Browsing by Author "Guden, Huseyin"

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    Decomposition Based Extended Project Scheduling for Make-To-Order Productiona
    (2021) Turkgenci, Arda; Guden, Huseyin; Gulsen, Mehmet
    Project scheduling has a critical function for many companies. Although there is a vast literature dedicated to the development of solution methodologies, the real-life applications of those techniques are few and often require over-simplification of the real-life problem. This study deals with the implementation of a project scheduling routine for a "make-to-order" machinery manufacturer. Although the problem is very similar to a resource-constrained project scheduling problem (RCPSP), which is a well-known and well-studied problem in the literature, it has multi-project and multi-mode components which make the project planning more challenging. Because of the multi-dimensional complexity of the problem, it is called a "Rich Project Scheduling Problem". Our approach employs two techniques to deal with the issue of complexity. The first one is regarding calculation of the latest start time for each activity in the project. The second one is the decomposition method that includes breaking down the big problem into small manageable pieces. The approach was tested on real-life problems of a machine-building company. We also built more complex test cases from the real projects for testing purposes. Our approach produced high-quality solutions to the complex project scheduling problems within reasonable time limits. This work contributes to current research in several ways. An extension to the RCPSP formulation to include multi-project and multi-mode problems is introduced and successfully used for solving real-life problems. Additionally, activities of an RCPSP can be split into multiple sub-activities. Doing so is called preemption. The proposed formulation permits mode-switching during the execution of an activity, and it uses an alternative methodology to calculate latest activity start times.
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    Inter City Bus Scheduling with Central City Location and Trip Selection
    (2020) Guden, Huseyin; Kececi, Baris; Karatas, Mumtaz; Yakici, Ertan; 0000-0002-6287-3216; E-4168-2018
    This study considers a real-life inter-city bus scheduling problem that incorporates central city locations and trip selection sub-problems. We seek to determine the size of the bus fleet, the cities to be served, the central cities, and the routes and schedules of buses in the fleet. For this purpose, we developed a number of investment scenarios, and for each scenario, we determined possible trip alternatives between cities and resulting expected profits. We then developed an integer linear programming model and a decomposition-based heuristic, which attempt to solve the problem with the objective of profit maximization Finally, we compare the performance of both solution approaches in terms of the solution quality and computation time for each of the scenarios. The results show that both methods are capable of achieving satisfactory performance for small and medium-size instances, whereas the heuristic outperforms the exact method significantly on large instances.