Multidimensional Problems in Granular Plasticity

该奖项支持建模，分析和计算的统一研究计划，以更好地表征和理解颗粒流，特别是存在间隙液的颗粒流。干燥颗粒材料可以被描述为物质的第四种状态。颗粒介质可以像固体一样承受应力，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。当变形时，颗粒状样品可能会膨胀或固结，这取决于包装条件。 这些特征导致了颗粒材料动力学的丰富性和范围与流体动力学相媲美。与此同时，用于技术应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。 在静电复印中使用墨粉时尤其如此，因为墨粉颗粒的小尺寸意味着高质量的复印件。 当它们运动时，这些小的轻颗粒（直径约10微米）受到周围气体的强烈影响，颗粒运动与流体运动紧密耦合。此外，由于货车德瓦尔斯引力，这些墨粉粉末是内聚的，常常倾向于结块。 通过流化和振动引入受控流体流动是打破内聚吸引力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物质。 由于大的加速度，间隙液再次在粒子的运动中起重要作用。 理论和数值技术将被用来描述状态图，研究倾斜下流化粉末层的稳定性，以及研究起泡和结块的开始。颗粒和流体的组合流动有许多其他的工业应用，如加压容器中的颗粒流动，催化裂化，润滑输送和传热。 在这些应用中，粉末的运输和处理是一个很大的困难。如果不更好地了解颗粒-流体流动，采用新颗粒技术的产品可能不会很快上线，也没有足够的可靠性。 在这方面，值得一提的是兰德公司的一项研究，该研究表明，由于无法准确预测粉末的行为，固体生产制造厂的平均生产能力为设计能力的63%，而液体生产厂的平均生产能力为84%。该项目期间进行的分析和计算，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.