依兰陨石坑形成过程数值模拟研究

Numerical simulation of Yilan crater formation process

基于iSALE-2D仿真代码对依兰陨石坑的形成过程进行了研究,采用欧拉算法开展数值模拟,探讨了依兰陨石坑的撞击条件,统计分析了成坑过程中熔化层的形成与分布规律,结合点源成坑相似律模型,拟合得到强度机制下的成坑半径关系式。研究结果表明一颗直径120 m、撞击速度12 km/s的花岗岩质小行星垂直撞击地表形成一个与依兰陨石坑形态相似的陨石坑,再现了成坑形成的3个阶段:接触与压缩阶段、开坑阶段、后期调整阶段。大部分熔体在坑底呈分层堆叠分布,少量熔体随抛射物沉积在靶体表面,呈离散状分布,完全熔化材料质量约为撞击体质量的24倍。直径120 m、撞击速度12 km/s工况模拟结果与拟合的成坑半径关系式结果相对误差10.3%。

The formation process of the Yilan crater was numerically studied based on the iSALE-2D simulation code.The Euler algorithm was used to carry out the numerical simulation,and eight groups of working conditions were simulated.According to the scaling law,it was determined that the projectile diameter range was 90 to 120 m,and the projectile velocity was 12 and 15 km/s.Simulation results under the corresponding working conditions within 150 s of impact were obtained,including the crater diameter,depth,and crater profile curve.The optimal impact conditions of the Yilan crater were studied,and the formation and distribution of the molten layer during the cratering process were statistically analyzed.Combined with the point source cratering similarity law model,the relationship of cratering radius under the strength mechanism was obtained by fitting.The research results show that,according to the comparison between the simulated data and actual exploration data,a granite asteroid with a diameter of 120 m and an impact velocity of 12 km/s vertically hits the surface,forming a crater with a shape similar to the Yilan crater.The crater has a final diameter of 1840 m and a crater edge depth of 263 m,which is in good agreement with the exploration data of the Yilan crater.Three stages of crater formation were reproduced:contact and compression,excavation,and modification.The distribution of the impact melting layer of the target plate material during the crater formation under the simulated conditions were revealed.The material melted completely when the peak pressure exceeds 56 GPa during the impact process,and this process was completed within 20 ms.Most melts was distributed at the bottom of the crater in layers and stacks,and a small amount of melts was deposited discretely on the surface of the target plate.The mass of the completely melted material is about 24 times the projectile mass.The relative error between the simulation results and the fitted crater radius relational results under the conditions with 120 m diameter and 12 km/s impact velocity is 10.3%.