Particle-Resolving Simulations of Cohesive Sediment Dynamics: Towards a Better Understanding of Sedimentation, Stability, and Erosion

粘性泥沙的动力学受重力、静力和水动力的相互作用所支配。地面实验室不允许孤立地研究粘聚力和粘附力，因为它们通常被重力和重力沉降的影响所掩盖。因此，现有的粘性泥沙动力学模型存在严重缺陷，无法得到可靠的颗粒间作用力大小以及由此产生的絮凝速率和可蚀性随颗粒尺寸、表面尺寸、颗粒材料和水盐度等参数变化的定标规律。这严重阻碍了对一系列环境系统的预测建模工作，在这些环境系统中，粘性沉积物发挥了中心作用，其中包括河流、湖泊、河口、沿海海洋、渔业和海底生境。通过使用粒子分辨直接数值模拟的复杂计算方法来量化粘性泥沙的动力学，拟议的研究将创建并分析一种独特类型的数据集，以提供絮凝和侵蚀过程的标度定律。这将通过增强最先进的内聚力数值模型来实现，该模型将使用在国际空间站(ISS)进行的微重力实验进行验证。所获得的数据可以作为粘聚力定标的基准，以在颗粒分辨直接数值模拟的框架内解释粘性泥沙及其周围流体的复杂相互作用。要问的问题是：(A)不同盐度和多孔性聚集体的影响能否纳入现有的相分辨模拟框架？(B)就实验基准数据而言，这种模型的准确性如何？(C)粘性泥沙的沉降速度如何随泥沙和含盐量的变化而变化？(D)团聚体的形成如何影响细颗粒沉积物和污染物/营养物的沉积行为？(E)在外部剪切力的影响下，粘性泥沙如何在改变水流条件时受到侵蚀和输送？(F)数字数据能否用于根据实验数据再现侵蚀和泥沙输移率的临界阈值？拟议的研究将在水利工程、水资源管理和地球物理科学中产生先进的预测模型。

The dynamics of cohesive sediment is governed by the interplay of gravitational, electrostatic and hydrodynamic forces. Earth-based laboratories do not allow for the investigation of cohesive and adhesive forces in isolation, as these are usually obscured by the effects of gravity and gravitational settling. Consequently, existing models for the dynamics of cohesive sediment have severe shortcomings, and reliable scaling laws for the magnitude of the inter-particle forces and the resulting flocculation rates and erodibility as functions of such parameters as grain size, surface size, grain material, and water salinity are not available. This represents a serious impediment for predictive modeling efforts of a range of environmental systems, in which cohesive sediment plays a central role, among them rivers, lakes, estuaries, the coastal ocean, fisheries and benthic habitats. By quantifying the dynamics of cohesive sediment using a sophisticated computational approach of particle-resolving Direct Numerical Simulations, the proposed research will create and analyze a unique type of dataset to provide scaling laws for flocculation and erosion processes. This will be accomplished by enhancing state-of-the-art numerical models for cohesive forces that will be validated using microgravity experiments carried out at the International Space Station (ISS). The obtained data can then serve as a benchmark for the scaling of cohesive forces to account for the complex interaction of cohesive sediment and its ambient fluid within the framework of particle-resolving Direct Numerical Simulations. Questions to be asked are (a) Can effects of varying salinity and porous aggregates be incorporated into the existing framework of phase-resolved simulations? (b) How accurate is such a model with respect to experimental benchmark data? (c) How do settling speeds of cohesive sediment vary as a function of sediment and salt concentration? (d) How does the formation of agglomerates impact on the depositional behavior of fine sediment and contaminants/nutrients? (e) How is cohesive sediment eroded and transported as it alters flow conditions under the influence of external shear? (f) Can the numerical data be used to reproduce critical thresholds for erosion and sediment transport rates from experimental data? The proposed research will result in advanced predictive models in hydraulic engineering, water resources management, and geophysical sciences.