Готові списки джерел за темами / Gap eigenmode

Добірка наукової літератури з теми "Gap eigenmode"

Автор: Grafiati

Опубліковано: 10 грудня 2022

Оновлено: 29 січня 2023

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Статті в журналах з теми "Gap eigenmode"

Chang, Lei. "Alfvénic gap eigenmode in a linear plasma with ending magnetic throats." Physics of Plasmas 25, no. 12 (December 2018): 122503. http://dx.doi.org/10.1063/1.5066047.

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Zhang, Chang-Qing, Cun-Jun Ruan, Ding Zhao, Shu-Zhong Wang, and Xiu-Dong Yang. "Complete eigenmode analysis of a ladder-type multiple-gap resonant cavity." Chinese Physics B 23, no. 8 (July 31, 2014): 088401. http://dx.doi.org/10.1088/1674-1056/23/8/088401.

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Chang, L., B. N. Breizman, and M. J. Hole. "Gap eigenmode of radially localized helicon waves in a periodic structure." Plasma Physics and Controlled Fusion 55, no. 2 (December 21, 2012): 025003. http://dx.doi.org/10.1088/0741-3335/55/2/025003.

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Tiainen, Teemu, and Markku Heinisuo. "Buckling length of a frame member." Rakenteiden Mekaniikka 51, no. 2 (December 8, 2018): 49–61. http://dx.doi.org/10.23998/rm.66836.

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In steel frame design, the definition of buckling lengths of members is a basic task. Computers can be used to calculate the eigenmodes and corresponding eigenvalues for the frames and using these the buckling lengths of the members can be defined using Euler's equation. However, it is not always easy to say, which eigenmode should be used for the definition of the buckling length of a specific member. Conservatively, the lowest positive eigenvalue can be used for all members. In this paper, methods to define the buckling length of a specific member is presented. For this assessment, two ideas are considered. The first one uses geometric stiffness matrix locally and the other one uses strain energy measures to identify members taking part in a buckling mode. The behaviour of the methods is shown in several numerical examples. Both methods can be implemented into automated frame design, removing one big gap in the integrated design. This is essential when optimization of frames is considered.

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Chang, Lei, Ning Hu, and Jianyao Yao. "Influence of number and depth of magnetic mirror on Alfvénic gap eigenmode." Chinese Physics B 25, no. 10 (September 23, 2016): 105204. http://dx.doi.org/10.1088/1674-1056/25/10/105204.

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Chang, Lei. "Preliminary computation of the gap eigenmode of shear Alfvén waves on the LAPD." Chinese Physics B 27, no. 12 (December 2018): 125201. http://dx.doi.org/10.1088/1674-1056/27/12/125201.

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J Kramer, G., C. Z Cheng, M. Podestà, and R. Nazikian. "Simulation of the eigenmode spectrum below the Toroidicity-induced Alfvén eigenmode gap generated by the coupling of Alfvén and slow-magnetosonic waves in tokamaks." Plasma Physics and Controlled Fusion 62, no. 7 (June 17, 2020): 075012. http://dx.doi.org/10.1088/1361-6587/ab9153.

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Al Ba'ba'a, H., M. Nouh, and T. Singh. "Dispersion and topological characteristics of permutative polyatomic phononic crystals." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 475, no. 2226 (June 2019): 20190022. http://dx.doi.org/10.1098/rspa.2019.0022.

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This work presents a comprehensive mathematical treatment of phononic crystals (PCs) which comprise a finite lattice of repeated polyatomic unit cells. Wave dispersion in polyatomic lattices is susceptible to changes in the local arrangement of the monatoms (subcells) constituting the individual unit cell. We derive and interpret conditions leading to identical and contrasting band structures as well as the possibility of distinct eigenmodes as a result of cyclic and non-cyclic cellular permutations. Different modes associated with cyclic permutations yield topological invariance, which is assessed via the winding number of the complex eigenmode. Wave topology variations in the polyatomic PCs are quantified and conditions required to support edge modes in such lattices are established. Next, a transfer function analysis of finite polyatomic PCs is used to explain the formation of multiple Bragg band gaps as well as the emergence of truncation resonances within them. Anomalies arising from the truncation of the infinite lattice are further exploited to design mirror symmetrical edge modes in an extended lattice. We conclude with a generalized explanation of the band gap evolution mechanism based on the Bode plot analysis.

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Terao, Takamichi. "Numerical methods for design of metamaterial photonic crystals and random metamaterials." EPJ Applied Metamaterials 9 (2022): 1. http://dx.doi.org/10.1051/epjam/2021012.

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Two-dimensional metamaterial photonic crystals (2DMPCs) composed of dispersive metamaterials in a positive-refractive-index medium were investigated by incorporating finite-difference time-domain calculations into the auxiliary differential equation method. A distinct band gap was formed and the effects of positional and size disorder when the dispersive metamaterials are aligned in air were elucidated. In addition, using the self-consistent finite-difference frequency-domain method, an eigenmode analysis of 2DMPCs with positional disorder was performed. Finally, a numerical method for the inverse design of binary random metamaterial multilayers was proposed.

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Varela, J., J. Huang, D. A. Spong, J. Chen, V. Chan, L. Garcia, A. Wingen, Y. Ghai, and Y. Zou. "Theoretical study of the Alfven eigenmode stability in CFETR steady state discharges." Nuclear Fusion 62, no. 3 (January 20, 2022): 036005. http://dx.doi.org/10.1088/1741-4326/ac4778.

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Abstract The aim of this study is to analyze the stability of Alfven eigenmodes (AE) in the China Fusion Engineering Test Reactor (CFETR) plasma for steady state operations. The analysis is done using the gyro-fluid code FAR3d including the effect of the acoustic modes, EP finite Larmor radius damping effects and multiple energetic particle populations. Two high poloidal β scenarios are studied with respect to the location of the internal transport barrier (ITB) at r/a ≈ 0.45 (case A) and r/a ≈ 0.6 (case B). Both operation scenarios show a narrow TAE gap between the inner-middle plasma region and a wide EAE gap all along the plasma radius. The AE stability of CFETR plasmas improves if the ITB is located inwards, case A, showing AEs with lower growth rates with respect to the case B. The AEs growth rate is smaller in the case A because the modes are located in the inner-middle plasma region where the stabilizing effect of the magnetic shear is stronger with respect to the case B. Multiple EP populations effects (NBI driven EP + alpha articles) are negligible for the case A, although the simulations for the case B show a stabilizing effect of the NBI EP on the n = 1 BAE caused by α particles during the thermalization process. If the FLR damping effects are included in the simulations, the growth rate of the EAE/NAE decreases up to 70%, particularly for n > 3 toroidal families. Low n AEs (n < 6) show the largest growth rates. On the other hand, high n modes (n = 6 to 15) are triggered in the frequency range of the NAE, strongly damped by the FLR effects.

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Більше джерел

Дисертації з теми "Gap eigenmode"

Chang, Lei. "The impact of magnetic geometry on wave modes in cylindrical plasmas." Phd thesis, 2013. http://hdl.handle.net/1885/11578.

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Both space and laboratory plasmas can be associated with static magnetic field, and the field geometry varies from uniform to non-uniform. This thesis investigates the impact of magnetic geometry on wave modes in cylindrical plasmas. The cylindrical configuration is chosen so as to explore this impact in a tractable but experimentally realisable configuration. Three magnetic geometries are considered: uniform, focused and rippled. For a uniform magnetic field, wave oscillations in a plasma cylinder with axial flow and azimuthal rotation are modelled through a two-fluid flowing plasma model. The model provides a qualitatively consistent description of the plasma configuration on a Radio Frequency (RF) generated linear magnetised plasma (WOMBAT, Waves On Magnetised Beams And Turbulence [Boswell and Porteous, Appl. Phys. Lett. 50, 1130 (1987)]), and yields agreement between measured and predicted dependences of the wave oscillation frequency with axial field strength. The radial profile of the density perturbation predicted by this model is consistent with the data. Parameter scans show that the dispersion curve is sensitive to the axial field strength and the electron temperature, and the dependence of the oscillation frequency with electron temperature matches the experiment. These results consolidate earlier claims that the density and floating potential oscillations are a resistive drift mode, driven! by the density gradient. This, to our knowledge, is the first detailed physics modelling of plasma flows in the diffusion region away from the RF source. For a focused magnetic field, wave propagations in a pinched plasma (MAGPIE, MAGnetised Plasma Interaction Experiment [Blackwell et al., Plasma Sources Sci. Technol. 21, 055033 (2012)]) are modelled through an ElectroMagnetic Solver (EMS) based on Maxwell's equations and a cold plasma dielectric tensor. [Chen et. al., Phys. Plasmas 13, 123507 (2006)] The solver produces axial and radial profiles of wave magnitude and phase that are consistent with measurements, for an enhancement factor of 9.5 to the electron-ion Coulomb collision frequency and a 12% reduction in the antenna radius. It is found that helicon waves have weaker attenuation away from the antenna in a focused field compared to a uniform field. This may be consistent with observations of increased ionisation efficiency and plasma production in a non-uniform field. The relationship between plasma density, static magnetic field strength and axial wavelength agrees well with a simple theory developed previously. More! over, the wave amplitude is lowered and the power deposited into the core plasma decreases as the enhancement factor to the electron-ion Coulomb collision frequency increases, possibly due to the stronger edge heating for higher collision frequencies. For a rippled magnetic field, the spectra of radially localised helicon (RLH) waves [Breizman and Arefiev, Phys. Rev. Lett. 84, 3863 (2000)] and shear AlfvÃ©n waves (SAW) in a cold plasma cylinder are investigated. A gap-mode analysis of the RLH waves is first derived and then generalised to ion cyclotron range of frequencies for SAW. The EMS is employed to model the spectral gap and gap eigenmode. For both the RLH waves and SAW, it is demonstrated that the computed gap frequency and gap width agree well with the theoretical analysis, and a discrete eigenmode is formed inside the gap by introducing a defect to the system's periodicity. The axial wavelength of the gap eigenmode is close to twice the system's periodicity, which is consistent with Bragg's law, and the decay length agrees well with the analytical estimate. Experimental realisation of a gap eigenmode on a linear plasma device such as the LArge Plasma Device (LAPD) [Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] may be possible by introducing a symmetry-breaking defect to the system's periodicity. Such basic science studies could provide the possibility to accelerate the science of gap mode formation and mode drive in toroidal fusion plasmas, where gap modes are introduced by symmetry-breaking due to toroidicity, plasma ellipticity and higher order shaping effects. These studies suggest suppressing drift waves in a uniformly magnetised plasma by increasing the field strength, enhancing the efficiency of helicon wave production of plasma by using a focused magnetic field, and forming a gap eigenmode on a linear plasma device by introducing a local defect to the system's periodicity, which is useful for understanding the gap-mode formation and interaction with energetic particles in fusion plasmas.

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Тези доповідей конференцій з теми "Gap eigenmode"

Zhao, Zhenjiang, Huan Li, Mohamad Mantash, and Tayeb A. Denidni. "Eigenmode Analysis of Printed-Ridge-Gap-Waveguide Cavity and Its Application to Antenna design." In 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting. IEEE, 2019. http://dx.doi.org/10.1109/apusncursinrsm.2019.8888730.

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Möller, Daniel, Maximilian Jüngst, Felix Holzinger, Christoph Brandstetter, Heinz-Peter Schiffer, and Sebastian Leichtfuß. "Numerical Investigation of Tip Clearance Flow Induced Flutter in an Axial Research Compressor." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56956.

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A flutter phenomenon was observed in a 1.5-stage configuration at the Darmstadt transonic compressor. This phenomenon is investigated numerically for different compressor speeds. The flutter occurs for the second eigenmode of the rotor blades and is caused by tip clearance flow which is able to pass through multiple rotor gaps at highly throttled operating points. The vibration pattern during flutter is accompanied by a pressure fluctuation pattern of the tip clearance flow which is interacting with the blade motion causing the aeroelastic instability. The velocity of the tip clearance flow fluctuation is about 50% of the blade tip speed for simulation and experiment and also matches the mean convective velocity inside the rotor gap. This is consistent for all compressor speeds. From this investigations, general guidelines are drawn which can be applied at an early stage during compressor design to evaluate the susceptibility to this kind of blade vibration.

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Nelson, E. B., J. D. Paduano, and A. H. Epstein. "Active Stabilization of Surge in an Axi-Centrifugal Turboshaft Engine." In ASME 1999 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/99-gt-438.

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Active stabilization of surge was implemented on an Allied Signal LTS-101 axi-centrifugal gas producer, reducing the surging mass flow by 1%, for an operating range increase of 11%. Control was achieved using high response sensors in the inlet and diffuser throat, coupled to actuators that injected air near the diffuser throat. System identification and modeling indicate that a classical surge-type eigenmode and an eigenmode associated with engine duct acoustics dominate the engine’s input-output properties. The surge eigenmode’s stability determines the open-loop surge mass flow. A robust linear controller with three inputs and one output stabilized this eigenmode without destabilizing the acoustic mode. The controller facilitated a 1% reduction in surging mass flow at 95% N1 corrected; this increases the engine’s choke to surge stable operating range by 11%. This paper elucidates the measured unsteady pre-surge behavior of the engine, and outlines a systematic procedure for surge control law development.

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Hall, Kenneth C., Răzvan Florea, and Paul J. Lanzkron. "A Reduced Order Model of Unsteady Flows in Turbomachinery." In ASME 1994 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1994. http://dx.doi.org/10.1115/94-gt-291.

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A novel technique for computing unsteady flows about turbomachinery cascades is presented. Starting with a frequency domain CFD description of unsteady aerodynamic flows, we form a large, sparse, generalized, non-Hermitian eigenvalue problem which describes the natural modes and frequencies of fluid motion about the cascade. We compute the dominant left and right eigenmodes and corresponding eigenfrequencies using a Lanczos algorithm. Then, using just a few of the resulting eigenmodes, we construct a reduced order model of the unsteady flow field. With this model, one can rapidly and accurately predict the unsteady aerodynamic loads acting on the cascade over a wide range of reduced frequencies and arbitrary modes of vibration. Moreover, the eigenmode information provides insights into the physics of unsteady flows. Finally we note that the form of the reduced order model is well suited for use in active control of aeroelastic and aeroacoustic phenomena.

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Sharabi, Yonatan, Alex Dikopoltsev, Eran Lustig, Yaakov Lumer, and Mordechai Segev. "Light Propagation in Spatio-Temporal Crystals." In CLEO: Applications and Technology. Washington, D.C.: Optica Publishing Group, 2022. http://dx.doi.org/10.1364/cleo_at.2022.jw5a.1.

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We study light propagation in spatio-temporal photonic crystals: media whose electromagnetic properties vary periodically in both time and space. We find unique eigenmodes inside mixed energy-momentum gaps, extracting energy and momentum from the modulation.

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Martin, Ivo, and Dieter Bestle. "Automated Mode Identification of Airfoil Geometries to Be Used in an Optimization Process." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56987.

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Extending the lifetime of modern gas turbines is becoming increasingly challenging. A proper method for exploiting further improvement potential is to utilize automatic design optimization techniques, where for example, optimization may help to prevent excitations of eigenmodes of compressor airfoils thus, decreasing service costs, by reducing the risk of high cycle fatigue. However, in some cases the avoidance of any excitation may be not possible or too expensive due to the loss of aerodynamic efficiency. Since different eigenmodes do not share the same risk of failure, this is also not always necessary. Numerical optimization may account for this by penalizing the various eigenmodes differently which, however, requires that a proper mode-recognition technique be robust against design and mesh changes during the optimization process. This paper will introduce such a technique based on self-organizing maps (SOM). It will be used to project the suction-side surface of different blade geometries and mesh types onto a standard map in order to make deformations comparable for classification techniques. This enables to apply e.g. the mode-assurance criteria (MAC) in order to find correlations between the actual and already classified reference modes. The method will be demonstrated on two rotor blades.

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Rass, Jens, Tim Wernicke, Simon Ploch, Moritz Brendel, Andreas Kruse, Andreas Hangleiter, Wolfgang Scheibenzuber, Ulrich T. Schwarz, Markus Weyers, and Michael Kneissl. "Polarization of eigenmodes and the effect on the anisotropic gain in laser structures on nonpolar and semipolar GaN." In Gallium Nitride Materials and Devices VII. SPIE, 2012. http://dx.doi.org/10.1117/12.907865.

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Klose, Arno H. "Advanced Ducted Engines: Impact of Unsteady Aerodynamics on Fan Vibration Properties." In ASME 1992 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1992. http://dx.doi.org/10.1115/92-gt-228.

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Fans of Advanced Ducted Engines (ADE) will be built from light-weight materials such as carbon-fibre-reinforced plastics (CFRP). Due to their low density, the aeroelastic behaviour of these fan blades is significantly different from that of conventional titanium fan blading. Calculations performed during the design of ADE fan bladings show that self-induced aerodynamic loads can significantly alter the resonant frequencies; furthermore, aerodynamic coupling of the different in-vacuo eigenmodes can occur. This is not the case for conventional titanium fan blading, where the vibration properties are largely unaffected by unsteady aerodynamic forces. It is concluded that for light-weight fan blading, it is necessary to take into account aerodynamic stiffening and aerodynamic mode coupling when computing eigenfrequencies and aeroelastic stability.

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Li, Xinyan, and Dan Zhao. "Feedback Control of Self-Sustained Nonlinear Combustion Oscillations." In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-42126.

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Detrimental combustion instability is unwanted in gas turbines, aeroengines and rocket motors. It is typically generated due to the dynamic coupling between unsteady heat release and acoustic pressure. To prevent the onset of combustion instability or dampen large-amplitude oscillations, the coupling must somehow be interrupted. In this work, we design and implement a sliding mode controller and observer to mitigate self-sustained combustion oscillations in an open-ended thermoacoustic system. An acoustically compact heat source is confined and modeled by using a modified form of King’s Law. Coupling the heat source model with a Galerkin series expansion of the acoustic pressure provides an approach to evaluate the performance of the sliding mode control. The thermoacoustic systems with different numbers of eigenmodes and actuators are considered. It is found that self-sustained limit cycle oscillations can be successfully produced from small perturbations in the thermoacoustic systems when the actuators are not actuated. Meanwhile, the system we modeled can be proved to be controllable and observable. In order to gain insight on the thermoacoustic mode selection and triggering, the acoustical energy exchange between neighboring eigenmodes are studied and discussed. As the controller-driven actuators are actuated, the limit cycle oscillations are quickly dampened. And both thermoacoustic systems are stabilized. The successful demonstration indicates that the sliding mode controller can be applied to stabilize unstable thermoacoustic systems, even with multiple eigenmodes.

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Krishna, C. Vamsi, and Santosh Hemchandra. "Reduced Order Modelling of Combustion Instability in a Backward Facing Step Combustor." In ASME 2013 Gas Turbine India Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gtindia2013-3559.

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This paper develops a fully coupled time domain Reduced Order Modelling (ROM) approach to model unsteady combustion dynamics in a backward facing step combustor. The acoustic field equations are projected onto the canonical acoustic eigenmodes of the systems to obtain a coupled system of modal evolution equations. The heat release response of the flame is modelled using the G-equation approach. Vortical velocity fluctuations that arise due to shear layer rollup downstream of the step are modelled using a simplified 1D-advection equation whose phase speed is determined from a linear, local, temporal stability analysis of the shear layer, just downstream of the step. The hydrodynamic stability analysis reveals a abrupt change in the value of disturbance phase speed from unity for Re < Recrit to 0.5 for Re > Recrit, where Recrit for the present geometry was found to be ≈ 10425. The results for self-excited flame response show highly wrinkled flame shapes that are qualitatively similar to those seen in prior experiments of acoustically forced flames. The effect of constructive and destructive interference between the two contributions to flame surface wrinkling results in high amplitude wrinkles for the case when Kc → 1.

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