半流化振动颗粒体系的动力学结构

The fluidization of discrete granules is an important difficulty faced by both engineers and scientists. Understanding the characteristics and the regularities of the fluidization process of a granular system, will not only help to promote the efficiency of industrial production, but also provide practical guidance for preventing and curbing natural disasters; Meanwhile, the dynamical heterogeneity and local fluidization observed in semi-fluidized granular systems are also hotspots in frontier research. Hence, we propose to perform quantitative investigation on the microscopic dynamical structures of a vibro-fluidized granular system, through both experiments and discrete element simulations. The study aims to find a universal characterization for different fluidized states of the granular system, and to understand the complex dynamics of a semi-fluidized system. By using this characterization method, the physical mechanism of the capillary-like and other related phenomena observed in vibro-fluidized granular system will be possibly clarified. It is very promising that the results of this research will produce a unified physical picture for various complex phenomena observed in vibrated granular systems, help to check the validation of the granular statics and hydrodynamics in different cases, and assist to solve different fluidization problems encountered in daily life.

离散态颗粒物质的流化问题是工程和科学领域共同面临的难题。理解颗粒体系的流化特征和规律，不仅有利于提高工业生产的效率，而且能够为预防和有效治理自然灾害提供一定程度的指导作用；同时，半流化状态颗粒体系表现出来的动力学各向异性及局域流化特征，也是当前科学领域重要的研究热点之一。本项目拟通过实验和离散元数值模拟相结合的方法，定量研究不同强度振动驱动颗粒体系的微观动力学结构特征，实现对其不同流化状态的普适表征，建立对半流化状态复杂行为的准确描述，并据此探索以振动颗粒体系类毛细行为为主的一类有争议宏观实验现象的内在机制。此项研究有望构建振动颗粒体系各种复杂现象的统一物理图像，帮助论证和检验颗粒体系静力学及流体力学理论的适用范围，指导解决各种颗粒流化相关的实际问题。

颗粒体系的流化普遍存在空间上的不均匀性，大部分受外力驱动的颗粒体系事实上是处于一种半流化状态，而不同半流化状态的颗粒体系往往可能表现出完全不同的宏观动力学行为。本项目通过实验和数值模拟研究了不同振动颗粒体系的不同流化行为，以探求其微观流化状态和宏观表现之间的关系。首先，我们研究了简单的准二维方形容器中的流化颗粒体系，定量分析了该体系从弱流化态到对流态变化时局域的静态结构及动力学特征。其次，我们详细测量了颗粒类毛细实验体系中的类毛细上升和下降数据，全方位探索了颗粒总量、粒径分散度等各种因素对观测结果的影响，并首次发现了该体系在较高振动强度下回到类毛细下降状态的重入行为。通过考虑体系内外管中颗粒流化状态以及成拱趋势的不同，我们用Janssen效应和动态Janssen效应全面地解释了该体系中的各种类毛细行为。最后，我们还研究了对称双仓体系中自发对称性破缺形成的颗粒表面高度差，并发现了该体系的高能量密度反转态可以通过耦合导致自发的振荡现象。上述所有的复杂宏观动力学行为，通过分析其对应体系内部的局域结构和流化状态，都在定性上得到了很好地理解。