Comprehensive Optimization Of Wagon-flow Allocation And Car-to-track Assignment At Railroad Technical Station

As the main station in the railroad network dealing with freight trains and vehicles,the operation capacity of the technical station has a direct impact on the quality and efficiency of railroad freight transportation and production.The daily work of the technical station is mainly organized through the preparation of various types of operation plans,and several optimization decision problems need to be solved.,among which,the wagon-flow determines the scheme of train connection,the engine scheduling determines the shunting operation plan of disassembling and marshalling of switch engines,the utilization of arrival and departure tracks determines the occupation scheme of inbound and outbound trains to the arrival and departure lines,the car-to-track assignment determines the occupation scheme of cars to shunting lines.It can be seen from the process of the technical operation of cars in the station that the wagon-flow allocation and the engine scheduling determine the transfer efficiency of cars and the quality of the operation plan of the technical station.At the same time,shunting line is a place where cars may stay for a long time from the end time of disassembling to the start time of marshalling,thus the car-to-track assignment affects the feasibility of wagon-flow allocation and engine scheduling.Therefore,in order to improve the feasibility of decision-making of wagon-flow allocation and engine scheduling,and improve the quality of the comprehensive preparation of operation plan,this paper specifically studies the optimization method of comprehensive problems of wagon-flow allocation,engine scheduling and car-to-track assignment in technical stations,mainly including the contents below:(1)Analyze the technological process of wagon-flow in station.By studying the specific methods of each technical operation carried out at the station,the contradictions between limited cars and the demand of depart trains,between the trains to be disassembled or to be marshalled and the limited switching-machine resources,and the conflicts between the cars disassembled and the limited shunting lines are both sorted out.In addition,the important optimization decision problems that need to be solved in the process of preparing the operation plan of the technical station is discussed,and analyzes the relationship of mutual promotion and restriction among the problems,thus the conclusion is drawn that the optimization of several problems in the preparation of operation plan can effectively improve the feasibility of the operation plan of railroad technical station.(2)The machine scheduling problem,minimum cost flows problem with minimum quantities and cumulative flow technology are briefly introduced,and the commonality between the above modeling theory and the technical operation of the technical station is explored.It can be concluded that the process of train disassembly and marshalling is similar to the operation of workpiece being processed,so the disassembly and marshalling operation can be regarded as a machine scheduling problem with release time and cut-off time.In the problem of estimation of wagon-flow,it is necessary to specify the marshalling content and the source of wagon-flow for the outbound train,and at the same time,the train must satisfy the assembly requirements,and consider the characteristic of taking cars between minimum tonnage rating or length to the maximal as the standard of being fully loaded trains.Therefore,the problem can be regarded as a minimum cost flows problem with minimum quantities.The cars shall slip into any shunting line in turn and the total length of the cars staying in the shunting line shall not exceed the effective length.In view of this limitation,the accumulative flow technique in queuing theory is introduced to measure the real-time change of shunting line capacity.(3)An integrated optimization model and algorithm for the comprehensive compilation of wagon-flow allocation and car-to-track assignment of railroad technical station is constructed.In order to accelerate the turnover time of cars at the station,the main objective of minimizing the total dwell time of cars is put forward;Based on the maximization of shunting line utilization efficiency,the secondary goal of minimizing the degree of violation of the fixed scheme of shunting line is put forward.By incorporate the secondary objective to the main,the model of integrated optimization plan of railroad technical station is established.Combined with the characteristics and requirements of the model,the three-stage decomposition algorithm is designed,and the original integrated optimization model is decomposed into two sub-models,namely,wagon-flow sub-model and car-to-track sub-model.First,the wagon-flow sub-model is solved.On this basis,a sub-model of adjustment is proposed,and on the basis that the operation scheme of engine scheduling is fixed,part of the marshalling content of the outbound train is adjusted to avoid a large number of cases of picking up cars in the middle of the shunting line,so as to increase the difficulty of subsequent application of shunting lines.Finally,the submodel of car-to-track assignment is solved,and the scheme of wagon-flow,engine scheduling and car-to-track assignment are obtained.(4)One demonstration example and one large-scale practical example are used to test the proposed integrated optimization model and algorithm.In order to verify the feasibility of the proposed method,a demonstration example is tested.The results show that the proposed integrated optimization model is difficult to converge in a reasonable time due to its large scale.However,the three-stage decomposition algorithm can solve the example to the optimum in a very short time,and the schemes of wagon-flow allocation,engine scheduling and car-to-track assignment are of good quality.On this basis,a large scale practical example is designed to verify the effectiveness of the algorithm.By testing,the proposed algorithm is able to obtain the schemes of wagon-flow allocation,engine scheduling and car-to-track assignment in no more than 2min.Based on this,it is proved that the optimization method proposed in this paper is suitable for solving the problem of synthesizing operation plan of railroad technical station of actual scale,and it has certain value in use.