CAREER: Predicting granular flows: Amorphous continuum modeling with a length-scale

1253228PI：卡姆林缺乏密集颗粒流动的可预测的通用模型是工程应用中的一个障碍，也是工业中一个昂贵的问题。对于发育良好的流体，已经提出了某些流变学方法，然而，这些方法在运动速度较慢的区域失效，在那里观察到明显不同的行为，多年来一直抵制理论治疗。建立一种综合了快、慢流机制以及适当的瞬态效应塑性关系的一般颗粒流模型，将是该领域向前迈出的重要一步，也是工程设计和地球物理学中一个有益的工具。受最近乳液流动研究成功的启发，该项目将研究一种非局部本构方法，其直接包含颗粒长度尺度可能提供缺失的部分。通过使用复杂的定制化有限元工具，初步测试表明，该策略可以定量准确地预测多种流动几何形状的流动，包括一种以前从未用连续介质模型描述过流场的几何形状。将进行某些附加测试，以澄清该模型的潜在局限性。为了超越成熟的行为并扩展模型，将进行研究以将该技术合并到临界状态框架中，以捕获瞬态膨胀/强化/软化效应。另一个目标是为非局部机制建立一个改进的理论，从而改进对边界条件和薄体效应的解释。一旦以这种方式理解了干流，将再次利用增强的有限元工具来模拟流体饱和颗粒。该模型的类似基础和用于乳剂的相关方法在颗粒物质和其他非晶态材料之间建立了重要的联系。流动-诱导-流动机制及其如此精确地再现流动和应力场的能力，表明了一种微观图景，可以解决微粒流动问题中的许多悬而未决的问题。理论研究将有助于澄清这一基本机制，提高对其他物质的推广。为实现非局部颗粒流动模型而开发的有限元工具也为颗粒系统中的多重耦合效应建模打开了大门——如前所述的流体渗透率，但可以想象的是其他效应的组合，如电场相互作用、扩散效应和热传导。由于颗粒流在工业、科学和工程中的许多基本应用，我们提出的方法及其证明的准确性将为预测一般情况下的流动提供关键工具。要进行的工作还包括重要的综合教育部分。PI在麻省理工学院进行了几项在线教育创新，并提出了一些使用在线工具改善住宅和公共教育的方法。麻省理工学院的“少数族裔科学与工程入门”项目也将进行演讲，这是一个为期六周的暑期项目，鼓励有才华的少数族裔学生攻读技术领域的学位。此外，PI将让本科生参与到研究过程中，并将研究问题融入到教学中。通过继续组织新英格兰材料与结构力学研讨会和美国科学学会离散材料连续描述小型研讨会，将在科学界产生更广泛的影响。

1253228PI: KamrinThe lack of a predictive, general model for dense granular flow is an obstacle in engineering applications and an expensive problem in industry. For well-developed flows, certain rheological approaches have been put forward, however these break down in regions of less rapid motion, where a markedly different behavior is observed that has resisted theoretical treatment for years. To produce a general granular flow model that combines the fast and slow regimes, together with appropriate plasticity relations for transient effects, would constitute a major step forward in the field and a lucrative tool in engineering design and geophysics. Inspired by recent successes in the study of emulsion flow, this project will investigate a nonlocal constitutive approach, whose direct inclusion of a particle length-scale may provide the missing piece. With sophisticated and customized finite-element tools, preliminary tests indicate that this strategy leads to quantitatively accurate well-developed flow predictions in multiple flow geometries, including one family of geometries whose flow fields have never previously been described by a continuum model. Certain additional tests will be performed to clarify potential limitations of the model. To move beyond well-developed behavior and broaden the model, research will be conducted to merge the technique within a critical-state framework to capture transient dilation/strengthening/softening effects. Another aim is to build an improved theory for the nonlocal mechanism, and in so doing improve the interpretation of boundary conditions and thin-body effects. Once dry flows are understood in this way, enhanced finite-element tools shall be taken advantage of yet again to model fluid-saturated grains. The similar foundations of this model and related approaches used for emulsions draw important connections between granular matter and other amorphous materials. The flow-induces-flow mechanism and its ability to reproduce flow and stress fields so accurately suggests a microscopic picture that could solve many open questions in particulate flow problems. The theoretical investigation will help clarify this basic mechanism to improve generalization to other matter. The finite-element tools developed to implement the nonlocal granular flow model also open the door to modeling multiple coupled effects in particulate systems --- fluid permeability as mentioned, but conceivably a combination of other effects like electric-field interactions, diffusing species effects, and heat conduction.Owing to the many fundamental applications of granular flow in industry, science, and engineering, the approach we propose together with its demonstrated accuracy will provide a key tool for predicting flows in general circumstances. The work to be carried out also involves a significant and integrated educational component. The PI has conducted several innovations in online education at MIT and proposes a number of ways to improve residential and public education using online tools. Presentations will also be made in the MIT Minority Introduction to Science and Engineering program, a six-week summer program encouraging talented minority students to pursue degrees in technical fields. Moreover, the PI will involve undergraduates in the research process and integrate research problems into his teaching. Broader impact within the scientific community will be made through continued organization of the New England Workshop on the Mechanics of Materials and Structures, and the APS mini-symposium Continuum Descriptions of Discrete Materials.