A model for cascading failures in complex networks

Large but rare cascades triggered by small initial shocks are present in most of the infrastructure networks. Here we present a simple model for cascading failures based on the dynamical redistribution of the flow on the network. We show that the breakdown of a single node is sufficient to collapse the efficiency of the entire system if the node is among the ones with largest load. This is particularly important for real-world networks with an highly hetereogeneous distribution of loads as the Internet and electrical power grids.Comment: 4 pages, 4 figure

Complex City Systems

Information and communications technology (ICT) is being exploited within cities to enable them to better compete in a global knowledge-based service-led economy. In the nineteenth and twentieth centuries, cities exploited large technical systems (LTSs) such as the telegraph, telephony, electrical networks, and other technologies to enhance their social and economic position. This paper examines how the LTS model applies to ICT deployments, including broadband network, municipal wireless, and related services, and how cities and city planners in the twenty-first century are using or planning to use these technologies. This paper also examines their motivations and expectations, the contribution to date, and the factors affecting outcomes. The findings extend the LTS model by proposing an increased role for organizations with respect to an individual agency. The findings show how organizations form themselves into networks that interact and influence the outcome of the system at the level of the city. The extension to LTS, in the context of city infrastructure, is referred to as the complex city system framework. This proposed framework integrates the role of these stakeholder networks, as well as that of the socioeconomic, technical, and spatial factors within a city, and shows how together they shape the technical system and its socioeconomic contribution. The CCS framework has been presented at Digital Cities Conferences in Eindhoven, Barcelona, Taiwan, London and at IBM’s Global Smart Cities Conference in Shanghai between 2010 and 2012. Its finding are timely in the context of major policy decisions on investments at regional, national and international level on ICT infrastructure and related service transformation, as well as the governance of such projects, their planning and their deployment

Creating a Network Model for the Integration of Dynamic and Static Supervisory Control and Data Acquisition (SCADA) Test Environment

Since 9/11 protecting our critical infrastructure has become a national priority. Presidential Decision Directive 63 mandates and lays a foundation for ensuring all aspects of our nation\u27s critical infrastructure remain secure. Key in this debate is the fact that much of our electrical power grid fails to meet the spirit of this requirement. My research leverages the power afforded by Electric Power and Communication Synchronizing Simulator (EPOCHS) developed with the assistance of Dr. Hopkinson, et al. The power environment is modeled in an electrical simulation environment called PowerWorld©. The network is modeled in OPNET® and populated with self-similar network and Supervisory Control and Data Acquisition (SCADA). The two are merged into one working tool that can realistically model and provide a dynamic network environment coupled with a robust communication methodology. This new suite of tools will enhance the way we model and test hybrid SCADA networks. By combining the best of both worlds we get an effective and robust methodology that correctly predicts the impact of SCADA traffic on a LAN and vice versa. This ability to properly assess data flows will allow professionals in the power industry to develop tools that effectively model future concepts for our critical infrastructure

Smart Senja electrical network expansion modeling

The addition of variable renewable energy sources into the electrical energy systems of the world has been increasing in recent years. This form of distributed energy production with high production volatility can introduce massive challenges in operating a lower voltage distribution network. One of these affected networks is on the island of Senja in northern Norway, with an eldering radial electrical network with a single connection to the national transmission grid. In this study, prescriptive analysis of the network through mathematical optimization is implemented to investigate if there are more effective solutions to this problem other than building more electrical lines. In selected parts of the island, the electrical network experiences electrical faults of different magnitude and concern affecting 1500 hours a year. In this thesis, the model GenX is presented which prescribes solutions reducing these faults to zero while also cutting costs compared to the baseline scenario of today’s system. Results from the model indicate that simple installments of distributed power generation in conjunction with electrical energy storage drastically improve network capacity and industrial expansion opportunities. Also investigated is the feasibility of operating the electrical network on the island without any connection to the external grid. Meant as a proof of concept for the application of mathematical optimization on electrical grids in other more remote parts of the world. The model proves that investments in local electricity production positively impact the system at a fraction of the cost of building new regional distribution infrastructure. Finally, some drawbacks of the chosen analytical tool used to construct the mathematical optimization model are presented alongside selected methods applicable to apprehend or circumvent these limitations

Resilience of the Critical Communication Networks Against Spreading Failures: Case of the European National and Research Networks

A backbone network is the central part of the communication network, which provides connectivity within the various systems across large distances. Disruptions in a backbone network would cause severe consequences which could manifest in the service outage on a large scale. Depending on the size and the importance of the network, its failure could leave a substantial impact on the area it is associated with. The failures of the network services could lead to a significant disturbance of human activities. Therefore, making backbone communication networks more resilient directly affects the resilience of the area. Contemporary urban and regional development overwhelmingly converges with the communication infrastructure expansion and their obvious mutual interconnections become more reciprocal. Spreading failures are of particular interest. They usually originate in a single network segment and then spread to the rest of network often causing a global collapse. Two types of spreading failures are given focus, namely: epidemics and cascading failures. How to make backbone networks more resilient against spreading failures? How to tune the topology or additionally protect nodes or links in order to mitigate an effect of the potential failure? Those are the main questions addressed in this thesis. First, the epidemic phenomena are discussed. The subjects of epidemic modeling and identification of the most influential spreaders are addressed using a proposed Linear Time-Invariant (LTI) system approach. Throughout the years, LTI system theory has been used mostly to describe electrical circuits and networks. LTI is suitable to characterize the behavior of the system consisting of numerous interconnected components. The results presented in this thesis show that the same mathematical toolbox could be used for the complex network analysis. Then, cascading failures are discussed. Like any system which can be modeled using an interdependence graph with limited capacity of either nodes or edges, backbone networks are prone to cascades. Numerical simulations are used to model such failures. The resilience of European National Research and Education Networks (NREN) is assessed, weak points and critical areas of the network are identified and the suggestions for its modification are proposed

Modelling of the Western University Campus Electrical Network for Infrastructural Interdependencies in a Disaster Response Network Enables Platform

The interdependencies that exist between multiple infrastructures can cause unexpected system behaviour when their component failure occurs due to large disruptions such as earthquake or Tsunami. The complexities of these interdependencies make it very difficult to effectively recover infrastructure because of the several challenges encountered. To overcome these challenges, a research program called Disaster Response Network Enabled Platform (DR-NEP) was initiated. This thesis deals with the modelling of electrical networks in order to study critical infrastructures interdependencies as a part of DR-NEP project. In first module of the thesis, the concept and understanding of interdependencies is presented. For studying the infrastructural interdependencies, three infrastructures are selected at Western campus: electrical power system, steam system and water systems. It is demonstrated that electrical infrastructure is the most significant infrastructure as all other infrastructures are dependent on electrical input. This thesis subsequently presents the development of a detailed model of the electrical power system of Western campus. This model is validated with actual measured data provided by the Western facilities management for different loading conditions and different feeder positions. Such a model has been developed for the first time at Western University. This model can be used not just for studying disaster scenarios but also for planning of future electrical projects and expansion of facilities in the Western campus. The second module of thesis deals with the different disaster scenarios, critical subsystems and the impact of appropriate decision making on the overall working of the Western campus, with a special focus on electrical power systems. The results from the validated electrical model are incorporated into the infrastructural interdependency software (I2Sim). A total of six disaster scenarios are studied; three involving the electrical power systems in collaboration with water and steam systems, and other three involving only the electrical power system. The study of interdependency during disasters is performed to generate a wiser decision making process. The results presented in this thesis are an important addition to the earlier work done in DRNEP project, which only involved three infrastructures: steam, condensate return, and water. In this iv thesis, the information on electrical networks which was earlier missing is provided through the validated electrical power model. It is demonstrated that decisions to reduce electrical power consumption on campus by evacuating campus areas are effective in stabilizing the hospital operations but not in maintaining Western business continuity. A decision to accommodate hospital activities according to power availability appears to be the better choice. The results presented in this thesis will help in a much better manner to pre-plan different preparedness strategies to deal with any future potential emergencies in the Western campus