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. / Master of Science / Mantle convection is the primary process in which heat is transferred from the interior of Earth to its exterior. It is a process that involves the physical movement of material in the mantle: hot material rises towards the surface and cools, while cold material sinks to the base and warms. This transferring of heat and energy is also the driving force behind plate tectonics, the process in which the surface of the Earth moves and changes with time. Plate tectonics is responsible for the formation of oceans, mountains, volcanoes, and trenches to name a few. Understanding the behavior of the mantle as it convects is crucial to understanding how the Earth and planetary bodies like it develop over time. In this work, I use the new modeling code ASPECT, Advanced Solver for Problems in Earths ConvecTion, to test various models in 2 and 3 dimensions. This is done to compare the results calculated by ASPECT with those of older, legacy codes for the purpose of benchmarking and growth of ASPECT. Insight is also gleaned into the large-scale factors that influence mantle convection and planetary development. My results show good agreement between results calculated by ASPECT and those of legacy codes, though there is some discrepancy in some values. The main values I present here are V<sub>RMS</sub>, the root mean square velocity, the average temperature, and the Nusselt number calculated for both the top and base of the models. In this work, I present these results and potential solutions to the discrepancies encountered.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/81621 |
| Date | 08 January 2018 |
| Creators | Euen, Grant Thomas |
| Contributors | Geosciences, King, Scott D., Weiss, Robert, Stamps, D. Sarah |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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