Araştırma Çıktıları / Research Outcomes
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Publication An Optimization Approach for a Fresh Food Supply Chain: An Application for the Orange Supply Chain Design in Turkey(2021) Gürkan Güven GÜNER Durdu Hakan UTKU; Güner, Gürkan Güven; Utku, Durdu Hakan; Türk Hava Kurumu Üniversitesi Mühendislik Fakültesi, Endüstri Mühendisliği Bölümü, Ankara Türkiye Türk Hava Kurumu Üniversitesi Mühendislik Fakültesi, Endüstri Mühendisliği Bölümü, Ankara TürkiyeThe optimization of supply chain problems in various industry areas is crucial in terms of controlling the quality of the products and costs during the supply chain processes. Protecting and controlling the quality of the product in the food supply chain processes while minimizing the cost is a difficult and critical problem in the food industry. In this study, an application of a model that integrates the quality of the food in decision-making on distribution and production in a food supply chain is implemented using real-life data in Turkey. The degradation of quality of products in storage or transportation is usually based on the storage temperature, storage time, and other constants such as activation energy. Therefore, prediction for the quality of food products is a complex task because of the dynamics of storage conditions and various product characteristics. A methodological approach is proposed to model the degradation of food quality in this study. The rate of quality degradation of food products is evaluated by the proposed approach. A mixed-integer programming model is developed for the optimization of distribution and production planning. To solve the problem, GAMS (General Algebraic Modeling System) CPLEX solver is used as an optimization tool. The results of the case study shows that the suggested model in this study is implementable to the problem with acceptable solution time. In addition, the suggested model is adaptable for different types of food supply chains. This study aims to develop a methodological approach that can be used as a guide for decision-makers.Publication An Inventory Optimization Model for a Textile Manufacturing Company(Ankara Yildirim Beyazit Universitesi, 2022-12-31) Adem PINAR; Utku, Durdu Hakan; Kasimoğlu, FatihInventory management is a crucial issue in most businesses from factories in industry to small and large organizations in the production or service sector. A company should determine an optimum inventory level between excessive inventory that takes up physical space, costs much, and lack of inventory which disrupts the supply chain causing unavailability of the product that makes customers change their idea and buy from another supplier. In this study, we first classify the items that the company manufactures by using ABC analysis and develop a mathematical model to minimize total cost to enable a better inventory management. We use ABC analysis method to evaluate products in a textile company in terms of importance and to track these products according to their priorities. Accordingly, we propose a mixed integer programming model to determine production quantities and inventory levels with minimum cost. The results shows that the company in concern can improve its total production and inventory costs by 3.8 percent.Publication A MIXED-INTEGER PROGRAMMING MODEL FOR THE JOB SCHEDULING PROBLEM IN A PRODUCTION COMPANY(Stratejik Arastirmalar ve Verimlilik Genel Mudurlugu Verimlilik Dergisi, 2022-01-31) Durdu Hakan UTKU; Karanfil ÖZYİĞİT; Esra Yağmur FARİZOĞLU; Utku, Durdu HakanPurpose: In this study, a mixed-integer programming model is developed to minimize the total lateness and total completion time of the jobs in an automotive company. In order to respond rapidly to the continuous customer demand through the production, the work schedule of engineers in the research and development department is considered flexibly. Methodology: In the study, the mixed-integer programming model is supported by the analytical hierarchy process model to determine the weighted values of total tardiness and total completion times. The developed model is applied to the automotive company using the real data and the problem is solved using the GAMS CPLEX 24.1.3 software. Findings: In this job scheduling problem, the total completion time is decreased to 622 hours from 10149 hours, maximum tardiness is decreased to 9 hours from 104 hours and total tardiness is decreased to 13 hours from 860 hours by using the proposed model. Originality: The proposed model is used for the job scheduling purpose in compliance with the structure of the automotive industry company using the machine scheduling modeling principles and Analytical Hierarchy Process together. Keywords: Parallel Machine Scheduling, Optimization, Mixed Integer Programming, Analytical Hierarchical Process.Publication AN ERGONOMIC CLASSROOM DESIGN APPLICATION AT A UNIVERSITY IN TURKEY(Stratejik Arastirmalar ve Verimlilik Genel Mudurlugu Verimlilik Dergisi, 2021-09-29) Durdu Hakan UTKU; Gürkan Güven GÜNER; Göktuğ ALTUĞ; Anıl GÜNEY; Utku, Durdu Hakan; Güner, Gürkan GüvenPurpose: Ergonomics is a branch of science that uses scientific methods to improve the workplaces and environments to maximize the comfort and safety of humans. In this study, we suggest new classroom furniture dimensions defining the problems about environmental factors in the classrooms such as noise, light, air conditioning, or temperature by considering the real data obtained from a university. Methodology: A questionnaire is prepared to determine the most complained problems by the students about the classroom furniture and environment. A total of 219 students participate in the questionnaire at a university in Ankara, Turkey. The dissatisfaction scores are evaluated for each question to define the most complained problems. Findings: The results show that most of the students are not satisfied with the use of tablet-armed chairs due to different reasons. To solve the problems, the anthropometric measurements of the students are evaluated. Based on these measurements, new furniture dimensions are suggested and compared with the existing ones. Originality: The ergonomic classroom design in this study is an original work that is designed according to the data obtained from the university in concern. It is aimed that the implemented methodology and the comprehensive literature review for the ergonomic classroom design in this study can be a source of inspiration for the educational institutions.Publication The hazardous waste location and routing problem: an application in Marmara Region in Turkey(Springer Science and Business Media LLC, 2020-01-30) Durdu Hakan Utku; Serpil Erol; Utku, Durdu HakanPublication A mathematical model on liquefied natural gas supply chain with uncertain demand(Springer Science and Business Media LLC, 2020-08-11) Durdu Hakan Utku; Betül Soyöz; Utku, Durdu HakanPublication An Application: A Model with Sequence Dependent Setup Times for Parallel Machines for the Die House Station in a White Goods Manufacturing Company(Osmaniye Korkut Ata Universitesi, 2021-03-02) Selin KASIMOĞLU; Gülce DEMİR; Berrak Pınar YAZ; Durdu Hakan UTKU; Utku, Durdu HakanExcessive buffer inventory may disrupt production and constitute one of the main problems. One of the ways of coping with the inventory problems in the mass production lines is to achieve and implement a detailed production schedule. In this study, a company with a mass production line in the white goods sector is in consideration. A mixed-integer programming model with sequence-dependent setup times has been developed to solve the excessive work in process problems for the dye house station in a white goods sector company. The developed model has been applied to the company to test the model by using real data and the problem has been solved by using the General Algebraic Modeling System (GAMS) CPLEX 24.1 solver.Publication Parametric and non-parametric tests for the evaluation of interlaminar fracture toughness of polymer composites(SAGE Publications, 2020-11-17) Hande Yavuz; Durdu Hakan Utku; Utku, Durdu HakanThis study is based on the statistical analysis of interlaminar fracture toughness of various laminated polymer composites used in aerospace applications through parametric and non-parametric tests. Tukey’s, Dunkan’s, two-sample t-test, and Kolmogorov–Smirnov tests are used to analyze tensile mode interlaminar fracture toughness of various fiber-reinforced polymer composites obtained by beam theory, modified beam theory, and modified compliance calibration method. Among the studied composite samples, modified compliance calibration method provided the highest average interlaminar fracture toughness, whereas the modified beam theory showed the lowest one. Room temperature cured carbon fiber-reinforced composite samples exhibited higher interlaminar fracture toughness than the autoclave cured samples. Two-sample t-test show that all methods are found coherent with each other in terms of being significantly different. On the contrary, Kolmogorov–Smirnov test revealed no significant difference. Besides, Tukey’s and Duncan’s tests exhibited almost the same results in regard to significant differences except those obtained by the modified compliance calibration method. Two-sample t-test method should have to be performed in order to observe significant relations rather than Kolmogorov–Smirnov test, since the results of Tukey’s and Duncan’s tests are only consistent with each other for the beam theory and modified beam theory method.Publication Improving Bottlenecks: An Automotive Company Application(European Journal of Science and Technology, 2022-04-16) Gizem SUBAŞI; Utku, Durdu Hakan; Kasimoğlu, FatihPublication An Application: A Multi-Mode Natural Gas and Liquefied Natural Gas Supply Chain Management Problem(Elsevier BV, 2022-08-17) Durdu Hakan UTKU; Utku, Durdu HakanNatural Gas (NG) and Liquefied Natural Gas (LNG) are environmentally friendly and price-competitive energy resources that can be used in every part of the world. In this study, we develop a mixed-integer programming model for the NG and LNG supply chain that includes the location of liquefaction plants, regasification units, storage facilities, and distribution hubs together with the routing of the vehicles for inland distribution of LNG and cryogenic vessels for sea transportation. Unlike other models in the literature, the location of the NG and LNG facilities and routing of vehicles of different modes are optimized by considering the minimization of costs by using the 𝜺 – Constraint method, and different transportation modes, like sea, road, and pipeline, are used together for better effectiveness and cost reduction. The developed model is applied to Turkey to check whether the model is viable for real-world systems