Algorithms for scheduling problems in flowshops subject to time constraints

Abstract

This dissertation focuses on scheduling problems in two-stage flowshops with a limited waiting time constraint and sequence-dependent setup times with objective of minimizing makespan, i.e., the maximum completion time of a given set of jobs. In these problems, the second operation of each job should be started within a certain period of time after the first operation of the job is completed, and the sequence-dependent setup times are incurred between jobs on the second stage. In this dissertation, we consider two different problems for flowshop scheduling, and develop algorithms for the problems. First, we consider a two-machine flowshop scheduling problem with limited waiting times and sequence-dependent setup times. In the two-machine flowshop, all jobs must be processed first on machine 1 and then machine 2. We develop dominance properties, lower bounds and upper bounds on the makespan for the problem, and suggest a branch and bound algorithm that is developed using these properties and bounds. Secondly, we consider a two-stage flowshop scheduling problem with limited waiting times and sequence-dependent setup times. In the two-stage flowshop, each stage consists of multiple identical parallel machines that can process the same set of jobs independently, and all jobs must be processed first on one of machines in stage 1 and then one of machines in stage 2. We develop heuristic algorithms, which are modified from well-known existing algorithms for other flowshop problems or newly developed. Performance of the suggested algorithms are evaluated through series of computational tests on test problems which are obtained from real data or generated in such a way that resulting problems reflect the real situations relatively well. Results of the computational tests show that the algorithms suggest in this dissertation give very good solutions in a reasonable amount of computational time. Also, the algorithms suggested in this dissertation can be used for operatio...