Critical infrastructure systems are essential for the continuous functionality of modern global societies. Some examples of these systems include electric energy, potable water, oil and gas, telecommunications, and the internet. Different topologies underline the structure of these networked systems. Each topology (i.e., physical layout) conditions the way in which networks transmit and distribute their flow. Also, their ability to absorb unforeseen natural or intentional disruptions depends on complex relations between network topology and optimal flow patterns. Most of the current research on large networks is focused on understanding their properties using statistical physics, or on developing advanced models to capture network dynamics. Despite these important research efforts, almost all studies concentrate on specific networks. This network-specific approach rules out a fundamental phenomenon that may jeopardize the performance predictions of current sophisticated models: network response is in general interdependent, and its performance is conditioned on the performance of additional interacting networks. Although there are recent conceptual advances in network interdependencies, current studies address the problem from a high-level point of view. For instance, they discuss the problem at the macro-level of interacting industries, or utilize economic input-output models to capture entire infrastructure interactions. This study approaches the problem of network interdependence from a more fundamental level. It focuses on network topology, flow patterns within the networks, and optimal interdependent system performance. This approach also allows for probabilistic response characterization of interdependent networked systems when subjected to disturbances of internal nature (e.g., aging, malfunctioning) or disruptions of external nature (e.g., coordinated attacks, seismic hazards). The methods proposed in this study can identify the role that each network element has in maintaining interdependent network connectivity and optimal flow. This information is used in the selection of effective pre-disaster mitigation and post-disaster recovery actions. Results of this research also provide guides for growth of interacting infrastructure networks and reveal new areas for research on interdependent dynamics. Finally, the algorithmic structure of the proposed methods suggests straightforward implementation of interdependent analysis in advanced computer software applications for multi-hazard loss estimation.

Security analysis of a power system requires a process called contingency analysis that analyzes results from all possible single contingencies (i.e. outages) in the system. The process of contingency analysis requires the definition of a parameter that is used to monitor a certain aspect of the system, which is called a performance index. The performance index definitions used traditionally have been highly nonlinear, and the results have not accurately predicted the outcome of the performance index in some cases. These incorrect results are referred to as misrankings since the contingency results are usually placed in order of severity so that the most severe cases are evident. This thesis considers a new definition of contingency ranking using a more linearized definition of the performance index. The construction of both the new, proposed definition and the classic definition both consider the current loading of circuits in the system as compared to their rated values. Specifically, the parameter measured by the proposed definition measures the difference, while the more nonlinear definition uses a ratio of the two quantities, which is then raised to a higher power. A small, four bus test system is used to demonstrate the benefits of the new, more linearized definition. The average percent error for all single line contingencies of the system decreased by over 9.5% using the proposed definition as compared to the previous one. This decrease in error allows this performance index to monitor a similar parameter (comparing current loading and current rating of the lines) and achieve a higher degree of accuracy. Further linearization of this proposed definition also shows a reduction in the average percent error by an additional 22% so that when compared to the original, highly nonlinear definition, the average error is reduced by almost 30%. By linearizing the definition of the performance index, the results are more accurate and misrankings are less likely to occur from the security analysis process.

Understanding the behavior of complex, large-scale, interconnected systems in a rigorous and structured manner is one of the most pressing scientific and technological challenges of current times. These systems include, among many others, transportation and communications systems, smart grids and power grids, financial markets etc. Failures of these systems have potentially enormous social, environmental and financial costs. In this work, we investigate the failure mechanisms of load-sharing complex systems. The systems are composed of multiple nodes or components whose failures are determined based on the interaction of their respective strengths and loads (or capacity and demand respectively) as well as the ability of a component to share its load with its neighbors when needed. Each component possesses a specific strength (capacity) and can be in one of three states: failed, damaged or functioning normally. The states are determined based on the load (demand) on the component. We focus on two distinct mechanisms to model the interaction between components strengths and loads. The first, a Loss of Strength (LOS) model and the second, a Customer Service (CS) model. We implement both models on lattice and scale-free graph network topologies. The failure mechanisms of these two models demonstrate temporal scaling phenomena, phase transitions and multiple distinct failure modes excited by extremal dynamics. We find that the resiliency of these models is sensitive to the underlying network topology. For critical ranges of parameters the models demonstrate power law and exponential failure patterns. We find that the failure mechanisms of these models have parallels to failure mechanisms of critical infrastructure systems such as congestion in transportation networks, cascading failure in electrical power grids, creep-rupture in composite structures, and draw-downs in financial markets. Based on the different variants of failure, strategies for mitigating and postponing failure in these critical infrastructure systems can be formulated.

Thesis (Ph. D.)--Ohio State University, 2007. / Full text release at OhioLINK's ETD Center delayed at author's request

Orientador: Prof. Dr. Rafael de Mattos Grisi / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Mestrado Profissional em Matemática em Rede Nacional, 2014. / O presente trabalho tem por objetivo relacionar o estudo de Passeios Aleatórios em uma e duas dimensões com o funcionamento de redes elétricas, por meio de modelagem matemática, para que tal relação possa ser aplicada ao estudo de conteúdos relativos ao ensino da matemática no Ensino Médio, em especial no que se refere a Probabilidade, Matrizes e Funções. Visando uma melhor organização dos conceitos e conteúdos abordados, o trabalho foi dividido em quatro capítulos. No primeiro capítulo serão apresentados os conceitos de Passeios Aleatórios em uma e duas dimensões, abordando o estudo de funções hamrônicas e de representação matricial de uma função harmônica. No segundo capítulo veremos métodos de resolução de funções harmônicas, em especial os métodos de relaxamentos, fazendo uma descrição e gerando uma motivação para o estudo do método, e o método de reolução por cadeias de Markov. O terceiro capítulo relaciona os conceitos até então estudados com redes elétricas, apresentando redes elétricas em uma e em duas dimensões, e também dando uma interpretação de voltagem e corrente, para na sequência apresentar uma interpretação probabilística de ambos. Por fim, no quarto capítulo são apresentadas atividades que podem ser realizadas em sala de aula, com alunos do Ensino Médio, para o estudo de Passeios Aleatórios, de forma simples e rápida, visando sua efetiva utilização em sala de aula. / This work aims to relate the Random Walks study in one and two dimensions with the operation of electrical networks, through mathematical modeling, that such a relationship can be applied to the study of material related to the teaching of mathematics in high school, in particular refers to Probability, Arrays and functions. For a better organization of the concepts covered and content, the work was divided into four chapters. Random Walks in the first chapter of the concepts will be presented in one and two dimensions, addressing the study hamrÃ'nicas functions and matrix representation of a harmonic function. In the second chapter we resolution methods of harmonic functions, particularly the relaxation methods, thereby generating a description and a motivation for the study of the method and reolução method of Markov chains. The third chapter lists the concepts studied hitherto grids, grids having in one and in two dimensions, and also giving an interpretation of voltage and current in response to forward a probabilistic interpretation of both. Finally, in the fourth chapter contains activities that can be performed in the classroom, with high school students to the study of Random Walks, simply and quickly, for their effective use in the classroom.

Orientadores: Christiano Lyra Filho, Celso Cavellucci / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-15T22:07:38Z (GMT). No. of bitstreams: 1 Queiroz_LeonardoMendoncaOliveirade_D.pdf: 3480667 bytes, checksum: 8aad553487af6ac62325d7f0f0893d60 (MD5) Previous issue date: 2010 / Resumo: Este trabalho estuda a estimação de perdas técnicas na distribuição de energia elétrica e apresenta uma análise para a definição dos níveis adequados dessas perdas. Ambas as abordagens são focadas na regulação. É apresentada uma metodologia de estimação das perdas técnicas de energia baseada no valor médio e na variância dos pontos da curva de carga. Essa metodologia pode ser aplicada alternativamente aos métodos baseados na perda de potência máxima, que inserem imprecisões desnecessárias para a estimativa das perdas de energia. Foram desenvolvidos modelos de regressão para a estimação das perdas técnicas em redes de distribuição de média e baixa tensão, objetivando utilizar o mínimo de informações possíveis para uma precisão adequada. Uma metodologia de geração de redes foi desenvolvida para o estudo desses modelos, de forma a disponibilizar redes com características semelhantes às redes reais. Também são propostos aprimoramentos na estimativa das perdas em transformadores e ramais de ligação. Adicionalmente, é apresentada uma análise dos níveis adequados de perdas técnicas na distribuição, utilizando-se técnicas de engenharia e benchmarking. As propostas deste trabalho sugerem aprimoramentos na regulação das perdas técnicas, tornando o método de estimação das perdas mais preciso e introduzindo a análise de eficiência das distribuidoras. / Abstract: This work studies technical losses estimation in power distribution systems and analyses the adequacy of the losses. Both approaches are carried in a regulatory perspective. It is presented a methodology to estimate energy losses from the mean and the variance of the load curve points. This methodology can be applied in substitution of methods based on maximum power losses, which inserts unnecessary inaccuracy to the procedure. Regression models were developed to estimate technical losses in medium and low voltage distribution networks, aiming to require less information as possible to meet an appropriate accuracy. A methodology of networks generation was developed to make available networks with characteristics similar to the ones presented by real networks. Improvements in transformers and service conductors losses estimation were also proposed. Engineering and benchmarking techniques were applied to analyze technical losses adequacy. The proposals presented in this work may improve technical losses regulation, making the estimation of losses more accurate and introducing efficiency analysis of power distribution companies. / Doutorado / Automação / Doutor em Engenharia Elétrica

Peer-to-peer networks and mobile ad hoc networks are emerging distributed networks that share several similarities. Fundamental among these similarities is the decentralized role of each participating node to route messages on behalf of other nodes, and thereby, collectively realizing communication between any pair of nodes. Messages are routed on a topology graph that is determined by the peer relationship between nodes. Although routing is fairly straightforward when the topology graph is static, dynamic variations in the peer relationship that often occur in peer-to-peer and mobile ad hoc networks present challenges to routing. In this thesis, we examine the interplay between routing messages and network topology design in two classes of these networks -- unstructured peer-to-peer networks and sparsely-connected mobile ad hoc networks. In unstructured peer-to-peer networks, we add structure to overlay topologies to support file sharing. Specifically, we investigate the advantages of designing overlay topologies with small-world properties to improve (a) search protocol performance and (b) network utilization. We show, using simulation, that "small-world-like" overlay topologies where every node has many close neighbors and few random neighbors exhibit high chances of locating files close to the source of file search query. This improvement in search protocol performance is achieved while decreasing the traffic load on the links in the underlying network. In the context of sparsely-connected mobile ad hoc networks where nodes provide connectivity via mobility, we present a protocol for routing in space and time where the message forwarding decision involves not only where to forward (space), but also when to forward (time). We introduce space-time routing tables and develop methods to compute these routing tables for those instances of ad hoc networks where node mobility is predictable over either a finite horizon or indefinitely due to periodicity in node motion. Furthermore, when the node mobility is unpredictable, we investigate several forwarding heuristics to address the scarcity in transmission opportunities in these sparsely-connected ad hoc networks. In particular, we present the advantages of fragmenting messages and augmenting them with erasure codes to improve the end-to-end message delivery performance.

This dissertation focuses on the material transport system design problem (MTSDP), integrating decisions of technology selection and flow network design. This research is motivated by the design of material transport systems (MTS) in manufacturing plants. The objective is to design a MTS with minimum lifetime costs, subject to service requirements, flow network restrictions, and limited resources. We characterize the MTSDP from the perspectives of task requirements, transport technology, and space utilization. A classification is proposed for transport technologies such that instances in the same class share the same properties, and a decision framework is proposed to emphasize the inter-relationships of three major decisions: task clustering, network connecting, and technology selection. We consider fixed and variable costs, arc capacities, and empty travel in our formulations. We propose two solution approaches for the MTSDP. The first is the compact formulation (CF) approach where the three major decisions are handled by a mixed integer non-linear programming (MINLP) formulation. Relaxation techniques are applied to linearize the model. The solution of the resulting linear formulation (MILP) provides a lower bound to that of MINLP. A tightened formulation reduces the computational time by a factor of 3.85. The experiment also shows that when control system costs are significant, designs with multiple-task clusters are more economical than those restricted to single-task clusters. The other approach is clustering/set partition (CSP), where the three decisions are decomposed and solved sequentially. In an example MTS design problem, three methods are compared: CSP, a GREEDY approach from the literature, and enumeration. CSP finds the optimal solution, while GREEDY results in 31% greater costs. A similar comparison with another example is made for the CF and CSP approaches. We apply the CSP approach in a case problem, using data from an auto parts manufacturer. We include flow path crossing constraints and perform experiments to determine solution quality over a range of small problem sizes. The largest difference from optimality is 3.34%, and the average is 0.98%. More importantly, based on these experiments, it seems there is no evidence that the difference percentage grows with an increase in the number of tasks.

Wireless sensor networks (WSN) are event based systems that rely on the collective effort of densely deployed sensor nodes continuously observing a physical phenomenon. The spatio-temporal correlation between the sensor observations and the cross-layer design advantages are significant and unique to the design of WSN. Due to the high density in the network topology, sensor observations are highly correlated in the space domain. Furthermore, the nature of the energy-radiating physical phenomenon constitutes the temporal correlation between each consecutive observation of a sensor node. This unique characteristic of WSN can be exploited through a cross-layer design of communication functionalities to improve energy efficiency of the network. In this thesis, several key elements are investigated to capture and exploit the correlation in the WSN for the realization of advanced efficient communication protocols. A theoretical framework is developed to capture the spatial and temporal correlations in WSN and to enable the development of efficient communication protocols. Based on this framework, spatial Correlation-based Collaborative Medium Access Control (CC-MAC) protocol is described, which exploits the spatial correlation in the WSN in order to achieve efficient medium access. Furthermore, the cross-layer module (XLM), which melts common protocol layer functionalities into a cross-layer module for resource-constrained sensor nodes, is developed. The cross-layer analysis of error control in WSN is then presented to enable a comprehensive comparison of error control schemes for WSN. Finally, the cross-layer packet size optimization framework is described.

Made available in DSpace on 2016-12-12T17:38:35Z (GMT). No. of bitstreams: 1 Ana Teruko.pdf: 11607034 bytes, checksum: 72b3906b42ad639d1abd56a8054d9ffe (MD5) Previous issue date: 2008-05-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The wireless communication in the residential automation has became a very promising technology due to the easinesses in the installation, and for its flexibility, mobility and scalability. Inside this context, the objective of this work is to analyze and to implement two wireless communication standard protocols: Bluetooth and ZigBee. They are used to analyze theirs functionalities and applications under a domestic environment. Firstly, the Bluetooth protocol was used in order to verify its operation because this one is an already well known protocol. Secondly, the ZigBee protocol - IEEE 802.15.4 MAC was also tested due to its new protocol applied to small data communication and its low baud rate, star topozlogy and low energy consumption, which allows the control of householdelectric network. The project consisted of monitoring, controlling and configuring washing machines by using a wireless network through a remote virtual interface. The user interface of this system was done through a PDA (Personal Digital Assistant), which allowed to change the times of washing programs manual or automatic mode. The results indicated the feasibility of monitoring and controlling household-electric by implementing the IEEE 802.15.4 MAC Layer of ZigBee protocol. This implementing reached the main characteristics as described above. The maximum distance achieved in a star topology in the typical residence was 14 meters, without using routers. This distance can be increased implementing full ZigBee Protocol. Although the project was developed to washing machine, it also can be implemented to other household-electrics, such as: microwaves, heaters, air conditioners, refrigerators, etc. / A comunicação sem fio em automação residencial tem se tornado uma tecnologia muito promissora devido às facilidades na instalação, flexibilidade, mobilidade e escalabilidade. Dentro deste contexto, o objetivo deste trabalho é analisar e implementar dois padrões de comunicação sem fio: Bluetooth e ZigBee, a fim de analisar suas funcionalidades e aplicações em ambiente doméstico. O protocolo Bluetooth por se tratar de um protocolo já consagrado no mercado, foi utilizado no controle remoto de uma máquina lavadora, como proposta inicial deste trabalho. Depois, o protocolo ZigBee - IEEE 802.15.4 MAC foi implementado, pois este padrão é um protocolo novo aplicado a comunicação com pequenos pacotes de dados, baixa taxa de transmissão, topologia estrela e baixo consumo de energia, que são características importantes para controle de uma rede de eletrodomésticos. O projeto consistiu em desenvolver um protótipo de hardware e de software para monitorar, controlar e parametrizar máquinas lavadoras de roupas numa rede sem fio através de uma interface virtual remota. Esta interface do usuário com a rede foi feita através de um PDA (Personal Digital Assistant) que permitiu alterar os tempos de programação da máquina no modo manual ou automático. Os resultados mostraram a viabilidade de se construir uma rede de eletrodomésticos, implementando a camada de enlace IEEE 802.15.4MAC do protocolo de comunicação ZigBee. Esta implementação atingiu as principais características descritas acima. A distância máxima alcançada na topologia estrela numa residência típica foi de 14 metros, sem o uso de roteadores. Esta distância poderá ser aumentada através da implementação da camada de rede ZigBee. Embora o projeto tenha sido desenvolvido utilizando máquinas lavadoras, pode-se estendêlo a outros eletrodomésticos tais como: fornos de microondas, aquecedores, condicionadores de ar, refrigeradores, etc.