The Multi-objective Optimization Of Multi-echelon Vehicle Routing Problem In Urban Freight Distribution

With the continuous growth of urban population,the continuous change of business formats and consumption patterns,the demand for small quantity and multi-batch distribution is growing.In the background of new retail,new circulation modes such as e-commerce and chain operation are developing rapidly,which is accompanied with the increasingly prominent diversification and individualization of distribution demand.As a result,distribution enterprises and retail enterprises are intensely determined to improve the efficiency of urban distribution and reduce the distribution cost.Consumers' expectations for efficient and convenient urban distribution services are increasing.Moreover,urban residents are strongly demanding to mitigate emissions and improve the urban environment.Consequently,taking the multi-echelon vehicle routing problem of urban freight distribution as the research object,and considering the characteristics of distance,time and density in freight distribution,the two-stage multi-objective optimization models are constructed in this paper,which contain the stages of "supply area-distribution center-retail store" and "retail store-customer".According to the two models,two improved multi-objective evolutionary algorithms are designed to solve them,so that we can get the distribution schemes that are minimizing distribution cost and maximizing customer satisfaction while meeting the distribution demand,mitigating congestion and reducing emissions,thus,theoretical basis and reference is provided to decision-makers.The main contents of this paper are as follows:Firstly,the multi-echelon vehicle routing optimization theory of urban freight distribution is summarized.Explain the concept and composition of urban freight transportation from three aspects: the elements of urban freight distribution,the participants of urban freight distribution,and the optimization objectives of urban freight distribution.On the basis of analyzing the characteristics of the multi-echelon distribution network in urban freight transportation,the multi-echelon vehicle routing problem is arranged,so the research objects and scope of this paper are defined.Then,the optimization of multi-objective problems is elaborated and analyzed.Secondly,a first stage optimization model for multi-echelon vehicle routing problem in urban freight distribution is introduced.The large-scale and high-loading distribution problems of "supply area-distribution center-retail store" stage in urban freight distribution are described and analyzed.In addition,some model hypotheses are proposed in line with the distribution characteristics of multi-supply warehouses,heterogeneous vehicles(different types of vehicles),multi-commodity and multi-objective,and then a multi-objective optimization model with minimum costs,least distribution vehicles and minimum carbon emissions as objective functions is constructed.An improved multi-objective evolutionary algorithm is designed correspondingly to solve the model,and the effectiveness of the model and algorithm are verified by numerical experiments.Thirdly,a second stage optimization model for multi-echelon vehicle routing problem in urban freight distribution is introduced.The multi-batch distribution problem of "retail store-customer" stage at the end segment of urban freight distribution is described and analyzed.In addition,some model hypotheses are proposed in line with the distribution characteristics of multi-distribution centers,time windows,open-type and multi-objective,and then a multi-objective optimization model with minimum costs,maximum customer satisfaction and minimum carbon emissions as objective functions is constructed.Similarly,another improved multi-objective evolutionary algorithm is designed correspondingly to solve the model,and the effectiveness of the model and algorithm are verified by numerical experiments.Aiming at the multi-echelon vehicle routing problem of urban freight distribution,the two-stage multi-objective optimization models are established in this paper,and the multi-objective evolutionary algorithms are improved to solve the models.In terms of theoretical application,this research will enrich the multi-objective optimization method about urban freight distribution network.When it comes to industry development,the research is conducive to promote the distribution industry to convert from pursuing only economic benefits to a balanced development of economic,environmental protection and resource conservation.Therefore,urban space resource will be used efficiently to realize the effect of mitigating congestion and reducing emission.