Bulletin of the American Physical Society
22nd Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 67, Number 8
Monday–Friday, July 11–15, 2022; Anaheim, California
Session C02: Shallow Bubble Collapse II / Ejecta SurfaceRecordings Available
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Chair: Fady Najjar, Lawrence Livermore Natl Lab Room: Anaheim Marriott Platinum 6 |
Monday, July 11, 2022 11:00AM - 11:15AM |
C02.00001: Understanding The Shallow Bubble Collapse Mechanism with Resolved 2D and 3D Hydrodynamic Computations David A Brantley, Garry R Maskaly, Fady M Najjar, Georges Akiki, William Moore Recent experiments have demonstrated that, under certain shock conditions, the Shallow Bubble Collapse (SBC) mechanism can produce ejecta with high areal masses (>300 mg/cm2) at elevated temperatures (>2500K) substantially above conditions observed for RMI ejecta. In this talk, we discuss methods for modeling SBC in 2D and 3D to understand the time evolution and structures. We show validation results for a series of experiments, as well as the sensitivity to modeling choices. We find that, while lower drive SBC experiments are relatively consistent with the experimental data, higher drives require additional model development. We also provide highlights from our computational SBC effort including recent GPU-accelerated 3D hydrodynamic calculations on the LLNL Lassen supercomputer. |
Monday, July 11, 2022 11:15AM - 11:30AM |
C02.00002: Applying Forward Modeling to Compare Asay Foils and Windows in Support of Shallow Bubble Collapse Mechanism William C Moore, Garry R Maskaly, Fady M Najjar, Gerald D Stevens Asay diagnostics have been prominently used for measuring ejecta momentum since being introduced by Asay et al. Such diagnostics typically utilizes an opaque foil of known mass. As ejecta are deposited on the foil surface, velocimetry measurements from the foil back surface are used to infer the momentum deposition and calculate the ejecta mass distribution. A transparent Asay window can be used in place of the opaque foil to allow for velocimetry measurements closer to the location of ejecta deposition. In the present work, cerium ejecta experiments are performed with both Asay foils and windows. These experimental diagnostics are forward modelled numerically using high-resolution hydrodynamic simulations for the cerium ejecta impacting the Asay windows and foils. For high momentum deposition rates, we found that the perturbations from individual ejecta coalesce into shocks, resulting in degenerate solutions of the ejecta mass distribution. By using an Asay window with an embedded mirror, the perturbations from the individual ejecta have less distance/time to coalesce before being measured via velocimetry. The talk will highlight the utility of forward models to identify the failure conditions of Asay foils and the uncertainty reduction of the corresponding Asay windows. |
Monday, July 11, 2022 11:30AM - 11:45AM |
C02.00003: Unifying failure: exploring the relationship between ejecta & spall Matthew A Brown, Robin J Williams 3D Large Eddy Simulation (LES) is used to explore the connections between ejecta and spall, in multiply shocked metal targets, having surfaces initially perturbed by periodic and non-periodic roughness profiles. |
Monday, July 11, 2022 11:45AM - 12:00PM |
C02.00004: Effects of defects on ejecta production in tin Frank J Cherne, Saryu J Fensin Defects in the form of scratches, dings, and dents can form on manufactured parts during handling beyond the typical machining process. The purpose of this work was to evaluate the effect of three types of defects that one might expect and how these defects may alter the production of ejecta from the surface. In this work, we present the observed effects on the mass and velocity time history produced from the three types of defects that were manufactured into the surface. The experiments nominally were performed at the same peak stress and pulse duration with data collected from the non-defected and defected surface. |
Monday, July 11, 2022 12:00PM - 12:15PM |
C02.00005: Modulation of Richtmyer-Meshkov Instability in Gas Gun Experiments Jeffrey H Nguyen, Sylvie Aubry, Michael R Armstrong, Andrew Hoff, Jonathan L Belof, Hector Lorenzana, Matthew Staska, Brandon M LaLone We modulate Richtmyer-Meshkov instability in gas gun experiments by modifying the free and impact surfaces of the copper targets. The sample free surface has various shapes including sinusoidal and square waves. The impact side of the targets are modulated by simple and graded density channels. With these variations, we demonstrate a level of control on velocity and formation of jetting from the sample free surface. Results are consistent with simulations. We present velocity and optical data from these experiments and comparison to simulations. |
Monday, July 11, 2022 12:15PM - 12:30PM |
C02.00006: Use of shock wavefront curvature to modulate RMI jet growth Michael R Armstrong, Jeffrey H Nguyen, Sylvie Aubry, William Schill, Jonathan L Belof, Hector Lorenzana In impact experiments, we modulate the shock wavefront curvature in PMMA/Ta composite samples prior to surface breakout at a V-groove in the PMMA. Upon breakout, a Richtmyer-Meshkov instability (RMI) jet is launched from the V-groove, which we observe using time-resolved x-ray imaging at the Dynamic Compression Sector. Transverse imaging of these samples enables the characterization of both the shock wavefront curvature internal to the sample prior to breakout, as well as the progress of the jet subsequent to breakout. We observe a clear correlation between the wavefront curvature and the jet velocity, suggesting that graded density materials may be used to mitigate or enhance the strength of the RMI. We present these data and compare to simulations. |
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