Network Layout Optimization for Urban Underground Logistics System
With the rapid development of the e-commerce environment,the timeliness and high fre-quency of urban logistics distribution have been caught in a paradoxical relationship with urban traffic conges-tion,environmental pollution,and availability of urban land resources.Seeing that traditional ground transpor-tation is difficult to fundamentally solve these problems and according to the idea of three-dimensional urban transportation planning,it is of great practical significance to divert some(or even all)urban cargo transporta-tion underground and build the underground logistics system.Compared with the existing urban logistics system,the urban underground logistics system is isolated from the ground environment and uses various automated equipment for logistics and transportation opera-tions,saving land resources while achieving high efficiency.On the other hand,since it is built underground of a city,it requires very high tunnel excavation technology and transportation equipment and is very expensive to build.Therefore,conventional ground logistics system operations planning method does not apply for its planning.Instead,it is necessary to comprehensively consider the construction of complex underground struc-tures,the design of underground logistics systems,and the positioning of the underground logistics system in the city.According to the characteristics of the urban underground logistics system,an underground logistics sys-tem composed of three-level nodes is designed.Among them,the primary node is a hub for the management and control of the urban underground logistics system,which is located on the ground and is mainly responsi-ble for transferring goods from the ground level to a second-level node.After receiving the goods,the second-level node will transfer the goods to the adjacent third-level node.The locations of the primary and second-level nodes determine the service objects and service coverage of the urban underground logistics system.The third-level nodes are directly set up in residential areas,shopping malls,central business districts and other gath-ering areas.After the goods arrive at the third-level nodes,the received goods will be distributed to customers on a building basis to complete the"last mile"delivery.The primary nodes on the ground are connected to each other through the road network,allowing cross-regional cargo transfer.Nodes at different levels are con-nected via pipeline structures.The pipeline structures of the primary nodes and the second-level nodes belong to the first-level pipelines.The second-level nodes can be connected by the first-level pipelines to form a net-work structure.The second-level nodes directly serve the adjacent third-level nodes.The third-level nodes are not connected to each other.If goods are to be transferred between two third-level nodes,it must be done through one or more second-level nodes.In order to fully consider the planning and layout of the logistics system and the spatial planning of the ur-ban underground logistics system,and avoid problems such as excessive subsequent operating costs and insuffi-cient distribution capacity caused by unreasonable network layout,while considering the construction cost of the underground logistics system and the utilization rate after its completion,a cost and utility rate based multi-objective and multi-constraint location-allocation model is established and then solved with the genetic algo-rithm to obtain the network layout plan and allocation decision,which is demonstrated to have solved the loca-tion-allocation problem of the second-level nodes,so is of certain referential value in the solution of the loca-tion-allocation problem of underground logistics nodes.
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