Doohwan Kim

The DEVS environment for high-performance modeling and simulation

DEVS-C++, a high-performance environment for modeling large-scale systems at high resolution, uses the DEVS (Discrete-EVent system Specification) formalism to represent both continuous and discrete processes. A prototype suggests that the DEVS formalism can be combined with genetic algorithms running in parallel to serve as the basis of a very general, very fast class of simulation environments.

DEVS-C++: a high performance modelling and simulation environment

Simulation of landscape ecosystems with high realism demands computing power greatly exceeding that of curent workstation technology. However, the prospects are excellent that modelling and simulation environments may be implemented on next-generation high-performance, heterogeneous distributed computing platforms. Computing technology is becoming powerful enough to support the voluminous amounts of knowledge/information necessary for representing such systems and the speed required of simulations to provide reliable answers in reasonable time. This paper provides an overview of a project to develop a high-performance modelling and simulation environment to support modelling of large-scale, high-resolution landscape systems: DEVS-C++, an implementation of discrete event system specification (DEVS) using container classes with C++.

Design of high level modelling / high performance simulation environments

Advances in massively parallel platforms are increasing the prospects for high performance discrete event simulation. Still the difficulty in parallel programming persists and there is increasing demand for high level support for building discrete event models to execute on such platforms. We present a parallel DEVS-based (Discrete Event System Specification) simulation environment that can execute on distributed memory multicomputer systems with benchmarking results of a class of high resolution, large scale ecosystem models. Underlying the environment is a parallel container class library for hiding the details of message passing technology while providing high level abstractions for hierarchical, modular DEVS models. The C++ implementation working on the Thinking Machines CM-5 demonstrates that the desire for high level modeling support need not be irreconcilable with sustained high performance.

SYSTEM ENTITY STRUCTURES FOR SUITES OF SIMULATION MODELS

We describe how to develop a suite of models in the MS4 Modeling Environment (MS4 Me). The approach employs the operation of merging of System Entity Structures supported by the environment. After construction, the suite of models can be hosted on Model Store, the cloud-based repository of models provided by MS4 systems as a basis for further collaborative model development. A suite of models, relating to Health Care is used as an example. In this paper, we review basic concepts of the SES needed to support of suites of simulation models. We then consider the concept of multiple aspects that provides more advanced capabilities to construct and manipulate suites of models. With this background, we go on to discuss a methodology for developing suites of simulation models and cloud-based technology for storing and sharing such models in a marketplace of models. Finally, we discuss future research and developments needed to bring the marketplace into common use by modeling and simulation practitioners.

DEVS/NS-2 Environment: An Integrated Tool for Efficient Networks Modeling and Simulation

This paper presents a new DEVS/NS-2 modeling and simulation environment which supports both high and low levels of abstraction for network modeling and simulation. DEVS (Discrete Event System Specification) is a well-defined mathematical formalism specification for structure and behavior of dynamic systems. The NS-2 is a discrete event network simulator, whose primary use is intended to build and run various detailed network models and protocols such as TCP/IP, satellite links, and wireless networks. By combining the two powerful modeling and simulation systems, the significant benefits attained by the interoperable simulation of DEVS and NS-2 are reduction of the cost, increased high and low level modeling power, and enhanced reusability. To integrate the systems seamlessly, two major challenges are addressed. The first challenge is to synchronize the different ways of handling event schedules by the two simulation systems. This paper illustrates how the simulation time advances of DEVS and NS-2 are synchronized with each other. The latter problem is related to assigning the appropriate level of model structure and behavior within the combined system. The details of low level network with protocol and component description is modeled by NS-2 while DEVS serves as controller by modeling the high level behavior (e.g. use case scenario builder) of target network models and interaction of the associated actors. In this paper, we take two examples of wireless sensor networks. The first example is to describe our approach to the development process for modeling and simulation in DEVS/NS-2 environment, and the purpose of the second example is to show how DEVS/NS-2 environment is efficient for military system applications. This example is extended to demonstrate an effective way to make a decision on the appropriate level of sensor nodes behavior. This leads to the discussion of tradeoffs between energy efficiency and effectiveness of decision making for the sensor network. The advantages and the disadvantages are discussed in the last part of this paper by comparing DEVS/NS-2 environment with its related studies such as DEVS BUS and OPNET.

A DEVS-based framework for simulation optimization: Case study of Link-11 gateway parameter tuning

Discrete event system specifications (DEVS) is a mathematical formalism based on system theoretic principles, which has evolved with state-of-technologies implementation over the past few decades. In this paper, we discuss a DEVS framework to solve parameter optimization problems. As a case study, we consider the Link-11 gateway that has been developed by the Joint Interoperability Test Command (JITC) is to provide interoperability between Link-11 network and TCP/IP network. The performance of Link-11 gateway is highly sensitive to the sampling rate of soundcards since the frame time of Link-11 signal is very short. Unfortunately, the sampling rate is not as accurate as it is specified by the manufacture of soundcards. A solution is to search for an optimized parameter that can be used to adjust the sampling rate. We apply an optimization technique to search for optimal sampling rate in modeling and simulation environment, DEVSJAVA. The DEVS-based framework can facilitate efficient global optimal parameter search capability and reduce execution time benefiting from its parallel and variable structure implementation.

DEVS model composition by system entity structure

The structural knowledge of a system represented in system entity structure (SES) supports the handling of organization issue in model compositions. A pruning operation results in a reduced structure, pruned entity structure (PES) that the SES is pruned to meet design objectives. The PES is eventually synthesized into a simulation model by combining it with models in the model base. SES is implemented in XML Metadata using Java language and Sun’s Document Object Models (DOM) specification. The SESBuilder1 software supports natural language input for an SES definition and XML instance generation of its PES. The coupling information expressed in natural language with restricted syntax processed by SESBuilder is used to compose models. As a real example, the compositions of Discrete Event Specification (DEVS) generator models, representing the US Climate Normals, are presented. The example presents the natural language input and XML instances for PES including coupling information in the SESBuilder.

A Framework for Rapid Configuration of Collaborative Aviation System-of-Systems Simulations

We propose a model-based framework to specify, integrate, and verify heterogeneous Software Integration Lab and System of Systems (SoS) simulations that include unmanned aviation mission systems during the early development and evaluation phases. This approach would bridge the currently separated development and test/training domains. We propose a tool suite for Rapid Configuration of Collaborative Aviation SoS Simulations (RCAS3.) This will provide a seamless plug-and-play framework that is highly adaptive and configurable while providing model transformation mechanisms to easily interface with High Level Architecture or other federated simulation protocols. RCAS3 will be built around already existing technologies: Aviation Scenario Definition Language Modeling, Discrete Event System Specification, and System Entity Structure implemented in RTSync’s MS4 Me. These will be augmented with an Architecture Analysis and Design Language (AADL)-based configuration and behavior analysis suite. This paper presents RCAS3 framework architecture and its underlying concepts.