Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session J1: DSIC: Detonation Modeling I |
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Chair: Gerrit Sutherland, ARL Room: Grand Ballroom I |
Tuesday, June 18, 2019 11:00AM - 11:15AM |
J1.00001: SDOT: A Three-dimensional Mesh-free Detonation Tracking Package Jin Yao A three-dimensional mesh-free detonation-shock-dynamics (DSD) front tracker that explicitly solves the detonation front propagation and boundary-angle condition is implemented. Compared to previously existing mesh-based DSD implementations, the new method has advantages with enhanced capabilities and potential lower computing cost. The new DSD front tracker uses marked particles to present the HE fronts and tracks the motion of these particles with a set of time dependent ODEs. The difficulty associated with an implicit DSD boundary treatment in three-dimensions is much reduced by an explicit methodology. In the case the solution enforcing a DSD angle on boundary does not exist, a dead-zone is naturally defined with trace of front-boundary particles. Particles are redistributed on the front with a desired resolution to maintain the quality of surface presentation. Comparisons between reactive-flow simulation and DSD tracking with SDOT show that with a properly calibrated evolution equation, the quality of DSD mesh-free tracking is comparable to DNS. Nevertheless, the SDOT DSD mesh-free tracking is several orders more efficient even in two-dimensions. [Preview Abstract] |
Tuesday, June 18, 2019 11:15AM - 11:30AM |
J1.00002: Toward a Reactive Flow Model Calibration Methodology Using Streamline-Based Fast-Running Models Michael Crochet, Sunhee Yoo Reactive flow models are a critical component used in hydrocodes to predict the behavior of energetic materials. The calibration of these models is often a time-consuming and computationally expensive process, requiring hundreds to thousands of simulation runs to obtain a single set of model parameters. To mitigate this expense, a technique informed by detonation shock dynamics (DSD) has been developed previously to determine the reactive rate model parameters, as an alternative to the use of hydrocodes during optimization. However, this method has some limitations in predicting important reaction zone flow field features, such as shock front corner turning. Here we explore the feasibility of a streamline-based approach to achieve flow field accuracy comparable to hydrocode simulations at a fraction of the expense. We first utilize the framework of Watt et al., where an existing set of ignition-and-growth (I&G) parameters for a known explosive is used to predict detonation speed, flow field and shock front curvature, with results compared to DSD theory and experiments. The inverse problem is then discussed, where a new set of I&G parameters is optimized to match experimentally-determined detonation speed and shock front geometry. [Preview Abstract] |
Tuesday, June 18, 2019 11:30AM - 12:00PM |
J1.00003: Mirrored continuum and molecular scale simulations of deflagration in a nano-slab of HMX Invited Speaker: D. Scott Stewart We (Chaudhuri, Joshi, Lee and Stewart) have developed a continuum modeling approach, grounded in classical physical chemistry, based on the following assumptions that the states in the material can be represented by local stationary averages of the pressure (stress), temperature, and mass fractions computed from atomistic simulation, and that the mixture has well-defined molecular components, each with a complete equation of state. The continuum model, ``Gibbs formulation'', applies to near-atomic length and time scales, which we identify as the scales where the lowest frequency, high energy phonons equilibrate in molecular mixtures, (about six atomic radii and six to ten vibrational periods). Phase changes and chemical changes due to reaction are not in (asymptotically, long-time) equilibrium, and changes are assumed to occur on much longer time scales than those required for stress and temperature equilibration. \par Recently in the Journal of Chemical Physics, J. Chem. Phys. 144, 184111 (2016), we carried out both atomistic molecular dynamics (MD) simulations and ``mirrored'' continuum simulations to model, thermal ignition of a nano-sized cube of explosive RDX. The CVE simulations of a constant volume explosions of RDX were performed using reactive molecular dynamics (RMD), that used REXAFF to model chemical changes in the MD simulation. The MD simulation was regarded as the exact molecular system. The continuum simulation was regarded as an interpretation and measurement of the average chemical changes between a set of identified chemical components of that molecular system. \par In this work we extend these ideas to include spatial averaging to study wave propagation and spatially distributed transport, combined with chemical reaction. Joshi and Chaudhuri used RMD to simulate a sustained spatially distributed deflagration in a nano-scale slab of HMX; Journal of Physical Chemistry C, 122, 14434-14446, (2018). Those RMD results are binned for macroscopic properties using the CV formulation by spatially averaging 20 bins. Mirrored continuum simulations considered only two components, reactant and product. Both atomistic and continuum simulations show a hot spot ignition followed by a structured deflagration that propagates through the HMX slab and are compared with good to excellent agreement. [Preview Abstract] |
Tuesday, June 18, 2019 12:00PM - 12:15PM |
J1.00004: Meso-Informed Scaled Unified Reactive Front (MISURF) burn model for the shock response of pressed HMX Sangyup Lee, Oishik Sen, Sidhartha Roy, H.S. Udaykumar A multi-scale framework for shock physics of heterogeneous energetic materials is necessary to calculate the response of the high explosives to transient shock loads. Since reaction progress critically depends on meso-scale hotspot initiation and growth, a multi-scale model requires information from the meso-scale to be communicated to macro-scales. Recently the a meso-informed ignition-and-growth MES-IG model was developed by the present group. Here, we demonstrate a meso-informed SURF model as an alternative; this model presents some improvements over the MES-IG approach. By adopting burn centers and scaled burn front radius concepts from SURF, a novel multi-scale reactive burn model is obtained. The key features of the model are the inclusion of inter-void spacings into the surrogate model for the hotspot ignition and growth rates and the calculation of a scale-free time constant as new quantities of interest (QoIs) in the MISURF framework. High resolution meso-scale calculations are used to inform a machine learning algorithm which constructs a surrogate model for the energy deposition rate via a reactive burn time scale ($\tau )$. The energy deposition rate surrogate model is used to close the homogenized macro-scale governing equations. The framework is validated against experimentally measured run-to-detonation data for pressed HMX. The MES-IG and MISURF models are compared and the relative advantages and disadvantages of the two meso-informed multi-scale modeling approaches are discussed. [Preview Abstract] |
Tuesday, June 18, 2019 12:15PM - 12:30PM |
J1.00005: Using the Pagosa SURF model to simulate fragment impact on energetic materials for safety applications Xia Ma, Brad Clements The Scaled Uniform Reactive Front (SURF) model, which is an HE reactive burn model, has been shown to accurately model plate impact experiments with a minimal number of parameters. We have implemented SURF, developed by Menikoff and Shaw, into LANL's Eulerian code Pagosa. It is suitable for high speed impact and captures the entire Shock-to-Detonation (SDT) process, including that observed with short shocks. SURF is able to capture short shocks and dead zones, which is critical for fragment impact simulations. Burn models like Forest Fire, which was used in Pagosa before SURF was implemented, cannot accurately predict dead zones. Pagosa SURF has then been shown to successfully model ball and fragment impacts on energetic materials. These successes support the notion that Pagosa SURF will be a reliable tool for a number of safety assessments. SURF is based on the physics of hotspots. Hot spots are triggered by the lead shock which naturally accounts for shock desensitization. SURF model uses the Hugoniot function to detect the leading shock. We will discuss the model and its implementation in Pagosa in our presentation. [Preview Abstract] |
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