Research On Model Construction And Calculation Of Urban Underground Freight Network System

With the increasingly serious situation of ground transportation and environmental pollution,the development of underground freight transportation systems to transfer cargo transportation from the ground to the underground is playing a more and more important role for alleviating the urban traffic situation and reducing environmental pollution.Underground logistics system is the method to solve the problems faced by urban development by adopting this strategy.In the process of underground logistics system planning,it is inevitable to face problems such as site selection and path optimization.If the logistics network nodes were not set up scientifically and rationally,and optimize the whole network structure,it will not only lead to excessive construction and operation costs which may reduce the decision-makers' determination to develop underground logistics systems,but also bring some problem such as the inefficiency of the system,bad orders that could not meet the freight need and so on.So,the urban underground logistics system network must be scientifically optimized.But because of the urban underground logistics system has a large scale,the number of transport and distribution nodes in the system is very large,and the complicated relationship between nodes is easy to cause the whole system changed even just one node change,it is necessary to systematically analyze all the factors that affect the underground logistics system when constructing the network layout of the underground logistics system.This thesis takes the urban underground logistics system as the research object,establishes an optimization model of the network structure of the underground logistics system based on the improved PGSA,optimizes the whole network structure,improve the operating efficiency,and provide policy makers with decision-making basis and theoretical reference.The thesis is mainly focus on the following aspects:Firstly,a general study of underground logistics systems based on improved PGSA.Based on the analysis of the overall characteristics of the underground logistics system and the effect of alleviating the problems faced by the urban development,clarify the limitations and deficiencies of the existing research methods and explain the key issues of the paper's research.Propose the method of node location,channel network design algorithm and simulation analysis of the underground logistics system,and explains the research route and technical framework of the paper.Secondly,proposes a network theoretical model of underground logistics system based on improved PGSA.Analyze the node location method in underground logistics network,acquire and filter the influencing factors that affect the cost of construction and daily operation of underground logistics systems and build vehicle distribution VRP models.Proposes the improvement measures of initial point cluster analysis,change of the search step length and introduce the algorithm termination mechanism based on the theoretical model.Analyzes the principle of the improved algorithm,and illustrate the necessity of the algorithm improvement based on the STEINLIB test database.Thirdly,An algorithm rehearsal was conducted on the theoretical model of an underground logistics system network based on the improved PGSA.Explain the basic flow of the improved PGSA optimization model,analyze every solve step in detail,design evaluation indicators,and verify the actual operation effect of the model through Flxsim simulation analysis.Finally,applying the model calculation results to the network optimization of underground logistics system in area A.By analysing the demand of region coordinates,traffic congestion index and L-OD matrix in area A,a distribution node location model was established,and then an optimization model for logistics network structure was established.The scientific and rationality of the model was verified by simulation.