This paper presents an introductory tutorial and illustration of the modeling capabilities of the Repast Simphony simulation framework using an agent-based model of regional natural gas and electric power system interdependencies. The natural gas transmission and distribution and electrical power companies are modeled as social agent organizations. The goal of the modeling exercise is to simulate impacts on the delivery of natural gas to the affected geographical regions and the effects of various policy models in the agent-based company models. Additionally, the estimate of cascading effects of natural gas loss on associated electric power infrastructure is investigated.

The physical layers in the simulation consists of a natural gas transmission network and DC electric transmission network.

The natural gas transmission model consists of a network of interconnected links and nodes, where the nodes function as delivery, receipt and/or pipeline termination points and the links function as gas pipelines that transport natural gas between nodes. Supplies, demands and compressor fuel usage values and compressor and pressure regulator characteristics may be modified to observe the effects on the network.

The DC electric network model considers a balance of demand and generation given the transmission topology. The nodes in the electric network represent generators and load points, while the links function as electrical transmission lines. The electric network model permits sensitivity analysis of line outages and shifts in generation. The two networks are connected via links between the natural gas network and gas-fired electric power plants (generators) in the electrical network. Each network is fairly large scale and contain several thousand nodes and links each.

The social agent layers consists of both regional and local gas transmission companies as well as local electrical power companies.

The regional natural gas transmission companies control the portion of the network between the gas supply and production sources. The local gas distribution company is responsible for delivery of the gas between the local city gates and the customer base (commercial and residential) Both natural gas companies share a common internal structure consisting of several groups such as operations, engineering and supply control. Each company group is modeled as a collection of different agent types, each with a unique type of behavior suited to their respective tasks. Certain agents act as a liaison between the companies and between the transmission and local distribution companies.

The social and physical agent models were developed in Repast [ROAD 2005], a widely used, free, and open source, agent-based modeling and simulation toolkit with three released platforms, namely Repast for Java, Repast for the Microsoft .NET framework, and Repast for Python Scripting (North et al 2005). Repast Simphony (Repast S) extends the Repast portfolio by offering a new approach to simulation development and execution (North et al 2006). Simphony goes beyond current model integration architectures that simultaneously require users with broad and deep knowledge in the application area, modeling, and software engineering. This broad skill set rarely exists within a single organization and is even less likely to be integrated into a working team. Simphony brings model integration tools directly to domain expert analysts (e.g., infrastructure specialists) without the need of software engineers, allowing users to develop integrated simulation modeling applications much more efficiently and economically than has been previously possible.

Simphony provides drag-and-drop user interfaces for: selecting from a repository of model components and tools (e.g., geographical information systems (GIS), visualization tools, statistical tools, and databases); creating new models using flow diagrams and agent-based model templates; assigning data sources such as GIS data, relational databases or real-time data feeds such as sensors; defining how components should interact; and controlling how the simulation is executed. The Simphony team is also investigating the use of grid computing technologies to provide large-scale simulation capabilities and distributed collaborative development of integrated national security applications.

To insure that Simphony directly addresses analyst's needs, its design is based on a “Use Case” approach where example applications are presented to end users and progressively refined using their suggestions. Several use cases are being developed including infrastructure interdependency; natural gas disruption fast turn around analysis; energy process and market analysis; supply network infrastructures; and manufacturing and industrial processes.

[ROAD 2005] Repast, ROAD (Repast Organization for Architecture and Design), 2005, Repast Home Page, Chicago, IL; available at http://repast.sourceforge.net.

[North, Howe, Collier, & Vos, 2005b] North, M.J., T.R. Howe, N.T. Collier, and J.R. Vos, 2005, “Repast Simphony Runtime System,” in C.M. Macal, M.J. North, and D. Sallach (eds.), Proceedings of the Agent 2005 Conference on Generative Social Processes, Models, and Mechanisms, ANL/DIS-06-1, co- sponsored by Argonne National Laboratory and The University of Chicago, Oct. 13–15.

[North, Collier, & Vos, 2006] North, M.J., N.T. Collier, and J.R. Vos, 2006, “Experiences Creating Three Implementations of the Repast Agent Modeling Toolkit,” ACM Transactions on Modeling and Computer Simulation 16(1):125, ACM (January): New York, NY.

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