Yazar "Gokcen, Hadi" seçeneğine göre listele

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    A genetic algorithm approach for optimising a closed-loop supply chain network with crisp and fuzzy objectives
    (TAYLOR & FRANCIS LTD, 2014) Demirel, Neslihan; Ozceylan, Eren; Paksoy, Turan; Gokcen, Hadi
    This paper proposes a mixed integer programming model for a closed-loop supply chain (CLSC) network with multi-periods and multi-parts under two main policies as secondary market pricing and incremental incentive policies. In the first policy, customers order and receive products from distribution centres, but at next period, they can trade among themselves with used products that are returned in a secondary market. Financial incentives are offered to the customers to influence the returns, and the correct amount of collections at different prices is determined by the second policy. In addition to the base case (crisp) formulation, a fuzzy multi-objective extension is applied to solve CLSC network problem with fuzzy objectives to represent vagueness in real-world problems. Then, developed genetic algorithm approach is applied to solve real size crisp and fuzzy CLSC problems. The effectiveness of the proposed meta-heuristic approach is investigated and illustrated by comparing its results with GAMS-CPLEX on a set of crisp/fuzzy problems with different sizes.
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    An integrated model to incorporate ergonomics and resource restrictions into assembly line balancing
    (TAYLOR & FRANCIS LTD, 2014) Kara, Yakup; Atasagun, Yakup; Gokcen, Hadi; Hezer, Seda; Demirel, Neslihan
    This study incorporates ergonomics and resource restrictions into assembly line balancing (ALB). For this purpose, an integrated model is proposed. The proposed model is essentially a cost-oriented formulation for ALB under psychological strain, physical strain, worker skills, multiple workers, equipment, working postures and illumination level restrictions. The integrated nature of the proposed model is one of its distinctive features in ALB literature. In addition, the proposed model modifies the existing restrictions by means of real-life facts and introduces two new restrictions arisen from the industry that have not been addressed in the literature. The model minimises the overall cost associated with operating costs of workforce and resources utilised under the ergonomics and resource restrictions. The model is illustrated and validated using some examples.
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    The location routing problem with arc time windows for terror regions: a mixed integer formulation
    (TAYLOR & FRANCIS LTD, 2018) Cetinkaya, Cihan; Gokcen, Hadi; Karaoglan, Ismail
    In this paper, we introduce a new variant of Location Routing Problem with the name of "Location Routing Problem with Arc Time Windows" (LRP_ATW), which emerges from the need of "safe transportation" in terror zones. In this specific problem, there are "arc time windows" on the arcs (roads) for transferring the vehicles like trucks and articulated lorries which means that these roads can be used for a specific period of time during a day. Within the scope of this paper, the problem and assumptions are described, and a Mixed Integer Programming (MIP) formulation is developed to solve the problem. Bounds are also improved using valid inequalities. The quality of the formulation is measured using the test problems in the literature. Computational results show that the proposed MIP formulation gives good quality results in a short computation time.
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    A SIMULATED ANNEALING APPROACH FOR PARALLEL ASSEMBLY LINE BALANCING PROBLEM
    (GAZI UNIV, FAC ENGINEERING ARCHITECTURE, 2009) Cercioglu, Hakan; Ozcan, Ugur; Gokcen, Hadi; Toklu, Bilal
    Production systems which has more than one assembly line is widely seen in industry. These lines produce same or similar products, and their cycle times are generally considered similar. So, Gokcen et al. (2006) suggested to combine workload of some stations on parallel consecutive lines, in a convenient way, for improving the resource utilization and the efficiency of the production system. This common balancing of more than one assembly line is named Parallel Assembly Line Balancing Problem (PALBP). The major aim of PALBP is to obtain minimum number of stations (or operators). In this paper, a simulated annealing (SA) based approach is developed for PALBP. This paper is built directly on the study of Gokcen et al. (2006). The proposed approach is illustrated with a numerical example and its performance is tested on data set taken from Gokcen et al. (2006). In the computational studies, for 95 test problems, the proposed approach found 47 proven optimal solutions and 6 solutions superior to Gokcen et al. (2006).
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    Two-stage vehicle routing problem with arc time windows: A mixed integer programming formulation and a heuristic approach
    (ELSEVIER SCIENCE BV, 2013) Cetinkaya, Cihan; Karaoglan, Ismail; Gokcen, Hadi
    In this paper, we introduce a new variant of the Vehicle Routing Problem (VRP), namely the Two-Stage Vehicle Routing Problem with Arc Time Windows (TS_VRP_ATWs) which generally emerges from both military and civilian transportation. The TS_VRP_ATW is defined as finding the vehicle routes in such a way that each arc of the routes is available only during a predefined time interval with the objective of overall cost minimization. We propose a Mixed Integer Programming (MIP) formulation and a heuristic approach based on Memetic Algorithm (MA) to solve the TS_VRP_ATW. The qualities of both solution approaches are measured by using the test problems in the literature. Experimental results show that the proposed MIP formulation provides the optimal solutions for the test problems with 25 and 50 nodes, and some test problems with 100 nodes. Results also show that the proposed MA is promising quality solutions in a short computation time. (C) 2013 Elsevier B.V. All rights reserved.