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.

这个NSF-CASIS项目将在国际空间站（ISS）和地球上进行一系列实验，以了解重力在泥泞动力学中的作用。众所周知，降雨触发了最近燃烧的斜坡上的泥流。野火过后，表面燃烧的土壤是防水或疏水的，可防止降雨并导致突然和快速的泥泞。野火后重力驱动的泥浆是不可预测的，突然发生，然后迅速下坡行驶，变成碎屑流，动员大而重的巨石。 2018年1月，在加利福尼亚州蒙特西托（Montecito），一次剧烈的15分钟爆发变成了毁灭性的碎片流，造成了21人死亡，造成了4.21亿美元的损失和关闭的关键过境走廊。实验将研究疏水土壤颗粒与气泡的附着如何导致形成聚集体，这可能会导致泥流中观察到的异常流动行为。粒子空气 - 水混合物形成有趣的结构（气泡，管道和簇），其形状主要由重力与气泡与防水颗粒之间的吸引力之间的平衡控制。 ISS和地球上的实验将使用由通过化学处理，空气和水制成的沙子组成的模型系统。混合后，该材料将流过有机玻璃通道，粒子运动和聚集体的演变将成像并与整体流动的特征相关。通过将ISS上的实验与地球上的实验进行比较，将了解重力在骨料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降雨强度和持续时间的影响，并可能导致更好的早期进行系统和风险评估。研究团队将包括学生，尤其是来自代表性不足的团体的学生，该项目将支持当地社区的高中生教育活动。 该项目的目的是在地球上和微重力条件下进行实验，以将泥流组成与微力水平的流和传输特性相关联。了解重力对流动空气水 - 粒子混合物的微结构变化的作用，尤其是在形成粒子浸泡聚集体的作用对于预测泥流的流变行为至关重要。实验将集中于泥流剪切行为如何取决于水，被困的空气和各种大小的颗粒的相对量。地球上的实验将确定混合物组成如何影响流动行为，并描述要在ISS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聚集在混合流和运输方面的后果。结果将用于得出可以描述混合物流动行为的方程，包括混合流变性对流动的影响。了解有关降雨强度和持续时间的泥石流启动过程将导致更准确的预测能力，以减轻泥石流的发作和发展，从而可以减轻灾难性损害。这一奖项反映了NSF的法定任务，并通过评估该基金会的知识绩效和广泛的影响来评估NSF的法定任务，并被视为值得的支持。