Simulation And Optimization Of The Core Process Of Transportation Operations In Railway Logistics Centers

The rational planning,design and operation of railway logistics centers plays an important role in improving the competitiveness of railway logistics service.Due to the long construction period and huge investment of the railway logistics centers,simulation has become an important means to effectively solve related problems of the terminal planning,design and operation organization.Transportation operations are the basis of various operations in railway logistics centers.Therefore,it is urgent and necessary to study the simulation modeling and optimization methods of the core process of transportation operations in railway logistics centers.Based on the characteristics of the transportation operation process,related methods and technologies involved in the operation simulation model of railway logistics centers have been studied by adopting the discrete system simulation method,multi-agent simulation technology,optimization theory,Petri Nets and other theoretical methods.Based on the detailed simulation of key operations,the core transportation operation simulation model of railway logistics centers is constructed,which focuses on the simulation of train operations,freight truck operations,and yard operations.Simultaneously,mathematical optimization models are introduced to optimize the simulation process.An operation simulation system of railway logistics center is developed based on the simulation model,with a view to providing effective auxiliary decision-making support tools for the planning,design and operation of China's railway logistics centers.The main contents of this dissertation include the following aspects:(1)The theory and methods of the core transportation operation simulation and optimization of railway logistics centers are studied.First,the relevant concepts of railway logistics centers and the scope of the core transportation operations are defined.Based on the theory of discrete event system simulation,the simulation emphases of core transportation operations in railway logistics center are summarized,and the key decision optimization problems considered in simulation modeling are analyzed.Then the basic content of the core transportation operation simulation and optimization is determined.Finally,the method of creating the simulation environment and the topological network of railway logistics center are proposed.On this basis,the theoretical framework for simulation modeling and optimization of core transportation operations is built.(2)The refined simulation method of gate operation considering the queuing strategies is studied.Based on analyzing the limitations of analytical model,the multiagent simulation technology is used to construct the gate operation simulation model.The simulation model takes into account the impact of random fluctuation factors on gate operation such as the arrival frequency of trucks,heterogeneity of gate service times,inspection abnormal events,and additional go-and-stop time.And the corresponding simulation module and mechanism are designed.Finally,the applicabilities of pooled and non-pooled queuing strategies are compared and analyzed based on the numerical experiment.Futhermore,a series of sensitivity analyses are performed on the factors which affects the operation of the gate operation based on the simulation model.(3)The integrated scheduling optimization of rail-mounted gantry cranes is studied.Specifically,a layered space-time network of gantry cranes and truck handling operations is constructed based on the space-time modeling approach.Then the integrated scheduling optimization model for gantry crane is constructed with the goal of minimizing the total time of handling operations.In order to overcome the complexity caused by the coupling constraints of the layered space-time network,an ADMM-based dual decomposition algorithm is designed.The original problem is decomposed into a series of space-time shortest path sub-problems through dual relaxation and linearization of the complex constraints.Finally,based on the numerical experiment,the validity of the model is verified.Furthermore,according to the comparative experiments with the RCPSP model,the advantages of the ADMM-based algorithm in terms of solution quality and efficiency are verified.The integrated scheduling optimization model provides decision-making support for the optimization of the handling operation simulation process.(4)The construction of the core transportation operation simulation model and the design of simulation system for the railway logistics centers are studied.Specifically,based on the research of refined simulation and optimization methods of key processes,a simulation logic framework based on the timed colored Petri Nets is established considering the overall process of the core transportation operations in railway logistics centers.Based on the analysis of the logical structure characteristics of various simulation events,three types of general transitions are designed.Then,the core transportation operation simulation model of railway logistics centers is constructed.Furthermore,a crane scheduling optimization method based on the rolling horizon scheme is proposed to make the optimization method effectively embedded in the simulation model.Finally,the core transportation operation simulation system of railway logistics centers is developed,and the main functions are explained.(5)A case study based on a comprehensive railway logistics center which locates in the southeast of China is analyzed.The effectiveness of the simulation model and system is verified.Moreover,several simulation tests are performed to analyze the equipment configuration and operation organization issues,and some optimization suggestions are proposed based on the simulation results,which further validates the effectiveness and practicability of this research...