ISS: A new paradigm for explaining catastrophic post-wildfire mudflows: transport phenomena and gravity-driven aggregation dynamics of hydrophobic particle-air-water mixtures

国际空间站：解释灾难性野火后泥石流的新范例：疏水性颗粒-空气-水混合物的传输现象和重力驱动的聚集动力学

• 批准号: 2025643
• 负责人: Ingrid Tomac
• 金额: $ 40万
• 依托单位: University of California-San Diego
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-10-01 至 2024-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2025643&HistoricalAwards=false
• 关键词: ISS; new; paradigm; explaining; catastrophic

This NSF-CASIS project will conduct a series of experiments on board the International Space Station (ISS) and on Earth to understand the role of gravity in the dynamics of mudflows. It is well established that rainfall triggers mudflows on recently burned slopes. After wildfires, the surficial burned soil is water-repellent or hydrophobic, preventing rain infiltration and leading to sudden and rapid mudflows. Post-wildfire gravity-driven mudflows are unpredictable, occur suddenly, and travel rapidly downhill, turning into debris flows and mobilizing large and heavy boulders. In January 2018 in Montecito, California, an intense 15-minute burst turned into a devastating debris flow which caused 21 deaths, led to $421 million in damages, and closed key transit corridors. The experiments will examine how the attachment of hydrophobic soil particles to air bubbles leads to the formation of aggregates that may give rise to the unusual flow behaviors observed in mudflows. Particle-air-water mixtures form interesting structures (bubbles, pipes and clusters) whose shapes are primarily governed by a balance between gravity and the attractive forces between air bubbles and water-repellent particles. The experiments on the ISS and on Earth will use a model system consisting of sand particles that have been made hydrophobic through a chemical treatment, air and water. After mixing, the material will flow through a plexiglas channel, and particle motions and evolution of aggregates will be imaged and correlated with characteristics of the overall flow. By comparing experiments on the ISS with those on Earth, the role of gravity in aggregate formation and flow behavior will be understood. The results of this study will help understand how mudslides are affected by rainfall intensity and duration and could lead to better early-warning systems and risk evaluation. The research team will include students, especially those from underrepresented groups, and the project will support educational activities to high-school students in local communities. The goal of this project is to run experiments on Earth and in microgravity conditions to correlate mudflow composition with flow and transport characteristics on a micromechanical level. An understanding of the role of gravity on microstructural changes in flowing air-water-particle mixtures and, in particular, on the formation of particle-bubble agglomerates is crucial for predicting the rheological behavior of mudflows. Experiments will focus on how mudflow shear behavior depends on relative amounts of water, trapped air, and particles of various sizes. Experiments on Earth will identify how the mixture composition affect flow behavior and will delineate critical parameter ranges to be tested on board the ISS. Microgravity experiments will study the dynamics of hydrophobic particle attachment to air bubbles and the consequences of agglomeration on mixture flow and transport. Results will be used to derive governing equations that can describe the flow behavior of the mixtures, including effects of mixture rheology on the flow. Understanding the processes of mudslide initiation with respect to rainfall intensity and duration will lead to a more accurate predictive capability for the onset and development of mudslides that could mitigate catastrophic damage.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 NSF-CASIS 项目将在国际空间站 (ISS) 和地球上进行一系列实验，以了解重力在泥石流动力学中的作用。众所周知，降雨会在最近被烧毁的斜坡上引发泥石流。野火发生后，表面烧焦的土壤具有防水性或疏水性，可防止雨水渗透并导致突然而快速的泥石流。野火后重力驱动的泥石流不可预测，发生突然，并迅速下坡，变成泥石流并移动大而重的巨石。 2018 年 1 月，加利福尼亚州蒙特西托发生了一场持续 15 分钟的强烈爆发，最终演变成毁灭性的泥石流，造成 21 人死亡，造成 4.21 亿美元的损失，并导致主要交通走廊关闭。这些实验将研究疏水性土壤颗粒与气泡的附着如何导致聚集体的形成，而聚集体可能会导致泥石流中观察到的异常流动行为。颗粒-空气-水混合物形成有趣的结构（气泡、管道和簇），其形状主要由重力以及气泡和防水颗粒之间的吸引力之间的平衡决定。国际空间站和地球上的实验将使用由沙粒、空气和水组成的模型系统，沙粒经过化学处理而变得疏水。混合后，材料将流过有机玻璃通道，颗粒运动和聚集体的演变将被成像并与整体流动的特征相关联。通过将国际空间站上的实验与地球上的实验进行比较，我们将了解重力在聚集体形成和流动行为中的作用。这项研究的结果将有助于了解泥石流如何受到降雨强度和持续时间的影响，并可能导致更好的预警系统和风险评估。研究团队将包括学生，特别是来自代表性不足群体的学生，该项目将支持当地社区高中生的教育活动。 该项目的目标是在地球上和微重力条件下进行实验，以在微机械水平上将泥浆流成分与流动和传输特性相关联。了解重力对流动空气-水-颗粒混合物微观结构变化的作用，特别是对颗粒-气泡团聚体形成的作用，对于预测泥浆流的流变行为至关重要。实验将重点研究泥浆流剪切行为如何取决于水、截留空气和各种尺寸颗粒的相对量。地球上的实验将确定混合物成分如何影响流动行为，并将描绘出在国际空间站上测试的关键参数范围。微重力实验将研究疏水颗粒附着在气泡上的动力学以及团聚对混合物流动和运输的影响。结果将用于推导控制方程，该方程可以描述混合物的流动行为，包括混合物流变学对流动的影响。了解泥石流引发过程与降雨强度和持续时间的关系，将为泥石流的发生和发展提供更准确的预测能力，从而减轻灾难性损害。该奖项反映了 NSF 的法定使命，并通过使用评估结果被认为值得支持。基金会的智力价值和更广泛的影响审查标准。