Viscous and Inertial Nonlocal Rheology of Dense Suspensions of Frictionless Particles

浸没的颗粒介质或致密浆料是密密麻麻的颗粒，悬浮在粘性液体中。它们存在于自然环境中，如山体滑坡、泥石流和水下雪崩，也存在于工业环境中，如推进剂浆和陶瓷材料加工。这些材料在环境危害中起着至关重要的作用，在这些环境危害中，由于暴雨、地震和人类的影响，大量的浓浆变得流动和坍落。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远的距离。该奖项的目标是发展实验、理论和计算方法，以准确预测当颗粒没有摩擦接触时这些致密浆料的扩散。这种认识对于避免或减少自然灾害的影响至关重要。此外，获得的数据将对有兴趣开发新工程材料的研究人员有用。该奖项的成果将被纳入康奈尔大学的课堂，以促进学生在数学和物理方面的积极学习和成功。计划举办各种外展活动，通过说明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很好的实验数据，证明在稠密的无摩擦悬浮液中，从粘性到惯性的转变发生在一个惊人的小粒子雷诺数下。结果提出了一种假设，即胶体力和流体动力的相互作用导致粒子簇的形成，这些粒子簇支配着动量在材料中的传递。因此，比粒径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转移的局部流变定律不足以解释致密悬浮液的行为及其转变。该奖项将发展基于碰撞动力学的星团形成的理论描述。利用从离散元模拟和实验中获得的微观结构的洞察力，将推导出用于作用于团簇的粘性应力和惯性冲击的非局部本构方程。先进的力显微镜将用于表征纳米分离时的粒子间相互作用，并指导模型悬浮液的开发。先进的实验技术，如光学索引匹配，x射线摄影和计算机断层扫描将与传统的流变学技术相结合，以了解微观结构的细节，同时测量宏观应力。将设计和研究存在瞬态效应和非均匀剪切场的实验流。该理论将应用于预测实际流动的动力学，如实验室规模的浸没泥沙流动，并将通过将结果与实验测量结果进行比较来改进。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

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.