Research On Joint Optimization Of Repositioning And Inventory Control Of Empty Containers In Port Group

Port integration has become the main development mode for coastal ports in China at present and in the future.Ports are transitioning from fierce competition and disorderly production to cooperative win-win and intensive development.Regional port integration is driving the continuous optimization of port service levels in China,and the comprehensive strength and competitiveness of ports are increasing rapidly.Due to the existence of the public hinterlands of the port groups,in addition to transporting empty and heavy containers by sea,each port within the port group also transports empty and heavy containers between the public hinterland container terminals within its coverage area,forming a sea-land empty container repositioning network within the regional port group.Due to the high cost of empty container management and the dual nature of containers as carriers and transporting goods,shipping companies often reduce container usage costs through repositioning.The problem of empty container inventory caused by repositioning also requires corresponding inventory control strategies for management.Therefore,in this context,this thesis proposes the joint optimization problem of empty container repositioning and inventory control in regional port groups,with the aim of reducing the total cost of empty container management for shipping companies.The specific research content is as follows:(1)A joint optimization model of empty container repositioning and storage in the hinterland of a regional port group under the sea-land collaborative mode was constructed for the sea-land empty container repositioning network.Under the premise of serving multiple ports with a single inland station,i.e.,"single station to multiple ports",this thesis optimizes the empty container repositioning plan between public hinterlands and ports,as well as between ports.And take the Liaoning coastal port group-Northeast hinterland as the object,this thesis solves the model.Sensitivity analysis was conducted on the selection of terminal service mode,unit rental cost,repositioning cost,empty container demand,and public hinterland quantity.The results showed that changes in empty container demand,including five public hinterland cities such as Shenyang and Harbin,as well as changes in public hinterland service mode and quantity,had the greatest impact on the total cost and empty container repositioning plan of shipping companies in Dalian Port,Yingkou Port,and Dandong Port.The supply of empty containers in the public hinterland can reduce the total cost of shipping companies by 33.01%,which proves that empty containers in the public hinterland are an important source of meeting the empty container demand of shipping companies.The coordinated repositioning of empty containers between sea and land within the port group is an effective way to control the total cost of shipping companies.(2)A joint optimization model for empty container repositioning and storage under quantitative inventory control strategy was constructed to address the dynamic characteristics of empty container repositioning problems.The algorithm combining Markov decision process with dynamic programming is used to dynamically optimize the empty container inventory threshold interval(D,U)of each port in the port group under the inventory control strategy.Based on this,the empty container repositioning,leasing and storage schemes between the public hinterlands of the port group and each port are optimized.Through empirical analysis,the joint optimization model under inventory control strategy can save shipping companies a total cost of 15.22%.Sensitivity analysis was conducted by selecting the number of public hinterland areas,the demand for empty containers in public hinterland areas and ports,unit rental cost,and unit inventory cost,thereby verifying that inventory control strategies can weaken the impact on shipping companies when the external environment changes.(3)A joint optimization model for empty container repositioning and storage in regional port groups was constructed based on the periodic inventory control strategy in response to the cyclical characteristics of container transportation.Dynamically and heuristic determined the maximum inventory level S under the periodic inventory control strategy.On this basis,the heuristic rules in the combination algorithm of dynamic programming and Markov decision process are updated to optimize the total cost of empty container management between the public hinterlands and the ports.And through sensitivity analysis,the various costs under the periodic inventory control strategy were compared with the quantitative inventory control strategy.The results showed that when factors such as the number of public hinterland terminals and unit inventory cost changed,the quantitative inventory control strategy was more advantageous in controlling the total cost.When the shipping market is in the off-season,periodic inventory control strategies are more suitable for shipping companies to reduce the total cost of empty container management.(4)A joint optimization model for port group empty container repositioning and storage based on distributed robust optimization was established to address the non stationary demand of empty containers.Taking into account the multi-directional empty container repositioning between various ports within the port group,between ports and hinterland terminals,as well as between hinterland terminals,and combining periodic and quantitative inventory control strategies,the various costs under non stationary demand and stationary demandconditions are compared.By deducing the deterministic transformation of the stochastic optimization model,a dynamic programming combing with simulated annealing algorithm is used to solve the model.The results indicate that non stationary demand requires shipping companies to pay higher empty container management costs compared to deterministic demand.Periodic inventory control strategies are more suitable for reducing the total cost of empty container management for shipping companies under uncertain empty container demand conditions.We selected parameters related to non stationary demand for sensitivity analysis,and the total cost in different scenarios will increase with the increase of uncertain parameters.Through the sensitivity analysis of reachability parameters between inland terminals,it is further proved that the empty container repositioning under the coordination of land and sea is superior.The research results of the thesis can promote shipping companies to explore new ways to reduce empty container management costs under the development model of port groups,and provide decision-making support for corresponding management personnel in operation scheduling.