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

河流是地貌特征，在景观演变中起着至关重要的作用。由于气候变化、严重干旱、洪水和人为干预导致河流景观发生变化，河流生态系统及其生态和经济价值以前所未有的方式做出反应，其中大多数情况目前无法预测。通过准确估计水流和泥沙运移的工具了解和预测河流系统中的瞬变动态仍然有限，部分原因是监测泥沙的困难，但也因为无法了解流体动力学。这项工作旨在为研究河流系统中湍流、泥沙输移和地貌变化之间的反馈提供一个理论和数值框架。首席研究人员和学生将开发和实施最先进的基于物理的模型，并辅助机器学习，使之能够量化和预测田间尺度河流中的水流和泥沙动力学。教育和推广计划与研究目标相结合，重点是(1)通过参与性写作创建一本科学漫画书，吸引大学、本科生和研究生水平的年轻女性进入地球科学，随后是高中课程开发，作为加强地球科学教学和促进性别平等的工具，以及(2)通过被认为是非正式学习环境的大学美术馆的公共推广。这项研究明确地阐述了复杂的流体动力学如何在河流环境中表现出来，例如大流量分离、二次流动、高速岩心骤降、速度反转和自由剪切层；以及宏观湍流在泥沙输移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中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改变最先进的状态。将开发一种基于物理和机器学习的混合算法，并将其与泥沙输运和地貌动力学解算器相结合，在不同的空间尺度上进行测试，从实验室到大河段。水地貌模型将使用大涡模拟(LES)技术来解决宏观湍流，并在计算域中预测含沙量和河床演变。基于机器学习算法的动态自适应、基于过程的区域重新划分将用于细化湍流结构占主导地位的地区的复杂地形，这是理解和量化回流区和骤降流中存在的侵蚀和沉积过程的基础，从而确保有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侧重于：(1)加强妇女和少数族裔的地球科学学习，(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中的代表性，创造新的性别平等扫盲。这一奖项反映了国家科学基金会的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，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.