Bridging the Spatial and Temporal Scales in Dense Granular Systems Description of Dense Granular Shear Flows

KondicDMS-0605857该项目的中心是分析和理解通过密集颗粒系统传播信息的本质。然后利用这些信号的特性来推断力和能量传递的基本物理机制。这些机制近来一直是大量研究的主题，因为了解颗粒之间的力是否以一种可以在椭圆、双曲线或抛物线框架下描述的方式传播是至关重要的。这个项目的出发点是发展大规模的离散元模拟，用于分析稠密颗粒系统对空间和时间相关扰动的响应。模拟的结果被用来帮助建立有效的模型，以在颗粒系统的微观(颗粒尺度)和细观(数百或数千颗粒)描述之间架起桥梁。同时考虑了静态和动态颗粒系统，使得分析颗粒动力学和信号传播之间的相互作用成为可能。这种设置还允许考虑稠密颗粒流的一些重要特征，如力各向异性的作用和潜在的微观结构。该项目是与杜克大学的实验工作密切合作进行的。致密的颗粒系统是软凝聚物质领域中最具挑战性的系统之一，特别是因为它们容易受到干扰，处于物质的固态和液态之间。对通过这些系统的信号传播的分析使我们能够理解微观尺度上的粒度如何影响宏观尺度的行为。这里使用的新的研究技术也可以应用于其他遇到堵塞的软凝聚物质系统，如乳剂、胶体、凝胶和泡沫。此外，通过颗粒状系统传播信号在许多实际问题中具有相当重要的意义，这些问题包括石油开采、振动沸腾床和一些重要的人道主义工作，如探雷。该项目解决了致密颗粒系统的静力学和动力学方面的基本问题；对这些基本概念的理解有助于未来在开发更好的模型方面取得进展，这些模型是许多颗粒材料应用所需的。

KondicDMS-0605857 The project centers on analyzing and understanding thenature of information propagation through dense granular systems. The properties of the signals are then used to deduce the basicphysical mechanisms of the force and energy transmission. Thesemechanisms have been the subject of considerable study latelybecause it is crucial to understand whether the forces betweengranular particles propagate in a manner that can be describedunder an elliptic, hyperbolic, or parabolic framework. Thestarting point of this project is development of large scalediscrete element simulations that are used to analyze response ofdense granular systems to space- and time-dependentperturbations. The results of the simulations are then employedto help formulate effective models for bridging the scalesbetween micro (grain scale) and meso (hundreds or thousands ofgrains) descriptions of granular systems. Both static anddynamic granular systems are considered, making it possible toanalyze the interplay between granular dynamics and signalpropagation. This setup also allows for considering someimportant features of dense granular flows, such as the role offorce anisotropy and underlying microstructure. The project iscarried out in close collaboration with experimental workperformed at Duke University. Dense granular systems are one of the most challengingsystems in the field of soft condensed matter, in particularbecause they are subject to jamming, and fall in between solidand liquid states of matter. Analysis of signal propagationthrough these systems allows us to understand how granularity ona micro scale influences macroscale behavior. The novel researchtechniques used here also can be applied to other soft condensedmatter systems that experience jamming, such as emulsions,colloids, gels, and foams. In addition, signal propagationthrough granular systems is of considerable importance in anumber of practical problems including oil recovery,vibrofluidized beds, and some important humanitarian efforts,such as detection of land mines. The project addresses basicissues in statics and dynamics of dense granular systems;understanding of these basic concepts allows for future progressin developing better models needed for numerous applications ofgranular materials.