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54th AIAA/SAE/ASEE Joint Propulsion Conference, 2018

作者： Chaplin, Vernon H. Polk, James E. Katz, Ira Anderson, John R. Williams, George J. Soulas, George C. Yim, John T. NASA Jet Propulsion Laboratory California Institute of Technology Electric Propulsion Group 4800 Oak Grove Dr PasadenaCA91109 United States NASA Jet Propulsion Laboratory California Institute of Technology Propulsion and Materials Engineering Section 4800 Oak Grove Dr PasadenaCA91109 United States NASA Jet Propulsion Laboratory California Institute of Technology Contamination Control Engineering Group 4800 Oak Grove Dr PasadenaCA91109 United States NASA Glenn Research Center Electric Propulsion Systems Branch 21000 Brookpark Rd ClevelandOH44135 United States

ISBN: (数字)9781624105708

ISBN: (纸本)9781624105708

Accelerator (accel) grid sputtering by ions formed through charge-exchange (CEX) reactions between beam ions and residual neutral gas is a critical life-limiting mechanism for gridded ion thrusters. The three-dimensional ion optics code CEX3D is designed to simulate this grid erosion for a single beamlet, with a particular emphasis on non-axisymmetric features such as the "pits and grooves" erosion commonly observed on the accel grid downstream face in two-grid thrusters. The treatment of CEX ions in the code was recently upgraded with a new particle-in-cell (PIC) module to account for the influence of these ions’ space charge on the electrostatic potential downstream of the grids. In order to achieve reasonable computation times while resolving the Debye length near the grids and avoiding gross violations of the Courant-Friedrichs-Lewy (CFL) condition, macroparticle velocities in the PIC calculation are limited through a rescaling procedure that preserves ion trajectories and space charge density. The code accounts for beam divergence, finite momentum transfer in CEX collisions, and radial losses of CEX ions from the beam;these effects are important for determining the CEX ion flux to the accel grid because the calculated potential downstream of the grids can become very flat. The upgraded code has been used to simulate operation of NASA’s Evolutionary Xenon Thruster (NEXT) during the 51 kHr Long Duration Test a selection of results is presented and compared with experimental data. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

关键词： Ion exchange

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Examination of acoustic insulation of composite metamaterials with negative stiffness elements inclusions 24

Examination of acoustic insulation of composite metamaterial...

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24th International Congress on Sound and Vibration, ICSV 2017

作者： Ampatzidis, Theofanis Chronopoulos, Dimitrios Antoniadis, Ioannis Institute for Aerospace Technology Composites Group University of Nottingham NG7 2RD United Kingdom Machine Design and Control Systems Section School of Mechanical Engineering National Technical University of Athens Greece

Damping is one of the most important properties of materials, being responsible for increased durability and conmfort of the structures. In this paper the damping enhancement of materials with internal oscillators is examined. Wave Finite Element (WFE) method is used to get the wave propagation of an two-dimensional layered mechanical material having embedded nonlinear internal oscillators acting as negative stiffness element. The acoustic properties of the panel are studied in a Statistical Energy Analysis (SEA) scheme.

关键词： Damping

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A Grassmann Matrix Approach for the Computation of Degenerate Solutions for Output Feedback Laws

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IFAC-PapersOnLine 2017年第1期50卷 10839-10844页

作者： Leventides J. Meintanis I. Karcanias N. University of Athens Department of Economics Section of Mathematics and Informatics Pezmazoglou 8 Athens Greece Systems and Control Research Centre School of Mathematics Computer Sciences and Engineering City University of London Northampton Square London EC1V 0HB United Kingdom

The paper is concerned with the improvement of the overall sensitivity properties of a method to design feedback laws for multivariable linear systems which can be applied to the whole family of determinantal type frequency assignment problems, expressed by a unified description, the so-called Determinantal Assignment Problem (DAP). By using the exterior algebra/algebraic geometry framework, DAP is reduced to a linear problem (zero assignment of polynomial combinants) and a standard problem of multilinear algebra (decomposability of multivectors) which is characterized by the set of Quadratic Plücker Relations (QPR) that define the Grassmann variety of P. This design method is based on the notion of degenerate compensator, which are the solutions that indicate the boundaries of the control design and they provide the means for linearising asymptotically the nonlinear nature of the problems and hence are used as the starting points to generate linearized feedback laws. A new algorithmic approach is introduced for the computation and the selection of degenerate solutions (decomposable vectors) which allows the computation of static and dynamic feedback laws with reduced sensitivity (and hence more robust solutions). This approach is based on alternative, linear algebra type criterion for decomposability of multivectors to that defined by the QPRs, in terms of the properties of structured matrices, referred to as Grassmann Matrices. The overall problem is transformed to a nonlinear maximization problem where the objective function is expressed via the Grassmann Matrices and the first order conditions for optimality are reduced to a nonlinear eigenvalue-eigenvector problem. Hence, an iterative method similar to the power method for finding the largest modulus eigenvalue and the corresponding eigenvector is proposed as a solution for the above problem. © 2017

关键词： Frequency assignment Linear multivariable systems Linear systems Output feedback control (linear case)

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System Properties of Implicit Passive Electrical Networks Descriptions

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IFAC-PapersOnLine 2017年第1期50卷 9242-9247页

作者： Karcanias N. Livada M. Leventides J. Systems and Control Research Centre School of Mathematics Computer Sciences & Engineering City University London Northampton Square London EC1V 0HB United Kingdom University of Athens Department of Economics Section of Mathematics and Informatics Pezmazoglou 8 Athens Greece

Redesigning systems by changing elements, topology, organization, augmenting the system by the addition of subsystems, or removing parts, is a major challenge for systems and control theory. A special case is the redesign of passive electric networks which aims to change the natural dynamics of the network (natural frequencies) by the above operations leading to a modification of the network. This requires changing the system to achieve the desirable natural frequencies and involves the selection of alternative values for dynamic elements and non-dynamic elements within a fixed interconnection topology and/or alteration of the interconnection topology and possible evolution of the network (increase of elements, branches). The use of state-space or transfer function models does not provide a suitable framework for the study of this problem, since every time such changes are introduced, a new state space or transfer function model has to be recalculated. The use of impedance and admittance modeling, provides a suitable framework for the study of network properties under the process of re-engineering transformations. This paper deals with the fundamental system properties of the impedance-admittance network description which provide the appropriate framework for network re-engineering. We identify the natural topologies expressing the structured transformations linked to the impedance-graph, admittance graph-topology of the network and examine issues such as network regularity, number of finite frequencies and provide characterization of them in terms of the basic network matrices. The implicit network representation introduced provides a natural framework for expressing the different types of re-engineering transformations which can be used for the study of the natural frequencies assignment. © 2017

关键词： linear networks Linear systems structured systems system models system theory

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Implementation of the KDamper concept to wind turbine towers 6

Implementation of the KDamper concept to wind turbine towers

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6th International Conference on Computational Methods in Structural Dynamics and Earthquake engineering, COMPDYN 2017

作者： Kapasakalis, K.A. Sapountzakis, E.I. Antoniadis, I.A. Institute of Structural Analysis and Antiseismic Reasearch School of Civil Engineering National Technical University of Athens Zografou Campus AthensGR-157 80 Greece Mechanical Design and Control Systems Section Mechanical Engineering Department National Technical University of Athens Zografou Campus AthensGR-157 80 Greece

ISBN: (纸本)9786188284418

A novel passive vibration isolation and damping concept is implemented to wind turbine towers in order to minimize their response, under wind or seismic loads. This concept, called KDamper, constitutes a combination of the classic Tunned Mass Damper isolation system (TMD) with negative stiffness elements. The formulation of the linear and non-liner dynamic problem is a prerequisite. A parametric study is performed to determine the optimal parameters of the KDamper which degradate the response. For this scope, the calculation process of the aerodynamic load that exerts along the tower of the wind turbine is described. A comparison with a non-isolated wind turbine, as long as with a TMD isolated wind turbine indicates that KDamper is a promising isolation system, offering numerous advantages, such as increased damping and simple technological implementations.

关键词： Wind turbines

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Ten quick tips for deep learning in biology

arXiv

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arXiv 2021年

作者： Lee, Benjamin D. Gitter, Anthony Greene, Casey S. Raschka, Sebastian Maguire, Finlay Titus, Alexander J. Kessler, Michael D. Lee, Alexandra J. Chevrette, Marc G. Stewart, Paul Allen Britto-Borges, Thiago Cofer, Evan M. Yu, Kun-Hsing Carmona, Juan Jose Fertig, Elana J. Kalinin, Alexandr A. Signal, Beth Lengerich, Benjamin J. Triche, Timothy J. Boca, Simina M. In-Q-Tel Labs School of Engineering and Applied Sciences Harvard University Department of Genetics Harvard Medical School United States Department of Biostatistics and Medical Informatics University of Wisconsin-Madison MadisonWI United States Morgridge Institute for Research MadisonWI United States Department of Systems Pharmacology and Translational Therapeutics Perelman School of Medicine University of Pennsylvania PhiladelphiaPA United States Department of Biochemistry and Molecular Genetics University of Colorado School of Medicine AuroraCO United States Center for Health AI University of Colorado School of Medicine AuroraCO United States Department of Statistics University of Wisconsin Madison United States Faculty of Computer Science Dalhousie University Canada University of New Hampshire Bioeconomy.XYZ United States Department of Oncology Johns Hopkins University United States Institute for Genome Sciences University of Maryland School of Medicine United States Genomics and Computational Biology Graduate Program University of Pennsylvania United States Department of Systems Pharmacology and Translational Therapeutics University of Pennsylvania United States Wisconsin Institute for Discovery Department of Plant Pathology University of Wisconsin-Madison United States Department of Biostatistics and Bioinformatics Moffitt Cancer Center TampaFL United States Section of Bioinformatics and Systems Cardiology Klaus Tschira Institute for Integrative Computational Cardiology University Hospital Heidelberg Germany University Hospital Heidelberg Germany Lewis-Sigler Institute for Integrative Genomics Princeton University PrincetonNJ United States Graduate Program in Quantitative and Computational Biology Princeton University PrincetonNJ United States Department of Biomedical Informatics Harvard Medical School United States Department of Pathology Brigham and Women's Hospital United States Philips Healthcare CambridgeMA United States Philips Research

Machine learning is a modern approach to problem-solving and task automation. In particular, machine learning is concerned with the development and applications of algorithms that can recognize patterns in data and use them for predictive modeling. Artificial neural networks are a particular class of machine learning algorithms and models that evolved into what is now described as deep learning. Given the computational advances made in the last decade, deep learning can now be applied to massive data sets and in innumerable contexts. Therefore, deep learning has become its own subfield of machine learning. In the context of biological research, it has been increasingly used to derive novel insights from high-dimensional biological data. To make the biological applications of deep learning more accessible to scientists who have some experience with machine learning, we solicited input from a community of researchers with varied biological and deep learning interests. These individuals collaboratively contributed to this manuscript's writing using the GitHub version control platform and the Manubot manuscript generation toolset. The goal was to articulate a practical, accessible, and concise set of guidelines and suggestions to follow when using deep learning. In the course of our discussions, several themes became clear: the importance of understanding and applying machine learning fundamentals as a baseline for utilizing deep learning, the necessity for extensive model comparisons with careful evaluation, and the need for critical thought in interpreting results generated by deep learning, among others. © 2021, CC BY.

关键词： Learning algorithms

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Implementation of the KDamper concept using disc springs

arXiv

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arXiv 2017年

作者： Sapountzakis, Ioannis E. Tranakidis, Pavlos G. Antoniadis, Ioannis A. Mechanical Design and Control Systems Section Mechanical Engineering Department National Technical University of Athens Heroon Polytechniou 9 Zografou15780 Greece

The KDamper is a novel passive vibration isolation and damping concept, based essentially on the optimal combination of appropriate stiffness elements, which include a negative stiffness element. The KDamper concept does not require any reduction in the overall structural stiffness, thus overcoming the corresponding inherent disadvantage of the "Quazi Zero Stiffness" (QZS) or "Negative Stiffness" (NS) isolators, which require a drastic reduction of the structure load bearing capacity. Compared to the traditional Tuned Mass damper (TMD), the KDamper can achieve better isolation characteristics, without the need of additional heavy masses, as in the case of the TMD. Contrary to the TMD and its variants, such as the inerter, the KDamper substitutes the necessary high inertial forces of the added mass by the stiffness force of the negative stiffness element. Among others, this can provide comparative advantages in the very low frequency range. It should be mentioned, that the KDamping concept does not simply refer to a discrete vibration absorption device, but it consists a general vibration ab-sorption concept, applicable also for the design of advanced materials or complex structures. Such a concept thus presents the potential for numerous implementations in a large variety of technological applications, while further potential may emerge in a multi- physics environment. The paper proceeds to a review of the optimal design and selection of the parameters of the KDamper, which follows exactly the classical approach used for the design of the TMD. The negative stiffness elements have been replaced with a set of Belleville (disc) springs. It should be mentioned that two different cases for an initial displacement and an initial velocity have been considered. It is thus theoretically proven that the KDamper can inherently offer far better isolation and damping properties than the TMD. Finally, an application concerning the implementation of the KDamper for the design of a

关键词： Stiffness

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Parameter optimization of the KDamper concept in seismic isolation of bridges using harmony search algorithm 6

Parameter optimization of the KDamper concept in seismic iso...

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6th International Conference on Computational Methods in Structural Dynamics and Earthquake engineering, COMPDYN 2017

作者： Syrimi, Panagiota G. Sapountzakis, Evangelos J. Tsiatas, George C. Antoniadis, Ioannis A. Institute of Structural Analysis and Antiseismic Research School of Civil Engineering National Technical University of Athens Zografou Campus AthensGR-157 80 Greece Department of Mathematics University of Patras PatrasGR-265 04 Greece Mechanical Design and Control Systems Section Mechanical Engineering Department National Technical University of Athens Zografou Campus AthensGR-157 80 Greece

ISBN: (纸本)9786188284418

In this paper a novel design methodology for seismic isolation of bridges is presented employing the KDamper passive system and the Harmony Search (HS) optimization algorithm. The implementation of the KDamper concept to the absorption of seismic excitation of bridge structures requires the solution of a linear dynamic problem during which the basic parameters of KDamper design must be predefined. As this selection appears to be a quite complex procedure, the need for an optimization process is of paramount importance. In our work, an emerging metaheuristic algorithm, the Harmony Search algorithm, which has been successfully applied to several engineering problems, is employed to obtain optimum design parameters for a typical bridge structure under seismic excitation. The optimal solution is obtained for a set of 5 earthquake excitation records using as objective function the Root Mean Square of the displacement ratio. Comparative results of the dynamic response between the initial and the isolated structure are presented to verify the effectiveness, validity and reliability of the proposed design method.

关键词： Optimization

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Hydrazine conservation for the dawn spacecraft operations at the dwarf planet ceres 27th

Hydrazine conservation for the dawn spacecraft operations at...

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27th AAS/AIAA Space Flight Mechanics Meeting, 2017

作者： Lim, Ryan S. Smith, Brett A. Feldman, Antonette W. Salami, Mana Planning and Execution Systems Section. M/S 264-853 Jet Propulsion Laboratory California Institute of Technology 4800 Oak Grove Drive PasadenaCA91109-8099 United States Guidance and Control Section. M/S 321-550G Jet Propulsion Laboratory California Institute of Technology 4800 Oak Grove Drive PasadenaCA91109-8099 United States Flight Systems Engineering Integration and Test Section. M/S 264-847 Jet Propulsion Laboratory California Institute of Technology 4800 Oak Grove Drive PasadenaCA91109-8099 United States

ISBN: (纸本)9780877036371

Dawn is a low-thrust interplanetary spacecraft currently orbiting the dwarf planet Ceres. After successfully completing its Vesta and Ceres prime missions, Dawn is now in its extended mission, continuously exploring Ceres. After losing the second reaction wheel assembly at the end of the Vesta mission, the feasibility of the Ceres mission was at risk due to the potentially significant increase in hydrazine consumption from using only the reaction control system thrusters. This paper summarizes the intense, collaborative efforts undertaken by the project to conserve hydrazine prior to Vesta departure, during cruise to Ceres, and throughout the Ceres mission. The project's efforts in minimizing the number of turns are discussed. A special emphasis is given to describing various efforts taken by the Attitude control Subsystem team in an attempt to reduce hydrazine consumption. These efforts include: changing default slew rates, control gain tuning, changing nadir pointing strategy with Ahead Cross Nadir pointing, hybrid control implementation using hydrazine based thrusters and two remaining reaction wheels, optimal science turn location analysis, and reaction wheel angular momentum management strategies for reducing the number of momentum unloadings. In addition to the Attitude control Subsystem team's efforts, the Mission Design and Navigation team's efforts taken in designing hydrazine friendly orbit transfers are discussed. The trade study performed collaboratively by the Attitude control Subsystem team and the Science Operations Support Team in choosing hydrazine friendly off-nadir targets is also discussed. Various simulation results are presented and compared against actual flight data obtained. Lastly, remaining hydrazine status at the end of the prime Ceres mission and the hydrazine management planning for the extended mission are discussed.

关键词： Attitude control

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Suboptimal gain functions of feedback particle filter derived from continuation method

Suboptimal gain functions of feedback particle filter derive...

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AIAA Guidance, Navigation, and control Conference, 2016

作者： Matsuura, Yuki Ohata, Ryusuke Nakakuki, Kenji Hirokawa, Rui Mitsubishi Electric Corp. Kamakura Works Guidance and Control Engineering Section Defense Sub-systems Engineering Department Kanagawa Japan

ISBN: (数字)9781624103896

ISBN: (纸本)9781624103896

This paper proposes a novel numerical approach to obtain gain functions of feedback particle filters (FPFs). Recent researches have provided several methods of control-based formulation for particle filters (PFs). These new PFs control transition between prior and posterior particles based on Bayes’ rule. FPF is one of them, and FPF uses feedback control based on optimal control theory to adjust probability density of the posteriors. The optimal gain function needs to be obtained at each time step by solving an Euler-Lagrange boundary value problem (E-L BVP) based on states of the particles. Therefore, several approximation approaches, such as Galerkin approximation and constant gain approximation, have been proposed as a suboptimal solution. Although these approaches provide a correct estimation for the nonlinear estimation problems, these have a difficulty of determining internal parameters called basis functions. Furthermore, clear guidelines for choosing basis functions are not provided yet. In this paper, we introduce a numerically suboptimal solution for the E-L BVPs without basis functions in order to enhance the ease of obtaining the gain functions. Our solution is a kind of continuation method, and the gain functions are obtained by updating the last gain functions at each time. Moreover, the E-L BVPs are approximated as forward differences in order to reduce the computational cost. We applied this method to popular benchmark problems of nonlinear estimation. It was found that our method exhibits lower estimation error than previous methods such as constant gain method. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

关键词： Feedback

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