Scopus İndeksli Yayınlar Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8651

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Now showing 1 - 10 of 166
  • Article
    Citation - WoS: 3
    Citation - Scopus: 3
    Ant Colony Optimization for Solving Large-Scale Bi-Level Network Design Problems
    (Pergamon-elsevier Science Ltd, 2025) Yakici, Ertan; Karatas, Mumtaz
    In this study, we consider a bi-level hierarchical network design problem that encompasses both gradual and cooperative coverage. The lower-level facility serves as the primary point of contact for customers, while the upper-level facility acts as a supplier for the lower-level facilities. We first present a mathematical formulation of the problem, followed by an Ant Colony Optimization (ACO) approach to solve it. We then compare the performance of our method with commercial exact solvers. Our experiments, conducted on instances of various sizes, show that while exact methods may succeed in the long run, our heuristic provides a fast and reliable option for operational decisions that need to be made in a short period of time. In nine out of twelve instances, the exact solver failed to find a feasible solution within three hours for the high-budget case and two hours for the low-budget case. In contrast, our heuristic had run times between 0.1 and 0.4 h for 50 iterations. We also compare the performance of ACO with that of a Genetic Algorithm (GA) to evaluate its effectiveness among heuristics. Our numerical results demonstrate that ACO outperforms GA. This study contributes to the literature by offering a solid theoretical framework for the problem and implementing ACO to solve a bi-level facility location problem. Our results demonstrate that ACO can deliver good solutions in a reasonable time and serves as a promising alternative.
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  • Article
    Citation - WoS: 5
    Citation - Scopus: 5
    Location and Routing of Armed Unmanned Aerial Vehicles and Carrier Platforms Against Mobile Targets
    (Pergamon-elsevier Science Ltd, 2024) Yakici, Ertan; Karatas, Mumtaz; Eriskin, Levent; Cicek, Engin
    In this study, we consider a real-life combinatorial optimization problem related to deploying and routing Unmanned Aerial Vehicles (UAVs) and naval carrier platforms. In particular, we seek to determine the initial locations for carrier platforms and the optimal type and number of UAVs to be stationed on each carrier platform as well as their spatial/temporal routes for engaging hostile surface targets in the region. Our modeling framework incorporates a number of realistic but challenging ingredients and assumptions such as the mobility of surface targets and carrier platforms during the mission, capacitated multiple platforms and UAVs, UAV-carrier platform compatibility, and allowance for different takeoff/land on platforms for UAVs. In the effort to represent the problem mathematically, we first formulated an Integer Linear Program (ILP) model which seeks to maximize the total time-dependent weights of the targets engaged. Next, we proposed a heuristic solution algorithm based on the ant colony optimization framework. Our computational experiments performed on instances with different sizes showed that the heuristic approach achieves high-quality solutions even for large-size problem instances in short CPU times.
  • Article
    Citation - WoS: 6
    Citation - Scopus: 6
    Mitigating Cavitation Effects on Francis Turbine Performance: a Two-Phase Flow Analysis
    (Pergamon-elsevier Science Ltd, 2025) Altintas, Burak; Ayli, Ece; Celebioglu, Kutay; Aradag, Selin; Tascioglu, Yigit
    Due to their ability to operate over a wide range of flow rates and generate high power, Francis turbines are the most widely used of hydroturbine type. Hydraulic turbines, are designed for specific flow and head conditions tailored to site conditions. However, Francis turbines can also be operated outside of design conditions due to varying flow and head values. Operation outside of design conditions can lead to cavitation. In this study, singlephase steady-state an alyses were conducted initially to examine cavitation in detail, followed by two-phase transient analyses. The results obtained from these analyses were compared to determine the cavitation characteristics of the designed turbine. The steady-state simulation results indicate the occurrence of cavitation, including traveling bubble and draft tube cavitation, under overload operating conditions. However, these cavitation characteristics are not observed in the two-phase transient simulation results under the same operating conditions. Additionally, the turbine efficiency is predicted to be higher in the transient simulation results. This is attributed to the frozen rotor interface used in the steady-state simulations, which over predicts flow irregularities. The reduced flow irregularities in the transient results have resulted in lower cavitation and losses, leading to higher predicted turbine efficiency.
  • Article
    Citation - WoS: 4
    Citation - Scopus: 4
    Transmittance of Gaussian Beams in Biological Tissues
    (Pergamon-elsevier Science Ltd, 2025) Ozcan, Murat Kaan; Gokce, Muhsin Caner; Baykal, Yahya
    The study examines the average transmittance of Gaussian beams passing through various biological tissues, taking into account the impact of turbulence, absorption, and scattering. The extended Huygens-Fresnel technique, which utilizes the power spectrum of turbulent biological tissues, is applied to determine the optical intensity at the observation point. Additionally, there are tabulated absorption and scattering coefficients available for the application of the Beer-Lambert law, facilitating the calculation of optical light attenuation in biological tissues. Examining the impact of turbulence, as well as absorption and scattering-induced attenuation on the Gaussian beam's propagation, the changes in transmittance are documented across different tissue parameters.
  • Article
    Citation - WoS: 2
    Citation - Scopus: 2
    Fractional Hamiltonian Systems: Nested Ellipsoids
    (Pergamon-elsevier Science Ltd, 2025) Ugurlu, Ekin
    In this paper, we introduce a singular fractional-order Hamiltonian system with several spectral parameters. Using the inertia indices of the corresponding Hermitian forms we provide a lower bound for the number of linearly independent integrable-square solutions. Moreover, we introduce the Titchmarsh-Weyl function together with an intermediate theorem on the number of the integrable-square solutions. At the end of the paper, we show that 2-sequential and 4-sequential scalar fractional-order differential equations can be embedded into such Hamiltonian systems.
  • Article
    Citation - WoS: 6
    Citation - Scopus: 5
    Understanding Location Choice of Syrian Refugees From Country To Neighbourhood Level: Opportunities, Restrictions and Expectations
    (Pergamon-elsevier Science Ltd, 2022) Kahraman, Z. Ezgi Haliloglu
    This study aimed to delve into distinct strands of the location choice (LC) of Syrian refugees by uncovering its determinants at country, city and neighbourhood levels from the narratives, along with the help of content analysis. Findings providing an aggregate explanation of the Syrian emplacement process revealed that Syrian refugees in Turkey, as active agents in the process, make their destination choices within opportunities and restrictions of different scales through the contribution of other agents, places and processes. Findings emphasizing time-and context-specific features -the transitivity, interrelatedness and multi-dimensionality (legal, economic, socio-cultural and spatial) of determinants of LC -showed that the opportunities and restrictions of LC influence Syrians' future expectations.
  • Article
    Citation - WoS: 99
    Citation - Scopus: 113
    Recent Developments of Energy Management Strategies in Microgrids: an Updated and Comprehensive Review and Classification
    (Pergamon-elsevier Science Ltd, 2023) Baleanu, Dumitru; Abbasi, Ali Reza
    Energy is one of the essential foundations for the sustainable development of human society, so its management is necessary. Energy management system (EMS) can be explained as the procedure of optimizing, planning, controlling, monitoring, and saving energy to maximize operations and efficiency and minimize consumption. Microgrid (MG) requires EMS as an efficient and optimal tool owing to the stochastic nature of electrical loads and renewable sources. Moreover, energy management system is responsible for operation of a MG in reliable, secure and economical manner in either states of grid-connected or disconnected. Many literatures have recently focused on the expansion of advanced strategies of the MG energy management for establishing a self-sustained MG in both industrial and academic research. Thus, a comparative research is needed for having a 360 degrees viewpoint of the energy management domain in MGs. In this regard, this research investigates a comparative and critical analysis of the developed strategies of the energy management for the MGs from different views and aspects from 2009 to 2022. The review strategy systematically adopted by the author includes: (i) Extracting research papers relevant to energy management in MGs; (ii) Filtering the significant papers to prepare a database of related research papers (iii) Classifying the used methods for EMS based on the technique, control strategies, and structure; (iv) Discussing potential directions for future studies. In a wider outlook, this research provides a systematic and updated review of energy management strategies for MGs developed by different researchers. The author hopes that academicians and practitioners can use the suggested framework as well as the offers presented for further studies on this significant yet sophisticated issue.
  • Article
    Citation - WoS: 11
    Citation - Scopus: 9
    Multimode Beam Propagation Through Atmospheric Turbulence
    (Pergamon-elsevier Science Ltd, 2024) Baykal, Yahya; Ata, Yalcin; Gercekcioglu, Hamza; Gokce, Muhsin Caner
    The investigation focuses on studying the propagation characteristics of multimode lasers in the turbulent amosphere. By employing the Huygens-Fresnel integral, we develop analytical formulations for various propagation parameters. These include the average intensity distribution, kurtosis parameter, beam spread, and the average transmittance of multimode beams in turbulent atmosphere. Our findings reveal that as the propagation distance or the structure constant of the atmosphere increases, i.e., turbulence becomes stronger, the kurtosis parameter and the beam spread increase. The multimode beam exhibits a Gaussian like intensity profile when the propagation distance is significantly increased or when the structure constant becomes sufficiently large. For the case of the Gaussian beam, the kurtosis parameter is found to be 3. The multimode beam's kurtosis parameter rises as the turbulence becomes stronger and eventually approaches 3. Raising the mode content leads to a rise in the average transmittance; however, it leads to a decline in the Kurtosis parameter and the beam spread.
  • Article
    Citation - WoS: 10
    Citation - Scopus: 11
    Is There Convergence in Renewable Energy Deployment? Evidence From a New Panel Unit Root Test With Smooth and Sharp Structural Breaks
    (Pergamon-elsevier Science Ltd, 2023) Omay, Tolga; Corakci, Aysegul
    This study examines whether the contribution of renewable energy to the total primary energy supply converges in a panel of 24 OECD countries over the period 1960-2020. To this end, a new panel unit root test that allows for both sharp and smooth breaks is proposed to test for the stochastic convergence hypothesis. Although renewable energy convergence is not rejected when the newly proposed test is applied to the full panel of OECD countries, it found only moderate support within the members of the panel using a sequential panel selection methodology. In fact, in two high-income OECD countries, the contribution of renewable energy to the primary energy supply shows no sign of convergence: Poland and Iceland. Therefore, the renewable energy shares seem to be converging to a common steady state in only a group of OECD countries over the long run. This uneven pattern of convergence, in turn, suggests that the OECD countries are still far away from developing a common sustainable renewable energy target, calling for urgent international policy cooperation to encourage the divergent econo-mies to seek out the menu of policies that ensure the worldwide success of renewable energy transformation.