The Dynamics Of The Long Heavy-Haul Train In Positioning Operation

The efficiency of rail freight tranportation is greatly improved by Heavy-haul transportation. Simultaneously, a large railway unloading system is also widely used, which mainly consists of the car dumper and railcar positioner. The train is hauled by the railcar positioner to locate at the specified location in the car dumper accurately and achieve unloading operation. These practices are known as train positioning operation. Different from the general train operation, all the necessary traction forces of the whole train movement are provided exclusively by the railcar positioner during the positioning operation. The inter-train coupler force and the unloading capacity of the car dumper are determined by the traction force, and the traction force is closely related to the structural design of the railcar positioner, the cost, lifetime and the job security. Many factors may affect the traction force of the railcar positioner in a complex form, such as the rail-track of train operation, the train weight, the mechanical characteristics of the coupler draft gear, the coupler gap, and the traction speed curve of the railcar positioner. Moreover, the train may perform reciprocating motion along the track during the positioning operation and the switch effect of the train running resistance will be appeared. The coupling of these complex factors will make the long heavy haul train be one of the most complex engineering nonlinear systems during the positioning operation.Some prominent problems exist in the current positioning operation cannot be solved through traditional train dynamics theory which mainly focuses on the trains in normal operation. Considering all factors comprehensively by this paper, the dynamics of long heavy haul train are studied during the positioning operation. The main contents are as follows:(1) Based on improving the traditional train longitudinal dynamic model, the heavy haul train longitudinal dynamics model is established, which includes the movement of the railcar positioner. The model can be applied on the longitudinal dynamics simulation for any marshaling trains in different types of track during positioning operations, and the characteristics have been fully considered that the motion the railcar positioner is known, but the traction force is not. Meanwhile, the model cannot only make a dynamics analysis, but a continuously analysis of the entire train hauled by railcar positioner during the positioning operation. The corresponding dynamics analysis software has been developed, according to the analysis, the result is consistent with the engineering practice. Based on the results of the analysis, the dynamic response of the long heavy haul train during positioning operations has been studied. Moreover, the study lays a theoretical foundation for the further research. (2) A further investigation of the mechanical model of the frictional draft gear has been conducted, and a new mechanical model combined with a contact friction research has been proposed. The damping force is a nonlinear function about the travel change rate of the draft gear, and the locking effect between the loading and unloading process is fully considered in this model. The model can not only simulate the dynamic impedance characteristics of the frictional draft gear, but also alleviate the difficulties of the numerical analysis.(3) Based on the traditional methods for calculating the train running resistance, a method that is according to the resistance value of sample points to construct the full line resistance curve has been proposed. Considering the real conditions of the freight yard track, the basic and additional resistances of the train are converted to the equivalent resistance of the track, and the corresponding values of any points that on any combinations of the corners, ramps and straight lines rail track are conveniently and rapidly computed with this method. The switching effect caused by the change of train running direction and the discontinuous effect of the train resistance caused by the different types of track connected are considered respectively. For a complex mixed track, a solving process about an equivalent track resistance of a detailed full line has been given through the implement of the developed software.(4) Fully considering the influence factors of the line conditions, the coupler gaps, draft gear characteristics, and the positioner traction velocity curves, many significant results are obtained through the dynamic analysis of the long heavy haul train in the positioning operation, such as the speed transfer law between the train, the coupler state transfer the law, the train length change law and the coupler force and traction force variation law. For each factor, the corresponding mode of the positioner running speed has been given by implementing the developed software and a reference is provided for the development of the scheme of the long heavy haul train in the positioning operation.(5) The curve of the positioner traction speed is optimized to reduce the traction force of the positioner. The long heavy haul train positioning operation is a complex nonlinear system, which appears that the relationship between the traction force and the braking force of the positioner is no longer a simple smooth function of the design parameters of the traction speed curve due to the various factors. The time-consuming sensitivity analysis for the traction velocity curve of the design parameters is extremely inconvenient. In view of the above, a more practical response surface method has been adopted to optimize the traction speed curve of the positioner. Through the developed software, the curve of the positioner traction speed has been optimized for a heavy haul train on the horizontal straight line during the positioning operation and the optimal speed curve of the positioner has been identified.