Experiments on Granular Fluctuation and Dissipation

摘要：宾夕法尼亚大学这个项目的目标是为颗粒材料在外力作用下如何流动和变形提供基本指导。实验方法将利用内部开发的现代光学技术。现代社会依赖于运输、储存、混合、粉碎和加工各种颗粒状物料，如食品、种子、矿物、矿石、建筑材料和药物药丸和粉末。然而，实际的应用程序是低效的，并受到诸如堵塞、错误包装和分离等灾难性故障的影响。该项目将通过建立微观粒度运动与由施加的力引起的宏观流动之间的基本联系，为改进工程实践奠定基础。除了应用之外，这个主题是基本的兴趣，因为颗粒材料是在已知物理世界边界的非线性远离平衡系统，并且因为它们与地球物理问题（如地震，泥石流，侵蚀和荒漠化）有丰富的联系。该项目将把现代物理和测量技术引入研究生和本科生的教育经验中，使他们直接参与前沿科学研究。技术摘要：宾夕法尼亚大学的这个项目的目标是测量颗粒尺度的动力学，并将颗粒介质的不同寻常的宏观力学特性联系起来。对于强强迫，微观动力学和宏观流动都是均匀的，并且可以用流体力学方法很好地描述。然而，对于低强迫，响应可能在时间上是间歇性的，在空间上是局部的。这种异构性在干扰方法上加剧了，并且对建模和应用程序都造成了破坏。该项目将利用高速视频显微镜以及内部开发的多斑动态光散射方法（称为斑可见光谱学）来阐明粒度行为。这些探测器将应用于堆和料斗流动，涉及撞击坑的流动，以及气体流态化的颗粒和棒。结果将与总体流动行为和流变性能相关联。总之，这将建立负责宏观尺度上注入能量耗散的基本微观涨落机制，以及它们对变形和流动的影响。该项目将把现代物理和测量技术引入研究生和本科生的教育经验中，使他们直接参与前沿科学研究。

NON-TECHNICAL ABSTRACT: The goal of this project at the University of Pennsylvania is to provide fundamental guidance for how granular materials flow and deform in response to applied forces. The experimental approach will leverage modern optical technologies developed in-house. Modern society relies on transporting, storing, mixing, crushing, and processing such diverse granular materials as foods, seeds, minerals, ores, building materials, and pharmaceutical pills & powders. However, actual applications are inefficient and subject to such catastrophic failures as clogging, mispacking, and demixing. This project will lay the basis for improved engineering practices by establishing the fundamental link between microscopic grain-scale motion and the macroscopic flows that result from applied forces. Besides applications, this topic is of basic interest both because granular materials are nonlinear far-from equilibrium systems at the boundary of the world of known physics, and because of their rich connections to geophysical problems such as earthquakes, mudslides, erosion, and desertification. The project will bring modern physics and measurement techniques into the educational experience of graduate and undergraduate students by involving them directly in cutting-edge scientific research.TECHNICAL ABSTRACT: The goal of this project at the University of Pennsylvania is to measure grain-scale dynamics and to connect with the unusual macroscopic mechanical properties of granular media. For strong forcing, both the microscopic dynamics and the macroscopic flows are homogeneous, and are reasonably well described by hydrodynamic approaches. However, for low forcing, the response can be intermittent in time and localized in space. Such heterogeneities are exacerbated on approach to jamming, and create havoc both for modeling as well as for applications. This project will elucidate grain-scale behavior using high-speed video microscopy, as well as a multispeckle dynamic light scattering method developed in-house and known as Speckle-Visibility Spectroscopy. These probes will be applied to heap and hopper flows, to flows involving impact cratering, and to gas-fluidized grains and rods. The results will be correlated with bulk flow behavior and to rheological properties. Altogether this will establish the fundamental microscopic fluctuation mechanisms responsible for the dissipation of energy injected at the macroscopic scale, and their consequences for deformation and flow. The project will bring modern physics and measurement techniques into the educational experience of graduate and undergraduate students by involving them directly in cutting-edge scientific research.