scholarly journals Kink Oscillations of Coronal Loops

2021 ◽  
Vol 217 (6) ◽  
Author(s):  
V. M. Nakariakov ◽  
S. A. Anfinogentov ◽  
P. Antolin ◽  
R. Jain ◽  
D. Y. Kolotkov ◽  
...  
Keyword(s):  
Oscillation Amplitude ◽  
Wave Theory ◽  
Coronal Loops ◽  
Steady Flows ◽  
Magnetohydrodynamic Wave ◽  
Minor Radius ◽  
Kink Waves ◽  
Major Radius ◽  
A Minor ◽  
Theoretical Results

AbstractKink oscillations of coronal loops, i.e., standing kink waves, is one of the most studied dynamic phenomena in the solar corona. The oscillations are excited by impulsive energy releases, such as low coronal eruptions. Typical periods of the oscillations are from a few to several minutes, and are found to increase linearly with the increase in the major radius of the oscillating loops. It clearly demonstrates that kink oscillations are natural modes of the loops, and can be described as standing fast magnetoacoustic waves with the wavelength determined by the length of the loop. Kink oscillations are observed in two different regimes. In the rapidly decaying regime, the apparent displacement amplitude reaches several minor radii of the loop. The damping time which is about several oscillation periods decreases with the increase in the oscillation amplitude, suggesting a nonlinear nature of the damping. In the decayless regime, the amplitudes are smaller than a minor radius, and the driver is still debated. The review summarises major findings obtained during the last decade, and covers both observational and theoretical results. Observational results include creation and analysis of comprehensive catalogues of the oscillation events, and detection of kink oscillations with imaging and spectral instruments in the EUV and microwave bands. Theoretical results include various approaches to modelling in terms of the magnetohydrodynamic wave theory. Properties of kink oscillations are found to depend on parameters of the oscillating loop, such as the magnetic twist, stratification, steady flows, temperature variations and so on, which make kink oscillations a natural probe of these parameters by the method of magnetohydrodynamic seismology.

scholarly journals Excitation of decay-less transverse oscillations of coronal loops by random motions

2020 ◽  
Vol 633 ◽  
pp. L8 ◽  
Author(s):  
A. N. Afanasyev ◽  
T. Van Doorsselaere ◽  
V. M. Nakariakov
Keyword(s):  
Broad Band ◽  
Random Excitation ◽  
Forced Oscillations ◽  
Oscillatory Process ◽  
Coronal Loops ◽  
Alternative Mechanism ◽  
Steady Flows ◽  
Kink Waves ◽  
Random Motions ◽  
Transverse Oscillations

Context. The relatively large-amplitude decaying regime of transverse oscillations of coronal loops has been known for two decades and has been interpreted in terms of magnetohydrodynamic kink modes of cylindrical plasma waveguides. In this regime oscillations decay in several cycles. Recent observational analysis has revealed so-called decay-less, small-amplitude oscillations, in which a multi-harmonic structure has been detected. Several models have been proposed to explain these oscillations. In particular, decay-less oscillations have been described in terms of standing kink waves driven with continuous mono-periodic motions of loop footpoints, in terms of a simple oscillator model of forced oscillations due to harmonic external force, and as a self-oscillatory process due to the interaction of a loop with quasi-steady flows. However, an alternative mechanism is needed to explain the simultaneous excitation of several longitudinal harmonics of the oscillation. Aims. We study the mechanism of random excitation of decay-less transverse oscillations of coronal loops. Methods. With a spatially one-dimensional and time-dependent analytical model taking into account effects of the wave damping and kink speed variation along the loop, we considered transverse loop oscillations driven by random motions of footpoints. The footpoint motions were modelled by broad-band coloured noise. Results. We found the excitation of loop eigenmodes and analysed their frequency ratios as well as the spatial structure of the oscillations along the loop. The obtained results successfully reproduce the observed properties of decay-less oscillations. In particular, excitation of eigenmodes of a loop as a resonator can explain the observed quasi-monochromatic nature of decay-less oscillations and the generation of multiple harmonics detected recently. Conclusions. We propose a mechanism that can interpret decay-less transverse oscillations of coronal loops in terms of kink waves randomly driven at the loop footpoints.

scholarly journals Seismology of kink oscillations in coronal loops: Two decades of resonant damping

2007 ◽  
Vol 3 (S247) ◽  
pp. 228-242 ◽  
Author(s):  
Marcel Goossens
Keyword(s):  
Wave Theory ◽  
Resonant Absorption ◽  
Mhd Waves ◽  
Coronal Loops ◽  
Equilibrium Models ◽  
Kink Waves ◽  
The Common ◽  
Uniform Equilibrium ◽  
Transverse Oscillations ◽  
Alfven Velocity

AbstractThe detection of rapidly damped transverse oscillations in coronal loops by Aschwanden et al. (1999) and Nakariakov et al. (1999) gave a strong impetus to the study of MHD waves and their damping. The common interpretation of the observations of these oscillations is based on kink modes. This paper reviews how the observed period and damping time can be reproduced by MHD wave theory when non-uniform equilibrium models are considered that have a transversal variation of the local Alfven velocity. The key point here is that resonant absorption cannot be avoided and occurs as natural damping mechanism for kink waves in non-uniform equilibrium models. The present paper starts with work by Hollweg & Yang (1988) and discusses subsequent developments in theory and their applications to seismology of coronal loops. It addresses the consistent use of observations of periods and damping times as seismological tools within the framework of resonant absorption. It shows that within the framework of resonant absorption infinitely many equilibrium models can reproduce the observed values of periods and damping times.

scholarly journals Finite Amplitude Stability of Internal Steady Flows of the Giesekus Viscoelastic Rate-Type Fluid

Entropy ◽  
2019 ◽  
Vol 21 (12) ◽  
pp. 1219 ◽  
Author(s):  
Mark Dostalík ◽  
Vít Průša ◽  
Karel Tůma
Keyword(s):  
Flow Field ◽  
Internal Flow ◽  
Wasserstein Distance ◽  
Finite Amplitude ◽  
Positive Definite ◽  
Weissenberg Number ◽  
Steady Flows ◽  
Positive Definite Matrices ◽  
Rate Type ◽  
Theoretical Results

Using a Lyapunov type functional constructed on the basis of thermodynamical arguments, we investigate the finite amplitude stability of internal steady flows of viscoelastic fluids described by the Giesekus model. Using the functional, we derive bounds on the Reynolds and the Weissenberg number that guarantee the unconditional asymptotic stability of the corresponding steady internal flow, wherein the distance between the steady flow field and the perturbed flow field is measured with the help of the Bures–Wasserstein distance between positive definite matrices. The application of the theoretical results is documented in the finite amplitude stability analysis of Taylor–Couette flow.

The Reflection of Waterhammer Pressure Waves From Minor Losses

1965 ◽  
Vol 87 (2) ◽  
pp. 445-451 ◽  
Author(s):  
D. N. Contractor
Keyword(s):  
Method Of Characteristics ◽  
Wave Theory ◽  
Pressure Waves ◽  
Transmitted Waves ◽  
Pressure Time ◽  
Classical Wave ◽  
Friction Term ◽  
Minor Losses ◽  
A Minor ◽  
Experimental Pressure

This paper deals with the reflection produced when a waterhammer pressure wave encounters any device that produces a sudden energy loss such as an orifice, a valve, or an elbow. The classical wave theory is used to determine the magnitudes of the reflected and the transmitted waves. The waterhammer equations, with the friction term included, are solved by the method of characteristics. The conditions at a minor loss are studied as a boundary condition to these equations. Agreement between theoretical and experimental pressure-time diagrams is sufficient to validate the theory.

Analysis of Impact to Counter Force and Internal Force in Different Arrangements of Minor Radius Curve Steel Box Girder Supporting Point

2012 ◽  
Vol 430-432 ◽  
pp. 1482-1485
Author(s):  
Quan Sheng Sun ◽  
Tong Wu
Keyword(s):  
Internal Force ◽  
Box Girders ◽  
Box Girder ◽  
Minor Radius ◽  
Supporting Point ◽  
Steel Box Girder ◽  
A Minor ◽  
The City ◽  
House Building ◽  
Bridge Position

The designing course of curve steel box girder always needs to consider the city roads and buildings.It make the bridge position not only span the traffic below,but also avoid the house building all around [1].So curve steel box girders always have bigger span,smaller radius and the settled pier position.Also,because of the light weight and the prominent effect of bending-torsion coupling [2],the supporting points of steel box girder often suspend under the improper designing.It impact the safety of bridge vastly.Seriously it can make bridges topple.This paper take the designing course of a minor radius curve steel box girder as background to research change law of counter force and internal force of steel box girder in different supporting point arrangement.

Contributions to the theory of stokes waves

1955 ◽  
Vol 51 (4) ◽  
pp. 713-736 ◽  
Author(s):  
S. C. De
Keyword(s):  
Wave Height ◽  
Flow Rate ◽  
Volume Flow Rate ◽  
Wave Theory ◽  
Finite Depth ◽  
Volume Flow ◽  
Steady Flows ◽  
Total Head ◽  
Stokes Waves ◽  
Fifth Order

ABSTRACTThe well-known Stokes theory (9, 10) of waves of permanent form in water of finite depth has been extended to the fifth order of approximation. The solutions have been first obtained in the form of equations for the space coordinates x and y as functions of the velocity potential Φ and stream function ψ. Expressions for the complex potential W in terms of the complex variable z ( = x + iy), the form of the wave profile, and the square of the wave velocity have been obtained to the fifth order.Expressions for the three physical quantities Q, R and S, where Q is the volume flow rate per unit span, R is the energy per unit mass (i.e. g times the total head, measuring heights from the bottom and pressures from atmospheric) and S is the momentum flow rate per unit spaa, corrected for pressure forces and divided by density, have been obtained to the fifth order. The values for the dimensionless quantities r = R/Rc and s = S/Sc, where Rc and Sc refer to the values of R and S for a critical stream of volume flow Q, are tabulated for certain values of the ratios mean depth to wavelength and amplitude to wavelength. The values of r and s thus obtained have been used to calculate the ratios of mean depth to wavelength and of wave height to wavelength according to the cnoidal wave theory as recently presented by Benjamin and Light-hill(1), and the results are found to be in satisfactory agreement with that from Stokes's theory for waves longer than six times the depth.The (r, s) diagram introduced in the recent work of Benjamin and Lighthill(1) has been further considered, and the unshaded part of the diagram referred to in that paper has been mapped with a network of curves for constant values of the ratios of mean depth to wavelength and of wave height to wavelength (Fig. 2). The third barrier to the existence of steady flows, corresponding to ‘waves of greatest height’ referred to in that paper, has also been indicated in Fig. 2.

Impact of Domain Wall Pinning on the Dielectric Loss of Relaxor Ferroelectrics

2014 ◽  
Vol 1058 ◽  
pp. 153-157
Author(s):  
Li Ben Li ◽  
Guo Ling Li ◽  
Ya Peng Zhou ◽  
Guo Zhong Zang
Keyword(s):  
Dielectric Constant ◽  
Dielectric Loss ◽  
Charge Density Wave ◽  
Density Wave ◽  
Wave Theory ◽  
Relaxor Ferroelectrics ◽  
Domain Wall Pinning ◽  
Density Wave Theory ◽  
Concentration Of Impurities ◽  
Theoretical Results

Charge density wave theory is used to investigate the dependence of dielectric loss of relaxor ferroelectrics on temperature, frequency and concentration of impurities. The dielectric loss originates from the local pinning. The competition between the local and collective pinning leads to a peak in the curve of dielectric loss v.s. temperature as well as the curve of dielectric constant v.s. temperature. The peak temperature of dielectric constant TL, increases with increasing frequency and with decreasing concentration of impurities. The maximum dielectric loss is in proportion to TL and in inverse proportion to the barrier height. Our theoretical results agree qualitatively with the experimental results.

scholarly journals Temporal evolution of oscillating coronal loops

2020 ◽  
Vol 638 ◽  
pp. A89 ◽  
Author(s):  
C. R. Goddard ◽  
G. Nisticò
Keyword(s):  
Emission Measure ◽  
Initial Perturbation ◽  
Active Regions ◽  
Coronal Loops ◽  
Magnetohydrodynamic Wave ◽  
Distribution Width ◽  
Local Medium ◽  
Dem Analysis ◽  
Using Data ◽  
Transverse Oscillations

Context. Transverse oscillations of coronal structures are currently intensively studied to explore the associated magnetohydrodynamic wave physics and perform seismology of the local medium. Aims. We make a first attempt to measure the thermodynamic evolution of a sample of coronal loops that undergo decaying kink oscillations in response to an eruption in the corresponding active region. Methods. Using data from the six coronal wavelengths of SDO/AIA, we performed a differential emission measure (DEM) analysis of 15 coronal loops before, during, and after the eruption and oscillation. Results. We find that the emission measure, temperature, and width of the DEM distribution undergo significant variations on timescales relevant for the study of transverse oscillations. There are no clear collective trends of increases or decreases for the parameters we analysed. The strongest variations of the parameters occur during the initial perturbation of the loops, and the influence of background structures may also account for much of this variation. Conclusions. The DEM analysis of oscillating coronal loops in erupting active regions shows evidence of evolution on timescales important for the study of oscillations. Further work is needed to separate the various observational and physical mechanisms that may be responsible for the variations in temperature, DEM distribution width, and total emission measure.

The Consistent Second-Order Wave Theory and Its Application to a Submerged Spheroid

1970 ◽  
Vol 14 (01) ◽  
pp. 23-50
Author(s):  
Young H. Chey
Keyword(s):  
Free Surface ◽  
Solid Wall ◽  
Three Dimensional ◽  
Wave Theory ◽  
Order Theory ◽  
Wave Resistance ◽  
Second Order ◽  
Surface Phenomena ◽  
First Order ◽  
Theoretical Results

Because of the recognized inadequacy of first-order linearized surface-wave theory, the author has developed, for a three-dimensional body, a new second-order theory which provides a better description of free-surface phenomena. The new theory more accurately satisfies the kinematic boundary condition on the solid wall, and takes into account the nonlinearity of the condition at the free surface. The author applies the new theory to a submerged spheroid, to calculate wave resistance. Experiments were conducted to verify the theory, and their results are compared with the theoretical results. The comparison indicates that the use of the new theory leads to more accurate prediction of wave resistance.

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