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Browsing by Author "Euen, Grant Thomas"

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    Geodynamic Modeling Applied to Venus
    Euen, Grant Thomas (Virginia Tech, 2023-05-23)
    Modern geodynamic modeling is more complex than ever, and has been used to answer questions about Earth pertaining to the dynamics of the convecting mantle and core, layers humans have never directly interacted with. While the insights gleaned from these models cannot be argued, it is important to ensure calculations are understood and behaving correctly according to known math and physics. Here I perform several thermal 3-D spherical shell tests using the geodynamic code ASPECT, and compare the results against the legacy code CitcomS. I find that these two codes match to within 1.0% using a number of parameters. The application of geodynamic modeling is also traditionally to expand our understanding of Earth; however, even with a scarcity of data modern methods can provide insight into other planetary bodies. I use machine learning to show that coronae, circular features on the surface of the planet Venus, are not randomly distributed. I suggest the idea of coronae being fed by secondary mantle plumes in connected clusters. The entirety of the Venusian surface is poorly understood as well, with a large percentage being topographically smooth and much younger than the planet's hypothesized age. I use modeling to test the hypothesis of a large impact being responsible for a major resurfacing event in Venus's history, and find three distinct scenarios following impact: relatively little change, some localized change evolving into resurfacing through geologic time, or large-scale overturn and injection of heat deep into the Venusian mantle.
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    Studying 3D Spherical Shell Convection using ASPECT
    Euen, Grant Thomas (Virginia Tech, 2018-01-08)
    ASPECT is a new convection code that uses more modern and advanced solver methods than geodynamics legacy codes. I use ASPECT to calculate 2-dimensional Cartesian as well as 2- and 3-dimensional spherical-shell convection cases. All cases use the Boussinesq approximation. The 2D cases come from Blankenbach et al. (1989), van Keken et al. (1997), and Davies et al. (in preparation). Results for 2D cases agree well with their respective benchmark papers. The time-evolutions of the root mean square velocity (Vrms) and Nusselt number agree, often to within 1%. The 3D cases come from Zhong et al. (2008). Modifications were made to the simple.cc and harmonic_perturbation.cc files in the ASPECT code in order to reproduce the initial conditions and temperature-dependence of the rheology used in the benchmark. Cases are compared using both CitcomS and ASPECT with different levels of grid spacing, as well as comparing uniform grid spacing and the ASPECT default grid spacing, which refines toward the center. Results for Vrms, average temperature, and Nusselt numbers at the top and bottom of the shell range from better than 1% agreement between CitcomS and ASPECT for cases with tetragonal planforms and 7000 Rayleigh number to as much as 44% difference for cases with cubic planforms and 10^5 Rayleigh number. For all benchmarks, the top Nusselt number from ASPECT is farthest from the reported benchmark values. The 3D planform and radially averaged quantity plots agree. I present these results, as well as recommendations and possible fixes for discrepancies in the results, specifically in the Nusselt numbers, Vrms, and average temperature.