摘要:

The general absence of static equilibrium of a close-packed array of parallel twisted flux tubes in a highly conducting medium is demonstrated by showing that the solutions to the equilibrium equation V2A+4πP'(A) = 0do not generally preserve the flux connections around each twisted tube as the functional form ofP(A) is varied. A special constraint on the variation ofP(A) is introduced, then, by the requirement that the flux connections be preserved. Hence we conclude that while a particular array of twisted tubes, described by the internal circulation of flux within each tube, may have an equilibrium for some suitably chosen functional formP(A), the array is generally in a state of nonequilibrium for lack of that precise functional form in the real world.

ISSN:0309-1929    

DOI:10.1080/03091928308221742

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Magnetic field generation in a continuous medium in processes without self-excitation—the so-called semi-dynamo, involving as essential elements both magnetohydrodynamic processes and the presence of an impressed e.m.f.—has been studied for the case of the topological pumping effect on the magnetic field generation by an impressed e.m.f. operating in a three-dimensional Bénard convection layer.

ISSN:0309-1929    

DOI:10.1080/03091928308221743

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Numerical solutions of the axisymmetric flows during the relatively early phase of spin-up from rest of a stratified fluid in a cylinder are presented. Detailed results are given for a cylinder of aspect ratio of O(l) and for a minute Ekman number, showing axisymmetric spin-up for three values of the stratification parameter. As the stratification increases, the meridional circulation is confined to a region closer to the Ekman layers. An axisymmetric shear wave propagates radially inward from the sidewall, but, unlike the strictly vertical front for a homogeneous fluid, the interface which separates rotating from nonrotating fluid is bow-shaped. For a stratified fluid, the axial vorticity distribution is nonuniform both in the vertical and in the radial directions. With increasing stratification, diffusive vorticity production near the sidewall is more pronounced. Axisymmetric flows in the early phase of spin-up of a stratified fluid are controlled by both the inviscid dynamic effect and the viscous diffusion effect. At a location close to the Ekman layers, the inviscid effect outweighs the viscous effect, in much the same way as in a homogeneous fluid. However, at a location close to mid-depth, the viscous diffusion effect, enhanced by substantial flow gradients in that region, is dominant. This points to the necessity of including the direct effect of viscous diffusion in the interior in formulating an analytical model of stratified spin-up problems.

ISSN:0309-1929    

DOI:10.1080/03091928308221744

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Numerical solutions for the impulsively started spin-up of a thermally stratified fluid in a cylinder with a perfectly conducting sidewall are presented. The meridional streamfunction plots show that, since the stratification constraint is less severe, the fluid penetrates to a higher level in the sidewall layer and that the corner jet is considerably weaker than for insulated sidewalls. For moderate stratification, the azimuthal flow in the bulk of the interior decays faster for a conducting sidewall. For strong stratification, in the region away from mid-depth the azimuthal flow decays faster for a conducting sidewall. However, for strong stratification and at locations close to mid-depth, since the viscous diffusion effects outweigh the effect of the meridional circulation, the azimuthal flow decays faster for an insulated sidewall.

ISSN:0309-1929    

DOI:10.1080/03091928308221745

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

A mathematical model is developed for the generation of mean zonal flows by thermal convection in rapidly rotating, self-gravitating spheres. The analysis is based on an expansion of the basic equations in terms of the Prandtl numberP, the amplitudeAof convection, and the parameter ϵ which is related to the curvature of the spherical surface. Mean zonal flows of the orderPA2ϵare found. Although the Boussinesq approximation is used throughout the analysis, the results compare reasonably well with the observations of zonal flows in the atmospheres of Jupiter and Saturn. In particular, the fact that the amplitude of the Jovian equatorial jet is low in comparison with the corresponding jet on Saturn is explained in terms of the low equatorial convective heat flux on Jupiter.

ISSN:0309-1929    

DOI:10.1080/03091928308221746

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor