3,916 research outputs found
On the single assignment p-Hub center problem
Cataloged from PDF version of article.We study the computational aspects of the single-assignment p-hub center problem on the basis of a basic model and a new model. The new model's performance is substantially better in CPU time than different linearizations of the basic model. We also prove the NP-Hardness of the problem. (C) 2000 Elsevier Science B.V. All rights reserved
A new model for the hazardous waste location-routing problem
Cataloged from PDF version of article.Hazardous waste management involves the collection, transportation, treatment and disposal of hazardous wastes. In this paper a new multiobjective location-routing model is proposed. Our model also includes some constraints, which were observed in the literature but were not incorporated into previous models. The aim of the proposed model is to answer the following questions: where to open treatment centers and with which technologies, where to open disposal centers, how to route different types of hazardous waste to which of the compatible treatment technologies, and how to route waste residues to disposal centers. The model has the objective of minimizing the total cost and the transportation risk. A large-scale implementation of the model in the Central Anatolian region of Turkey is presented. © 2005
The P-Hub maximal covering problem and extensions for gradual decay functions
Cataloged from PDF version of article.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. (C) 2015 Elsevier Ltd. All rights reserved
The latest arrival hub location problem for cargo delivery systems with stopovers
Cataloged from PDF version of article.In this paper, we concentrate on the service structure of ground-transportation based cargo delivery companies. The
transient times that arise from nonsimultaneous arrivals at hubs (typically spent for unloading, loading, and sorting operations)
can constitute a significant portion of the total delivery time for cargo delivery systems. The latest arrival hub location
problem is a new minimax model that focuses on the minimization of the arrival time of the last item to arrive, taking
into account journey times as well as the transient times at hubs. We first focus on a typical cargo delivery firm operating in
Turkey and observe that stopovers are essential components of a ground-based cargo delivery system. The existing formulations
of the hub location problem in the literature do not allow stopovers since they assume direct connections between
demand centers and hubs. In this paper, we propose a generic mathematical model, which allows stopovers for the latest
arrival hub location problem. We improve the model using valid inequalities and lifting. We present computational results
using data from the US and Turkey.
2007 Elsevier Ltd. All rights reserved
Designing emergency response networks for hazardous materials transportation
Cataloged from PDF version of article.Undesirable consequences of dangerous goods incidents can be mitigated by quick arrival of specialized response
teams at the accident site. We present a novel methodology to determine the optimal design of a specialized team
network so as to maximize its ability to respond to such incidents in a region. We show that this problem can be
represented via a maximal arc-covering model.We discuss two formulations for the maximal arc-covering problem,
a known one and a new one. Through computational experiments, we establish that the known formulation has
excessive computational requirements for large-scale problems, whereas the alternative model constitutes a basis
for an efficient heuristic. The methodology is applied to assess the emergency response capability to transport
incidents, that involve gasoline, in Quebec and Ontario. We point out the possibility of a significant improvement
via relocation of the existing specialized teams, which are currently stationed at the shipment origins.
2005 Elsevier Ltd. All rights reserved
Release Time Scheduling and Hub Location for Next-Day Delivery
Cataloged from PDF version of article.Inspired by a real-life problem faced by one of the largest ground-based cargo companies of Turkey, the current study
introduces a new facet to the hub location literature. The release time scheduling and hub location problem aims to select a
specified number of hubs from a fixed set of demand centers, to allocate each demand center to a hub, and to decide on the
release times of trucks from each demand center in such a way that the total amount of cargo guaranteed to be delivered
to every potential destination by the next day is not below a threshold and the total routing cost is minimized. The paper
introduces integer programming models to solve this problem in the special cases when the cargo uniformly arrives to each
demand center during the day and the more realistic pattern of when the cargo arrivals exhibit a piecewise linear form.
Several classes of valid inequalities are proposed to strengthen the formulations. Extensions with multiple service levels
and discrete sets for release times are also discussed. Computational results show the computational viability of the models
under realistic scenarios as well as the validity of the proposed problems in answering several interesting questions from
the cargo sector’s perspective
A new formulation approach for location routing problems
Cataloged from PDF version of article.A Location-Routing Problem (LRP) combines two difficult problems, facility location and vehicle routing, and as such it is inherently hard to solve. In this paper, we propose a different formulation approach than the common arc-based product-flow (Arc-BPF) approach in the literature. We associate product amounts to the nodes of the network resulting in a node-based product-flow (Node-BPF) formulation. Our main objective is to develop LRP models with fewer constraints and variables, which can be solved more efficiently. To introduce the proposed approach, we reformulate a complex four-index Arc-BPF LRP model from the literature as a three-index Node-BPF model, which computationally outperforms the former. We then introduce a heuristic method
Distribution network design on the battlefield
Cataloged from PDF version of article.Ammunition, whether it be an arrow in the middle ages, a lead bullet in the 1800s, or a laser guided smart bomb today, has been the most prominent factor in determining the outcome of combat. Failing to supply the required amount of ammunition properly may lead to defeat. Our main objective in this study is to provide a decision support tool that can help plan ammunition distribution on the battlefield. We demonstrate through an extensive literature review that the existing models are not capable of handling the specifics of the problem in this study. To this end, we propose a novel three-layer commodity-flow location routing formulation that distributes multiple products, respects hard time windows, allows demand points to be supplied by more than one vehicle or depot, and locates facilities at two different layers. We derive several valid inequalities to speed up the solution time of our model, illustrate the performance of the model in several realistically sized scenarios, and report encouraging results. Finally, we introduce a dynamic model that designs the distribution system in consecutive time periods for the entire combat duration. © 2010 Wiley Periodicals, Inc. Naval Research Logistics 58: 188–209, 201
Multimodal hub location and hub network design
Cataloged from PDF version of article.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
A tabu-search based heuristic for the hub covering problem over incomplete hub networks
Cataloged from PDF version of article.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
- …