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) Uğuz, Selman; 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: 4
Agent-Based Optimization To Estimate Nash Equilibrium in Power Markets
(Taylor & Francis Inc, 2013) Yücekaya, Ahmet; Valenzuela, Jorge
In most deregulated power markets firms bid daily into a day-ahead power market. The auction mechanism supply and demand determine the equilibrium at each hour. In this environment firms aim to maximize their revenues by carefully determining their bids. This requires the development of effective computational methods that help them estimate their competitors' behaviors under incomplete information. In this article an agent-based method that uses particle swarm optimization is described to simulate the behavior of market participants. Particle swarm optimization is used in the bidding process and an agent-based model is applied to find a Nash equilibrium. Different stopping conditions are used to determine the equilibrium. Experimental results are presented for two power systems.
Citation Count: 3
Analytic Network Process (anp) for Solar Power Plant Location Problem
(Institute of Industrial Engineers, 2010) Ayağ, Zeki; Samanlıoğlu, Funda
Solar energy is the most readily available source of energy and one of the most important sources of the renewable energy because it is non-polluting and helps in lessening the greenhouse effect. Main problem of establishing a solar power plant is to determine its location. In the presence of many location alternatives and evaluation criteria a multiple-criteria decision making problem arises. In this work the location problem will be solved by using Analytic Network Process (ANP) to figure out the most satisfying alternative. A numerical example is also included to show the proposed methodology in Turkey.
Citation Count: 10
Application of Epidemic Models To Phase Transitions
(Taylor & Francis Ltd, 2012) Bilge, Ayşe Hümeyra; Pekcan, Önder; Gürol, M. V.
The Susceptible-Infected-Recovered (SIR) and Susceptible-Exposed-Infected-Recovered (SEIR) models describe the spread of epidemics in a society. In the typical case, the ratio of the susceptible individuals fall from a value S-0 close to 1 to a final value S-f, while the ratio of recovered individuals rise from 0 to R-f = 1 - S-f. The sharp passage from the level zero to the level R-f allows also the modeling of phase transitions by the number of "recovered" individuals R(t) of the SIR or SEIR model. In this article, we model the sol-gel transition for polyacrylamide-sodium alginate (SA) composite with different concentrations of SA as SIR and SEIR dynamical systems by solving the corresponding differential equations numerically and we show that the phase transitions of "classical" and "percolation" types are represented, respectively, by the SEIR and SIR models.
Citation Count: 12
A Combined Fuzzy Ahp-Goal Programming Approach To Assembly-Line Selection
(IOS Press, 2007) Ayağ, Zeki; Özdemir, Rıfat Gürcan
In mass production assembly-line balancing (ALB) problem has been a critical and repetitive issue for companies for long time. On the other hand equipment selection for stations has also been another important problem at the design stage of an assembly-line system. In this paper both problems are handled simultaneously. Therefore first goal programming (GP) method a well-suited technique is used to develop a preemptive formulation to joint both of the problems when the nature of the problem consists of several conflicting objectives and some mathematical constraints on solutions. Second an AHP method based on fuzzy scales which is incorporated with the GP is also used due to the fact that it takes both qualitative and quantitative judgments of decision-maker(s) into consideration to rank the equipment alternatives for stations by weight. The fuzzy AHP as one of the most commonly used multiple-criteria decision making (MCDM) methods has been effectively used for more than decade in both academic research and practice and takes the vagueness and uncertainty on judgments of decision-maker(s) into consideration due to the fact that the crisp pairwise comparison in the conventional AHP seems to insufficient and imprecise to capture the right judgments of decision-maker(s). In short in this study a combined fuzzy AHP-GP approach is proposed to evaluating assembly-line design alternatives with equipment selection. An integer GP formulation is constructed which also uses the fuzzy AHP scores of equipment alternatives and employs them as one of the goals. Then the mathematical model is solved to find out the ultimate alternative in terms of the minimized equipment cost and the maximized preference measures of decision-maker(s). The proposed approach is also illustrated on a sample case study.
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: 3
Determining Master Schedule of Surgical Operations by Integer Programming: a Case Study
(Institute of Industrial Engineers, 2010) Samanlıoğlu, Funda; Ayağ, Zeki; Batili, Burcin; Evcimen, Esra; Yılmaz, Gulsah; Atalay, Ozlem
Fixed amounts of available Operating Room (OR) time compatibility of ORs and restrictions related to surgery equipment and surgeon availabilities complicate the process of preparing the master surgical schedule at hospitals. In this research an integer programming model and its application at Etiler World Eye Hospital (in Turkey) are presented in order to create a master surgical schedule that includes the most common surgery types on weekly basis and resolves surgeon equipment and operating room restriction and availability issues. The integer programming model utilizes the available OR time at the hospital by minimizing the total underallocation of OR time with respect to targeted OR time of surgeons taking into consideration surgeon equipment and OR restrictions and availabilities. The mathematical model is then solved using a commercial solver to obtain a weekly master surgical schedule for the hospital.
Citation Count: 2
Efficient Approaches for Furnace Loading of Cylindrical Parts
(Elsevier Science Inc, 2014) Osman, Mojahid Saeed; Ram, Bala; Samanlıoğlu, Funda
This paper addresses the heat treatment operation in a manufacturing plant that produces different types of cylindrical parts. The immediate prior process to heat treatment is furnace-loading where parts are loaded into baskets. The furnace-loading process is complex and involves issues relating to geometry and heterogeneity in the parts and in their processing requirements. Currently furnace-loading is accomplished by operator ingenuity ; consequently the parts loaded in heat treatment often do not use furnace capacity adequately. Efficiency in furnace operation can be achieved by improving basket utilization which is determined by the furnace-loading process. This paper describes the development of integer and mixed integer LP models for 3D loading of cylindrical parts into furnace baskets. The models consider the exact location of parts to be loaded on the basket and incorporate three models with different objectives ; the first addresses the nesting of parts within one another the second addresses the number of basket layers used and the third addresses the number of baskets used. (C) 2013 Elsevier Inc. All rights reserved.
Citation Count: 0
Energy Storage With Pumped Hydrostorage Systems Under Uncertainty
(Springer International Publishing Ag, 2015) Yücekaya, Ahmet
Energy storage is becoming an important problem as the difference between supply and demand becomes sharper and the availability of energy resources is not possible all the time. A pumped hydrostorage system (PHSS) which is a special type of hydroelectric power plant can be used to store energy and to use the water more efficiently. When the energy demand and the energy price are high (peak hours) the water at upper reservoir is used to generate electricity and the water is stored in the lower reservoir. Revenue is gained from the power sale to the market. When the demand and the energy price are low (off-peak hours) the water at lower reservoir is pumped back to the upper reservoir. Cheap electricity is used to pump the water. The hourly market price and water inflow are uncertain. The main objective of a company is to find an operation schedule that will maximize its revenue. The hourly electricity prices and the water inflow to the reservoir are important parameters that determine the operation of the system. In this research we present the working mechanism of the PHSS to store energy and to balance the load changes due to demand.
Citation Count: 2
An Equivalence Class Decomposition of Finite Metric Spaces Via Gromov Products
(Elsevier Science Bv, 2017) Bilge, Ayşe Hümeyra; Çelik, Derya; Koçak, Şahin
Let (X, d) be a finite metric space with elements P-i, i = 1,..., n and with the distance functions d(ij) The Gromov Product of the "triangle" (P-i, P-j, P-k) with vertices P-t, P-j and P-k at the vertex Pi is defined by Delta(ijk) = 1/2(d(ij) + d(ik) - d(jk)). We show that the collection of Gromov products determines the metric. We call a metric space Delta-generic, if the set of all Gromov products at a fixed vertex P-i has a unique smallest element (for i = 1,., n). We consider the function assigning to each vertex P-i the edge {P-i, P-k} of the triangle (P-i, P-j, P-k) realizing the minimal Gromov product at P-i and we call this function the Gromov product structure of the metric space (X, d). We say two Delta-generic metric spaces (X, d) and (X, d') to be Gromov product equivalent, if the corresponding Gromov product structures are the same up to a permutation of X. For n = 3, 4 there is one (Delta-generic) Gromov equivalence class and for n = 5 there are three (Delta-generic) Gromov equivalence classes. For n = 6 we show by computer that there are 26 distinct (Delta-generic) Gromov equivalence classes. (C) 2017 Elsevier B.V. All rights reserved.
Citation Count: 21
Evaluation of Water Supply Alternatives for Istanbul Using Forecasting and Multi-Criteria Decision Making Methods
(Elsevier Ltd, 2020) Savun Hekimoğlu, Başak; Erbay, Barbaros; Hekimoğlu, Mustafa; Burak, Selmin
Water scarcity is one of the most serious problems of the future due to increasing urbanization and water demand. Urban water planners need to balance increasing water demand with water resources that are under increasing pressure due to climate change and water pollution. Decision makers are forced to select the most appropriate water management alternative with respect to multiple, conflicting criteria based on short and long term projections of water demand in the future. In this paper, we consider water management in Istanbul, a megacity with a population of 15 million. Purpose: The purpose of this paper is to develop a method combining demand forecasting with multi-criteria decision making (MCDM) methods to evaluate five different water supply alternatives with respect to seven criteria using opinions of experts and stakeholders from different sectors. Methodology: To combine forecasting with MCDM, we design a data collection method in which we share our demand forecasts with our experts. For demand forecasting, we compare Holt-Winters, Seasonal Autoregressive Integrated Moving Average (S-ARIMA), and feedforward Artificial Neural Network (ANN) models and select S-ARIMA as the best forecasting model for monthly water consumption data. Generated demand projections are shared with experts from different sectors and collected data is evaluated with Fuzzy Theory using two distinct MCDM models: Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) and Preference Ranking Organization Method for Enrichment Evaluations (PROMETHEE). Also our analyses are complemented with two sensitivity analyses. Findings: Our results indicate that greywater reuse is the best alternative to satisfy the growing water demand of the city whereas all experts find desalination and inter-basin water transfer as the least attractive solutions. In addition, we adopt the PROMETHEE GDSS procedure to obtain a GAIA plane indicating consensus among experts. Furthermore, we find that our results are moderately sensitive to the number of experts and they are insensitive to changes in experts’ evaluations. Novelty: To the best of our knowledge, our study is the first one incorporating water demand and supply management concepts into the evaluation of alternatives. From a methodological perspective, water demand projections have never been used in an MCDM study in the literature. Also, this paper contributes to the literature with a mathematical construction of consensus and Monte Carlo simulations for the sufficiency of experts consulted in a study.
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 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: 3
A Fuzzy ANP Approach To Evaluate Computer Simulation Packages
(Inderscience Enterprises Ltd., 2016) Ayağ, Zeki
In this study an intelligent approach is presented to help any simulation practitioner to evaluate simulation software alternatives and determine the best satisfying one based on his/her needs. On the other hand this evaluation process is a typical multiple criteria decision making (MCDM) problem in the presence of evaluation criteria and a set of possible alternatives and there are many methods in the literature which have been used to successfully carry out this difficult and time-consuming process. In this paper one of these methods the analytic network process (ANP) method integrated with alpha-cut fuzzy logic is used because it can accommodate the variety of interactions dependencies and feedback between higher and lower level elements rather than analytic hierarchy process (AHP). In addition an alpha-cut fuzzy extension of ANP uses uncertain human preferences as input information in the decision-making process. Instead of using the classical eigenvector prioritisation method in AHP only employed in the prioritisation stage of ANP an alpha-cut fuzzy logic method providing more accuracy on judgements is applied. The resulting alpha-cut fuzzy ANP enhances the potential of the conventional ANP for dealing with imprecise and uncertain human comparison judgements. © Copyright 2016 Inderscience Enterprises Ltd.
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) Ayağ, Zeki; Samanlıoğlu, Funda
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: 42
A Fuzzy Qfd Approach To Determine Supply Chain Management Strategies in the Dairy Industry
(Springer, 2013) Ayağ, Zeki; Samanlıoğlu, Funda; Büyükozkan, Gülçin
The aim of this study is to identify the crucial logistics requirements and supply chain management (SCM) strategies for the dairy industry. For product or service development quality function deployment (QFD) is a useful approach to maximize customer satisfaction. The determination of design requirements and supply chain management strategies are important issues during QFD processes for product or service design. For this reason a fuzzy QFD methodology is proposed in this study to determine these aspects and to improve customer satisfaction. Qualitative information is converted firstly into quantitative parameters and then this data is combined with other quantitative data to parameterize two multi-objective mathematical programming models. In the first model the most important logistic requirements for the company are determined based on total technical importance total cost total feasibility and total value increment objectives and in the second model based on these objectives appropriate supply chain management strategies are determined. Finally a case study from the Turkish dairy industry is given to illustrate the proposed approach.

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