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 M2: Detonations and Shock-Induced Chemistry IV |
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Chair: Nir Goldman, Lawrence Livermore National Laboratory Room: Grand Ballroom IV-V |
Wednesday, June 29, 2011 11:00AM - 11:15AM |
M2.00001: Computational Study of 3-D Hot-Spot Initiation in Shocked Insensitive High-Explosive F.M. Najjar, W.M. Howard, L.E. Fried High explosive shock sensitivity is controlled by a combination of mechanical response, thermal properties, and chemical properties. The interplay of these physical phenomena in realistic condensed energetic materials is currently lacking. A multiscale computational framework is developed investigating hot spot (void) ignition in a single crystal of an insensitive HE, TATB. Atomistic MD simulations are performed to provide the key chemical reactions and these reaction rates are used in 3-D multiphysics simulations. The multiphysics code, ALE3D, is linked to the chemistry software, Cheetah, and a three-way coupled approach is pursued including hydrodynamics, thermal and chemical analyses. A single spherical air bubble is embedded in the insensitive HE and its collapse due to shock initiation is evolved numerically in time; while the ignition processes due chemical reactions are studied. Our current predictions showcase several interesting features regarding hot spot dynamics including the formation of a ``secondary'' jet. Results obtained with hydro-thermo-chemical processes leading to ignition growth will be discussed for various pore sizes and different shock pressures. LLNL-ABS-471438. [Preview Abstract] |
Wednesday, June 29, 2011 11:15AM - 11:30AM |
M2.00002: A Simple Model for the Dependence on Local Detonation Speed (D) of the Product Entropy (S) David Hetherington The generation of a burn time field as a pre-processing step ahead of a hydrocode calculation has been mostly upgraded in the explosives modelling community from the historical model of single-speed programmed burn to DSD. However, with this advance has come the problem that the previously conventional approach to the hydrodynamic stage of the model results in S having the wrong correlation with D. Instead of being higher where the detonation speed is lower, i.e. where reaction occurs at lower compression, the conventional method leads to S being lower where D is lower, resulting in a completely fictitious enhancement of available energy where the burn is degraded! A technique is described which removes this deficiency of the historical model when used with a DSD-generated burn time field. By treating the conventional JWL equation as a semi- empirical expression for the local expansion isentrope, and constraining the local parameter set for consistency with D, it is possible to obtain the two desirable outcomes that the model of the detonation wave is internally consistent, and S is realistically correlated with D. [Preview Abstract] |
Wednesday, June 29, 2011 11:30AM - 11:45AM |
M2.00003: High Explosive Verification and Validation: Systematic and Methodical Approach Christina Scovel, Ralph Menikoff Verification and validation of high explosive (HE) models does not fit the standard mold for several reasons. First, there are no non-trivial test problems with analytic solutions. Second, an HE model depends on a burn rate and the equation of states (EOS) of both the reactants and products. Third, there is a wide range of detonation phenomena from initiation under various stimuli to propagation of curved detonation fronts with non-rigid confining materials. Fourth, in contrast to a shock wave in a non-reactive material, the reaction-zone width is physically significant and affects the behavior of a detonation wave. Because of theses issues, a systematic and methodical approach to HE V{\&}V is needed. Our plan is to build a test suite from the ground up. We have started with the cylinder test and have run simulations with several EOS models and burn models. We have compared with data and cross-compared the different runs to check on the sensitivity to model parameters. A related issue for V{\&}V is what experimental data are available for calibrating and testing models. For this purpose we have started a WEB based high explosive database (HED). The current status of HED will be discussed. [Preview Abstract] |
Wednesday, June 29, 2011 11:45AM - 12:00PM |
M2.00004: Simulations of Chemical Reactivity of Insensitive Energetic Materials Under Thermal and Shock Conditions Riad Manaa, Evan Reed, Laurence Fried, Nir Goldman Results of quantum based simulations of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) crystals under thermal decomposition (high density and temperature) and shock compression conditions are presented. We conducted constant volume-temperature simulations, ranging from 0.35 to 2 nanoseconds, at $\rho $= 2.87 g/cm$^{3 }$at$^{ }$T= 3500, 3000, 2500, and 1500 K, and $\rho $= 2.9 g/cm$^{3 }$and 2.72 g/cm$^{3}$, at T = 3000 K. We also simulated crystal TATB's reactivity under steady overdriven shock compression at shock speeds of 8, 9, and 10 km/s for up to 0.43 ns duration. These simulations have enabled us to track the reactivity of TATB well into the formation of several stable gas products, such as H$_{2}$O, N$_{2}$, and CO$_{2}$. Our simulations revealed a hitherto unidentified region of high concentrations of nitrogen-rich heterocyclic clusters in reacting TATB, whose persistence impede further reactivity towards final products of fluid N$_{2}$ and solid carbon. Our simulations also predict significant populations of charged species such as NCO$^{-}$, H$^{+}$, OH-, H$_{3}$O$^{+}$, and O$^{-2}$, the first such observation in a reacting explosive. A reduced four steps, global reaction mechanism with Arrhenius kinetic rates for the decomposition of TATB, along with comparative thermo-chemical decomposition kinetics has been constructed and will be discussed. [Preview Abstract] |
Wednesday, June 29, 2011 12:00PM - 12:30PM |
M2.00005: Picosecond timescale detonation of hydrogen azide (HN3) Invited Speaker: Chemical reactions are thought to occur on nanosecond or longer timescales in carbon-containing condensed phase energetic materials. Here we perform the first atomistic simulation of a primary (very sensitive) energetic material, HN3, from the beginning to the end of the chemical evolution and find that the timescale for complete decomposition is only 10 picoseconds, orders of magnitude shorter than that of known materials. This timescale is approaching the fundamental limiting timescale for chemistry, i.e. vibrational timescale. We explore potential deviations of ultrafast detonation from the classical picture where chemistry is slower. The simulations are accomplished using a multi-scale shock simulation method that utilizes the DFTB tight binding method. [Preview Abstract] |
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