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小行星撞击地球的超高速问题

HYPERVELOCITY ISSUES OF EARTH IMPACT BY ASTEROIDS

  • 摘要: 小行星撞击地球是人类生存面临的潜在威胁之一.在小行星进入地球大气与撞击地球表面过程中,存在烧蚀、解体、空中爆炸、火球、撞击成坑、反溅碎片云、地震以及海啸等一系列复杂的物理化学和力学现象.本文梳理和归纳了与这些现象相关的超高速空气动力学问题和超高速碰撞动力学问题.小行星进入地球大气的超高速空气动力学问题有:极高速(V = 12 ~ 20km/s)进入条件下的气动力与轨迹,极高速进入条件下的小行星气动加热与烧蚀机理,极高速气动加热条件下的小行星结构传热与热响应,极高速进入条件下的高温气体效应,小行星进入过程的物理特征.小行星撞击地球的超高速碰撞动力学问题有:陆地撞击成坑与反溅碎片云,海洋撞击与海啸,撞击过程的地震效应.由于小行星撞击地球与超高速飞行器的再入过程在速度、材料和结构上存在较大差异,针对这些超高速问题,现有的研究手段在地面试验和数值计算两方面都存在不足.最后,从小行星进入地球大气的弹道方程、质量损失方程、解体判据和解体模型等出发,初步建立了小行星进入与撞击效应分析评估模型,并对Chelyabinsk和Tunguska两次流星事件进行了分析,重构了进入与爆炸解体过程,评估了空爆火球在地面所导致的超压和热辐射损伤.

     

    Abstract: Asteroid impact on the Earth is one of the potential threats to human beings. There are a series of complex physical, chemical and mechanical phenomena in the process of asteroids entry to the earth's atmosphere and impacting the earth's surface, such as ablation, disintegration, airburst, fireballs, impact craters, ejecta debris, earthquakes, and tsunamis. In this paper, scientific issues on hypervelocity aerodynamics and hypervelocity impact dynamics behind these phenomena are summarized and discussed. The hypervelocity aerodynamic issues include: aerodynamic forces and trajectory during ultra-high velocity (V =12 ~ 20 km/s) entry, aerodynamic heating and ablation mechanism of asteroids, heat transfer and thermal response of asteroid structure, high-temperature gas effects, physical characteristics of asteroid entry process. The hypervelocity impact dynamics include: cratering and ejecta debris of land impact, ocean impact and tsunamis, earthquake effects caused by impact. Because the entry and impact process of asteroid and man-made hypervelocity flight vehicles are quite different in velocity, material and structure, the existing research methods are insufficient in both ground test and numerical calculation. Finally, based on trajectory equations, mass loss equation, criterion of fragmentation and model of fragmentation, a model for analysis and evaluation of asteroid entry and impact effect is established, and the Chelyabinsk and Tunguska events are analyzed and reconstructed, together with the overpressure and thermal radiation damage caused by fireballs.

     

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