| Container drayage transportation is a main section in land transportation of containers,which can provide transportation service from terminals to consignees or from consignors to terminals.Compared with other transportation modes,shorter transportation time and higher cost are the characteristics of the drayage transportation.The time of trucks arriving at terminals influences the queuing time of trucks at terminals.Meanwhile,the travel time of trucks between two geographical positions is easily changed.A reasonable and stable truck scheduling scheme is more important.Therefore,a container drayage transportation problem considering the queuing time and the uncertain travel time is studied in this thesis.The uncertain drayage problem is solved by robust optimization methods.The main research contents are as follows:(1)A large number of domestic and international journals and conference proceedings are consulted.The related fields of the drayage problem considering the queuing time under uncertain scenarios are reviewed.First,according to whether the time windows of terminals are considered,the study of the drayage problem is divided into two categories.Then,according to the queuing process of trucks at terminals,the literatures about queuing time are summarized from three aspects as follows:the queuing process at gates with or without considering yards,the process involving trucking companies.Later,the researches about uncertain problems are classified by forms of uncertain parameters and the differences of robust optimization criteria.(2)Expected queuing time of trucks at terminals is described by a function of expected queuing time.During a planning period,trucks can convey full or empty containers.The drayage problem considering the queuing time is described by a determined-activities-on-vertex(DAOV)graph.An integer programming mathematical model is built.Based on a large number of instances that are randomly generated,the correctness and speed of solution of the model are validated.Meanwhile,compared with other methods of estimating queuing time,the validity and practical significance of the proposed method are proved.(3)The influence of the travel time on the scheduling scheme is considered.The travel time is described by scenario sets.With the DAOV graph,the robust optimization method on the basic of scenario sets is used to solve the uncertain drayage problem.A nonlinear mathematical model is built and linearized.The correctness is analyzed by experiments.Compared with the objective values of the optimal solution in each scenario,it is proved that the robustness of solution is obtained by paying a certain price.Meanwhile,the sensitivities of important parameters in the model are analyzed.It is concluded that the more conservative the solution is,the more time they will consume to complete all tasks.(4)The robust optimization method based on a relative regret value is used to solve the uncertain drayage problem.The differences between the two methods are as follows.Situations where solutions are not feasible in some scenarios are needed to handle in the robust optimization method used in(3)out of the model.However,only solutions that are feasible in each scenario are accepted in the robust method based on a relative regret value.The objective is minimizing the expected time of completing all tasks in all scenarios.A mixed integer nonlinear model is established.The correctness of the model is proved by experiments.The impact of relative regrets on the completing time is explored.Finally,the time of completing all tasks is compared under different robust optimization criteria. |
