results can provide theoretical guidance for the EMU vehicle suspension parameter design.