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    A Multi-Objective Perspective to Satellite Design and Reliability Optimization
    (Pergamon-Elsevier Science Ltd, 2024) Tetik, Taha; Daş, Gülesin Sena; Birgören, Burak
    Development of a communication satellite project is highly complicated and expensive which costs a few hundred million dollars depending on the mission in space. Once a satellite is launched into orbit, it has to operate in harsh environmental conditions including radiation, solar activity, meteorites, and extreme weather patterns. Since there is no possibility of physical maintenance intervention in space, reliability is a critical attribute for all space and satellite projects. Therefore, the redundancy philosophy and reliability measures are taken into account in the design phase of a satellite to prevent the loss of functionality in case of a failure in orbit. This study aims to optimize the payload design of a communication satellite by considering the system's reliability, power consumption and cost simultaneously. Since these objectives are conflicting in their nature, a multi-objective optimization approach is proposed. We offer a systematic approach to the satellite design by determining the best redundancy strategy considering contradictory objectives and onboard constraints in the multibillion-dollar satellite industry. The proposed approach promotes trade-offs and sensitivity analyses between cost, power consumption and system reliability in the early design phase of satellites using Compromise Programming. By using different sets of weights for the objectives in our model, it is possible to address different types of satellites depending on their mission and priorities. Because of the NP-Hard characteristics of the reliability optimization problem and the nonlinear equation in the proposed model, the Simulated Annealing algorithm is utilized to solve the problem. As a case analysis, the implementation is carried out on the design of a communication satellite system with active hot-standby and warm-standby onboard redundancy schemes. Results reveal that huge savings in million dollars can be attained as a result of approximately 5% reduction in reliability.
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    A set partitioning based goal programming model for the team formation problem
    (Wiley, 2022) Daş, Gülesin Sena; Altınkaynak, Büşra; Göçken, Tolunay; Türker, Ahmet Kürşad
    In this paper, we offer a multi-objective set-partitioning formulation for team formation problems using goal programming. Instead of selecting team members to teams, we select suitable teams from a set of teams. This set is generated using a heuristic algorithm that uses the social network of potential team members. We then utilize the proposed multi-objective formulation to select the desired number of teams from this set that meets the skill requirements. Therefore, we ensure that selected teams include individuals with the required skills and effective communication with each other. Two real datasets are used to test the model. The results obtained with the proposed solution are compared with two well-known approaches: weighted and lexicographic goal programming. Results reveal that weighted and lexicographic goal programming approaches generate almost identical solutions for the datasets tested. Our approach, on the other hand, mostly picks teams with lower communication costs. Even in some cases, better solutions are obtained with the proposed approach. Findings show that the developed solution approach is a promising approach to handle team formation problems.
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    A two-stage stochastic model for an industrial symbiosis network under uncertain demand
    (Elsevier Science Inc, 2024) Daş, Gülesin Sena; Yeşilkaya, Murat; Birgören, Burak
    Industrial Symbiosis (IS) networks are structures built by volunteer companies with the aim of exchanging unused or residual resources, benefiting all participating companies. The profitability of these volunteer companies is critical as it affects the sustainability of these networks. Fluctuations in a participating company's production level can potentially disrupt its network by altering the quantity and availability of wastes and by-products. In light of these considerations, we analyse the impact of fluctuations in demand for final products of the companies on company profitability, and waste and by-product usage. For this purpose, we formulated a two-stage stochastic programming model and solved it using the Sample Average Approximation (SAA) method. We tested our model on a theoretical IS network comprising companies in the forest products industry. The results demonstrate that companies in the network keep exchanging by-products and remain profitable despite uncertainties in demand. Consequently, we conclude that the established network exhibits resilience to demand fluctuations, which is an important aspect of its sustainability.
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    An intrusion detection system based on a hybrid tabu-genetic algorithm
    (Institute of Electrical and Electronics Engineers Inc., 2017) Bakour, Khaled; Daş, Gülesin Sena; Ünver, H. Murat
    In this paper, we proposed a framework for detecting network's intrusions using Genetic Algorithm (GA) with multiple criteria. First of all, we build an intrusion detection system (IDS) using a pure GA with multiple selection methods. Then, we proposed one of the few hybrid algorithms in the literature, which is hybridized using a GA and a Tabu search (TS) algorithm. The proposed hybrid algorithm and the pure GA were tested to detect malicious traffic using DARPA dataset. The test results revealed that the proposed hybrid algorithm gives a higher Detection Rate (DR) and Detection Accuracy (AC) compared to the pure GA. © 2017 IEEE.
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    Comparison of Fuzzy Solution Approaches for a Bilevel Linear Programming Problem
    (Springer Science and Business Media Deutschland GmbH, 2023) Altınkaynak, Büşra; Göçken, Tolunay; Yeşilkaya, Murat; Birgören, Burak; Daş, Gülesin Sena
    In this study, we consider solution approaches used to solve the proposed bilevel linear programming model for an Industrial Symbiosis network. We first solve this model with the well-known Karush-Kuch-Tucker (KKT) approach. However, transforming a bilevel programming model with the KKT approach increases the number of variables and constraints. For this reason, we use the fuzzy programming approach and the fuzzy goal programming approaches as alternatives to the KKT approach. Next, we compare the results of the KKT approach with these methods and examine the suitability of these approaches to solve our bilevel problem. Unlike previous studies, which claimed that fuzzy approaches mostly outperform the KKT approach, in our case, the best solution is obtained with the KKT approach. This is most probably because these approaches ignore the hierarchical nature of the problem. We believe that more research on fuzzy approaches is needed to evaluate the suitability of these approaches for solving bilevel programming problems. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.
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    KOBİ'lerde ekipman etkinliğinin iyileştirilmesinde TEE tabanlı yeni bir yaklaşım: bir ahşap işleme kuruluşunda uygulama
    (2017) Yasin, Mehmet Fatih; Daş, Gülesin Sena
    Bu çalışmada, Küçük ve Orta Ölçekli bir işletmede (KOBİ) ekipman etkinliğini arttırmak için ToplamEkipman Etkinliği (TEE) kavramına dayanan yeni bir yöntem sunulmuştur. Bilindiği üzere TEE'nin amacı,sistemdeki ekipman kayıplarını ortaya çıkararak ekipmanın üretkenliğinin arttırılmasına olanaksağlamaktır. Ancak, KOBİ'lerin bu araçtan faydalanmalarının önünde çeşitli güçlükler mevcuttur. Bunlarınbaşında KOBİ'lerin bu tür iyileştirme çalışmalarına zaman ve para ayırmada yaşadıkları güçlüklergelmektedir. Bu çalışmalar esnasında yaşanan bir diğer güçlük ise TEE uygulamasının faaliyet gösterilenendüstriye ve üretim ortamına göre değişiklik göstermesidir. Bu çalışmada, yukarıda bahsedilen güçlüklergöz önünde bulundurularak TEE tabanlı yeni bir yöntem önerilmiştir. Önerilen yöntem, (kısıtlı kaynaklarıolan) KOBİ'lerde yürütülen iyileştirme çalışmalarında "Hangi ekipmana ne kadar iyileştirmeyapılmalıdır?" sorusuna cevap vermeye çalışmaktadır. Bir ahşap işleme kuruluşunda uygulanan yöntemin,seçilen makinanın TEE değeri %64,7'den %72,4'e çıkardığı ve bunun seçilen hattın etkinliğini de olumluetkilediği gözlenmiştir.
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    Modeling an Industrial Symbiosis Network using Bilevel Programming
    (IEEE, 2021) Daş, Gülesin Sena; Yeşilkaya, Murat; Altınkaynak, Büşra; Birgören, Burak
    In this study, we propose a bilevel programming model for a theoretical industrial symbiosis network located in an Eco-Industrial Park. Plants in this forest products-based network comprising a sawmill, a plywood manufacturer, a particleboard producer, a fiberboard producer and a pellet producer aim to minimize their production related costs. On the other hand, the park authority aims to minimize the use of raw materials to foster by-product exchange in the park. Therefore, we propose a bilevel programming model where the park authority is the upper-level decision-maker/leader and the plants in the network are the lower-level decision makers/followers. Our aim is to investigate the effects of industrial symbiosis on emissions and the profitability of the companies. Results show only by decreasing raw material use, companies in such a network could stay profitable without increasing emissions.
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    Türkiye orman ürünleri sektörünün döngüsel ekonomi ve endüstriyel simbiyoz bağlamında değerlendirilmesi
    (2023) Yeşilkaya, Murat; Daş, Gülesin Sena; Yaşin, Mehmet Fatih
    Dünya nüfusunun artması ve teknolojik gelişmeler hızlı kentleşme ve sanayileşmeye yol açmıştır. Ancak artan sanayileşme nedeniyle ortaya çıkan çevre sorunları daha büyük bir endişe haline gelmiştir. Günümüzde birçok ülke, üretime bağlı çevre sorunlarını ortadan kaldırmak için Döngüsel Ekonomi politikalarıyla temiz ve sürdürülebilir üretimi desteklemektedir. Bu ülkeler, Döngüsel Ekonomi bağlamında çeşitli endüstrilerde Endüstriyel Simbiyoz (ES) uygulamalarını desteklemektedir. Orman ürünleri endüstrisi, Dünyadaki başarılı ES uygulamalarının odak noktasındaki sektörlerden biridir. Bu sektörün doğal hammaddelere bağımlılığı, orman varlığının yüksek olduğu ülkeler için bu sektörü daha kritik hale getirmiştir. Bu çalışmanın amacı Türkiye'deki orman ürünleri endüstrisinin ES’nin uygulanabilirliğini tartışmaktır. İlk olarak orman ürünleri endüstrisine dayalı Dünya'da yapılmış iyi ES uygulamalarını incelenmiştir. Ardından, bu ES ağlarındaki işbirlikleri ve potansiyel malzeme, yan ürün ve atık akışlarını belirlenmiştir. Bu değerlendirmenin ışığında, ES'nin Türk orman endüstrisi için uygulanabilirliğine ilişkin bir SWOT analizi sunulmuştur. SWOT analizi sonuçları, Türkiye orman ürünleri sektörüne dayalı ES ağları kurmanın mümkün olduğunu göstermektedir. Ancak işletmeler, ES hakkında farkındalık yaratarak bu ağlara katılmaya teşvik edilmelidir. Bu ağlara katılımı artırmak için vergi muafiyetleri, girdi fiyatlarında indirim gibi destekler tasarlanmalıdır.