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

粘性沉积物的动力学受重力、静电力和水动力的相互作用支配。地面实验室不允许单独研究内聚力和粘附力，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，颗粒间作用力的大小以及由此产生的絮凝速率和可蚀性作为粒度、表面尺寸、颗粒材料和水盐度等参数的函数的可靠标度规律是不可用的。这对一系列环境系统的预测建模工作构成了严重障碍，在这些系统中，粘性沉积物起着核心作用，其中包括河流、湖泊、河口、沿海海洋、渔业和底栖生物栖息地。通过使用粒子解析直接数值模拟的复杂计算方法来量化粘性沉积物的动力学，本研究将创建和分析一种独特的数据集，以提供絮凝和侵蚀过程的尺度规律。这将通过加强最先进的内聚力数值模型来实现，这些模型将通过在国际空间站（ISS）进行的微重力实验进行验证。所获得的数据可以作为内聚力尺度的基准，以解释颗粒解析直接数值模拟框架内粘性沉积物及其周围流体的复杂相互作用。需要提出的问题是(a)是否可以将不同盐度和多孔聚集体的影响纳入相分辨模拟的现有框架？(b)这种模型相对于实验基准数据有多准确？(c)粘性沉积物的沉降速度如何随沉积物和盐浓度的变化而变化？(d)团块的形成如何影响细沉积物和污染物/营养物的沉积行为？(e)粘性泥沙在外部剪切作用下改变流动条件时是如何被侵蚀和运移的？(f)能否利用数值数据从实验数据中再现侵蚀和泥沙输送率的临界阈值？这项研究将为水利工程、水资源管理和地球物理科学提供先进的预测模型。

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.