共查询到18条相似文献，搜索用时 140 毫秒
1.
含粘滞性弱磁化吸积盘的轴对称脉动不稳定性 总被引：1，自引：0，他引：1
本文讨论了一种含扩散型粘滞的弱磁化等温吸积盘模型，在此模型中研究了扩散型粘滞、垂向磁场Bz和环向磁场B对轴对称脉动不稳定性的影响．结果表明，对于轴对称扰动，一般情况下盘内存在四种轴对称振荡模式．其中二种模式是脉动不稳定的，粘滞和磁场对它们表现为非稳因素；而另外二种模式是稳定的，粘滞和磁场对它们表现为致稳因素．此外我们还注意到，Bz和B主要影响近轴向的脉动不稳定性，扩散型弱粘滞主要影响径向脉动不稳定性． 相似文献
2.
本文从磁流体动力学方程组出发,用微扰法得出含三维磁场等温薄吸积盘的径向、轴向及环向不稳定性的色散方程．并详细讨论了磁场各分量对吸积盘不稳定性的影响．结果表明,磁场的径向和环向分量对磁声模和非轴对称模的不稳定性的增加起着主要的作用,且径向振荡大于轴向振荡．这一模型有利于解释ＦＵＯｒｉｏｎｉｓ和ＴＴａｕｒｉＳｔａｒｓ的周期光变现象 相似文献
3.
含三维磁场等温薄吸积盘的振荡不稳定性 总被引：1，自引：1，他引：0
本从磁流体动力学方程组出发,用微扰法得出含三维磁场等温薄吸积盘的径向,轴向及环向不稳定性的色散方程,并详细讨论了磁场各分量对吸积盘不稳定性的影响。结果表明,磁场的径向和环向分量对磁场声模和非轴对称模的不稳定性的增加起着主要的作用,且径向振荡大于轴向振荡,这一模型有利于解释ＦＵＯｒｉｏｎｉｓ和ＴＴａｕｒｉＳｔａｒｓ的周期光变现象。 相似文献
4.
从流体动力学方程出发,用微扰法得出含平流双温吸积盘的径向、环向不稳定性的色散方程．并对平流和径向粘滞力对双温吸积盘的影响进行了较详细的讨论．结果表明：平流和径向粘滞力对声模有较大的影响,且不改变粘滞模和热模的稳定性质．而环向扰动对吸积盘的各种模有着较明显的作用．这一模型有利于解释活动天体的周期和准周期光变现象． 相似文献
5.
通过对含平流双温吸积盘的不稳定性研究 ,发现较小的平流对几何薄、辐射致冷为主的吸积盘的两个声模有较大的影响 ;并不影响几何slim、辐射致冷的吸积盘的稳定性质。同时还发现 ,当考虑环向扰动时 ,吸积盘的不稳定性质与纯径向扰动情况下有较大的区别 相似文献
6.
弱磁化等温薄吸积盘的轴对称脉动不稳定性 总被引：1，自引：0，他引：1
本文在不考虑粘滞律的条件下，较详细地讨论了弱磁化等温薄吸积盘的轴对称脉动不稳定性．结果表明，对轴对称扰动，盘内存在４种轴对称振荡模式．仅当Ｂｚ和Ｂφ同时存在时磁场才能影响这些振荡模式的不稳定性．Ｂｚ和Ｂφ对其中２种角频率较高的振荡模式（对应于ωＩ）表现为非稳因素，而对其中２种角频率较低的振荡模式（对应于ωＩ）表现为致稳因素． 相似文献
7.
从流体动力学方程出发,用微扰法得出含平流双温吸积盘的径向,环向不稳定性的色散方程,并对平流和径向粘滞力对双温吸积盘的影响进行了较详细的讨论。结果表明：平流和径向粘滞力对声模有较大的影响,且不改变粘滞模和热模的稳定性质。而环向扰动对吸积盘的各种模有着较明显的作用,这一模型有利于解释活动天体的周期和准周期光变现象。 相似文献
8.
弱磁化等温薄吸积盘的轴对称脉动不稳定性 总被引：1，自引：0，他引：1
本在不考虑粘滞律的条件下，较详细地讨论了弱磁化等温薄吸积盘的轴对称脉动不稳定性，结果表明，对轴对称扰动，盘内存在４种轴对称振荡模式，仅当Ｂｚ和Ｂψ同时存在时磁场才能影响这些振荡模式的不稳定性。Ｂｚ和Ｂψ对其中２种角频率较高的振荡模式表现为非稳因素，而对其中２种角频率较低的振荡模式表现为致稳因素。 相似文献
9.
本文采用微扰方法导出色散方程，并在四种情况下详细讨论了薄吸积盘的不稳定性。结果表明：在纯粘滞和纯磁场盘中都存在脉动不稳定性。而且在吸积盘内同时考虑粘滞和磁场时，存在两种不稳定性，一种是脉动不稳定性，另一种是单调不稳定性。同时数值计算还表明，脉动不稳定性更可能存在于盘的内区，而单调不稳定性则只在盘的外区，对短波扰动才有意义。这些结果为解释ＢＬＬａｃ天体、Ｓｅｙｆｅｒｔ星系及类星体等活动星系核的光变现象进一步提供了理论依据。 相似文献
10.
磁化吸积盘的不稳定性研究 总被引：1，自引：0，他引：1
从磁流体动力学方程组出发,用微扰法得到的色散方程中含有环向磁场.利用全新的反常粘滞和反常阻抗,对吸积盘进行数值计算,结果表明,只有竖直方向的弱磁场才可以引发一种单调不稳定性.磁场对粘性吸积盘表现为非稳定性因素,增长率随磁场的增强而增大,且最大增长率大于理想情况下的值.垂向磁场足够强时,单调不稳定性不会出现. 相似文献
11.
Ding Shi-Xue Yang Lan-Tian Liu Xiao-Ci Wu Xue-Bing 《Astrophysics and Space Science》2000,272(4):383-394
The radial-azimuthal instability of gas-pressure-dominated accretion disk with advection is examined in this paper. We find
that the including of very little advection has significant effects on two acoustic modes, which are no longer complex conjugates
of each other. They increase the instability of the O-mode and damp that of the I-mode. We also find that when the azimuthal
perturbations are considered, the stability properties of disk are different from that in pure radial perturbation case. The
increase of azimuthal wave number will stabilize the acoustic modes but make the viscous mode more unstable and does not change
the thermal mode very much for optically thin disk. The I-mode is more stable. The O-mode, viscous mode and thermal mode tend
to become more unstable with the increase of azimuthal perturbation wavenumber for optically thick disk. For a geometrically
slim, advection-dominated disk, the increasing of azimuthal perturbations make thermal mode more unstable and acoustic mode
more stable.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
V. V. Prudskikh 《Astronomy Letters》2012,38(1):45-50
We consider nonaxisymmetric magnetosonic oscillations of a radially stratified, weakly ionized protoplanetary disk with a
vertical magnetic field. The combined effect of the Hall electric field and the density and magnetic field inhomogeneities
present in the disk has been previously predicted to lead to an instability of its small azimuthal perturbations. We revise
the previous results and take into account the effect of inhomogeneous ionization of the protoplanetary material related to
the inhomogeneity of the disk medium. We show that the instability criterion is governed by three parameters: the magnetic
field and ionization fraction gradients and the plasma β. We have found that at high values of β typical of protoplanetary disks, the instability does not manifest itself if the gradients are directed oppositely. In the
case of codirectional gradients, the interaction of magnetosonic fluctuations with inhomogeneities of a fixed size is resonant
in character, giving rise to an instability in a narrow range of wave numbers. 相似文献
13.
Ding Shi-Xue Yang Lan-Tian Wu Xue-Bing Lu Ye 《Monthly notices of the Royal Astronomical Society》2000,317(4):737-742
The radial–azimuthal instability of a hot two-temperature accretion disc with advection is examined in this paper. We find that the inclusion of very little advection has significant effects on two acoustic modes for a geometrically thin, cooling-dominated two-temperature disc, but has no effect on acoustic modes for a geometrically slim, cooling-dominated two-temperature disc. We also find that, when azimuthal perturbations are considered, the stability properties of the disc are different from those in the pure radial perturbation case. An increase of the azimuthal wavenumber will stabilize the acoustic modes but make the viscous and thermal modes more unstable for a geometrically thin, cooling-dominated two-temperature disc. It makes the thermal mode more unstable and the acoustic mode more stable, but only affects the instability of the viscous mode for short-wavelength perturbations for a geometrically slim, cooling-dominated two-temperature disc. For a geometrically slim, advection-dominated two-temperature disc, the increase of the azimuthal perturbation makes the I- and O-modes more stable and the thermal mode more unstable, but has no effect on the viscous mode. 相似文献
14.
We analyse the behaviour of linear magnetohydrodynamic perturbations of a coronal arcade modelled by a half-cylinder with an azimuthal magnetic field and non-uniform radial profiles of the plasma pressure, temperature, and the field. Attention is paid to the perturbations with short longitudinal (in the direction along the arcade) wavelengths. The radial structure of the perturbations, either oscillatory or evanescent, is prescribed by the radial profiles of the equilibrium quantities. Conditions for the corrugation instability of the arcade are determined. It is established that the instability growth rate increases with decreases in the longitudinal wavelength and the radial wave number. In the unstable mode, the radial perturbations of the magnetic field are stronger than the longitudinal perturbations, creating an almost circularly corrugated rippling of the arcade in the longitudinal direction. For coronal conditions, the growth time of the instability is shorter than one minute, decreasing with an increase in the temperature. Implications of the developed theory for the dynamics of coronal active regions are discussed. 相似文献
15.
The spatial structure and stability properties of the coupled Alfvén and drift compressional modes in a space plasma are studied in a gyrokinetic framework in a model taking into account field-line curvature and plasma and magnetic field inhomogeneity across the magnetic shells. The perturbation is found to be localized in two transparent regions, the Alfvén and drift compressional transparent regions, where the wave vector radial component squared is positive. Both regions are bounded by the resonance and cut-off surfaces, where the wave vector radial component turns into infinity and zero, respectively. An existence of the drift compressional resonance is one of the most important results of this work. It is argued that on the surface of this resonance the longitudinal and azimuthal components of the wave's magnetic field have a pole and logarithmic singularities, respectively. The instability conditions and expressions for the growth rate of the coupled modes have been obtained. In the Alfvénic transparent region, an instability occurs in the presence of the negative plasma temperature gradient. This instability does not lead to a non-stationary wave behavior: all the energy gained from the resonance particles was finally absorbed owing to any dissipation process. In a drift compressional transparent region, a necessary condition for the instability is the growth of the temperature with the radial coordinate. The growth rate is almost independent of the radial coordinate, which means that the wave energy gained from the particles cannot disappear. It will lead to an ever increasing wave amplitude, and no stationary picture for the unstable drift compressional mode is possible. 相似文献
16.
The instability of axisymmetric flows of ideal incompressible fluid with respect to infinitesimal perturbations with the nonconservation of angular momentum is investigated by numerically integrating the differential equations of hydrodynamics. The problem has been solved for two types of rotation profiles of an unperturbed flow: with zero and nonzero pressure gradients at the flow boundaries. Both rigid and free boundary conditions have been considered. The stability of axisymmetric flows with free boundaries is of great importance in disk accretion problems. Our calculations have revealed a crucial role of the flow pattern near the boundaries in the instability of the entire main flow. When the pressure gradient at the boundaries is zero, there is such a limiting scale of perturbations in azimuthal coordinate that longer-wavelength perturbations grow, while growing shorter-wavelength perturbations do not exit. In addition, for a fixed radial flow extent, there exists a nonzero minimum amplitude of the deviation of the angular velocity from the Keplerian one at which the instability vanishes. For a nonzero pressure gradient at the boundaries, the flow is unstable with respect to perturbations of any scale and at any small deviation of the angular velocity from the Keplerian one. 相似文献
17.
Gravitational instability of the dust layer formed after the aggregates of dust particles settle toward the midplane of a protoplanetary disk under turbulence is considered. A linearized system of hydrodynamic equations for perturbations of dust (monodisperse) and gas phases in the incompressible gas approximation is solved. Turbulent diffusion and the velocity dispersion of solid particles and the perturbation of gas azimuthal velocity in the layer upon the transfer of angular momentum from the dust phase due to gas drag are taken into account. Such an interaction of the particles and the gas establishes upper and lower bounds on the perturbation wavelength that renders the instability possible. The dispersion equation for the layer in the case when the ratio of surface densities of the dust phase and the gas in the layer is well above unity is obtained and solved. An approximate gravitational instability criterion, which takes the size-dependent stopping time of a particle (aggregate) in the gas into account, is derived. The following parameters of the layer instability are calculated: the wavelength range of its subsistence and the dependence of the perturbation growth rate on the perturbation wavelength in the circumsolar disk at a radial distance of 1 and 10 AU. It is demonstrated that at a distance of 1 AU, the gas–dust disk should be enriched with solids by a factor of 5–10 relative to the initial abundance as well as the particle aggregates should grow to the sizes higher than about 0.3 m in order for the instability to emerge in the layer in the available turbulence models. Such high disk enrichment and aggregate growth is not needed at a distance of 10 AU. The conditions under which this gravitational instability in the layer may be examined with no allowance made for the transfer of angular momentum from the gas in the layer to the gas in a protoplanetary disk outside the layer are discussed. 相似文献
18.
Norman R. Simon 《Astrophysics and Space Science》1977,51(1):205-215
The classical theory of stability of dynamical systems is employed to demonstrate that traditional definitions of pulsational instability cannot be directly applied to stars in thermal imbalance. In particular, it is shown that, for the case of thermal imbalance, pulsational displacements and pulsational velocities have separate and distincte-folding times. This being true, a broadened set of definitions becomes necessary, and we formulate such a set, again with reference to the classical theory. In accordance with the new definitions, it is argued that the development of observable pulsations requires as a necessary condition infinitesimal instability of both absolute displacement and velocity. If either one is unstable without the other, this constitutes a class of (probably) non-pulsational instability, not previously treated in the astrophysical literature. Finally, it is shown that the stability of stars in thermal imbalance may be evaluated according to the present definitions by employing either of two existing theories — the energy approach due to Demaret 91974; 1975; 1976) or the small perturbation technique of Coxet al. (1973). 相似文献