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 L3: Detonation and Shock-Induced Chemistry: Dynamics and Corner Turning |
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Chair: Larry Hill, Los Alamos National Laboratory Room: Grand Ballroom FG |
Tuesday, July 11, 2017 3:45PM - 4:00PM |
L3.00001: Coupling Detonation Shock Dynamics in a Consistent Manner to Equations of State William Belfield In hydrocode simulations, detonating high explosives (HE) are often modelled using programmed burn. Each HE cell is assigned a ``burn time'' at which it should begin to behave as HE products in the subsequent simulation. Traditionally, these burn times were calculated using a Huygens construction to propagate the detonation wave at a constant speed corresponding to the planar Chapman-Jouguet (CJ) velocity. The Detonation Shock Dynamics (DSD) model improves upon this approach by treating the local detonation velocity as a function of wave curvature, reflecting that the detonation speed is not constant in reality. However, without alterations being made, this variable detonation velocity is inconsistent with the CJ velocity associated with the HE products equation of state (EOS). Previous work [1] has shown that the inconsistency can be resolved by modifying the HE product EOS, but this treatment is empirical in nature and has only been applied to the JWL EOS. This work investigates different methods to resolve the inconsistency that are applicable both to JWL and to tabular HE product EOS, and their impact on hydrocode simulations. [1] Hetherington, D {\&} Whitworth, N. ``A simple model for the dependence on local detonation speed of the product entropy." AIP Conf. Proc. 1426. (2012) [Preview Abstract] |
Tuesday, July 11, 2017 4:00PM - 4:15PM |
L3.00002: Detonation Shock Dynamics Modelling with Arbitrary Boundaries Alexander Hodgson The Detonation Shock Dynamics (DSD) model can be used to predict detonation wave propagation in a high explosive (HE). The detonation wave is prescribed a velocity that depends on its curvature. Additionally, the angle between the wave and the HE boundary may not exceed a specified ``boundary angle'', the value of which depends on the HE and its confining material(s). The level-set method is commonly used to drive DSD computation. Boundary conditions are applied to the level-set field at the charge edges to maintain the explosive boundary angle criteria. The position of the boundary must be accurate and continuous across adjacent cells to achieve accurate and robust results. This is mainly an issue for mixed material meshes where the boundary does not coincide with the cell boundaries. For such meshes, a set of volume fractions defines the amount of material in each cell. The boundary is defined implicitly by the volume fractions, and must be reconstructed to an explicit form for use in DSD. This work describes a novel synthesis of the level-set method and simulated annealing, an optimisation method used to reconstruct the boundary. The accuracy and robustness of the resulting DSD calculation are evaluated with a range of test problems. [Preview Abstract] |
Tuesday, July 11, 2017 4:15PM - 4:30PM |
L3.00003: Unconfined Cone Tests using Shock-fitting Christopher Romick, Tariq Aslam There is a prevailing utilization of shock-capturing schemes which can be problematic in regions near discontinuities. The inherent viscosity in these methods gives rise to a smooth shock; however, this comes at the expense of thickening the shock and yields ambiguity in actual shock state. Furthermore, shock-capturing also suffers from an order of accuracy reduction due to the shock. With the use of shock-fitting, both the explicit shock state and order of accuracy of the scheme can be recovered. These methods separate the ambient upstream and smooth reactive flow behind the front and explicitly enforces the jump conditions at the boundary. However, these methods typically suffer from two main drawbacks : 1) secondary unfitted shocks interacting with fitted surfaces and 2) the restriction to very simple geometries, e. g. rectangular charges or right circular cylindrical charges. The first issue is addressed by adding a switch lowering the local order of the algorithm near the fitted shock when a secondary discontinuity is present. In order to further extend the shock-fitting method to more complex geometries, it is modified to allow for the width of the charge to vary with time. This allows for the examination of axisymmetrical cone tests in high-explosive (HE) geometries. [Preview Abstract] |
(Author Not Attending)
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L3.00004: Detonation Corner Turning Investigations in Non-TATB Based Explosives Octavio Cervantes, John Molitoris, Philip Souers Previous work in TATB based explosives shows impaired detonation corner-turning (DCT) leading to the formation of dead-zones (DZ) - regions of the energetic material that never detonate. Work by others reported the formation of dead-zones in Composition B, but subsequent experimental work at Lawrence Livermore National Laboratory (LLNL) in Composition B did not verify this. Here we report on current research at LLNL examining detonation corner turning in a range of near- ideal and non-ideal explosives including: C-4, Composition B, PBXN-109, and others. Other work examines the question of whether DCT-DZ are properties of non-ideal high- explosives. Our results are compared with DCT-DZ issues in LX-17, a TATB based explosive. The important question we endeavor to answer is whether DCT--DZ issues are a property of non-ideal explosives or an intrinsic behavior of TATB based energetic materials. High-resolution x-ray image data will be presented along with numerical modeling to help understand these data. All work was performed at the LLNL High Explosives Application Facility using our unique time sequence flash x- ray capabilities. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC. LLNL-ABS-708964 [Preview Abstract] |
Tuesday, July 11, 2017 4:45PM - 5:00PM |
L3.00005: Modeling Ignition of HMX with the Gibbs Formulation Kibaek Lee, D. Scott Stewart We present a HMX model with the Gibbs formulation in which stress tensor and temperature are assumed to be in local equilibrium, but phase/chemical changes are not assumed to be in equilibrium. We assume multi-components for HMX including beta- and delta-phase, liquid, and gas phase of HMX and its gas products. Isotropic small strain solid model, modified Fried Howard liquid EOS, and ideal gas EOS are used for its relevant component. Phase/chemical changes are characterized as reactions and are in individual reaction rate. Maxwell-Stefan model is used for diffusion. Excited gas products in the local domain lead unreacted HMX solid to the ignition event. Density of the mixture, stress, strain, displacement, mass fractions, and temperature are considered in 1D domain with time histories. [Preview Abstract] |
Tuesday, July 11, 2017 5:00PM - 5:15PM |
L3.00006: Analog System of Detonations with Loss and Stability of the Analog System Yuanxiang Sun, Cheng Wang Analog system of detonation is a simplified model of the Euler system. Analog system removes unnecessary details of the Euler system and reduces mathematical difficulty Analog system with losses and reaction mechanism that applicable for condensed-phase detonation is studied to examine whether the analog system in this paper is valid Details are as follows: 1. The relationship of detonation velocity vs. loss parameter is analytically solved, and a minimal state-dependence of the reaction rate$ n$ required for this relationship to exhibit a critical behavior (i.e., a turning point) is examined The results agree with the limits which derived from Euler system. 2. Normal-mode method is used to study the stability of the analog system. A radiation (closure) condition is derived and applied at the end of the reaction zone. An analysis is performed to investigate whether the ideal, steady-state detonation can keep stable to small perturbations 3. Because analog system with loss can be more unstable than the ideal one. An numerical simulation is used to examine the detonation stability near the loss limits. The results above show that the analog system is basically valid for condensed-phase detonation [Preview Abstract] |
Tuesday, July 11, 2017 5:15PM - 5:30PM |
L3.00007: Detonation corner turning in vapor-deposited explosives using the micromushroom test Alexander S. Tappan, Cole D. Yarrington, Robert Knepper Detonation corner turning describes the ability of a detonation wave to propagate into unreacted explosive that is not immediately in the path normal to the wave. The classic example of corner turning is cylindrical and involves a small diameter explosive propagating into a larger diameter explosive as described by Los Alamos' Mushroom test (e.g. (Hill, Seitz et al. 1998)), where corner turning is inferred from optical breakout of the detonation wave. We present a complimentary method to study corner turning in millimeter-scale explosives through the use of vapor deposition to prepare the slab (quasi-2D) analog of the axisymmetric mushroom test. Because the samples are in a slab configuration, optical access to the explosive is excellent and direct imaging of the detonation wave and ``dead zone'' that results during corner turning is possible. Results are compared for explosives that demonstrate a range of behaviors, from pentaerythritol tetranitrate (PETN), which has corner turning properties that are nearly ideal; to HNAB (hexanitroazobenzene), which has corner turning properties that reveal a substantial dead zone. Results are discussed in the context of microstructure and detonation failure thickness. [Preview Abstract] |
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