The Optimization Study Of Railway Empty Container Reposition Problem Under Uncertain Environment

The structure of China's cargo transportation is unreasonable at the present stage.For example,the proportion of highways transportation is too large,as a result that railway freight transportation cannot take advantage of medium and long distance.Railway container transportation has long been the development direction of railway freight transportation in the future due to its transportation safety,convenient cargo handling,simplified packaging,and suitable for multimodal transportation.However,the problem of empty container reposition has always restricted the development of railway container transportation.There are many factors lead up to empty container reposition,among which the uncertain factor in the railway container transportation system is the root and main cause.With the development of marketoriented reform of railway freight transportation,the uncertain factors in the railway container transportation system are gradually increasing.Therefore,study the uncertain factors affecting the transportation of railway containers and consider the empty container reposition problem under uncertain environment it is of theoretical value and practical significance.Therefore,based on the research of the uncertain factors such as the uncertainty of empty container supply demand,the uncertainty of empty container transportation time,the uncertainty of container cargo organization form and the discreteness anomaly,the paper concentrate on the study of optimization of empty container reposition problem under uncertain environment.First of all,in view of the macro empty container reposition plan between railway groups,the supply and demand are always forecasted before the plan.The error exists,which makes the empty container reposition plan under deterministic conditions not feasible and cannot solve the problem effectively.Therefore,let the predicted supply and demand of railway groups be the net demand,and the disturbance range is reasonably set according to the predicted error band,then the two-stage robust optimization method is applied.According to the conservative degree of the decision maker,different risk preferences are selected to formulate the macro empty container reposition plan.At the same time,the plan apply compensation measures to seek a balance between the optimality and feasibility under uncertain environment.The example shows that although "the price of robust" is paid to prevent uncertainty,but the total cost of empty container reposition can be effectively reduced when the disturbance occurs.Secondly,for the real-time dynamic empty container reposition plan formulation method for each container freight station in a certain railway group,the two-stage decision model is established because of the high uncertainty of real-time demand and high timeliness requirements.In the first stage,the fuzzy inventory management model is used to manage the empty container inventory of each container freight station in the fuzzy environment.By applying the model,optimal empty container reposition volume and optimal lack of container capacity for every freight station are determined.The second stage uses robust soft time window to optimize the real-time reposition plan between the container freight stations under the uncertain empty container transportation time.The example shows that the operation of fuzzy inventory management reduces the total cost of empty container reposition,which explains the necessity of inventory management for empty containers.At the same time the results shows uncertain empty container transportation time will increase the total cost of empty container reposition,which indicates the importance of on-time transportation.