Multidimensional Problems in Granular Plasticity

该奖项支持一个统一的建模、分析和计算研究计划，以更好地描述和理解颗粒流，特别是存在间隙流体的颗粒流。颗粒材料可以被描述为第四种物质状态。颗粒介质可以支持像固体一样的应力，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。当颗粒样品变形时，颗粒样品可能会膨胀或固结，具体取决于填充条件。这些特点导致了颗粒材料的动力学，其丰度和范围可与流体动力学相媲美。同时，用于技术应用的颗粒材料正变得越来越小，因此，间隙流体的存在变得越来越重要。这在静电复印中使用碳粉时尤其如此，在静电印刷中，粉末颗粒的小尺寸意味着更高质量的复印。当它们移动时，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密切耦合。此外，由于范德华的吸引，这些碳粉粉末具有凝聚力，经常倾向于结块。通过流态化和振动引入受控流体流动是打破粘聚力和控制颗粒运动的常见机制。在另一种截然不同的应用中，干燥和涂布较大颗粒(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，间隙流体在粒子的运动中再次扮演着重要的角色。理论和数值技术将被用来描述状态图，研究倾斜下流态化粉末层的稳定性，并研究气泡和结块的开始。颗粒和流体的组合流动还有许多其他工业应用，如加压容器中的颗粒流动，催化裂化，润滑输送和热传递。在这些应用中，粉末的运输和处理是一个非常困难的问题。如果没有对颗粒-流体流动的更好了解，采用新颗粒技术的产品可能不会那么快地上线，也不会有足够的可靠性。在这方面，兰德公司的一项研究表明，由于无法准确预测粉末行为，固体生产工厂的平均产能为设计产能的63%，而液体生产工厂的平均产能为84%，这是有用的。在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.