Browsing by Subject "Hub location problem"

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Open Access
Benders decomposition algorithms for two variants of the single allocation hub location problem
(Springer, 2019) Ghaffarinasab, N.; Kara, Bahar Y.
The hub location problem (HLP) is a special type of the facility location problem with numerous applications in the airline industry, postal services, and computer and telecommunications networks. This paper addresses two basic variants of the HLP, namely the uncapacitated single allocation hub location problem (USAHLP) and the uncapacitated single allocation p-hub median problem (USAp HMP). Exact solution procedures based on Benders decomposition algorithm are proposed to tackle large sized instances of these problems. The standard Benders decomposition algorithm is enhanced through implementation of several algorithmic refinements such as using a new cut disaggregation scheme, generating strong optimality cuts, and an efficient algorithm to solve the dual subproblems. Furthermore, a modern implementation of the algorithm is used where a single search tree is established for the problem and Benders cuts are successively added within a branch-and-cut framework. Extensive computational experiments are conducted to examine the efficiency of the proposed algorithms. We have been able to solve all the instances of the problems from all three main data sets of the HLP to optimality in reasonable computational times.
Open Access
A hub covering model for cargo delivery systems
(Wiley, 2007) Tan, Pınar Z.; Kara, Bahar Y.
The hub location problem appears in a variety of applications including airline systems, cargo delivery systems, and telecommunication network design. When we analyze the application areas separately, we observe that each area has its own characteristics. In this research we focus on cargo delivery systems. Our interviews with various cargo delivery firms operating in Turkey enabled us to determine the constraints, requirements, and criteria of the hub location problem specific to the cargo delivery sector. We present integer programming formulations and large-scale implementations of the models within Turkey. The results are compared with the current structure of a cargo delivery firm operating in Turkey.
Open Access
Hub location problem for air-ground transportation sistems with time restrictions
(2006) Elmastaş, Seda
In this thesis, we study the problem of designing a service network for cargo delivery sector. We analyzed the structure of cargo delivery firms in Turkey and identified the features of the network. Generally, in the literature only one type of vehicle is considered when dispatching cargo. However, our analysis showed that in some cases both planes and trucks are used for a better service quality. Therefore, we seek a design in which all cargo between origin and destinations is delivered with minimum cost using trucks or planes within a given time bound. We call the problem “Time Constrained Hierarchical Hub Location Problem (TCHH)” and propose a model for it. The model includes some non-linear constraints. After linearizations, the TCHH is solved with data taken from cargo delivery firms. The computational results are reported and comparison with the current structure of a cargo delivery firm is given.
Open Access
The latest arrival hub location problem
(Institute for Operations Research and the Management Sciences (INFORM), 2001) Kara, B. Y.; Tansel, B. Ç.
The traditionally studied hub location problems in the literature pay attention to flight times but not to transient times spent at hubs for unloading, loading, and sorting operations. The transient times may constitute a significant portion of the total delivery time for cargo delivery systems. We focus on the minimization of the arrival time of the last arrived item in cargo delivery systems and develop a model that correctly computes the arrival times by taking into account both the flight times and the transient times. Nonlinear and linear integer formulations are given and computational results are provided. The effects of delays on the system performance are analyzed.
Open Access
Modeling and analysis of issues in hub location problem
(1999) Kara, Bahar Yetiş
The hub location problem has been around for more than 10 years. The first mathematical model was formulated by O’Kelly (1986) which is a quadratic integer program. Since then, nearly all of the researchers in this area have concentrated on developing ’good’ linearizations. However, there are many aspects of the problem that need to be analyzed. In this dissertation, we investigate some of these issues. We first study the application areas of the hub location problem and clarify the underlying assumptions of the real world problems which lead to the customarily defined hub location problem. We identify a certain problem characteristic of cargo delivery systems, which is one of the major application areas of the hub location problem, which is not satisfactorily modeled by means of the customarily defined hub location models. We propose a new hub location model that captures the specific requirements that are particular to cargo delivery systems. Another issue that we concentrate on is the identification, modeling and analysis of the hub location problem under different performance measures, namely minimax and covering criteria. We propose new integer programming models for the hub location problem under minimax and covering objectives. Both of the new models are the result of a different way of approaching the problem and their computational performance is far more superior than the performance of the various linearizations of the basic models proposed for these problems in the literature.
Open Access
Modeling and heuristic approaches for the Hub covering problem over incomplete Hub networks
(2009) Çalık, Hatice
Hubs are the accumulation points within the transportation and the telecommunication networks that collect and distribute the flow or data, which is originated from a starting point and needs to be transferred to a destination point. The main application areas of the hub location problem are airline systems, telecommunication network design and cargo delivery systems. In the literature, a common treatment of hub location problems is under the classification dating back to the location literature. In this classification, four different types are identified. Namely, the p-hub median problem, the hub location problem with fixed costs, the p-hub center problem, and the hub covering problem in the literature. In most of the hub location studies, the hub networks are assumed to be complete; however, the observations on the real life cases showed that this may not be the case. Therefore, in this thesis, we relax this assumption and focus on the single allocation version of the hub covering problem over incomplete hub networks. We propose two new mathematical formulations and a tabu search based heuristic algorithm for this problem. We perform several computational experiments on the formulations with the CAB data set from the literature and a larger scale network corresponding to the cities in Turkey. The results we obtained from our experimentations reveals that designing incomplete hub networks to provide service within a given service time bound is cost effective in accordance with designing complete hub networks.
Open Access
The P-Hub maximal covering problem and extensions for gradual decay functions
(Elsevier, 2015) Peker, M.; Kara, B. Y.
The p-hub maximal covering problem aims to find the best locations for hubs so as to maximize demands within a coverage distance with a predetermined number of hubs. Classically, the problem is defined in the framework of binary coverage only; an origin-destination pair is covered if the cost (time, etc.) is lower than the critical value, and not covered at all if the cost is greater than the critical value. In this paper, we extend the definition of coverage, introducing "partial coverage", which changes with distance. We present new and efficient mixed-integer programming models that are also valid for partial coverage for single and multiple allocations. We present and discuss the computational results with different data sets.
Open Access
P-hub maximal covering problem and extensions for gradual decay functions
(2013) Peker, Meltem
Hubs are special facilities that serve as switching, transshipment and sorting nodes in many to many distribution systems. The hub location problem deals with the selection of the locations of hub facilities and finding assignments of demand nodes to hubs simultaneously. The p-hub maximal covering problem, that is one of the variations of the hub location problems, aims to find locations of hubs so as to maximize the covered demand that are within the coverage distance with a predetermined number of hubs. In the literature of hub location, p-hub maximal covering problem is conducted in the framework of only binary coverage; origin-destination pairs are covered if the total path length is less than coverage distance and not covered at all if the path length exceeds the coverage distance. Throughout this thesis, we extend the definition of coverage and introduce “partial coverage” that changes with the distance, to the hub location literature. In this thesis, we study the p-hub maximal covering problem for single and multiple allocations and provide new formulations that are also valid for partial coverage. The problems are proved to be NP-Hard. We even show that assignment problem with a given set of hubs for the single allocation version of the problem is also NP-Hard. Computational results for all the proposed formulations with different data sets are presented and discussed.
Open Access
Spatial analysis of single allocation hub location problems
(Springer, 2016) Peker, M.; Kara, B. Y.; Campbell, J. F.; Alumur, S. A.
Hubs are special facilities that serve as switching, transshipment and sorting nodes in many-to-many distribution systems. Flow is consolidated at hubs to exploit economies of scale and to reduce transportation costs between hubs. In this article, we first identify general features of optimal hub locations for single allocation hub location problems based on only the fundamental problem data (demand for travel and spatial locations). We then exploit this knowledge to develop a straightforward heuristic methodology based on spatial proximity of nodes, dispersion and measures of node importance to delineate subsets of nodes likely to contain optimal hubs. We then develop constraints for these subsets for use in mathematical programming formulations to solve hub location problems. Our methodology can also help narrow an organization’s focus to concentrate on more detailed and qualitative analyses of promising potential hub locations. Results document the value of including both demand magnitude and centrality in measuring node importance and the relevant tradeoffs in solution quality and time.
Open Access
The stratified p-hub center and p-hub maximal covering problems
(Elsevier Ltd, 2022-02-01) Yetiş Kara, Bahar; Ghaffarinasab, N.; Campbell, J. F.
Hub networks are the foundation of many transportation and distribution systems, and real-world hub networks often transport freight or passengers of different service classes. This paper introduces the stratified multiple allocation p-hub center and p-hub maximal covering problems where the traffic corresponding to each origin–destination (O/D) pair is divided into different strata each having a specific service level requirement. The problems are formulated as mixed-integer linear programming (MILP) models and efficient Benders decomposition algorithms are developed for solving large instances. Extensive computational experiments are conducted to demonstrate the efficiency of the proposed mathematical models and the solution algorithms. MILP formulations are also proposed for the generalized versions of the problems that include fixed set-up costs for hubs and hub arcs. Results indicate that the optimal sets of hub locations and hub arcs when considering different strata can be quite dissimilar to those of the traditional p-hub center or p-hub maximal covering problem, but are similar to those of hierarchical hub location problems. Furthermore, models are provided and solved for multi-modal stratified hub location problems with fixed setup costs for hubs and hub arcs. Optimal results show a wide range of network topologies that can be generated, as compared to the classical versions.