| Truck escape ramps can forcefully decelerate runaway vehicles on long and steep downhill sections to protect life and property of drivers.However,the current research on truck escape ramps in China is insufficient,and the relevant standards to guide the construction of truck escape ramps are not yet perfect,which leads to a high probability of accidents on the truck escape ramps in China.Therefore,this thesis uses the method of combing theory and application to study stopping process of runaway vehicles on truck escape ramps.It is expected that the research results can provide reference for optimizing the design of truck escape ramps.Established the driver-vehicle-road model to study driving process of runaway vehicles on exit ramps.Firstly,by analyzing the lateral stability of the runaway vehicles on exit ramps,the maximum entry angles of the truck escape ramps were derived.Secondly,based on vehicle dynamics,the driver-vehicleroad model on exit ramp was established.Finally,this model was used to analyze the influence of entry angles on stability of runaway vehicles,and length of the normal sections of exit ramps for different combinations of superelevation,vehicle speed and gradient is calculated and the method to optimize the exit ramp design was proposed.Established the runaway vehicle three-dimensional discrete element model to study the stopping process of runaway vehicles on arrester bed.Firstly,the interaction mechanism between the tire and the aggregate of runaway vehicles on arrester bed was studied,including the basic theory of the particle discrete element method,the ways of kinetic energy consumption of vehicles,the flow deformation of the aggregate and the force of the tire;Secondly,the segmented modeling method was used to establish the runaway vehicle three-dimensional discrete element model including the suspension.Triaxial compression tests were used to calibrate the micro-parameters of aggregate particles,actual vehicle tests were used to calibrate micro-parameters of the tire;Finally,the advantages of the runaway vehicle three-dimensional discrete element model were proved through comparative analysis experiments.This model was used to study the influence of aggregate particle size,brake bed gradient,load,vehicle speed and other factors on the stopping process of runaway vehicles and methods for optimizing design of truck escape ramps were proposed. |
