Browsing by Author "Erel, Erdal"

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Citation Count: Hazır, Ö., Günalay, Y., Erel, E. (2008). Customer order scheduling problem: a comparative metaheuristics study. International Journal of Advanced Manufacturing Technology, 37(5-6), 589-598. http://dx.doi.org/10.1007/s00170-007-0998-8
Customer order scheduling problem: a comparative metaheuristics study
(Springer London Ltd, 2008) Hazır, Öncü; Günalay, Yavuz; Erel, Erdal; 56488; 3019; 1986
The customer order scheduling problem (COSP) is defined as to determine the sequence of tasks to satisfy the demand of customers who order several types of products produced on a single machine. A setup is required whenever a product type is launched. The objective of the scheduling problem is to minimize the average customer order flow time. Since the customer order scheduling problem is known to be strongly NP-hard, we solve it using four major metaheuristics and compare the performance of these heuristics, namely, simulated annealing, genetic algorithms, tabu search, and ant colony optimization. These are selected to represent various characteristics of metaheuristics: nature-inspired vs. artificially created, population-based vs. local search, etc. A set of problems is generated to compare the solution quality and computational efforts of these heuristics. Results of the experimentation show that tabu search and ant colony perform better for large problems whereas simulated annealing performs best in small-size problems. Some conclusions are also drawn on the interactions between various problem parameters and the performance of the heuristics
Citation Count: Hazır, Ö., Haouari, M., Erel, E. (2010). Discrete time/cost trade-off problem: A decomposition-based solution algorithm for the budget version. Computer & Operations Research, 37(4), 649-655. http://dx.doi.org/10.1016/j.cor.2009.06.009
Discrete time/cost trade-off problem: A decomposition-based solution algorithm for the budget version
(Pergamon-Elsevier Science, 2010) Hazır, Öncü; Haouari, Mohamed; Erel, Erdal; 56488; 1986
This paper investigates the budget variant of the discrete time/cost trade-off problem (DTCTP). This multi-mode project scheduling problem requires assigning modes to the activities of a project so that the total completion time is minimized and the budget and the precedence constraints are satisfied. This problem is often encountered in practice as timely completion of the projects without exceeding the budget is crucial. The contribution of this paper to the literatures is to describe an effective Benders Decomposition-based exact algorithm to solve the DTCTP instances of realistic sizes. Although Benders Decomposition often exhibits a very slow convergence, we have included several algorithmic features to enhance the performance of the proposed tailored approach. Computational results attest to the efficacy of the proposed algorithm, which can solve large-scale instances to optimality.
Citation Count: Hazir, Oncu; Erel, Erdal; Gunalay, Yavuz, "Robust optimization models for the discrete time/cost trade-off problem", International Journal of Production Economics, Vol.130, No.1, (2011).
Robust Optimization Models for the Discrete Time/Cost Trade-Off Problem
(Elsevier Science BV, 2011) Hazır, Öncü; Erel, Erdal; Günalay, Yavuz
Developing models and algorithms to generate robust project schedules that are less sensitive to disturbances are essential in today's highly competitive uncertain project environments. This paper addresses robust scheduling in project environments; specifically, we address the discrete time/cost trade-off problem (DTCTP). We formulate the robust DTCTP with three alternative optimization models in which interval uncertainty is assumed for the unknown cost parameters. We develop exact and heuristic algorithms to solve these robust optimization models. Furthermore, we compare the schedules that have been generated with these models on the basis of schedule robustness. (C) 2010 Elsevier B.V. All rights reserved.
Citation Count: Hazir, Oencue; Haouari, Mohamed; Erel, Erdal, "Robust scheduling and robustness measures for the discrete time/cost trade-off problem", European Journal of Operatıonal Research, Vol. 207, No. 2, pp. 633-643, (2010)
Robust Scheduling and Robustness Measures for the Discrete Time/Cost Trade-Off Problem
(Elsevier Science BV, 2010) Hazır, Öncü; Erel, Erdal; Haouari, Mohamed; 4168
Projects are often subject to various sources of uncertainties that have a negative impact on activity durations and costs. Therefore, it is crucial to develop effective approaches to generate robust project schedules that are less vulnerable to disruptions caused by uncontrollable factors. In this paper, we investigate the robust discrete time/cost trade-off problem, which is a multi-mode project scheduling problem with important practical relevance. We introduce surrogate measures that aim at providing an accurate estimate of the schedule robustness. The pertinence of each proposed measure is assessed through computational experiments. Using the insights revealed by the computational study, we propose a two-stage robust scheduling algorithm. Finally, we provide evidence that the proposed approach can be extended to solve a complex robust problem with tardiness penalties and earliness revenues. (C) 2010 Elsevier B.V. All rights reserved.