We apply the spatially and temporally periodic boundary conditions devised by Kraynik and Reinelt (Int. J. Multiphase Flow 18 (1992) 1045) to an atomic fluid undergoing planar elongational flow and describe several al...
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We apply the spatially and temporally periodic boundary conditions devised by Kraynik and Reinelt (Int. J. Multiphase Flow 18 (1992) 1045) to an atomic fluid undergoing planar elongational flow and describe several algorithms which efficiently apply the required nonstandard periodic boundary conditions. These periodic boundary conditions guarantee unrestricted simulation times, and are simply implemented if a rotational transformation is first applied to the coordinates of all atoms such that one of the cell boundaries aligns with the direction of elongation. While in the transformed frame one can apply either Lagrangian rhomboid (LR) or "deforming brick" (DB) periodic boundary conditions to all particle coordinates and relative distances. The latter (DB) scheme turns out to be very similar in form to standard Lees-Edwards periodic boundary conditions for planar shear flow, and both the LR and DB schemes are shown to be equivalent and numerically highly efficient. (C) 1999 Elsevier Science B.V.
This paper presents a system for statistical multiplexing of several compressed video programs using MPEG-2-compatible video encoders. We propose a new external joint rate control algorithm to dynamically distribute t...
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This paper presents a system for statistical multiplexing of several compressed video programs using MPEG-2-compatible video encoders. We propose a new external joint rate control algorithm to dynamically distribute the channel bandwidth among the program encoders such that the video quality is approximately equal in all programs. In our algorithm, the bit rate of each encoder is updated on the basis of the relative complexities of the programs measured at boundaries of groups of pictures (GOPs) and whenever scene changes are detected. The proposed algorithm requires no external preprocessing of the input video sources. Furthermore, as compared with previous work in this area, our algorithm is not restricted to operate only with encoders having the same GOP structure. Thus, the GOP boundaries at the different encoders need not be synchronized. Bit rate changes take place only at GOP boundaries, allowing the encoders to operate at a constant bit rate within GOPs. Overall, this results in a piecewise variable bit rate compression for each of the encoders. We also describe a strategy for decreasing the reaction delay of the system for scene changes. Experimental results show that the proposed multiprogram video compression system results in good picture quality with no external preprocessing, despite its relative simplicity.
We present the control and design of a vertical transparent multizone furnace which can operate in the temperature range of 25-750 degrees C and deliver thermal gradients of 2-45 degrees C/cm for the commercial applic...
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We present the control and design of a vertical transparent multizone furnace which can operate in the temperature range of 25-750 degrees C and deliver thermal gradients of 2-45 degrees C/cm for the commercial applications to crystal growth. A multivariable projective control algorithm is used for the temperature control. The controller accounts for the inevitable zone to zone thermal interactions. In addition, the control system operates such that the thermal profile is maintained under the thermal load of crystal, thus boundary conditions on crystal growth ampoules can be predetermined prior to crystal growth. Temperature profiles for the growth of crystals via directional solidification, vapor transport techniques, and multiple gradient applications can be easily implemented. The unique feature of its transparency and stable thermal profiles make the furnace useful for the determination of process parameters that optimize crystal growth conditions. (C) 1999 Elsevier Science Ltd. All rights reserved.
Linearization, interpolation and end-point constraints are combined to derive a receding horizon predictive control algorithm for continuous-time non-linear systems which are subject to input constraints. The algorith...
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Linearization, interpolation and end-point constraints are combined to derive a receding horizon predictive control algorithm for continuous-time non-linear systems which are subject to input constraints. The algorithm makes extensive use of the 'tail' of input/output state trajectories, namely the extension to current time of trajectories computed at the previous time instant. Through this device, the algorithm has guaranteed feasibility and stability and has some desirable attributes with respect to dynamic performance. The results of the paper are illustrated by a model of a coupled tank system.
This paper presents a test method for real-time earthquake simulation studies of large scale test structures. The method, effective force testing (EFT), is based on a force control algorithm. For systems that can be m...
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This paper presents a test method for real-time earthquake simulation studies of large scale test structures. The method, effective force testing (EFT), is based on a force control algorithm. For systems that can be modeled as a series of lumped masses (e.g., frame structures where masses are assumed lumped at the floor levels), the EFT forces are known a priori for any acceleration record. As opposed to the pseudodynamic test method (a displacement-based control. procedure), there is no computational time required for the EFT method in determining the required force signal;it is known prior to the test once the structural mass and ground acceleration record to be simulated are determined. Research has been conducted on a single-degree-of-freedom system at the University of Minnesota to investigate the potential of the EFT method. A direct application of the method was found ineffective because the actuator was unable to apply force at the natural frequency of the structure owing to actuator/control/structure interaction. However, numerical simulations and experimental implementation indicated that an additional velocity feedback loop incorporated into the control system can overcome this problem while maintaining the ability to do real-time testing.
The differential quadrature element method (DQEM) has been proposed. The element weighting coefficient matrices are generated by the differential quadrature (DQ) or generic differential quadrature (GDQ). By using the ...
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The differential quadrature element method (DQEM) has been proposed. The element weighting coefficient matrices are generated by the differential quadrature (DQ) or generic differential quadrature (GDQ). By using the DQ or GDQ technique and the mapping procedure the governing differential or partial differential equations, the transition conditions of two adjacent elements and the boundary conditions can be discretized. The overall algebraic equation system can be obtained by assembling all of the discretized equations. This method can convert a generic engineering or scientific problem having an arbitrary domain configuration into a computer algorithm. The DQEM analysis can be carried out by the adaptive refinement procedure. The development of adaptive DQEM refinement analysis procedure for fluid mechanics problems is carried out. Numerical results are presented. (C) 1999 Elsevier Science S.A. All rights reserved.
Inferential estimation and control are techniques tailored for processes with severe sampling limitations on key process measurements. Often such systems have complex, time-varying dynamics making sustainable control ...
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Inferential estimation and control are techniques tailored for processes with severe sampling limitations on key process measurements. Often such systems have complex, time-varying dynamics making sustainable control performance an elusive target. As potential solutions, adaptive and robust control have been suggested with varying degrees of success. In this work, robust control principles are used to develop a tuning procedure for an adaptive inferential control algorithm, in order to monitor and optimize control performance. The primary advantage of the technique is that performance-robustness targets are maintained despite changes in system dynamics. A case study is used to demonstrate the utility of the technique highlighting the performance enhancements provided by the combination of adaptive and robust inferential control. Copyright (C) 1999 John Wiley & Sons, Ltd.
In this paper, an implementable algorithm that enables to robustly control batch processes is proposed. The resulting state feedback algorithm is based on repeated on-line solution of constrained open loop min-max pro...
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In this paper, an implementable algorithm that enables to robustly control batch processes is proposed. The resulting state feedback algorithm is based on repeated on-line solution of constrained open loop min-max problems associated to the worst-case perturbations and/or uncertainties. These solutions are then used in a receding horizon scheme in order to yield a robust state feedback controller. A novel algorithm is proposed for the solution of the open loop constrained minmax problems that is based on chattering control combined with the variable stabilizing penalty approach. Simulations are provided in order to illustrate the effectiveness of the proposed control algorithm.
Evolvable hardware (EHW) refers to one particular type of hardware whose architecture, structure and functions change dynamically and autonomously in order to improve its performance in performing certain tasks. The e...
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Evolvable hardware (EHW) refers to one particular type of hardware whose architecture, structure and functions change dynamically and autonomously in order to improve its performance in performing certain tasks. The emergence of this new field has been influenced profoundly by the progress in reconfigurable hardware and evolutionary computation. Traditional hardware is notorious for its inflexibility. It is impossible to change the hardware's structure and functions once it is made. However, most real-world problems are not fixed. They change with time. In order to deal with these problems efficiently and effectively, different hardware structures are necessary. EHW provides an ideal approach making hardware 'soft' by adapting the hardware structure to a problem dynamically. There have been some concerns in recent years over the black-box nature of EHW, since it is often very difficult to analyze and understand circuits evolved by evolutionary algorithms. These concerns are natural and appear in other bio-.inspired systems as well, such as in artificial neural networks.
A powers-of-two algorithm is described that automatically creates discrete, well-defined, and unique result sets, displaying them in decreasing order of likely relevance. All computations are transparent, and a simple...
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A powers-of-two algorithm is described that automatically creates discrete, well-defined, and unique result sets, displaying them in decreasing order of likely relevance. All computations are transparent, and a simple query form allows the searcher to focus on the choice of terms and their sequence-an implicit indicator of their relative importance. The program can be used with traditional databases or with search engines designed for the Word Wide Web. It also can be used with an intelligent agent to search the Web with a pushdown store, returning only those items that best reflect the searcher's stated interests.
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