Simulation Practice and Theory最新文献

A modelling approach of complex systems is presented. The goal is to define a modular and non-causal representation able to describe hybrid dynamics, and to generate automatically the models corresponding to the different configurations of the real system. These models can then be used to simulate process evolution. In this paper, we define the structure of the basic model blocks and the interactions of these blocks through different kinds of signals.

The approach presented in this article is based on the real time simulation of p-time Petri net for the real time scheduling of batch systems. After defining the different kinds of constraints that can exist in a linear hybrid production system, we present the conflict resolution principle used by a token player algorithm at the global coordination level.

Simulation research in construction has been focussed mainly on the modelling of construction processes. However, most construction projects involve the building of structures with complex dependencies and structural relationships among its component parts. Manually generating simulation models of such structures is extremely difficult. The problem is exacerbated in a field like construction due to the paucity of simulation expertise. This paper presents a method for circumventing the problem through the development of an intuitive and structured approach for the automated generation of simulation models using the object-oriented programming paradigm. The approach was implemented using MODSIM II and tested using a two-component structure with intra-component and sequential inter-component dependencies. The simulation outputs were compared with that of a manually generated simulation model. The implementation was further tested using a 12-component structure with intra-component, sequential inter-component and continuous partial concurrent dependencies.

Standard clock approach is used to simulate a number of parametric variants of a single system. In this paper, we discuss a distributed implementation of the standard clock approach to simulation on networks of heterogeneous UNIX workstations. The implementation follows the client/server model, each server process that runs on a separate workstation, simulates a certain number of variants. The goal of the research is to determine the reduction in the total simulation time as more workstations are added to the run. The simulation completion time, which is considered as the performance measure, depends on the assignment of variants to workstations. We use two different load balancing techniques: (1) a static load balancing that is based on estimated cost of each variant and (2) a dynamic load balancing that migrates variants between workstations, based on their estimated performance during the simulation process. Simple queuing models are used to study the performance. Numerical results obtained from real-time simulations on a network of up to seven workstations are used to investigate the speedup and the efficiency of both the implementation and the load balancing techniques.

The standard approach to analyzing the results of probabilistic simulation rests on the use of classical statistics. In this paper, we explore the use of Bayesian statistics as an alternative. This makes it possible to incorporate prior information into the analysis of simulation results in a formal and rigorous manner, through the use of prior distributions. The Bayesian approach will typically yield improved analyses, by better taking into account what is actually known and what is not known about the system to be simulated (assuming that the prior distributions themselves adequately represent this knowledge). We briefly review Bayesian methods for readers who are not familiar with this type of analysis and suggest ways in which these methods can be applied to simulation. Specifically, we explore the use of Bayesian statistics for verification and validation of simulation models and for simulation output analysis, in both cases using priors on the performance measures of interest. We then study the use of prior distributions on the input parameters to the simulation, as a way to quantify the effects of input uncertainties on both the mean and the uncertainty of the performance measures of interest, and discuss Bayesian and related methods for choosing input distributions. Finally, we briefly consider the use of a joint prior on both the input parameters and the resulting performance measures. Bayesian methods are particularly appropriate for use in practice when simulations are costly, or when input uncertainties are large. Our work provides guidance on the use of Bayesian methods for simulation analysis. We hope that it will stimulate readers to learn more about this important subject, and also encourage further research in this area.

A detailed model of a radiotelescope (yoke on king post parabolic antenna) is developed. It uses modelling concepts that have been successfully applied to industrial robotic systems. In this approach, the interactions between the different dynamically coupled subsystems are viewed as disturbances whose dynamic behaviours are known. The proposed controller for the radiotelescope was developed by using a gain-scheduling strategy, which has the advantage of using known parameters for every region of operation. Thus, the computational complexity is substantially decreased and, in consequence, the parameters for each region of operation can be independently computed by inexpensive stand-alone microcomputers.

The aim of this paper is to present a full-digital implementation of indirect field oriented controlled (IFOC) induction motor drive with a personal computer (PC) and as much standardized hardware as possible. The complex functions required by IFOC induction motor drive have been executed by PC on line. Computer simulations of the IFOC induction motor drive with tuning rotor resistance have been carried out to test the validity of the proposed method at nominal and zero speed. For the experimental prototype, we use a current regulated-pulse width modulated-voltage source inverter (CR-PWM-VSI) fed induction motor drive. Experimental results of the IFOC induction motor drive obtained on a PC-based system are presented.

The field of advanced distributed simulation (ADS) has emerged and evolved since the 1980s. Developments are driven largely from within the United States (US) Department of Defense (DoD). This paper summarizes the history and evolution of ADS, detailing recent developments, notably the high level architecture (HLA). The implications of the HLA for data collection and analysis are discussed. Current approaches are reviewed including one of the largest ADS projects to date, the synthetic theatre of war (STOW), and its approach to data collection. We consider the impact of ADS beyond military training and discuss future development of ADS technology.

Cochlear implants are electronic devices intended to restore the sense of hearing in deaf people by direct electrical stimulation of the auditory nerve fibres that are still present in the deaf inner ear. Unfortunately, the clinical outcome is not very predictable. In this study a computational model is presented that can predict the neural response to an arbitrary cochlear implant. It first computes the potential distribution set up in a three-dimensional, spiralling volume conduction model of the auditory part of the inner ear (cochlea) and then applies a nerve fibre model to construct input/output curves and excitation profiles of the auditory nerve. As an initial validation the results are compared with experimentally induced electrically evoked auditory brainstem responses. In the light of the favourable results, we conclude that the model can serve as a tool for designing future cochlear implants. In combination with electrophysiological measurements in the individual patient it is applicable as an implant fitting tool.

A model for the evolution of biological systems in the absence of a nucleic acid-like genome is proposed and applied to model the earliest living organisms – protocells composed of membrane encapsulated peptides. Assuming that the peptides can make and break bonds between amino acids, and bonds in non-functional peptides are more likely to be destroyed than in functional peptides, it is demonstrated that the catalytic capabilities of the system as a whole can increase. This increase is defined to be non-genomic evolution. The relationship between the proposed mechanism for evolution and recent experiments on self-replicating peptides is discussed.