Venus, Ceres, Earth: Geodynamic Modeling Group Al- location Request

I am requesting 1.5M units split evenly between Blueridge, Newriver, and Cascades for the next year to work on the research associated with the project Venus, Ceres, Earth: Geodynamic Modeling Group. (I realize the units are different across the different platforms but evenly splitting seems reasonable.) If you want to get more fine grained, then the hours are based on the machines we have been using. To keep from stepping on each other, we’ve all been focusing on different machines. Grant has been using newriver for the Venus work, so 200,000 on newriver. Josh has been using blueridge for Mars to 384,000 hours on blueridge. I have been using cascades for the Ceres work, so 138,240 hours on cascades for Ceres. Shangxin uses whichever machine has the lowest total for his north american work, so split the 576,000 core hours across the three systems. This is slightly smaller than what we have requested in previous years, reflecting the fact that some of our projects are nearing completion and we anticipate spending more time writing papers and proposals in the coming year than computing. The justification is given below. I have updated the grants (nothing new) and publications page (three new publications).

Results from Previous Year

We publised papers on Venus and Ceres this past year with a number of other papers nearing submission and/or being written. Shangxin Liu has submitted one paper (needs extensive revisions, more to do with writing and organization than modeling) and is about to submit a second paper on his algorithm development for calculating the gravitational potential from an arbirtatry mesh, which we need because of the development of adaptive mesh refinement. The second paper should be submitted to Geophysical Journal International in a couple of weeks. In addtion, Grant Euen defended his MS. thesis, Studying 3D Spherical Shell Convection using ASPECT, on December 6th, 2017. We are working to convert that thesis into a manuscript, which we hope to submit this fall to the journal Geoscientific Model Development.

Ceres

I am actively using new river to model the tectonic and thermal evolution of the icy dwarf planet Ceres. This is ongoing work that I have described for several years (indeed two papers have been published in the past year) and I am working on another manuscript now, so the number of calculations is winding down. 2

Planned Usage

Ceres

I anticipate 10 model runs will be needed in the next year for Ceres with 96 cores. Each run will take on the order of 144 hours. This set of runs will consume 10x96x144 = 138,240 core hours.

Eastern North America

Shangxin has been spent a lot of time with the spherical finite element code ASPECT, to understand the flow pattern, topography, and gravity of Eastern North America. This has finally paid off in a manuscript, Global modeling of mantle flow constrained by geoid and plate motions, which we submitted to Geochemistry, Geophysics, Geosystems this spring. This work used seismic tomography much like a medical CAT scan to estimate the internal density variations within the Earth and these internal density variations drive creeping flow in the solid Earth that drives observed plate motions and causes long-wavelength gravity anomalies. Shangxing wrote a module to calculate the gravitational potential from these model (something that can be compared with observations from Earth). He spent consider- able time this past year benchmarking his new code against published results and that paper is nearly ready to submit to Geophysical Journal International, titled A benchmark study of incompressible Stokes flow in a 3-D spherical shell using ASPECT. For the coming year Shangxin is working on modeling seismic data with a technique that runs on a laptop and revising the two papers he has submitted. He has an ambitious final project for his thesis to model mantle flow beneath Eastern North America at very high resolution to compare with the available seismic data. This will require the adaptive meshing algorithms in ASPECT and it could require extensive resources, perhaps beyond ARC and will require us to seek resources at XCEDE. I anticipate that he will be testing this problem using ARC resources in the fall and spring and I estimate we will need on the order of 20 model runs with up to 400 cores running for 48-72 hours. Therefore we request 72x400x20 = 576,000 core hours for this project.

Mars

Josh is continuing to work on melting on Mars. This work is timely with the anticipated arrival of the Mars InSight spacecraft this December. He has submitted several highly- competitive proposals that reviewed well but not well enough to fund. Josh will present his first reasults at AGU in the fall and I anticipate his computing usage will ramp up as he finishes the testing and algorithm phase of his work and moves into the research phase. I anticipate his Mars problems will require 96 cores with 100 hours per run. (Mars is smaller than Earth and Venus and does not require the same resolution that Shangxin and Grant 3 need for Earth and Venus) I anticipate he will need 30-40 runs over the course of the next year. Therefor we request 40x96x100 = 384,000 core hours for this project.

Venus

After finishing up his MS work on ASPECT modeling, Grant is moving into a Ph.D. project looking at impacts and how they might have affected the lithosphere of Venus through time. As we start this work, I anticipate this year will be testing and code developing with work starting in a 2D geometry. The following year, if this is successful in debugging and initial testing, he will need significantly more resources. I estimate Grant will require 200,000 core hours for the coming year for this project.

ASPECT Benchmarking

What started as a small project ended up becoming a masters thesis. Grant finally has exccellent agreement between ASPECT and previously published results. We are working on converting the thesis into a paper. I anticipate this will require a few additional model runs to fill in graphs that he did not have time to complete. I anticipate 10 runs of 48 hours each on 200 cores, therefore I request 96,000 core hours for this project.

Total Requested

The total of the numbers above comes to just under 1,400,000 core hours. Rounding up for visualization, analysis and anticipated mistakes, I ask for 1,500,000 core hours for the coming year.

Code Details and Scaling

The following information about the code and scaling has been submitted in previous years so I have not included it. We are working on Aspect scaling. Given that Aspect is built on Trilinois and deal.II both of which are documented to scale well, we are confident that Aspect scales well. The primary references for Aspect are given below. M. Kronbichler and T. Heister and W. Bangerth, High Accuracy Mantle Convection Simu- lation through Modern Numerical Methods, Geophysics Journal International, 191, 12–29, 2012. doi: 10.1111/j.1365-246X.2012.05609.x T. Hester, J. Dannberg, R. Gassm´’oller, and W. Bangerth, High accuracy mantle convection simulation through modern numerical methods II: realistic models and problems, Geophysics Journal International, 210, 833-851, 2017. doi: 10.1093/gji/ggx195 4

Another resource is the thesis by Grant Euen, Studying 3D Spherical Shell Convection using ASPECT which can be found in the VT repository. https://vtechworks.lib.vt.edu/handle/10919/81621 and the source is here: https://geodynamics.org/cig/software/aspect/