SIMULATION: Transactions of The Society for Modeling and Simulation International

Hu, Xiaolin; Sun, Yi; Ntaimo, Lewis

doi: 10.1177/0037549711414592pmid: N/A

DEVS-FIRE is a discrete event system specification (DEVS) model for simulating wildfire spread and suppression. It employs a cellular space model to simulate fire spread and agent models that interact with the cellular space to simulate fire suppression with realistic tactics. The complex interplay among forest cells and agents calls for formal treatment of the fire spread and fire suppression models to verify the correctness of DEVS-FIRE. This paper gives formal design specifications of fire spread and suppression agent models used in DEVS-FIRE and applies DEVS-FIRE to both artificially generated and real topography, fuels and weather data for a study area located in the US state of Texas. The paper also develops a new method, called pre_Schedule, for scheduling ignition events of forest cells more efficiently than the original onTime_Schedule event scheduling method used in DEVS-FIRE. Simulation results show the performance improvement of the new method, and demonstrate the utility of DEVS-FIRE as a viable discrete event model for wildfire simulations.

Nutaro, James; Kuruganti, Phani Teja; Protopopescu, Vladimir; Shankar, Mallikarjun

doi: 10.1177/0037549711401000pmid: N/A

The efficient and accurate management of time in simulations of hybrid models is an outstanding engineering problem. General a priori knowledge about the dynamic behavior of the hybrid system (i.e. essentially continuous, essentially discrete, or ‘truly hybrid’) facilitates this task. Indeed, for essentially discrete and essentially continuous systems, existing software packages can be conveniently used to perform quite sophisticated and satisfactory simulations. The situation is different for ‘truly hybrid’ systems, for which direct application of existing software packages results in a lengthy design process, cumbersome software assemblies, inaccurate results, or some combination of these independent of the designer’s a priori knowledge about the system’s structure and behavior. The main goal of this paper is to provide a methodology whereby simulation designers can use a priori knowledge about the hybrid model’s structure to build a straightforward, efficient, and accurate simulator with existing software packages. The proposed methodology is based on a formal decomposition and re-articulation of the hybrid system; this is the main theoretical result of the paper. To set the result in the right perspective, we briefly review the essentially continuous and essentially discrete approaches, which are illustrated with typical examples. Then we present our new, split system approach, first in a general formal context, then in three more specific guises that reflect the viewpoints of three main communities of hybrid system researchers and practitioners. For each of these variants we indicate an implementation path. Our approach is illustrated with an archetypal problem of power grid control.

Grinblat, Guillermo L; Ahumada, Hernán; Kofman, Ernesto

doi: 10.1177/0037549711399935pmid: N/A

In this work, we explore the usage of quantized state system (QSS) methods in the simulation of networks of spiking neurons. We compare the simulation results obtained by these discrete-event algorithms with the results of the discrete time methods in use by the neuroscience community. We found that the computational costs of the QSS methods grow almost linearly with the size of the network, while they grows at least quadratically in the discrete time algorithms. We show that this advantage is mainly due to the fact that QSS methods only perform calculations in the components of the system that experience activity.

Jarrah, Moath; Zeigler, Bernard

doi: 10.1177/0037549710385744pmid: N/A

Different negotiation engineering domains require the system designer to tailor the negotiation framework according to the domain under which it will be used. This process of system design is timely consuming when supporting different geographically distributed and dynamic environments. Here we show a methodology to design negotiation systems by integrating domain-dependent message structure ontology with domain-independent marketplace architecture. The methodology gives the system designers a powerful modeling tool that can be used to tailor the framework in order to support different negotiation behaviors under different domains. The system entity structure formalism is used to build the domain-dependent ontology while the finite deterministic discrete event system formalism is used to build the marketplace model. The discrete event system with service oriented architecture simulation environment was employed to demonstrate a proof of concept of applicability to web service domains.

Gudiño-Mendoza, Berenice; López-Mellado, Ernesto; Alla, Hassane

doi: 10.1177/0037549710388749pmid: N/A

This paper deals with modeling and simulation of water distribution systems using Hybrid Petri Nets. A methodology for building a Timed Hybrid Petri Net (THPN) model is proposed; the model is derived from a set of equations describing conservation of mass and energy that specify the behaviour of a water distribution network. A simulation technique for the execution of a THPN in which the transitions firing velocities are established from the linearised conservation of energy equations is presented; it shows both transient and steady state for the analysis of hydraulic networks. Based on this technique, a simulator in Matlab has been developed.

Cambronero, M Emilia; Díaz, Gregorio; Martínez, Enrique; Valero, Valentín; Tobarra, Llanos

doi: 10.1177/0037549710372098pmid: N/A

In this paper we introduce a tool called the Web Service Translation tool (WST), which we are developing to implement a methodology for the design, validation and verification of Web Services with timed restrictions. This methodology works by making several translations, from phase to phase in the software development life cycle, where the system is represented at each phase by XML models. We use XSL Transformations (XSLT), which is a language for transforming XML documents. The purpose of these translations is to generate XML code automatically for a Web Service system and to obtain Web Services description models with Timed Automata for validating and verifying composite Web Services with time restrictions.

Gitau, Margaret W; Chiang, Li-Chi; Sayeed, Mohamed; Chaubey, Indrajeet

doi: 10.1177/0037549711402524pmid: N/A

Models are increasingly being used to quantify the effects of best management practices (BMPs) on water quality. While these models offer the ability to study multiple BMP scenarios, and to analyze impacts of various management decisions on watershed response, associated analyses can be very computationally intensive due to a large number of runs needed to fully capture the various uncertainties in the model outputs. There is, thus, the need to develop suitable and efficient techniques to handle such comprehensive model evaluations. We demonstrate a novel approach to accomplish a large number of model runs with Condor, a distributed high-throughput computing framework for model runs with the Soil and Water Assessment Tool (SWAT) model. This application required more than 43,000 runs of the SWAT model to evaluate the impacts of 172 different watershed management decisions combined with weather uncertainty on water quality. The SWAT model was run in the Condor environment implemented on the TeraGrid. This framework significantly reduced the model run time from 2.5 years to 18 days and enabled us to perform comprehensive BMP analyses that may not have been possible with traditional model runs on a few desktop computers. The Condor system can be used effectively to make Monte Carlo analyses of complex watershed models requiring a large number of computational cycles.