Simulation Practice and Theory最新文献

Two accelerated simulation techniques, Importance Sampling and RESTART, are analyzed in the context of the class of Markovian fluid models, widely used in broadband communication networks. The different terms corresponding to their computational cost are exposed and evaluated for a sample case. Importance Sampling is found to be preferable (i.e. to present the lower computational cost) for the simulation of very rare events and large systems. A tentative criterion is proposed for the a priori selection of the computationally lighter simulation technique, based on the system size and on the probability of the event being estimated.

Simulation software has reached a technological level that provides high flexibility and integration capabilities necessary for product design, development and manufacturing efficiency. It appears in the aerospace industry, and the potential of simulation has not been fully recognised, although it is now becoming a matter of interest through the documented benefits it has provided. This paper discusses the issues of selection and integration that can be achieved with simulation within an aerospace company. This also discusses the practical difficulties of data transfer and management that would be encountered in the development of an integrated simulation environment.

In this paper we discuss different algorithms to select final states after scattering within the full band ensemble Monte Carlo (MC) simulation framework. Faster computers have made it possible to use more elaborated microscopic models for simulation of advanced semiconductor devices. Microscopic details like the band structures, the phonon dispersions and k-vector dependent deformation potentials are becoming accessible, which demand good algorithms for the selection of final states after scattering. The algorithm should also be adapted for a numerical representation of the band structure. Such an algorithm based on the rejection method is presented, which has been studied and compared in terms of efficiency and accuracy with two other algorithms for final state selection. The rejection algorithm is considered as suitable for anisotropic scattering mechanisms and when a relatively slow method is used for calculation of the wave-function overlap integral. It is shown that an accurate model of acoustic phonon scattering results in two characters of the process: one short-q process and one long-q process, very similar to a nonpolar optical intervalley process.

It is argued that the data collection process is the most crucial stage in the model building process. This is primarily due to the influence that data has in providing accurate simulation results. Data collection is an extremely time consuming process predominantly because the task is manually orientated. Hence, automating this process of data collection would be extremely advantageous. This paper presents how simulation could utilise the Corporate Business Systems as the simulation data source. Subsequently a unique interface could be implemented to provide these data directly to the simulation tool. Such an interface would prove to be an invaluable tool for users of simulation.

The objective of this study is to improve the pricing efficiency of wholesale fish markets by applying the framework of the price decision support system (PDSS). The Pu-Shin wholesale fish market, in Taiwan, is a case used to illustrate this procedure. We first established a simulation model for the operation of the Pu-Shin wholesale fish market, including all possible factors that may affect the auction time. Secondly, we setup a regression model for auction pricing and auction time of each section from the results of the model. Using this information, we established a PDSS for the Pu-Shin wholesale fish market to help decision-makers improve pricing functions.

Fault detection and diagnosis (FDD) can be realized with models. It can be used to find the cause of the degradation on energy efficiency and indoor climate quality in building heating, ventilation and air-conditioning (HVAC) systems. Real buildings are diverse. It requires a general modeling method. General modeling concept comprises three steps: hierarchical modeling procedure, parameterization and tuning procedure. In the procedure of hierarchical modeling, the process is split into levels ranging from global to micro level. The objective is to detect faults on the various levels. Consequently, different models for each level should be built. It is important to increase the accuracy of the models and let the models applicable for FDD on building HVAC systems. Parameterization and tuning procedure are necessary. An example model for a real air-conditioned room shows the results of general models and the results after tuning.

A new model of hydraulic elevator dynamics has been developed. It includes an improved dynamic friction model. This hydraulic elevator dynamics model is used in a new input–output based discrete adaptive sliding mode control algorithm comprised of an integral action, a nonlinear output feedback, and an adjustable sliding mode. The characteristic feature of the algorithm is an on-line update of the hyperplane coefficients and the integral gain to enable improved control loop behavior. Compared with the optimally tuned PID controller applied to a hydraulic elevator system, the new controller exhibits an increased robustness with regard to model uncertainties, unknown external disturbances and changes in the operation conditions, as well as much better velocity tracking characteristics.

A practical application of the modelling and validation of an open-chain industrial manipulator is presented in this paper. Both mechanical and electrical equations of motion were used to provide a complete model description. A model was obtained to enable an optimal path-planning controller to be designed. The paper describes how the equations of motion were derived and how the key parameters were obtained. The manipulator was simulated with TELEGRIP software. A validation procedure is illustrated and its' limitations exposed. The overall motion was found to give an agreement with the model predictions to within 86% for the smallest link and better than 96% for the major joints.