5. Simulation Analysis
As discussed in Section4, the proposed model is a multiobjective integer linear programming model. In the following analysis, Xpress-IVE module [37] is employed as the mixed integer linear programming (MILP) solver, which is installed in a PC with Pentium 2.4 GHz processor and 2 GRAM.
The analysis is conducted in two steps. First, a case is demonstrated. Second, the model is solved with different parameter settings. Because the model is multiobjective, it will be transferred into a single objective model by adjusting the other objectives to be constraints. With the five objectives, the minimization of used trucks can be restricted by constraints conveniently. First, the numbers of used trucks for inbound or outbound will not be large. Second, the numbers can be adjusted by setting the upper bounds. Therefore, in the following, these two objectives are taken as constraints by adjusting IVN and OVN. Another two objectives are to minimize the costs of inbound and outbound VRP routes. The fifth objective is to minimize the waiting time