Study On Optimization Of Transportation Scheme Of High-speed Rail Express Adapting To The Demand For Subdivided Time-limit

It is one of the core tasks of the daily transportation organization of high-speed rail express delivery to carry out the transportation scheme scientifically and reasonably.In view of the contradiction between the growth of the total amount of express delivery and the exuberant demand for high-speed rail express encouraged by the national policy,as well as the current unitary transport plan,from the point of view of improving transport efficiency,the optimization of the transportation scheme under the current passenger EMU piggybacking transportation mode is studied,which aims to make efficient use of passenger transport capacity,meet the time limitation of goods delivery,and promote the medium-and short-term development of high-speed rail express delivery.The main contents of this thesis are as follows:(1)Basic theory and method of high-speed rail express transportation scheme optimization are studied.Based on the basic theories of high-speed rail express market demand,product supply with subdivided time-limit,and transportation organization,the organizational characteristics and business process of high-speed rail express delivery under the piggybacking mode are analyzed,and the content of the transportation scheme and its influencing factors are pointed out.Furthermore,going deep into the problem,the relevant theoretical methods and solutions are expounded and defined.(2)The problem of generating optional sets of transportation schemes in bus piggyback mode is studied.A space-time network of high-speed rail express delivery including train schedule and the changes of cargo state is constructed,furthermore,the transportation scheme is abstracted as a network path problem,and a space-time path generation model is constructed.The model takes the shortest transportation time as the optimization objective,comprehensively considers the actual operation requirements such as transit times,connection time and residence time,and realizes the generation of multiple alternative paths in the form of adding constraints one by one.A numerical example is given to verify the effectiveness of the model and the practical feasibility of the generated paths.(3)The optimization problem of high-speed rail express transportation scheme considering subdivided time-limit is studied,that is,to consider the product classification and time-limit characteristics of high-speed rail express delivery on the basis of the results of(2),and select from the alternative transportation schemes set.Specifically,the timelimit of product and the posting time are brought into the attribute of cargo flow variables,the time parameters of each transportation scheme are calculated,and the optimization model of transportation scheme considering subdivided time-limit is constructed by taking the minimum transportation cost and overdue penalty cost as the objective function.In addition,a solution algorithm based on Lagrange relaxation is designed.The case network in(2)is used as an example to verify the effectiveness of the model and algorithm,and the results show the decisive influence for the delivery time-limit of goods and the posting time of consigner on the choice of transportation scheme.(4)Case study.An empirical study is carried out on the background of Beijing-TianjinHebei region.The gravity model method is used to calculate the OD volume of highspeed rail express delivery in this area,and 284 alternative trains are selected to empirically test the models and algorithms in(2)and(3).Firstly,the practical feasibility of the model and algorithm is verified through the results,and the transportation scheme and the utilization of the train capacity are further analyzed.Secondly,the adaptability of the network capacity under the continuous growth of transport volume is studied.It is found that the bottleneck section of the network may appear in 2024,and the network may reach capacity saturation in 2026.Then,the measures to improve the capacity supply are put forward.Thirdly,in view of different product structures,several experiments are conducted to analzes the change trend of punctual delivery rate and enterprise income under the adjustment of product structure,and the optimization strategy of product structure is further discussed.