Minimizing the makespan for the flow shop scheduling problem with availability constraints

This paper deals with the scheduling of a flow shop with availability constraints (FSPAC). In such a problem, machines are not continuously available for processing jobs due to a preventive maintenance activity. A small number of solution methods exists in the literature for solving problems with at most two machines and to the author's knowledge only a few of them make use of the non-preemptive constraint. In this paper, two variants of the non-preemptive FSPAC with an arbitrary number of machines and an arbitrary number of unavailability periods on each of them are considered. In the first variant, starting times of maintenance tasks are fixed while in the second one the maintenance tasks must be performed on given time windows. Since the FSPAC is NP-hard in the strong sense, a heuristic approach based on a genetic algorithm and a tabu search is proposed to approximately solve the makespan minimization problem. Computational experiments are performed on randomly generated instances to show the efficiency of the proposed approaches.