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Prediction and Uncertainty in Computational Modeling of Complex Phenomena: A Whitepaper

Description: This report summarizes some challenges associated with the use of computational science to predict the behavior of complex phenomena. As such, the document is a compendium of ideas that have been generated by various staff at Sandia. The report emphasizes key components of the use of computational to predict complex phenomena, including computational complexity and correctness of implementations, the nature of the comparison with data, the importance of uncertainty quantification in comprehending what the prediction is telling us, and the role of risk in making and using computational predictions. Both broad and more narrowly focused technical recommendations for research are given. Several computational problems are summarized that help to illustrate the issues we have emphasized. The tone of the report is informal, with virtually no mathematics. However, we have attempted to provide a useful bibliography that would assist the interested reader in pursuing the content of this report in greater depth.
Date: January 20, 1999
Creator: Trucano, T.G.
Partner: UNT Libraries Government Documents Department

The role of dynamic experimentation for computation analysis

Description: In this paper a brief description of dynamic techniques commonly available for determining material property studies is presented. For many impact applications, the material generally experiences a complex loading path. In most cases, the initial loading conditions can be represented by the shock commonly referred to as the Hugoniot state. Subsequent loading or release structure, i.e., off-Hugoniot states would however be dependent on the physical processes dominating the material behavior. The credibility of the material model is tested by the accuracy of predictions of off-Hugoniot states. Experimental techniques commonly used to determine off-Hugoniot states are discussed in this survey.
Date: March 1, 1995
Creator: Chhabildas, L.C. & Trucano, T.G.
Partner: UNT Libraries Government Documents Department

Confidence in ASCI scientific simulations

Description: The US Department of Energy`s (DOE) Accelerated Strategic Computing Initiative (ASCI) program calls for the development of high end computing and advanced application simulations as one component of a program to eliminate reliance upon nuclear testing in the US nuclear weapons program. This paper presents results from the ASCI program`s examination of needs for focused validation and verification (V and V). These V and V activities will ensure that 100 TeraOP-scale ASCI simulation code development projects apply the appropriate means to achieve high confidence in the use of simulations for stockpile assessment and certification. The authors begin with an examination of the roles for model development and validation in the traditional scientific method. The traditional view is that the scientific method has two foundations, experimental and theoretical. While the traditional scientific method does not acknowledge the role for computing and simulation, this examination establishes a foundation for the extension of the traditional processes to include verification and scientific software development that results in the notional framework known as Sargent`s Framework. This framework elucidates the relationships between the processes of scientific model development, computational model verification and simulation validation. This paper presents a discussion of the methodologies and practices that the ASCI program will use to establish confidence in large-scale scientific simulations. While the effort for a focused program in V and V is just getting started, the ASCI program has been underway for a couple of years. The authors discuss some V and V activities and preliminary results from the ALEGRA simulation code that is under development for ASCI. The breadth of physical phenomena and the advanced computational algorithms that are employed by ALEGRA make it a subject for V and V that should typify what is required for many ASCI simulations.
Date: June 1, 1998
Creator: Ang, J.A.; Trucano, T.G. & Luginbuhl, D.R.
Partner: UNT Libraries Government Documents Department

Simulation of armor penetration by tungsten rods: ALEGRA validation report

Description: Results from simulations of the impact and penetration of tungsten alloy rods into thick rolled armor plates are presented. The calculations were performed with the CTH and ALEGRA computer codes using the DOE massively parallel TFLOPS computer co-developed by Sandia National Laboratory and Intel Corporation. Comparisons with experimental results are presented. Agreement of the two codes with each other and with the empirical results for penetration channel depth and radius is very close. Other shock physics and penetration features are also compared to simulation results.
Date: November 1, 1997
Creator: Carroll, D.E.; Hertel, E.S. Jr. & Trucano, T.G.
Partner: UNT Libraries Government Documents Department

Analysis of Radiation-Driven Explosive Flyers

Description: There is great interest in being able to use the x-ray output from a Z-pinch for equation of state measurements at extreme conditions. However, the direct x-ray output form the pinch produces a very sharp and rapidly attenuating pressure pulse in target materials. To obtain high quality measurements with this source, a mechanism for generating non-attenuating waves is needed. One possibility involves using the x-ray source to throw a near-normal density intermediate drive at the target, a situation similar to more conventional configurations. To scope out preliminary design parameters, they used the ALEGRA code to simulate a number of different possibilities involving the driver and the gap between it and the target. They used a somewhat idealized radiation source--a main x-ray pulse 30 ns long at its base and peaking at a blackbody temperature of 100 eV. The calculations suggest that a 100-micron aluminum driver with a 90-micron gap will yield a 15-ns-wide non-attenuating pulse with an amplitude of over 250 GPa.
Date: July 19, 1999
Creator: Lawrence, R.J.; Asay, J.R.; Trucano, T.G. & Hall, C.A.
Partner: UNT Libraries Government Documents Department

A Methodology to Validate 3-D Arbitrary Lagrangian Eulerian Codes with Applications to Alegra

Description: In this study we provided an experimental test bed for validating features of the Arbitrary Lagrangian Eulerian Grid for Research Applications (ALEGRA) code over a broad range of strain rates with overlapping diagnostics that encompass the multiple responses. A unique feature of the ALEGRA code is that it allows simultaneous computational treatment, within one code, of a wide range of strain-rates varying from hydrodynamic to structural conditions. This range encompasses strain rates characteristic of shock-wave propagation (107/s) and those characteristics of structural response (102/s). Most previous code validation experimental &udies, however, have been restricted to simulating or investigating a single strain-rate regime. What is new and different in this investigation is that we have performed well-controlled and well-instrumented experiments, which capture features relevant to both hydrodynamic and structural response in a single experiment. Aluminum was chosen for use in this study because it is a well-characterized material. The current experiments span strain rate regimes of over 107/s to less than 102/s in a single experiment. The input conditions were extremely well defined. Velocity interferometers were used to record the high' strain-rate response, while low strain rate data were collected using strain gauges. Although the current tests were conducted at a nominal velocity of - 1.5 km/s, it is the test methodology that is being emphasized herein. Results of a three-dimensional experiment are also presented.
Date: November 4, 1998
Creator: Chhabildas, L.C.; Duggins, B.D.; Konrad, C.H.; Mosher, D.A.; Perry, J.S.; Reinhart, W.D. et al.
Partner: UNT Libraries Government Documents Department

An Investigation of Wavelet Bases for Grid-Based Multi-Scale Simulations Final Report

Description: The research summarized in this report is the result of a two-year effort that has focused on evaluating the viability of wavelet bases for the solution of partial differential equations. The primary objective for this work has been to establish a foundation for hierarchical/wavelet simulation methods based upon numerical performance, computational efficiency, and the ability to exploit the hierarchical adaptive nature of wavelets. This work has demonstrated that hierarchical bases can be effective for problems with a dominant elliptic character. However, the strict enforcement of orthogonality was found to be less desirable than weaker semi-orthogonality or bi-orthogonality for solving partial differential equations. This conclusion has led to the development of a multi-scale linear finite element based on a hierarchical change of basis. The reproducing kernel particle method has been found to yield extremely accurate phase characteristics for hyperbolic problems while providing a convenient framework for multi-scale analyses.
Date: November 1, 1998
Creator: Baty, R.S.; Burns, S.P.; Christon, M.A.; Roach, D.W.; Trucano, T.G.; Voth, T.E. et al.
Partner: UNT Libraries Government Documents Department

Recent progress in ALEGRA development and application to ballistic impacts

Description: ALEGRA is a multi-material, arbitrary-Lagrangian-Eulerian (ALE) code for solid dynamics being developed by the Computational Physics Research and Development Department at Sandia National Laboratories. It combines the features of modem Eulerian shock codes, such as CTH, with modem Lagrangian structural analysis codes. With the ALE algorithm , the mesh can be stationary (Eulerian) with the material flowing through the mesh, the mesh ran move with the material (Lagrangian) so there is no flow between elements, or the mesh motion can be entirely independent of the material motion (Arbitrary). All three mesh types can coexist in the same problem and any mesh may change its type during the calculation. In this paper we summarize several key capabilities that have recently been added to the code or are currently being implemented. As a demonstration of the capabilities of ALEGRA, we have applied it to the experimental data taken by Silsby.
Date: December 1, 1996
Creator: Summers, R.M.; Peery, J.S.; Wong, M.W.; Hertel, E.S. Jr.; Trucano, T.G. & Chhabildas, L.C.
Partner: UNT Libraries Government Documents Department

Use of Z-pinch radiation sources for high-pressure shock wave studies

Description: The authors are developing a new shock wave diagnostic using Z pinch sources for high-pressure equation of state (EOS) measurements. Specifically, they are employing VISAR interferometry to measure the particle velocity of shocked materials and fiber optic probes to measure the shock speed. Combination of these measurements will allow absolute EOS data with Z accelerators. This report is a progress report on the development of this new approach to EOS measurements; however, preliminary data obtained with the diagnostics are encouraging. With further development of Z pinch sources, it is envisioned that a variety of EOS and constitutive property measurements can be made. Time-resolved wave profile measurements will then provide a variety of EOS and material property data, such as isentropic EOS, initial compressive strength and shock-induced compressive strength, dynamic tensile strength, kinetics of phase transitions, and surface stability studies.
Date: August 1998
Creator: Asay, J. R.; Konrad, C. H.; Hall, C. A.; Trott, W. M.; Chandler, G. A.; Fleming, K. J. et al.
Partner: UNT Libraries Government Documents Department

Use of Z pinch radiation sources for high pressure shock wave studies

Description: Recent developments in pulsed power technology demonstrate use of intense radiation sources (Z pinches) for driving planar shock waves in samples with spatial dimensions larger than possible with other radiation sources. Initial indications are that the use of Z pinch sources can be used to produce planar shock waves in samples with diameters of a few millimeters and thicknesses approaching one half millimeter. These dimensions allow increased accuracy of both shock velocity and particle velocity measurements. The Z pinch radiation source uses imploding metal plasma induced by self-magnetic fields applied to wire arrays to produce high temperature x-ray environments in vacuum hohlraum enclosures. Previous experiments have demonstrated that planar shock waves can be produced with this approach. A photograph of a wire array located inside the vacuum hohlraum is shown here. Typically, a few hundred individual wires are used to produce the Z pinch source. For the shock wave experiments being designed, arrays of 120 to 240 tungsten wires with a diameter of 40 mm and with individual diameters of about 10 {micro}m are used. Preliminary experiments have been performed on the Z pulsed radiation source to demonstrate the ability to obtain VISAR measurements in the Z accelerator environment. Analysis of these results indicate that another effect, not initially anticipated, is an apparent change in refractive index that occurs in the various optical components used in the system. This effect results in an apparent shift in the frequency of reflected laser light, and causes an error in the measured particle velocity. Experiments are in progress to understand and minimize this effect.
Date: August 1, 1998
Creator: Asay, J.R.; Konrad, C.H.; Hall, C.A.; Trott, W.M.; Chandler, G.A.; Holland, K.G. et al.
Partner: UNT Libraries Government Documents Department

Peer Review Process for the Sandia ASCI V and V Program: Version 1.0

Description: This report describes the initial definition of the Verification and Validation (V and V) Plan Peer Review Process at Sandia National Laboratories. V and V peer review at Sandia is intended to assess the ASCI code team V and V planning process and execution. Our peer review definition is designed to assess the V and V planning process in terms of the content specified by the Sandia Guidelines for V and V plans. Therefore, the peer review process and process for improving the Guidelines are necessarily synchronized, and form parts of a larger quality improvement process supporting the ASCI V and V program at Sandia.
Date: January 1, 2001
Creator: Pilch, M.; Trucano, T.G.; Peercy, D.E.; Hodges, A.L.; Young, E.R. & Moya, J.L.
Partner: UNT Libraries Government Documents Department

Swords to plowshares: Shock wave applications to advanced lithography

Description: Extreme UltraViolet Lithography (EUVL) seeks to apply radiation in a wavelength region centered near 13 nm to produce microcircuits having features sizes 0.1 micron or less. A critical requirement for the commercial application of this technology is the development of an economical, compact source of this radiation which is suitable for lithographic applications. A good candidate is a laser-plasma source, which is generated by the interaction of an intermediate intensity laser pulse (up to 10{sup 12} W/cm{sup 2}) with a metallic target. While such a source has radiative characteristics which satisfy the needs of an EUVL source, the debris generated during the laser-target interaction strikes at the economy of the source. Here, the authors review the use of concepts and computer modeling, originally developed for hypervelocity impact analysis, to study this problem.
Date: March 1, 1995
Creator: Trucano, T. G.; Grady, D. E.; Kubiak, G. D.; Kipp, M. E.; Olson, R. E. & Farnsworth, A.
Partner: UNT Libraries Government Documents Department

ALEGRA -- code validation: Experiments and simulations

Description: In this study, the authors are providing an experimental test bed for validating features of the ALEGRA code over a broad range of strain rates with overlapping diagnostics that encompass the multiple responses. A unique feature of the Arbitrary Lagrangian Eulerian Grid for Research Applications (ALEGRA) code is that it allows simultaneous computational treatment, within one code, of a wide range of strain-rates varying from hydrodynamic to structural conditions. This range encompasses strain rates characteristic of shock-wave propagation (10{sup 7}/s) and those characteristic of structural response (10{sup 2}/s). Most previous code validation experimental studies, however, have been restricted to simulating or investigating a single strain-rate regime. What is new and different in this investigation is that the authors have performed well-instrumented experiments which capture features relevant to both hydrodynamic and structural response in a single experiment. Aluminum was chosen for use in this study because it is a well characterized material--its EOS and constitutive material properties are well defined over a wide range of loading rates. The current experiments span strain rate regimes of over 10{sup 7}/s to less than 10{sup 2}/s in a single experiment. The input conditions are extremely well defined. Velocity interferometers are used to record the high strain-rate response, while low strain rate data were collected using strain gauges.
Date: March 16, 1998
Creator: Chhabildas, L.C.; Konrad, C.H.; Mosher, D.A.; Reinhart, W.D; Duggins, B.D.; Rodeman, R. et al.
Partner: UNT Libraries Government Documents Department

Experimental Bench Mark Data for ALEGRA Code Validations

Description: In this study experiments of increasing complexity have been conducted to provide a data base for validating features of the Arbitrary Lagrangian Eulerian Grid for Research Applications (ALEGRA) code over a broad range of strain rates with overlapping diagnostics that encompass multiple responses. This range encompasses strain rates characteristic of shock-wave propagation (10<sup>7</sup>/s) and those chameteristics of structural response (10<sup>2</sup>/s). The tests matrix consists of two experimental series; the first being a simple system test with diagnostics that capture features relevant to both the high strain-rate hydrodynamic response and the low strain-rate structural response of the target. The second series of experiments increased the complexity of tests with the addition of foam to the original simple series. The input conditions are extremely well defined. Velocity interferometers are used to record the high strain-rate response, while the low strain-rate data were collected using strain, carbon and PVDF gauges.
Date: June 23, 1999
Creator: Chhabildas, L.C.; Kipp, M.E.; Konrad, C.H.; Mann, G.A.; Mosher, D.A.; Peery, J.S. et al.
Partner: UNT Libraries Government Documents Department