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  • FLUID MECHANICS AND HEAT TRANSFER  (4)
  • LUNAR AND PLANETARY EXPLORATION  (3)
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  • 1
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    Characteristics-based methods applied to infinite Prandtl number thermal convection in the hard turbulent regime (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Characteristics-based methods for the advection-diffusion equation are presented and directly applied to study thermal convection with extremely large Rayleigh number (Ra). It is shown that the operator-splitting method for advection-diffusion problems is very accurate for determining the advected field at extremely high Peclet number (Pe). The technique presented is considered to have great potential for solving advection-dominated problems, while the Langrangian method is more accurate for lower Pe. It is noted that the accuracy of these characteristics-based methods strongly depends on the quality of interpolation. The computational time for the operator-splitting method grows with the number of time steps employed. The Langrangian method was used for simulations of convection at very high Ra, up to 3 x 10 to the 9th, and time-dependent, thermal convection solutions were obtained for infinite Prandtl number.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 3; 2105-211
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  • 2
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    The effects of Venusian mantle convection with multiple phase transitions (1992)
    In:  CASI
    Details
    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
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  • 3
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    Simulation of particle mixing by turbulent convective flows on the connection machine (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Mixing of particles by chaotic flow fields was simulated on the Connection Machine. Each cell was assigned to the processor, and the coordinates of particles residing on the cell were kept in the local memory of the processor. This approach implies the exchange between the local memories, when a particle moves from one cell to another. Approximately 10 exp 5 particles were injected into a time-dependent flow field obtained by solving the nonlinear system of partial differential equations describing turbulent thermal convection. The flow field was calculated on a CRAY, and data were transferred to a CM-200 through a high-speed HIPPI channel.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: In: Supercomputing '92; Proceedings of the Conference, Minneapolis, MN, Nov. 16-20, 1992 (A94-10682 01-62); p. 294-300.
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  • 4
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    Plume structures in the hard-turbulent regime of three-dimensional infinite Prandtl number convection (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Numerical simulations of three-dimensional infinite Prandtl number thermal convection with Rayleigh number (Ra) up to 10 exp 8 are reported. Convection with Ra higher than 10 exp 7 is characterized by the appearance of disconnected thermal plumes. The smaller plumes are detached by the currents produced by the larger plumes. The low wavenumber portion of a thermal power spectrum near the boundary layer becomes flat at high Ra, while the spectrum measured in the interior shows a positive slope for low wavenumbers. Differences are found in the thermal spectra between 2D and 3D models.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Geophysical Research Letters (ISSN 0094-8276); 20; 5; p. 383-386.
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  • 5
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    Three-dimensional fully spectral numerical method for mantle convection with depth-dependent properties (1994)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A semi-implicit fully spectral collocation method for the simulation of three-dimensional mantle convection with depth-dependent thermo-dynamic and transport properties is presented. The variable property Navier-Stokes equation expressed in terms of the primitive variable velocity and pressure is solved with the mass continuity and temperature equations. The periodic horizontal boundary conditions allow a Fourier expansion for the two horizontal directions. The stress-free, impermeable isothermal boundary conditions along with the depth dependent coefficients are handled with a Chebyshev expansion in the vertical direction. In the limit of an infinite Prandtl number appropriate to mantle convection, the inertial terms in the momentum equation are unimportant. In this case an explicit solution of a Poisson equation for pressure can be avoided; instead a fourth-order equation for vertical velocity can be solved. Simultaneous imposition of both impermeable and continuity boundary conditions during the vertical velocity evaluation is discussed. The pressure distributions on the top and bottom bounding planes were determined by means of an influence matrix technique. The numerical method employed here avoids time-splitting errors and enforces velocity boundary conditions and continuity over the entire domain, including the boundaries, to machine accuracy. Strongly time-dependent three-dimensional solutions up to a surface Rayleigh number of 1 x 10(exp 7) have been obtained. Strong upwellings, pulsating chaotically, are formed by the collective merging of cylindrical plumes.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 113; 1; p. 62-74
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  • 6
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    Axisymmetric spherical shell models of mantle convection with variable properties and free and rigid lids (1992)
    In:  Other Sources
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    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.
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  • 7
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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
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