Obtaining optimal and approximate solutions to the problem of scheduling inbound and outbound trucks in cross docking operations

Abstract: The thesis focuses on optimization of inbound and outbound truck scheduling with thegoal of minimizing total operation time of cross docking. A model of cross docking isdeveloped; two different methods are applied on the model in order to find an optimaldocking sequence for receiving and shipping trucks and their assignment to receiving andshipping docks, and product routing from receiving to shipping trucks.The two methods used were mathematical modeling and heuristic algorithm. For the firstmethod, a mixed integer programming model was developed to minimize total operationtime; AMPL modeling language is used for the mathematical modeling for small sizedproblems. For the second method, a heuristic algorithm was developed to find nearoptimal solutions fast and was used for problems of larger size. In order to examine theperformance of heuristic algorithm, small problems were solved by both mathematicalmodel and the heuristic algorithm.The results from the mathematical model and the heuristic algorithm are very close withslight differences in receiving and shipping truck docking sequence, and in productrouting between these two methods. In addition, the heuristic algorithm also calculatesnumber of products transferring from receiving trucks to the temporary storage as well asthe number of products transferring from the temporary storage to shipping truck incontrary to the mathematical model. Total number of units of products passing throughthe temporary storage calculated by heuristic algorithm is presented and it can be seenthat the heuristic algorithm transfers to the temporary storage as few products as possible.Furthermore, in cases that receiving and shipping trucks are divided into groups orclusters in the cross docking operation, heuristic algorithm can be used to calculateoptimal number of receiving and shipping docks based on preferences of total operationtime or total number of products passing through the temporary storage.Another issue which is focused on is the problem of dock door assignment. Closeshipping docks to each receiving dock are determined and the percentage of productstransferred from a receiving dock to its close shipping docks is calculated as a method tomeasure the performance of the dock assignment solution.