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Öğe A Comprehensive Analysis on the Iterated Greedy Algorithm(Igdir University, 2021) Demir, YunusGenerally, optimization is the achievement of the best result under certain constraints. Basically, the approaches developed for the solution of optimization problems are examined under two groups as exact solution methods and approximate solution methods. Exact solution methods guarantee the optimum, but they cannot produce solutions in an acceptable time for large-scale real-life problems of NP-Hard. Therefore, the researchers draw great attention to the meta-heuristic methods, which are one of the approximate solution methods, because they can provide quality solutions at an acceptable time. In this study, a detailed analysis of the iterative greedy algorithm, which is an easy-to-apply and effective meta-heuristic, was conducted. In the relevant meta-heuristic, each operator is discussed under subheadings. Iterative greedy algorithm approaches developed for various problems are presented to the reader with their advantages and disadvantages. In summary, in this study, it is aimed to contribute to the Turkish literature about the iterative greedy algorithm, which has many aspects in common with various meta-heuristics such as taboo, annealing simulation, and iterative local search.Öğe A New Mathematical Model for Assembly Line Worker Assignment and Balancing(Igdir University, 2019) Yılmaz, Hamid; Demir, YunusAim of assembly line balancing is to assign the product parts to the workstations that constitute the assembly line. Worker assignment problem is a new problem variety in assembly lines that typically is met in different situations in which the workforce is not homogeneous. This problem is different from the well-known simple assembly line balancing problem from the view point of task execution times of nonhomogeneous workers. In this paper, we introduce a new mathematical formulation with objective function to minimize the cycle time for the assembly line worker assignment and balancing problem (ALWABP). GUROBI solver is used for the problem solution. The mathematical model is examined by using a standard test problem set. As a result of the experiments, it is observed that the proposed mathematical model is more effective in terms of solution quality and CPU time than the current mathematical method.Öğe A Novel Approach for Optimum Planning of Bobbin Boilers in Textile Industry(Ege Universitesi, 2022) Demir, Yunus; İnan, KemalAs 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.Öğe A Problem-Solving Environment to Teach Students Assembly Line Balancing Techniques(2019) Yılmaz, Hamid; Demir, YunusAssembly 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.Öğe An Application on Flexible Job Shop Scheduling Problem with Iterated Greedy Algorithm(Igdir University, 2021) Demir, YunusOptimization is the selection of the best possible solution (min / max) under certain criteria. For the solution of optimization problems; many approaches have been developed in different classes such as exact solution methods, approximation methods, meta-heuristic techniques. However, the enormous size of real-life problems have led researchers to meta-heuristic techniques that provide acceptable solutions in a short time. In this study, an application has been made with the iterated greedy algorithm, which stands out with its simple structure. Flexible job shop scheduling problem is addressed for application. Basically, the iterative greedy algorithm starts the optimization process with a single solution. The current solution then enters the construction-destruction phase to find a better solution. The solution obtained after this stage is replaced with the incumbent solution according to the previously determined acceptance criteria. This cycle, which consists of two operators, construction and destruction, continues until a certain stopping criterion is met. In this study, a problem-specific critical path-based approach was developed in the construction-destruction phase. In addition, a novel approach based on the acceptance of solutions of decreasing quality depending on the number of iterations is proposed. The aim of this study is to contribute to the limited Turkish literature on the application of meta-heuristic algorithms in various fields.Öğe An efficient lexicographic approach to solve multi-objective multi-port fabric dyeing machine planning problem(Elsevier, 2023) Demir, YunusIn this study, the fabric dyeing process in a towel manufacturing factory is investigated, focusing on the batching of towel fabric bolts with different quantities and features belonging to different orders in multi-port dyeing machines. This research differs from previous studies in several aspects. Firstly, it is considered three different objectives: total tardiness, total number of washes (sequence-dependent setups), and total machine fixed cost. These objectives have not been simultaneously optimized in previous studies, making our approach unique. Secondly, we adopt a lexicographic optimization approach to prioritize these objectives according to the company's requirements. This allows to find solutions that are optimal in terms of one objective while satisfying the constraints imposed by the other objectives. Lastly, it is proposed a novel lexicographic multi-objective genetic algorithm, which extends the traditional single-objective genetic algorithm, to effectively solve large-sized problems. Overall, our study not only addresses a real-life problem in the textile industry but also introduces innovative techniques and approaches for optimizing multiple objectives in a scheduling context. & COPY; 2023 Elsevier B.V. All rights reserved.Öğe An iterated greedy algorithm for the planning of yarn-dyeing boilers(Wiley, 2024) Demir, YunusYarn 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.Öğe Bir süpermarket zincirinde iki seviyeli tedarikçi yönetimli stok problemi için etkili bir sezgisel yöntem(2023) Demir, Yunus; Keskin, Muhammed EmreBu çalışmada, yüksek müşteri talebi değişkenliği ile karşı karşıya olan bir zincir marketin gerçek hayat sevkiyat problemine odaklanılmıştır. Firma, mağazalarını bulundukları bölgelere göre gruplandırmış ve her mağaza grubunun ikmali için bir dağıtım merkezi (DM) oluşturmuştur. Düzenli aralıklarla bu DM’lerden kendine bağlı olan mağazalara ikmal yapılmaktadır. Mevcut durumda firma, mağazalardan gelen yüksek talep değişkenliğine cevap verebilmek için çok yüksek sözleşme maliyetleri pahasına DM’lerdeki işçi sayısını artırıp azaltmaktadır. Buna rağmen mağazaların talepleri zamanında karşılanamamakta ve satış kaybı yaşanmaktadır. Bu çalışmada, değişkenliğin getirdiği bu olumsuz etkileri minimize etmek üzere DM’ler için sevkiyat planı oluşturulması problemi ele alınmıştır. Önce problemin doğrusal programlama modeli geliştirilmiştir. Büyük boyutlu örnekler için geliştirilen model cevap vermediğinden çözüm için iki farklı sezgisel önerilmiştir. Ayrıştırma (decomposition) yaklaşımı olarak isimlendirilen ilk yöntemde, geliştirilen model her mağaza için ayrı ayrı uygulanmıştır. İkinci sezgisel yaklaşımda problem ulaştırma modeline dönüştürülerek ele alınmıştır. Çözüm için iki aşamalı bir yöntem benimsenmiştir. Önerilen çözüm yöntemlerinin etkinliği, çeşitli boyutlardaki test verisi kullanarak karşılaştırmalı bir şekilde sunulmuştur. Elde edilen sonuçlar önerilen ulaştırma modeli temelli yaklaşımın devasa boyutlardaki gerçek hayat problemlerine kabul edilebilir zamanda ve her hangi bir ticari çözücüye ihtiyaç duymaksızın kaliteli çözümler üretebildiğini göstermiştir.Öğe BULANIK TOPSIS YÖNTEMİYLE TÜRKİYE’NİN YERLİ OTOMOBİLİ İÇİN EN UYGUN FABRİKA YERİNİN SEÇİMİ(2019) Yıldız, Aytaç; Demir, YunusGirişimciler 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.Öğe HIERARCHICAL MATHEMATICAL MODELLING APPROACH FOR A CASE STUDY IN UNIVERSITY TIMETABLING(Yildiz Technical Univ, 2019) Demir, Yunus; Celik, CaferThis 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.Öğe Mathematical Programming with C#.NET(Fevzullah TEMURTAŞ, 2021) Demir, YunusMathematical programming (optimization) is the expression of decision problems with mathematical equations. In this study, tools used for solving mathematical models are introduced. In particular, solution tools that should serve as embedded in various C#.Net software projects, namely software libraries, are mentioned. These libraries are effective tools for building and solving mathematical models like writing ordinary .NET code. In addition, providing access to more than one solver with the same syntax brings these tools to the fore in mathematical optimization. In the continuation of the study, the Google OR-Tools library, which is offered free of charge, is mentioned in detail. Solvers in the Or-Tools library and some solvers accessible by this library are tested with a sample problem and their solution speeds are presented in a comparative way. It is thought that this study, which is intended to contribute to the Turkish literature, will be beneficial for both practical life practitioners and theorists.
