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arXiv 2024年

作者： Berretti, M. Stangalini, M. Verth, G. Jafarzadeh, S. Jess, D.B. Berrilli, F. Grant, S.D.T. Duckenfield, T. Fedun, V. University of Trento Via Calepina 14 Trento38122 Italy University of Rome Tor Vergata Department of Physics Via della Ricerca Scientifica 3 Rome00133 Italy ASI Italian Space Agency Via del Politecnico snc Rome00133 Italy Plasma Dynamics Group School of Mathematics and Statistics The University of Sheffield Hicks Building Hounsfield Road SheffieldS3 7RH United Kingdom Max Planck Institute for Solar System Research Justus-von-Liebig-Weg 3 Göttingen37077 Germany Niels Bohr International Academy Niels Bohr Institute Blegdamsvej 17 CopenhagenDK-2100 Denmark Astrophysics Research Centre School of Mathematics and Physics Queen’s University Belfast Northern Ireland BelfastBT7 1NN United Kingdom Department of Physics and Astronomy California State University Northridge NorthridgeCA91330 United States Plasma Dynamics Group Department of Automatic Control and Systems Engineering The University of Sheffield Mappin Street SheffieldS1 3JD United Kingdom

It is well known that the dominant frequency of oscillations in the solar photosphere is ≈3 mHz, which is the result of global resonant modes pertaining to the whole stellar structure. However, analyses of the horizontal motions of nearly 1 million photospheric magnetic elements spanning the entirety of solar cycle 24 have revealed an unexpected dominant frequency, ≈5 mHz, a frequency typically synonymous with the chromosphere. Given the distinctly different physical properties of the magnetic elements examined in our statistical sample, when compared to largely quiescent solar plasma where ≈3 mHz frequencies are omnipresent, we argue that the dominant ≈5 mHz frequency is not caused by the buffeting of magnetic elements, but instead is due to the nature of the underlying oscillatory driver itself. This novel result was obtained by exploiting the unmatched spatial and temporal coverage of magnetograms acquired by the Helioseismic and Magnetic Imager (HMI) on board NASA’s Solar Dynamics Observatory (SDO). Our findings provide a timely avenue for future exploration of the magnetic connectivity between sub-photospheric, photospheric, and chromospheric layers of the Sun’s dynamic atmosphere. Copyright © 2024, The Authors. All rights reserved.

关键词： Magnetic structure

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Detection and classification of turn fault and high-resistance connection fault in inverter-fed permanent magnet machines based on high-frequency signals

Detection and classification of turn fault and high-resistan...

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作者： Hu, Rongguang Wang, Jiabin Mills, Andrew Chong, Ellis Sun, Zhigang Department of Electronics and Electrical Engineering University of Sheffield Sheffield United Kingdom Department of Automatic Control and System Engineering University of Sheffield Sheffield United Kingdom Electrical Capability Group Rolls-Royce plc Derby United Kingdom

Winding turn fault and high-resistance connection (HRC) fault will lead to different consequences and require different mitigation actions. In this study, the differentiating features between a turn fault and HRC fault are analysed and compared in a three-phase surface-mounted permanent magnet machine fed by the inverter with pulse-width-modulation voltages. The resultant high-frequency components in both voltages and currents are utilised for the fault detection and classification based on the high-frequency impedance and ripple current, without requiring modifications to the machine or interface design. Extensive simulations show that this method is capable of fault detection and classification in both transient and steady-state operations. © 2019 Institution of engineering and Technology. All rights reserved.

关键词： Permanent magnets

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On feasible sets for coalitional MPC

On feasible sets for coalitional MPC

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IEEE Annual Conference on Decision and control

作者： P. R. Baldivieso Monasterios P. A. Trodden M. Cannon Department of Automatic Control & Systems Engineering University of Sheffield Sheffield UK Department of Engineering Science University of Oxford Oxford UK

ISBN: (数字)9781728113982

ISBN: (纸本)9781728113999

This paper presents novel results and observations on the analysis of tube-based controllers for Large-Scale systems. These systems group several, possibly heterogeneous, interconnected subsystems into a single entity. Different subgroupings of subsystems lead to different coupling structures that have an impact on the design of robust decentralised controllers. We study the nesting properties of feasible regions and robust positive invariant sets for different partitions of the large-scale system in terms of partial order relations induced by the power set of the elements composing it.

关键词： Electron tubes controllability Robustness Economic indicators Couplings Large-scale systems

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The temporal and spatial evolution of MHD wave modes in sunspots

arXiv

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arXiv 2023年

作者： Albidah, A.B. Fedun, V. Aldhafeeri, A.A. Ballai, I. Jess, D.B. Brevis, W. Higham, J. Stangalini, M. Silva, S.S.A. MacBride, C.D. Verth, G. Department of Mathematics College Of Science Majmaah University P.O Box 66 Majmaah11952 Saudi Arabia Plasma Dynamics Group Department of Automatic Control and Systems Engineering The University of Sheffield Mappin Street SheffieldS1 3JD United Kingdom Mathematics and Statistic Department Faculty of Science King Faisal University Al-Hassa P.O. Box 400 Hofuf31982 Saudi Arabia Plasma Dynamics Group School of Mathematics and Statistics The University of Sheffield Hicks Building Hounsfield Road SheffieldS3 7RH United Kingdom Astrophysics Research Centre School of Mathematics and Physics Queen’s University Belfast BelfastBT7 1NN United Kingdom Department of Physics and Astronomy California State University Northridge NorthridgeCA91330 United States School of Engineering Pontificia Universidad Católica de Chile Chile School of Environmental Sciences Department of Geography and Planning University of Liverpool Roxby Building LiverpoolL69 7ZT United Kingdom ASI Italian Space Agency Via del Politecnico snc Rome00133 Italy

Through their lifetime sunspots undergo a change in their area and shape and, as they decay, they fragment into smaller structures. Here, for the first time we analyze the spatial structure of magneto-hydrodynamic (MHD) slow body and fast surface modes in observed umbrae as their cross-sectional shape changes. The Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) techniques were used to analyze 3 and 6 hours SDO/HMI time series of Doppler velocities at the photospheric level of approximately circular and elliptically shaped sunspots. Each time series were divided equally into time intervals, to evidence the change of the sunspots’ shape. To identify physical wave modes, the POD/DMD modes were cross-correlated with a slow body mode model using the exact shape of the umbra, whereas the shape obtained by applying a threshold level of the mean intensity for every time interval. Our results show that the spatial structure of MHD modes are affected, even by apparently small changes of the umbral shape, especially in the case of the higher-order modes. For the datasets used in our study, the optimal time intervals to consider the influence of the change in the shape on the observed MHD modes is 37 - 60 minutes. The choice of these intervals is crucial to properly quantify the energy contribution of each wave mode to the power spectrum. © 2023, CC0.

关键词： Dynamic mode decomposition

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Implicit IDA-PBC for Underactuated Mechanical systems: An LMI-based Approach

Implicit IDA-PBC for Underactuated Mechanical Systems: An LM...

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IEEE Conference on Decision and control

作者： Oscar B. Cieza Fernando Castaños Johann Reger Control Engineering Group Technische Universität Ilmenau Ilmenau Germany Automatic Control Department Cinvestav Mexico D.F. Mexico

ISBN: (数字)9781728113982

ISBN: (纸本)9781728113999

Recently, the Interconnection and Damping Assignment Passivity-Based control (IDA-PBC) methodology has been extended to underactuated mechanical systems in implicit port-Hamiltonian representation. The method is not restricted to holonomic systems, does not require a positive-definite target inertia matrix and, under general conditions, avoids the need for solving partial differential equations. In this paper we simplify the conditions for (local) stability and present equivalent matching equations. In addition, we exploit the inherent polynomial structure of implicit systems modeled in Euclidean space, such that the implicit IDA-PBC problem can be cast as a linear matrix inequality problem. The method is applicable to desired Hamiltonians with arbitrary polynomial order. The proposed methodology is validated on the portal crane and the cart-pole system.

关键词： Mathematical model Mechanical systems Stability analysis Kinetic theory Damping Partial differential equations Linear matrix inequalities

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Abstractions of linear dynamic networks for input selection in local module identification

arXiv

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arXiv 2019年

作者： Weerts, Harm H.M. Linder, Jonas Enqvist, Martin Hof, Paul M J Van den Control Systems Group Department of Electrical Engineering Eindhoven University of Technology Netherlands ABB Corporate Research Västerås Sweden Division of Automatic Control Linköping University Sweden

In abstractions of linear dynamic networks, selected node signals are removed from the network, while keeping the remaining node signals invariant. The topology and link dynamics, or modules, of an abstracted network will generally be changed compared to the original network. Abstractions of dynamic networks can be used to select an appropriate set of node signals that are to be measured, on the basis of which a particular local module can be estimated. A method is introduced for network abstraction that generalizes previously introduced algorithms, as e.g. immersion and the method of indirect inputs. For this abstraction method it is shown under which conditions on the selected signals a particular module will remain invariant. This leads to sets of conditions on selected measured node variables that allow identification of the target module. Copyright © 2019, The Authors. All rights reserved.

关键词： Network theory (graphs)

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Solar Vortex Tubes: Vortex Dynamics in the Solar Atmosphere

arXiv

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arXiv 2020年

作者： Silva, Suzana S.A. Fedun, Viktor Verth, Gary Rempel, Erico L. Shelyag, Sergiy Department of Physics Aeronautics Institute of Technology So Jos dos Campos Brazil Plasma Dynamics Group Department of Automatic Control and Systems Engineering University of Sheffield Sheffield United Kingdom Plasma Dynamics Group School of Mathematics and Statistics University of Sheffield Sheffield United Kingdom Department of Mathematics Aeronautics Institute of Technology So Jos dos Campos Brazil School of Information Technology Deakin University Geelong Australia

In this work, a state-of-the-art vortex detection method, Instantaneous Vorticity Deviation, is applied to locate three-dimensional vortex tube boundaries in numerical simulations of solar photospheric magnetoconvection performed by the MURaM code. We detected three-dimensional vortices distributed along intergranular regions and displaying coned shapes that extend from the photosphere to the low chromosphere. Based on a well-defined vortex center and boundary, we were able to determine averaged radial profiles and thereby investigate the dynamics across the vortical flows at different height levels. The solar vortex tubes present nonuniform angular rotational velocity, and, at all height levels, there are eddy viscosity effects within the vortices, which slow down the plasma as it moves toward the center. The vortices impact the magnetic field as they help to intensify the magnetic field at the sinking points, and in turn, the magnetic field ends up playing an essential role in the vortex dynamics. The magnetic field was found to be especially important to the vorticity evolution. On the other hand, it is shown that, in general, kinematic vortices do not give rise to magnetic vortices unless their tangential velocities at different height levels are high enough to overcome the magnetic tension. Copyright © 2020, The Authors. All rights reserved.

关键词： Vortex flow

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A framework for Operational Security Metrics Development for industrial control environment

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Journal of Cyber Security Technology 2018年第3-4期2卷 201-237页

作者： Ani, Uchenna P. Daniel He, Hongmei Tiwari, Ashutosh Manufacturing Informatics Centre School of Aerospace Transport and Manufacturing Cranfield University Bedford United Kingdom Department of Automatic Control and Systems Engineering The University of Sheffield Sheffield United Kingdom

Security metrics are very crucial towards providing insights when measuring security states and susceptibilities in industrial operational environments. Obtaining practical security metrics depend on effective security metrics development approaches. To be effective, a security metrics development framework should be scope-definitive, objective-oriented, reliable, simple, adaptable, and repeatable (SORSAR). A framework for Operational Security Metrics Development (OSMD) for industry control environments is presented, which combines concepts and characteristics from existing approaches. It also adds the new characteristic of adaptability. The OSMD framework is broken down into three phases of: target definition, objective definition, and metrics synthesis. A case study scenario is used to demonstrate an instance of how to implement and apply the proposed framework to demonstrate its usability and workability. Expert elicitation has also be used to consolidate the validity of the proposed framework. Both validation approaches have helped to show that the proposed framework can help create effective and efficient ICS-centric security metrics taxonomy that can be used to evaluate capabilities or vulnerabilities. The understanding from this can help enhance security assurance within industrial operational environments. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis group.

关键词： OSMD framework security metrics Operational Security metrics industry control environments security measurement

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

Variable speed control in wells turbine-based oscillating wa...

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2017年第六届电力科学与工程国际会议

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)

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 nonuniform 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.

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

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On closed-loop dynamics of ADMM-based MPC

arXiv

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arXiv 2019年

作者： Darup, Moritz Schulze Book, Gerrit Automatic Control Group Department of Electrical Engineering and Information Technology Universität Paderborn Warburger Straße 100 Paderborn33098 Germany

This paper studies the closed-loop dynamics of linear systems under approximate model predictive control (MPC). More precisely, we consider MPC implementations based on a finite number of ADMM iterations per time-step. We first show that the closed-loop dynamics can be described based on a nonlinear augmented model. We then characterize an invariant set around the augmented origin, where the dynamics become linear. Finally, we investigate the performance of the approximate MPC for various choices of the ADMM parameters based on a comprehensive numerical benchmark. Copyright © 2019, The Authors. All rights reserved.

关键词： Model predictive control

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