Research On Mechanism Of Airbag Ejection And Its Application In Virtual Collision Of Locomotive And Vehicle

With the rapid development of high-speed railways and the continuous improvement of rail vehicle operating speeds,the problem of passive safety of trains has become more prominent.The collision test bench of railway vehicles is an important research platform to realize passive safety protection,and the research of its driving ejective method has been paid more and more attention by people.The current driving system of rail vehicle collision test bench has the disadvantages of low accuracy,high energy consumption,high noise,high cost and difficult maintenance.In order to solve this problem,the airbag-driven ejection test method which is used to achieve the ejection and collision test of component level,car end structure and scaled vehicles has been proposed.The railway vehicle ejection virtual crash test system based on this method has the advantages of rapid response,variable stiffness,low noise,etc.,and has broad application prospects in the collision test of rail vehicles.At present,there are few research on the ejection mechanism of the airbag,the accumulated research results are insufficient,and the necessary theoretical research and engineering practice are lacking.Therefore,on the basis of fully summarizing relevant domestic and foreign researches,the following work has been carried out in this thesis:(1)research on the nonlinear static and dynamic mechanical properties of the airbag;(2)research on the ejection performance of the airbag with influence factors;(3)the parameters optimization of the airbag ejection performance;(4)research on virtual collision test system of the airbag ejection;(5)application research on virtual collision test system of the airbag ejection.This research work provides theoretical guidance for revealing the ejection mechanism of the airbag,improving the ejection performance,and providing theoretical guidance for the application of the airbag ejection in the virtual collision of the rail vehicle ejection.The highlights of the thesis are as follows:On the basis of the nonlinear theory of airbag,using the fluid-structure coupling method of airbag inflating action,the tension-compression finite element model and vibration finite element model which can characterize the static and dynamic characteristics of airbag were established.Firstly,the static tension and compression tests of the airbag under the initial pressure were carried out,and the static load characteristics of the airbag under different tension and compression displacements were studied.The correctness of the tension-compression finite element model of airbag was verified by experiments.Secondly,the influence of frequency and amplitude excitation on the axial dynamic mechanical characteristics of airbag was studied experimentally.The lower vibration frequency had a greater influence on the axial load characteristics.By increasing the frequency of airbag,the stability of the axial load could be improved.Finally,based on the dynamic vibration finite element model,the influence of different vibration frequencies and amplitudes on the radial dynamic mechanical characteristics of airbag was further studied.The influence of frequency on the radial load of airbag was significant,and it shows an approximate linear relationship.To explore the ejection performance of airbag,we developed the finite element model of airbag ejection with inflatable action and verified the correctness of the model by ejection experiment test.The effects of the initial pressure,the compression displacement,mass flow and cord parameters on the ejection performance of airbag was studied.The results show that by increasing the initial pressure and mass flow can significantly improve the performance of the ejection,compression displacement effect secondly,cord parameters affect for the performance of the ejection is limited,but the increase of cord layers can improve the stability of airbag.Through the numerical analysis of the ejection model,the oscillatory phenomenon of the airbag is reappeared,and the existence of the oscillatory phenomenon is confirmed by the ejection experiment test.The numerical analysis results of the ejection model explained the cause of the vibration phenomenon in detail,revealed the action mechanism of the airbag in the ejection process and given the solution to suppress the oscillation.In view of the existing airbag geometry structure,the influence of geometric parameters on the ejection performance was studied,and the influence law was obtained.The optimized geometry parameters of airbag were obtained through comparative analysis.The relationships among initial pressure,compression displacement,wall thickness,ejection mass and ejection velocity were studied,and the correlation between different parameters and ejection velocity of airbag was obtained.A characterization method of series and parallel about airbag combination was proposed,and the prediction model of airbag ejection performance was established based on series and parallel number,initial pressure,airbag diameter and ejection mass by using DOE design method and response surface method.By using multi-island genetic algorithm,the optimal combination parameters of virtual collision test equipment for airbag ejection under different impact energy levels are obtained,which provides theoretical basis and experimental data support for the selection of collision test parameterization scheme.In order to solve the problem of pressure loss in the process of airbag ejection,the influence of different cylinder volumes on the airbag chamber pressure was studied,and the design method of variable volume cylinder was proposed.At the same time,the realization method of the test trolley braking under the action of hydraulic pressure is proposed.According to the functional requirements of rail vehicle collision and the ejection mechanism of airbag,the structure of air cylinder,test trolley and control brake device were designed respectively,and a virtual collision test system for airbag ejection was established,which provided a reference for the engineering practice of airbag ejection in rail vehicle collision test bench.The virtual collision analysis model of anti-climbing energy absorption device was established,and the deformation mode and collision energy absorption characteristics were studied.The effectiveness of the virtual collision test system for airbag ejection was verified by collision test.The virtual collision analysis model of the vehicle-end structure was established,and the deformation mode of the structure and the wheel-rail contact collision response relationship of the test trolley were studied.The impact energy absorption characteristics of the vehicle-end chassis and the driver’s cab structure,as well as the vertical lift and lateral offset of the test trolley were obtained.Through virtual collision analysis,the reliability of the virtual collision test system for airbag ejection is verified,and the engineering application of component-level energy absorption device,vehicle end underframe and vehicle end cab structure in airbag ejection virtual collision test system is realized.In this thesis,the ejection performance of airbag is obtained by theoretical analysis,experimental research and numerical analysis,and the ejection mechanism of airbag is revealed.Through the prediction model of airbag ejection performance,the rapid optimization of airbag combination parameters under different impact energy levels is realized.On the basis of the system provided,the virtual crash analysis of the component level anti-climbing energy absorption device and the vehicle end structure is realized,which shorts the design cycle of the airbag ejection collision test,provides theoretical support for the passive safety research of rail vehicles,promotes the development of related collision tests,and has high engineering reference value.