Modeling and scheduling a case of flexible flowshops: Total weighted tardiness minimization

Two of the most realistic assumptions in the field of scheduling are the consideration of setup and transportation times. In this paper, we study the flexible flowshop scheduling where setup times are anticipatory sequence-dependent and transportation times are job-independent. We also assume that there are several transporters to carry jobs. The objective is to minimize total weighted tardiness. We first formulate the problem as a mixed integer linear programming (MILP) model. With this, we solve small-sized instances to optimality. Since this problem is known to be NP-hard, we then propose an effective metaheuristic to tackle large-sized instances. This metaheuristic, called electromagnetism algorithm (EMA), originates from the attraction–repulsion mechanism of the electromagnetism theory. We conduct a series of experiments and complete statistical analyses to evaluate the performance of the proposed MILP model and EMA. On a set of instances, we first tune the parameters of EMA. Then, the efficiency of the model and general performance of the proposed EMA are assessed over a set of small-sized instances. To further evaluate EMA, we compare it against two high performing metaheuristics existing in the literature over a set of large-sized instances. The results demonstrate that the proposed MILP model and EMA are effective for this problem.