Endüstri Mühendisliği Bölümü Koleksiyonu

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

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Citation - WoS: 0
Ahp-Based Approach To Evaluate Solar Power Plant Location Alternatives
(Intl Inst Social & Economic Sci, 2016) Ayağ, Zeki; 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 - WoS: 6
Citation - Scopus: 11
An Analysis of Price Spikes and Deviations in the Deregulated Turkish Power Market
(Elsevier, 2019) Gayretli, Gizem; Bilge, Ayşe Hümeyra; Yücekaya, Ahmet; Yücekaya, Ahmet Deniz; Bilge, Ayşe Hümeyra
The successful operation of a real time market is related to the planning in the day ahead market. We analyze the day ahead and real time market data for the Turkish power market for the period 2012-2015 to classify price spikes and their causes. We also focus on the levels of deviation between the day ahead market values and the real time market values. We define price deviation and load deviation ratios to measure the level of deviation both in price and demand. The analysis for the load is based on load shedding and cycling values. We analyze the mean and standard deviation in market prices and we determine the price spike as a two sigma deviation from the mean value. It is shown that 60% of the price deviation ratios are in the range of ( +/- 20%), while 44% are in the range of ( +/- 10%) and 35% are in the range of (+/- 5%). We also show that 56.9% of the spikes are due to problems in the generation of natural gas based power plants which affect the day ahead and real time prices. A total of 29.2% of the spikes are due to power plant and system failures that affect only real time prices. The share of high temperature based spikes is 13.9% which is a result of air conditioner usage.
Citation - Scopus: 87
An Analytic Network Process-Based Approach To Concept Evaluation in a New Product Development Environment
(Taylor & Francis, 2007) Ayağ, Zeki; Ayağ, Zeki; Özdemir, Rifat Gürcan
Selecting the best product concept is one of the most critical tasks in a new product development (NPD) environment. Making decisions at this stage becomes very difficult due to imprecise and uncertain product requirements. So the evaluation process of determining the most satisfying conceptual design has been a very vital issue for companies to survive in fast-growing markets for a long time. Therefore most companies have used various methods to successfully carry out this difficult and time-consuming process. Of these methods an analytic hierarchy process (AHP) has been widely used in multiple-criteria decision-making problems (i.e. concept selection equipment evaluation). In this study however we use an analytic network process (ANP) a more general form of AHP due to the fact that AHP cannot accommodate the variety of interactions dependencies and feedback between higher and lower level elements. Briefly in this paper an ANP-based approach is presented to evaluate a set of conceptual design alternatives in order to reach to the best concept satisfying the needs and expectations of both customers and company. In addition a numerical example is presented to illustrate the proposed approach.
Citation - WoS: 2
Citation - Scopus: 2
Babbling Through Social Media: a Cross-Country Study Mapping Out Social Networks Using Ewom Intentions
(Springer, 2023) Zülal, İşler; Kıygı Çallı, Meltem; Kıygı-Çallı, Meltem; El Oraiby, Maryam
This research aims to determine the factors affecting the users’ electronic word-of-mouth (eWOM) seeking and sharing intentions and to reveal the interactions among and within clusters using social network analysis (SNA). This study includes three hierarchical sub-studies conducted in two countries, Turkey and Poland. First, we develop a segmentation for social networking site (SNS) users based on the frequency of sharing product-related information on SNSs. Second, we investigate the impact of several factors that affect eWOM seeking and sharing intentions using regression analysis. In the second sub-study, we also include the identified segments developed in the first sub-study as another factor that may have differentiated eWOM intentions. Third, to understand the degree of interaction among SNS users, we apply an SNA using the forecasted eWOM intentions scores from the second sub-study, which gives us hypothetical social networks. The results of SNA present strong interactions inter- and intra-clusters in both countries. Some key findings include the identification of three SNS user segments, including “Middlers,” that may be of particular interest to brands. We also find that in terms of eWOM intentions, users in Turkey are more active than in Poland. Although some predictors of eWOM seeking and sharing intentions differ between the two countries, users intend to be more active in eWOM seeking than in eWOM sharing. The comparative study provides valuable insights for decision-makers to engage different market segments via SNSs with various proposed features using suggested information contents for selected product categories.
Citation - WoS: 11
Citation - Scopus: 15
Bidding of Price Taker Power Generators in the Deregulated Turkish Power Market
(Pergamon-Elsevier Science Ltd, 2013) Yücekaya, Ahmet; Yücekaya, Ahmet Deniz; Yücekaya, Ahmet
In deregulated power markets power firms bid into the day-ahead power market either with buy offers or sell offers. The auction mechanism and competition determine the equilibrium price and quantity for each hour. If the bid price of a company is below the market clearing price then the offer of the company is accepted and rewarded with the market price. A company can be a price maker or price taker depending on the capacity it offers to the market. A price-taker unit must determine the right offer that will maximize their profit given price uncertainty and blind auction rules. This paper first examines power supply in the Turkish electricity market and bidding process. Then a marginal cost-based Monte Carlo method is developed to determine hourly and block bidding strategies of price taker units. Historical market prices are then implemented in a normal distribution to generate hourly price scenarios. A solution methodology is developed that maximizes the expected profit of each hourly and block bidding strategy over price scenarios. The generator is able to both evaluate the hourly bidding and block bidding strategies and find the best bidding strategy that will be submitted to the market using the proposed methodology. The model is illustrated for two coal units in Turkish power market and the results are presented. (C) 2013 Elsevier Ltd. All rights reserved.
Citation - Scopus: 2
Cad Software Evaluation for Product Design To Exchange Data in a Supply Chain Network
(ExcelingTech Publishers, 2015) Ayağ, Zeki; 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 - WoS: 0
Citation - Scopus: 0
Canonical Forms for Families of Anti-Commuting Diagonalizable Linear Operators
(Elsevier Science Inc, 2012) Kumbasar, Yalcin; Bilge, Ayşe Hümeyra; Bilge, Ayşe Hümeyra
It is well known that a commuting family of diagonalizable linear operators on a finite dimensional vector space is simultaneously diagonalizable. In this paper we consider a family A = {A(a)} A(a) : V -> V a = 1... N of anti-commuting (complex) linear operators on a finite dimensional vector space. We prove that if the family is diagonalizable over the complex numbers then V has an A-invariant direct sum decomposition into subspaces V(alpha) such that the restriction of the family A to V(alpha) is a representation of a Clifford algebra. Thus unlike the families of commuting diagonalizable operators diagonalizable anti-commuting families cannot be simultaneously digonalized but on each subspace they can be put simultaneously to (non-unique) canonical forms. The construction of canonical forms for complex representations is straightforward while for the real representations it follows from the results of [A.H. Bilge S. Kocak S. Uguz Canonical bases for real representations of Clifford algebras Linear Algebra Appl. 419 (2006) 417-439]. (C) 2011 Elsevier Inc. All rights reserved.
Citation - WoS: 0
Citation - Scopus: 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 - WoS: 0
Citation - Scopus: 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 - WoS: 15
Citation - Scopus: 19
A Combined Fuzzy Ahp-Simulation Approach To Cad Software Selection
(Taylor & Francis Ltd, 2010) Ayağ, Zeki; 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 - WoS: 40
Citation - Scopus: 42
Computing Trade-Offs in Robust Design: Perspectives of the Mean Squared Error
(Pergamon-Elsevier Science Ltd, 2011) Shin, Sangmun; Samanlıoğlu, Funda; Samanlıoğlu, Funda; Cho, Byung Rae; Wiecek, Margaret M.
Researchers often identify robust design as one of the most effective engineering design methods for continuous quality improvement. When more than one quality characteristic is considered an important question is how to trade off robust design solutions. In this paper we consider a bi-objective robust design problem for which Pareto solutions of two quality characteristics need to be obtained. In practical robust design applications a second-order polynomial model is adequate to accommodate the curvature of process mean and variance functions thus mean-squared robust design models frequently used by many researchers would contain fourth-order terms. Consequently the associated Pareto frontier might be non-convex and supported and non-supported efficient solutions needs to be generated. So the objective of this paper is to develop a lexicographic weighted-Tchebycheff based bi-objective robust design model to generate the associated Pareto frontier. Our numerical example clearly shows the advantages of this model over frequently used weighted-sums model. (C) 2010 Elsevier Ltd. All rights reserved.
Citation - WoS: 1
Citation - Scopus: 1
The Critical Point of a Sigmoidal Curve
(Babeș-Bolyai University, 2020) Bilge, Ayşe Hümeyra; 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 - WoS: 25
Citation - Scopus: 33
Demand Uncertainty and Inventory Turnover Performance an Empirical Analysis of the Us Retail Industry
(Emerald Group Publishing Limited, 2016) Hancerliogullari, Gulsah; Ağca Aktunç, Esra; Sen, Alper; Aktunç, Esra Ağca
Purpose - The purpose of this paper is to investigate the impact of demand uncertainty on inventory turnover performance through empirical modeling. In particular the authors use the inaccuracy of quarterly sales forecasts as a proxy for demand uncertainty and study its impact on firm-level inventory turnover ratios. Design/methodology/approach - The authors use regression analysis to study the effect of various measures on inventory performance. The authors use a sample financial data for 304 publicly listed US retail firms for the 25-year period from 1985 to 2009. Findings - Controlling for the effects of retail segments and year it is found that inventory turnover is negatively correlated with mean absolute percentage error of quarterly sales forecasts and gross margin and positively correlated with capital intensity and sales surprise. These four variables explain 73.7 percent of the variation across firms and over time and 93.4 percent of the within-firm variation in the data. Practical implications - In addition to conducting an empirical investigation for the sources of variation in a major operational metric the results in this study can also be used to benchmark a retailer's inventory performance against its competitors. Originality/value - The authors develop a new proxy to measure the demand uncertainty that a firm faces and show that this measure may help to explain the variation in inventory performance.
Citation - WoS: 0
Citation - Scopus: 0
Development of a Parallel 3d Navier–stokes Solver for Sediment Transport Calculations in Channels
(MDPI AG, 2020) Kirkil, Gökhan; 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 - WoS: 91
Effects of Cylinder Reynolds Number on the Turbulent Horseshoe Vortex System and Near Wake of a Surface-Mounted Circular Cylinder
(Amer Inst Physics, 2015) Kirkil, Gökhan; Kirkil, Gökhan; Constantinescu, George
The turbulent horseshoe vortex (HV) system and the near-wake flow past a circular cylinder mounted on a flat bed in an open channel are investigated based on the results of eddy-resolving simulations and supporting flow visualizations. Of particular interest are the changes in the mean flow and turbulence statistics within the HV region as the necklace vortices wrap around the cylinder's base and the variation of the mean flow and turbulence statistics in the near wake in between the channel bed and the free surface. While it is well known that the drag crisis induces important changes in the flow past infinitely long circular cylinders the changes are less understood and more complex for the case of flow past a surface-mounted cylinder. This is because even at very high cylinder Reynolds numbers Re-D the flow regime remains subcritical in the vicinity of the bed surface due to the reduction of the incoming flow velocity within the bottom boundary layer. The paper provides a detailed discussion of the changes in the flow physics between cylinder Reynolds numbers at which the flow in the upstream part of the separated shear layers (SSLs) is laminar (Re-D = 16 000 subcritical flow regime) and Reynolds numbers at which the transition occurs inside the attached boundary layers away from the bed and the flow within the SSLs is turbulent (Re-D = 5 * 10(5) supercritical flow regime). The changes between the two regimes in the dynamics and level of coherence of the large-scale coherent structures (necklace vortices vortex tubes shed in the SSLs and roller vortices shed in the wake) and their capacity to induce high-magnitude bed friction velocities in the mean and instantaneous flow fields and to amplify the near-bed turbulence are analyzed. Being able to quantitatively and qualitatively describe these changes is critical to understand Reynolds-number-induced scale effects on sediment erosion mechanisms around cylinders mounted on a loose bed which is a problem of great practical relevance (e.g. for pier scour studies). (C) 2015 AIP Publishing LLC.
Citation - Scopus: 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 - WoS: 5
Citation - Scopus: 5
Epidemic Models for Phase Transitions: Application To a Physical Gel
(Taylor & Francis Ltd, 2017) Bilge, Ayşe Hümeyra; Bilge, Ayşe Hümeyra; Pekcan, Önder; Pekcan, Mehmet 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 - WoS: 67
Citation - Scopus: 91
Evaluating Machine Tool Alternatives Through Modified Topsis and Alpha-Cut Based Fuzzy Anp
(Elsevier Science Bv, 2012) Ayağ, Zeki; Ayağ, Zeki; Özdemir, Rıfat Gürcan
The problem of machine tool selection among available alternatives has been critical issue for most companies in fast-growing markets for a long time. In the presence of many alternatives and selection criteria the problem becomes a multiple-criteria decision making (MCDM) machine tool selection problem. Therefore most companies have utilized various methods to successfully carry out this difficult and time-consuming process. In this work both of the most used MCDM methods the modified TOPSIS and the Analytical Network Process (ANP) are introduced to present a performance analysis on machine tool selection problem. The ANP method is used to determine the relative weights of a set of the evaluation criteria as the modified TOPSIS method is utilized to rank competing machine tool alternatives in terms of their overall performance. Furthermore in this paper we use a fuzzy extension of ANP a more general form of AHP which uses uncertain human preferences as input information in the decision-making process because AHP cannot accommodate the variety of interactions dependencies and feedback between higher and lower level elements. Instead of using the classical eigenvector prioritization method in AHP only employed in the prioritization stage of ANP a fuzzy logic method providing more accuracy on judgments is applied. The resulting fuzzy ANP enhances the potential of the conventional ANP for dealing with imprecise and uncertain human comparison judgments. The proposed approach is also applied for a real-life case in a company. (C) 2012 Elsevier B.V. All rights reserved.
Citation - WoS: 18
Citation - Scopus: 22
Evaluation of Influenza Intervention Strategies in Turkey With Fuzzy Ahp-Vikor
(Hindawi LTD, 2019) Samanlıoğlu, Funda; 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 - WoS: 34
Citation - Scopus: 45
Evaluation of the Covid-19 Pandemic Intervention Strategies With Hesitant F-Ahp
(Hindawi, 2020) Samanlıoğlu, Funda; 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.

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