Scheduling flowshops with initial availability constraint: analysis of solutions and constructive heuristics

In this paper, we address the problem of scheduling a set of jobs in a flowshop with makespan objective. In contrast to the usual assumption of machine availability presented in most research, we consider that machines may not be available at the beginning of the planning period, due to processing of previously scheduled jobs. We first formulate the problem, analyse the structure of solutions depending on a number of factors (such as machines, jobs, structure of the processing times, availability vectors, etc.), and compare it with its classical counterpart. Results indicate that the problem under consideration presents a different structure of solutions, and that it is easier than the classical permutation flowshop problem. In view of these results, we propose and test a number of fast heuristics for the problem.