| At present,the traffic congestion in large cities and megacities in China is becoming more and more serious,which challenges the urban public transport system.To solve this problem,virtual track train(VTT),a novel mode of urban rail transit,began to develop in China.The complex urban road and changeable operation conditions cause a severe challenge to the safe operation of VTT.Therefore,it is enssential to master the dynamic behavior of the VTT during opeation.However,there is little research on the VTT,especially the dynamic behavior of such system needs to be further investigated to support the design,operation and maintenance of the VTT.To solve this problem,based on the structural characteristics and working mechanism of the VTT,and combined with the vehicle system dynamics theory,multi-rigid body dynamics theory and the tire-road interactions,the dynamic behaviors of the VTT are systematically studied in the thesis.It mainly includes the following parts:Firstly,based on the real vehicle structure and its subsystems of the VTT,a three-dimensional spatial dynamic model of the train considering the car body,suspension,wheel,carbody connections,tyre-road interactions and road irregularities is developed based on the classical dynamic theory,and the differential motion equations of the system are derived.Further,a body-seat subsystem is developed and integrated into the whole train dynamics model.And then,a three-dimensional dynamics theoretical model of VTT running along a straight road is finised.On the other hand,based on the theory of multi-body dynamics and the working mechanism of steering system,combined with the designed proportional integral derivative(PID)controller,a multi-body dynamics model of VTT with path tracking performance is established.Furhter,a rigid-flexible coupled multi-body dynamics model of VTT considering the elastic deformation of the top and lower crossbeams of the suspension is constructed.In addition,the random irregularity spatial distribution of the left and right wheels on the road surface is obtained using the harmonic function superposition method,which can more truly reflect the dynamic characteristics of the VTT running on different roads.The tyre-road interaction is modeled by magic formula.Then,the running stability of VTT on a straight road is evaluated using the three-dimensional dynamics theoretical model of such train.Monte Carlo method and Latin hypercube sampling method are used to construct the simulation framework for random response analysis of VTT.The random dynamic performance of the system under random geometric irregularity excitation,random mass and suspension parameters of complex road is investigated.In addition,the random response characteristics and running stability of the VTT are analyzed and evaluated in detail under different operation conditions,such as different running speeds and road class.Next,the differences between front wheel steering and four-wheel steering are compared in detail using the established multibody dynamics model of VTT.The dynamic performance of VTT running on curved road is comprehensively investigated from two aspects of running stability and safety.Moreover,aiming at the key factors affecting the dynamic behaviors of the VTT during operation,based on the train multibody dynamics model,the influence of road longitudinal adhesion limit and wheel torque on the longitudinal dynamic behavior of the train,and the influence of road lateral adhesion limit on the lateral dynamic behavior of the train is analyzed in detail,respectively.The dynamic behavior of VTT under different road adhesion limits and different opertaion conditions is revealed.The effects of the air spring stiffness and damping on the vertical dynamic behavior of the VTT are analyzed to master the dynamic behavior evolution of VTT with different suspension parameters.Finally,based on the rigid-flexible coupled dynamics model of the VTT and the dynamic stress solution method of flexible body,the dynamic stress characteristics of the top and low crossbeams of the train suspension system are analyzed.On the basis,the dynamic stress characteristics of the suspension systems are compared and analyzed under the condition of VTT with the two steering modes of front-wheel steering and four-wheel steering.The dynamic stress response characteristics of the suspension system under different operation conditions are studied when the VTT runs on the straight road and curve road. |
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