Simulation Practice and Theory最新文献

The major problem in building qualitative models via on-line qualitative system identification is how to filter the spurious constraints that are generated from the qualitative reasoning technique. This paper proposes a solution to this problem by an integration of genetic algorithms (GA) and qualitative reasoning. The paper will demonstrate the use of qualitative reasoning to partition the input quantity space into different subsystems, and implementation of GAs to filter and optimize the predicted constraints. The proposed method is verified by simulated examples that suggest the algorithm converges to the optimal point with high speed.

Alecsis behavioral simulator and its mixed-signal hardware description language (HDL) AleC++ form an open simulation environment, where electronic circuits and non-electrical systems can be analyzed. This paper describes some of the features of AleC++ language, namely mainly those that are not in accordance with the IEEE standard for VHDL and VHDL-AMS, but are very useful for modeling complex systems.

Noting the increasing use of discrete-event simulation directly by non-specialists, this paper considers the significance of methodology and reports results from a survey of user practice in experimentation. The inquiry addressed practitioners engaged in “steady-state” type problems and the outcomes reveal that simulation practice is more strongly influenced by user judgement than formal disciplines. This may, with experienced simulation specialists, lead to correct run control and results interpretation but, with non-specialists, there is higher risk. Particular areas of concern are identified and the study also considers further support that simulation software might bring to the experimentation process.

The recent rapid growth in the Internet and the use of this technology for corporate intranets presents new opportunities for parallel discrete event simulation. Previously, this was the province of specialist groups with dedicated computer facilities, whereas it is now feasible to use small PCs that communicate via TCP/IP. This paper describes research in distributed discrete event simulation using the three-phase approach and implemented in Java using standard Internet technologies. Two specific implementations are described, one for client/server work and the other a distributed, parallel simulator using conservative synchronisation protocols. The problem of managing shared states with competing resources is specifically discussed. They demonstrate proof of concept and contain important aspects of detailed implementation, but have not been used for experimentation to estimate aspects such as speed or message loads.

This article examines sectoring as a methodology of improving the efficiency of discrete event simulation of autonomous object movement in 3-D space. Efficiency is defined as the ability to reduce the amount of pairwise comparisons needed to completely execute the intended system. Sectoring involves partitioning the simulation trajectory space and allows for a reduction of the number of queries required between objects in order to determine upcoming events. However, the crossing of sector boundaries becomes an additional event to track and compute. A simulation of moving objects in 3-D space was constructed using MODSIM™. This simulation was verified and used to gather significant output data. The results indicated that, within the specific experimental range, sectoring provides up to 52% improvement in simulation efficiency when compared to no sectoring.

In a stochastic simulation context, iterative methods of optimization, which perform at each step of their optimization procedure a comparison between two different values of the objective function, need the use of statistical tests in order to properly evaluate and compare the simulation results. However, when the objective function to be optimized is a multicriteria function involving several performance measures, classical statistical procedures, which do not take into account the correlation between the performance measures, could reject acceptable solutions. To avoid this, we propose an efficient and rigorous statistical procedure already used in a multicriteria context, Hotelling’s T² procedure. This paper shows that this procedure is very well adapted when the problem is to compare simultaneously several criteria in a stochastic simulation–optimization context.

The objective of this paper is to show how system dynamics could contribute to improving the knowledge of the complex logistic behavior of an integrated food industry. After a short presentation of this research, the structure of a generic model and some significant practical simulation results are presented as applied to the field of poultry production and processing. As an example of application, the consequences of the dioxin infection to the supply chain of the chicken industry is described, and certain recommendations to the managers are additionally proposed.