1,720,971 research outputs found
A command governor approach to plasma shape control
No full textThe paper deals with the application of the socalled Command Governor (CG) approach to the shape control of plasmas in thermonuclear fusion reactors. A primal internal loop controlling the plasma-wall gaps is designed first and a CG device is then tuned to modify, whenever necessary, the reference to the primal loop, taking into account constraints due to voltages saturations on the converters, currents limitations in the active coils, force limits on the mechanical structures, minimum clearance between the plasma and the vacuum chamber wall, maximum induced forces on coils. The reference signal modification is accomplished through an online optimization procedure which embodies plasma model forecasts computed along a finite time virtual receding horizon as usual in model predictive paradigms. The ITER (International Thermonuclear Experimental Reactor) tokamak is assumed as a case study. Numerical simulations are carried out on a numerical nonlinear model taking into account almost a hundred of constraints. ©2009 IEEE
Constrained plasma shape control in ITER
No full textThis paper presents an application of a novel constrained control methodology known as Command Governor (CG) to the shape control of plasmas in thermonuclear fusion reactors. The CG strategy is based on predictive control ideas and consists in modifying, whenever necessary, the reference signal supplied to a primal internal loop controlling the plasma distance from the internal walls of the tokamak, taking into account constraints due to voltages saturations on the converters, currents limitations in the active coils for magnetic confinement, force limits on the mechanical structures, minimum clearance between the plasma and the vacuum chamber wall, maximum induced forces on coils. The reference signal modification is accomplished through an on-line optimization procedure which embodies plasma model forecasts computed along a finite time virtual receding horizon. A numerical example with about a hundred of constraints, is developed with reference to ITER
Constrained control strategies to improve safety and comfort on aircraft
No full textThe present paper explores the possibility of applying to an aircraft a novel constrained control methodology known as the command governor to improve flight safety and comfort. The proposed strategy is based on predictive control ideas and consists of the separate design of two control actions: an inner primal linear controller that guarantees the tracking of the controlled variables in the absence of constraints and an outer nonlinear static device (the command governor) that is compelled to modify, whenever necessary, the reference signals supplied to the inner controller by taking into account the limitations imposed by the aerodynamics, structures, actuators, and onboard comfort requirements. The reference signal modification is accomplished through an online constrained optimization procedure, which embodies the future plant evolution computed along a finite virtual time horizon. Two numerical examples are developed on a high-performance military aircraft and a small commercial aircraft. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved
A constrained control strategy for the shape control in thermonuclear fusion tokamaks
No full textThe paper deals with the application of the so-called Reference (or Command) Governor constrained control strategy to the shape control of plasmas in thermonuclear fusion reactors with the main scope of optimizing tokamak operations also in conditions very close to the operating envelope limits. A primal inner loop controlling the plasma-wall distance is first designed; the Reference Governor device is then tuned to modify, whenever necessary, the reference signals to the inner loop, on the basis of constraints due to voltage saturations on the power supply converters, limitations of currents in the active control coils, minimum clearance between the plasma surface and the vacuum chamber wall, maximum induced magnetic fields and forces on coils. As usual in model predictive paradigms, the reference signal modification is accomplished through an on-line optimization procedure which embodies plasma model forecasts computed along a finite time virtual receding horizon. The ITER (International Thermonuclear Experimental Reactor) tokamak is assumed as the case study. Numerical simulations are carried out on a finite elements nonlinear model taking into account induced currents in the passive structures. The proposed application shows how almost a hundred constraints can be managed on-line by the Reference Governor. © 2012 Elsevier Ltd. All rights reserved
A hybrid real-time supervisory scheme for nonlinear systems
No full textIn this paper we develop a hybrid supervisory control architecture in a real-time environment for constrained nonlinear systems. The strategy is based on Command Governor (CG) ideas that are here specialized in order to take into account both time-varying set-points and constraints. Experimental results on a laboratory four-tank test-bed are presented. © 2011 AACC American Automatic Control Council
A Hybrid Real-Time Command Governor Supervisory Scheme for Constrained Control Systems
No full textIn this paper, we develop a hybrid supervisory control architecture in a real-time environment for constrained control systems. The strategy is based on Command Governor (CG) ideas that are here specialized to consider both time-varying set-points and constraints. The significance of the method mainly lies on its capability to avoid constraints violation and loss of stability regardless of any configuration change occurrence in the plant/constraint structure by replacing the current CG with a new on-line computed unit. A real-time scheme is an extremely appealing choice because of its numerous engineering applications: automobile industry, defense and aerospace, chemical and nuclear plant applications, multimedia/telecommunications, and so on. Experimental results on a laboratory four-tank test-bed and simulations on a Cessna 182 aircraft model show the effectiveness of the proposed strategy
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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