Publications

Tuminaro, Raymond S.; Siefert, Christopher S.; Bochev, Pavel B.

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Siefert, Christopher S.; Meredith, Logan M.; McGregor, Duncan A.

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Robinson, Allen C.; Mosso, Stewart J.; Siefert, Christopher S.; Hu, Jonathan J.

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Kramer, Richard M.; Siefert, Christopher S.; Voth, Thomas E.

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Kramer, Richard M.; Siefert, Christopher S.; Voth, Thomas E.

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Gaidamour, Jeremie G.; Hu, Jonathan J.; Siefert, Christopher S.; Tuminaro, Raymond S.

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Niederhaus, John H.; Siefert, Christopher S.; Petney, Sharon P.

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Siefert, Christopher S.

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Siefert, Christopher S.; Voth, Thomas E.; Bochev, Pavel B.

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Siefert, Christopher S.; Bochev, Pavel B.; Kramer, Richard M.; Voth, Thomas E.; Cox, James C.

Surface effects are critical to the accurate simulation of electromagnetics (EM) as current tends to concentrate near material surfaces. Sandia EM applications, which include exploding bridge wires for detonator design, electromagnetic launch of flyer plates for material testing and gun design, lightning blast-through for weapon safety, electromagnetic armor, and magnetic flux compression generators, all require accurate resolution of surface effects. These applications operate in a large deformation regime, where body-fitted meshes are impractical and multimaterial elements are the only feasible option. State-of-the-art methods use various mixture models to approximate the multi-physics of these elements. The empirical nature of these models can significantly compromise the accuracy of the simulation in this very important surface region. We propose to substantially improve the predictive capability of electromagnetic simulations by removing the need for empirical mixture models at material surfaces. We do this by developing an eXtended Finite Element Method (XFEM) and an associated Conformal Decomposition Finite Element Method (CDFEM) which satisfy the physically required compatibility conditions at material interfaces. We demonstrate the effectiveness of these methods for diffusion and diffusion-like problems on node, edge and face elements in 2D and 3D. We also present preliminary work on h -hierarchical elements and remap algorithms.

Lin, Paul L.; Rajamanickam, Sivasankaran R.; Siefert, Christopher S.; Bettencourt, Matthew T.; Cyr, Eric C.; Domino, Stefan P.; Fisher, Travis C.; Hoemmen, Mark F.; Hu, Jonathan J.; Phipps, Eric T.; Prokopenko, Andrey V.

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Hu, Jonathan J.; Devine, Karen D.; Hoemmen, Mark F.; Lin, Paul L.; Rajamanickam, Sivasankaran R.; Roberts, Nathan V.; Siefert, Christopher S.; Trott, Christian R.; Prokopenko, Andrey P.

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Siefert, Christopher S.; Smith, Timothy A.; Ridgway, Elliott M.

As the number of supported platforms for SNL software increases, so do the testing requirements. This increases the total time spent between when a developer submits code for testing, and when tests are completed. This in turn leads developers to hold off submitting code for testing, meaning that when code is ready for testing there's a lot more of it. This increases the likelihood of merge conflicts which the developer must resolve by hand -- because someone else touched the files near the lines the developer touched. Current text-based diff tools often have trouble resolving conflicts in these cases. Work in Europe and Japan has demonstrated that, using programming language aware diff tools (e.g., using the abstract syntax tree (AST) a compiler might generate) can reduce the manual labor necessary to resolve merge conflicts. These techniques can detect code blocks which have moved, as opposed than current text-based diff tools, which only detect insertions / deletions of text blocks. In this study, we evaluate one such tool, GumTree, and see how effective it is as a replacement for traditional text-based diff approaches.

Siefert, Christopher S.; Kramer, Richard M.; Bochev, Pavel B.; Voth, Thomas E.

Abstract not provided.

Roberts, Nathan V.; Carleton, James B.; Dong, Wen D.; Petney, Sharon P.; Robinson, Allen C.; Siefert, Christopher S.

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Journal of Computational Physics

Kramer, Richard M.; Siefert, Christopher S.; Voth, Thomas E.; Bochev, Pavel B.

A discrete De Rham complex enables compatible, structure-preserving discretizations for a broad range of partial differential equations problems. Such discretizations can correctly reproduce the physics of interface problems, provided the grid conforms to the interface. However, large deformations, complex geometries, and evolving interfaces makes generation of such grids difficult. We develop and demonstrate two formally equivalent approaches that, for a given background mesh, dynamically construct an interface-conforming discrete De Rham complex. Both approaches start by dividing cut elements into interface-conforming subelements but differ in how they build the finite element basis on these subelements. The first approach discards the existing non-conforming basis of the parent element and replaces it by a dynamic set of degrees of freedom of the same kind. The second approach defines the interface-conforming degrees of freedom on the subelements as superpositions of the basis functions of the parent element. These approaches generalize the Conformal Decomposition Finite Element Method (CDFEM) and the extended finite element method with algebraic constraints (XFEM-AC), respectively, across the De Rham complex.

Tuminaro, Raymond S.; Hu, Jonathan J.; Siefert, Christopher S.

Abstract not provided.

Siefert, Christopher S.; Tuminaro, Raymond S.; Domino, Stefan P.; Robinson, Allen C.

In this report we summarize research into new parallel algebraic multigrid (AMG) methods. We first provide a introduction to parallel AMG. We then discuss our research in parallel AMG algorithms for very large scale platforms. We detail significant improvements in the AMG setup phase to a matrix-matrix multiplication kernel. We present a smoothed aggregation AMG algorithm with fewer communication synchronization points, and discuss its links to domain decomposition methods. Finally, we discuss a multigrid smoothing technique that utilizes two message passing layers for use on multicore processors.

Prokopenko, Andrey V.; Siefert, Christopher S.; Hu, Jonathan J.; Hoemmen, Mark F.; Klinvex, Alicia M.

This is the definitive user manual for the I FPACK 2 package in the Trilinos project. I FPACK 2 pro- vides implementations of iterative algorithms (e.g., Jacobi, SOR, additive Schwarz) and processor- based incomplete factorizations. I FPACK 2 is part of the Trilinos T PETRA solver stack, is templated on index, scalar, and node types, and leverages node-level parallelism indirectly through its use of T PETRA kernels. I FPACK 2 can be used to solve to matrix systems with greater than 2 billion rows (using 64-bit indices). Any options not documented in this manual should be considered strictly experimental .

Siefert, Christopher S.; Hu, Jonathan J.; Fisher, Travis C.; Domino, Stefan P.

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Doney, Robert D.; Siefert, Christopher S.; Niederhaus, John H.

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Siefert, Christopher S.

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Siefert, Christopher S.

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Steiner, Adam M.; Siefert, Christopher S.; Shipley, Gabriel A.; Redline, Erica M.; Dickens, Sara D.; Jaramillo, Rex J.; Chavez, Tom C.; Hutsel, Brian T.; Frye-Mason, Gregory C.; Peterson, Kyle J.; Bell, Kate S.; Balogun, Shuaib A.; Losego, Mark D.; Sammeth, Torin M.; Kern, Ian J.; Harjes, Cameron D.; Gilmore, Mark A.; Lehr, Jane M.

Abstract not provided.

Tuminaro, Raymond S.; Gaidamour, Jeremie G.; Gerstenberger, Axel G.; Siefert, Christopher S.

Abstract not provided.