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 H6: TMS: First-principles and Molecular Dynamics II |
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Chair: Rebecca Lindsey, LLNL Room: Broadway III/IV |
Tuesday, June 18, 2019 9:15AM - 9:30AM |
H6.00001: New GSD modeling for air blast wave supported by non-uniform flow Sunhee Yoo, George Butler This paper describes our research~to find a way to model complex shock interactions using Geometrical Shock Dynamics (GSD) as a more efficient alternative to computationally expensive hydrodynamic simulation. The "classical" GSD, as initially described by Whitham, describes shock propagations in which the flow immediately behind the shock front is uniform. However many other shock dynamics phenomena in air, such as the Taylor point blast wave, are not characterized by a uniform flow behind the shock, so Whitham's GSD theory cannot provide an accurate shock simulation. We thus have developed a new expanded GSD (EGSD) model that can portray shock propagation with a non-uniform flow state behind the shock, which can arise from Taylor point blast and from a finite-sized, condensed explosive detonation. The new EGSD model is the first model to our knowledge that relates GSD theory to explosive properties to study the intensity of air blast waves from an explosive detonation. In this paper we have also introduced a spline technique, a shape preserving approximation in the EGSD simulation, for stable and accurate numerical simulation. This is critical for tracking the transition from regular to irregular shock reflections and the dynamics of local discontinuities, which come from shock reflections and the formation of Mach stems. [Preview Abstract] |
Tuesday, June 18, 2019 9:30AM - 9:45AM |
H6.00002: Inverse Problem for PSPI Experiments Rodney Clifton, Siyuan Song, tong jiao Rodney J. Clifton, Siyuan Song, Tong Jiao -/authors- -abstract- Material response at front face of target rear plate in Pressure-Shear Plate Impact (PSPI) experiments has been determined directly from measured velocity-time profiles at traction-free rear face of the target plate. Conceptual advance is the recognition that the usual forward problem for a mixed initial and boundary value problem can be reformulated as an initial value problem by a change of independent variables. Based on this reformulation the governing system of first-order, quasilinear, hyperbolic partial differential equations has been solved by a second order accurate characteristics method. While applications have been made to PSPI experiments, the approach applies equally well to the more commonly used configuration of normal impact. The new methodology requires an accurate constitutive model for the rear plate of the target assembly . When such a model is available, the inverse problem approach provides a convenient means for extending PSPI experiments into higher impact-velocity regimes where the rear plate is no longer the hard, elastic material that was envisioned in earlier development of PSPI experiments. Extensive results are presented for the cases where the sandwiching plates used in the PSPI experiments are made of tungsten carbide. [Preview Abstract] |
Tuesday, June 18, 2019 9:45AM - 10:00AM |
H6.00003: Improved data processing for frequency domain interferogram Zhicheng Zhong, Hao Jiang, Shiyuan Liu Frequency domain interferometer is a common method to detect the dynamic response in laser-induced shock wave loading experiments. When the FFT method is used to extract the phase and amplitude of the frequency domain interferogram (FDI), the data truncation of the fringes and the window profile that used to cut out the 1st order alternating item can greatly influence the accuracy and precision of the data processing. In order to improve the performance of FDI interpretation, we first carry out an error analysis on the conventional method and propose an improved procedure by introducing a Gaussian envelope to the fringes as well as using a self-designed flat-top cap window to isolate the 1st order alternating item. Results of a series simulated experiments demonstrate that the proposed approach can significantly and effectively reduce the data processing error in FDI interpretation. [Preview Abstract] |
Tuesday, June 18, 2019 10:00AM - 10:15AM |
H6.00004: Shaped Charge Automated Design: Applying DAKOTA to Kinetic Energy Optimization Sebastian Konewko, John Borg Advances in computational power present an opportunity to further optimize the design of an engineered energetic system. This work presents the application of a proposed optimization scheme which combines the shock-physics hydrocode CTH with the DAKOTA optimization package to automate shaped-charge jet design. The formation of an explosively driven hypervelocity jet can be simulated using CTH. The performance of the jet can be characterized by selecting any number of metrics and writing these metrics as a basis function; a simple example may be a summation of the kinetic energy of the jet within a specified region of the computational domain. DAKOTA uses several different optimization algorithms (parametric, genetic, gradient decent) to optimize this basis function. By parameterizing the initial liner shape and thickness, many iterations can be executed to establish the surface of the basis function. Once an optimization algorithm is selected, DAKOTA automatically iterates on the parameters controlling the charge's liner to find any local extrema of this surface. A converged solution is presented herein. [Preview Abstract] |
Tuesday, June 18, 2019 10:15AM - 10:30AM |
H6.00005: A parallel algorithm to create long polymer chains in molecular dynamics Nicolas Pineau, Claire Lemarchand, David Bousquet, Benoit Schnell Generating initial configurations of polymer melts above the entanglement molecular weight is a challenge in molecular dynamics and Monte Carlo simulations. In this presentation, we describe an algorithm mimicking a chemical polymerization adapted to all-atom force fields. The principle of this algorithm is to start from a bath of monomers between which bonds are created and relaxed sequentially. Our implementation is parallel and efficient. The parallelization is that of a classical molecular dynamics code and enables the user to generate large systems, up to 7 million atoms. The efficiency of the algorithm comes from the linear scaling between the simulation time and the chain length in the limit of very long chains. The implementation is able to produce long polymer chains, up to 2000 carbon atoms, with thermodynamic, global, and local structural properties in good agreement with their counterparts obtained experimentally, by other numerical algorithms, and by the Gaussian chain model. Finally, the algorithm proposed in this work is versatile in nature because the bond creation can be easily modified to create copolymers, block copolymers and mixtures of polymer melts with other material. [Preview Abstract] |
Tuesday, June 18, 2019 10:30AM - 10:45AM |
H6.00006: Materials Dynamics Descriptors Determined by MD Data. Sven Rudin How do we choose descriptors for the dynamic behavior of a material? An information science-based possibility builds upon an approach to analyze the atomic movement in a material simulated with molecular dynamics [Physical Review B 97, 134114 (2018)]. By sampling the correlated atomic movement, a set of collective vibrational modes are defined that show no correlation between them. These ``Principal Vibrational Modes'' (PVMs) represent a transparent framework to understand and describe a material's nonlinear dynamical properties. The mode with the largest amplitude, e.g., emerges as a natural descriptor indicating the structural phase. The PVMs constitute a list of dynamics descriptors that is ordered according to the modes' amplitudes. Collective atomic movement with large amplitudes generally correlates with important materials behavior and properties. This suggests the PVMs can serve as dynamics descriptors of materials. [Preview Abstract] |
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