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A data-driven peridynamic continuum model for upscaling molecular dynamics

D'Elia, Marta; Silling, Stewart; Yu, Yue; You, Huaiqian

Nonlocal models, including peridynamics, often use integral operators that embed lengthscales in their definition. However, the integrands in these operators are difficult to define from the data that are typically available for a given physical system, such as laboratory mechanical property tests. In contrast, molecular dynamics (MD) does not require these integrands, but it suffers from computational limitations in the length and time scales it can address. To combine the strengths of both methods and to obtain a coarse-grained, homogenized continuum model that efficiently and accurately captures materials’ behavior, we propose a learning framework to extract, from MD data, an optimal Linear Peridynamic Solid (LPS) model as a surrogate for MD displacements. To maximize the accuracy of the learnt model we allow the peridynamic influence function to be partially negative, while preserving the well-posedness of the resulting model. To achieve this, we provide sufficient well-posedness conditions for discretized LPS models with sign-changing influence functions and develop a constrained optimization algorithm that minimizes the equation residual while enforcing such solvability conditions. This framework guarantees that the resulting model is mathematically well-posed, physically consistent, and that it generalizes well to settings that are different from the ones used during training. We illustrate the efficacy of the proposed approach with several numerical tests for single layer graphene. Our two-dimensional tests show the robustness of the proposed algorithm on validation data sets that include thermal noise, different domain shapes and external loadings, and discretizations substantially different from the ones used for training.

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TYPE Other Report YEAR 2021
DOIOSTI

AEVmod – Atomic Environment Vector Module Documentation

Najm, Habib N.; Yang, Yoona

This report outlines the mathematical formulation for the atomic environment vector (AEV) construction used in the aevmod software package. The AEV provides a summary of the geometry of a molecule or atomic configuration. We also present the formulation for the analytical Jacobian of the AEV with respect to the atomic Cartesian coordinates. The software provides functionality for both the AEV and AEV-Jacobian, as well as the AEV-Hessian which is available via reliance on the third party library Sacado.

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TYPE SAND Report YEAR 2021
DOIOSTI

Spontaneous Imbibition Tests and Parameter Estimation in Volcanic Tuff

Kuhlman, Kristopher L.; Mills, Melissa M.; Heath, Jason E.; Paul, Matthew J.; Wilson, Jennifer E.; Bower, John E.

We present a dynamic laboratory spontaneous imbibition test and interpretation method, demonstrated on volcanic tuff samples from the Nevada National Security Site. The method includes numerical inverse modeling to quantify uncertainty of estimated two-phase fluid flow properties. As opposed to other approaches requiring multiple different laboratory instruments, the dynamic imbibition method simultaneously estimates capillary pressure and relative permeability from one test apparatus.

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TYPE SAND Report YEAR 2021
DOIOSTI

Validation of the SCEPTRE Boltzmann-CSD Solver

Drumm, Clifton R.; Fan, Wesley C.

A new Boltzmann-CSD solver has been developed within the SCEPTRE radiation-transport code, based on the 1st-order form of the transport equation, using discontinuous finite elements in space and energy and discrete ordinates in angle. The Boltzmann-CSD solver has been validated against experimental data for electron energy deposition distributions and for electron emission spectra. Comparison of the calculated results with experimental data shows excellent agreement for many of the test configurations and reasonable agreement for other test configurations. The tests have also been modeled with the ITS Monte Carlo code, which also shows excellent to reasonable agreement with the SCEPTRE results and experimental data. The SCEPTRE Boltzmann-CSD solver relies on electron cross sections generated by the legacy CEPXS code, which currently is limited to electron-only Boltzmann-CSD cross sections. Performing full electron-photon radiation transport with the Boltzmann-CSD solver will require further development in the cross section generating code. For the energy- deposition calculations, neglecting photon transport results in at most about 5% overprediction of the energy deposition for high-energy electrons on high-Z targets, and relatively insignificant difference for the other test configurations.

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TYPE SAND Report YEAR 2021
DOIOSTI

Empirical Model of Puncture Energy for Metals

Albelo-Cortes, Josean; Alqawasmi, Laith; Jacobowitz, J.; Hubbard, Neal B.

The purpose of this work is to fit a previously developed empirical equation for puncture energy to simulation data. The conservative puncture energy equation could be used to expedite the process of performing calculations in the development of safety measures, avoiding the need to create complex finite element models for specific puncture scenarios. A total of 108 simulations are developed by varying coupon thickness, coupon material, probe shape, and probe diameter. The simulations are comprised of a low-velocity probe puncturing the coupons, from which the probe kinetic energy change is calculated. The empirical equation is fit to the dimensions, material properties, and energy results using a non-linear least-squares regression method within Python, which determines the two constant parameters for each fit. More statistically significant fit results are achieved by separating the data by probe shape and coupon material.

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TYPE SAND Report YEAR 2021
DOIOSTI

Comparison of Tempered and Truncated Fractional Models

Olson, Hayley

Tempered fractional operators are able to model effects that classical partial differential equations cannot quite capture. For example, this includes the super- and subdiffusion effects that are present in hydrology and geophysics models. However, tempered fractional operators are computationally intensive. We analyze a truncated variation of the fractional operators, which are less computationally intensive, in an effort to use them in place of the more complex tempered variation. In particular, we train parameters of the truncated operator using neural networks in order to optimize the difference of the actions of the two operators.

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TYPE Other Report YEAR 2021
DOIOSTI

Review of Release Behavior of Hydrogen & Natural Gas Blends from Pipelines

Baird, Austin R.; Glover, Austin M.; Ehrhart, Brian D.

Hydrogen can be used to reduce carbon emissions by blending into other gaseous energy carriers, such as natural gas. However, hydrogen blending into natural gas has important implications for safety which need to be evaluated. Hydrogen has different physical properties than natural gas, and these properties affect safety evaluations concerning a leak of the blended gas. The intent of this report is to begin to investigate the safety implications of blending hydrogen into the natural gas infrastructure with respect to a leak event from a pipeline. A literature review was conducted to identify existing data that will better inform future hazard and risk assessments for hydrogen/natural gas blends. Metrics with safety implications such as heat flux and dispersion behavior may be affected by the overall blend ratio of the mixture. Of the literature reviewed, there was no directly observed separation of the hydrogen from the natural gas or methane blend. No literature was identified that experimentally examined unconfined releases such as concentration fields or concentration at specific distances. Computational efforts have predicted concentration fields by modified versions of existing engineering models, but the validation of these models is limited by the unavailability of literature data. There are multiple literature sources that measured flame lengths and heat flux values, which are both relevant metrics to risk and hazard assessments. These data can be more directly compared to the outputs of existing engineering models for validation.

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TYPE SAND Report YEAR 2021
DOIOSTI

Thermodynamically consistent semi-compressible fluids: A variational perspective

Journal of Physics A: Mathematical and Theoretical

Eldred, Christopher; Gay-Balmaz, Francois

This paper presents (Lagrangian) variational formulations for single and multicomponent semi-compressible fluids with both reversible (entropy-conserving) and irreversible (entropy-generating) processes. Semi-compressible fluids are useful in describing low-Mach dynamics, since they are soundproof. These models find wide use in many areas of fluid dynamics, including both geophysical and astrophysical fluid dynamics. Specifically, the Boussinesq, anelastic and pseudoincompressible equations are developed through a unified treatment valid for arbitrary Riemannian manifolds, thermodynamic potentials and geopotentials. By design, these formulations obey the 1st and 2nd laws of thermodynamics, ensuring their thermodynamic consistency. This general approach extends and unifies existing work, and helps clarify the thermodynamics of semi-compressible fluids. To further this goal, evolution equations are presented for a wide range of thermodynamicvariables: entropy density s, specific entropy η, buoyancy b, temperature T, potential temperature O and a generic entropic variable Χ; along with a general definition of buoyancy valid for all three semicompressible models and arbitrary geopotentials. Finally, the elliptic equation for the pressure perturbation (the Lagrange multiplier that enforces semicompressibility) is developed for all three equation sets in the case of reversible dynamics, and for the Boussinesq/anelastic equations in the case of irreversible dynamics; and some discussion is given of the difficulty in formulating it for the pseudoincompressible equations with irreversible dynamics.

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TYPE Journal Article YEAR 2021
DOIOSTIScopus

Electron emission from fluorene (C13H10) upon 3.5 MeV/u Si8+ion impact: Double differential distributions

Journal of Physics B: Atomic, Molecular and Optical Physics

Bagdia, Chandan; Mandal, Anuvab; Bhattacharjee, Shamik; Nrisimha Murty, M.; Misra, Deepankar; Champion, Christophe; Gulyas, Laszlo; Weck, Philippe F.; Tribedi, Lokesh C.

We have studied the electron emission from one of the polycyclic aromatic hydrocarbon (PAH) molecules namely, fluorene (C13H10), upon 3.5 MeV/u Si8+ ion impact. The experimentally measured absolute double differential cross sections (DDCS) are compared with the continuum distorted wave-eikonal initial state (CDW-EIS) model and the first Born approximation including correct boundary conditions (CB1). The measurements are carried out in the ejected e-energy range of 1 eV-400 eV and in the angular range of 20 -160 . We have obtained the single differential and the total cross sections (TCSs) of e-emission as well. The CB1 calculation largely underestimates the data. The CDW-EIS model, which is applied for the PAH molecule for the first time, provides an overall better agreement with the double differential, single differential and TCS data. The DDCS data for fluorene has also been compared with that for CH4 molecule, at a few angles. The forward-backward angular asymmetry shows a relatively flatter distribution compared to the theoretical predictions. The contribution due to the giant plasmon resonance could not be clearly observed except a mild indication in the asymmetry parameter. The angular distribution of the carbon KLL Auger electron cross section shows certain variations. The study of the KLL hyper-satellite component indicates the double K-ionization cross section is about 8.6% of the single K-ionization one.

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TYPE Journal Article YEAR 2021
DOIOSTIScopus

Fire-Induced Pressure Response and Failure Characterization of PCV/SCV/3013 Containers - Phase 3

Mendoza, Hector; Baird, Austin R.; Gill, Walter; Figueroa Faria, Victor G.; Mcclard, James; Sprankle, Ray; Hensel, Steve; Michel, Danielle; Adee, Shane M.

Several Department of Energy (DOE) facilities have materials stored in robust, welded, stainless - steel containers with presumed fire - induced pressure response behaviors. Lack of test data related to fire exposure requires conservative safety analysis assumptions for container response at these facilities. This conservatism can in turn result in the implementation of challenging operational restrictions with costly nuclear safety controls. To help address this issue for sites that store DOE 3013 stainless - steel containers, a series of ten tests were undertaken at Sandia National Laboratories. The goal of this test series was to obtain the response behavior for various configurations of DOE 3013 containers with various payload compositions when exposed to one of two ASTM fire conditions. Key parameters measured in the test series included identification of failure - specific characteristics such as pressure, temperature, and whether or not a vessel was breached during a test . Numerous failure - specific characteristics were identified from the ten tests. This report describes the implementation and execution of the test series performed to identify these failure - specific characteristics. Discussions on the test configurations, payload compositions, thermal insults, and experimental setups are presented. Test results in terms of pressurization and vessel breach (or no - breach) are presented along with corresponding discussions for each test.

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TYPE SAND Report YEAR 2021
DOIOSTI

An efficient method to estimate the probability density of seismic Green's functions

Poppeliers, Christian; Preston, Leiph

We present a computationally efficient method to approximate the probability distribution of seismic Green's functions given the uncertainty of an Earth model. The method is based on the Karhunen-Loève (KL) theorem and an approximation of the Green's function (or seismogram) covariance. Using Monte Carlo (MC) simulations as a control case, we demonstrate that our KL-based method can accurately reproduce a probability distribution of seismograms that results from an uncertain Earth model for a MC-derived seismogram covariance. We then describe a method to estimate the covariance of the seismograms resulting from those Earth models that is not based on MC simulations. We use the estimated Green's function covariance in conjunction with our KL-based method to produce a Green's function probability distribution, and compare that distribution to a Green's function probability distribution produced using a MC finite difference method. We find that the Green's function probability distribution approximated using our KL-based method generally mimics that produced using the MC simulations, especially for direct-arriving body waves. However the accuracy of the KL-based method generally decreases for later times in the simulated Green's function distribution.

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TYPE SAND Report YEAR 2021
DOIOSTI

Approximating and incorporating model uncertainty in an inversion for seismic source functions: Preliminary results

Poppeliers, Christian; Preston, Leiph

We present preliminary work on propagating model uncertainty into the estimation of the time domain source time functions of the seismic source. Our method is based on an estimated model covariance function, which we estimate from the data. The model covariance function is then used to construct a suite of surrogate Greens functions which we use in a Monte Carlo type inversion scheme. The result is a probability density function of the six independent source time functions, each of which corresponds to an individual component of the seismic moment tensor. We compare the results of our method with those obtained using a computationally expensive finite difference Monte Carlo method and find that our new method produces results that are deficient in low frequencies. The advantage of our new method, which we term the Karhunen-Loeve Monte Carlo (KLMC) method, is that is several orders of magnitude faster than our current method, which uses a finite difference scheme to produce the suite of forward models.

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TYPE SAND Report YEAR 2021
DOIOSTI

Background measurement methods for opacity experiments conducted at the Z facility

Review of Scientific Instruments

Dunham, G.S.; Nagayama, Taisuke; Bailey, James E.; Loisel, Guillaume P.

Laboratory experiments typically test opacity models by measuring spectrally resolved transmission of a sample using bright backlight radiation. A potential problem is that any unaccounted background signal contaminating the spectrum will artificially reduce the inferred opacity. Methods developed to measure background signals in opacity experiments at the Sandia Z facility are discussed. Preliminary measurements indicate that backgrounds are 9%-11% of the backlight signal at wavelengths less than 10 Å. Background is thus a relatively modest correction for all Z opacity data published to date. Future work will determine how important background is at longer wavelengths.

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TYPE Journal Article YEAR 2021
DOIOSTIScopus

Tuning the critical Li intercalation concentrations for MoX2 (X= S, Se, or Te) bilayer phase transitions

Physical Review Materials

Spataru, Catalin D.

Transition metal dichalcogenides, such as MoS2, are known to undergo a structural phase transformation as well as a change in the electronic conductivity upon Li intercalation. These properties make them candidates for charge-tunable ion-insertion materials that could be used in electrochemical devices. In this paper, we study the phase stability and electronic structure of H and T' Li-intercalated MoX2 bilayers with X = S, Se, or Te. Using first-principles calculations in combination with classical and machine learning modeling approaches, we find that the H phase is more stable at low Li concentration for all X and the critical Li concentration at which the T'→H transition occurs decreases with increasing mass of X. Furthermore, the relative free energy of the two phases becomes less sensitive to Li insertion with increasing atomic mass of the chalcogen atom X. While the electronic conductivity increases with increasing ion concentration at low concentrations, we do not observe a (positive) conductivity jump at the phase transition from H to T'.

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TYPE Journal Article YEAR 2021
DOIOSTIScopus

BioRAM Security User Guide

Caskey, Sue C.; Astuto Gribble, Lisa A.; Walker, Helene C.; Halkjaer-Knudsen, Vibeke N.

Sandia National Laboratories’ Global Chemical and Biological Security program (SNL/GCBS) has an on-going mission to enhance laboratory biosafety and biosecurity. SNL/GCBS has developed robust biosafety and biosecurity risk assessment methodologies and tools to aid laboratories seeking to implement biosecurity as advocated in the recently released World Health Organization’s “Biorisk Management: Laboratory Biosecurity Guidance.” BioRAM Security (BioRAM) is one of these tools. This tool was designed to complement the “Laboratory Biosecurity Handbook” written by Ren Salerno and Jennifer Gaudioso (Salerno, 2007). BioRAM was originally developed under the Sandia National Laboratories Laboratory Directed Research and Development (LDRD) process and has been updated with support from the US Department of Health Centers for Disease Control Select Agent Program, the US Department of State Biosecurity Engagement Program, and by funding from Sandia National Laboratories’ Associated Laboratories Directors.

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TYPE Other Report YEAR 2021
OSTIDOI

Global System Reduction Order Modeling for Localized Feature Inclusion

Journal of Vibration and Acoustics

Brink, Adam R.; Quinn, D.D.

The development of reduced-order models remains an active research area, despite advances in computational resources. The present work develops a novel order-reduction approach that is designed to incorporate isolated regions that contain, for example, nonlinearitites or accumulating damage. The approach is designed to use global modes of the overall system response, which are then naturally coupled to the response in the isolated region of interest. Two examples are provided to demonstrate both the accuracy and the computational efficiency of the proposed approach. The performance of this approach is compared to the exact response corresponding to a finite element simulation for the chosen problems. In addition, the accuracy and computational efficiency are shown relative to a standard Galerkin reduction based on the linear normal modes. It is found that the proposed reduction offer computational efficiency comparable to a Galerkin reduction, but more accurately represents the response of the system when both are compared to the finite element simulation.

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TYPE Journal Article YEAR 2021
DOIOSTIScopus

Randomized algorithms for generalized singular value decomposition with application to sensitivity analysis

Numerical Linear Algebra with Applications

Hart, Joseph L.; Van Bloemen Waanders, Bart; Saibaba, Arvind K.

The generalized singular value decomposition (GSVD) is a valuable tool that has many applications in computational science. However, computing the GSVD for large-scale problems is challenging. Motivated by applications in hyper-differential sensitivity analysis (HDSA), we propose new randomized algorithms for computing the GSVD which use randomized subspace iteration and weighted QR factorization. Detailed error analysis is given which provides insight into the accuracy of the algorithms and the choice of the algorithmic parameters. We demonstrate the performance of our algorithms on test matrices and a large-scale model problem where HDSA is used to study subsurface flow.

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TYPE Journal Article YEAR 2021
DOIOSTIScopus
Results 10801–11000 of 99,299
Results 10801–11000 of 99,299