Browsing by Author "Karaşan, Oya Ekin"

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Open Access
A branch-and-cut algorithm for the alternative fuel refueling station location problem with routing
(INFORMS, 2019) Arslan, O.; Karaşan, Oya Ekin; Mahjoub, A. R.; Yaman, Hande
Because of the limited range of alternative fuel vehicles (AFVs) and the sparsity of the available alternative refueling stations (AFSs), AFV drivers cooperatively deviate from their paths to refuel. This deviation is bounded by the drivers’ tolerance. Taking this behavior into account, the refueling station location problem with routing (RSLP-R) is defined as maximizing the AFV flow that can be accommodated in a road network by locating a given number of AFSs while respecting the range limitation of the vehicles and the deviation tolerance of the drivers. In this study, we develop a natural model for the RSLP-R based on the notion of length-bounded cuts, analyze the polyhedral properties of this model, and develop a branch-and-cut algorithm as an exact solution approach. Extensive computational experiments show that the algorithm significantly improves the solution times with respect to previously developed exact solution methods and extends the size of the instances solved to optimality. Using our methodology, we investigate the tradeoffs between covered vehicle flow and deviation tolerance of the drivers and present insights on deviation characteristics of drivers in a case study in California.
Open Access
Branch-and-price approaches for the network design problem with relays
(Elsevier, 2018) Yıldız, B.; Karaşan, Oya Ekin; Yaman, Hande
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.
Open Access
Cirosu düşük perakende noktalarına Unilever ürünlerinin dağıtımı için karma sistem tasarımı
(TMMOB Makina Mühendisleri Odası, 2007) Körpeoğlu, Ersin; Nadar, Emre; Bozkaya, Efe Burak; Sever, Derya; Karaşan, Oya Ekin
Unilever’in doğrudan ulaşamadığı düşük potansiyelli ama sayıca fazla perakendecilere Unilever ürünlerini ulaştırmayı amaçlayan bu projede, öncelikle bu noktalara hizmet vermeyi engelleyen etkenler belirlenmiştir. Başta yüksek ulaşım maliyetleri olmak üzere sistemdeki bu etkenleri ortadan kaldırmak amacıyla, firmanın istekleri doğrultusunda bir karma dağıtım sistemi tasarlanmıştır. Sıcak satış, telefonla satış ve depodan satış bölümlerinden oluşan bu sistem; doğrusal olmayan tamsayılı programlama tekniğiyle modellenmiş ve tanımlanan ek kısıtlar ile doğrusal hale getirilmiştir. Problemin boyutunun büyük olması nedeniyle CPLEX ile doğrudan çözülemeyen modelimiz için buluşsal bir algoritma geliştirilmiştir. Buluşsal algoritmanın başarısını ölçmek amacıyla model, kesin olarak çözülebildiği 37 tane koşturum örneği için buluşsal algoritma ile kıyaslanmış; buluşsal algoritmanın en iyi değerinin modelin en iyi değerinden ortalama %14.6 saptığı, 37 koşturumun 14’ünde algoritmanın en iyi hedef değerini verdiği gözlemlenmiştir. Modelleme sürecinde rassal olmadığı kabul edilen parametrelerin benzetim çalışması aracılığıyla rassal olduğu durumun ele alınmasıyla, modelin belirsizlik içeren durumlarda da işlevselliğini koruduğu gösterilmiştir. Veritabanı ve müşteri kartı tasarımı gibi yan uygulamalarla da desteklenen proje, firma yönetimi tarafından pilot uygulamaya alınmıştır. Sonuç olarak firmaya karlı ve esnek bir dağıtım kanalı oluşturulmuş ve düşük potansiyelli perakende noktalarına düşük maliyetle ulaşım sağlanmıştır.
Open Access
Hub location, routing, and route dimensioning: strategic and tactical intermodal transportation hub network design
(Institute for Operations Research and the Management Sciences (INFORMS), 2021-10) Yıldız, Barış; Yaman, Hande; Karaşan, Oya Ekin
We propose a novel hub location model that jointly eliminates some of the traditional assumptions on the structure of the network and on the discount as a result of economies of scale in an effort to better reflect real-world logistics and transportation systems. Our model extends the hub literature in various facets: instead of connecting nonhub nodes directly to hub nodes, we consider routes with stopovers; instead of connecting pairs of hubs directly, we design routes that can visit several hub nodes; rather than dimensioning pairwise connections, we dimension routes of vehicles; and rather than working with a homogeneous fleet, we use intermodal transportation. Decisions pertinent to strategic and tactical hub location and transportation network design are concurrently made through the proposed optimization scheme. An effective branch-and-cut algorithm is developed to solve realistically sized problem instances and to provide managerial insights.
Open Access
On envy-free perfect matching
(Elsevier, 2019) Arbib, C.; Karaşan, Oya Ekin; Pınar, Mustafa
Consider a situation in which individuals –the buyers –have different valuations for the products of a given set. An envy-free assignment of product items to buyers requires that the items obtained by every buyer be purchased at a price not larger than his/her valuation, and each buyer’s welfare (difference between product value and price) be the largest possible. Under this condition, the problem of finding prices maximizing the seller’s revenue is known to be APX -hard even for unit-demand bidders (with several other inapproximability results for different variants), that is, when each buyer wishes to buy at most one item. Here, we focus on Envy-free Complete Allocation, the special case where a fixed number of copies of each product is available, each of the n buyers must get exactly one product item, and all the products must be sold. This case is known to be solvable in O(n4) time. We revisit a series of results on this problem and, answering a question found in Leonard (1983), show how to solve it in O(n3) time by connections to perfect matchings and shortest paths.
Open Access
Radio Communications Interdiction Problem under deterministic and probabilistic jamming
(Elsevier, 2019) Tanergüçlü, Türker; Karaşan, Oya Ekin; Akgün, I.; Karaşan, Ezhan
The Radio Communications Interdiction Problem (RCIP) seeks to identify the locations of transmitters on the battlefield that will lead to a robust radio communications network by anticipating the effects of intentional radio jamming attacks used by an adversary during electronic warfare. RCIP is a sequential game defined between two opponents that target each other’s military units in a conventional warfare. First, a defender locates a limited number of transmitters on the defender’s side of the battlefield to optimize the relay of information among its units. After observing the locations of radio transmitters, an attacker locates a limited number of radio jammers on the attacker’s side to disrupt the communication network of the defender. We formulate RCIP as a binary bilevel (max–min) programming problem, present the equivalent single level formulation, and propose an exact solution method using a decomposition scheme. We enhance the performance of the algorithm by utilizing dominance relations, preprocessing, and initial starting heuristics. To reflect a more realistic jamming representation, we also introduce the probabilistic version of RCIP where a jamming probability is associated at each receiver site as a function of the prevalent jamming to signal ratios leading to an expected coverage of receivers as an objective function. We approximate the nonlinearity in the jamming probability function using a piecewise linear convex function and solve this version by adapting the decomposition algorithm constructed for RCIP. Our extensive computational results on realistic scenarios show the efficacy of the solution approaches and provide valuable tactical insights.