Multidimensional Problems in Granular Plasticity

该奖项支持一个统一的建模、分析和计算研究项目，以更好地表征和理解颗粒流动，特别是存在间隙流体的颗粒流动。干燥的颗粒状物质可以被表征为物质的第四种状态。颗粒状介质可以像固体一样承受压力，但也可以像液体一样流动，或者在某些条件下像气体一样流动。在变形时，颗粒状试样可能膨胀或固结，这取决于包装条件。这些特征导致颗粒材料的动力学，其丰富性和范围可与流体动力学相媲美。同时，在技术应用中使用的颗粒材料变得越来越小，因此，间隙流体的存在变得越来越重要。在静电复印中使用碳粉尤其如此，其中功率颗粒的小尺寸意味着更高质量的副本。当它们移动时，这些小的光粒子（直径约10微米）受到周围气体的强烈影响，粒子运动与流体运动密切相关。此外，由于范德华引力，这些碳粉具有粘性，往往容易结块。通过流态化和振动引入受控流体流动，是打破粘性吸引和控制颗粒运动的常见机制。在一个非常不同的应用中，干燥和涂覆较大颗粒（直径约500微米）的新想法使用平板的快速垂直振动来加速颗粒质量。由于大的加速度，间隙流体在颗粒运动中再次起重要作用。理论和数值技术将用于表征状态图，研究流化粉末层在倾斜下的稳定性，并研究冒泡和结块的发生。颗粒和流体的组合流动还有许多其他工业应用，如压力容器中的颗粒流动，猫裂，润滑输送和传热。在这些应用中，粉末的运输和处理呈现出显著的困难。如果对颗粒流体流动没有更好的了解，利用新颗粒技术的产品可能不会很快上线，也不会有足够的可靠性。在这方面，值得注意的是，兰德公司（Rand Corporation）的一项研究表明，由于无法准确预测粉末的行为，固体生产工厂的平均运行能力为设计能力的63%，而液体生产工厂的平均运行能力为84%。在这个项目中进行的分析和计算，以及其他学术和工业研究人员的实验，将有助于提供这些流动所需的特征。

This award supports a unified research program of modeling, analysisand computation to better characterize and understand granular flows,in particular, granular flows in the presence of interstitial fluid.Dry granular materials may be characterized as a fourth state of matter.Granular media can support stresses like a solid, but alsocan flow like a liquid, or, under some conditions, like a gas.While deforming, a granular sample may dilate or consolidate,depending on packing conditions. These features lead to a dynamics of granular materials whose richness and scope rivals that of fluid dynamics.At the same time, particle materials used in technological applications arebecoming smaller, and, consequently, the presence of interstitial fluid isbecoming increasingly important. This is particularly truein the use of toner powders in xerography, where the small sizeof the power particles means higher quality copies. As they move, these small light particles (about 10 micron diameter) are strongly influenced by the surrounding gas, and particle motion is intimately coupled to fluid motion.Furthermore, owing to van der Waals attraction, these toner powdersare cohesive, often tending to clump. The introduction of controlled fluid flow, through fluidization and vibration, is a common mechanismfor breaking the cohesive attractions and controlling particle motion.In a very different application, new ideas for drying and coatinglarger particles (about 500 micron diameter) use rapid vertical vibration of a flat plate to accelerate a granular mass. Because of the large acceleration, interstitial fluid again plays an important role in the motion of particles. Theoretical and numerical techniques will be used tocharacterize state diagrams, study the stability of layers of fluidized powderunder tilting, and study the onset of bubbling and clumping.The combined flow of particles and fluid has many other industrialapplications, such as particle flow in pressurized vessels, cat-cracking,transport by lubrication, and heat transfer. In these applications, transport and handling of powders presents a significant difficulty.Without a better understanding of particle-fluid flows, products thatexploit new particle technologies may not come on-line as quickly, nor withsufficient reliability. In this regard, it is useful tonote a study by the Rand Corporation showing that, because of aninability to accurately predict powder behavior, solids-producingmanufacturing plants performed on average at 63% of design capacity,compared to 84% for liquids-producing plants.The analysis and computations performed during this project, together withexperiments by other academic and industrial researchers,will help to provide the needed characterization of these flows.