DSpace Communidade:http://repositorio.ufla.br/jspui/handle/1/322018-02-18T20:13:40Z2018-02-18T20:13:40ZSistema de monitoramento e notificação de distúrbios na tensão elétrica para estações remotas de comunicação e Smart GridsGallo, Wesley Natanaelhttp://repositorio.ufla.br/jspui/handle/1/284472018-01-24T15:36:01Z2018-01-24T00:00:00ZTítulo: Sistema de monitoramento e notificação de distúrbios na tensão elétrica para estações remotas de comunicação e Smart Grids
Autor: Gallo, Wesley Natanael
Resumo: The increasing importance of mobile communication technologies in recent years can be noticed by the significant increase in the use of mobile devices such as smartphones, GPS navigators and monitoring devices that use wireless networks as communication platforms. The communication stations that support the operations of these networks, such as Wi-Fi, GSM and proprietary protocols with licensed frequencies, among others, often operate in remote locations, under adverse conditions, in which the electric energy networks are most vulnerable to failures and degradations. In this work, the development of a real-time system for monitoring and detecting disturbances on the electric network is proposed. The developed approach has the objective of supporting the remote communication stations, promoting the communication of flaws to the operators and integrating this scenario with the concept of Smart Grid. This project is based on the Arduino platform employed as a computer resource in the data gathering process and as a redundant communication with the use of Ethernet and GSM network interfaces. In order to measure the signals of the electric line with Arduino, a signal conditioning circuit was employed. To detect voltage disturbances, we used a method based on Euclidean distance. This method was implemented in the Arduino platform and real-time requirements were considered. In addition, we implemented a web interface for monitoring the energy quality with the use of graphs and for configuring parameters, such as detection sensitivity and notification criteria. The results showed efficiency in monitoring the quality of the electric energy and in the communication of the voltage disturbances. In addition, the redundant communication approach, using a private network and GSM, improves the reliability of flaws notification, resulting in another step towards integration with Smart Grids.2018-01-24T00:00:00ZLower bounds and exact algorithms for the quadratic minimum spanning tree problemPereira, Dilson LucasGendreau, MichelCunha, Alexandre Salles dahttp://repositorio.ufla.br/jspui/handle/1/156282017-11-06T19:46:34Z2015-11-01T00:00:00ZTítulo: Lower bounds and exact algorithms for the quadratic minimum spanning tree problem
Autor: Pereira, Dilson Lucas; Gendreau, Michel; Cunha, Alexandre Salles da
Resumo: We address the quadratic minimum spanning tree problem (QMSTP), the problem of finding a spanning tree of a connected and undirected graph such that a quadratic cost function is minimized. We first propose an integer programming formulation based on the reformulation–linearization technique (RLT). We then use the idea of partitioning spanning trees into forests of a given fixed size and obtain a QMSTP reformulation that generalizes the RLT model. The reformulation is such that the larger the size of the forests, the stronger lower bounds provided. Thus, a hierarchy of formulations is obtained. At the lowest hierarchy level, one has precisely the RLT formulation, which is already stronger than previous formulations in the literature. The highest hierarchy level provides the convex hull of integer feasible solutions for the problem. The formulations introduced here are not compact, so the direct evaluation of their linear programming relaxation bounds is not practical. To overcome that, we introduce two lower bounding procedures based on Lagrangian relaxation. These procedures are embedded into two parallel branch-and-bound algorithms. As a result of our study, several instances in the literature were solved to optimality for the first time.2015-11-01T00:00:00ZBranch-and-cut and branch-and-cut-and-price algorithms for the adjacent only quadratic minimum spanning tree problemPereira, Dilson LucasGendreau, MichelCunha, Alexandre Salles dahttp://repositorio.ufla.br/jspui/handle/1/156272017-11-06T19:34:14Z2015-01-01T00:00:00ZTítulo: Branch-and-cut and branch-and-cut-and-price algorithms for the adjacent only quadratic minimum spanning tree problem
Autor: Pereira, Dilson Lucas; Gendreau, Michel; Cunha, Alexandre Salles da
Resumo: The quadratic minimum spanning tree problem (QMSTP) consists of finding a spanning tree of a graph G such that a quadratic cost function is minimized. In its adjacent only version (AQMSTP), interaction costs only apply for edges that share an endpoint. Motivated by the weak lower bounds provided by formulations in the literature, we present a new linear integer programming formulation for AQMSTP. In addition to decision variables assigned to the edges, it also makes use of variables assigned to the stars of G. In doing so, the model is naturally linear (integer), without the need of implementing usual linearization steps, and its linear programming relaxation better estimates the interaction costs between edges. We also study a reformulation derived from the new model, obtained by projecting out the decision variables associated with the stars. Two exact solution approaches are presented: a branch-and-cut-and-price algorithm, based on the first formulation, and a branch-and-cut algorithm, based on its projection. Our computational results indicate that the lower bounds introduced here are much stronger than previous bounds in the literature. Being designed for the adjacent only case, our duality gaps are one order of magnitude smaller than the Gilmore–Lawler lower bounds for AQMSTP. As a result, the two exact algorithms introduced here outperform the previous exact solution approaches in the literature. In particular, the branch-and-cut method we propose managed to solve AQMSTP instances with as many as 50 vertices to proven optimality.2015-01-01T00:00:00ZA comparison of several models for the hamiltonian p-median problemGollowitzer, StefanGouveia, LuisLaporte, GilbertPereira, Dilson LucasWojciechowski, Adamhttp://repositorio.ufla.br/jspui/handle/1/156102017-10-31T17:49:04Z2014-07-01T00:00:00ZTítulo: A comparison of several models for the hamiltonian p-median problem
Autor: Gollowitzer, Stefan; Gouveia, Luis; Laporte, Gilbert; Pereira, Dilson Lucas; Wojciechowski, Adam
Resumo: The Hamiltonian p-median problem consists of determining p disjoint cycles of minimum total cost covering all vertices of a graph. We present several new and existing models for this problem, provide a hierarchy with respect to the quality of the lower bounds yielded by their linear programming relaxations, and compare their computational performance on a set of benchmark instances. We conclude that three of the models are superior from a computational point of view, two of which are introduced in this article2014-07-01T00:00:00Z