Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session L3: First-Principles and Molecular Dynamics Calculations VII: Multiscale Modeling |
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Chair: Jonathan Zimmerman, Sandia National Laboratories Room: Renaissance Ballroom AB |
Wednesday, June 29, 2011 9:15AM - 9:30AM |
L3.00001: Mesoscopic simulations of Nitromethane Jean-Bernard Maillet, Emeric Bourasseau, Nicolas Desbiens, Gabriel Stoltz We present recent developments of the Dissipative Particle Model that allow simulating the physico-chemical behavior of a molecular material at the mesoscale level. Several ingredients have been added to the previous model (see JB Maillet, L. Soulard and G. Stoltz, Europhys. Lett., \textbf{78}, 68001 (2007)), in particular concerning the intermolecular force field and the contributions of the internal degrees of freedom. Multiple steps chemistry is handled through the use of additional degrees of freedom. This model is applied to micron scale simulations of nitromethane, both at equilibrium and under shock conditions. [Preview Abstract] |
Wednesday, June 29, 2011 9:30AM - 9:45AM |
L3.00002: Particle Based Multi-Scale Modeling of the Dynamic Response of RDX Joshua D. Moore, Sergei Izvekov, John K. Brennan, Martin Lisal Modeling the thermal and mechanical response of nanocomposites atomistically, despite growing computational power and resources, remains a challenge due to the length and time scales required. To overcome these challenges, we have used multiscale modeling to bridge the atomistic and microscale levels of description by coarse-graining RDX through force-matching, resulting in density-dependent potentials. The resulting model reproduces several atomistic properties within reasonable agreement from ambient to high pressures for the molecular crystal. Despite this, the model cannot account for accurate energy and momentum exchange due to mechanical stimulation via traditional molecular dynamics due to coarse-graining of the intramolecular degrees of freedom. To correct this, we account for momentum and energy transfer in mechanical shock treatments by utilizing the constant energy Dissipative Particle Dynamics method (DPD-E). In this talk, we will present results for mechanical and thermal shock loading of our MS-CG model of RDX using DPD-E. Various modeling parameters have been investigated for sensitivity. Results will be assessed by comparison to both atomistic simulation and experiment. [Preview Abstract] |
Wednesday, June 29, 2011 9:45AM - 10:15AM |
L3.00003: Multiscale Modeling of Energetic Materials: Easy to Say, Harder to Do Invited Speaker: In recent years, multiscale modeling has routinely been included in materials research programs (including those involving energetic materials). However, too often multiscale modeling is applied in a piecemeal fashion due to the fledgling state of multiscale modeling. While the concept of multiscale modeling of energetic materials is straightforward, practical implementation of this type of hierarchical modeling is hindered by numerous technical challenges. This talk reports on our efforts in establishing a multiscale modeling capability to predict energetic material response and includes a discussion of emerging models, methods and software, stumbling blocks, and lessons learned in this new area of exploration within our laboratory. [Preview Abstract] |
Wednesday, June 29, 2011 10:15AM - 10:30AM |
L3.00004: Mesoscale Simulation of Shocked PMP Foams T.A. Haill, T.R. Mattsson, S. Root, D.G. Schroen, D.G. Flicker Hydrocarbon foams are commonly used in HEDP experiments, and are subject to shock compression from tens to hundreds of GPa. Modeling foams is challenging due to the heterogeneous character of the foam. A quantitative understanding of foams under strong dynamic compression is sought. We use Sandia's ALEGRA-MHD code to simulate 3D mesoscale models of pure poly(4-methyl-1-petene) (PMP) foams. We employ two models of the initial polymer-void structure of the foam and analyze the statistical properties of the initial and shocked states. We compare the simulations to multi-Mbar shock experiments at various initial foam densities and flyer impact velocities. Scatter in the experimental data may be a consequence of the initial foam inhomogeneity. We compare the statistical properties the simulations with the scatter in the experimental data.\\[4pt] Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U. S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Wednesday, June 29, 2011 10:30AM - 10:45AM |
L3.00005: A New Method for Large Scale Molecular Dynamics Simulations of Shock-Induced Ejecta Production on Petaflopic Computer Olivier Durand, Laurent Soulard We propose a new method for modelling large scale shock-induced ejecta production using petaflopic molecular dynamics (MD) simulations. A copper crystal with a sinusoidal surface finish representative of the roughness arising from a machine polishing is divided into a bulk and a surface part. The bulk part is simulated using the Hugoniostat technique, which allows a very large number of particles to reach a Hugoniot equilibrium state in a short physical time by the mean of a quasi-equilibrium MD simulation. The surface part is simulated with the NVE ensemble in order to account for the non-equilibrium character of the ejection process. With this method, the particle size distribution generated by a system with 5$\times $10$^{8}$ to 10$^{9}$ atoms and different depths of defect is studied. Our MD results show that the particle size distributions exhibit a power law scaling in good agreement with the percolation theory. This theory suggests that the production of ejecta clusters is due to large-scale fluctuations present near a critical point, where there is no dominant characteristic scale. [Preview Abstract] |
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