Publications

Alvin, Kenneth F.; Laros, James H.; Hoekstra, Robert J.; Collis, Samuel S.; Lujan, Jim L.

Abstract not provided.

Laros, James H.; Collis, Samuel S.; Alvin, Kenneth F.

Abstract not provided.

Krebs, Jerome R.; Ober, Curtis C.; Smith, Thomas M.; Overfelt, James R.; Collis, Samuel S.; von Winckel, Gregory J.; van Bloemen Waanders, Bart G.; Downey, Nathan J.; Aldridge, David F.

Abstract not provided.

Hendrickson, Bruce A.; Alvin, Kenneth F.; Miller, Leann A.; Collis, Samuel S.

Abstract not provided.

SEG Technical Program Expanded Abstracts

Ober, Curtis C.; Smith, Thomas M.; Overfelt, James R.; Collis, Samuel S.; von Winckel, Gregory J.; van Bloemen Waanders, Bart G.; Downey, Nathan J.; Mitchell, Scott A.; Bond, Stephen D.; Aldridge, David F.; Krebs, Jerome R.

The need to better represent the material properties within the earth's interior has driven the development of higherfidelity physics, e.g., visco-tilted-transversely-isotropic (visco- TTI) elastic media and material interfaces, such as the ocean bottom and salt boundaries. This is especially true for full waveform inversion (FWI), where one would like to reproduce the real-world effects and invert on unprocessed raw data. Here we present a numerical formulation using a Discontinuous Galerkin (DG) finite-element (FE) method, which incorporates the desired high-fidelity physics and material interfaces. To offset the additional costs of this material representation, we include a variety of techniques (e.g., non-conformal meshing, and local polynomial refinement), which reduce the overall costs with little effect on the solution accuracy.

Rajamanickam, Sivasankaran R.; Parks, Michael L.; Collis, Samuel S.

The Computer Science Research Institute (CSRI) brings university faculty and students to Sandia National Laboratories for focused collaborative research on computer science, computational science, and mathematics problems that are critical to the mission of the laboratories, the Department of Energy, and the United States. The CSRI provides a mechanism by which university researchers learn about and impact national— and global—scale problems while simultaneously bringing new ideas from the academic research community to bear on these important problems. A key component of CSRI programs over the last decade has been an active and productive summer program where students from around the country conduct internships at CSRI. Each student is paired with a Sandia staff member who serves as technical advisor and mentor. The goals of the summer program are to expose the students to research in mathematical and computer sciences at Sandia and to conduct a meaningful and impactful summer research project with their Sandia mentor. Every effort is made to align summer projects with the student's research objectives and all work is coordinated with the ongoing research activities of the Sandia mentor in alignment with Sandia technical thrusts. For the 2013 CSRI Proceedings, research articles have been organized into the following broad technical focus areas — Computational Mathematics and Algorithms, Combinatorial Algorithms and Visualization, Advanced Architectures and Systems Software, Computational Applications — which are well aligned with Sandia's strategic thrusts in computer and information sciences.

Ober, Curtis C.; Smith, Thomas M.; van Bloemen Waanders, Bart G.; Collis, Samuel S.

Abstract not provided.

Parks, Michael L.; Lehoucq, Richard B.; Bond, Stephen D.; Summers, Randall M.; Collis, Samuel S.

Abstract not provided.

Journal of Computational Physics

Scovazzi, Guglielmo S.; Collis, Samuel S.; Gerstenberger, Axel G.

We present a new approach to the simulation of gravity-driven viscous fingering instabilities in porous media flow. These instabilities play a very important role during carbon sequestration processes in brine aquifers. Our approach is based on a nonlinear implementation of the discontinuous Galerkin method, and possesses a number of key features. First, the method developed is inherently high order, and is therefore well suited to study unstable flow mechanisms. Secondly, it maintains high-order accuracy on completely unstructured meshes. The combination of these two features makes it a very appealing strategy in simulating the challenging flow patterns and very complex geometries of actual reservoirs and aquifers. This article includes an extensive set of verification studies on the stability and accuracy of the method, and also features a number of computations with unstructured grids and non-standard geometries.

Spotz, William S.; Collis, Samuel S.

Abstract not provided.

Spotz, William S.; Collis, Samuel S.

Abstract not provided.

Proposed for publication in Computational Geosciences (Springer publiushing Company).

Gerstenberger, Axel G.; Scovazzi, Guglielmo S.; Collis, Samuel S.

Abstract not provided.

Scovazzi, Guglielmo S.; Collis, Samuel S.; Gerstenberger, Axel G.

Abstract not provided.

Ober, Curtis C.; van Bloemen Waanders, Bart G.; Collis, Samuel S.

Abstract not provided.

Collis, Samuel S.; Ober, Curtis C.; Overfelt, James R.; Young, Joseph G.

Abstract not provided.

Collis, Samuel S.; Ober, Curtis C.; van Bloemen Waanders, Bart G.

Abstract not provided.

Collis, Samuel S.; Ober, Curtis C.; Overfelt, James R.

Abstract not provided.

Siirola, John D.; Adams, Brian M.; Collis, Samuel S.; Griffith, Richard O.; Mish, Kyran D.; Pinar, Ali P.

Abstract not provided.

Siirola, John D.; Adams, Brian M.; Collis, Samuel S.; Griffith, Richard O.; Mish, Kyran D.; Pinar, Ali P.

Abstract not provided.

Collis, Samuel S.; Ober, Curtis C.; van Bloemen Waanders, Bart G.

This abstract explores the potential advantages of discontinuous Galerkin (DG) methods for the time-domain inversion of media parameters within the earth's interior. In particular, DG methods enable local polynomial refinement to better capture localized geological features within an area of interest while also allowing the use of unstructured meshes that can accurately capture discontinuous material interfaces. This abstract describes our initial findings when using DG methods combined with Runge-Kutta time integration and adjoint-based optimization algorithms for full-waveform inversion. Our initial results suggest that DG methods allow great flexibility in matching the media characteristics (faults, ocean bottom and salt structures) while also providing higher fidelity representations in target regions. Time-domain inversion using discontinuous Galerkin on unstructured meshes and with local polynomial refinement is shown to better capture localized geological features and accurately capture discontinuous-material interfaces. These approaches provide the ability to surgically refine representations in order to improve predicted models for specific geological features. Our future work will entail automated extensions to directly incorporate local refinement and adaptive unstructured meshes within the inversion process.

Society of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010

Smith, Thomas M.; Collis, Samuel S.; Ober, Curtis C.; Overfelt, James R.; Schwaiger, Hans F.

Motivated by the needs of seismic inversion and building on our prior experience for fluid-dynamics systems, we present a high-order discontinuous Galerkin (DG) Runge-Kutta method applied to isotropic, linearized elasto-dynamics. Unlike other DG methods recently presented in the literature, our method allows for inhomogeneous material variations within each element that enables representation of realistic earth models — a feature critical for future use in seismic inversion. Likewise, our method supports curved elements and hybrid meshes that include both simplicial and nonsimplicial elements. We demonstrate the capabilities of this method through a series of numerical experiments including hybrid mesh discretizations of the Marmousi2 model as well as a modified Marmousi2 model with a oscillatory ocean bottom that is exactly captured by our discretization.

Heroux, Michael A.; Edwards, Harold C.; Williams, Alan B.; Collis, Samuel S.

Abstract not provided.

Bochev, Pavel B.; Collis, Samuel S.; Jones, Reese E.; Lehoucq, Richard B.; Parks, Michael L.; Scovazzi, Guglielmo S.; Silling, Stewart A.; Templeton, Jeremy A.

This report is a collection of documents written as part of the Laboratory Directed Research and Development (LDRD) project A Mathematical Framework for Multiscale Science and Engineering: The Variational Multiscale Method and Interscale Transfer Operators. We present developments in two categories of multiscale mathematics and analysis. The first, continuum-to-continuum (CtC) multiscale, includes problems that allow application of the same continuum model at all scales with the primary barrier to simulation being computing resources. The second, atomistic-to-continuum (AtC) multiscale, represents applications where detailed physics at the atomistic or molecular level must be simulated to resolve the small scales, but the effect on and coupling to the continuum level is frequently unclear.

Stewart, James R.; Collis, Samuel S.

Abstract not provided.

Zimmerman, Jonathan A.; Collis, Samuel S.; Fang, H.E.; Lee, Jean L.; Lehoucq, Richard B.; Moody, Neville R.; Plimpton, Steven J.

Abstract not provided.