Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session O6: Focus Session: Ejecta Physics III |
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Chair: William Buttler, Los Alamos National Laboratory Room: Regency Ballroom E |
Wednesday, July 12, 2017 9:15AM - 9:30AM |
O6.00001: Comparative simulations of microjetting using atomistic and continuous approaches in presence of viscosity and surface tension Olivier Durand, Laurent Soulard, Stephane Jaouen, Olivier Heuze, Laurent Colombet, Emmanuel Cieren We compare, at similar scales, the processes of microjetting and ejecta production from shocked roughened metal surfaces by using atomistic and continuous approaches. The atomistic approach is based on very large scale molecular dynamics (MD) simulations. The continuous approach is based on Eulerian hydrodynamics simulations with adaptive mesh refinement; the simulations take into account the effects of viscosity and surface tension, and they use an equation of state calculated from the MD simulations. The microjetting is generated by shock-loading above its fusion point a three-dimensional tin crystal with an initial sinusoidal free surface perturbation, the crystal being set in contact with a vacuum. Several samples with homothetic wavelengths and amplitudes of defect are simulated in order to investigate the influence of the viscosity and surface tension of the metal. The simulations show that the hydrodynamic code reproduces with a very good agreement the distributions, calculated from the MD simulations, of the ejected mass and velocity along the jet. Both codes exhibit also a similar phenomenology of fragmentation of the metallic liquid sheets ejected. [Preview Abstract] |
Wednesday, July 12, 2017 9:30AM - 9:45AM |
O6.00002: Bubble and spike velocities in shock-driven ejecta Varad Karkhanis, Praveen Ramaprabhu, James Hammerberg, Frank Cherne, Malcolm Andrews Using detailed continuum hydrodynamics and molecular dynamics simulations, we apply the nonlinear Richtmyer-Meshkov theory to characterize bubble and spike growth in shock-driven ejecta. We find the asymptotic bubble velocity prediction given by [1] is in excellent agreement with the simulations, when a nonlinear correction for bubbles suggested by [2] is used in that model. Asymptotic spike velocities on the other hand, depend on the initial conditions such as the initial amplitudes, and spike curvature as pointed out by [3]. The asymptotic spike velocities are predicted by applying separate correction factors to the initial growth rate [from 4] as well as the late-time velocities, where both effects can depend on the initial amplitudes [2,5]. For non-sinusoidal surfaces, the expressions for spike and bubble velocities must be modified [6] by replacing the perturbation wavelength with $\lambda_{eff} $, the effective wavelength of an equivalent sinusoid with the same missing area. We verify these ideas with simulations (continuum and MD) at different amplitudes, initial perturbation shapes, and shock strength. [1] K. O. Mikaelian, Phys Rev Lett 80, 508 (1998). [2] W. T. Buttler et al., J Fluid Mech 703, 60 (2012). [3] Q. Zhang, Phys Rev Lett 81, 3391 (1998). [4] K. A. Meyer and P. J. Blewett, Phys Fluids 15, 753 (1972). [5] G. Dimonte and P. Ramaprabhu, Phys Fluids 22, 014104 (2010). [6] F. J. Cherne et al., J Appl Phys 118, 185901 (2015). [Preview Abstract] |
Wednesday, July 12, 2017 9:45AM - 10:15AM |
O6.00003: Ejecta Production and Properties Invited Speaker: Robin Williams The interaction of an internal shock with the free surface of a dense material leads to the production of jets of particulate material from the surface into its environment. Understanding the processes which control the production of these jets – both their occurrence, and properties such as the mass, velocity, and particle size distribution of material injected – has been a topic of active research at AWE for over 50 years. I will discuss the effect of material physics, such as strength and spall, on the production of ejecta, drawing on experimental history and recent calculations, and consider the processes which determine the distribution of particle sizes which result as ejecta jets break up. \copyright{} British Crown Owned Copyright 2017/AWE [Preview Abstract] |
Wednesday, July 12, 2017 10:15AM - 10:30AM |
O6.00004: Simulation of Ejecta Production and Mixing Process of Sn Sample under shock loading Pei Wang, Dawei Chen, Haiquan Sun, Dongjun Ma Ejection may occur when a strong shock wave release at the free surface of metal material and the ejecta of high-speed particulate matter will be formed and further mixed with the surrounding gas. Ejecta production and its mixing process has been one of the most difficult problems in shock physics remain unresolved, and have many important engineering applications in the imploding compression science. The present paper will introduce a methodology for the theoretical modeling and numerical simulation of the complex ejection and mixing process. The ejecta production is decoupled with the particle mixing process, and the ejecta state can be achieved by the direct numerical simulation for the evolution of initial defect on the metal surface. Then the particle mixing process can be simulated and resolved by a two phase gas-particle model which uses the aforementioned ejecta state as the initial condition. A preliminary ejecta experiment of planar Sn metal Sample has validated the feasibility of the proposed methodology. [Preview Abstract] |
Wednesday, July 12, 2017 10:30AM - 10:45AM |
O6.00005: Density functional theory study of CeD$_{\mathrm{x}}$ with application to ejecta break-up in reactive gases Josiah Bjorgaard, Daniel Sheppard When ejecta are produced in a reactive gas, the diffusion of the reacting gas into the ejecta particles may have an important effect on break-up. This can influence the rate of break-up, particle size, and composition. In this study, density functional theory calculations were performed to explore the properties of CeD$_{\mathrm{x}}$in support of experiments of Ce ejected into Dgas. Under these conditions, the diffusion of D into Ce ejecta is of fundamental importance to the ejecta physics. We perform quantum molecular dynamics simulations to derive fundamental quantities including temperature dependent diffusion coefficients, $x$dependent heat capacity, and reflectivity. Our results are interpreted in terms of relative phase composition of ejecta and discussed in application to experiments. [Preview Abstract] |
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