Browsing by Author "Alumur, S. A."

Now showing 1 - 7 of 7

Open Access
The design of single allocation incomplete hub networks
(Elsevier, 2009) Alumur, S. A.; Kara, B. Y.; Karasan, O. E.
The hub location problem deals with finding the location of hub facilities and allocating the demand nodes to these hub facilities so as to effectively route the demand between any origin-destination pair. In the extensive literature on this challenging network design problem, it has widely been assumed that the subgraph induced by the hub nodes is complete. Relaxation of this basic assumption constitutes the starting point of the present work. In this study, we provide a uniform modeling treatment to all the single allocation variants of the existing hub location problems, under the incomplete hub network design. No network structure other than connectivity is imposed on the induced hub network. Within this context, the single allocation incomplete p-hub median, the incomplete hub location with fixed costs, the incomplete hub covering, and the incomplete p-hub center network design problems are defined, and efficient mathematical formulations for these problems with O (n3) variables are introduced. Computational analyses with these formulations are presented on the various instances of the CAB data set and on the Turkish network.
Open Access
Hierarchical multimodal hub location problem with time-definite deliveries
(Elsevier, 2012) Alumur, S. A.; Yaman, H.; Kara, B. Y.
Hierarchical multimodal hub location problem is a cost-minimizing hub covering problem where two types of hubs and hub links, accounting for ground and air transportation, are to be established, while ensuring time-definite deliveries. We propose a mixed-integer programming formulation and perform a comprehensive sensitivity analysis on the Turkish network. We show that the locations of airport hubs are less sensitive to the cost parameters compared to the locations of ground hubs and it is possible to improve the service quality at not much additional cost in the resulting multimodal networks. Our methodology provides the means for a detailed trade-off analysis.
Open Access
Multimodal hub location and hub network design
(2012) Alumur, S. A.; Kara, B. Y.; Karasan O. E.
Through observations from real life hub networks, we introduce the multimodal hub location and hub network design problem. We approach the hub location problem from a network design perspective. In addition to the location and allocation decisions, we also study the decision on how the hub networks with different possible transportation modes must be designed. In this multimodal hub location and hub network design problem, we jointly consider transportation costs and travel times, which are studied separately in most hub location problems presented in the literature. We allow different transportation modes between hubs and different types of service time promises between origin– destination pairs while designing the hub network in the multimodal problem. We first propose a linear mixed integer programming model for this problem and then derive variants of the problem that might arise in certain applications. The models are enhanced via a set of effective valid inequalities and an efficient heuristic is developed. Computational analyses are presented on the various instances from the Turkish network and CAB data set.
Open Access
Perspectives on modeling hub location problems
(Elsevier, 2020-10-02) Alumur, S. A.; Campbell, J. F.; Contreras, I.; Yetiş Kara, Bahar; Marianov, V.; O’Kelly, M. E.
The aim of this paper is to provide insights for better modeling hub location problems to help create a road map for future hub location research. We first present a taxonomy to provide a framework for the broad array of hub location models, and then seek to identify key gaps in the literature that provide opportunities for better models. We provide some new perspectives in several areas, including the historical evolution of hub location research, models for economies of scale, and relevant characteristics of different applications. We also provide a succinct summary of state-of-the-art formulation and solution approaches. We conclude with a set of themes that can be addressed in the future for better modeling hub location problems.
Open Access
Recent advances in location analysis
(Elsevier Ltd, 2015) Alumur, S. A.; Kara, B. Y.
[No abstract available]
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
A tabu-search based heuristic for the hub covering problem over incomplete hub networks
(Elsevier, 2009) Calık H.; Alumur, S. A.; Kara, B. Y.; Karasan, O. E.
Hub location problems deal with finding the location of hub facilities and with the allocation of demand nodes to these located hub facilities. In this paper, we study the single allocation hub covering problem over incomplete hub networks and propose an integer programming formulation to this end. The aim of our model is to find the location of hubs, the hub links to be established between the located hubs, and the allocation of non-hub nodes to the located hub nodes such that the travel time between any origin-destination pair is within a given time bound. We present an efficient heuristic based on tabu search and test the performance of our heuristic on the CAB data set and on the Turkish network.