Unifying Granular Flows

CBET-0828514 Campbell从采矿到化工再到制药等行业，每天都要处理数千吨的颗粒物料。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，处理大量的低价值材料可能会很昂贵，并可能使项目不经济。同时，高价值的产品必须小心处理，以避免损坏，从而造成巨大的经济损失。然而，颗粒材料的力学行为还没有得到很好的理解。 经典的颗粒流已经在两种极限流状态下进行了研究-快速流或“快速流”状态和缓慢流或准静态流状态。人们对这两者之间发生的情况知之甚少，没有这些信息，甚至不可能量化每种流型有效的条件。最近，PI已经能够填补这个中间空间，并创建统一的流程图，涵盖所有制度的颗粒流行为-至少对简单的材料。关键是包括作为流变参数，颗粒间接触的刚度，将单个颗粒的弹性特性与散装材料的弹性特性联系起来的特性-从而将固体特性带回颗粒固体的流变学中。他将颗粒流分为两大类。在弹性状态下，颗粒被锁定在力链中，与它们的邻居持续接触;应力由这些接触的变形产生，因此与接触刚度成比例。在惯性状态下，流动变得与刚度无关。这些被进一步细分为四个子制度，弹性准静态，旧的准静态制度，弹性惯性时，惯性效应具有可比的顺序，惯性非碰撞制度，表现为惯性，但粒子在集群中相互作用，惯性碰撞制度，其中二元接触占主导地位（旧的快速流动制度）。 该项目的目标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动状态，模拟将用于指导设计的环形简单剪切流变仪。此外，对实验本身的模拟将深入了解剪切单元内发生的情况，并有助于解释结果。反过来，这些实验将指导未来的模拟开发。一个特定的目标将是确定适当的接触模型，允许模拟复制实验。最后，模拟将扩展到进一步探索弹性颗粒流变学。智力优点：弹性理论是变革性的，是第一个统一的理论颗粒流，并填写了整个流程图，连接快速和准静态区域和所有的干预制度。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，但它仍然证明了必须以某种形式应用于更复杂系统的基本标度律，从而为颗粒流理论的未来扩展提供了关键。拟议的工作包括实验验证的弹性模型，以及开始其扩展到更复杂的system.Broader的影响：准静态和快速流动模型被纳入了大量的各种计算机模型，用于设计应用的化学，制药，采矿，建筑，农业，石油，地质技术，以及危害评估。在根据弹性理论生成流图之前，没有办法确定模型有效的条件。因此，这项工作将最终开始投入的角度来看，过去40年的颗粒流理论。与此同时，它将防止由于错误的模型应用于工业问题而导致的代价高昂的错误。教育影响：南加州大学教授的课程通过学校DEN网络广泛传播，现在可以在全球范围内通过互联网上的流媒体视频点播。特别是，颗粒流理论构成了P.I.的课程，AME 533多相流。此外，南加州大学位于低收入，主要是非洲裔美国人，地区，中南部洛杉矶，并有许多社区外展计划，以连接当地居民和学生。在过去，PI。资助了三名女博士生最后，PI与另一位教授合作，引进代表性不足的暑期实习生，其中许多来自波多黎各大学，提供实践经验，并传授模拟技术。特别强调将放在模拟技术，因为大多数流变规模的模拟，现在可以在家用PC上进行。这将允许实习生在夏季结束时回家继续合作。

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.