Simulation Practice and Theory最新文献

The awareness of simulation technologies within the UK is relatively small when compared with the USA. Subsequently several large US companies have been able to overcome the difficulties in adopting new technology into their business and introduce simulation. This paper investigates the problems encountered and the practices helping to successfully implement simulation into a company environment. Details of a major survey conducted to determine the approaches taken by large automotive and aerospace companies within these two countries are outlined. The survey highlighted differences in the development of simulation within 12 large companies, the extent of the difference and the reasons why these differences exist.

Architectures for the design of soft real-time systems typically do not facilitate the use of performance tools that will enable a designer to analyse quantitatively the system. Elementary intercommunication data areas, whose behaviours are characterised by interaction protocols, are the building blocks of many soft real-time systems. Pools are one of these blocks. Although the performance of the whole system can be also determined by simulation, in this article we propose new analytical approximations for basic and priority pools. Basic pool modelling is based on semaphore queues whereas priority pool modelling is inspired in classical non-pre-emptive priority queues.

We describe a HLA-based Stochastic Petri Nets (SPN) Simulation Engine that has been developed in order to study distributed behaviour of SPN. We simulate a Federation constituted from SPN (sub) models. Two approaches are considered: (1) a single Petri Nets (PN) is decomposed into subnets which are executed on different heterogeneously connected computers (2) different PN which model different processes are combined into a single distributed simulation. We use a sender/receiver SPN-model to illustrate these approaches and to explore the impact of time management services applied in the implementation of the SPN distributed simulation engine.

The High Level Architecture's (HLA) Data Distribution Management (DDM) services are the most recent in a succession of systems designed to reduce the amount of data received by individual simulations in large-scale distributed simulations. A common optimization in these interest management systems is the use of multicast groups for sending data to a selected subset of all potential receivers. The use of multicast has met with considerable success in this application. However, its use to date has relied on a priori knowledge of communication patterns between simulations and static assignment of multicast groups to these patterns. As larger, more complex, and less predictable simulations are built, the need has arisen for more efficient use of multicast groups as they are a restricted resource [3Com Corporation, Scaling Performance and Managing Growth with the CoreBuilder 3500 Layer 3 Switch (available at http://www.3com.com/products/dsheets/400347a.html) lists a limit of 6 K, the highest number identified while Synthetic Theater of War (STOW) (D. Van Hook, RITN IM and IM history, personal communication, January 1996) had a hardware limit of approximately 1000. A typical workstation network interface card has only a few (H. Abrams, Extensible interest management for scalable persistent distributed virtual environments, Ph.D. Dissertation, Naval Postgraduate School, December 1999)]. This paper presents two algorithms for performing grouping, and the message delivery time improvements resulting from applying the algorithms to selected data sets.

The high level architecture (HLA) is a standard for federations of distributed simulations that exchange run-time data. HLA's data distribution management (DDM) services reduce data delivered to simulations based on their declarations of data produced and required. The HLA specifications, including DDM, were changed substantially from the Department of Defense 1.3 standard to the IEEE 1516 standard. The two DDM specifications' (DDM 1.3 and DDM 1516) power to define intersimulation data flows are compared. A transformation from DDM 1.3 to DDM 1516 configurations and a mapping from DDM 1516 to DDM 1.3 configurations prove that the DDM specifications are equivalently powerful.

We propose a novel design environment for developing multi-agent systems (MASs) for applications in mobile robotics. Because emergent behavior phenomena make it next to impossible to directly synthesize viable MAS designs from specifications, extensive simulation studies are needed to evaluate these designs. Furthermore, due to the fact that the design space for MASs systems is combinatorially large, the evaluation of candidate designs must be done in a hierarchical, multi-resolution, parallel and distributed manner.

Our proposed design environment is based on US Department of Defense's high-level architecture (HLA), an established software infrastructure for heterogeneous, distributed simulations. The proposed environment automatically generates and manages HLA federations (i.e., collections of distributed and/or parallel simulation and service federates) that communicate over runtime infrastructure (RTI) software buses. Each federation simulates a different candidate design for the MAS under development. Federations execute independently and in parallel. Our proposed design environment's refinement component uses a genetic algorithm (GA) to select the best candidate designs from the current generation and generates a set of refined, next-generation, candidate designs. A federation is created and managed for each of the next-generation designs and the automatic design process is repeated.

In this paper, we propose a Bi-directional Fragmental Pipelining (BFP) technique and its variable buffer size data-caching scheme BFP_V to reduce the disk I/O bandwidth requirement for multimedia servers. Our mathematical analysis shows that the BFP technique is superior to the traditional unidirectional pipelining technique in terms of memory buffer space requirement. We further demonstrate that the memory buffer management using BFP_V is better than that of using the fixed buffer size approach BFP_F. We have mathematically proved that BFP_V saves more disk I/O bandwidth than BFP_F does using the same memory buffer space. Our simulation results have quantitatively confirmed our analysis.

The direction that web-based simulation modelling is taking is determined and deliberated. Environments and languages for web-based simulation are reviewed, particularly Java-based approaches. Web-based applications are discussed. After proposing a summary of the review, ways of working that will have an unpredictable effect on the future of simulation modelling are proposed. The future direction of web-based simulation is speculated on, given the argument pursued in the paper.

This paper describes the tool Pansym for biomedical system modeling which has been designed primarily for representation of kinetics, transport and metabolism of biological substances. New modeling tools are needed in this research field because available simulation environments are often limited when applied to multidisciplinary studies in biomedicine. The aim of the new software is to allow a flexible specification of system structures using concurrently different formalisms that are conventionally used in different modeling domains. Starting from an intuitive model specification, mathematical system equations are first derived in symbolic form and subsequently coded as source code for different target applications. This multidomain modeling environment was built using bond graphs as common basis for automated analysis of system structures and symbolic derivation of system equations. Preliminary experience with the software showed that the adopted design strategy comes up to expectations, especially as regards the definition of complex hierarchical models that exhibit interactions between heterogeneous subsystems, e.g. cardiovascular and metabolic functions. Moreover, the specification of model structures is close to graphical object representation which helps defining a model of a system more in terms of its structure rather than its equations.