Endüstri Mühendisliği Bölümü / Department of Industrial Engineering
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Publication Metadata only Tedarikçi Seçimi ve Değerlendirmesi Problemine Bir Yaklaşım: Analitik Hiyerarşi Süreci Yöntemi(1995) AKTİN, AYŞE TÜLİN; 109203Publication Metadata only Joint Decision Making for Production and Marketing(1995) Ulusoy, Gündüz; AKTİN, AYŞE TÜLİN; 109203The prosperity of a firm depends highly on the functional integration of its various departments, and in particular the cooperation between the production and the marketing departments appears to have a large impact on the well-being of a firm. The aim of this study is to model an aggregate production planning problem that considers the production and marketing functions in a simultaneous manner. The developed multi-period, multi-product model with the objective of profit maximization reflects the characteristics of both departments. Demand for each product in each period is generated through the use of demand functions. The advertising efficiency and price of the products are determined within the model. The cash outflow for advertising expenditures is approximated by a quadratic cost function, and the production cost exhibits economies of scale. Also, stockouts are taken into consideration in the form of backlogging. A solution methodology consisting of two phases is developed, and cases displaying some important characteristics are generated and solved in order to test the performance of the proposed model. This methodology incorporates linear mixed integer programming which is embedded in two different search techniques, along with a dynamic programming-based heuristic procedure.Publication Metadata only Sipariş Üzerine Üretimde Ürün Ailelerine Bağlı Bir Üretim Planlama Yaklaşımı(1996) Özdamar, Linet; AKTİN, AYŞE TÜLİN; 109203; 57877Publication Metadata only An Application of the Analytic Hierarchy Process to the Supplier Selection Problem(1997) Barbarosoğlu, Gülay; AKTİN, AYŞE TÜLİN; 109203Publication Metadata only Capacity Driven Due Date Settings in Make-to-Order Production Systems(1997-03-14) Özdamar, Linet; AKTİN, AYŞE TÜLİN; 57877; 109203Due date setting is a difficult task for make-to-order companies and requires efficient capacity and lead time management. In the job-shop literature, production planning for make-to-order companies is tackled by using shop floor scheduling algorithms coupled with simulation. However, capacity management cannot be realized in the most detailed phase of planning and should be carried out at a higher decision level so that work loads are smoothed over time. A linear capacity planning model is proposed for dealing with problems of load leveling in bottleneck departments over a planning horizon. In this model, end items in each order are conveniently grouped into product families so that the proposed model becomes tractable in terms of practical problem sizes. Capacity constraints are included in the model and covers a number of future periods with known firm orders. The objective is to minimize total backorder and overtime costs. In this context, an order is assumed to be backordered if it is delivered some weeks later than that of its arrival. Actually, the time during which an order is backordered represents the production lead time for that order. Furthermore, the production lead time of each order is constrained by an order specific maximum lead time determined as a company policy. The output of the model conveys weekly order release and delivery times which serve as order due dates. Hence, lead time management and due date setting as well as load leveling are achieved by the proposed model. Since the model does not take family set-up times into consideration, an iterative algorithm which balances over time, the additional capacity demanded by set-up times, is proposed. The production plan developed for the bottleneck department is propagated to the other stages of the production system through a binary LP model whose binary variables are reduced at every stage. The proposed multi-stage planning system is applied for planning production in a manufacturing company which makes/assembles custom kitchen cupboards. The case study demonstrates the advantages of the system.Publication Metadata only A Reference Model for Competitive Power Assessment of Industrial Companies(2000) Kaylan, Ali Rıza; AKTİN, AYŞE TÜLİN; 109203Publication 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 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 An integrated approach to evaluating conceptual design alternatives in a new product development environment(TAYLOR & FRANCIS LTD, 4 PARK SQUARE, MILTON PARK, ABINGDON OX14 4RN, OXON, ENGLAND, 2005-02-15) Ayağ, ZekiAs many companies have demonstrated over time, a conceptual design for a new product contributes greatly to an improvement in competitiveness, because it permits a reduction of costs, an increase in quality, and, often, a shortening of the time necessary to get the product on the market. That is why the evaluation of conceptual design alternatives created in a new product development (NPD) environment has long been very vital and a critical point for the future Success Of companies in fast-growing markets. These alternatives can be evaluated using the analytic hierarchy process (AHP), one of the most commonly used Multiple criteria decision making (MCDM) techniques. This technique is used to reduce the number of conceptual design alternatives after ranking them using the scores obtained from the process. Furthermore, another technique, simulation analysis integrated with the AHP, is also used to help decision makers (product engineers or managers) perform economic analyses of the AHP's high-score alternatives using data from the generated simulation model of a real-life manufacturing system in which the final alternative is produced. In short, the objectives of this research are: first, to use the AHP technique to evaluate conceptual design alternatives in a NPD environment; second, to use a simulation generator integrated with this technique in order to perform economic analyses for the AHP's high-score alternatives. Finally, the results of both techniques, simulation and AHP, are used in a benefit/cost (B/C) analysis to reach a final decision on the conceptual design alternatives.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 simulation model for long-term analysis of the electricity market(European Council Modelling & Simulation, School Computing & Mathematics, Nottingham Trent Univ, Burton Street, Nottingham, Ng1 4Bu, England, 2006) Or, İlhan; Paşaoğlu Kılanç, Güzay; 144701; 207355After the liberalization of the electricity generation industry, capacity expansion decisions are made by multiple self-oriented power companies. Unlike the regulated environment, decision-making of market participants is now guided by price signal feedbacks and by an imperfect foresight of the future market conditions that they will face. In such an environment, decision makers need to understand long-term dynamics of the supply and demand side of the power market. To visualize the competitive electricity power market dynamics, a simulation model based on system dynamic philosophy is developed in this study. The developed model includes the demand module, the capacity expansion module, the power generation sector, an accounting and financial module, various competitors and a bidding mechanism (power pooling system). By means of such a decision tool, companies and regulators have a better opportunity to understand possible consequences of different decisions that they may make under different policies and market conditions. The main part of the paper is devoted to a detailed presentation of the model. At the end, some findings of the preliminary scenario analysis are discussed.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 An Intelligent Approach to ERP Software Selection Through Fuzzy ANP(TAYLOR & FRANCIS LTD, 4 PARK SQUARE, MILTON PARK, ABINGDON OX14 4RN, OXON, ENGLAND, 2007) Özdemir, Rifat Gürcan; Ayağ, Zeki; TR8785; TR141173During the implementations of enterprise resource planning (ERP) systems, most companies have experienced some problems, one of which is how to determine the best ERP software satisfying their needs and expectations. Because improperly selected ERP software may have an impact on the time required, and the costs and market share of a company, selecting the best desirable ERP software has been the most critical problem for a long time. On the other hand, selecting ERP software is a multiple-criteria decision-making (MCDM) problem, and in the literature, many methods have been introduced to evaluate this kind of problem, one of which is the analytic hierarchy process (AHP), which has been widely used in MCDM selection problems. However, in this paper, we use a fuzzy extension of an analytic network process (ANP), a more general form of AHP, which uses uncertain human preferences as input information in the decision-making process, because the 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 the AHP, only employed in the prioritization stage of ANP, a fuzzy-logic method providing more accuracy on judgements is applied. The resulting fuzzy ANP enhances the potential of the conventional ANP for dealing with imprecise and uncertain human comparison judgements. In short, in this paper, an intelligent approach to ERP software selection through a fuzzy ANP is proposed by taking into consideration quantitative and qualitative elements to evaluate ERP software alternatives.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 Parallel computing in Asian option pricing(ELSEVIER SCIENCE BV, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS, 2007-03) Sak, Halis; Özekici, Süleyman; Boduroğlu, İlkay; TR32631We discuss the use of parallel computing in Asian option pricing and evaluate the efficiency of various algorithms. We only focus on "backward-starting fixed strike" Asian options that are continuously averaged. We implement a partial differential equation (PDE) approach that involves a single state variable to price the Asian option, and implement the same methodology to price a standard European option to check for accuracy. A parabolic PDE is solved by using both explicit and Crank-Nicolson's implicit finite-difference methods. In particular, we look for algorithms designed for implementing the computations in massively parallel processors (MPP). We evaluate the performance of the algorithms by comparing the numerical results with respect to accuracy and wall-clock time of code executions. Codes are executed on a Linux PC cluster. (c) 2006 Elsevier B.V. All rights reserved.Publication Metadata only An analytic network process-based approach to concept evaluation in a new product development environment(TAYLOR & FRANCIS LTD, 4 PARK SQUARE, MILTON PARK, ABINGDON OX14 4RN, OXON, ENGLAND, 2007-06) Özdemir, Rifat Gürcan; Ayağ, Zeki; TR141173; TR8785Selecting 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.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 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 An integrated approach to the one-dimensional cutting stock problem in coronary stent manufacturing(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2009-07-16) Özdemir, Rifat Gürcan; AKTİN, AYŞE TÜLİN; TR109203; TR141173This paper presents a two-stage approach for pattern generation and cutting plan determination of the one-dimensional cutting stock problem. Calculation of the total number of patterns that will be cut and generation of the cutting patterns are performed in the first stage. On the other hand, the second stage determines the cutting plan. The proposed approach makes use of two separate integer linear programming models. One of these models is employed by the first stage to generate the cutting patterns through a heuristic procedure with the objective of minimizing trim loss. The cutting patterns obtained from Stage I are then fed into the second stage. In this stage, another integer linear programming model is solved to form a cutting plan. The objective of this model is to minimize a generalized total cost function consisting of material inputs, number of setups, labor hours and overdue time: subject to demand requirements, material availability, regular and overtime availability, and due date constraints. The study also demonstrates an implementation of the proposed approach in a coronary stent manufacturer. The case study focuses on the cutting phase of the manufacturing process followed by manual cleaning and quality control activities. The experiments show that the proposed approach is suitable to the conditions and requirements of the company. (C) 2008 Elsevier B.V. All rights reserved.Publication Metadata only Multi Objective New Product Development In Bakery Production Under Fuzzy Demand Parameters(Ios Press, Nieuwe Hemweg 6B, 1013 Bg Amsterdam, Netherlands, 2010) Özdemir, Rifat Gürcan; Çiçek, Burçin; Özenç, Derya; TR141173This paper deals with the problem of multi objective new product development and its solution with an intelligent approach. The proposed approach uses fuzzy parameters for economic analysis and combines a multi-criteria decision making method to goal programming. In economic analysis, fuzzy life cycle costs and fuzzy life cycle pricing are considered with respect to demand changes during life cycle of new product alternatives. Fuzzy equivalent worth of each new product alternative is determined using fuzzy life cycle monetary input, and results are input to the multi-criteria analysis. The selected multi-criteria analysis tool is TOPSIS in the paper and some additional judgmental criteria are also considered to rank new product alternatives. The preference weights used to rank alternatives are then fed to a goal programming model which makes an ultimate selection of new product(s) to be produced in the manufacturing system under capacity, sales potential, and workforce balance constraints. The goal programming model has an objective of minimizing the weighted sum of positive deviation from target total cost and negative deviation from target total preference weights. The proposed approach is then implemented using real data of a continuous production system for the need of introducing new products into market.