A novel and unified solution to multi-phase mass flows

泥石流是由重力驱动的土、沙、岩石和水的混合流动。固体颗粒和粘性流体控制着流体的流变性能，它们之间的耦合对流体动力学有重要影响。泥石流可以大大增加其体积和破坏潜力，并通过夹带河床沉积物而变得异常流动。混合成分的演变可以显著改变颗粒和流体的空间分布，从而改变摩擦阻力和粘滞阻力。因此，在泥石流动力学中，强烈依赖于物质组成的侵蚀-沉积和固流相分离起着至关重要的作用。正确理解这些复杂的物理过程对于准确描述冲击力、淹没区、景观演变和制定可靠的减灾计划非常重要。预测泥石流中潜在的侵蚀、相分离和沉积过程是长期存在的挑战。然而，由于缺乏数据和合适的模型，目前还没有包括观测到的侵蚀过程、被侵蚀物质的夹带和扩散过程、颗粒分选过程、相分离过程、堤防形成过程和沉积模式的脉动预测方法。基于明确考虑局部流动成分变化的侵蚀-沉积和相分离的创新力学模型（波恩大学），以及独特的井控开创性实验（乌得勒支大学）的验证，我们的目标是为这些真正的多相三维质量流动问题开发一种新颖，统一，高效和完全耦合的解决方案。与通常使用的单相模型相比，包含粘性流体、细颗粒和粗颗粒的三相混合物可以更好地描述泥石流，因此提出的模型由包括屈服强度在内的三相组成。由于波浪色散在陆块撞击水体时起着至关重要的作用，我们的新模型包括了非流体静力效应。最大的优点是，通过提出的统一三相方法，可以实现侵蚀、相分离、泥石流向浊流转变等现实的相互联系过程及其对流动结构、组成和沉积的影响。该模型将通过结合所有复杂控制过程的多组分侵蚀泥石流进行新的实验来验证。这些过程包括干燥和饱和层的侵蚀、夹带作用、颗粒分选、相分离、堤/叶状结构的形成、从陆上到海底环境的流动转化以及碎屑沉积随储层液面变化的演化。因此，本项目产生了一个先进的开源质量流模拟模型，旨在准确预测泥石流动力学、相分离、侵蚀、沉积和跳动。因此，该模型将在很大程度上帮助减轻泥石流危害，减少全世界的损失和死亡人数。

Debris flows are gravity driven mixture flows of soil, sand, rock and water. The solid particles and viscous fluid governs the rheological properties, and their coupling significantly influences the dynamics. Debris flows can dramatically increase their volume and destructive potential, and become exceptionally mobile by entraining bed sediment. The mixture composition can evolve to strikingly change the spatial distribution of particles and fluid, and thus frictional and viscous resistance. So, erosion-deposition and phase-separation between solid and fluid, which strongly depend on material composition, play a critical role in debris flow dynamics. Proper understanding of these complex physical processes is very important in accurate description of impact forces, inundation areas, landscape evolution and developing reliable mitigation plans. Predicting the underlying processes of erosion, phase-separation and deposition in debris flow are long-standing challenges. However, due to lack of data and suitable models, there exists no runout prediction method that includes observed processes of erosion, entrainment and diffusion of eroded material, grain sorting, phase-separation, levee formation and deposition patterns.Based on innovative mechanical models for erosion-deposition and phase-separation that explicitly consider changes in local flow compositions (Univ. Bonn), and their validations with unique well controlled pioneering experiments (Univ. Utrecht), we aim to develop a novel, unified, efficient and fully coupled solution to these true multi-phase, three-dimensional mass flow problems. As debris flows are better described by a three-phase mixture that include viscous fluid, and fine and coarse grains as compared to often used single-phase models, proposed model consists of three-phases including yield strength. As wave-dispersion plays a critical role when a landmass impacts a water body, our novel model includes non-hydrostatic effects. Great advantage is that with such a proposed unified three-phase approach, realistic inter-connected processes of erosion, phase-separation, flow transformation from debris flow to turbidity current and their influences on the flow structure, composition and deposition can be achieved. The model will be validated by conducting new experiments with multi-component erosive debris flows combining all complex governing processes. These processes include erosion of dry and saturated beds, entrainment, particle sorting, phase-separation, levee/lobe formation, flow transformation from the subaerial to submarine environment and evolution of debris deposits with variable reservoir fluid level. Thus, this project results in an advanced open source mass flow simulation model aiming to accurately predict debris flow dynamics, phase-separation, erosion, deposition and runout. As such, the model will substantially help debris-flow hazard mitigation and reduce damage and fatalities worldwide.