CAREER: Understanding the Physics of Turbulent Flow, Erosion and Depositional Patterns in River Systems

河流是在景观演变中起重要作用的地貌特征。由于气候变化、严重的干旱、洪水和人类干预，河流景观发生了变化，河流生态系统及其生态和经济价值以前所未有的方式响应，而这些情况中的大多数目前还无法预测。通过准确估计水流和泥沙输送的工具来理解和预测河流系统的瞬态动力学仍然有限，部分原因是监测泥沙的困难，但也因为无法理解流体动力学。本研究旨在为研究河流水系湍流、输沙和地貌变化之间的反馈提供理论和数值框架。首席研究员和学生将在机器学习的帮助下开发和实施最先进的基于物理的模型，以量化和预测现场尺度河流的流量和沉积物动态。与研究目标相结合的教育和推广计划侧重于(1)通过参与编写科学漫画书，吸引大学、本科和研究生阶段的年轻女性参与地球科学，随后开发高中课程，作为加强地球科学教学法和促进性别平等的工具；(2)通过被认为是非正式学习环境的大学艺术博物馆进行公众推广。该研究明确地解决了复杂流体动力学在河流环境中的表现，如大规模流动分离、二次流动、高速岩心俯冲、速度反转和自由剪切层；宏观湍流在泥沙输运和河流形态动力学中的作用。总体目标是在量化和预测控制河流系统形态动力学变化的流体和沉积物耦合机制的基本物理方面转变最先进的技术。将在不同的空间尺度（从实验室到大河段）开发和测试一种基于物理/机器学习的混合算法，并结合泥沙输送和形态动力学求解器。水形态动力学模型将使用大涡模拟（LES）技术来解决宏观湍流，并在计算域内预测沉积物浓度和河床演变。基于机器学习算法的动态自适应，基于过程的域重新网格划分将应用于细化湍流结构占主导地位的地区的复杂地形，这是理解和量化再循环带和俯冲流中存在的侵蚀和沉积过程的基础，从而确保足够的空间尺度分辨率来表示地貌过程。一旦基本框架得到验证，它就可以适应不同的河流环境，以测试其时空可转移性。教育部分的预期社会成果集中在：(1)加强妇女和少数民族的地球科学学习；(2)改变地球科学界对妇女的刻板印象；(3)增加妇女在地球科学领域的代表性，并创造新的性别平等素养。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Rivers are geomorphologic features that play an essential role in landscape evolution. As the river landscape changes due to climate change, severe droughts, floods, and human interventions, the fluvial ecosystems and their ecological and economic values respond in unprecedented ways, and the majority of these cases cannot currently be predicted. Understanding and predicting transient dynamics in river systems through tools that accurately estimate flow and sediment transport is still limited, partially because of the difficulty of monitoring sediment but also because of the inability to understand the fluid dynamics. This work aims to provide a theoretical and numerical framework to study the feedback between turbulent flow, sediment transport, and geomorphologic changes in river systems. The principal investigator and students will develop and implement state-of-the-art physically-based models aided by machine learning that allow the quantification and forecasting of the flow and sediment dynamics in field-scale rivers. The education and outreach plan, integrated with the research objectives, focuses on (1) engaging young women at college, undergraduate, and graduate levels into Earth science, through participatory writing for the creation of a science comic book, followed by high school curriculum development, as tools to enhance Earth science pedagogy and promote gender equity, and (2) public outreach through the university art museum that is considered to be an informal learning environment.This study addresses explicitly how convoluted fluid dynamics manifest in fluvial environments, such as regions of massive flow separation, secondary flows, high-velocity core plunges, velocity inversions, and free shear layers; and the role played by macro-turbulence in sediment transport and river morpho-dynamics. The overall objective is to transform the state of the art in quantifying and predicting the fundamental physics of the coupled fluid and sediment mechanisms that control the morpho-dynamic changes in fluvial systems. A hybrid physics-based/ machine learning algorithm coupled with a sediment transport and morphodynamic solver will be developed and tested at different spatial scales, from laboratory to large river reaches. The hydro-morphodynamic model will use the Large Eddy Simulation (LES) techniques to resolve macro-turbulence and predict the sediment concentration and riverbed evolution in the computational domain. A dynamically adaptive, process-based domain re-meshing, based on machine learning algorithms, will be applied to refine the complex topography in areas where turbulent structures are dominant and fundamental to understanding and quantifying erosion and depositional processes present in recirculation zones and plunging flows, thus ensuring a sufficient spatial scale resolution to represent geomorphologic processes. Once the fundamental framework is validated, it could be adapted to different river environments to test its spatio-temporal transferability. The expected societal outcomes of the educational component are focused on: (1) enhancing Earth science learning among women and racial minorities, (2) modifying stereotypes of women in the Earth science community, and (3) increasing the representation of women in Earth science and creating new literacy in gender equity.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.