摘要:

The energy and entropy evolutions of two-dimensional interacting internal gravity waves and turbulence in the (x, z) plane are studied in inviscid, viscous decay and forced-dissipative numerical simulation experiments using a spectral model. In each case the entropy evolution is compared with that predicted by the eddy-damped quasinormal Markovian (EDQNM) closure formulated by Carnevale and Frederiksen (1983) for two-dimensional internal waves. Although there is no spectral gap between the internal waves and the turbulence in the experiments, we define a transition wavenumberk1such that for wave-numbersk≪k1wave motion predominates and for wavenumbersk≫k1turbulence is dominant. In both experiments in which wave motion is generated from turbulence and in which turbulence is generated from wave instability, it is found that the entropy production and energy transfers are inhibited for increased, Brunt-Väisälä frequencies or transition wavenumbers.

ISSN:0309-1929    

DOI:10.1080/03091928408230363

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The ray method is used to study slow hydromagnetic waves in an incompressible, inviscid, perfectly conducting fluid of constant density in the presence of a constant toroidal magnetic field. The fluid is bounded below by a rigid sphere and above by a rigid spheroidal surface, and the mean fluid layer thickness is assumed to be small. Both the general time-dependent and time-harmonic (free oscillation) problems are studied and dispersion relations and conservation laws are derived. These results are applied to free oscillations with constant azimuthal wave number in a spherical shell and then compared to those of previous authors. Such oscillations propagate to the east and are trapped between circles of constant latitude. Wave propagation in axisymmetric shells is then studied with emphasis on the relationship between shell shape and direction of propagation, and it is found that such shells can sustain westward propagating modes wherever the shell thickness decreases sufficiently rapidly from a maximum at the poles to zero at the equator; no shells exist which can sustain westward propagation at the equator.

ISSN:0309-1929    

DOI:10.1080/03091928408230364

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The energy method of Bernsteinet al.(1958) was used by Schindleret al.(1983) to derive a useful form of the linearised potential energy for coronal arcades. The basic state magnetic field and plasma are assumed to be in magnetohydrostatic equilibrium and independent of variations along the length of the arcade. A sufficient condition for stability is derived and is applied to two particular magnetic structures. When the axial field component vanishes, this condition becomes necessary and suficient.

ISSN:0309-1929    

DOI:10.1080/03091928408230365

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

It is shown that flows satisfying Blumen's (1968) quasigeostrophic, baroclinic generalisation of Arnol'd's (1965) sufficient condition for stability must be zonally-symmetric if the boundary conditions are zonally-symmetric. A similar restriction applies to the criteria established by Benziet al.(1982) for equivalent-barotropic flow.

ISSN:0309-1929    

DOI:10.1080/03091928408230366

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

On a step shelf, the scattering of an incident shelf wave by a semi-infinitely long, thin barrier located along the outer edge of the shelf is solved using an approximate Wiener-Hopf technique. Within the flat channel enclosed by the barrier, the incoming energy flux from the first mode shelf wave is essentially all transferred to the zeroth channel mode, which corresponds to the Kelvin wave modified by the rigid lid approximation. Other evanescent modes are excited, but all decay rapidly with distance. The problem is relevant to the diffraction of long period waves by a long thin island, or a chain of islands or coral reefs, which fringe a continental shelf.

ISSN:0309-1929    

DOI:10.1080/03091928408230367

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

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.

ISSN:0309-1929    

DOI:10.1080/03091928408230368

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

ISSN:0309-1929    

DOI:10.1080/03091928408230369

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

ISSN:0309-1929    

DOI:10.1080/03091928408230370

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

ISSN:0309-1929    

DOI:10.1080/03091928408230371

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor