Unifying Granular Flows

CBET-0828514 Campbell从采矿到化工再到制药等行业，每天处理数千吨颗粒状材料。它们的价值从每吨几美分到每克几千美元不等。如果处理效率低下，处理大量小价值材料的成本可能会很高，并可能使项目变得不经济。同时，高价值产品必须谨慎处理，避免损坏，从而造成较大的经济损失。然而，颗粒材料的力学行为还没有被很好地理解。经典的颗粒流已被研究在两个极限流区--快流区或“快流区”和慢流区或准静态区。对于两者之间发生了什么，人们一直知之甚少，没有这些信息，甚至不可能量化每一种流动制度有效的条件。最近，P.I.已经能够填补这一中间空间，并创建涵盖颗粒流动行为的所有区域的统一流程图--至少对于简单的材料来说是这样。关键是将颗粒间接触的硬度作为流变学参数，即将单个颗粒的弹性特性与块状材料的弹性特性联系起来的特性--从而将固体特性重新纳入颗粒固体的流变学。他将颗粒流分为两个大的区域。在弹性状态下，粒子被锁定在与相邻粒子持续接触的力链中；应力是由这些接触的变形产生的，因此与接触刚度成正比。在惯性状态下，流动变得与刚度无关。这些子区被进一步细分为四个子区，弹性-准静态区，旧的准静态区，当惯性效应具有类似的阶数时的弹性-惯性区，惯性-非碰撞区，其惯性行为，但粒子在团簇中相互作用，以及惯性-碰撞区，其中二元接触为主(旧的急流区)。该项目的目标将是通过耦合实验和计算机模拟来扩展这项工作，以进一步充实流变行为。模拟和实验之间的耦合将以几种方式发生。首先，由于这些是新的和不太了解的流型，将使用模拟来指导环形简单剪切流变仪的设计。此外，对实验本身的模拟将深入了解剪切单元内部发生的事情，并有助于解释结果。反过来，这些实验将指导未来的模拟发展。一个特别的目标将是确定足够的接触模型，使模拟能够重复实验。最后，模拟将扩展到进一步探索弹性颗粒流变学。智能优点：弹性理论是第一个统一的颗粒流动理论，并填写了整个流程图，连接快速和准静态区域和所有中间区域。虽然目前，像大多数颗粒理论一样，它仅限于具有简单接触模型的单分散球体，但它仍然证明了基本的标度定律，这些定律必须以某种形式应用于更复杂的系统，从而为颗粒流理论的未来扩展提供了关键。拟议的工作包括对弹性模型进行实验验证，并开始将其扩展到更复杂的系统。广泛的影响：准静态和快速流动模型正在被纳入各种计算机模型，这些计算机模型用于化工、制药、采矿、建筑、农业、石油、岩土工程以及危险评估的设计应用。直到从弹性理论产生的流程图，才能确定模型在什么条件下有效。因此，这项工作最终将开始透视过去40年的颗粒流理论。同时，它将防止由于错误的模式应用于工业问题而导致的代价高昂的错误。教育影响：在南加州大学教授的课程通过学校DEN网络广泛分发，该网络现已在全球范围内提供，并通过互联网上的流媒体视频进行点播。特别是，颗粒流理论占P.I.S课程AME533多相流的很大一部分。此外，南加州大学位于洛杉矶中南部一个以非裔美国人为主的低收入地区，有许多社区外联计划，以联系当地居民和学生。过去，P.I.曾资助过三名女性博士生。最后，P.I.正在与另一位教授合作，引进人数不足的暑期实习生，其中许多人来自波多黎各大学，以传授实践经验，并教授模拟技术。将特别强调模拟技术，因为大多数流变学模拟现在可以在家用PC上执行。这将允许实习生在夏末回家后继续合作。

CBET-0828514CampbellMany thousands of tons of granular material are handled daily in industries ranging from mining to chemical to pharmaceutical. Their values range from cents per ton to thousands of dollars per gram. Handling massive amounts of small-value material can be expensive if done inefficiently and potentially make a project uneconomical. At the same time, high-valued products must be handled carefully to avoid damage with consequently large economic losses. Yet the mechanical behavior of granular materials is not well understood. Classically granular flow have been studied in two limiting flow regimes - the fast-flow or "rapid flow" regime and the slow-flow or quasistatic flow regime. There has been little understanding as to what occurs in between, and without that information, it has been impossible to even quantify the conditions under which each flow regime is valid. Recently, the P.I. has been able to fill in this intervening space and create unified flowmaps covering all regimes of granular flow behavior - at least for simple materials. The key was including as a rheological parameter, the stiffness of the interparticle contacts, the property that links the elastic properties of individual particles to the elastic properties of the bulk material - and thus to bring solid properties back into the rheology of granular solids. He divided granular flows into two broad regimes. In theElastic regime, particles are locked in force chains in persistent contact with their neighbors; the stresses are generated by the deformation of those contacts and are thus proportional to the contact stiffness. In the Inertial regime flows become independent of the stiffness. These were further subdivided into four sub-regimes, Elastic-Quasistatic, the old quasistatic regime, the Elastic-Inertial when inertial effects have comparable order, the Inertial-non-Collisional regime, which behave inertially, but the particle interact in cluster, and the Inertial- Collisional regime, where binary contacts dominate (the old Rapid-flow regime). The goal of the project will be to extend this work through coupled experiments and computer simulations to further flesh out the rheological behavior. The coupling between simulation and experiment will occur in several ways. First, as these are new and not-well understood flow regimes, simulations will be used to guide the design of an annular simple shear rheometer. Also, simulations of the experiments themselves will yield insight into what is happening inside the shear cell and aid in the interpretation of the results. In turn, the experiments will guide future simulation development. A particular goal will be to determine adequate contact models that allow the simulations to replicate the experiments. Finally, the simulations will be extended to further probe elastic granular rheology.Intellectual Merit: The elastic theory is transformative in being the first unified theory of granular flow and fills out the entire flowmap, connecting the rapid and quasistatic regions and all the intervening regimes. While at the moment, like most granular theories, it is limited to monodisperse spheres with simple contact models, it nonetheless demonstrates the fundamental scaling laws that must in some form apply to more complex systems and thus provides the key to future expansion of granular flow theories. The proposed work involves experimental verification of the elastic model as well as a start on its extension to more complicated systems.Broader Impact: Quasistatic and rapid flow models are being incorporated in a large variety of computer models used in design applications for the chemical, pharmaceutical, mining, construction, agriculture, petroleum, geo-technical, as well as hazard assessment. Until the flowmaps that were generated from the elastic theory, there was no way to determine the conditions under which the models were valid. Thus this work will finally begin to put into perspective, the last 40 years of granular flow theory. At the same time, it will prevent costly errors resulting from the misapplication of the wrong model to an industrial problem.Educational Impact: Courses taught at USC receive wide distribution over the school DEN network, now available worldwide and on demand by streaming video on the internet. In particular, granular flow theory makes up a large portion of the P.I.'s course, AME533 Multiphase Flows. In addition, USC is located in a low-income, largely African-American, area, South Central Los Angeles, and has many community outreach programs to connect with local residents and students. In the past the P.I. has supported three female PhD students. Finally the P.I. is partnering with another professor to bring in underrepresented summer interns, many from the University of Puerto Rico, to give hands on experience and to educate in simulation techniques. Particular emphasis will be put on the simulation techniques as most rheological scale simulations can now be performed on home PC's. This will permit the intern to continue the collaboration when he or she has returned home at the end of the summer.