| With the development of the sharing economy in the express industry,the rapid development of the express industry under the joint distribution,the traffic jam in Chinese cities is becoming more and more serious.The challenge facing urban express is how to improve transportation efficiency,reduce labor intensity and carbon emissions of delivery vehicles while ensuring its own interests.The most critical point is to improve customer satisfaction.In this paper,we will study how to select the appropriate vehicle combination to systematically plan the distribution route under the circumstances of definite and uncertain road travel time under joint distribution.In order to quickly respond to the dynamic changes of customer demand,we will timely adjust the vehicle route and reasonably arrange the distribution vehicles to deliver and collect goods at customer points,which will provide practical and theoretical significance for the distribution of express enterprises.Firstly,this paper expounds the research background and significance,summarizes the existing problems in domestic and foreign research,and arranges chapters for the full text.Secondly,research is carried out on the optimization of the route of urban express delivery vehicles under joint distribution,which is mainly divided into two situations: the determination of the travel time of the road section and the uncertainty,and in each case,it is divided into not considering and considering the time-varying needs of customers.Then four sub-problems are derived: route optimization of delivery vehicles without considering the time-varying needs of customers under the determination of road section traffic time,route optimization of delivery vehicles with considering the time-varying needs of customers under the determination of road section traffic time,robust optimization of delivery vehicle routes without considering customer time-varying needs under uncertain road section travel time,and robust optimization of delivery vehicle routes with considering customer time-varying needs under uncertain road section travel time.The specific problem characteristics and actual situation are analyzed for each problem,and the mathematical model was established with the minimum total cost and maximum average customer satisfaction as the objective function,and the constraints of service times and vehicle loading of each customer point were taken as constraints.In the case of uncertain travel time of the road section,the model contains uncertain parameters,so the robust discrete optimization theory is used for the equivalent transformation of the model.Considering the time-varying needs of customers,a two-stage multi-objective multi-vehicle model is established.The first stage model is based on static initial optimization,and the second stage model is based on dynamic customer optimization.According to the constructed mathematical model,the NSGA-Ⅱ algorithm is designed,the bidirectional quantity mapping real number coding is adopted,and the binary tournament method is adopted when selecting individual operations,and the crossover and mutation operations are designed for the characteristics of chromosomes.Finally,the thesis summarizes the work and puts forward the future research direction.In this paper,an example is designed for each subproblem to verify the accuracy of the model and algorithm.Combined with the actual road network,the parameters of vehicles and customer points are input,and the results are obtained by running MATLABR2017 a software.The results show that two or more Pareto solutions can be obtained for each subproblem.It shows that the NSGA-Ⅱ algorithm designed in this paper can effectively solve the routing optimization model of multi-objective and multi-vehicle pickup and delivery vehicles with certain road section travel time and the routing robust optimization model of multi-objective and multi-vehicle pickup and delivery vehicles with uncertain road section travel time.The results of this study can help express delivery enterprises to arrange the two-way transportation needs of urban express delivery and realize reasonable and efficient operation.The environment and conditions considered by each sub-problem are different,so decision-makers can choose different schemes according to different circumstances.In this way,the reasonable arrangement of vehicle route,take and send the goods for efficient processing,improve customer satisfaction,so that the distribution of vehicles to complete the transportation task safely and economically. |
