Endüstri Mühendisliği Bölümü Koleksiyonu

Permanent URI for this collectionhttps://gcris.khas.edu.tr/handle/20.500.12469/48

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Citation Count: 5
(3+3+2) warped-like product manifolds with Spin(7) holonomy
(Elsevier Science Bv, 2011) Bilge, Ayşe Hümeyra; Bilge, Ayşe Hümeyra
We consider a generalization of eight-dimensional multiply warped product manifolds as a special warped product by allowing the fiber metric to be non-block diagonal. We define this special warped product as a (3 + 3 + 2) warped-like manifold of the form M = F x B. where the base B is a two-dimensional Riemannian manifold and the fibre F is of the form F = F-1 x F-2 where the F-i(i = 1 2) are Riemannian 3-manifolds. We prove that the connection on M is completely determined by the requirement that the Bonan 4-form given in the work of Yasui and Ootsuka [Y. Yasui and T. Ootsuka Spin(7) holonomy manifold and superconnection Class. Quantum Gravity 18(2001)807-816] be closed. Assuming that the F-i are complete connected and simply connected it follows that they are isometric to S-3 with constant curvature k > 0 and the Yasui-Ootsuka solution is unique in the class of (3 + 3 + 2) warped-like product metrics admitting a specific Spin(7) structure. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.
Citation Count: 0
Chelate extraction of transition metal ions by ethylene diamine diacetic acid with n-substituted octadecyl groups
(Taylor & Francis Inc, 2002) Bıçak, Niyazi; Şungur, Şana Kutun; Tan, Nükhet; Gazi, Mustafa
An organic-soluble chelating agent NN'-di-n-octadecyl ethylenediamine-NN'-diacetic acid (DOED) has been synthesized in two steps by (i) condensation of dibromoethane with 1-amino octadecane (octadecylamine) and (ii) subsequent reaction with sodium chloro acetate in alcohol-water mixture. The chelating agent in 2-ethylhexanol-cyclohexanol (1:1) solutions shows extremely high chelating ability for Ni(II) Co(II) Cu(II) Fe(111) Cr(III) and Cd(II) ions in neutral aqueous solutions. Extractions take place by the formation of (1:1) ligand-to-metal complexes and extraction coefficients are in the range 0.74-0.99. The ligand can be regenerated almost quantitatively by washing its complexes with 1M HCl and 0.2 M NaOH solutions successively. In each extraction step the organic solution exhibits a clear-cut phase separation and does not need salting out. The chelating agent can be regenerated and recycled more than 24 times without losing its extracting ability due to nonhydrolyzability of linkages in its structure. Experiments indicate that in high metal concentrations (more than 1 M) the solvent mixture itself is able to extract appreciable amounts of metal ions (33-53%). The solubility in organic solvents induced by long aliphatic chains seems to be general and the method presented offers possibility of large scale chelate extraction of metal ions of relatively low concentrations.
Citation Count: 15
A combined fuzzy AHP-simulation approach to CAD software selection
(Taylor & Francis Ltd, 2010) Ayağ, Zeki
In this paper a combined approach where the fuzzy analytic hierarchy process (AHP) and simulation come together is presented to select the best computer-aided design (CAD) software out of the available options in the market. The fuzzy AHP is used due to the vagueness and uncertainty of the judgements of a decision maker(s) because the crisp pair-wise comparison in the conventional AHP seems to be insufficient and imprecise to capture the right judgements of the decision maker(s). In this study first the fuzzy AHP is used to reduce a possible number of alternatives for the CAD system to an acceptable level for further study simulation analysis. Secondly a simulation generator as an integrated part of the fuzzy AHP is used to try the remaining alternatives on the generated model of a real-life product organisation in which the final alternative will be used. The results of simulation experiments are obtained and then evaluated to reach to the ultimate CAD alternative.
Citation Count: 5
Conformal and generalized concircular mappings of Einstein-Weyl manifolds
(2010) Özdeğer, Abdülkadir
In this article after giving a necessary and sufficient condition for two Einstein-Weyl manifolds to be in conformal correspondence we prove that any conformal mapping between such manifolds is generalized concircular if and only if the covector field of the conformal mapping is locally a gradient. Using this fact we deduce that any conformal mapping between two isotropic Weyl manifolds is a generalized concircular mapping. Moreover it is shown that a generalized concircularly flat Weyl manifold is generalized concircular to an Einstein manifold and that its scalar curvature is prolonged covariant constant. © 2010 Wuhan Institute of Physics and Mathematics.
Citation Count: 3
Detached eddy simulation of shallow mixing layer development between parallel streams
(Elsevier Science Bv, 2015) Kirkil, Gökhan
Results of a high resolution Detached Eddy Simulation (DES) are used to characterize the evolution of a shallow mixing layer developing between two parallel streams in a long open channel with a smooth flat bed and medium size dunes. The study discusses the vertical non-uniformity in the mixing layer structure and provides a quantitative characterization of the growth of the large-scale quasi two-dimensional (2D) coherent structures with the distance from the splitter plate. Results show that in streamwise sections situated between 75D (D is the channel depth) and 1501) from the splitter plate the width of the mixing layer close to the free surface is 20-30% more than the width in the near-bed region. This is mostly because of the tilting of the mixing layer interface on the low-speed side toward the low speed stream as the free surface is approached. Power spectra of the horizontal velocity components near the free surface show the presence of a -3 subrange corresponding to inverse energy cascade in two-dimensional turbulence at streamwise locations situated more than 10D from the splitter plate consistent with the presence of large-scale quasi 2D horizontal eddies and the transfer of energy (inverse energy cascade) from the smaller scales toward these eddies. Consistent with visualizations of the mass transport of a passive scalar within the mixing layer close to the free surface the estimated streamwise length of the quasi 2D mixing layer eddies is about 2.5-3.0 times larger than the local width of the mixing layer. The presence of large-scale roughness elements in the form of an array of two-dimensional dunes with a maximum height of 0.25D (D is the channel depth) induces a much more rapid and larger shift of the centerline of the mixing layer due to the increased influence of the bottom roughness. (C) 2014 International Association for Hydro-environment Engineering and Research Asia Pacific Division. Published by Elsevier B.V. All rights reserved.
Citation Count: 1
Determination of epidemic parameters from early phase fatality data: A case study of the 2009 A(H1N1) pandemic in Europe
(World Scientific Publ Co Pte Ltd, 2018) Bilge, Ayşe Hümeyra; Samanlıoğlu, Funda
This paper demonstrates that the susceptible-infected-removed (SIR) model applied to the early phase of an epidemic can be used to determine epidemic parameters reliably. As a case study the SIR model is applied to the fatality data of the 2009 fall wave cycle of the A(H1N1) pandemic in 12 European countries. It is observed that the best estimates of the basic reproduction number R-0 and the mean duration of the infection period 1/eta lie on a curve in the scatterplots indicating the existence of a nearly-invariant quantity which corresponds to the duration of the epidemic. Spline interpolation applied to the early phase of the epidemic an approximately 10-week period together with a future control point in the stabilization region is sufficient to estimate model parameters. The SIR model is run over a wide range of parameters and estimates of R0 in the range 1.2-2.0 match the values in the literature. The duration of the infection period 1/eta is estimated to be in the range 2.0-7.0 days. Longer infection periods are tied to spatial characteristics of the spread of the epidemic.
Citation Count: 8
Determining matchdays in sports league schedules to minimize rest differences
(ELSEVIER, 2020) Çavdaroğlu, Burak; Atan, Tankut
Many sports leagues first announce the games to be played in each round and then determine their matchdays as the season progresses. This study focuses on the fairness criterion of minimizing the total rest difference among opposing teams to find the matchdays for an announced schedule. We show that the problem is decomposable into optimizing the rounds separately. We also provide a polynomial-time exact algorithm for canonical schedules.
Citation Count: 0
Development of a parallel 3D navier–stokes solver for sediment transport calculations in channels
(MDPI AG, 2020) Kirkil, Gökhan
We propose a method to parallelize a 3D incompressible Navier–Stokes solver that uses a fully implicit fractional-step method to simulate sediment transport in prismatic channels. The governing equations are transformed into generalized curvilinear coordinates on a non-staggered grid. To develop a parallel version of the code that can run on various platforms, in particular on PC clusters, it was decided to parallelize the code using Message Passing Interface (MPI) which is one of the most flexible parallel programming libraries. Code parallelization is accomplished by “message passing” whereby the computer explicitly uses library calls to accomplish communication between the individual processors of the machine (e.g., PC cluster). As a part of the parallelization effort, besides the Navier–Stokes solver, the deformable bed module used in simulations with loose beds are also parallelized. The flow, sediment transport, and bathymetry at equilibrium conditions were computed with the parallel and serial versions of the code for the case of a 140-degree curved channel bend of rectangular section. The parallel simulation conducted on eight processors gives exactly the same results as the serial solver. The parallel version of the solver showed good scalability.
Citation Count: 17
Evaluation of Influenza Intervention Strategies in Turkey with Fuzzy AHP-VIKOR
(Hindawi LTD, 2019) Samanlıoğlu, Funda
In this study, a fuzzy AHP-VIKOR method is presented to help decision makers (DMs), especially physicians, evaluate and rank intervention strategies for influenza. Selecting the best intervention strategy is a sophisticated multiple criteria decision-making (MCDM) problem with potentially competing criteria. Two fuzzy MCDM methods, fuzzy analytic hierarchy process (F-AHP) and fuzzy VIsekriterijumska optimizacija i KOmpromisno Resenje (F-VIKOR), are integrated to evaluate and rank influenza intervention strategies. In fuzzy AHP-VIKOR, F-AHP is used to determine the fuzzy criteria weights and F-VIKOR is implemented to rank the strategies with respect to the presented criteria. A case study is given where a professor of infectious diseases and clinical microbiology, an internal medicine physician, an ENT physician, a family physician, and a cardiologist in Turkey act as DMs in the process.
Citation Count: 17
Fuzzy AHP-GRA approach to evaluating energy sources: a case of Turkey
(EMERALD GROUP PUBLISHING LTD, 2020) Samanlıoğlu, Funda; Ayağ, Zeki
Purpose Since the demand for energy has dramatically increased in the countries which have fast-growing population and economy, they have faced with a critical problem of how to evaluate a set of potential energy sources (i.e. nuclear, natural gas, bio, geothermal, hydro, wind and solar) and choose the ultimate energy source for their needs. On the other hand, this critical problem turns into a multiple-criteria decision-making (MCDM) in the presence of a set of energy source alternatives and evaluation criteria. In literature, there are many MCDM methods introduced to solve for different kinds of problems. The purpose of this paper is to present an integrated approach for evaluating energy sources using fuzzy AHP and GRA, with a case for Turkey. Design/methodology/approach In this paper, the analytic hierarchy process (AHP) and grey relational analysis (GRA) methods are used because of their advantages for similar problems. On the other hand, due to the fact that the conventional AHP by a nine-point scale and GRA method using a scale with crisp values can be unable to handle to capture the right judgments of a decision-maker(s), to reflect the vagueness and uncertainty on the judgments of a decision-maker, the fuzzy logic is integrated with the AHP and GRA. Findings The contributions of the paper to the literature are given in two dimensions as follows: it presents an integrated approach for complex decision processes with subjective data or vague information; the proposed approach, the fuzzy AHP-GRA method for energy source selection, is unique for the related problem in literature. The results of the proposed model from the case of Turkey will help practitioners and experts of how to apply it to the similar problems in the field of energy management. Social implications On the other hand, the proposed approach, the fuzzy AHP-GRA for energy source selection can also be an intelligent tool for public and private energy companies in Turkey, as well as others in the world. Originality/value On the other hand, in this paper, to the best of the authors' knowledge, the study contributes to the literature that the first time, they use the fuzzy alpha-cut AHP and GRA in fuzzy environment for energy source evaluation problem.
Citation Count: 47
A fuzzy AHP-PROMETHEE II approach for evaluation of solar power plant location alternatives in Turkey
(IOS Press, 2017) Samanlıoğlu, Funda; Ayağ, Zeki
Solar energy produced through a solar power plant is a freely available non-polluting renewable source of energy that reduces the greenhouse effect. Selecting the best location for a solar power plant among several location alternatives is a complicated multiple criteria decision making (MCDM) problem since several potentially conflicting quantitative and qualitative criteria needs to be taken into consideration. In this paper of the most commonly used MCDM methods in literature
Citation Count: 56
A Fuzzy AHP-TOPSIS-Based Group Decision-Making Approach to IT Personnel Selection
(Springer, 2018) Samanlıoğlu, Funda; Taşkaya, Yunus Emre; Gülen, Utku Can; Çokcan, Oğulcan
Global competition and the rapid development of information technologies force organizations to continuously change their ways. Nowadays organizations need personnel who make a difference through innovative ideas and who keep up with the rapid changes. In this paper the personnel selection process in a Turkish dairy company's information technology (IT) department is discussed as a group multi-criteria decision-making problem. The main purpose of the paper is to select the best employee candidate for an IT department by integrating fuzzy analytic hierarchy process (fuzzy AHP) with Chang's (Eur J Oper Res 95(3):649-655 1996) extent analysis and fuzzy The Technique for Order of Preference by Similarity to Ideal Solution (fuzzy TOPSIS). Decision makers' (DMs) verbal evaluations are included in the process using intuitionistic fuzzy numbers. In fuzzy AHP-TOPSIS calculations during the group decision-making process hierarchical level weights reflecting the importance of DMs' verbal evaluations are utilized. First with fuzzy AHP the importance weights of thirty sub-criteria are determined and then with fuzzy TOPSIS five IT personnel alternatives are ranked utilizing the weights obtained with fuzzy AHP.
Citation Count: 11
A fuzzy AHP-VIKOR approach for evaluation of educational use simulation software packages
(IOS Press, 2019) Samanlıoğlu, Funda; Ayağ, Zeki
In this study, an intelligent, integrated approach is presented to help educators select the best simulation software package. Selecting the best simulation software package for educational use is a complex multiple criteria decision making (MCDM) problem with several potentially conflicting quantitative and qualitative criteria. In this paper, two fuzzy MCDM methods; fuzzy Analytic Hierarchy Process (F-AHP) and fuzzy VIsekriterijumska optimizacija i KOmpromisno Resenje (F-VIKOR) are integrated to evaluate educational use simulation software package alternatives. In the proposed fuzzy AHP-VIKOR approach, F-AHP is used to determine the fuzzy criteria weights and F-VIKOR is applied to rank simulation software package alternatives with respect to these criteria. A case study is given where several educational use simulation software packages in Turkey are evaluated and ranked.
Citation Count: 10
A fuzzy ANP-based GRA approach to evaluate ERP packages
(IGI Global, 2019) Ayağ, Zeki; Yücekaya, Ahmet
One of the major problems that most companies face with during the implementation of an ERP system is to determine the best satisfying ERP software based on their needs and expectations. Because an improperly selected ERP software might lead to time loss and increased costs and in the long run a loss of market share. Therefore the ERP evaluation process for companies becomes to a vital point. On the other hand evaluating ERP software alternatives under a set of criteria leads us to a multiple-criteria decision making (MCDM) problem and needs to use proper MCDM methods. In the current literature a number of the MCDM methods have been proposed to solve these kinds of problems both of which are the analytic network process (ANP) of Saaty and grey relational analysis (GRA) which has been widely used in solving MCDM selection problems in various fields. Moreover in this article the authors used the fuzzy extension of the ANP method to reflect the uncertainty and ambiguity of decision maker(s) into problem in order to reach more reliable solution. As the fuzzy ANP method was used to calculate the priority weights of the evaluation criteria the GRA method with fuzzy interval-values was employed to rank a set of the possible ERP software alternatives. The proposed approach was also validated in a case study to show its applicability to potential readers and practitioners. Copyright © 2019 IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited.
Citation Count: 17
Fuzzy ANP-Based PROMETHEE II Approach for Evaluation of Machine Tool Alternatives
(IOS Press, 2016) Samanlıoğlu, Funda; Ayağ, Zeki
Machine tool selection process has been a critical issue for companies for years since improper selection of a machine tool might cause many problems affecting negatively the productivity precision flexibility and company's responsive manufacturing capabilities. On the other hand selecting the best machine tool from its increasing number of existing alternatives in the market is a multiple-criteria decision making (MCDM) problem in the presence of many quantitative and qualitative attributes. Therefore most companies have utilized various methods to successfully carry out this difficult and time-consuming process. In this paper both of the most used MCDM methods
Citation Count: 2
Generalized Einstein tensor for a Weyl manifold and its applications
(Springer Heidelberg, 2013) Özdeğer, Abdülkadir
It is well known that the Einstein tensor G for a Riemannian manifold defined by R (alpha) (beta) = g (beta gamma) R (gamma I +/-) where R (gamma I +/-) and R are respectively the Ricci tensor and the scalar curvature of the manifold plays an important part in Einstein's theory of gravitation as well as in proving some theorems in Riemannian geometry. In this work we first obtain the generalized Einstein tensor for a Weyl manifold. Then after studying some properties of generalized Einstein tensor we prove that the conformal invariance of the generalized Einstein tensor implies the conformal invariance of the curvature tensor of the Weyl manifold and conversely. Moreover we show that such Weyl manifolds admit a one-parameter family of hypersurfaces the orthogonal trajectories of which are geodesics. Finally a necessary and sufficient condition in order that the generalized circles of a Weyl manifold be preserved by a conformal mapping is stated in terms of generalized Einstein tensors at corresponding points.
Citation Count: 20
A hesitant fuzzy linguistic terms set-based AHP-TOPSIS approach to evaluate ERP software packages
(Emerald Group Publishing Ltd, 2020) Samanlıoğlu, Funda; Ayağ, Zeki
Purpose In this paper, two popular multiple-criteria decision-making (MCDM) methods with hesitant fuzzy logic approach; hesitant fuzzy analytic hierarchy process (hesitant F-AHP) and hesitant fuzzy the technique for order preference by similarity to ideal solution (HF-TOPSIS) are integrated as HF-AHP-TOPSIS to evaluating a set of enterprise resource planning (ERP) alternatives and rank them by weight to reach to the ultimate one that satisfies the needs and expectations of a company. Design/methodology/approach Selecting the best ERP software package among the rising number of the options in market has been a critical problem for most companies for a long time because of the reason that an improper ERP software package might lead to many issues (i.e. time loss, increased costs and a loss of market share). On the other hand, finding the best ERP alternative is a comprehensive MCDM problem in the presence of a set of alternatives and several potentially competing quantitative and qualitative criteria. Findings In this integrated approach, the hesitant F-AHP is used to determine the criteria weights, as the hesitant F-TOPSIS is utilized to rank ERP package alternatives. The proposed approach was also validated in a numerical example that has five ERP package alternatives and 12 criteria by three decision-makers in order to show its applicability to potential readers and practitioners. Research limitations/implications If the number of the alternatives and criteria are dramatically increased beyond reasonable numbers, the reaching to final solution will be so difficult because of the great deal of fuzzy based calculations. Therefore, the number of criteria and alternatives should be at reasonable numbers. Practical implications The proposed approach was also validated in a illustrated example with the five ERP package options and 12 criteria by the three decision-makers in order to show its applicability to potential readers and practitioners. Originality/value Furthermore, in literature, to the best of our knowledge, the authors did not come cross any work that integrates the HF-AHP with the HF-TOPSIS for ERP software package selection problem.
Citation Count: 14
An intelligent approach for the evaluation of innovation projects
(IOS Press, 2020) Samanlıoğlu, Funda; Ayağ, Zeki
In this study, an intelligent approach is presented for the evaluation and selection of innovation projects. Selecting the best innovation project is a complicated multiple criteria decision making (MCDM) problem with several potentially competing quantitative and qualitative criteria. In this paper, two hesitant fuzzy MCDM methods; hesitant fuzzy Analytic Hierarchy Process (hesitant F-AHP) and hesitant fuzzy VIsekriterijumska optimizacija i KOmpromisno Resenje (hesitant F-VIKOR) are integrated to evaluate and rank innovation projects. In the hesitant fuzzy AHP-VIKOR, hesitant F-AHP is used to find fuzzy evaluation criteria weights and hesitant F-VIKOR is implemented to rank innovation project alternatives. A numerical example is given where five innovation projects are evaluated based on nine criteria by three decision makers.
Citation Count: 4
Large Eddy Simulation of Wind Flow over A Realistic Urban Area
(MDPI, 2020) Kirkil, Gökhan; Lin, Ching-Long
A high-resolution large eddy simulation (LES) of wind flow over the Oklahoma City downtown area was performed to explain the effect of the building height on wind flow over the city. Wind flow over cities is vital for pedestrian and traffic comfort as well as urban heat effects. The average southerly wind speed of eight meters per second was used in the inflow section. It was found that heights and distribution of the buildings have the greatest impact on the wind flow patterns. The complexity of the flow field mainly depended on the location of buildings relative to each other and their heights. A strong up and downflows in the wake of tall buildings as well as large-scale coherent eddies between the low-rise buildings were observed. It was found out that high-rise buildings had the highest impact on the urban wind patterns. Other characteristics of urban canopy flows, such as wind shadows and channeling effects, are also successfully captured by the LES. The LES solver was shown to be a powerful tool for understanding urban canopy flows; therefore, it can be used in similar studies (e.g., other cities, dispersion studies, etc.) in the future.
Citation Count: 4
Managing Fuel Coal Supply Chains With Multiple Objectives and Multimode Transportation
(AMER SOC ENGINEERING MANAGEMENT, 2013) Yücekaya, Ahmet; Yücekaya, Ahmet
Power companies require sophisticated tools to manage fuel-coal supply chains which include multiple suppliers coal contracts and multimode transportation routes. In this article a multi-objective model which is integrated with multi-attribute decision-making for the selection of suppliers transportation routes and coal orders is developed. The model simultaneously optimizes multiple objectives such as minimizing purchase costs transportation costs and ash output and it also presents a decision framework on the selection of suppliers transportation routes and coal products that will achieve these objectives. The network and capacity constraints of suppliers and transportation routes are included in the model. The study utilizes multi-objective linear programming and well-known decision rules such as minimax maximin and compromise programming and Analytic Hierarchy Process is employed to determine preferred solutions. The methodology for the solution is illustrated via a case study and an alternative evaluation process is presented. The study demonstrates that the model can be used by power companies to find desired solutions as it provides an opportunity for the inclusion of the preferences of decision-makers and adjustments of the weights for each objective.

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