Granular Gases of Anisotropic Particles

与连续介质类似，人们可以为颗粒材料定义不同的聚集状态。颗粒气体是像土星环或沙尘暴这样的固体粒子的松散集合。与原子或分子气体不同，碰撞是耗散的，为了保持运动状态，必须不断提供能量。这种能量通过碰撞进入不同的转动和平移自由度来分配。颗粒气体在微重力条件下最容易制备。尽管它们非常适合研究多粒子系统的统计动力学，但实验研究很少。这主要是由于在准备微重力实验和实施适当的激发方面存在困难。我们研究了形状各向异性粒子的颗粒气体，并重点研究了以下问题：-动能如何在自由度之间分配？-当没有能量供应时，这种气体如何冷却？-激发参数与颗粒温度之间的关系？-粒子的空间分布和冷却气体中的动量是什么？第一次实验已经由REXUS项目的学生完成，记录了大约100秒的视频序列，在零重力下弱激发的气体。这些实验在获得的数据质量方面处于国际一流水平。现有的数据只评估了很小的一部分。2012年，这一提议的首席调查员将试探性地利用STIG-B火箭(Armadillo AerSpace)进行亚轨道飞行。此外，我们还将进行落塔实验，以研究激发参数和颗粒几何形状的影响。对迄今可获得的数据和未来几个月内预期的数据进行评估，以及解释和建模，是一项全面而雄心勃勃的计划，应在该项目范围内完成。这将在理解颗粒气体和验证现有模型方面带来质的新见解。

Similar to continua, one can define different states of aggregation for granular materials. Granular gases are loose ensembles of solid particles like the Saturn rings or sand storms. In contrast to atomic or molecular gases, collisions are dissipative and energy has to be supplied continuously in order to keep the state of motion. This energy is distributed by collisions into the diffferent rotational and translational degrees of freedom. Granular gases are prepared most easily under microgravity conditions. Although they are uniquely suited for studies of statistical dynamics of multiparticle systems, there are only few experimental studies. This is primarily due to the difficulties in the preparation of microgravity experiments and the implementation of a suitable excitation. We investigate granular gases of shape-anisotropic particles and focus on the following questions:- How does the kinetic energy distribute among the degrees of freedom?- How do such gases cool, when no energy is supplied?- What is the relation between excitation parameters and granular temperature?- What is the spatial distribution of the particles and the dynamic quantities in the cooling gas?First experiments were performed already by students within the REXUS program, about 100 sec of video sequences of a weakly excited gas in zero gravity were recorded. These experiments are, regarding the quality of the data obtained, on international top level. The available data have been evaluated only to a very small part. Further experiments will be performed tentatively by the principal investigator of this proposal in 2012 on a suborbital flight with a STIG-B rocket (Armadillo Aerospace). In addition, we will perform drop tower experiments to study influences of excitation parameters and particle geometries. The evaluation of the data available so far and those expected within the next months, as well as interpretation and modeling, are a comprehensive and ambitious program that shall be accomplished within this project. This will lead to qualitatively new insights in the understanding of granular gases and the verification of existing models.