摘要:

An investigation is made of the wavenumber selection of baroclinic disturbances in the rotating, differentially heated annulus flow system with a three-dimensional fully nonlinear high resolution model. Along the constant thermal contrast of 10°C that traverses the nondimensional parameter space defined by the laboratory experiments of Pfefferet al.(1980b), a series of numerical experiments with a quiescent-start initial condition is conducted to explore the equilibrated flow regimes as a function of the rotation rate of the annulus.

ISSN:0309-1929    

DOI:10.1080/03091929408203644

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Arnol'd's second hydrodynamical stability theorem, proven originally for the two-dimensional Euler equations, can establish nonlinear stability of steady flows that are maxima of a suitably chosen energy-Casimir invariant. The usual derivations of this theorem require an assumption of zero disturbance circulation. In the present work an analogue of Arnol'd's second theorem is developed in the more general case of two-dimensional quasi-geostrophic flow, with the important feature that the disturbances are allowed to have non-zero circulation. New nonlinear stability criteria are derived, and explicit bounds are obtained on both the disturbance energy and potential enstrophy which are expressed in terms of the initial disturbance fields. While Arnol'd's stability method relies on the second variation of the energy-Casimir invariant being sign-definite, the new criteria can be applied to cases where the second variation is sign-indefinite because of the disturbance circulations. A version of Andrews' theorem is also established for this problem.

ISSN:0309-1929    

DOI:10.1080/03091929408203645

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We describe the results of a benchmark study of numerical codes designed to treat problems of high Prandtl number convection in three-dimensional Cartesian geometry. In addition, quantitative results from laboratory convection experiments are compared with numerical data. The cases of bimodal convection at constant viscosity and of square cell convection for temperature-dependent viscosity have been selected.

ISSN:0309-1929    

DOI:10.1080/03091929408203646

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A fully three-dimensional kinematic model is applied to simulate the evolution of the magnetic field in a small (120 pc in size) volume of the turbulent interstellar medium in the presence of the field diffusion. Turbulent motions are approximated by a sequence of non-overlapping in time vortices having the form of rotating gas columns much longer than the parcel size. A combined action of vertical vortices and those inclined at the angle of 30° to the galactic plane is considered. Due to the Coriolis force and density stratification their motions have a non-zero helicity. The magnetic field is found to evolve towards the structure resembling a fragment of a twisted flux tube, well-ordered over the volume analyzed. Its sense of twisting is determined by the vortex helicity.

ISSN:0309-1929    

DOI:10.1080/03091929408203647

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The problem of stellar surface oscillations under the action of perturbations in the inner layers of the star is considered. A one-dimensional hydrodynamical model is adopted to describe relatively short (compared with the stellar radius) perturbations of gas in a non-stationary gravity field. The Legendre transformation technique is used to obtain exact solutions describing the star's surface oscillations. It is shown that if the perturbations in the inner layers of the star have small energy, then the extreme characteristics of the star surface oscillations (displacement and velocity) do not depend on the nonlinearity of the problem, and thus, they can be calculated in the frame-work of a linear hydrodynamical model. The criterion for breaking of the wave coming to the star's surface is obtained. It is found that this criterion can be defined by solving the linear problem and therefore having a very clear physical sense (the ratio of the wave acceleration to the acceleration due to gravity). It is shown that the variable part of the gravity field is responsible for gas oscillations as a whole, which does not influence decisively the wave dynamics of the stellar surface. The spectrum of stellar surface oscillations is calculated.

ISSN:0309-1929    

DOI:10.1080/03091929408203648

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor