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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6

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Department: search.filters.department.Department of Industrial EngineeringSubject: search.filters.subject.Engineering

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Now showing 1 - 8 of 8
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    PublicationOpen Access
    Branch-and-price approaches for the network design problem with relays
    (Elsevier, 2018) Karasan, Oya Ekin; Yaman, Hande; Department of Industrial Engineering; Yıldız, Barış; Faculty Member; Department of Industrial Engineering; College of Engineering; 258791
    With different names and characteristics, relays play a crucial role in the design of transportation and telecommunication networks. In transportation networks, relays are strategic locations where exchange of drivers, trucks or mode of transportation takes place. In green transportation, relays become the refuelling/recharging stations extending the reach of alternative fuel vehicles. In telecommunication networks, relays are regenerators extending the reach of optical signals. We study the network design problem with relays and present a multi-commodity flow formulation and a branch-and-price algorithm to solve it. Motivated by the practical applications, we investigate the special case where each demand has a common designated source. In this special case, we can show that there exists an optimal design that is a tree. Using this fact, we replace the multi-commodity flow formulation with a tree formulation enhanced with Steiner cuts. Employing a branch-and-price-and-cut schema on this formulation, we are able to further extend computational efficiency to solve large problem instances.
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    PublicationOpen Access
    Analysis of a group purchasing organization under demand and price uncertainty
    (Springer, 2018) Department of Business Administration; Department of Industrial Engineering; Tan, Barış; Karabağ, Oktay; Faculty Member; Resercher; Department of Business Administration; Department of Industrial Engineering; College of Administrative Sciences and Economics; College of Engineering; 28600; N/A
    Based on an industrial case study, we present a stochastic model of a supply chain consisting of a set of buyers and suppliers and a group purchasing organization (GPO). The GPO combines orders from buyers in a two-period model. Demand and price in the second period are random. An advance selling opportunity is available to all suppliers and buyers in the first-period market. Buyers decide how much to buy through the GPO in the first period and how much to procure from the market at a lower or higher price in the second period. Suppliers determine the amount of capacity to sell through the GPO in the first period and to hold in reserve in order to meet demand in the second period. The GPO conducts a uniform-price reverse auction to select suppliers and decides on the price that will be offered to buyers to maximize its profit. By determining the optimal decisions of buyers, suppliers, and the GPO, we answer the following questions: Do suppliers and buyers benefit from working with a GPO? How do the uncertainty in demand, the share of GPO orders in the advance sales market, and the uncertainty in price influence the players' decisions and profits? What are the characteristics of an environment that would encourage suppliers and buyers to work with a GPO? We show that a GPO helps buyers and suppliers to mitigate demand and price risks effectively while collecting a premium by serving as an intermediary between them.
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    PublicationOpen Access
    An empirical analysis of the main drivers affecting the buyer surplus in E-auctions
    (Taylor _ Francis, 2018) Department of Business Administration; Department of Industrial Engineering; Karabağ, Oktay; Tan, Barış; Faculty Member; Department of Business Administration; Department of Industrial Engineering; College of Administrative Sciences and Economics; College of Engineering; N/A; 28600
    We empirically examine the impacts of the product category, the auction format, the 2008 global financial crisis, the group purchasing, the contract type, the platform ownership, and the number of participating suppliers on the buyer surplus obtained from e-auctions. To this end, we collect a unique dataset from a purchasing organisation that offers e-auction solutions to its corporate customers. By using a standard Tobit model, we show that the product categories, the auction type, and the number of participating suppliers have significant effects on the decrease in the procurement prices with respect to the minimum of the initial submitted bids. It is observed that the 2008 global financial crisis led to an increase in the buyer surplus. We classify the product categories into three groups based on their impacts on the average of the decrease in the procurement prices. We show that the average decrease in procurement prices is higher for the group purchasing option than for the individual buying option. It is concluded that the types of contract between buyers and auctioneer and the platform ownership have no statistically significant effects on the average decrease in procurement prices.
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    PublicationOpen Access
    An improved lower bound on the competitive ratio of deterministic online algorithms for the multi-agent k-Canadian Traveler Problem
    (Finding Press, 2022) Shiri, Davood; Department of Industrial Engineering; Salman, Fatma Sibel; Faculty Member; Department of Industrial Engineering; College of Engineering; 178838
    We present an improved lower bound on the competitive ratio of deterministic online algorithms for the multi-agent k-Canadian Traveler Problem.
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    PublicationOpen Access
    Pricing and lot-sizing decisions for perishable products when demand changes by freshness
    (American Institute of Mathematical Sciences, 2021) Kaya, Onur; Department of Industrial Engineering; Bayer, Halit; Department of Industrial Engineering; Graduate School of Sciences and Engineering
    Perishable products like dairy products, vegetables, fruits, pharmaceuticals, etc. lose their freshness over time and become completely obsolete after a certain period. Customers generally prefer the fresh products over aged ones, leading the perishable products to have a decreasing demand function with respect to their age. We analyze the inventory management and pricing demand function. A stochastic dynamic programming model is developed in when and how much inventory to order and how to price these products considering their freshness over time. We prove the characteristics of the optimal solution of the developed model and extract managerial insights regarding the optimal inventory and pricing strategies. The numerical studies show that dynamic pricing can lead to signiffcant savings over static pricing under certain parameter settings. In addition, longer replenishment cycles are seen under dynamic pricing compared to static pricing, even though similar uantities are ordered in each replenishment.
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    PublicationOpen Access
    GoNDEF: an exact method to generate all non-dominated points of multi-objective mixed-integer linear programs
    (Springer, 2019) Department of Industrial Engineering; N/A; Türkay, Metin; Rasmi, Seyyed Amir Babak; Faculty Member; PhD Student; Department of Industrial Engineering; College of Engineering; Graduate School of Sciences and Engineering; 24956; N/A
    Most real-world problems involve multiple conflicting criteria. These problems are called multi-criteria/multi-objective optimization problems (MOOP). The main task in solving MOOPs is to find the non-dominated (ND) points in the objective space or efficient solutions in the decision space. A ND point is a point in the objective space with objective function values that cannot be improved without worsening another objective function. In this paper, we present a new method that generates the set of ND points for a multi-objective mixed-integer linear program (MOMILP). The Generator of ND and Efficient Frontier (GoNDEF) for MOMILPs finds that the ND points represented as points, line segments, and facets consist of every type of ND point. First, the GoNDEF sets integer variables to the values that result in ND points. Fixing integer variables to specific values results in a multi-objective linear program (MOLP). This MOLP has its own set of ND points. A subset of this set establishes a subset of the ND points set of the MOMILP. In this paper, we present an extensive theoretical analysis of the GoNDEF and illustrate its effectiveness on a set of instance problems.
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    PublicationOpen Access
    Crowd-shipping service network design problem
    (Pamukkale University / Pamukkale Üniversitesi, 2022) Department of Industrial Engineering; Yıldız, Barış; Faculty Member; Department of Industrial Engineering; College of Engineering; 258791
    With the rising concerns over the increasing costs and negative externalities of city logistics, the need for innovative approaches to come up with low-cost and environmentally friendly distribution systems is on the rise. One such innovative approach is crowd-shipping (CS). In this model, which aims to combine packet and passenger transfers to utilize redundant transportation capacity, the individuals who want to earn small compensations and/or help the environment are employed to carry out package transfers between service points on the paths of their already planned trips. In this study, we introduce the strategic level CS network design problem, which needs to be solved to determine the locations and the capacities of the service points in the urban area to establish an efficient CS delivery system. We propose a novel Benders Decomposition algorithm to solve this challenging problem that we model as a scenario-based two-stage stochastic integer program. The results of our comprehensive numerical experiments attest to the efficacy of the approach to solve practical size problem instances and provide significant managerial insights, showing that such a well-designed CS network can provide savings (in terms of both economic and environmental costs), even in the case of express package transfers with very stringent delivery lead time restrictions. In particular, our results show that by carefully choosing the locations and the capacities of the service points, it is possible to carry out a significant portion of express deliveries with the crowd provided delivery capacity (up to 56% in our experiments) without deploying a very large number of them (less than 60 in all our experiment) in the region, indicating the strong potential and applicability of the CS delivery systems in real world delivery operations. / Şehir içi dağıtım faaliyetlerinin artan maliyetleri ve neden olduğu sorunlar (trafik, çevre kirliliği, gürültü, araç kazaları, vb.) hakkında artan kaygılar, bu alanda yenilikçi yaklaşımlara olan ihtiyacı giderek artırmaktadır. Ön plana çıkan söz konusu yaklaşımlardan birisi de Kitle destekli dağıtım (KDD) modelidir. Yolcu ve paket taşımacılığını bütünleştirerek atıl araç kapasitelerinin faydalı bir şekilde kullanılmasını amaçlayan bu modelde, kişilerin küçük ekonomik kazançlar sağlamak ve/veya dağıtım faaliyetlerinin çevreye verdiği zararları azaltılmasına katkı sunmak amacıyla kendi seyahatleri sırasında yolları üzerindeki servis noktaları arasında paket taşımacılığı yapması öngörülmektedir. Bu çalışmada, KDD faaliyetlerinin etkin bir şekilde yürütebilmesi için gerekli olan servis noktalarının/paket otomatlarının şehrin hangi noktalarına hangi kapasiteler ile kurulması gerektiğini belirlemek için çözülmesi gereken stratejik seviye “KDD servis ağı tasarımı” problemini literatüre tanıtıyoruz. İki seviyeli, senaryo tabanlı belirsiz bir tamsayılı program olarak modellediğimiz problemin çözümü için etkin bir Benders Ayrıştırma algoritması önermekteyiz. Gerçekleştirdiğimiz geniş kapsamlı hesapsal çalışmalar geliştirdiğimiz çözüm yönteminin etkinliğini ortaya koymakta, önemli yönetimsel çıkarımlar sunmaktadır. Elde ettiğimiz sonuçlar, hızlı paket taşımacılığı gibi oldukça zorlu ve maliyetli (ekonomik ve çevresel) bir dağıtım faaliyeti için iyi tasarlanmış bir KDD modelinin önemli kazanımlar sağlayabileceğini göstermektedir. Nispeten küçük sayıda (çalıştığımız problem örneklerinde en fazla 60 adet) servis noktaları ile dağıtımların önemli bir kısmının (çalıştığımız problem örneklerinde %56’ya kadar) “kitle” tarafından yapıldığı etkin bir KDD sisteminin teşkil edilebileceğini gösteren bu sonuçlar, önerilen yenilikçi yaklaşımın uygulanabilirliği konusunda önemli ipuçları vermektedir.
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    PublicationOpen Access
    Supervised learning-based approximation method for single-server open queueing networks with correlated interarrival and service times
    (Taylor _ Francis, 2021) Department of Industrial Engineering; Department of Business Administration; N/A; Tan, Barış; Khayyati, Siamak; Faculty Member; Department of Industrial Engineering; Department of Business Administration; College of Engineering; College of Administrative Sciences and Economics; Graduate School of Sciences and Engineering; 28600; N/A
    Efficient performance evaluation methods are needed to design and control production systems. We propose a method to analyse single-server open queueing network models of manufacturing systems composed of delay, batching, merge and split blocks with correlated interarrival and service times. Our method (SLQNA) is based on using a supervised learning approach to determine the mean, the coefficient of variation, and the first-lag autocorrelation of the inter-departure time process as functions of the mean, coefficient of variation and first-lag autocorrelations of the interarrival and service times for each block, and then using the predicted inter-departure time process as the input to the next block in the network. The training data for the supervised learning algorithm is obtained by simulating the systems for a wide range of parameters. Gaussian Process Regression is used as a supervised learning algorithm. The algorithm is trained once for each block. SLQNA does not require generating additional training data for each unique network. The results are compared with simulation and also with the approximations that are based on Markov Arrival Process modelling, robust queueing, and G/G/1 approximations. Our results show that SLQNA is flexible, computationally efficient, and significantly more accurate and faster compared to the other methods.