Subharmonic dynamo action of fluid motions with two-dimensional periodicity

1995 ◽  
Vol 448 (1933) ◽  
pp. 237-244 ◽  
Keyword(s):  
Magnetic Field ◽  
Velocity Field ◽  
Velocity Fields ◽  
Two Dimensional ◽  
Dynamo Action ◽  
Spatial Periodicity ◽  
The Magnetic Field ◽  
Steady Velocity

Kinematic dynamos based on steady velocity fields with two-dimensional periodicity are analysed numerically. The velocity fields of the study by G. O. Roberts (1972) are used and the analysis is extended to the case when the spatial periodicity of the magnetic field differs from that of the velocity field not only in the homogeneous third direction. While the solutions of Roberts correspond to the most efficient dynamos in most cases, there are some cases in which spatially subharmonic dynamos are preferred.

Plane MHD Steady Flows with Constantly Inclined Magnetic and Velocity Fields

1975 ◽  
Vol 53 (23) ◽  
pp. 2613-2616 ◽  
Author(s):  
O. P. Chandna ◽  
H. Toews ◽  
V. I. Nath
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Velocity Field ◽  
Fluid Flows ◽  
Velocity Fields ◽  
Steady Flows ◽  
Physical Conditions ◽  
Zero Current ◽  
Necessary And Sufficient ◽  
The Magnetic Field

Plane steady state viscous fluid flows, in which the magnetic field and velocity field are constantly inclined to one another, are considered. Necessary and sufficient physical conditions have been derived for flows with zero current density and the general solutions for these flows are obtained. Irrotational flows and flows with straight streamlines are also studied.

scholarly journals The effect of velocity shear on dynamo action due to rotating convection

2013 ◽  
Vol 717 ◽  
pp. 395-416 ◽  
Author(s):  
D. W. Hughes ◽  
M. R. E. Proctor
Keyword(s):  
Magnetic Field ◽  
Velocity Field ◽  
Large Scale ◽  
Mean Field ◽  
Magnetic Reynolds Number ◽  
Velocity Shear ◽  
Magnetic Field Generation ◽  
Dynamo Action ◽  
Rotating Convection ◽  
The Magnetic Field

AbstractRecent numerical simulations of dynamo action resulting from rotating convection have revealed some serious problems in applying the standard picture of mean field electrodynamics at high values of the magnetic Reynolds number, and have thereby underlined the difficulties in large-scale magnetic field generation in this regime. Here we consider kinematic dynamo processes in a rotating convective layer of Boussinesq fluid with the additional influence of a large-scale horizontal velocity shear. Incorporating the shear flow enhances the dynamo growth rate and also leads to the generation of significant magnetic fields on large scales. By the technique of spectral filtering, we analyse the modes in the velocity that are principally responsible for dynamo action, and show that the magnetic field resulting from the full flow relies crucially on a range of scales in the velocity field. Filtering the flow to provide a true separation of scales between the shear and the convective flow also leads to dynamo action; however, the magnetic field in this case has a very different structure from that generated by the full velocity field. We also show that the nature of the dynamo action is broadly similar irrespective of whether the flow in the absence of shear can support dynamo action.

Berechnung der mittleren Lorentz-Feldstärke für ein elektrisch leitendes Medium in turbulenter, durch Coriolis-Kräfte beeinflußter Bewegung

1966 ◽  
Vol 21 (4) ◽  
pp. 369-376 ◽  
Author(s):  
M. Steenbeck ◽  
F. Krause ◽  
K.-H. Rädler
Keyword(s):  
Magnetic Field ◽  
Velocity Field ◽  
Velocity Fields ◽  
Rotating Stars ◽  
Correlation Tensor ◽  
Coriolis Forces ◽  
Electrically Conducting ◽  
Electrically Conducting Fluid ◽  
The Magnetic Field ◽  
Component Parallel

A turbulent, electrically conducting fluid containing a magnetic field with non-vanishing meanvalue is investigated. The magnetic field strength and the conductivity may be so small that the turbulence is not influenced by the action of the LORENTZ force.The average of the crossproduct of velocity and magnetic field is calculated in a second approximation. It contains the averages of the products of two components of the velocity field, i. e. the components of the correlation tensor.Here the structure of the correlation tensor is determined for a medium with gradients of density and/or turbulence intensity, furthermore the turbulent motion is influenced by CORIOLIS forces.As the main result is shown that in those turbulent velocity fields the average crossproduct of velocity and magnetic field generally has a non-vanishing component parallel to the average magnetic field.Such a turbulence may be present in rotating stars. Consequences concerning the selfexcited build up of steller magnetic fields are discussed in a following paper.

scholarly journals THE ENERGY EIGENVALUES OF THE TWO DIMENSIONAL HYDROGEN ATOM IN A MAGNETIC FIELD

2006 ◽  
Vol 15 (06) ◽  
pp. 1263-1271 ◽  
Author(s):  
A. SOYLU ◽  
O. BAYRAK ◽  
I. BOZTOSUN
Keyword(s):  
Magnetic Field ◽  
Hydrogen Atom ◽  
Iteration Method ◽  
Weak Magnetic Field ◽  
The Other ◽  
Asymptotic Iteration Method ◽  
Iterative Approach ◽  
Two Dimensional ◽  
Energy Eigenvalues ◽  
The Magnetic Field

In this paper, the energy eigenvalues of the two dimensional hydrogen atom are presented for the arbitrary Larmor frequencies by using the asymptotic iteration method. We first show the energy eigenvalues for the case with no magnetic field analytically, and then we obtain the energy eigenvalues for the strong and weak magnetic field cases within an iterative approach for n=2-10 and m=0-1 states for several different arbitrary Larmor frequencies. The effect of the magnetic field on the energy eigenvalues is determined precisely. The results are in excellent agreement with the findings of the other methods and our method works for the cases where the others fail.

scholarly journals The influence of resistivity gradients on shock conditions for a Petschek reconnection geometry

2016 ◽  
Vol 34 (4) ◽  
pp. 421-425
Author(s):  
Christian Nabert ◽  
Karl-Heinz Glassmeier
Keyword(s):  
Magnetic Field ◽  
Necessary Conditions ◽  
The Other ◽  
Diffusion Region ◽  
Two Dimensional ◽  
Characteristic Velocity ◽  
Magnetohydrodynamic Equations ◽  
One Dimensional ◽  
The Magnetic Field ◽  
Alfven Velocity

Abstract. Shock waves can strongly influence magnetic reconnection as seen by the slow shocks attached to the diffusion region in Petschek reconnection. We derive necessary conditions for such shocks in a nonuniform resistive magnetohydrodynamic plasma and discuss them with respect to the slow shocks in Petschek reconnection. Expressions for the spatial variation of the velocity and the magnetic field are derived by rearranging terms of the resistive magnetohydrodynamic equations without solving them. These expressions contain removable singularities if the flow velocity of the plasma equals a certain characteristic velocity depending on the other flow quantities. Such a singularity can be related to the strong spatial variations across a shock. In contrast to the analysis of Rankine–Hugoniot relations, the investigation of these singularities allows us to take the finite resistivity into account. Starting from considering perpendicular shocks in a simplified one-dimensional geometry to introduce the approach, shock conditions for a more general two-dimensional situation are derived. Then the latter relations are limited to an incompressible plasma to consider the subcritical slow shocks of Petschek reconnection. A gradient of the resistivity significantly modifies the characteristic velocity of wave propagation. The corresponding relations show that a gradient of the resistivity can lower the characteristic Alfvén velocity to an effective Alfvén velocity. This can strongly impact the conditions for shocks in a Petschek reconnection geometry.

scholarly journals INCREASING THE EFFICIENCY OF MULTY-VARIANT CALCULATIONS OF ELECTROMAGNETIC FIELD DISTRIBUTION IN MATRIX OF A POLYGRADIENT SEPARATOR

2021 ◽  
Author(s):  
Jasim Mohmed Jasim Jasim ◽  
Iryna Shvedchykova ◽  
Igor Panasiuk ◽  
Julia Romanchenko ◽  
Inna Melkonova
Keyword(s):  
Magnetic Field ◽  
Field Distribution ◽  
Three Dimensional ◽  
Magnetic Potential ◽  
Geometric Parameters ◽  
Two Dimensional ◽  
Air Gaps ◽  
Vector Magnetic Potential ◽  
Electromagnetic Separator ◽  
The Magnetic Field

An approach is proposed to carry out multivariate calculations of the magnetic field distribution in the working gaps of a plate polygradient matrix of an electromagnetic separator, based on a combination of the advantages of two- and three-dimensional computer modeling. Two-dimensional geometric models of computational domains are developed, which differ in the geometric dimensions of the plate matrix elements and working air gaps. To determine the vector magnetic potential at the boundaries of two-dimensional computational domains, a computational 3D experiment is carried out. For this, three variants of the electromagnetic separator are selected, which differ in the size of the working air gaps of the polygradient matrices. For them, three-dimensional computer models are built, the spatial distribution of the magnetic field in the working intervals of the electromagnetic separator matrix and the obtained numerical values of the vector magnetic potential at the boundaries of the computational domains are investigated. The determination of the values of the vector magnetic potential for all other models is carried out by interpolation. The obtained values of the vector magnetic potential are used to set the boundary conditions in a computational 2D experiment. An approach to the choice of a rational version of a lamellar matrix is substantiated, which provides a solution to the problem according to the criterion of the effective area of the working area. Using the method of simple enumeration, a variant of the structure of a polygradient matrix with rational geometric parameters is selected. The productivity of the electromagnetic separator with rational geometric parameters of the matrix increased by 3–5 % with the same efficiency of extraction of ferromagnetic inclusions in comparison with the basic version of the device

scholarly journals DEPENDENCE OF THE MAGNETIC FIELD GENERATION MODELS OF IN MODEL OF A αΩ-DYNAMO ON THE INTENSITY OF A POWER TYPE α GENERATOR

2019 ◽  
pp. 58-66
Author(s):  
А.Н. Годомская ◽  
О.В. Шереметьева
Keyword(s):  
Magnetic Field ◽  
Comparative Analysis ◽  
Velocity Field ◽  
Dynamic Model ◽  
Radial Component ◽  
Magnetic Field Generation ◽  
Power Type ◽  
Exponential Kernel ◽  
Field Generation ◽  
The Magnetic Field

В динамической модели -динамо с переменной интенсивностью -генератора моделируются инверсии магнитного поля. Изменение интенсивности -генератора как следствие синхронизации высших мод поля скоростей и магнитного поля регулируется функцией Z(t) со степенным ядром. Получены режимы динамо для двух видов радиальной составляющей в скалярной параметризации -эффекта. Проведён анализ результатов в зависимости от изменения показателя степени ядра функции Z(t), а также сравнительный анализ с результатами исследования 10, где использовано показательное ядро функциии Z(t). In the dynamic model -dimensions are simulated reversions of the magnetic field with a varying intensity of the -generator. The change of the -generator intensity as a result of synchronization of higher modes of the velocity field and the magnetic field is regulated by a function Z(t) with a power kernel. Dynamo modes are obtained for two types of radial component in the scalar parameterization of the -effect. The results were analyzed depending on the change in the exponent of the kernel of the function Z(t), also a comparative analysis with the results of the study 10, where the exponential kernel of the function Z(t) was used.

Kinematic dynamo problem in a linear velocity field

1984 ◽  
Vol 144 ◽  
pp. 1-11 ◽  
Author(s):  
Ya. B. Zel'Dovich ◽  
A. A. Ruzmaikin ◽  
S. A. Molchanov ◽  
D. D. Sokoloff
Keyword(s):  
Magnetic Field ◽  
Spatial Distribution ◽  
Velocity Field ◽  
Random Matrix ◽  
Magnetic Energy ◽  
Linear Velocity ◽  
Finite Conductivity ◽  
Kinematic Dynamo ◽  
Linear Velocity Field ◽  
The Magnetic Field

A magnetic field is shown to be asymptotically (t → ∞) decaying in a flow of finite conductivity with v = Cr, where C = Cζ(t) is a random matrix. The decay is exponential, and its rate does not depend on the conductivity. However, the magnetic energy increases exponentially owing to growth of the domain occupied by the field. The spatial distribution of the magnetic field is a set of thin ropes and (or) layers.

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