Elisa Castorini

Stability of a Distributed Generation Network Using the Kuramoto Models

We derive a Kuramoto-like equation from the Cardell-Ilic distributed electrical generation network and use the resulting model to simulate the phase stability and the synchronization of a small electrical grid. It is well-known that a major problem for distributed generation is the frequency stability. This is a non linear problem and proper models for analysis are sorely lacking. In our model nodes are arranged in a regular lattice; the strength of their couplings are randomly chosen and allowed to vary as square waves. Although the system undergoes several synchronization losses, nevertheless it is able to quickly resynchronize. Moreover, we show that the synchronization rising-time follows a power-law.

The DIESIS Approach to Semantically Interoperable Federated Critical Infrastructure Simulation

Critical infrastructures (CI) such as telecommunication or the power grids and their dependencies are getting increasingly complex. Understanding these – often indirect –dependencies is a vital precondition for the prevention of cross sector cascading failures of CI. Simulation is an important tool for CI dependency analysis, the test of methods for risk reduction, and as well for the evaluation of past failures. Moreover, interaction of such simulations with external threat models, e.g., a river flood model and economic models, may assist in what-if decision-making processes. The simulation of complex scenarios involving several different CI sectors requires the usage of heterogeneous federated simulations of CI. However, common standards for modelling and interoperability of such federated CI simulations are missing. In this paper, we present a novel approach for coupling CI simulations, developed and realised in the EU project DIESIS. The DIESIS core technologies for coupling CI simulations include a middleware that enables semantic interoperability of the federate simulators, a systematic, service-oriented approach to set up and run such federations, and, most importantly, a scenario-based architecture concept for modelling and federated simulation of CI. The architecture foresees a flexible pair-wise (lateral) coupling of simulators. DIESIS has implemented a demonstrator as a proof of concept for its approach and technologies, by coupling four different simulation systems (three interacting CIs and an external, common threat). In this paper, we focus on the architectural concept and the interoperability middleware that realises this concept and allows the coupling of heterogeneous simulation systems using various time and data models. We show how the ontology-based Knowledge Based System (KBS) is integrated and used in the overall system. Then, we discuss the basic technical concepts as well as the results obtained with the demonstrator. The proposed architecture is open for further extensions. Ultimately, the proposed approach shall form the basis of a future standard coupling middleware for federated CI simulations.

An ontological approach to simulate critical infrastructures

Abstract This paper presents a Knowledge Base System (KBS) as a key component of a federated simulation framework aimed at investigating the dependencies among Critical Infrastructures (CIs). The KBS, based on the ontological formalism, represents the properties and the relations of each simulation domain and the dependency relations among different domains. Some auxiliary data structures, necessary to model the interaction among the simulators of different CIs, have been defined and have been populated through suitable queries to the KBS. The adoption of the ontological formalism allowed the definition of a common formalism to deal with the heterogeneity arising from the presence of different domains.

Using ontologies for the federated simulation of critical infrastructures

Abstract This paper presents a Knowledge Base System (KBS) as a key component of a federated simulation framework aimed at investigating the dependencies among Critical Infrastructures (CIs). The KBS, based on the ontological formalism, represents the properties and the relations of each simulation domain and the dependency relations among different domains. Some auxiliary data structures, necessary to model the interaction among the simulators of different CIs, have been defined and have been populated through suitable queries to the KBS. The adoption of the ontological formalism allowed the definition of a common formalism to deal with the heterogeneity arising from the presence of different domains.

Ontological Framework to Model Critical Infrastructures and their Interdependencies

This paper presents a Knowledge Base System (KBS) as a key component of a federated simulation framework which allows the investigation of (inter)dependencies among Critical Infrastructures (CIs). The KBS supports the federated simulation framework by using the ontological formalism to represent specific CI domains and their dependencies. The main advantage of the proposed ontological formalism consists on the abstraction of the description from the technological (i.e. simulation) level: the scenario can be described with a formalism used by the experts of the various CI domains.The proposed approach has been validated on a realistic scenario with actual data derived from the Rome city area. This scenario has been then used as testbed for a federated distributed simulation.

Optimal routing and resource allocation in multi-hop wireless networks

This paper addresses the problem of simultaneously optimizing power consumption and routing in multi-hop wireless networks while forcing the satisfaction of the required transmission demands between given origin–destination pairs. We devise a linear programming model for the selection of optimal routes and transmission schemes where both the power and link capacity levels are suitably discretized. Since the constraint matrix of such a model contains a huge number of columns, we propose an exact algorithm for its solution based on a column-generation approach. The associated column-generation procedure is based on the solution of linear integer programming models. We report some computational results on networks with up to 65 nodes, showing the feasibility of our solution approach.

Routing and scheduling in wireless ad hoc networks

Computing capacity bounds of ad hoc networks, as well as optimizing radio resource allocation in order to approach those bounds is a hard task that have recently attracted the interest of the research community. In this paper we address the problem of jointly optimizing the routing of flows, the transmission scheduling over wireless links along the path, and the emitted power for bandwidth guaranteed traffic demands. We propose a mixed integer linear programming model which considers the signal to interference and noise ratio at receiver and accounts for the effect of adaptive transmission rate through a set of discrete link capacity and power values. To find the optimal solution of the proposed problem we provide an algorithm based on column generation. Reported numerical results on networks with up to 50 nodes and 170 links show the effectiveness of the proposed approach even with quite bit problem instances.