Browsing by Author "Ozturk, Cemalettin"

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A Multi-objective Approach to Flight Scheduling and Fleet Assignment in Hub Network
(Springer, 2025) Melis Tan Tacoglu; Mustafa Arslan Ornek; Cemalettin Öztürk; Ornek, Mustafa Arslan; Ozturk, Cemalettin; Tacoglu, Melis Tan
The hub-and-spoke (HS) network is a widely used business strategy by airlines to optimize their operations and increase their reach by connecting multiple destinations through a central hub and the majority of the passengers are transit passengers. The airline schedule planning process starts with the flight scheduling problem (FSP) to generate a timetable in advance of six months. Then the fleet assignment problem (FAP) is examined to determine aircraft types. This sequential solution approach causes suboptimal solutions and the schedule must be adjusted to increased demand. Due to the complexity of this problem this study focuses specifically on incremental schedule design with one hub two-flight leg network. This study presents a Multi-Objective Mixed Integer Programming Model for integrated FSP and FAP to adjust the generated timetable with launching new flights. Two solution approaches are proposed to decide the new proposed flight’s time aircraft type and passenger assignment: the Weighted Goal Programming Model (WGPM) and the Lexicographic Goal Programming Model (LGPM). This study shows that there is a conflicting relationship between cost and C02 emissions in the flight scheduling process. If carbon dioxide emissions are prioritized airlines need to schedule more flights with small-capacity aircraft. © 2025 Elsevier B.V. All rights reserved.
Citation - WoS: 2
Citation - Scopus: 4
Combinatorial optimization methods for yarn dyeing planning
(Springer, 2025) Ege Duran; Cemalettin Öztürk; Mustafa Arslan Ornek; Duran, Ege; Ozturk, Cemalettin; Ornek, M. Arslan
Managing yarn dyeing processes is one of the most challenging problems in the textile industry due to its computational complexity. This process combines characteristics of multidimensional knapsack bin packing and unrelated parallel machine scheduling problems. Multiple customer orders need to be combined as batches and assigned to different shifts of a limited number of machines. However several practical factors such as physical attributes of customer orders dyeing machine eligibility conditions like flotte color type chemical recipe and volume capacity of dye make this problem significantly unique. Furthermore alongside its economic aspects minimizing the waste of natural resources during the machine changeover and energy are sustainability concerns of the problem. The contradictory nature of these two makes the planning problem multi-objective which adds another complexity for planners. Hence in this paper we first propose a novel mathematical model for this scientifically highly challenging yet very practical problem from the textile industry. Then we propose Adaptive Large Neighbourhood Search (ALNS) algorithms to solve industrial-size instances of the problem. Our computational results show that the proposed algorithm provides near-optimal solutions in very short computational times. This paper provides significant contributions to flexible manufacturing research including a mixed-integer programming model for a novel industrial problem providing an effective and efficient adaptive large neighborhood search algorithm for delivering high-quality solutions quickly and addressing the inefficiencies of manual scheduling in textile companies, reducing a time-consuming planning task from hours to minutes. © 2025 Elsevier B.V. All rights reserved.
Citation - WoS: 14
Citation - Scopus: 15
Integer and constraint programming model formulations for flight-gate assignment problem
(SPRINGER HEIDELBERG, 2022) M. Arslan Ornek; Cemalettin Ozturk; Ipek Sugut; Sugut, Ipek; Ornek, M. Arslan; Ozturk, Cemalettin
Flight-gate assignment problems are complex real world problems involving different constraints. Some of these constraints include plane-gate eligibility assigning planes of the same airline and planes getting service from the same ground handling companies to adjacent gates buffers for changes in flight schedules night stand flights priority of some gates over others and so on. In literature there are numerous models to solve this highly complicated problem and tackle its complexity. In this study first we propose two different integer programming models namely timetabling and assignment based models and then a scheduling based constraint programming model to solve the problem to optimality. These models prove to be highly efficient in that the computational times are quite short. We also present the results for one day operation of an airport using real data. Finally we present our conclusions based on our study along with the possible further research.
Citation - WoS: 5
Citation - Scopus: 7
Model-based heuristic for counter assignment problem with operational constrains: A case study
(ELSEVIER SCI LTD, 2019) M. Arslan Ornek; Cemalettin Ozturk; Ipek Sugut; Sugut, Ipek; Ornek, M. Arslan; Ozturk, Cemalettin
Check-in counters have a great impact on the quality of service for airports. It is airport management's responsibility to provide check-in counters to airlines. Each check-in group (i.e. flights sharing the same resources) has a counter demand and this gives rise to a counter assignment problem. This is due to a number of objectives and constraints under which check-in groups are allocated to check-in counters. In this paper we develop an Integer Programming model to optimally assign incoming flights to check-in counters and propose a decomposition algorithm to solve the allocation problem in a reasonable time. Computational results from a medium sized airport indicate a better utilisation of check-in counters enabling airport management to reduce/postpone investment in additional check-in counters.
Citation - WoS: 3
Citation - Scopus: 4
Optimisation and heuristic approaches for assigning inbound containers to outbound carriers
(Routledge info@tandf.co.uk, 2017) Cemalettin Öztürk; F. Zeynep Sargut; Mustafa Arslan Ornek; D. T. Eliiyi; Ozturk, Cemalettin; Sargut, F. Zeynep; Ornek, M. Arslan; Türsel Eliiyi, Deniz; Eliiyi, Deniz Tursel
Due to economical and/or geographical constraints most of the time overseas containers cannot be directly shipped to their destinations. These containers visit transhipment ports where they are first unloaded and temporarily stored and then loaded onto smaller vessels (feeders) to be transported to their final destinations. The assignment of these containers to outbound vessels necessitates several factors to be taken into account simultaneously. In this paper we develop a mathematical model to reflect multiple objectives with priorities and to assign these containers to different vessels at the transit container port terminal. Although we solve a single-objective (with the weighted sum of objectives) mathematical model to optimality we also propose two heuristic approaches to solve this complex problem for a transit agency. The first heuristic is shipment based and has four variants differing in how the opportunity costs of the assignments are calculated. The second greedy heuristic is trip based where the goal is to maximise the capacity utilisation of the vessels. The heuristics return very promising solutions in ignorable computational times. We also provide real-life cases and present our conclusions. © 2017 Elsevier B.V. All rights reserved.