Viscous and Inertial Nonlocal Rheology of Dense Suspensions of Frictionless Particles

浸没颗粒介质或稠密浆料是悬浮在粘性液体中的密集颗粒。它们存在于自然环境中，如滑坡，泥石流和水下雪崩，以及工业环境中，如推进剂浆料和陶瓷材料加工。这种材料在环境危害中起着至关重要的作用，在环境危害中，大量的稠密泥浆变得移动的，并因暴雨、地震和人为影响而坍塌。在这种灾难性的流动中，颗粒可能会在短时间内失去接触并传播很长的距离。该奖项的目标是开发实验，理论和计算方法，以准确预测这些致密浆料的蔓延时，颗粒没有摩擦接触。这种理解对于避免或减少自然灾害的影响至关重要。此外，所获得的数据将对有兴趣开发新工程材料的研究人员有用。该奖项的结果将被纳入康奈尔大学的课程，以促进学生在数学和物理方面的积极学习和成功。计划开展各种外展活动，通过展示工程科学的社会影响，激发K-12学生对工程的兴趣。研究人员最近提供了解析度很高的实验数据，证明在无摩擦的稠密悬浮液中，从粘性到惯性状态的转变发生在令人惊讶的小颗粒雷诺数。这些结果表明了一个假设，即胶体和流体动力的相互作用导致形成颗粒簇，这些颗粒簇主导了整个材料的动量传输。 因此，比颗粒尺寸更大的长度尺度可能起作用。因此，目前基于二元碰撞和动量传递的局部流变学定律不足以解释稠密悬浮体的行为及其转变。该奖项将开发基于碰撞动力学的集群形成的理论描述。非局部本构方程占的粘性应力和惯性的影响，作用于集群将使用洞察到从离散元模拟和实验获得的微观结构。先进的力显微镜将用于表征纳米分离的颗粒间相互作用，并指导模型悬浮液的开发。先进的实验技术，如光学指数匹配，X射线照相术，计算机断层扫描将与传统的流变技术相结合，以了解微观结构的细节，同时测量宏观应力。实验流将被设计和研究，其中瞬态效应和非均匀剪切场。该理论将被应用于预测实际流动的动力学，如实验室规模的浸没沉积物流动，并将通过将结果与实验测量结果进行比较来完善。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

Immersed granular media or dense slurries are densely packed grains suspended in a viscous liquid. They are found in natural environments, such as landslides, mudslides, and underwater avalanches, and in industrial settings, such as propellant slurries and ceramic material processing. Such materials play a crucial role in environmental hazards in which large volumes of dense slurries become mobile and slump triggered by heavy rainfall, earthquakes, and human influences. In such catastrophic flows, grains may lose contact and spread for long distances in a short time. The goal of this award is to develop experimental, theoretical, and computational methods to accurately predict the spread of these dense slurries when the grains are not in frictional contact. This understanding is essential to avoid or reduce the impacts of natural disasters. In addition, data acquired will be useful to researchers interested in developing new engineering materials. Results from this award will be incorporated into classes at Cornell University to promote active learning and student success in mathematics and physics. Various outreach activities are planned to inspire interest in engineering among K-12 students by illustrating the societal impact of engineering science.Researchers have recently provided well-resolved experimental data demonstrating that the transition from viscous to inertial regime in dense frictionless suspensions occurs at a surprisingly small particle Reynolds number. The results suggest a hypothesis that the interplay of colloidal and hydrodynamic forces leads to the formation of clusters of particles which dominate the transmission of momentum across the material. Therefore, larger length scales than the particle size may play a role. Consequently, the current local rheological laws based on binary collisions and transfer of momentum are inadequate in explaining the behavior of dense suspensions and their transition. This award will develop a theoretical description of cluster formation based on collisional dynamics. Nonlocal constitutive equations accounting for the viscous stresses and inertial impacts acting on the clusters will be derived using insight into the microstructure obtained from discrete element simulations and experiments. Advanced force microscopy will be used to characterize interparticle interactions at nanometer separations and guide the development of model suspensions. Advanced experimental techniques such as optical indexed-matching, X-ray radiography, and computed tomography will be coupled with conventional rheometry techniques to understand the details of microstructure while measuring the macroscopic stresses. Experimental flows will be designed and studied in which transient effects and inhomogeneous shear fields are present. The theory will be applied to predict the dynamics of practical flows such as lab-scale immersed sediment flows and will be refined by comparing the results with experimental measurements.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.