Browsing by Author "Yaman, Hande"
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Item Open Access Bilkent Üniversitesi personel taşıma sistemi için etkin ve ekonomik çözüm(TMMOB Makina Mühendisleri Odası, 2004) Dinçerler, V. Alptekin; Güven, N. Engin; Tanrıkulu, M. Mustafa; Temel, Melih; Yitmen, Mehmet; Yaman, HandeBilkent Üniversitesi, personeline kampus ve şehrin çeşitli noktaları arasında taşıma hizmeti vermektedir. Bu amaçla kurulmuş olan ulaşım sisteminin ölçeği ve maliyeti oldukça büyüktür. Bu çalışmanın amacı bu hizmeti, hizmetin kalitesini ve personel memnuniyetini gözardı etmeksizin mümkün olan en düşük maliyetle sunmaktır. Çalışmanın temel unsurları, ulaşım sisteminin incelenmesi ve durak yerleri, güzergahlar ve her güzergahta kullanılacak taşıt cinsi hakkında eniyi çözümün bulunmasıdır. Araç olarak bir Coğrafi Bilgi Sistemleri (CBS) yazılımı olan ArcView GIS'den yararlanılmış ve geliştirilen sezgisel yöntemler bu yazılım üzerinde kodlanmıştır. Önerilen sistem ile maliyette %6.48 oranında azalma sağlanabilecektir. Ayrıca, inşa edilen metro ağının ulaşım sistemine getirebileceği iyileştirmeler de bu çalışmada incelenmiştir.Item Open Access A branch-and-bound algorithm for team formation on social networks(Institute for Operations Research and the Management Sciences (INFORMS), 2021) Berktaş, Nihal; Yaman, HandeThe team formation problem (TFP) aims to construct a capable team that can communicate and collaborate effectively. The cost of communication is quantified using the proximity of the potential members in a social network. We study a TFP with two measures for communication effectiveness; namely, we minimize the sum of communication costs, and we impose an upper bound on the largest communication cost. This problem can be formulated as a constrained quadratic set covering problem. Our experiments show that a general purpose solver is capable of solving small and medium-sized instances to optimality. We propose a branch-and-bound algorithm to solve larger sizes: we reformulate the problem and relax it in such a way that it decomposes into a series of linear set covering problems, and we impose the relaxed constraints through branching. Our computational experiments show that the algorithm is capable of solving large-size instances, which are intractable for the solver. Summary of Contribution: This paper presents an exact algorithm for the Team Formation Problem (TFP), in which the aim is, given a project and its required skills, to construct a capable team that can communicate and collaborate effectively. This combinatorial opti mization problem is modeled as a quadratic set covering problem. The study provides a novel branch-and-bound algorithm where a reformulation of the problem is relaxed so that it decomposes into a series of linear set covering problems and the relaxed constraints are imposed through branching. The algorithm is able to solve instances that are intractable for commercial solvers. The study illustrates an efficient usage of algorithmic methods and modelling techniques for an operations research problem. It contributes to the field of computational optimization by proposing a new application as well as a new algorithm to solve a quadratic version of a classical combinatorial optimization problem.Item 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, HandeBecause 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.Item Open Access Branch-and-price approaches for the network design problem with relays(Elsevier, 2018) Yıldız, B.; Karaşan, Oya Ekin; Yaman, HandeWith 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.Item Open Access Convex hull results for the warehouse problem(Elsevier B.V., 2018) Wolsey, L. A.; Yaman, HandeGiven an initial stock and a capacitated warehouse, the warehouse problem aims to decide when to sell and purchase to maximize profit. This problem is common in revenue management and energy storage. We extend this problem by incorporating fixed costs and provide convex hull descriptions as well as tight compact extended formulations for several variants. For this purpose, we first derive unit flow formulations based on characterizations of extreme points and then project out the additional variables using Fourier-Motzkin elimination. It turns out that the nontrivial inequalities are flow cover inequalities for some single node flow set relaxations.Item Open Access Damacana su pazar analizi ve dağıtım ağı tasarımı(TMMOB Makina Mühendisleri Odası, 2007) Ayabakan, Sezgin; Çelik, Ayşe; Erdoğan, Ezgi; Karakan, Ceylan; Koçak, Serkan; Konur, Dinçer; Yaman, HandeDamacana su pazarı Türkiye’de hızlı bir büyüme potansiyeline sahiptir. Coca Cola İçecek A.Ş. Mahmudiye su tesislerini satın alarak doğal kaynak suyu üretimine başlamıştır. Şirket Ankara’da Damla markası adı altında damacana suyu satmaya karar vermiştir. Bu çalışmada Damla damacana suyu için bir dağıtım ağı tasarımı yapılmıştır. Bunun için Ankara’daki damacana su satış potansiyeli saptanmış, açılacak olan bayilerin yerleri, hizmet alanları, kapasiteleri, gerekli işçi ve araç sayıları belirlenmiştir.Item Open Access Essays on some combinatorial optimization problems with interval data(1999) Yaman, HandeIn this study, we investigate three well-known problems, the longest path problem on directed acyclic graphs, the minimum spanning tree problem and the single machine scheduling problem with total flow time criterion, where the input data for all problems are given as interval numbers. Since optimal solutions depend on the realization of the data, we define new optimality concepts to aid decision making. VVe present characterizations for these “optimal” solutions and suggest polynomial time algorithms to find them in some special cases.Item 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 EkinWe 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.Item Open Access A hybrid polyhedral uncertainty model for the robust network loading problem(Springer, New York, 2011) Altın, A.; Yaman, Hande; Pınar, Mustafa Ç.; Gülpınar, G.; Harrison, P.; Rüstem, B.Item Open Access k-node-disjoint hop-constrained survivable networks: polyhedral analysis and branch and cut(Springer-Verlag France, 2018) Diarrassouba, I.; Mahjoub, M.; Mahjoub, A. R.; Yaman, HandeGiven a graph with weights on the edges, a set of origin and destination pairs of nodes, and two integers L ≥ 2 and k ≥ 2, the k-node-disjoint hop-constrained network design problem is to find a minimum weight subgraph of G such that between every origin and destination there exist at least k node-disjoint paths of length at most L. In this paper, we consider this problem from a polyhedral point of view. We propose an integer linear programming formulation for the problem for L ∈{2,3} and arbitrary k, and investigate the associated polytope. We introduce new valid inequalities for the problem for L ∈{2,3,4}, and give necessary and sufficient conditions for these inequalities to be facet defining. We also devise separation algorithms for these inequalities. Using these results, we propose a branch-and-cut algorithm for solving the problem for both L = 3 and L = 4 along with some computational results.Item Open Access Multi-stage stochastic programming for demand response optimization(Elsevier, 2020-02-19) Şahin, Munise Kübra; Çavuş, Özlem; Yaman, HandeThe increase in the energy consumption puts pressure on natural resources and environment and results in a rise in the price of energy. This motivates residents to schedule their energy consumption through demand response mechanism. We propose a multi-stage stochastic programming model to schedule different kinds of electrical appliances under uncertain weather conditions and availability of renewable energy. We incorporate appliances with chargeable and dischargeable batteries to better utilize the renewable energy sources. Our aim is to minimize the electricity cost and the residents’ dissatisfaction. We use a scenario groupwise decomposition (group subproblem) approach to compute lower and upper bounds for instances with a large number of scenarios. The results of our computational experiments show that the approach is very effective in finding high quality solutions in small computation times. We provide insights about how optimization and renewable energy combined with batteries for storage result in peak demand reduction, savings in electricity cost and more pleasant schedules for residents with different levels of price sensitivity.Item Open Access New exact solution approaches for the split delivery vehicle routing problem(Springer Verlag, 2018) Özbaygın, Gizem; Karasan, Oya Ekin; Yaman, HandeIn this study, we propose exact solution methods for the split delivery vehicle routing problem (SDVRP). We first give a new vehicle-indexed flow formulation for the problem and then a relaxation obtained by aggregating the vehicle-indexed variables over all vehicles. This relaxation may have optimal solutions where several vehicles exchange loads at some customers. We cut off such solutions, in a nontraditional way, either by extending the formulation locally with vehicle-indexed variables or by node splitting. We compare these approaches using instances from the literature and new randomly generated instances. Additionally, we introduce two new extensions of the SDVRP by restricting the number of splits and by relaxing the depot return requirement and modify our algorithms to handle these extensions.Item Open Access p-center problems(Springer, 2015) Çalık, Hatice; Labbé, M.; Yaman, Hande; Laporte, G.; Nickel, S.; Gama, F. S. daA p-center is a minimax solution that consists in a set of p points that minimizes the maximum distance between a demand point and a closest point belonging to that set. We present different variants of that problem. We review special polynomial cases, determine the complexity of the problems and present mixed integer linear programming formulations, exact algorithms and heuristics. Several extensions are also reviewed.Item Open Access The periodic vehicle routing problem with driver consistency(Elsevier, 2019) Rodríguez-Martín, I.; Salazar-González, J. -J.; Yaman, HandeThe Periodic Vehicle Routing Problem is a generalization of the classical capacitated vehicle routing problem in which routes are determined for a planning horizon of several days. Each customer has an associated set of allowable visit schedules, and the objective of the problem is to design a set of minimum cost routes that give service to all the customers respecting their visit requirements. In this paper we study a new variant of this problem in which we impose that each customer should be served by the same vehicle/driver at all visits. We call this problem the Periodic Vehicle Routing Problem with Driver Consistency. We present an integer linear programming formulation for the problem and derive several families of valid inequalities. We solve it using an exact branch-and-cut algorithm, and show computational results on a wide range of randomly generated instances.Item Open Access Shelter location and evacuation route assignment under uncertainty: a benders decomposition approach(INFORMS Inst.for Operations Res.and the Management Sciences, 2018) Bayram, V.; Yaman, HandeShelters are safe facilities that protect a population from possible damaging effects of a disaster. For that reason, shelter location and traffic assignment decisions should be considered simultaneously for an efficient evacuation plan. In addition, as it is very difficult to anticipate the exact place, time, and scale of a disaster, one needs to take into account the uncertainty in evacuation demand, the disruption/degradation of evacuation road network structure, and the disruption in shelters. In this study, we propose an exact algorithm based on Benders decomposition to solve a scenario-based two-stage stochastic evacuation planning model that optimally locates shelters and that assigns evacuees to shelters and routes in an efficient and fair way to minimize the expected total evacuation time. The second stage of the model is a second-order cone programming problem, and we use duality results for second-order cone programming in a Benders decomposition setting. We solve practical-size problems with up to 1,000 scenarios in moderate CPU times. We investigate methods such as employing a multicut strategy, deriving Pareto-optimal cuts, and using a preemptive priority multiobjective program to enhance the proposed algorithm. We also use a cutting plane algorithm to solve the dual subproblem since it contains a constraint for each possible path. Computational results confirm the efficiency of our algorithms.Item Open Access Stochastic lot sizing problem with nervousness considerations(Elsevier, 2018) Koca, E.; Yaman, Hande; Aktürk, M. SelimIn this paper, we consider the multistage stochastic lot sizing problem with controllable processing times under nervousness considerations. We assume that the processing times can be reduced in return for extra cost (compression cost). We generalize the static and static-dynamic uncertainty strategies to eliminate setup oriented nervousness and control quantity oriented nervousness. We restrict the quantity oriented nervousness by introducing a new concept called promised production amounts, and considering new range constraints and a nervousness cost function. We formulate the problem as a second-order cone mixed integer program (SOCMIP), and apply the conic strengthening. We observe the continuous mixing set substructure in our formulation that arises due the controllable processing times. We reformulate the problem by using an extended formulation for the continuous mixing set and solve the problem by a branch-and-cut approach. The computational experiments indicate that the reformulation reduces the root gaps and this helps to solve the problem in less computation times. Moreover, in our computational experiments we investigate the impact of new restrictions, specifically the additional cost of eliminating the setup oriented nervousness, on the total costs and the system nervousness. Our computational results clearly indicate that we could significantly reduce the nervousness costs and generate more stable production schedules with a relatively small increase in the total cost.Item Open Access A stochastic programming approach for Shelter location and evacuation planning(EDP Sciences, 2018) Bayram, V.; Yaman, HandeShelter location and traffic allocation decisions are critical for an efficient evacuation plan. In this study, we propose a scenario-based two-stage stochastic evacuation planning model that optimally locates shelter sites and that assigns evacuees to nearest shelters and to shortest paths within a tolerance degree to minimize the expected total evacuation time. Our model considers the uncertainty in the evacuation demand and the disruption in the road network and shelter sites. We present a case study for a potential earthquake in Istanbul. We compare the performance of the stochastic programming solutions to solutions based on single scenarios and mean values