Dynamics of Energetic Events in Condensed Phase Media

当能量释放的速率超过能量所沉积的物质的强度时，就会发生高能量事件。在这些条件下，介质的后续动力学由可压缩（非线性）波（如激波）控制。虽然这些现象远远超出日常经验，但它们在许多自然过程和技术应用中发挥着重要作用。本实验和理论研究计划将集中于涉及能量事件动力学的问题和应用的三个主题，重点是问题的非线性波方面。**离散爆轰：爆震波在高能物质中传播，在传播过程中释放储存的能量，是具有重要技术应用的高能量事件的一个例子，因为炸药广泛用于采矿和土方移动。作者、他的同事和其他地方的研究人员最近的实验结果已经确定了爆震波在异质、凝聚相材料中的行为，这些行为不能用纯粹的经典、基于连续体的爆震波传播模型来解释。这些结果表明，发生在中尺度上的现象（如颗粒、空隙等）可能对波的传播有重要影响。本研究计划将进一步通过实验研究这种效应，并开发一种方法来模拟由离散的高能事件主导的介质中的爆轰传播。**内爆动力学：暴露于高动态事件的材料的响应也是相当有趣的。我和我的学生最近进行了一项关于冲激内爆的气瓶动力学的研究。这项工作最初是由下面描述的超高速发射器的发展所推动的，但与利用热核聚变发电（即惯性约束和磁化目标聚变）的方法直接相关。我们将在拟议的项目下继续这些研究，重点关注固体和液体中动态加载的收敛几何形状（内爆圆柱腔）的稳定性，以确定可以实现的对称压缩的极限，以及材料特性和流体动力不稳定性的作用。**超高速发射和撞击：高能事件的另一个例子是轨道碎片或微流星体对航天器的超高速撞击。由于在地球轨道上发生的一连串失控的碰撞产生了新的碎片，这个日益严重的问题现在得到了广泛的认识。这些类型的撞击以7至70公里/秒的速度发生（对于自然产生的微流星体），目前还无法在实验室中实现。当撞击超过10 km/s时，撞击产生的压力足以克服外层电子壳层之间的排斥力屏障，从而产生新的结构相变，并且在压力释放后，许多工程材料进入混合液体和蒸汽状态的区域。由于无法在实验室中进行实验，这些现象以前没有被研究过。我在麦吉尔大学的团队最近开发了一种独特的超高速发射器，它使用炸药动态内爆发射器推进剂气体，现在已经证明有能力超过传统发射器的弹丸速度。该研究计划将继续发展超高速发射装置，并将其应用于撞击物理的基本问题以及航天器屏蔽感兴趣的材料的检查。

Highly energetic events occur when the rate of energy release exceeds the strength of the material into which the energy is deposited. Under these conditions, the ensuing dynamics of the media is governed by compressible (nonlinear) waves such as shock waves. While these phenomena are far outside everyday experience, they play an important role in a number of natural processes and technological applications. This proposed experimental and theoretical research program will focus on three topics involving the problems and applications of the dynamics of energetic events, with an emphasis on the nonlinear wave aspects of the problems.**Discrete Detonation: The propagation of detonation waves through energetic material, releasing stored energy as it propagates, is an example of a highly energetic event with important technological applications, since explosives are extensively used in mining and earth moving. Recent experimental results by the author, his colleagues, and researchers elsewhere have identified behavior of detonation waves in heterogeneous, condensed phase materials that cannot be explained by purely classical, continuum-based models of detonation wave propagation. These results suggest that phenomena occurring at the mesoscale (e.g., grains, voids, etc.) may have significant influence on the propagation of the wave. This research program will further investigate this effect experimentally as well as develop a methodology for modeling detonation propagation in media dominated by discrete, energetic events.**Implosion Dynamics: The response of materials exposed to highly dynamic events is also of considerable interest. My students and I have recently undertaken a study of the dynamics of cylinders that are impulsively imploded. This work was originally motivated by the development of the hypervelocity launcher described below, but has direct relevance to approaches to harness thermonuclear fusion for power generation (i.e., inertial confinement and magnetized target fusion). We will be continuing these studies under the proposed program, focusing upon the stability of dynamically loaded converging geometries (imploding cylindrical cavities) in both solids and liquids in order to determine the limits to symmetric compression that can be achieved and the role of material properties and hydrodynamic instabilities.**Hypervelocity Launcher and Impact: Another example of an energetic event is the hypervelocity impact of orbital debris or micrometeoroids on spacecraft. This mounting problem is now widely recognized due to the runaway cascade of collisions generating new debris in Earth orbit. These types of impacts occur at speeds of 7 to 70 km/s (for naturally occurring micrometeoroids), a regime that is not presently accessible in the laboratory. At impacts exceeding 10 km/s, the impact-generated pressures are sufficient to overcome the repulsion barrier between outer electron shells, giving rise to novel structural phase transitions, and upon pressure release, many engineering materials enter a region of mixed liquid and vapor states. These phenomena have not been previously studied due to their experimental inaccessibility in the laboratory. A unique hypervelocity launcher that uses explosives to dynamically implode the launcher propellant gas has recently been developed by my group at McGill, and has now demonstrated the ability to exceed the projectile velocity of conventional launchers. This research program will continue the development of the hypervelocity launcher and apply it to both fundamental problems in impact physics as well as examination of materials of interest for spacecraft shielding.