用超高速成像和SPH模拟观测撞击点附近的撞击喷出物及其比较
Impact Ejecta near the Impact Point Observed using Ultra-high-speed Imaging and SPH Simulations, and a Comparison of the Two Methods
摘要：
预计与撞击速度相当的高速撞击喷出物将有助于行星体之间的物质运输和喷出物远离撞击坑的沉积。我们研究了高速喷出物的行为产生的角度为45和90度，使用实验和数值方法。千叶工业大学行星探索研究中心（日本）开发的实验系统使我们能够观察喷出物的初始生长。我们成功地成像高速喷出物在0.2 $\mathrm{μ}$ s的时间间隔为4.8 mm直径的聚碳酸酯弹丸到聚碳酸酯板上的影响，在约4 km s $^{-1}$的冲击速度。光滑粒子流体动力学（SPH）模拟的各种数值分辨率进行了相同的影响条件有关的实验。我们比较了实验和模拟的喷出物的形态和速度，我们证实了高分辨率模拟的密切匹配（$\geq10^6$ SPH粒子代表抛射体）。根据高分辨率模拟得到的喷出物速度分布，斜撞击的高速喷出物的喷出速度远大于垂直撞击的喷出速度。在斜撞击中，平行于目标表面的穿透射弹的平移运动可能在喷出物的根部造成长期、持续的加速。
英文摘要：
High-speed impact ejecta at velocities comparable to the impact velocity are expected to contribute to material transport between planetary bodies and deposition of ejecta far from the impact crater. We investigated the behavior of high-speed ejecta produced at angles of 45 and 90 degrees, using both experimental and numerical methods. The experimental system developed at the Planetary Exploration Research Center of Chiba Institute of Technology (Japan) allowed us to observe the initial growth of the ejecta. We succeeded in imaging high-speed ejecta at 0.2 $\mathrm{μ}$s intervals for impacts of polycarbonate projectiles of 4.8 mm diameter onto a polycarbonate plate at an impact velocity of ~4 km s$^{-1}$. Smoothed particle hydrodynamics (SPH) simulations of various numerical resolutions were conducted for the same impact conditions as pertaining to the experiments. We compared the morphology and velocities of the ejecta for the experiments and simulations, and we confirmed a close match for high-resolution simulations (with $\geq10^6$ SPH particles representing the projectile). According to the ejecta velocity distributions obtained from our high-resolution simulations, the ejection velocities of the high-speed ejecta for oblique impacts are much greater than those for vertical impacts. The translational motion of penetrating projectiles parallel to the target surface in oblique impacts could cause long-term, sustained acceleration at the root of the ejecta.
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