摘要:

We study the bifurcation to steady two-dimensional convection with the heat flux prescribed on the fluid boundaries. The fluid is weakly non-Boussinesq on account of a slight temperature dependence of its material properties. Using expansions in the spirit of shallow water theory based on the preference for large horizontal scales in fixed flux convection, we derive an evolution equation for the horizontal structure of convective cells. In the steady state, this reduces to a simple nonlinear ordinary differential equation. When the horizontal scales of the cells exceed a certain critical size, the bifurcation to steady convection is subcritical and the degree of subcriticality increases with increasing cell size.

ISSN:0309-1929    

DOI:10.1080/03091928208209011

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

It is shown that the turning surfaces associated with internal waves in a uniformly rotating, density stratified, Boussinesq fluid in the presence of an arbitrary gravitational field are regular points for the governing eigenvalue differential equation. The results are illustrated for two particular examples that have geophysical and astrophysical significance, namely radially directed spherical gravity, and the gravitational field in a rapidly rotating cylinder.

ISSN:0309-1929    

DOI:10.1080/03091928208209012

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

A mathematical model of the flow and temperature distribution of polythermal glaciers or ice sheets is deduced. Cold ice is treated as a non-linear viscous heat conducting fluid, while temperate ice is regarded as a binary mixture of ice and water. The simplest mixture concept with two balance laws of mass but only one balance law of momentum and energy is proposed. The field equations for the ice and water content and the boundary conditions which must hold at the free surface, at the ice-water interface, at the cold-temperature transition surface and at the rock-bed are deduced. In particular it is shown that an earlier formulation of polythermal ice due to Fowler and Larson (1978) is inconsistent. No boundary value problems are solved as the emphasis is on the physical motivation and justification of the principles.

ISSN:0309-1929    

DOI:10.1080/03091928208209013

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

This paper is concerned with the dielectrophoretic instability of a spherical shell of fluid. A dielectric fluid, contained in a spherical shell, with rigid boundaries is subjected to a simultaneous radial temperature gradient and radial a.c. electric field. Through the dependence of the dielectric constant on temperature, the fluid experiences a body force somewhat analogous to that of gravity acting on a fluid with density variations. Linear perturbation theory and the assumption of exchange of stabilities lead to an eighth order differential equation in radial dependence of the perturbation temperature. The solution to this equation, satisfying appropriate boundary conditions, yields a critical value of the electrical Rayleigh number and corresponding critical wave number at which convective motion begins. The dependence of each critical number is presented as a function of the gap size and temperature gradient. In the limit of zero shell thickness both the critical Rayleigh number and critical wave number agree with results for the case in the infinite plane problem.

ISSN:0309-1929    

DOI:10.1080/03091928208209014

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The equilibrium structure of an axisymmetric magnetic flux tube confined by an external pressurepe(Z)that varies along the length of the tube is studie. In the past, most work has concentrated onslenderflux tubes, where the effects of transverse structure and radial fields are neglected. Here the aim is to explore the properties of thick tubes, in order to see to what extent the slender tube theory is valid. The main results are:

ISSN:0309-1929    

DOI:10.1080/03091928208209015

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

It is shown that, for general homogeneous turbulence, the anti-symmetric part of the spectrum tensor can be expressed in terms of a single scalar functionH(k,ω)(the helicity spectrum function). Under the first-order smoothing approximation, the coefficientsαijβijkin the expansion of the mean electromotive force in terms of the mean magnetic field are determined;αijis a weighted integral ofH(k,ω), andβijkcontains a partβ(a)ijkwhich is likewise a weighted integral ofH(k, ω). When the turbulence is axisymmetric,β(a)ijkcontains Rädler's (1969a) “Ω ∧ J-effect”. It is shown that when the turbulence is statistically symmetric about a plane perpendicular to the axis of symmetry, thenβij= O but the Rädler effect is non-zero. Explicit expressions forαijandβijkare given when the velocity field is generated by random forcing in a rotating medium. Finally, it is shown by means of a local analysis that the Rädler effect, in conjunction with uniform mean shear, can give rise to non-oscillatory dynamo action, and it is argued that this effect may be significant in the well-mixed interior of a stellar convection zone, where by symmetry the α-effect may be weak.

ISSN:0309-1929    

DOI:10.1080/03091928208209016

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The α2-dynamo equations with the α-tensor derived by Wälder, Deinzer and Stix (1978) are solved numerically in spherical geometry. It is found that this anisotropic α2-dynamo yields both steady and oscillatory solutions, which depend on the parameters of anisotropy. A local model in cartesian geometry predicts the oscillatory and steady regime satisfactorily. From the results it is estimated whether this dynamo could be applied to the solar magnetic field. The results show that steady solutions are excited in general at lower critical Reynolds numbers than oscillatory solutions.

ISSN:0309-1929    

DOI:10.1080/03091928208209017

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The induced magnetic field in the Earth's mantle is computed for an electrical conductivity of the mantle of form σ = σa(a/r)αwhereais the core radius. When the inducing core motion is a uniform westward drift of −10−10s−1relative to the mantle, the retarding couple reaches −1019Nm. This result can be obtained with values σαand α such that the time scale of screening, μσa2/α2, is still below 10 years. The retarding couple, and in particular the contribution from the higher field harmonics, increases with increasing concentration of the conducting layer towards the core-mantle boundary. Deviations from the average torque balance of order 10% of the retarding couple can account for the “decade fluctuations” in the Earth's rate of rotation.

ISSN:0309-1929    

DOI:10.1080/03091928208209018

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Edited by Sir Harrie Massey. Gordon and Breach Science Publishers, 1980. xxxiv + 349 pp. (£19) (ISBN 0677 161905)

ISSN:0309-1929    

DOI:10.1080/03091928208209019

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Edited by C. J. Harris. Academic Press, 1979. 816 pp. (£19.80, $48.00) (ISBN 0 123283507)

ISSN:0309-1929    

DOI:10.1080/03091928208209020

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor