共查询到20条相似文献，搜索用时 187 毫秒
1.
应用并改进了由Ｃｈａｎｄｒａｓｅｋｈａｒ提出的一个变换,以改变磁流体力学方程组的形式。将动量守恒方案成一个物理变量的二次方程,研究了磁流体力学流动演化的非线性性质,特别注意突变过程,本导出的理论结果表明,磁流体力学流动能被分成一些分支,虽然在分支之间的跳跃（突变）可有大一些和小一些之分。进行了关于太阳日珥的数值试验;它们进一步直接表明理论结果的正确性。而且,虽然三个守恒定律所涉及的数量之间可以相 相似文献
2.
孙凯 《中国天文和天体物理学报》1997,(2)
本文介绍关于磁流体力学（ＭＨＤ）流动理论研究的一些结果．在所研究的流动中，允许流速垂直于磁场，允许各物理量随时间变化．在各有关的守恒定律和感应方程中引进代换，不经过求解，用严格的解析方法获得了有关解的某些性质．文中给出一个简单的例子．在其中计算二维沿磁力线的稳恒态ＭＨＤ流动． 相似文献
3.
孙凯 《中国天文和天体物理学报》1995,(4)
本文报告了在日冕或其他天体物理环境中，沿磁力线流动的稳恒态磁流体力学流动的一个定理和一个重要关系。它们是利用宏观动能密度对磁能密度的比例导出的。 相似文献
4.
关于日冕中稳恒态磁流体力学流动的一个定理 总被引：1，自引：1，他引：0
本报告了在日冕或其他天体物理环境中，沿磁力线流动的稳恒态磁流体力学流动的一个定理和一个重要关系。它们是利用宏观动能密度对磁能密度的比例导出的。 相似文献
5.
本介绍关于磁流体力学流动理论研究的一些结果，在所研究的流动中，允许流速垂直于磁场，允许各物理量随时间变化。在各有关的守恒定律和感应方程中引进代换，不经过求解，用严格的解析方法获得了有关解的某些性质，中给出一个简单的例子，在其中计算二维沿磁力线的稳恒态ＭＨＤ流动。 相似文献
6.
《天文学进展》2016,(4)
辐射磁流体力学(RMHD)是磁流体力学和等离子体物理学一个新的分支,它研究与辐射有显著能量和/或动量交换的磁流体动力学行为。天体辐射磁流体力学描述天体等离子体在宏观尺度上的电磁相互作用、结构、辐射、动力学和爆发现象。"天体辐射磁流体力学"是中国科学院数理学部2015—2016年度所支持的一个学科发展战略研究项目,其目的是评估这一生长中的学科分支的发展态势、国内外研究现状、适用的主要科学对象和发展战略,重点设定在三维数值模拟研究,或广义而言,数值实验研究。为了推动RMHD三维数值实验研究,这一专卷收入了天体物理学、太阳和空间物理学、受控等离子体实验等领域关于RMHD研究的部分调研和评述报告。 相似文献
7.
8.
许多行星 (如木卫三 ,水星 ,地球 ,木星和土星 )和恒星 (如太阳 )具有内部磁场。对这些磁场的存在和变化的解释对行星科学家和天体物理学家是一个巨大的挑战。本文试图总结行星和恒星的导电流体内部磁流体力学研究的新近发展和困难。一般由热对流驱动的流动通过磁流体力学过程产生并维持在行星和恒星中的磁场。在行星中磁流体力学过程强烈地受到转动 ,磁场和球几何位型的综合影响。其动力学的关键方面涉及科里奥利力和洛伦兹力间的相互作用。在太阳中其流线 ,即处于对流层的薄的剪切流层在太阳的磁流体力学过程中扮演了一个基本的角色 ,并由之产生了 1 1年的太阳黑子周期。本文也给出了一个新的非线性三维太阳发电机模型。 相似文献
9.
许多行星（如木卫三，水星，地球，木星和土星）和恒星（如太阳）具有内部磁场。对这些磁场的存在和变化的解释对行星科学家和天体物理学家是一个巨大的挑战。本文试图总结行星和恒星的导电流体内部磁流体力学研究的新近发展和困难。一般由热对流驱动的流动通过磁流体力学过程产生并维持在行星和恒星中的磁场。在行星中磁流体力学过程强烈地受到转动，磁场和球几何位型的综合影响。其动力学的关键方面涉及科里奥利力和洛伦兹力间的相互作用。在太阳中其流线，即处于对流层的薄的剪切流层在太阳的磁流体力学过程中扮演了一个基本的角色，并由之产生了11年太阳黑子周期。本文也给出了一个新的非线性三维太阳发电机模型。 相似文献
10.
本文研究了磁流体力学与高频等离子体波（ 包括纵横模式） 之间的精巧的相互作用。研究表明,这些等离激元会在电流片内诱发一种阻抗不稳定,并最终导至磁重联,出现爆发性不稳定。在高涨的离声湍动情况下,高温电流片模型必须采用反常电导率,而非库仑电导率。理论估算的结果与观测相一致。因此这种计及等离激元有质动力作用的新磁重联理论,基本上能解释耀斑现象。 相似文献
11.
The possibility that the type of magnetohydrodynamic (MHD) discontinuity changes as the plasma flow conditions gradually change is investigated in a general form. The conservation laws in MHD admit such transitions if there exist the so-called transition solutions that simultaneously satisfy two types of discontinuities. These solutions have been sought for. The system of possible transitions between MHD discontinuities obtained on their basis is presented in a clear schematic form. The ultimate general scheme of transitions includes all of the previously described schemes of transitions known to us. The system of discontinuities and transitions between them is studied in a self-consistent solution of the analytical problem of reconnection in a strong magnetic field. 相似文献
12.
M. Yokosawa 《Astrophysics and Space Science》1982,84(1):225-242
A mechanism is proposed for the formation of collimated beams in radio galaxies. The collimated flows which are non-thermally driven by high energy particles and magneto-hydrodynamic (MHD) waves are presented. The galactic nucleus surrounded by a cool gas is investigated. The cool gas accretes onto the nucleus and the accretion matter can confine the wave zone around the nucleus in which the high energy particles are completely locked to the MHD waves. When a quasi-radial magnetic field is embedded in the accretion flow, the MHD wave packets are collimated into the direction of symmetry axis of the galactic nuclear disc. The fluid around the nucleus is considered to be accelerated and heated by the MHD waves and ejected along the axis.A complete set of hydrodynamic equations which contain the energy transfers of high energy particles and MHD waves is presented. One-dimensional flows which are in pressure equilibrium with the surrounding accretion matter are calculated. When the energy density of the MHD waves is higher than that of the thermal energy, the fluid flow is strongly collimated in a narrow beam. When the MHD waves are strongly damped by the resistivity of the fluid at the great distance from the galactic centre, the collimated beam broadly reexpands. On the basis of the collimated beams driven by high energy particles, the radio morphology of the double radio sources is discussed. 相似文献
13.
Masayoshi Yokosawa 《Astrophysics and Space Science》1986,119(1):213-215
A mechanism is proposed for the formation of collinated beams in radio galaxies. Collimated flows are considered to be non-thermally driven by high energy particles and magneto-hydrodynamic (MHD) waves. The galactic nucleus is regarded as being surrounded by a cool gas. The cool gas accretes onto the nucleus, and then the high energy particles are completely locked to the MHD waves. When a quasi-radial magnetic field is embedded in the accretion flow, the resulting MHD wave packets are collimated into the direction of the symmetry axis of the galactic nuclear disc. The fluid around the nucleus is considered to be accelerated and heated by these MHD waves. The fluid beam is ejected along the symmetry axis.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
14.
Phasespace transport of a quasi-neutral multi-fluid plasma over the solar wind MHD termination shock
We study the physics of a multi-ion MHD shock, i.e. an MHD shock feature that forms when a supersonic flow of mixed ion populations is forced to adapt itself to a pressure obstacle further downstream. We shall describe this situation by using a multi-fluid approach for a mixture of ion populations with different specific masses and charges per ion species. First we calculate the effective electric potential that forces the plasma bulk to decelerate to the downstream bulk flow velocity which also then defines that system into which the downstream magnetic field is frozen-in. Then we calculate the unavoidable ion-specific overshoot velocities and gain from them, requesting energy conservation, the ion-specific contributions to the downstream thermal energies and pressures. The aim thereby is to find the solution for the MHD status of the downstream flow of the plasma mixture, specifically for a proton-electron plasma. We derive an implicit equation for the effective compression ratio and explicit relations for the different, downstream ion and electron temperatures as function of the multi-fluid compression ratio s. The resulting actual multi-fluid compression ratio s eff is found by adding up all the partial downstream pressures and comparing it with the upstream ram pressure. As we can show, the electron pressure is the dominant contribution to the total downstream plasma pressure. 相似文献
15.
我们在文[1]的启发下,计算了磁中性线附近异极性磁区相互入侵(或挤压)引起的等离子体动力学问题。气体初态取用流行的宁静太阳光球色球大气模型,即非等温的密度指数变化的重力分层大气。采用Lagrangian格式数值求解自洽的MHD方程,这可使入侵力学变得直观明显——磁场随流体而运动。我们的新结果是入侵流动在光球低层产生出强的水平磁场(即强的横向场),但光球高层和色球低层的磁结构却变化不大,有力地支持了文[13]提出的光球色球里可能出现磁流体力学间断面的概念。入侵确实在磁中性线附近建立了电流片,但这电流片主要在光球低层,其量级和观测一致。另外还显示垂直下降运动也可能导致异极磁区的入侵。尽管在MHD~1方程里包含了电阻耗散和热传导流,但计算证明它们对入侵力学影响不大,热传导的作用只是使气体温度分布逐渐趋于宁静太阳分布(尽管高度变了)。 相似文献
16.
AMR Simulations of Magnetohydrodynamic Problems by the CESE Method in Curvilinear Coordinates 总被引：1，自引：0，他引：1
The objective of this paper is to present new extensions of the space – time conservation element and solution element (CESE)
method for simulations of magnetohydrodynamic (MHD) problems in general curvilinear coordinates by using an adaptive mesh
refinement (AMR) grid system. By transforming the governing MHD equations from the physical space (x,y,z) to the computational space (ξ,η,ζ) while retaining the form of conservation, the CESE method is established for MHD in the curvilinear coordinates. Utilizing
the parallel AMR package PARAMESH, we present the first implementation of applying the AMR CESE method for MHD (AMR-CESE-MHD)
in both Cartesian and curvilinear coordinates. To show the validity and capabilities of the AMR-CESE-MHD code, a suite of
numerical tests in two and three dimensions including ideal MHD and resistive MHD are carried out, with two of them in both
Cartesian and curvilinear coordinates. Numerical tests show that our results are highly consistent with those obtained previously
by other authors, and the results under both coordinate systems confirm each other very well. 相似文献
17.
The resonances that appear in the linear compressible MHD formulation of waves are studied for equilibrium states with flow. The conservation laws and the jump conditions across the resonance point are determined for 1D cylindrical plasmas. For equilibrium states with straight magnetic field lines and flow along the field lines the conserved quantity is the Eulerian perturbation of total pressure. Curvature of the magnetic field lines and/or velocity field lines leads to more complicated conservation laws. Rewritten in terms of the displacement components in the magnetic surfaces parallel and perpendicular to the magnetic field lines, the conservation laws simply state that the waves are dominated by the parallel motions for the modified slow resonance and by the perpendicular motions for the modified Alfvén resonance.The conservation laws and the jump conditions are then used for studying surface waves in cylindrical plasmas. These waves are characterized by resonances and have complex eigenfrequencies when the classic true discontinuity is replaced by a nonuniform layer. A thin non-uniform layer is considered here in an attempt to obtain analytical results. An important result related to earlier work by Hollweg et al. (1990) for incompressible planar plasmas is found for equilibrium states with straight magnetic field lines and straight velocity field lines. For these equilibrium states the incompressible and compressible surface waves have the same frequencies at least in the long wavelength limit and there is an exact correspondence with the planar case. As a consequence, the conclusions formulated by Hollweg et al. still hold for the straight cylindrical case. The effects of curvature are subsequently considered. 相似文献
18.
Resonantly driven Alfvén waves are studied in non-uniform stationary magnetic flux tubes. Analytic dissipative MHD solutions are obtained for the Lagrangian displacement and the Eulerian perturbation of the total pressure. These analytic solutions are valid in the dissipative layer and in the two overlap regions to the left and the right of the dissipative layer. From these analytic solutions we obtain the fundamental conservation law and the jump conditions for resonantly driven Alfvén waves in magnetic flux tubes with an equilibriun flow. The fundamental conservation law and the jump conditions depend on the equilibrium flow in a more complicated way than just a Doppler shift. The effects of an equlibrium flow are not to be predicted easily in general terms with the exception that the polarization of the driven Alfvén waves is still in the magnetic surfaces and perpendicular to the magnetic field lines as it is in a static flux tube. 相似文献
19.
K. Tsinganos N. Vlahakis S.V. Bogovalov C. Sauty E. Trussoni 《Astrophysics and Space Science》2004,293(1-2):55-66
A brief review is given of some results of our work on the construction of (I) steady and (II) time-dependent MHD models for nonrelativistic and relativistic astrophysical outflows and jets, analytically and numerically. The only available exact solutions for MHD outflows are those in separable coordinates, i.e., with the symmetry of radial or meridional self-similarity. Physically accepted solutions pass from the fast magnetosonic separatrix surface in order to satisfy MHD causality. An energetic criterion is outlined for selecting radially expanding winds from cylindrically expanding jets. Numerical simulations of magnetic self-collimation verify the conclusions of analytical steady solutions. We also propose a two-component model consisting of a wind outflow from a central object and a faster rotating outflow launched from a surrounding accretion disk which plays the role of the flow collimator. We also discuss the problem of shock formation during the magnetic collimation of wind-type outflows into jets. 相似文献
20.
This paper considers driven resonant nonlinear slow magnetohydrodynamic (MHD) waves in dissipative steady plasmas. A theory developed by Ruderman, Hollweg, and Goossens (1997) is used and extended to study the effect of steady flows on the nonlinear resonant behaviour of slow MHD waves in slow dissipative layers. The method of matched asymptotic expansions is used to describe the behaviour of the wave variables in the slow dissipative layer. The nonlinear analogue of the connection formulae for slow MHD waves obtained previously by Goossens, Hollweg, and Sakurai (1992) and Erdélyi (1997) in linear MHD, are derived. The effect of an equilibrium flow results partly in a Doppler shift of the available frequency for slow resonance and partly in the modification of the width of the dissipative layer. 相似文献