Star p-hub median problem with modular arc capacities

Cataloged from PDF version of article.We consider the hub location problem, where p hubs are chosen from a given set of nodes, each nonhub node is connected to exactly one hub and each hub is connected to a central hub. Links are installed on the arcs of the resulting network to route the traffic. The aim is to find the hub locations and the connections to minimize the link installation cost.We propose two formulations and a heuristic algorithm to solve this problem. The heuristic is based on Lagrangian relaxation and local search.We present computational results where formulations are compared and the quality of the heuristic solutions are tested. 2007 Elsevier Ltd. All rights reserved

Solving Hub Network Problem Using Genetic Algorithm

This paper addresses a network problem that described as follows. There are n ports that interact, and p of those will be designated as hubs. All hubs are fully interconnected. Each spoke will be allocated to only one of available hubs. Direct connection between two spokes is allowed only if they are allocated to the same hub. The latter is a distinct characteristic that differs it from pure hub-and-spoke system. In case of pure hub-and-spoke system, direct connection between two spokes is not allowed. The problem is where to locate hub ports and to which hub a spoke should be allocated so that total transportation cost is minimum. In the first model, there are some additional aspects are taken into consideration in order to achieve a better representation of the problem. The first, weekly service should be accomplished. Secondly, various vessel types should be considered. The last, a concept of inter-hub discount factor is introduced. Regarding the last aspect, it represents cost reduction factor at hub ports due to economies of scale. In practice, it is common that the cost rate for inter-hub movement is less than the cost rate for movement between hub and origin/destination. In this first model, inter-hub discount factor is assumed independent with amount of flows on inter-hub links (denoted as flow-independent discount policy). The results indicated that the patterns of enlargement of container ship size, to some degree, are similar with those in Kurokawa study. However, with regard to hub locations, the results have not represented the real practice. In the proposed model, unsatisfactory result on hub locations is addressed. One aspect that could possibly be improved to find better hub locations is inter-hub discount factor. Then inter-hub discount factor is assumed to depend on amount of inter-hub flows (denoted as flow-dependent discount policy). There are two discount functions examined in this paper. Both functions are characterized by non-linearity, so there is no guarantee to find the optimal solution. Moreover, it has generated a great number of variables. Therefore, a heuristic method is required to find near optimal solution with reasonable computation time. For this reason, a genetic algorithm (GA)-based procedure is proposed. The proposed procedure then is applied to the same problem as discussed in the basic model. The results indicated that there is significant improvement on hub locations. Flows are successfully consolidated to several big ports as expected. With regards to spoke allocations, however, spokes are not fairly allocated

Air Taxi Skyport Location Problem for Airport Access

Witnessing the rapid progress and accelerated commercialization made in recent years for the introduction of air taxi services in near future across metropolitan cities, our research focuses on one of the most important consideration for such services, i.e., infrastructure planning (also known as skyports). We consider design of skyport locations for air taxis accessing airports, where we present the skyport location problem as a modified single-allocation p-hub median location problem integrating choice-constrained user mode choice behavior into the decision process. Our approach focuses on two alternative objectives i.e., maximizing air taxi ridership and maximizing air taxi revenue. The proposed models in the study incorporate trade-offs between trip length and trip cost based on mode choice behavior of travelers to determine optimal choices of skyports in an urban city. We examine the sensitivity of skyport locations based on two objectives, three air taxi pricing strategies, and varying transfer times at skyports. A case study of New York City is conducted considering a network of 149 taxi zones and 3 airports with over 20 million for-hire-vehicles trip data to the airports to discuss insights around the choice of skyport locations in the city, and demand allocation to different skyports under various parameter settings. Results suggest that a minimum of 9 skyports located between Manhattan, Queens and Brooklyn can adequately accommodate the airport access travel needs and are sufficiently stable against transfer time increases. Findings from this study can help air taxi providers strategize infrastructure design options and investment decisions based on skyport location choices.Comment: 25 page

Solving uncapacitated hub location problem using Hopfield-Tank type artificial neural networks

Merkez üslerin yerleşim noktalarının belirlenmesi ve merkez üsler ağının tasarlanmasını içeren merkez üslerin konumlandırılması problemi konum teorisi alanında yaygın olarak çalışılmaktadır. Bu çalışmada, kapasite sınırlamasının olmadığı, sabit konumlandırma maliyetlerinin olduğu, tek tahsisli merkez üsleri konumlandırma problemi için yapay sinir ağı (YSA) temelli bir çözüm yöntemi önerilmiştir. Ayrıca tavlama benzetimine dayanan bir yöntem de geliştirilmiştir. Yöntemin etkinliğini test etmek için, literatürde sıklıkla kullanılan test veri seti kullanılarak, YSA temelli yöntem için elde edilen sonuçlar ile literatürde yer alan en iyi çözümler ve tavlama benzetiminden elde edilen sonuçlar karşılaştırılmıştır.Anahtar Kelimeler: Merkez üsler, yapay sinir ağları, Hopfield-Tank, tavlama benzetimi. In many transportation and telecommunication networks, the cost of carrying a unit of traffic between two points decreases as the capacity of the connection joining the two points increases. It is possible to facilitate this connection by building dedicated channels between each pair of nodes that communicate with each other. However, this would result in higher costs. Because of this fact, it is often convenient to design networks in which traffic is concentrated on high capacity links, even if this traffic travels longer distances. In order to facilitate the flow of the traffic between nodes so as to decrease the overall cost of transportation, some centers known as hubs are introduced. Airline passenger flow, cargo or postal delivery networks, large telecommunication networks are examples of networks utilizing hubs. The problem addressed in this study is the uncapacitated single allocation hub location problem (USAHLP) in which, given n interacting nodes in a network, hubs are fully interconnected and each spoke is assigned to a unique hub. In this study, a solution method based on an artificial neural network framework for the USAHLP is introduced. The heuristic based on simulated annealing is also developed. To present its effectiveness, the solutions of this ANN-based method is compared with the best solutions presented in the literature and the solutions of simulated annealing based heuristic by considering CAB data set. Keywords: Hub location, artificial neural network, Hopfield-Tank, simulated annealing

The hierarchical hub median problem with single assignment

Cataloged from PDF version of article.We study the problem of designing a three level hub network where the top level consists of a complete network connecting the so-called central hubs and the second and third levels are unions of star networks connecting the remaining hubs to central hubs and the demand centers to hubs and central hubs, respectively. The problem is to decide on the locations of a predetermined number of hubs and central hubs and the connections in order to minimize the total routing cost in the resulting network. This problem includes the classical p-hub median problem as a special case. We also consider a version of this problem where service quality considerations are incorporated through delivery time restrictions. We propose mixed integer programming models for these two problems and report the outcomes of a computational study using the CAB data and the Turkey data. 2009 Elsevier Ltd. All rights reserved

The design of single allocation incomplete hub networks

Cataloged from PDF version of article.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 Oðn3Þ variables are introduced. Computational analyses with these formulations are presented on the various instances of the CAB data set and on the Turkish network. 2009 Elsevier Ltd. All rights reserved

Network hub locations problems: the state of the art

Cataloged from PDF version of article.Hubs are special facilities that serve as switching, transshipment and sorting points in many-to-many distribution systems. The hub location problem is concerned with locating hub facilities and allocating demand nodes to hubs in order to route the traffic between origin-destination pairs. In this paper we classify and survey network hub location models. We also include some recent trends on hub location and provide a synthesis of the literature. (C) 2007 Elsevier B.V. All rights reserved

Hub Location Problem with Allowed Routing between Nonhub Nodes

In this study, we relax one of the general assumptions in the hub location literature by allowing routed flows between nonhub nodes. In hub networks, different flows are consolidated and routed via collection, interhub, and distribution arcs. Due to consolidation, some flows travel long paths despite closeness of their origin and destination. In this study, we allow direct flows by penalizing by a scalar factor of original cost of transshipment between these arcs. We present mathematical models for median, center, and set covering versions of the problem for single- and multi-allocation cases. We test the models with the CAB and TR data sets. We discuss the properties of established direct connections for different models by using another mathematical model where the number of direct flows is bounded and interpret the effect of changes in problem parameters. © 2015 by The Ohio State University