Collaborative Research: Statistical mechanics of dense suspensions - dynamical correlations and scaling theory

合作研究：稠密悬浮液的统计力学 - 动力学相关性和标度理论

• 批准号: 2228681
• 负责人: Bulbul Chakraborty
• 金额: $ 26.97万
• 依托单位: Brandeis University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-02-01 至 2026-01-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2228681&HistoricalAwards=false
• 关键词: Collaborative; Research; Statistical; mechanics; dense

This award supports research and education on dense suspensions, specifically a collection of rough particles suspended in a fluid like water: cornstarch is a good example of such a system. Similar dense suspensions include cement, ceramics, and mud. These suspensions are often so packed with particles that small changes in flow rate may cause them to stop flowing and jam into a solid. Surprisingly, a predictive theory for this behavior is lacking. One obstacle is figuring out how interactions between two particles cause the behavior seen when many particles are put together. The research supported by this award is focused on creating understanding using a combination of theory, numerical simulations, and analysis of experimental data. Since the behavior of suspensions is easily accessible in experiments and numerical simulations that show good agreement, they are an ideal system for exploring the larger question of how materials change properties due to flow conditions. The team is committed to outreach and diversity-in-education efforts: a novel approach to exposing the basic science through on-stage dramatization will be undertaken with collaborators in New York City, while both investigators will mentor undergraduate research students with recruitment from under-represented groups a priority.This award supports research and education to develop understanding of microscopic correlations and macroscopic behavior in dense, shear-thickening suspensions. Using a discrete-particle simulation approach that incorporates particle frictional contact at stress above a threshold level, the behavior of the discontinuous shear thickening (DST) and shear jamming (SJ) transitions will be explored. The focus will be on measuring dynamical, or motion variable, correlations such as the spatial and temporal correlation of fluctuating velocities and rotational motions. This will be complemented by analysis of divergent shear and normal stress as jamming is approached; the analysis will apply methods of crossover scaling, a renormalization group method especially useful when behavior is influenced by two singular points: this is seen in the current system as it undergoes two forms of jamming, one due to geometrically-determined frictionless contacts at vanishing stress and the other due to stress-induced frictional contacts at large stress. The continuum description of suspension flow in a novel direction, by extension of recent approaches to describe the emergent elasticity of jammed amorphous packings will also be investigated. This direction of work is based on a postulate that rigidity on progressively larger scales is induced by increase of the stress, which in a sufficiently dense suspension leads to a percolation of rigidity and jamming; the continuum theory is based in the investigation of motion correlations by simulation. To explore more complex kinematics, simulation of a spatially varying flow mimicking active microrheology, in which a probe particle is pulled through a dense suspension, will be undertaken.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.

该奖项支持对致密悬浮液的研究和教育，特别是悬浮在水等流体中的粗糙颗粒的集合：玉米淀粉是此类系统的一个很好的例子。类似的稠密悬浮液包括水泥、陶瓷和泥浆。这些悬浮液通常充满颗粒，流速的微小变化可能会导致它们停止流动并堵塞成固体。令人惊讶的是，缺乏这种行为的预测理论。一个障碍是弄清楚两个粒子之间的相互作用如何导致许多粒子放在一起时看到的行为。该奖项支持的研究重点是结合理论、数值模拟和实验数据分析来加深理解。由于悬浮液的行为很容易在实验和数值模拟中获得，并且显示出良好的一致性，因此它们是探索材料如何因流动条件而改变特性这一更大问题的理想系统。该团队致力于教育的推广和多元化工作：将与纽约市的合作者一起采用一种通过舞台戏剧化来揭示基础科学的新颖方法，而两位研究人员将指导本科生，并从低年级招募学生。该奖项支持研究和教育，以加深对致密、剪切增稠悬浮液中微观相关性和宏观行为的理解。使用离散粒子模拟方法，结合高于阈值水平的应力下的粒子摩擦接触，将探索不连续剪切增厚（DST）和剪切干扰（SJ）转变的行为。 重点是测量动态或运动变量相关性，例如波动速度和旋转运动的空间和时间相关性。 当接近干扰时，将通过分析发散剪切和法向应力来补充这一点；该分析将应用交叉缩放方法，这是一种重正化群方法，当行为受到两个奇异点影响时特别有用：这在当前系统中可以看到，因为它经历了两种形式的干扰，其中一种是由于应力消失时几何确定的无摩擦接触造成的另一个是由于大应力下应力引起的摩擦接触。还将研究通过扩展最近描述堵塞非晶填料的涌现弹性的方法，以新的方向对悬浮液流进行连续描述。这一工作方向基于这样一个假设：逐渐增大的尺度上的刚性是由应力的增加引起的，在足够稠密的悬浮液中会导致刚性渗透和堵塞；连续统理论基于通过模拟研究运动相关性。为了探索更复杂的运动学，将模拟活跃微流变学的空间变化流动，其中探针粒子被拉过致密悬浮液。该奖项反映了 NSF 的法定使命，并通过使用基金会的评估进行评估，被认为值得支持。智力价值和更广泛的影响审查标准。