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    BULANIK TOPSIS YÖNTEMİYLE TÜRKİYE’NİN YERLİ OTOMOBİLİ İÇİN EN UYGUN FABRİKA YERİNİN SEÇİMİ
    (2019) Yıldız, Aytaç; Demir, Yunus
    Girişimciler için, hangi sektörde faaliyet göstermelerinin yanı sıra işletmeyi nereye kuracakları da önemlidir. Çünkü yanlış bir karardan dolayı uygun olmayan bir yere işletmenin kurulması yüksek maliyetlere, nitelikli işgücüne sahip olamama ve yeterli sayıda müşteriye ulaşamama gibi sorunlara sebep olabilir. Yer seçimi problemi, içerisinde birçok kriteri ve belirsizliği barındıran, bundan dolayı da bulanık bir davranış sergileyen bir karar problemidir. Bu gibi karar problemlerinin çözümünde Çok Kriterli Karar Verme (ÇKKV) gibi bilimsel yöntemlerin kullanılması karar vericilere kolaylık sağlamaktadır. Bu çalışmada, Türkiye için stratejik bir öneme sahip yerli otomobil üretimi için en uygun yerin seçilmesi amaçlanmış ve bu amaç için bulanık ortamlarda karar vermeyi kolaylaştıran bulanık TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) yöntemi kullanılmıştır. Yedi alternatif yer (Kocaeli, Bursa-Gemlik, Sakarya, Konya, İzmir-Aliağa, Adana ve Eskişehir) literatür taraması neticesinde belirlenen beş ayrı kritere göre (ekonomik, coğrafi konum, altyapı, teknik ve sosyal özellik) değerlendirilmiştir. Çalışma sonunda yakınlık katsayısı en yüksek olan Bursa-Gemlik alternatifi, yerli otomobil için en uygun fabrika yeri olarak belirlenmiştir.
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    HIERARCHICAL MATHEMATICAL MODELLING APPROACH FOR A CASE STUDY IN UNIVERSITY TIMETABLING
    (Yildiz Technical Univ, 2019) Demir, Yunus; Celik, Cafer
    This work presents a mathematical modelling based approach including many constraints encountered at Universities in Turkey. As in many other countries also in Turkey it appears that universities are too autonomous, and they have medley of individual requirements and constraints. This condition makes it very difficult to suggest a generalized model and a solution algorithm for university timetabling problem (UTP). In general, in this paper it is aimed to design compatible and flexible approach to generate timetable so as to meet all the requirements of Turkish universities. First, by reviewing the studies in which mathematical modelling approaches were used, comprehensive information about the subject has been presented. Then, proposed hierarchical mathematical modelling approach is described (HMMA). Since (UTP) is highly context-dependent the results of this study couldn't been compared to those of the studies which are published already. Proposed approach is tested 2015-2016 academic year winter term data of Ataturk University Engineering Faculty and obtained results are presented comparatively with results obtained from manual preparation in terms of seven objectives.
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    An iterated greedy algorithm for the planning of yarn-dyeing boilers
    (Wiley, 2022) Demir, Yunus
    Yarn dyeing is a critical link in the textile production chain that consumes the most time and energy. Today's dyeing shops receive hundreds of demands with thousands of different colors, different due dates, and different production requirements. This situation has made it very difficult for the human brain to create a minimum-cost production plan by complying with the due dates. In this study, a real-life problem of a company operating in the textile industry is discussed and a solution has been developed for the planning of yarn-dyeing boilers. The application was held in Bursali Textile, which is the major towel manufacturer operating in Turkey. The problem dealt with is basically in the nature of the variable-size bin-packing problem (VSBPP). The limited availability of bins (boilers) of different sizes and the packing of the items (yarn work orders) with due date constraints are the original aspects of this study. Multi-objective mixed integer programming model is developed to minimize two objectives. For the solution, the preemptive method called the lexicographic approach, in which the objectives are solved in order, is preferred. As the first objective, the overcapacity usage is minimized and then the second objective, which is the boiler usage cost, is minimized. Given that the VSBPP is strongly NP-hard, an iterated greedy algorithm with two different decoding approaches is proposed. Computational experiments were conducted on 20 randomly generated benchmark instances and a real-world industrial dataset. The numerical results show that good solutions can be obtained in seconds using the proposed approaches.
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    A Novel Approach for Optimum Planning of Bobbin Boilers in Textile Industry
    (Ege Universitesi, 2022) Demir, Yunus; İnan, Kemal
    As in all sectors, the fierce competition in the world affects the textile sector deeply. It is an inevitable necessity for companies to reduce their costs in order to survive while maintaining their profitability. In this study, an applied efficiency study was conducted for the bobbin dyeing process, which is one of the important elements of the textile industry. In the application made in Bursah Tekstil Ltd. Sti., the problem of sequencing the lots waiting to be dyed in the bobbin dye boilers has been discussed. Integer linear model and iterative greedy-based heuristic are proposed to solve the problem. Sequencing made with the developed method resulted in an improvement of 17% in terms of the number of boiler washes and 13% in terms of total tardiness compared to the manual sequencing.
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    A Problem-Solving Environment to Teach Students Assembly Line Balancing Techniques
    (2019) Yılmaz, Hamid; Demir, Yunus
    Assembly line balancing is a production planning strategy that has been widely used in industrial applications. Most line balancing problems are known as nondeterministic polynomial time (NP-hard) problem, and they have different structures and solution methodology approaches. In this study, newly developed production planning software which is called Visual Assembly Line Balancing Software (VALBS) is introduced for educational purposes. The aim of the software is to support teaching activity for assembly line balancing techniques; facilitate understanding characteristics of different assembly lines and solution approaches, and enable to compare the results of them. The proposed VALBS is easy to use in various manufacturing environments, and suitable to support teaching line balancing procedures in undergraduate students. The software was used in classes of industrial and mechanical engineering students and feedbacks of students measured by Likert Scale survey. The results show that proposed visual software is an effective method to teach line balancing procedures.