Endüstri Mühendisliği Bölümü Koleksiyonu

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

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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: 0
AHP-BASED APPROACH TO EVALUATE SOLAR POWER PLANT LOCATION ALTERNATIVES
(Intl Inst Social & Economic Sci, 2016) Ayağ, Zeki
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 hierarchy process (AHP) to figure out the most satisfying alternative. A numerical example is also included to show the proposed methodology in Turkey. . . . .
Citation Count: 3
Analytic Network Process (ANP) for solar power plant location problem
(Institute of Industrial Engineers, 2010) Samanlıoğlu, Funda; Ayağ, Zeki
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: 2
Cad software evaluation for product design to exchange data in a supply chain network
(ExcelingTech Publishers, 2015) Ayağ, Zeki
The sharing information in a supply chain environment especially CAD models and drawings are so important companies. So the selection of the most satisfying computer-aided design (CAD) software which enables to exchange data through supply chain network has been major issues for companies in a supply chain. The selection process of CAD software among the raising number of alternatives in the market has been very vital and critical issue for companies that aim to make their design and engineering related activities automated towards computer integrated manufacturing (CIM) environment. Therefore most companies have used various methods to successfully carry out this difficult and time-consuming process. Of these methods Analytic Hierarchy Process (AHP) has been widely used for Multiple Criteria Decision Making (MCDM) problems in both academic researches and practices. But in some cases due to the vagueness and uncertainty on judgments of the decisionmaker(s) the crisp pair wise comparison in the conventional AHP seems to be insufficient and imprecise to capture the right judgments of decision-maker(s). Therefore a fuzzy logic is introduced in the pair wise comparison of AHP to make up for this deficiency in the conventional AHP called as fuzzy AHP. In this paper a fuzzy AHP-based approach is proposed to evaluate a set of CAD software alternatives in the market to reach the best satisfying one based on the needs of company. © ExcelingTech Pub UK.
Citation Count: 0
Chebyshev nets formed by Ricci curves in a 3-dimensional Weyl space
(Elsevier Science Bv, 2005) Yıldırım, Gülçin Çivi; Özdeğer, Abdülkadir
In this paper Ricci curves in a 3-dimensional Weyl space W-3(g T) are defined and it is shown that any 3-dimensional Chebyshev net formed by the three families of Ricci curves in a W-3(g T) having a definite metric and Ricci tensors is either a geodesic net or it consists of a geodesic subnet the members of which have vanishing second curvatures. In the case of in indefinite Ricci tensor only one of the members of the geodesic subnet under consideration has a vanishing second curvature. (c) 2004 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: 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: 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: 0
A Comparative Study of Energy Models for Turkish Electricity Market Using LEAP
(IEEE Computer Society, 2019) Kirkil, Gökhan; Kirkil, Gökhan; Çelebi, Emre
Fossil fuel thermal power plants constitute a large part of the Turkish electricity generation capacity. Turkish government has been developing several energy policy documents to evaluate how various renewable energy sources of the country can be utilized optimally in the generation of electricity within the next 30 years. This study considers three scenarios in the transition to renewable energy for Turkey; the business as usual (BAU), energy conservation (EC) and renewable energy (REN) scenarios. EC scenario considers the use of energy-efficient appliances and imposing a carbon tax, whereas REN scenario considers increasing the share of the renewable energy sources as much as possible in the power generation mix. These scenarios were evaluated in terms of cost and environmental impact. The LEAP (Long-range Energy Alternatives Planning Model) was used in the research. The REN scenario has been shown to be the optimal energy policy option for Turkey in terms of cost and environmental impact.
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: 1
The critical point of a sigmoidal curve
(Babeș-Bolyai University, 2020) Bilge, Ayşe Hümeyra; Özdemir, Yunus
Let y(t) be a monotone increasing curve with lim(t ->+/-infinity) y((n))(t) = 0 for all n and let t(n) be the location of the global extremum of the nth derivative y((n))(t). Under certain assumptions on the Fourier and Hilbert transforms of y(t), we prove that the sequence {t(n)} is convergent. This implies in particular a preferred choice of the origin of the time axis and an intrinsic definition of the even and odd components of a sigmoidal function. In the context of phase transitions, the limit point has the interpretation of the critical point of the transition as discussed in previous work [3].
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: 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: 0
Electricity market equilibrium models with dynamic demand functions
(2013) Çelebi, Emre
Many electricity market models have either mostly ignored the demand response to changing prices (e.g. day-ahead models with mostly fixed demand) or at the other extreme they assumed that the full demand response occurred within one hour. Moreover the capital stock adjustment and the forward-looking nature of consumers are usually omitted. In this paper we propose variational inequality models for electricity markets with dynamic demand models where the intertemporal nature of consumption (i.e. the current consumption decision affects capital stock/habits and thus the future preferences and demand) is recognized. It is intended that the proposed models would develop a framework for electricity market equilibrium models that incorporate the dynamics of the demand side. © 2013 IEEE.
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: 5
Epidemic models for phase transitions: application to a physical gel
(Taylor & Francis Ltd, 2017) Bilge, Ayşe Hümeyra; Pekcan, Önder; Kara, Selim; Öğrenci, Arif Selçuk
Carrageenan gels are characterized by reversible sol-gel and gel-sol transitions under cooling and heating processes and these transitions are approximated by generalized logistic growth curves. We express the transitions of carrageenan-water system as a representative of reversible physical gels in terms of a modified Susceptible-Infected-Susceptible epidemic model as opposed to the Susceptible-Infected-Removed model used to represent the (irreversible) chemical gel formation in the previous work. We locate the gel point T-c of sol-gel and gel-sol transitions and we find that for the sol-gel transition (cooling) T-c > T-sg (transition temperature) i.e. T-c is earlier in time for all carrageenan contents and moves forward in time and gets closer to T-sg as the carrageenan content increases. For the gel-sol transition (heating) T-c is relatively closer to T-gs
Citation Count: 31
Evaluation of the COVID-19 Pandemic Intervention Strategies with Hesitant F-AHP
(Hindawi, 2020) Samanlıoğlu, Funda; Kaya, Burak Erkan
In this study, a hesitant fuzzy AHP method is presented to help decision makers (DMs), especially policymakers, governors, and physicians, evaluate the importance of intervention strategy alternatives applied by various countries for the COVID-19 pandemic. In this research, a hesitant fuzzy multicriteria decision making (MCDM) method, hesitant fuzzy Analytic Hierarchy Process (hesitant F-AHP), is implemented to make pairwise comparison of COVID-19 country-level intervention strategies applied by various countries and determine relative importance scores. An illustrative study is presented where fifteen intervention strategies applied by various countries in the world during the COVID-19 pandemic are evaluated by seven physicians (a professor of infectious diseases and clinical microbiology, an infectious disease physician, a clinical microbiology physician, two internal medicine physicians, an anesthesiology and reanimation physician, and a family physician) in Turkey who act as DMs in the process.
Citation Count: 0
Flow and Turbulence Structure Around an In-Stream Rectangular Cylinder with Scour Hole
(TSINGHUA UNIV, 2013) Kirkil, Gökhan; Constantinescu, George
An eddy resolving technique is used to reveal the unsteady dynamics of the coherent structures present in the flow field around an in-stream vertical cylinder with a scour hole at a channel Reynolds number of 240000. Such an investigation is important as most of the erosion around obstacles present in alluvial streams takes place after a scour hole of sufficiently large dimensions to stabilize the large-scale oscillations of the horseshoe vortex (HV) system has formed. The cylinder has a rectangular section and is placed perpendicular to the incoming flow. The geometry of the scour hole is obtained from an experiment. The mechanisms driving the bed erosion during the advanced stages of the scour process around the vertical plate are discussed. Simulation results demonstrate the critical role played by these large-scale turbulent eddies and their interactions in driving the local scour. Results show that important changes in the structure of the wake (e. g. the wake loses its undular shape due to suppression of the anti-symmetrical shedding of the roller vortices) and the nature of the interactions between the necklaces vortices of the HV system and the eddies present inside the detached shear layers (DSLs) occurs as the scour process proceeds. This means that information on the vortical structure of the flow at the initiation of the scour process or during its initial stages are insufficient to understand the local scour mechanisms.

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