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A novel approach to identify resonant MHD wave modes in solar pores and sunspot umbrae: B-ω analysis

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arXiv 2021年

作者： Stangalini, Marco Jess, D.B. Verth, G. Fedun, V. Fleck, B. Jafarzadeh, S. Keys, P.H. Murabito, M. Calchetti, D. Aldhafeeri, A.A. Berrilli, F. Del Moro, D. Jefferies, S.M. Terradas, J. Soler, R. ASI Italian Space Agency Via del Politecnico snc Rome00133 Italy Astrophysics Research Centre School of Mathematics and Physics Queen’s University Belfast BelfastNorthern IrelandBT7 1NN United Kingdom Department of Physics and Astronomy California State University Northridge NorthridgeCA91330 United States Plasma Dynamics Group School of Mathematics and Statistics The University of Sheffield Hicks Building Hounsfield Road SheffieldS3 7RH United Kingdom Plasma Dynamics Group Department of Automatic Control and Systems Engineering The University of Sheffield SheffieldS1 3JD United Kingdom ESA Science and Operations Department NASA/GSFC Code 671 GreenbeltMD20771 United States Rosseland Centre for Solar Physics University of Oslo P.O. Box 1029 Blindern OsloNO-0315 Norway Institute of Theoretical Astrophysics University of Oslo P.O. Box 1029 Blindern OsloNO-0315 Norway INAF-OAR National Institute for Astrophysics Monte Porzio Catone RM00041 Italy Department of Physics University of Rome Tor Vergata Via della Ricerca Scientifica 1 Rome00133 Italy Mathematics and Statistic Department Faculty of Science King Faisal University Al-Hassa P.O. Box 400 Hofuf31982 Saudi Arabia Department of Physics and Astronomy Georgia State University GA30303 United States Institute for Astronomy University of Hawaii HI96768-8288 United States Departament de Física Universitat de les Illes Balears Palma de MallorcaE-07122 Spain Universitat de les Illes Balears Palma de MallorcaE-07122 Spain

The umbral regions of sunspots and pores in the solar photosphere are generally dominated by 3 mHz oscillations, which are due to p-modes penetrating the magnetic region. In these locations, wave power is also significantly reduced with respect to the quiet Sun. However, here we study a pore where the power of the oscillations in the umbra is not only comparable, or even larger than that of the quiet Sun, but the main dominant frequency is not 3 mHz as expected, but instead 5 mHz. By combining Doppler velocities and spectropolarimetry and analysing the relationship between magnetic field strength and frequency, the resultant B − ω diagram reveals distinct ridges which are remarkably clear signatures of resonant MHD oscillations confined within the pore umbra. In addition to velocity oscillations, we demonstrate that these modes are also accompanied by magnetic oscillations, as predicted from MHD theory. The novel technique of B − ω analysis, proposed in this Letter, opens an exciting new avenue for identifying MHD wave modes in the umbral regions of both pores and sunspots. Copyright © 2021, The Authors. All rights reserved.

关键词： Wave power

Variable speed control in wells turbine-based oscillating water column devices: optimum rotational speed

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IOP Conference Series: Earth and Environmental Science 2018年第1期136卷

作者： J Lekube A J Garrido I Garrido Automatic Control Group (ACG). Institute of Research and Development of Processes (IIDP). Department of Automatic Control and Systems Engineering Faculty of Engineering of Bilbao University of the Basque Country (UPV/EHU) Bilbao Spain

The effects of climate change and global warming reveal the need to find alternative sources of clean energy. In this sense, wave energy power plants, and in particular Oscillating Water Column (OWC) devices, offer a huge potential of energy harnessing. Nevertheless, the conversion systems have not reached a commercially mature stage yet so as to compete with conventional power plants. At this point, the use of new control methods over the existing technology arises as a doable way to improve the efficiency of the system. Due to the non-uniform response that the turbine shows to the rotational speed variation, the speed control of the turbo-generator may offer a feasible solution for efficiency improvement during the energy conversion. In this context, a novel speed control approach for OWC systems is presented in this paper, demonstrating its goodness and affording promising results when particularized to the Mutriku's wave power plant.

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Modelling 3D magnetic networks in a realistic solar atmosphere

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arXiv 2019年

作者： Gent, Frederick A. Snow, Ben Fedun, Viktor Erdélyi, Robertus Academy of Finland ReSoLVE Centre of Excellence Department of Computer Science Aalto University FI-02150 Finland College of Engineering Mathematics and Physical Sciences University of Exeter EX4 4QF United Kingdom School of Mathematics Statistics and Physics Newcastle University NE1 7RU United Kingdom School of Mathematics and Statistics University of Sheffield S3 7RH United Kingdom Plasma Dynamics Group Department of Automatic Control and Systems Engineering University of Sheffield S1 3JD United Kingdom Department of Astronomy Eötvös Loránd University Pázmány Péter sétány 1/A Budapest H-1117 Hungary

The magnetic network extending from the photosphere (solar radius ' R) to lower corona (R + 10 Mm) plays an important role in the heating mechanisms of the solar atmosphere. Here we further develop the models with realistic open magnetic flux tubes of the authors in order to model more complicated configurations. Closed magnetic loops, and combinations of closed and open magnetic flux tubes are modelled. These are embedded within a stratified atmosphere, derived from observationally motivated semi-empirical and data-driven models subject to solar gravity and capable of spanning from the photosphere up into the chromosphere and lower corona. Constructing a magnetic field comprising self-similar magnetic flux tubes, an analytic solution for the kinetic pressure and plasma density is derived. Combining flux tubes of opposite polarity it is possible to create a steady background magnetic field configuration modelling a solar atmosphere exhibiting realistic stratification. The result can be applied to SOHO/MDI and SDO/HMI and other magnetograms from the solar surface, upon which photospheric motions can be simulated to explore the mechanism of energy transport. We demonstrate this powerful and versatile method with an application to Helioseismic and Magnetic Imager data. Copyright © 2019, The Authors. All rights reserved.

关键词： 3D modeling

Modeling and MPPT control of a Tidal stream generator

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Modeling and MPPT control of a Tidal stream generator

International Conference on control, Decision and Information Technologies (CoDIT)

作者： Khaoula Ghefiri Soufiene Bouallègue Joseph Haggège Izaskun Garrido Aitor J. Garrido Department of Automatic Control and Systems Engineering Automatic Control Group - ACG Bilbao Spain University of Tunis El Manar Laboratory of Research in Automatic Control - LA.R.A Tunis Tunisia Universidad del Pais Vasco Bilbao PaÃs Vasco ES

This paper deals with the design, modeling and control of a Tidal Stream Generator (TSG) system including a tidal turbine, a rotor shaft and a Doubly Fed Induction Generator (DFIG). Below high tidal speed the system is regulated so that for every tidal velocity reaches the maximum power. A rotational speed control based-Maximum Power Point Tracking (MPPT) for a TSG is investigated to provide the suitable rotational speed to the system in order to track the maximum power and thus keeping the pitch angle null. Two study cases were proposed to test the performance of the control strategy. The obtained results show that the proposed control provide satisfactory tracking of the MPPT reference.

关键词： Turbines Velocity control Rotors Tides Maximum power point trackers

Numerical Evaluation of a Robust Self-Triggered MPC Algorithm

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IFAC-PapersOnLine 2016年第22期49卷 151-156页

作者： Brunner, Florian D. Heemels, W.P.M.H. Allgöwer, Frank Institute for Systems Theory and Automatic Control University of Stuttgart Pfaffenwaldring 9 Stuttgart70569 Germany Control System Technology Group Department of Mechanical Engineering Eindhoven University of Technology Netherlands

We present numerical examples demonstrating the efficacy of a recently proposed self-triggered model predictive control scheme for disturbed linear discrete-time systems with hard constraints on the input and state. In order to reduce the amount of communication between the controller and the actuator, the control input is not re-computed at each point in time but only at certain sampling instances. These instances are determined in a self-triggered fashion in the sense that at every sampling instant the next sampling instant is computed as a function of the current system state. A compact set in the state space, whose size is a design parameter in the control scheme, is stabilized. © 2016

关键词： Discrete time control systems Digital control systems Model predictive control Predictive control systems Robustness (control systems) control inputs control schemes Design parameters Hard constraints Linear discrete time systems Predictive control Sampling instants Self triggered controls

A novel tube-based output feedback MPC for constrained linear systems

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A novel tube-based output feedback MPC for constrained linea...

American control Conference

作者： Sankaranarayanan Subramanian Sergio Lucia Sebastian Engell Process Dynamics and Operations Group TU Dortmund Germany Otto-von-Guericke-University Magdeburg Laboratory for Systems Theory and Automatic Control Institute of Automation Engineering Germany

ISBN: (纸本)9781509045839

Model Predictive control (MPC) is an advanced strategy for the control of multi-variable and constrained dynamical systems. Tube-based MPC is a robust control technique that handles uncertainties present in the model. Since full state information is seldom available in practical systems, the estimation error must also be taken into account in addition to model uncertainties to achieve closed-loop stability and constraint satisfaction despite estimation and model errors. In this paper, we propose a novel strategy for the design of a tube-based output feedback MPC which is independent of the estimation method employed. We formulate a control policy by choosing a candidate estimate that is consistent with the reachable sets of the system under control. The proposed method can be combined with any estimation scheme as long as the assumed error bounds are satisfied. We show that the proposed method is recursively feasible, robustly exponentially stable, and performs better than other available strategies.

关键词： Maximum Allowable Concentration Linear system control strategy Output feedback constraint satisfaction problems model error control technology model uncertainty Statistical analysis

Sparse iterative learning control with application to a wafer stage: Achieving performance, resource efficiency, and task flexibility

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arXiv 2017年

作者： Oomen, Tom Rojas, Cristian R. Eindhoven University of Technology Faculty of Mechanical Engineering Control Systems Technology Group PO Box 513 Eindhoven5600MB Netherlands Automatic Control Lab Electrical Engineering KTH - Royal Institute of Technology StockholmS-100 44 Sweden

Trial-varying disturbances are a key concern in Iterative Learning control (ILC) and may lead to inefficient and expensive implementations and severe performance deterioration. The aim of this paper is to develop a general framework for optimization-based ILC that allows for enforcing additional structure, including sparsity. The proposed method enforces sparsity in a generalized setting through convex relaxations using 1norms. The proposed ILC framework is applied to the optimization of sampling sequences for resource efficient implementation, trial-varying disturbance attenuation, and basis function selection. The framework has a large potential in control applications such as mechatronics, as is confirmed through an application on a wafer stage. Copyright © 2017, The Authors. All rights reserved.

关键词： Two term control systems

Flows and magnetic field structures in reconnection regions of simulations of the solar atmosphere: do flux pile-up models work?

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arXiv 2018年

作者： Shelyag, S. Litvinenko, Y.E. Fedun, V. Verth, G. González-Avilés, J.J. Guzmán, F.S. Department of Mathematics Physics and Electrical Engineering Northumbria University Newcastle upon TyneNE1 8ST United Kingdom Department of Mathematics University of Waikato P. B. 3105 Hamilton New Zealand Plasma Dynamics Group Department of Automatic Control and Systems Engineering University of Sheffield SheffieldS1 3JD United Kingdom Plasma Dynamics Group School of Mathematics and Statistics University of Sheffield SheffieldS3 7RH United Kingdom Instituto de Geofísica Unidad Michoacán Universidad Nacional Autónoma de México MoreliaMichoacán Mexico Laboratorio de Inteligencia Artificial y Supercómputo Instituto de Física y Matemáticas Universidad Michoacana de San Nicolás de Hidalgo. MoreliaMichoacán Mexico

Aims. We study the process of magnetic field annihilation and reconnection in simulations of magnetised solar photosphere and chromosphere with magnetic fields of opposite polarities and constant numerical resistivity. Methods. Exact analytical solutions for reconnective annihilations are used to interpret the features of magnetic reconnection in simulations of flux cancellation in the solar atmosphere. We use MURaM high-resolution photospheric radiative magneto-convection simulations to demonstrate the presence of magnetic field reconnection consistent with the magnetic flux pile-up models. Also, a simulated data-driven chromospheric magneto-hydrodynamic simulation is used to demonstrate magnetic field and flow structures, which are similar to the ones theoretically predicted. Results. Both simulations demonstrate flow and magnetic field structures roughly consistent with accelerated reconnection with magnetic flux pile-up. The presence of standard Sweet-Parker type reconnection is also demonstrated in stronger photospheric magnetic fields. Copyright © 2018, The Authors. All rights reserved.

关键词： Magnetic flux

Call for papers: Special issue of international journal of robust and nonlinear control: "stochastic predictive control"

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International Journal of Robust and Nonlinear control 2016年第16期26卷 3670-3670页

作者： Quevedo, Daniel E. Chatterjee, Debasish Automatic Control Group Paderborn University EIM-E Warburgerstrasse 100 Germany Systems and Control Engineering IIT Bombay Powai Mumbai400076 India

September 2016 Special Issue of International Journal of Robust and Nonlinear control seeks to collect the current state-of-the-art directions in theoretical foundations and applications of stochastic model predictive control, with contributions from the finest researchers who are working in this area. With the steady growth in the availability of fast computing machines, control techniques based on algorithmic selection of actions derived from optimisation of a suitable performance index have gained prominence. Model predictive control, a framework that is based on such algorithmic selection procedures, has evolved over the years into one of the most useful and applicable control synthesis techniques currently available to a control engineer.

关键词： Model predictive control