Research On Dynamic Interaction Between Heavy-Haul Train And Track Under Longitudinal Impact

The increases of train length and axle load bring the severe challenge to the operation of heavy-haul train. The issues of train longitudinal impact, wheel-rail dynamic interaction and train running safety become increasingly urgent. Expecially, the mutual effect between the train longitudinal impact and the wheel-rail dynamic interaction is more obvious. It is one of the urgent needs to explore the action mode and influence of the train longitudinal impact on the heavy-haul train-track system. In this regard, taking the large marshalling heavy-haul train as the research object, this paper carries out the investigation on the dynamic interaction between heavy-haul train and track under the longitudinal impact.Firstly, from the viewpoint of the heavy-haul train running conditions and its mechanics relationship, this paper analyzes the basic principles of the interaction between adjacent vehicles and the interaction between train and track. Based on the train longitudinal dynamics theory and the vehicle-track coupled dynamics theory, a three dimensional heavy-haul train-track coupled dynamics model is established. The large-scale system model includes several submodels:the heavy-haul locomotive model, the freight wagon model, the wheel-rail dynamic interaction model, the ballasted track model, the coupler-buff model as well as the cross and vertical section model of railway lines. For the typical heavy-haul locomotive with traction motor suspended on wheelsets, the factors of motor vibration, traction force, brake force, and coupler force are considered. In the freight wagon model, the brake shoe pressure and the pneumatic brake force are also taken into account. The calculation method of wheel-rail creepage and creep forces are presented, to deal with the large slide phenomenon occuring in the wheel-rail contact surface. The coupler forces in three dimension are calculated using the coupler and draft gear model.Then, the simulation analysis software HTTSISIM is developed. In order to solve the vibration of the coupled system efficiently, a "two step method" is presented and the basic principle for the train modeling in three dimensions is put forward. The software is validated by comparing the calculated results with the results obtained from the field test and the commercial simulation software. There are five certification cases considered, including the coupler motion on a S-shape curve, the dynamic performance of a 10000t unit heavy-haul train in the process of electric brake operation, the longitudinal impact of 20000t combined train, the wheel-rail dynamic interaction of heavy-haul freight wagon on a curved track, and the dynamic responses of the ballasted track under heavy-haul loads. The calculated results of HTTSISIM agree well with the tested results, which certify that the developed software can be used in the research of heavy-haul train and track dynamics.Taking the 10 OOOt unit train and the 20 OOOt combined train as examples, the generating process of the longitudinal impact in the trains is analyzed. Under the operation conditions of the train traction, electric brake and pneumatic brake, the longidinal dynamic responses calculated by the traditional train longitudinal dynamics model and the three-dimensional train model are compared. It can be found that, in the case of the pneumatic brake, there is little difference in the calculated results for two train dynamics models. But in the conditions of electric brake and traction, slight difference of calculation results exists for these two models, and the maximum coupler force difference is below 16%. Meanwhile, the influence of track random irregularity on the train longitudinal impact is investigated. It is shown that the track excitation affects the train longitudinal dynamics in a smaller extent. Combining with the force-bearing characteristics of railway vehicle in the process of the train traction and brake, the wheel-rail forces caused by the longitudinal coupler force are analyzed. The results indicate that the axle-load of locomotive will transfer greatly in the traction and electric brake conditions, and the axle-load changing rate can reach 10%. However, when the penumatic brake is implemented, the axle-load transfer rate is below 3%. For the wheel-rail lateral force, both the coupler force and coupler swing angle have a significant influence on it, while the traction and brake movement affect the wheel-rail interaction slightly.On this basis, referring to the configurations of the vertical section gradient and the gradient difference of heavy-haul railway lines at home and abroad, the calculation conditions of different vertical sections are set on a straight line. Taking the train penumatic brake and release operation as the research conditions, the longitudinal impact, wheel-rail dynamic interaction and dynamic response of track structures for the 10 OOOt unit train and 20 OOOt combined train are analyzed. When the air brake is applied in the trains, the maximum coupler-press force occurs in the freight wagon couplers. Due to the high stabilizing-coupler ability of the freight wagon, the coupler will not unidirectionally rotate and the wheel-rail dynamic interaction keeps in a low level. For the 20 OOOt train, the locomotives distributed in the middle part are subjected to a large coupler-press force. As the locomotive stabilizing-coupler ability is limited, the coupler will angle easily, which induces larger wheel-rail lateral forces in the locomotive and worse dynamic performance of its neighbor freight wagon. In the concave vertical curve, the wheel-rail interaction of the middle locomotive is most violent. As the air brake is released, the coupler lateral tilt angles of locomotive and freight wagon will fluctuate near the centering position.Finally, aiming at the curved track, the curve negotiation characteristics of the heavy-haul vehicle are investigated. The results show that the suspension systems in the front and rear bogies have different load-bearing behaviors when the vehicle passes through a curve, especially on the transition curves. This is mainly attributed to the superelevation angle differences between the wheelset, bogie frame and car body. Then, taking the railway lines with the different combinations of cross and vertical section as examples, the longitudinal impact and wheel-rail dynamic interaction of 10 OOOt unit train and 20 OOOt train are analyzed under the pneumatic brake conditions. The results show that the values of the coupler pendulum angles in the freight wagon are mainly determined by the curve shape while the coupler force has little influence on them. However, the coupler force can be converted to wheel-rail forces, which leads to the more severe wheel-rail dynamic interaction in freight wagon system. For the locomotive, the coupler angle consists of two components. One is the angle caused by the curve geometric shape, the other one is the additional pendulum angle induced by the insufficient stabilizing-coupler ability of the locomotive. In the concave vertical curve, the longitudinal coupler force is the largest. In this condition, the wheelset lateral force of locomotive increases by 45% compared with corresponding idle state. And also the track structure has a large displacement. Under the longitudinal impact, the running safety of heavy-haul train is threatened seriously. When the pneumatic brake is released on curved track, the large tension force occurring in the draft and buff gear system will keep the coupler in the centring position, which greatly decreases the coupler angle caused by the curved track.