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  • Lunar and Planetary Science and Exploration  (2)
  • Acoustics  (1)
  • 1
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    Protoplanetary Nebula Evolution using the Beta Viscosity Model (2003)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The evolutionary dynamics of a protoplanetary disk is an important component of the planet formation process. In particular, the dynamic and thermodynamic field plays a critical role in chemical evolution, the migration of dust particles in the nebula, and the radial transport of meteoritic components. The dynamic evolution is investigated using analytical solutions of the surface density transport equations using a turbulence model based on hydrodynamic generation of turbulence. It captures the major properties of the disk including region of separation between radial inflow and-outflow and the evolution of the central plane temperature. The analytical formulas are compared with available numerical solutions based on the alpha viscosity model. The beta viscosity model, heretofore used for steady-state disks, is shown to be a useful approximation for unsteady problems.
    Keywords: Lunar and Planetary Science and Exploration
    Type: DPS Meeting; Sep 02, 2002 - Sep 06, 2002; Monterey, CA; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Numerical Wave Propagation 211 Based on Wave Primitives (1994)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: Compact higher order finite difference equations are applied to a sequence of problems in wave propagation and aeroacoustics. Systems of PDE's are reduced to a sequence of simple wave primitives using a local eigenvector decomposition. The wave primitives are first order PDE's in two independent variable and allow natural boundary conditions to be imposed for both single- and multidimensional problems. The method uses a "discrete dispersion relation" approach to obtain high order approximations to the wave primitives on a 3 spatial point / 2 time level computational molecule. The scheme is fourth order accurate for the class of system with constant coefficients, e.g., those that support exponential solutions. Weakly non-linear PDE's are solved in a similar manner using a variant of the "method of frozen coefficients." Experience with the new algorithm for linear, non-linear, and multi-dimensional test problems will be described.
    Keywords: Acoustics
    Type: ICASE/LaRC Workshop on Benchmark Problems in Computational Aeroacoustics; Oct 24, 1994 - Oct 26, 1994; Hampton, VA; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    A New Model for Water Vapor/Ice Abundance in a Protoplanetary Nebula (2006)
    In:  Other Sources
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    Publication Date: 2019-07-19
    Description: Water is a unique substance in the protoplanetary nebula since both solid and gaseous phases coexist in large quantities. Quantitative estimates of their relative abundances are important parameters regarding the physical state of the nebula and planet formation processes. This new model is based on computing the chemical evolution of water molecules until its partial pressure is sufficient to pierce the vapor pressure curve for water. The point at which this occurs relative to its steady state values determines final gas/ice ratios. The wide range of temperatures and densities in typical protoplanetary disks result in a range of gadice ratios. It is found that although ice dominates the mid and far nebula, water vapor is predominant in the centerplane region of the near nebula and above the disk photosphere. An interesting near nebula effect is the appearance of a cloud of water ice at the temperature inversion elevation surrounded by vapor above and below. This work is partially supported by the NASA Astrobiology Institute.
    Keywords: Lunar and Planetary Science and Exploration
    Type: 2006 DPS Meeting; Oct 08, 2006 - Oct 13, 2006; Pasadena, CA; United States
    Format: text
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    NASA TECHNICAL REPORTS
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