Endüstri Mühendisliği Bölümü / Department of Industrial Engineering
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Publication Metadata only A Combined Fuzzy AHP-goal Programming Approach to Assembly-Line Selection(IOS PRESS, NIEUWE HEMWEG 6B, 1013 BG AMSTERDAM, NETHERLANDS, 2007) Ayağ, Zeki; Özdemir, Rifat Gürcan; TR141173; TR8785In 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.Publication Metadata only A Cutting Sequencing Approach to Modular Manufacturing(Emerald Group Publishing Limited, 2004) Özdemir, Rifat Gürcan; AKTİN, AYŞE TÜLİN; 109203In this study, a two‐stage algorithm is developed for the cutting sequencing problem in a modular manufacturing system consisting of four basic workstations. Since the flexibility of the system is dependent upon the cutting stage of raw materials, the study focuses particularly on this workstation. In the first stage of the algorithm, an integer linear programming model is used to determine the number of hardboards that will be cut. The model is tested with two different objective functions. In the second stage, a heuristic which takes into account the due date of the products is developed to obtain the real‐time sequencing of these cutting patterns on the shop floor. The algorithm is further implemented in a furniture manufacturer that operates on a make‐to‐order basis. The results of the existing and proposed system are compared, and the proposed algorithm is found to provide a useful tool in such a real‐life planning problem.Publication Metadata only A Decision Support Model for Customer Value Assessment and Supply Quota Allocation(TAYLOR & FRANCIS LTD, 11 NEW FETTER LANE, LONDON EC4P 4EE, ENGLAND, 2000-09) Barbarasoğlu, G; Yazgaç, Ayşe Tülin; AKTİN, AYŞE TÜLİNThe aim of this study is to develop a decision support tool for a supplier in a value-chain environment. The supplier under consideration is assumed to provide a strategic product to a number of customers and needs to allocate his capacity among them in a way to maximize his business value. First, an analytic hierarchy process (AHP) structure is designed to represent the criteria which are identified from the supplier's point of view to assess customer performance, and customer priorities are obtained by using the AHP composition principle. Then, these are deployed in numerical algorithms which aim to allocate the total supply capacity among customers as supply quotas. The approach is implemented in an electric motor manufacturer in Turkey, which possesses high competitive power with advanced manufacturing technology.Publication Metadata only A decision support tool for the analysis of pricing, investment and regulatory processes in a decentralized electricity market(ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND, 2008-04) Paşaoğlu Kılanç, Güzay; Or, İlhan; TR207355; TR144701After the liberalization of the electricity generation industry, capacity expansion decisions are made by multiple self-oriented power companies. Unlike the centralized environment, decision-making of market participants is now guided by price signal feedbacks and by an imperfect foresight of the future market conditions (and competitor actions) that they will face. In such an environment, decision makers need to better understand long-term dynamics of the Supply and demand sides of the power market. In this Study, a system dynamics model is developed, to better understand and analyze the decentralized and competitive electricity market dynamics in the long run. The developed simulation model oversees a 20-year planning horizon; it includes a demand module, a capacity expansion module, a power generation module, in accounting and finance module, various competitors, a regulatory body and a bidding mechanism. Many features, singularities and tools of decentralized markets, such as; capacity withholding, enforced divestment, long-term contracts, price-elastic demands, incentives/disincentives, are also incorporated into the model. Public regulators and power companies are potential users of the model, for learning and decision support in policy design and strategic planning. Results of scenario analysis are presented to illustrate potential use of the model. (C) 2008 Elsevier Ltd. All rights reserved.Publication Metadata only A fuzzy AHP approach to evaluating machine tool alternatives(SPRINGER, VAN GODEWIJCKSTRAAT 30, 3311 GZ DORDRECHT, NETHERLANDS, 2006-04) Ayağ, Zeki; Özdemir, Rifat Gürcan; TR8785; TR141173Selecting process of a machine tool has been very important issue for companies for years, because the improper selection of a machine tool might cause of many problems affecting negatively on 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 market are multiple-criteria decision making (MCDM) problem in the presence of many quantitative and qualitative attributes. Therefore, in this paper, an analytic hierarchy process (AHP) is used for machine tool selection problem due to the fact that it has been widely used in evaluating various kinds of MCDM problems in both academic researches and practices. However, due to the vagueness and uncertainty on judgments of the decision-maker(s), the crisp pair wise comparison in the conventional AHP seems to insufficient and imprecise to capture the right judgments of decision-maker(s). That is why; fuzzy number logic is introduced in the pair wise comparison of AHP to make up for this deficiency in the conventional AHP. Shortly, in this study, an intelligent approach is proposed, where both techniques; fuzzy logic and AHP are come together, referred to as fuzzy AHP. First, the fuzzy AHP technique is used to weight the alternatives under multiple attributes; second Benefit/Cost (B/C) ratio analysis is carried out by using both the fuzzy AHP score and procurement cost, of each alternative. The alternative with highest B/C ratio is found out and called as the ultimate machine tool among others. In addition, a case study is also presented to make this approach more understandable for a decision-maker(s).Publication Metadata only A fuzzy AHP-based simulation approach to concept evaluation in a NPD environment(TAYLOR & FRANCIS INC, 325 CHESTNUT ST, SUITE 800, PHILADELPHIA, PA 19106 USA, 2005-09) Ayağ, ZekiThe evaluation process of conceptual design alternatives in a new product development environment is a critical point for companies who operate in fast-growing markets. Various methods exist that are able to successfully carry out this difficult and time-consuming process. One of these methods, the Analytic Hierarchy Process (AHP) has been widely used to solve multiple-criteria decision-making problems (i.e., concept evaluation, equipment selection) in both academic research and in industrial practice. However, due to vagueness and uncertainty in the decision-maker's judgment, a crisp, pair-wise comparison with a conventional AHP may be unable to accurately capture the decision-maker's judgment. Therefore, fuzzy logic is introduced into the pair-wise comparison in the AHP to compensate for this deficiency in the conventional. AHP. This is referred to as fuzzy AHP. In this paper, a fuzzy AHP method is used to reduce a set of conceptual design alternatives by eliminating those whose scores (or weights) are smaller than a predetermined constant value obtained under certain circumstances. Then, simulation analysis is integrated with the fuzzy AHP method, and the hybrid method is used to help the decision-makers (product engineers or managers) evaluate the remaining alternatives from the fuzzy AHP method. A real-life manufacturing system is used as the testbed for the proposed techniques. Finally, the results of both techniques, fuzzy AHP and simulation, are used for Preference Ratio analysis to reach to the final alternative.Publication Metadata only A Fuzzy Risk Assessment Model for Hospital Information System Implementation(Pergamon-Elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington, Oxford Ox5 1Gb, England, 2012-01) Özok, Ahmet Fahri; Yücel, Gülçin; Hoege, B.; Çebi, Selçuk; 207507; 202323; 24803There is research which reveals negative effects of IT applications in the healthcare sector on both patients and staff. Therefore, methods are necessary to predict the risk of new healthcare information technology in order to reduce the unintended results of new applications. A new predictive risk assessment model for a hospital information system (HIS) has been developed in this paper to estimate risk before the implementation of new HIS. The methodology consists of analytic network process (ANP), reality-design gap evaluation and fuzzy inference system. An application of the proposed algorithm has been applied for a research and education hospital in Istanbul, Turkey. Risk magnitude of a new HIS implementation for the hospital is found as major with a belief of 100%. The relative importances of risk factors for HIS implementation success are obtained. The most effective factors on the HIS implementation are found as technological factors; usefulness, compatibility, user involvement and ease of use. These factors are followed by organizational factors; training and organizational commitment. The most important individual factor is also found as user's previous HIS experience. A risk assessment model has been proposed in this paper. The model processes experts' evaluations defined in linguistic forms when there is no sufficient data and it integrates possible risk factors into the decision-making process of risk assessment. In the model, a reality-design gap analysis is used to determine risk likelihood instead of directly risk evaluation. (C) 2011 Elsevier Ltd. All rights reserved.Publication Metadata only A Holistic Approach For The Optimization of Offshore Wind Farm Layouts Considering Cable Layouts(2019-08) Alabaş Uslu, Çiğdem; ÜLKÜ, İLAYDA; 51700A wind farm, mainly, is composed of a set of turbines, one or more transmitters and a set of electrical cable connections between turbines and transmitters. Determination of turbine locations within the farm to maximize total power generation is called turbine location (TL) problem. Relative turbine positions affect the amount of overall energy because of wake effects. Determination of cable connections among turbines and transmitters to collect produced energy by turbines at transmitters is called cable layout (CL) problem. While TL problem is directly effective on the total energy production in the farm, CL problem indirectly affects the total energy due to the power losses. In the literature, TL and CL problems are solved sequentially where the layout found by solving of TL is used as an input of CL problem. To minimize wake effects in TL problem, distances between turbine pairs should be increased, however, as the distances are increased the cable cost increases in CL problem. A new mathematical model is developed to deal with simultaneously solving of TL and CL problems. A set of test instances are used to show the performance of the proposed model. The experiments show the practical use of the proposed holistic model.Publication Metadata only A Hybrid Approach for Fuzzy Clustering and Assembly Line Balancing Problems(2013) Tarhan, İbrahim Ethem; Demiere, Murat; Yahya, Mehmet; Fakı, Filiz; Özdemir, Rifat Gürcan; 114926; 141173Publication Metadata only A Hybrid Approach To Concept Selection Through Fuzzy Analytic Network Process(Pergamon-Elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington, Oxford Ox5 1Gb, England, 2009-02) Ayağ, Zeki; Özdemir, Rifat Gürcan; TR8785; TR141173Evaluating conceptual design alternatives in a new product development (NPD) environment has been one of the most critical issues for many companies which try to survive in the fast-growing world markets. Therefore, most companies have used various methods to successfully carry out this difficult and time-consuming evaluation process. Of these methods, analytic hierarchy process (AHP) has been widely used in multiple-criteria decision-making (MCDM) problems. But, in this study, we used analytical network process (ANP), a more general form of AHP, instead of AHP due to the fact that AHP cannot accommodate the variety of interactions, dependencies and feedback between higher and lower level elements. Furthermore, in some cases, due to the vagueness and uncertainty on the judgments of a decision-maker, the crisp pairwise comparison in the conventional ANP is insufficient and imprecise to capture the right judgments of the decision-maker. Therefore, a fuzzy logic is introduced in the pairwise comparison of ANP to make up for this deficiency in the conventional ANP, and is called as fuzzy ANP. In short, in this paper, a fuzzy ANP-based approach is proposed to evaluate a set of conceptual design alternatives developed in a NPD environment in order to reach to the best one satisfying both the needs and expectations of customers, and the engineering specifications of company. In addition, a numerical example is presented to illustrate the proposed approach. (C) 2008 Elsevier Ltd. All rights reserved.Publication Metadata only A mathematical model for the delivery routing problem via drones(Pamukkale Üniversitesi, 2019) Han, Sinem; Özer, Begüm; Alioğlu, Barış; POLAT, ÖZGÜR; AKTİN, AYŞE TÜLİNLogistics sector aims to distribute merchandise to designated places on time, while focusing on the entire process that starts from storing the goods at warehouses. Transportation by land is the most common and preferred way in logistics in terms of cost and service. Studies have been going on for drone transportation with the purpose of reducing the service time and making the process automated. Advancement of this technology has led to an increase in transportation with drones. Traffic is a huge problem in land transportation causing delays in delivery time. Furthermore, nature and economy are affected because of the CO2 emission, which is a consequence of intense traffic. In this study, utilizing drones for delivery is proposed with the aim of increasing customer satisfaction and minimizing transportation cost per delivery in a green way. Istanbul's Bakirkoy district is selected as the implementation region, and daily drug delivery to pharmacies with drones is examined. In the first stage, a mathematical model that uses pharmacy coordinates as an input is developed for clustering analysis. In the second stage, one of these clusters is selected, and the location of the drone center that will serve pharmacies in the cluster is obtained by center of gravity method. Then, a vehicle routing model is proposed for finding the drone routes and calculating the total distance travelled within this cluster. Mathematical models are solved with GAMS/CPLEX solver. It is believed that this study will trigger new studies in "green delivery" literature in near future.Publication Metadata only A Mathematical Programming Approach to Multi-Way Kidney Transplantation(2015-07) Kutlu, Fatma; Girgin, S.; YÜKSEKTEPE, FADİME ÜNEY; AKTİN, AYŞE TÜLİN; 273471; 108243Publication Metadata only A mathematical programming approach to paired kidney exchange: the case of Turkey(2018-08) Akın, Barış; YÜKSEKTEPE, FADİME ÜNEY; AKTİN, AYŞE TÜLİN; GÜNDOĞDU, FATMA KUTLU; 273471; 108243; 109203Background: Kidney exchange has become a very common and important treatment alternative for patients suffering from serious kidney diseases with incompatible donors. Factors such as blood type, HLA matches and PRA existence are considered to determine compatibility. In a paired exchange, two incompatible patient-donor pairs switch their donors who are compatible with the other recipient. Currently, each hospital in Turkey operates individually in a decentralized manner using its own list. This list may contain patients having more than one incompatible donor, which differentiates the current work from those existing in literature. Methods: In this study, mathematical models are developed to propose an easy and practical approach for the paired kidney exchange problem in Turkey. Data are generated by employing a real data set provided by a hospital specialized in kidney transplantation. Results: The optimal solutions are obtained by using GAMS/CPLEX, and different scenario analyses are performed to measure the impact of "gender differences" and "age" on the solution. Furthermore, the original patient-donor list provided by the hospital is used to compare the model's solution with the planned transplantations. The study also evaluates a centralized approach which integrates all hospitals performing paired kidney exchange in Istanbul. Conclusions: As the optimal solution of the model is obtained in a basis of seconds, the developed approach offers an easy and applicable procedure for paired kidney exchange. Comparison of decentralized and centralized approaches reveals that the centralized approach is more favorable in terms of HLA compatibility and number of transplantations.Publication Metadata only A measurement tool for customer relationship management processes(Emerald Group Publishing Limited, Howard House, Wagon Lane, Bingley Bd16 1Wa, W Yorkshire, England, 2011) Öztayşi, Başar; Sezgin, Selime; Özok, Ahmet Fahri; 150000; 207507Purpose - Customer relationship management (CRM) projects have a low success rate, which can be solved by better measurement of CRM process. The purpose of this paper is to define the CRM processes within a company and propose a tool for CRM measurement. Design/methodology/approach - An empirical study is conducted in industrial organizations in Turkey. The research is designed according to scale development literature. The responses from various industries (manufacturing, information technologies, tourism, service, retail, finance, logistics) were collected. Using exploratory factor analysis, 167 valid responses are analyzed. Findings - The paper provides a general understanding of CRM processes in customer-oriented perspective and proposes a measurement tool that addresses seven main processes which are: targeting management, customer information management, production/service customization, expansion management, referrals management, termination management and win back. Practical implications - The results of the analysis provides useful information for managers to define, measure and improve CRM process. Originality/value - The paper provides an enhanced review about CRM measurement literature. Based on this review, the paper defines seven CRM processes and maintains a tool for evaluation of these processes within a company.Publication Metadata only A new mathematicalpProgramming aapproach to wind farm layout problem under multiple wake effects(2019) Alabaş Uslu, Çiğdem; ÜLKÜ, İLAYDA; 51700; 126061Wind farm layout optimization is one of the challenging problems in thefield of renewable energy. In thepresent study, a new nonlinear mathematical model for layout of wind turbines under multiple wakeeffects is proposed considering two objective functions separately: maximization of total power pro-duction and minimization of cost per power. To incorporate multiple wake effects into the proposedmodel, Jensen's wake decay model is employed. It was proven that the proposed model has totallyunimodularity property and according to this property, relaxation of binary decision variables relatedwith the wind turbine locations makes the model relatively simple to solve. Computational study revealsthat results of total power production and cost of power obtained from the proposed model outperformthat of the previous studies in the literature on a set of example cases and therefore, can be used to layoutmore productive wind farms.Publication Metadata only A novel approach to cutting decision trees(Springer, 233 Spring Street, New York, Ny 10013, United States, 2014-09) YÜKSEKTEPE, FADİME ÜNEY; 108243In data mining, binary classification has a wide range of applications. Cutting Decision Tree (CDT) induction is an efficient mathematical programming based method that tries to discretize the data set on hand by using multiple separating hyperplanes. A new improvement to CDT model is proposed in this study by incorporating the second goal of maximizing the distance of the correctly classified instances to the misclassification region. Computational results show that developed model achieves better classification accuracy for Wisconsin Breast Cancer database and Japanese Banks data set when compared to existing piecewise-linear models in literature. Furthermore, remarkable results are obtained for the well-known benchmarking data sets (Buba Liver Disorders, Blood Tranfusion and Pima Indian Diabetes) when compared to the original CDT model.Publication Metadata only A novel fuzzy TOPSIS method using emerging interval-valued spherical fuzzy sets(2019-06-03) Kahraman, Cengiz; GÜNDOĞDU, FATMA KUTLUAll the extensions of ordinary fuzzy sets with three-dimensional membership functions such as intuitionistic fuzzy sets, second type intuitionistic fuzzy sets (or Pythagorean fuzzy sets) and neutrosophic sets aim at defining the judgments of decision makers/ experts with a more detailed description. As a new extension of intuitionistic fuzzy sets of second type, the emerging spherical fuzzy sets (SFS) have been proposed by Kutlu Gundogdu and Kahraman (2019b). In spherical fuzzy sets, the sum of membership, non-membership and hesitancy degrees must satisfy the condition0 <= mu(2) + v(2) + pi(2) <= 1 in which these parameters are assigned independently. SFS is an integration of Pythagorean fuzzy sets and neutrosophic sets. In this paper, novel interval-valued spherical fuzzy sets are introduced with their score and accuracy functions; arithmetic and aggregation operations such as interval-valued spherical fuzzy weighted arithmetic mean operator and interval-valued spherical fuzzy geometric mean operator. Later, interval-valued spherical fuzzy sets are employed in developing the extension of TOPSIS under fuzziness. Then, we use the proposed interval-valued spherical fuzzy TOPSIS method in solving a multiple criteria selection problem among 3D printers to verify the developed approach and to demonstrate its practicality and effectiveness. A comparative analysis with single-valued spherical TOPSIS is also performed.Publication Metadata only A Novel Hesitant Fuzzy EDAS Method and Its Application to Hospital Selection(2018-09) Kahraman, Cengiz; Civan, Hatice Nida; GÜNDOĞDU, FATMA KUTLU; 273471; 9178Publication Open Access A novel spherical fuzzy analytic hierarchy process and its renewable energy application(2020-03-01) Kutlu Gündoğdu Fatma; Kahraman, CengizThe extensions of ordinary fuzzy sets such as intuitionistic fuzzy sets, Pythagorean fuzzy sets, and neutrosophic sets, whose membership functions are based on three dimensions, aim at collecting experts’ judgments more informatively and explicitly. In the literature, generalized three-dimensional spherical fuzzy sets have been introduced by Kutlu Gündoğdu and Kahraman (J Intell Fuzzy Syst 36(1):337–352, 2019a), including their arithmetic operations, aggregation operators, and defuzzification operations. In this paper, our aim is to extend classical analytic hierarchy process (AHP) to spherical fuzzy AHP (SF-AHP) method and to show its applicability and validity through a renewable energy location selection example and a comparative analysis between neutrosophic AHP and SF-AHP.Publication Metadata only A novel VIKOR method using spherical fuzzy sets and its application to warehouse site selection(2019) Kahraman, Cengiz; GÜNDOĞDU, FATMA KUTLUThe extensions of ordinary fuzzy sets such as intuitionistic fuzzy sets (IFS), Pythagorean fuzzy sets (PFS), and neutrosophic sets (NS), whose membership functions are based on three dimensions, aim at collecting experts' judgments more informatively and explicitly. In the literature, generalized three-dimensional spherical fuzzy sets have been developed by Kutlu Gundogdu and Kahraman (2019), including their arithmetic operations, aggregation operators, and defuzzification operations. Spherical Fuzzy Sets (SFS) are a new extension of Intuitionistic, Pythagorean and Neutrosophic Fuzzy sets, a SFS is characterized by a membership degree, a nonmembership degree, and a hesitancy degree satisfying the condition that their squared sum is equal to or less than one. These sets provide a larger preference domain in 3D space for decision makers (DMs). In this paper, our aim is to extend classical VlseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR) method to spherical fuzzy VIKOR (SF-VIKOR) method and to show its applicability and validity through an illustrative example and to present a comparative analysis between spherical fuzzy TOPSIS (SF-TOPSIS) and SF-VIKOR. We handle a warehouse location selection problem with four alternatives and four criteria in order to demonstrate the performance of the proposed SF-VIKOR method.