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  • 1
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    The effects of Venusian mantle convection with multiple phase transitions (1992)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Recently there was a flurry of activities in studying the effects of phase transitions in the Earth's mantle. From petrological and geophysical considerations, phase-transitions would also play an important role in venusian dynamics. The basic differences between the two planets are the surface boundary conditions, both thermally and mechanically. In this vein we have studied time-dependent mantle convection with multiple phase transitions and depth-dependent thermal expansivity (alpha is approximately rho(exp -6)), based on high-pressure and temperature measurements. Both the olivine-spinel and spinel-perovskite transitions were simulated by introducing an effective thermal expansivity, as described. Used together with the extended Boussinesq Approximation this method serves as a powerful tool to examine the effects of phase transitions on convection at relatively low computational costs.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Papers Presented to the International Colloquium on Venus; p 121-122
    Format: application/pdf
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  • 2
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    Axisymmetric spherical shell models of mantle convection with variable properties and free and rigid lids (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Axisymmetric spherical shell numerical simulations of mantle convection were carried out to investigate the influence of two end-member surface stress conditions: stress-free and rigid. These correspond approximately to a subducting or a rigid lithosphere and can be seen as end-member models of the surface of Venus. Our model assumed an effective Rayleigh number of 3 x 10 exp 6, similar to that for earth, and included uniform internal heating and depth-dependent thermal expansivity and thermal conductivity. The simulations utilized a Newtonian viscosity which was constant or varied with depth and/or temperature. We show how the temperature, speed, and vorticity fields change qualitatively and quantitatively with surface temperature, surface stress condition, internal heating and viscosity distribution. We find that a rigid lid and viscosity which increases with depth both promote steady large-scale circulation with smaller-scale circulation in the upper mantle.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E12; p. 20,899-20,923.
    Format: text
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  • 3
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    Compressible convection in a viscous Venusian mantle (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Finite element simulations of axisymmetric spherical shell compressible convection were carried out to investigate the effect of various surface boundary conditions in a Venusian mantle, employing a thermal expansivity alpha which decreased with depth, a uniform viscosity an order of magnitude greater than the earth's, and zero and chondric quantities of internal heating. As long as hot plumes from the core-mantle boundary were strong, the convection pattern was typical of that for variable alpha flow; that is, it was characterized by steady upflowing regions, unsteady collections of downflowing plumes, and large aspect ratio cells. Increases in the internal heating or the temperature T0 at the top of the convecting layer weakened the hot plumes and, therefore, decreased the width of the cells. A rigid surface increased the internal temperature and also decreased the width of convection cells. Extensive regions of subadiabaticity were found in the mantle. These results are compared with those for fully three-dimensional convection under similar conditions (Schubert et al., 1990).
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 15
    Format: text
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