Granular Fluctuation and Dissipation

颗粒涨落和耗散

• 批准号: 0305106
• 负责人: Douglas Durian
• 金额: $ 36.11万
• 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: 2003
• 资助国家: 美国
• 起止时间: 2003-06-01 至 2005-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0305106&HistoricalAwards=false
• 关键词: Granular; Fluctuation; Dissipation

This experimental research is directed at the response of noncohesive granular materials to applied forces. Strong forcing can create smooth hydrodynamic-like flow, but with microscopic fluctuations and inelastic grain-grain collisions that limit the speed of flow. Weak forcing can lead to intermittent avalanche-like flow or no flow at all. Similar behavior occurs in other materials, like foams or dense colloids or supercooled liquids; the detailed phenomenology and extent of analogy are at the forefront of condensed matter physics, under the name of jamming. Here the grain-scale fluctuations will be measured by high-speed video and by a new quasielastic laser light scattering method we call "speckle-visibility spectroscopy". One thust is to explore the extent to which the microscopic dynamics are quantitatively analogous to fluctuations in a thermal equilibrium system. Another thrust is to relate the fluctuations to dissipation, particularly in the context of impact cratering. The graduate and undergraduate students involved in this research will be trained in cutting-edge experimental technology; this will prepare them for a range of careers in academia, industry or government.%%%This research is aimed at fundamental puzzles in how granular systems, like sand, respond to applied forces. Modern society relies on handling all sorts of granular materials, ranging from foods to building supplies to pharmaceuticals and more. Yet actual equipment is surprisingly prone to sudden failure, like clogging or jamming or demixing. Ultimately, this is because we still don't know how applied forces on large systems cause relative motion between neighboring grains, which is how energy is dissipated. Here the proposed work will break new ground by combining high-speed video with a newly invented laser light scattering method. This will allow study of grain motion and energy dissipation at short enough scales to capture the crucial physics, which was not possible with prior means. Students in this program receive rigorous training in experimental methods involving modern electronic and optical physics, and can pursue careers in academic or industrial science or engineering.***

本实验研究非粘性颗粒材料对外力的响应。 强作用力可以产生平滑的流体动力学般的流动，但微观波动和非弹性颗粒之间的碰撞限制了流动的速度。 弱的强迫会导致间歇性的雪崩式流动或根本没有流动。 类似的行为发生在其他材料中，如泡沫或致密胶体或过冷液体;详细的现象学和类比的程度处于凝聚态物理学的最前沿，以干扰的名义。 在这里，颗粒尺度的波动将通过高速视频和一种新的准弹性激光散射方法来测量，我们称之为“斑点可见度光谱学”。 一个重点是探索微观动力学在多大程度上与热平衡系统中的涨落定量相似。 另一个重点是将波动与耗散联系起来，特别是在撞击坑的情况下。 参与这项研究的研究生和本科生将接受尖端实验技术的培训;这将为他们在学术界，工业界或政府部门的一系列职业生涯做好准备。这项研究的目的是解决颗粒系统（如沙子）如何响应外力的基本难题。 现代社会依赖于处理各种颗粒状材料，从食品到建筑材料到药品等等。 然而，实际的设备是令人惊讶的倾向于突然故障，如堵塞或堵塞或分层。 最终，这是因为我们仍然不知道在大型系统上施加的力如何引起相邻颗粒之间的相对运动，这就是能量如何耗散。 在这里，拟议的工作将开辟新的地面相结合的高速视频与新发明的激光散射方法。 这将允许在足够短的尺度上研究晶粒运动和能量耗散，以捕获关键的物理学，这是以前的手段所不可能的。 该项目的学生接受涉及现代电子和光学物理实验方法的严格培训，并可以从事学术或工业科学或工程领域的职业。*