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  • GEOPHYSICS  (10)
  • ASTROPHYSICS  (7)
  • FLUID MECHANICS AND HEAT TRANSFER  (2)
  • 1
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    Turbulent compressible convection in a deep atmosphere. III - Tests on the validity and limitation of the numerical approach (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effects of various approximations on the results of three-dimensional computation of turbulent compressible convection are examined and related to the phenomenon of bubble breaking in stellar convection. The problem of viscosity and the numerical issue of efficiency versus accuracy in such computations are discussed, and a model is formulated and tested with regard to turbulent viscosity and accuracy. Results on the convergence to a statistically stationary state, the effects of time accuracy on the statistics, the effects of the adjustable constant parameter c(mu), and the effects of aspect ratio, horizontal grid size, and vertical grid distribution are discussed. A preliminary look at the three-dimensional flow structure is given.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 307; 222-241
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  • 2
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    What causes the buoyancy reversal in compressible convection? (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The problem posed by the existence of a negative buoyancy work region at the top of cellular type convection in a deeply stratified superadiabatic layer (Massaguer and Zahn, 1980) is addressed. It is approached by studying two-dimensional cellular compressible convection with different physical parameters. The results suggest that a large viscosity, together with density stratification, is responsible for the buoyancy reversal. The numerical results obtained are analyzed. It is pointed out, however, that in an astrophysical situation a fluid involved in convection will generally have very small viscosity. It is therefore thought unlikely that buoyancy reversal occurs in this way.
    Keywords: ASTROPHYSICS
    Type: Astrophysics and Space Science (ISSN 0004-640X); 95; 2, Se; 453-457
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  • 3
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    Global electron density distributions from topside soundings. (1969)
    In:  Other Sources
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    Publication Date: 2011-08-12
    Description: Global electron density distribution morphology in topside ionosphere during sunspot minimum from Alouette 1 and 2 ionograms
    Keywords: GEOPHYSICS
    Type: ; ADEMIE DES SCIENCES
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  • 4
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    Model studies of the kinked Z trace in topside ionograms. (1969)
    In:  Other Sources
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    Publication Date: 2011-08-12
    Description: Propagation characteristic model study of kinked Z trace observed on topside ionograms and explained by magnetoionic theory
    Keywords: GEOPHYSICS
    Type: ; ADEMIE DES SCIENCES
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  • 5
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    A variable mixing-length ratio for convection theory (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: It is argued that a natural choice for the local mixing length in the mixing-length theory of convection has a value proportional to the local density scale height of the convective bubbles. The resultant variable mixing-length ratio (the ratio between the mixing length and the pressure scale height) of this theory is enhanced in the superadiabatic region and approaches a constant in deeper layers. Numerical tests comparing the new mixing length successfully eliminate most of the density inversion that typically plagues conventional results. The new approach also seems to indicate the existence of granular motion at the top of the convection zone.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 244
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  • 6
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    Non-radiative Energy from Differential Rotation in Hot Stars (1985)
    In:  CASI
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    Publication Date: 2014-09-16
    Description: A model of differential rotation is proposed for the upper radiative envelopes of hot stars, and it is suggested that the actions of such motions can be the source of energy for heating the coronae.
    Keywords: ASTROPHYSICS
    Type: The Origin of Nonradiative Heating(Momentum in Hot Stars; p 164-168
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  • 7
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    Turbulent compressible convection in a deep atmosphere. I - Preliminary two-dimensional results (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The turbulent convection of a compressible fluid in a deep atmosphere is simulated by two-dimensional numerical computations, displaying coexisting 'cells' whose sizes range from the total depth of the convection zone to the smallest scale height at the top. While the largest cells traverse the entire zone, smaller ones are clustered near the top. The vertical correlation length of the vertical velocity is proportional to the local pressure or density scale height, in a way reminiscent of the concept of mixing length.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 263
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  • 8
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    Application of the alternating direction implicit method to the computation of time-dependent compressible convective flows (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 9
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    ADI on staggered mesh - A method for the calculation of compressible convection (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: An alternating direction implicit (ADI) method has been applied to a staggered grid for the computation of convection in a highly stratified fluid. Since artificial viscosity is not needed, subtle effects like the onset of convection can be studied. These computations compare well with the 2-D results by Graham (1975) and also agree with standard Boussinesq results when taken to that limit. Good efficiency has been achieved with a time step hundreds of times larger than the stability limit imposed by the explicit treatment of diffusion and the Courant number is not restricted to be below 1. The Navier-Stokes equation contains cross spatial derivatives which are treated explicitly in most ADI schemes. The destabilizing effect of such a practice on a 2-D model system with second-order spatial derivative terms only was analyzed and found to be not excessive.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 47; July 198
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  • 10
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    Turbulent compressible convection in a deep atmosphere. II - Two-dimensional results for main-sequence A5 and F0 type envelopes (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: In the present two-dimensional numerical study of turbulent compressible convection in the A5 and F0 main-sequence envelope types, ionization effects are included in the equation of state of the gas, and radiative transfer is modeled in a diffusive process with tabulated gas opacities. It is noted that the thermal effects of ionization significantly affect the dynamics of the flows and that an inversion of the mean density can be created and sustained in a dynamical situation. The substantial differences in the flows of A5 and F0 indicate development trends in the transition from the radiative to the convective mode of energy transport. As convection becomes more effective, the flow becomes more turbulent and the scaling effects of local scale heights become more significant.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 282; 550-556
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