69,384 research outputs found
Identification of heat exchange process in the evaporators of absorption refrigerating units under conditions of uncertainty
Проведено аналіз функціонування випарників абсорбційно-холодильних установок блоку вторинної конденсації типового для України агрегату синтезу аміаку. Обґрунтована необхідність мінімізації температури вторинної конденсації за рахунок створення автоматизованої адаптивної системи оптимального програмного управління. Встановлені рівняння для чисельної оцінки невизначеності теплового навантаження випарника та коефіцієнту теплопередачі. Розроблено алгоритмічне забезпечення щодо розв’язання задач ідентифікації та створення математичної моделі. Визначена технічна структура автоматизованої системи для їх реалізації
CSI technology validation on an LSS ground experiment facility
The test bed developed at JPL for experimental evaluation of new technologies for the control of large flexible space structures is described. The experiment consists of a flexible spacecraft dynamic simulator, sensors, actuators, a microcomputer, and an advanced programming environment. The test bed has been operational for over a year, and thus far nine experiments were completed or are currently in progress. Several of these experiments were reported at the 1987 CSI conference, and several recent ones are documented in this paper, including high order adaptive control, non-parametric system identification, and mu-synthesis robust control. An aggressive program of experiments is planned for the forseeable future
Adaptive control of large space structures using recursive lattice filters
The use of recursive lattice filters for identification and adaptive control of large space structures is studied. Lattice filters were used to identify the structural dynamics model of the flexible structures. This identification model is then used for adaptive control. Before the identified model and control laws are integrated, the identified model is passed through a series of validation procedures and only when the model passes these validation procedures is control engaged. This type of validation scheme prevents instability when the overall loop is closed. Another important area of research, namely that of robust controller synthesis, was investigated using frequency domain multivariable controller synthesis methods. The method uses the Linear Quadratic Guassian/Loop Transfer Recovery (LQG/LTR) approach to ensure stability against unmodeled higher frequency modes and achieves the desired performance
StocHy: automated verification and synthesis of stochastic processes
StocHy is a software tool for the quantitative analysis of discrete-time
stochastic hybrid systems (SHS). StocHy accepts a high-level description of
stochastic models and constructs an equivalent SHS model. The tool allows to
(i) simulate the SHS evolution over a given time horizon; and to automatically
construct formal abstractions of the SHS. Abstractions are then employed for
(ii) formal verification or (iii) control (policy, strategy) synthesis. StocHy
allows for modular modelling, and has separate simulation, verification and
synthesis engines, which are implemented as independent libraries. This allows
for libraries to be easily used and for extensions to be easily built. The tool
is implemented in C++ and employs manipulations based on vector calculus, the
use of sparse matrices, the symbolic construction of probabilistic kernels, and
multi-threading. Experiments show StocHy's markedly improved performance when
compared to existing abstraction-based approaches: in particular, StocHy beats
state-of-the-art tools in terms of precision (abstraction error) and
computational effort, and finally attains scalability to large-sized models (12
continuous dimensions). StocHy is available at www.gitlab.com/natchi92/StocHy
Process operating mode monitoring : switching online the right controller
This paper presents a structure which deals with
process operating mode monitoring and allows the control law reconfiguration
by switching online the right controller. After a short
review of the advances in switching based control systems during
the last decade, we introduce our approach based on the definition
of operating modes of a plant. The control reconfiguration
strategy is achieved by online selection of an adequate controller,
in a case of active accommodation. The main contribution lies
in settling up the design steps of the multicontroller structure
and its accurate integration in the operating mode detection and
accommodation loop. Simulation results show the effectiveness
of the operating mode detection and accommodation (OMDA)
structure for which the design steps propose a method to study the
asymptotic stability, switching performances improvement, and
the tuning of the multimodel based detector
Ground-based adaptive optics coronagraphic performance under closed-loop predictive control
The discovery of the exoplanet Proxima b highlights the potential for the
coming generation of giant segmented mirror telescopes (GSMTs) to characterize
terrestrial --- potentially habitable --- planets orbiting nearby stars with
direct imaging. This will require continued development and implementation of
optimized adaptive optics systems feeding coronagraphs on the GSMTs. Such
development should proceed with an understanding of the fundamental limits
imposed by atmospheric turbulence. Here we seek to address this question with a
semi-analytic framework for calculating the post-coronagraph contrast in a
closed-loop AO system. We do this starting with the temporal power spectra of
the Fourier basis calculated assuming frozen flow turbulence, and then apply
closed-loop transfer functions. We include the benefits of a simple predictive
controller, which we show could provide over a factor of 1400 gain in raw PSF
contrast at 1 on bright stars, and more than a factor of 30 gain on
an I = 7.5 mag star such as Proxima. More sophisticated predictive control can
be expected to improve this even further. Assuming a photon noise limited
observing technique such as High Dispersion Coronagraphy, these gains in raw
contrast will decrease integration times by the same large factors. Predictive
control of atmospheric turbulence should therefore be seen as one of the key
technologies which will enable ground-based telescopes to characterize
terrrestrial planets.Comment: Accepted to JATI
Chance in the Modern Synthesis
The modern synthesis in evolutionary biology is taken to be that period in
which a consensus developed among biologists about the major causes of
evolution, a consensus that informed research in evolutionary biology for
at least a half century. As such, it is a particularly fruitful period to consider
when reflecting on the meaning and role of chance in evolutionary explanation.
Biologists of this period make reference to “chance” and loose cognates
of “chance,” such as: “random,” “contingent,” “accidental,” “haphazard,” or
“stochastic.” Of course, what an author might mean by “chance” in any specific context varies.
In the following, we first offer a historiographical note on the synthesis.
Second, we introduce five ways in which synthesis authors spoke about
chance. We do not take these to be an exhaustive taxonomy of all possible
ways in which chance meaningfully figures in explanations in evolutionary
biology. These are simply five common uses of the term by biologists at this
period. They will serve to organize our summary of the collected references to
chance and the analysis and discussion of the following questions:
• What did synthesis authors understand by chance?
• How did these authors see chance operating in evolution?
• Did their appeals to chance increase or decrease over time during the synthesis?
That is, was there a “hardening” of the synthesis, as Gould claimed
(1983)
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