| In order to study the influences of train braking on tunnel structure perturbation, and explore the responses of tunnel structure under the condition of train brake considering the thermal mechanical coupling effects. The three-dimensional directly thermo-mechanical coupling finite element model of wheel/rail in the train braking and the calculation model of the three-dimensional tunnel structure are established by the finite element software ANSYS,and the detailed parameters of models are selected carefully. The wheel/rail friction heat in the train braking and the vibration responses of tunnel are analyzed. At last some important research results are gotten.At first, this paper deduces the heat transfer control equation of wheel/rail friction in strain braking, and finite element iterative equations of the structure vibration of train-tunnel are given. Secondly, three-dimensional directly thermo-mechanical coupling finite element model of wheel/rail in the train braking and the calculation model of the three-dimensional tunnel structure are established. The detailed material and mechanical parameters are listed. The calculation methods of finite element model are explained.Finally, the vibration characteristics of wheel/rail system and the wheel/rail friction heat distributions in the train braking are calculated and analyzed. The elastic foundation vibration acceleration values of rail are seen as the tunnel structure vibration excitation, and the responses of the tunnel structure is studied under those excitation. The time history curves of tunnel structure at different position and the cloud pictures of tunnel structure at the end of train braking are presented. The main research results are as follows.In the static contact of wheel/rail in the train braking. The contact patch shape of wheel/rail is similar to ellipse, and its area is about 113mm2. The maximum equivalent stress of wheel is 599.3MPa, and the location of maximum equivalent stress stands 0.45 mm distance from the wheel surface. And the maximum equivalent stress value of rail is 559.6MPa, its point locates 0.17 mm distance rail surface. In terms of transient thermal analysis of wheel/rail in the train braking. Firstly, the relationships between wheel/rail friction heat and friction coefficient are analyzed. The calculation results show that temperature fields and their contours on the rail surface change more obviously with the brake speed increases when the friction coefficient changes with temperature. It is mainly due to the the bending deformation of rail and the elastic-plastic deformation of wheel/rail contact region cause a continuous change of the main vector direction of the forward movement of the train and the slightly vertical movement of wheel. The different temperature fields and their outer contours on the rail surface have similar features when the friction coefficient is constant, but different from the results of friction coefficient changing with temperature. In addition, the friction heatinfluence depth changes from 2.6mm to 3.4mm in the train braking. As for the wheels, the centers of high temperature regions on the wheel surfaces locate the front of temperature fields when the friction coefficient changing with temperature at the train braking speed is1m/s. But at the same train braking speed, the high temperature areas locate the center of the temperature field when the friction coefficient is constant. In addition, the temperature area between the highest and lowest temperature when the friction coefficient with the temperature changes is greater than its result of the friction coefficient is constant.The influences of strong convective heat transfer coefficients on the temperature fields and heat flux of rail surface are very small when the train pass through the tunnel. And their influences on the temperature fields are in the range of 10℃. The calculation results show that the influences of the strong convection environment of tunnel on the temperature fields of wheel/rail caused by train braking in a short time can be ignored. Thus, the convection heat transfer coefficient can be taken as 20W/(m2·℃)~25W/(m2·℃).In the aspects of the vibration of tunnel structure. The vibrations of tunnel structure change obviously with the train braking. The maximum and minimum vibration acceleration values of the tunnel-liner structure are 0.4332 g and-0.5873 g respectively. The maximum and minimum values of vertical displacement caused by the train braking are1.031 mm and-1.947 mm respectively. In terms of stress and strain, stress and strain present cyclical changes as the train braking. Tunnel structure will be in a circulating load conditions when the train is braking. The vibration direction of the lateral stress/strain at the top of tunnel lining structure is opposite to the bottom, but the vertical stress/strain vibration direction of the left tunnel lining structure is same as the right side. At the same time, the vertical strain at the top and bottom tunnel arch are big at the end of train braking. And in the tunnel bottom,there will become half-ellipses compression region.The research results in this paper will play a positive role in the generation mechanisms of friction heat and the temperature field distributions of the wheel/rail at the train braking. At the same time, these results will supplement and perfect the vibration when the train pass the tunnel. |
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