One-dimensional moving window atomistic framework to model long-time shock wave propagation
One-dimensional moving window atomistic framework to model long-time shock wave propagation
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DOI：
10.1016/j.cma.2020.113290
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发表时间：
2020-11
影响因子：
7.2
通讯作者：
Alexander S. Davis;V. Agrawal
中科院分区：
文献类型：
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作者：
Alexander S. Davis;V. Agrawal
我们开发了一个长时间的移动窗口框架，利用分子动力学（MD）来模拟冲击波通过一维原子链的传播。移动窗口公式“跟随”冲击波的传播，使我们能够比传统的非平衡MD （NEMD）模拟更长的时间来模拟冲击波的传播。该公式还显著减小了所需的域大小，从而降低了总体计算成本。该区域被划分为包含激波的纯原子“窗口”区域，两侧是边界或两端包含连续激波条件的“连续”区域。杂散波反射通过采用一种阻尼带法，使用朗格万恒温器局部应用于每个连续区的原子来去除。移动窗口效应是通过向窗口和边界区域添加/移除原子来实现的，因此激波前沿无限期地聚焦在窗口区域的中心。我们使用Lennard-Jones、改进的Morse或嵌入式原子模型（EAM）原子间势来模拟铜原子一维链的冲击。我们首先进行验证研究，以确保分别正确实施恒温器、势函数和阻尼带方法。接下来，我们跟踪传播激波，并将实际激波速度和平均粒子速度与其相应的分析输入值进行比较。从这些比较中，我们优化了给定“晶格”方向的线性激波Hugoniot关系，并将这些结果与文献中的结果进行了比较。当纳入线性激波方程时，这些新的Hugoniot参数显示可以产生平稳的激波前。最后，我们对非定常结构激波进行了几纳秒的一维移动窗口模拟，并对激波前缘宽度的增加进行了表征。
We develop a long-time moving window framework using Molecular Dynamics (MD) to model shock wave propagation through a one-dimensional chain of atoms. The moving window formulation “follows” a propagating shock wave allowing us to model shock wave propagation much longer than conventional non-equilibrium MD (NEMD) simulations. This formulation also significantly decreases the required domain size and thus reduces the overall computational cost. The domain is divided into a purely atomistic “window” region containing the shock wave flanked by boundary or “continuum” regions on either end which incorporate continuum shock conditions. Spurious wave reflections are removed by employing a damping band method using the Langevin thermostat applied locally to the atoms in each continuum region. The moving window effect is achieved by adding/removing atoms to/from the window and boundary regions, and thus the shock wave front is focused at the center of the window region indefinitely. We simulate the shock through a one-dimensional chain of copper atoms using either the Lennard-Jones, modified Morse, or Embedded Atom Model (EAM) interatomic potential. We first perform verification studies to ensure proper implementation of the thermostat, potential functions, and damping band method, respectively. Next, we track the propagating shock and compare the actual shock velocity and average particle velocity to their corresponding analytical input values. From these comparisons, we optimize the linear shock Hugoniot relation for the given “lattice” orientation and compare these results to those in literature. When incorporated into the linear shock equation, these new Hugoniot parameters are shown to produce a stationary shock wave front. Finally, we perform one-dimensional moving window simulations of an unsteady, structured shock up to a few nanoseconds and characterize the increase in the shock front’s width.