Dynamics of Slow Granular Flow

慢速颗粒流动力学

• 批准号: 0070329
• 负责人: Douglas Durian
• 金额: $ 37.5万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-04-15 至 2003-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0070329&HistoricalAwards=false
• 关键词: Dynamics; Slow; Granular; Flow

This experimental condensed matter physics project will investigate the dynamics of granular flows that exhibit on/off intermittency. Such behavior is very common, but traditional measurement techniques do not have sufficient resolution and dynamic range to capture the very rapid grain-grain collisions and the slow on/off switching of the flows. A new approach will be employed in which this information is extracted from the second- and fourth-order intensity correlation functions for temporal fluctuations in the intensity of light multiply-scattered by the sample. Data will be obtained for intermittent surface flows (avalanches), Couette flows (stick-slip), and vibrated flows (periodic). Particular interest is in the crossover between smooth and intermittent flows as a function of forcing rate. This should aid in testing and developing theories, which are currently limited to either quasi-static or fully-fluidized regimes. This should be useful in a wide variety of industries, where transport and processing of granular materials is now accomplished only with great inefficiency. Insight may also be gained into closely related geophysical events such as landslides, erosion, and earthquakes. The project provides excellent training for graduate students in state-of-the art experimental methods and for introducing them to materials and topics at the forefront of modern condensed matter physics.%%%This experimental condensed matter physics project investigates the microscopic dynamics of granular flows that are slow and, hence, intermittent. Such behavior is familiar to anyone who has slowly poured a small amount of sand from a bucket, or rice from a bag, or tried to shake out one pill from a bottle. These flows are all smooth, like a liquid, only if very fast; if slow, they are intermittent via a series of avalanches. This behavior is important in a wide variety of industries, where foods, pharmaceutical and ceramic powders, building materials, raw ores, etc. need to be -but are often not- processed and transported efficiently without jamming. This behavior is also important in geophysical events such as landslides, erosion, and earthquakes. In spite of their ubiquity and importance, slow flows and the crossover to smooth fast flows are not yet understood. Current engineering theories are applicable only to smooth flows, and current physics theories are applicable only to very infrequent flows; none can capture the full range of behavior. The usual experimental methods are also incapable of simultaneously capturing the rapid grain motion during flow along with the slow on-off switching of the flow itself. This project will do so, for the first time, by state-of-the-art techniques involving photon correlations from laser light bounced off a sample. In addition to practical impact on industry and geophysics, this project will provide excellent training for students in new experimental methods and will introduce them to materials and topics at the forefront of modern condensed matter physics.

这个实验性凝聚态物理项目将研究表现出开/关间歇性的颗粒流的动力学。这种行为非常常见，但传统的测量技术没有足够的分辨率和动态范围来捕获非常快速的颗粒与颗粒的碰撞以及流动的缓慢开/关切换。将采用一种新方法，从二阶和四阶强度相关函数中提取该信息，以了解样本多重散射光强度的时间波动。将获得间歇表面流（雪崩）、库埃特流（粘滑流）和振动流（周期性）的数据。特别令人感兴趣的是平滑流和间歇流之间的交叉作为强制速率的函数。这应该有助于测试和发展理论，这些理论目前仅限于准静态或完全流化状态。这应该在许多行业中都有用，在这些行业中，颗粒材料的运输和加工现在只能以非常低的效率完成。还可以深入了解密切相关的地球物理事件，例如山体滑坡、侵蚀和地震。该项目为研究生提供最先进的实验方法方面的优秀培训，并向他们介绍现代凝聚态物理最前沿的材料和主题。%%%该实验凝聚态物理项目研究颗粒流的微观动力学速度很慢，因此是间歇性的。对于那些慢慢地从桶中倒入少量沙子、从袋子中倒出少量大米、或试图从瓶子中摇出一颗药丸的人来说，这种行为是很熟悉的。这些流动都是平滑的，就像液体一样，但前提是速度非常快；如果速度很慢，它们就会通过一系列雪崩而间歇性地发生。这种行为在许多行业中都很重要，在这些行业中，食品、药品和陶瓷粉末、建筑材料、原矿石等需要（但通常不会）在不堵塞的情况下进行有效加工和运输。这种行为在山体滑坡、侵蚀和地震等地球物理事件中也很重要。尽管慢流普遍存在且很重要，但慢流和平滑快速流的交叉尚不清楚。当前的工程理论仅适用于平滑流动，当前的物理理论仅适用于非常罕见的流动；没有人能够捕获全部行为。通常的实验方法也无法同时捕获流动过程中颗粒的快速运动以及流动本身的缓慢开关。该项目将首次利用最先进的技术来实现这一目标，该技术涉及从样品反射的激光的光子相关性。除了对工业和地球物理学的实际影响外，该项目还将为学生提供新实验方法的良好培训，并向他们介绍现代凝聚态物理前沿的材料和主题。