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1.
H. K. Moffatt 《地球物理与天体物理流体动力学》2013,107(1):95-97
Abstract By T. G. Cowling. Adam Hilger Ltd, x + 136 pp. £10.00 (ISBN O 85274 300 9) July 1976. 相似文献
2.
Abstract This paper experimentally investigates the convective planform near critical in a fluid layer whose temperature-dependent viscosity varies from top to bottom by up to a factor of 1500. Convection occurs in three different planforms: rolls, hexagons and squares. The square planform, which appears only for fluids with viscosity variation greater than about 50, replaces the hexagonal convection pattern as the Rayleigh number increases much above critical. The large amplitude of hexagonal convection with strong viscosity variation precludes studying the hexagon-square transition with perturbation methods of the type used to study the hexagon-roll transitions at smaller viscosity variations. 相似文献
3.
Edgar Knobloch 《地球物理与天体物理流体动力学》2013,107(6):535-536
We present three-dimensional (3D) solutions of the magnetohydrostatic equations in the co-rotating frame of reference outside a magnetized rigidly rotating cylinder. We make no symmetry assumption for the magnetic field, but to be able to make analytical progress we neglect outflows and specify a particular form for the current density. The magnetohydrostatic equations can then be reduced to a single linear partial differential equation for a pseudo-potential U, from which the magnetic field can be calculated by differentiation. The equation for U can be solved by standard methods. The solutions can also be used to determine the plasma pressure, density and temperature as functions of all three spatial coordinates. Despite the obvious limitations of this approach, it can, for example, be used as a simple tool to create 3D models for the closed field line regions of rotating magnetospheres without rotational symmetry. 相似文献
4.
B. R. Morton 《地球物理与天体物理流体动力学》2013,107(3-4):277-308
Abstract Vorticity, although not the primary variable of fluid dynamics, is an important derived variable playing both mathematical and physical roles in the solution and understanding of problems. The following treatment discusses the generation of vorticity at rigid boundaries and its subsequent decay. It is intended to provide a consistent and very broadly applicable framework within which a wide range of questions can be answered explicitly. The rate of generation of vorticity is shown to be the relative tangential acceleration of fluid and boundary without taking viscosity into account and the generating mechanism therefore involves the tangential pressure gradient within the fluid and the external acceleration of the boundary only. The mechanism is inviscid in nature and independent of the no-slip condition at the boundary, although viscous diffusion acts immediately after generation to spread vorticity outward from boundaries. Vorticity diffuses neither out of boundaries nor into them, and the only means of decay is by cross-diffusive annihilation within the fluid. 相似文献
5.
日心距离０．３ＡＵ以内形成的磁流体慢激波在向行星际空间传播过程中，通过向上游发出快压缩波而不断减弱．所发出的快压缩波经非线性变陡转化为快激波，形成由原慢激波和新生快激波构成的激波系统．强度不断减弱的慢激波将逐渐演变为准切向间断．这可能是在１ＡＵ附近很少观测到慢激波的重要原因． 相似文献
6.
从Ｒａｎｋｉｎｅ－Ｈｕｇｏｎｉｏｔ关系出发，以激波切向磁场ξ、上游激波角θ１和等离子体β１值为参数研究各类激波解的特性及相互关系，阐明各类激波强度随介质β值的变化规律．结果指出：（１）在ξ＜－１的Ⅰｂ型中间激波区和ξ＞４的快激波区存在双解；（２）慢激波可以直接和中间激波连接，但不能和快激波直接连接；（３）各类激波强度（用激波密度比衡量）随β１值均有变化：Ⅰｂ型中间激波上支随β１值增加而下降，下支则上升；Ⅰａ型中间激波和慢激波都随β１值增加而下降；快激波双解区上支随β１值增加而下降。下支上升；快激波在１＜ξ＜４区间的解随β１值增加而上升。 相似文献
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8.
We present simulations of the 3D nonlinear induction equation in order to investigate the temporal evolution of large-scale magnetic fields in spiral galaxies. Our model includes differential rotation, ambipolar diffusion and, based on small-scale turbulence, eddy diffusivity and the tensorial -effect with magnetic feedback. The nonaxisymmetric spiral pattern and – if considered – the vertical stratification of the galaxy are represented in its density and turbulence profile.
Neglecting vertical stratification the lifetime and geometry of an initial magnetic field depend on the correlation time of interstellar turbulence
corr
. Short correlation times increase the lifetime of the initial magnetic field, but the field is rapidly wound up. Its pitch-angles develop to zero. The magnetic field has disappeared after at most 1 to 1.5 Gyr. A resonance like phenomenon is found by tuning the pattern velocity of the galactic spiral. The simulations then show an exceptional amplification of the magnetic field in the case that the pattern speed and a magnetic drift velocity have similar values.
Considering a vertical stratification we achieve sufficiently long living grand-designed magnetic fields excited by dynamo action. The behaviour and geometry of the resulting field is again significantly influenced by the correlation time
corr
. Small values of
corr
lead to axisymmetric fields with small pitch-angles and field-concentration between the spiral arms. Increasing the correlation time the solutions show larger pitch-angles; and depending on very large correlation times the galactic dynamo rather generates fields clearly within the spiral arms and having a bisymmetric structure. 相似文献
9.
Accretion disks orbiting black holes power high-energy systems such as X-ray binaries and Active Galactic Nuclei. Observations
are providing increasingly detailed quantitative information about such systems. This data has been interpreted using standard
toy-models that rely on simplifying assumptions such as regular flow geometry and a parameterized stress. Global numerical
simulations offer a way to investigate the basic physical dynamics of accretion flows without these assumptions and, in principle,
lead to a genuinely predictive theory. In recent years we have developed a fully three-dimensional general relativistic magnetohydrodynamic
simulation code that evolves time-dependent inflows into Kerr black holes. Although the resulting global simulations of black
hole accretion are still somewhat simplified, they have brought to light a number of interesting results. These include the
formation of electro-magnetically dominated jets powered by the black hole’s rotation, and the presence of strong stresses
in the plunging region of the accretion flow. The observational consequences of these features are gradually being examined.
Increasing computer power and increasingly sophisticated algorithms promise a bright future for the computational approach
to black hole accretion. 相似文献
10.
The theory of magnetohydrodynamic (MHD) waves in solar coronal slabs in a zero-β configuration and for parallel propagation of waves does not allow the existence of surface waves. When oblique propagation
of perturbations is considered, both surface and body waves are able to propagate. When the perpendicular wavenumber is larger
than a certain value, the body kink mode becomes a surface wave. In addition, a sausage surface mode is found below the internal
cutoff frequency. When nonuniformity in the equilibrium is included, surface and body modes are damped by resonant absorption.
In this paper, first, a normal-mode analysis is performed and the period, the damping rate, and the spatial structure of the
eigenfunctions are obtained. Then, the time-dependent problem is solved, and the conditions under which one or the other type
of mode is excited are investigated. 相似文献