Publications

Littlewood, David J.

Abstract not provided.

D'Elia, Marta D.; Bochev, Pavel B.; Perego, Mauro P.; Trageser, Jeremy T.; Littlewood, David J.

We develop and analyze an optimization-based method for the coupling of a static peridynamic (PD) model and a static classical elasticity model. The approach formulates the coupling as a control problem in which the states are the solutions of the PD and classical equations, the objective is to minimize their mismatch on an overlap of the PD and classical domains, and the controls are virtual volume constraints and boundary conditions applied at the local-nonlocal interface. Our numerical tests performed on three-dimensional geometries illustrate the consistency and accuracy of our method, its numerical convergence, and its applicability to realistic engineering geometries. We demonstrate the coupling strategy as a means to reduce computational expense by confining the nonlocal model to a subdomain of interest, and as a means to transmit local (e.g., traction) boundary conditions applied at a surface to a nonlocal model in the bulk of the domain.

Littlewood, David J.; Wood, Mitchell A.; Montes de Oca Zapiain, David M.; Rajamanickam, Sivasankaran R.; Trask, Nathaniel A.

This report includes a compilation of several slide presentations: 1) Interatomic Potentials for Materials Science and Beyond–Advances in Machine Learned Spectral Neighborhood Analysis Potentials (Wood); 2) Agile Materials Science and Advanced Manufacturing through AI/ML (de Oca Zapiain); 3) Machine Learning for DFT Calculations (Rajamanickam); 4) Structure-preserving ML discovery of a quantum-to-continuum codesign stack (Trask); and 5) IBM Overview of Accelerated Discovery Technology (Pitera)

Trask, Nathaniel A.; D'Elia, Marta D.; Littlewood, David J.; Silling, Stewart A.; Trageser, Jeremy T.; Tupek, Michael R.

Nonlocal models naturally handle a range of physics of interest to SNL, but discretization of their underlying integral operators poses mathematical challenges to realize the accuracy and robustness commonplace in discretization of local counterparts. This project focuses on the concept of asymptotic compatibility, namely preservation of the limit of the discrete nonlocal model to a corresponding well-understood local solution. We address challenges that have traditionally troubled nonlocal mechanics models primarily related to consistency guarantees and boundary conditions. For simple problems such as diffusion and linear elasticity we have developed complete error analysis theory providing consistency guarantees. We then take these foundational tools to develop new state-of-the-art capabilities for: lithiation-induced failure in batteries, ductile failure of problems driven by contact, blast-on-structure induced failure, brittle/ductile failure of thin structures. We also summarize ongoing efforts using these frameworks in data-driven modeling contexts. This report provides a high-level summary of all publications which followed from these efforts.

Littlewood, David J.; Seleson, Pablo D.; Pasetto, Marco P.; John, Yohan J.; Trageser, Jeremy T.

Abstract not provided.

Littlewood, David J.; Jones, Reese E.; Plews, Julia A.; Hetmaniuk, Ulrich L.; Lifflander, Jonathan

Abstract not provided.

World Congress in Computational Mechanics and ECCOMAS Congress

Littlewood, David J.; Jones, Reese E.; Morales, Nicolas M.; Plews, Julia A.; Hetmaniuk, Ulrich; Lifflander, Jonathan J.

Software development for high-performance scientific computing continues to evolve in response to increased parallelism and the advent of on-node accelerators, in particular GPUs. While these hardware advancements have the potential to significantly reduce turnaround times, they also present implementation and design challenges for engineering codes. We investigate the use of two strategies to mitigate these challenges: the Kokkos library for performance portability across disparate architectures, and the DARMA/vt library for asynchronous many-task scheduling. We investigate the application of Kokkos within the NimbleSM finite element code and the LAMÉ constitutive model library. We explore the performance of DARMA/vt applied to NimbleSM contact mechanics algorithms. Software engineering strategies are discussed, followed by performance analyses of relevant solid mechanics simulations which demonstrate the promise of Kokkos and DARMA/vt for accelerated engineering simulators.

Littlewood, David J.; Plews, Julia A.; Morales, Nicolas M.; Jones, Reese E.

Abstract not provided.

van Bloemen Waanders, Bart G.; Littlewood, David J.; Turner, Daniel Z.; Parks, Michael L.

Abstract not provided.

Sansom, Kurt R.; Dark, Julia D.; Littlewood, David J.; Trageser, Jeremy T.

Abstract not provided.

Jones, Reese E.; Rimsza, Jessica R.; Littlewood, David J.; LaForce, Tara

Abstract not provided.

Littlewood, David J.; Foster, John E.; Seleson, Pablo D.

Abstract not provided.

Littlewood, David J.; Belcourt, Kenneth N.; Le, San L.; Lester, Brian T.; Munday, Lynn B.; Perez, Jorge P.; Xavier, Patrick X.

Abstract not provided.

Littlewood, David J.

Abstract not provided.

Littlewood, David J.; Rimsza, Jessica R.; Frederick, Jennifer M.; Jones, Reese E.; LaForce, Tara

Abstract not provided.

Littlewood, David J.

Abstract not provided.

Handbook of Nonlocal Continuum Mechanics for Materials and Structures

D'Elia, Marta D.; Bochev, Pavel B.; Littlewood, David J.; Perego, Mauro P.

Nonlocal continuum theories for mechanics can capture strong nonlocal effects due to long-range forces in their governing equations. When these effects cannot be neglected, nonlocal models are more accurate than partial differential equations (PDEs); however, the accuracy comes at the price of a prohibitive computational cost, making local-to-nonlocal (LtN) coupling strategies mandatory. In this chapter, we review the state of the art of LtN methods where the efficiency of PDEs is combined with the accuracy of nonlocal models. Then, we focus on optimization-based coupling strategies that couch the coupling of the models into a control problem where the states are the solutions of the nonlocal and local equations, the objective is to minimize their mismatch on the overlap of the local and nonlocal problem domains, and the virtual controls are the nonlocal volume constraint and the local boundary condition. The strategy is described in the context of nonlocal and local elasticity and illustrated by numerical tests on three-dimensional realistic geometries. Additional numerical tests also prove the consistency of the method via patch tests.

Merewether, Mark T.; Crane, Nathan K.; Plews, Julia A.; de Frias, Gabriel J.; Le, San L.; Littlewood, David J.; Mosby, Matthew D.; Pierson, Kendall H.; Porter, V.L.; Shelton, Timothy S.; Thomas, Jesse D.; Tupek, Michael R.; Veilleux, Michael V.; Xavier, Patrick G.; Scherzinger, William M.; Lester, Brian T.

Accurate and efficient constitutive modeling remains a cornerstone issue for solid mechanics analysis. Over the years, the LAME advanced material model library has grown to address this challenge by implement- ing models capable of describing material systems spanning soft polymers to stiff ceramics including both isotropic and anisotropic responses. Inelastic behaviors including (visco)plasticity, damage, and fracture have all incorporated for use in various analyses. This multitude of options and flexibility, however, comes at the cost of many capabilities, features, and responses and the ensuing complexity in the resulting imple- mentation. Therefore, to enhance confidence and enable the utilization of the LAME library in application, this effort seeks to document and verify the various models in the LAME library. Specifically, the broader strategy, organization, and interface of the library itself is first presented. The physical theory, numerical implementation, and user guide for a large set of models is then discussed. Importantly, a number of verifi- cation tests are performed with each model to not only have confidence in the model itself but also highlight some important response characteristics and features that may be of interest to end-users. Finally, in looking ahead to the future, approaches to add material models to this library and further expand the capabilities are presented.

Merewether, Mark T.; Plews, Julia A.; Crane, Nathan K.; de Frias, Gabriel J.; Le, San L.; Littlewood, David J.; Mosby, Matthew D.; Pierson, Kendall H.; Porter, V.L.; Shelton, Timothy S.; Thomas, Jesse D.; Tupek, Michael R.; Veilleux, Michael V.; Xavier, Patrick G.; Clutz, Christopher J.R.; Manktelow, Kevin M.

Presented in this document is a small portion of the tests that exist in the Sierra/SolidMechanics (Sierra/SM) verification test suite. Most of these tests are run nightly with the Sierra/SM code suite, and the results of the test are checked versus the correct analytical result. For each of the tests presented in this document, the test setup, a description of the analytic solution, and comparison of the Sierra/SM code results to the analytic solution is provided. Mesh convergence is also checked on a nightly basis for several of these tests. This document can be used to confirm that a given code capability is verified or referenced as a compilation of example problems. Additional example problems are provided in the Sierra/SM Example Problems Manual. Note, many other verification tests exist in the Sierra/SM test suite, but have not yet been included in this manual.

Littlewood, David J.; van Bloemen Waanders, Bart G.; Hegde, Arun S.; Cook, Adam W.

Abstract not provided.

Merewether, Mark T.; Plews, Julia A.; Crane, Nathan K.; de Frias, Gabriel J.; Le, San L.; Littlewood, David J.; Mosby, Matthew D.; Pierson, Kendall H.; Porter, V.L.; Shelton, Timothy S.; Thomas, Jesse D.; Tupek, Michael R.; Veilleux, Michael V.; Xavier, Patrick G.; Manktelow, Kevin M.; Clutz, Christopher J.R.

Presented in this document are the theoretical aspects of capabilities contained in the Sierra / SM code. This manuscript serves as an ideal starting point for understanding the theoretical foundations of the code. For a comprehensive study of these capabilities, the reader is encouraged to explore the many references to scientific articles and textbooks contained in this manual. It is important to point out that some capabilities are still in development and may not be presented in this document. Further updates to this manuscript will be made as these capabilities come closer to production level.

Perez, Jorge P.; Littlewood, David J.; Bennett, Janine C.; Hollman, David S.; Lifflander, Jonathan; Wilke, Jeremiah J.

Abstract not provided.

Littlewood, David J.; Perez, Jorge P.; Tupek, Michael R.; Lester, Brian T.

Abstract not provided.

Littlewood, David J.; Foster, John E.; Seleson, Pablo D.

Abstract not provided.

Littlewood, David J.; Lester, Brian T.; Tupek, Michael R.

Abstract not provided.