Experiments on Granular Fluctuation and Dissipation

非技术摘要：宾夕法尼亚大学这个项目的目标是为颗粒材料如何在外力作用下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材料，如食品、种子、矿物、矿石、建材和药丸和粉末。然而，实际应用程序的效率很低，并且容易出现堵塞、打包错误和分离等灾难性故障。该项目将通过建立微观颗粒尺度运动和外力产生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，这个主题还具有基本的意义，因为颗粒材料是远离已知物理世界边界的平衡系统的非线性物质，也因为它们与地震、泥石流、侵蚀和沙漠化等地球物理问题有着丰富的联系。该项目将把现代物理和测量技术带到研究生和本科生的教育经验中，让他们直接参与尖端科学研究。技术摘要：宾夕法尼亚大学这个项目的目标是测量颗粒尺度的动力学，并与颗粒介质不寻常的宏观力学性质相联系。对于强强迫，微观动力学和宏观流动都是均匀的，并可以用流体动力学方法很好地描述。然而，对于低强迫，响应在时间上是间歇性的，在空间上是局部的。这种异质性在干扰方法上加剧，并对建模和应用程序都造成了严重破坏。该项目将使用高速视频显微镜以及内部开发的称为斑点可见度光谱的多斑点动态光散射方法来阐明颗粒尺度行为。这些探头将应用于堆流和料斗流、涉及撞击凹坑的流以及气体流态化的颗粒和棒材。结果将与整体流动行为和流变性相关联。总之，这将建立基本的微观涨落机制，负责宏观尺度上注入的能量的耗散，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带入研究生和本科生的教育经验，让他们直接参与尖端科学研究。

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.