水下滑坡失稳后演化过程的水土耦合机理和数值模型研究

The subaqueous landslide could cause intense marine environmental disaster in very large region. The post-failure evolution of the subaqueous landslide is the key issue for its unbelievable long range of sediment transport. The coupling effect between soil deformation and ambient water flow in this stage is crucial in this problem. This proposal focuses on the interfacial coupling and particle-water coupling mechanisms between soil and water. By introducing the refractive index matching technique and the florescence and scatter light-based PIV (PTV) technique, we are going to carry out series of soil water coupling experiments in which more information can be extracted comparing with the previous study. Also, the fluid field between parcel of particles will be studied using the CFD-DEM coupling method, and the influence of ambient fluid on the particle movement could be studied. In this way, three topics will be discussed: 1, how the interaction between water and soil shape the changing interface. 2, how does the ambient water change the interaction process between particles, especially in the evolution processes of the phase change of the granular assemble. 3, how does these two mechanism, i.e. the interfacial coupling mechanism and the particle coupling mechanism, interact with each other in the different stage of the debris body evolution. By this study, we can understand the soil-water coupling mechanism ruled by both interfacial and particle coupling and build up a theory for this complex problem. Further, a non-dimensional number representing the relative strength of these two mechanisms might be found to characterize the different sub-stage of the subaqueous landslide post-failure stage. A practical simulation model for subaqueous landslide evolution simulation is promised, and a simple two-dimensional depth averaged model for engineering use that could represent the above mechanism will be built up.

水下滑坡可能带来大范围、高强度的海洋环境灾害。本项目针对水下滑坡失稳后的演化过程这一重要科学问题，从土体与水体的耦合作用出发，以水土界面耦合机制和颗粒耦合机制为切入点，引入透明土、散射光—荧光示踪PIV（PTV）等新实验技术，开展水土耦合实验研究。获取土体内部结构和颗粒运动等以往实验中不易观测的关键信息，结合CFD-DEM数值模拟技术，得到颗粒间细观流场对颗粒运动的影响。深入研究：1.水和土体的相互作用如何塑造界面变化；2.周围水体如何影响土体从颗粒固体向颗粒液体（颗粒气体）的转化；3.在水下滑坡失稳后阶段上述两个机制如何共同作用等三个关键问题。从而回答水下滑坡失稳后演化阶段，水土的界面耦合及颗粒耦合的作用机制这一科学问题；分析影响因素及规律，探寻水下滑坡状态转化的临界参数；建立有实用前景的水下滑坡失稳后阶段的动力学模拟和预测模型。为水下滑坡灾害的预测和评估提供理论基础和数值分析工具。

针对水下滑坡失稳后演化过程的动力学机制和数值预测模型这一重要科学问题，项目从土体与周围水体的强耦合作用出发，以界面耦合机制和颗粒耦合机制为切入点，引入透明土、散射光—荧光示踪 PIV（PTV）等实验手段，开展了系统性的水下颗粒溃坝运动实验，首次得到了液体黏度、相对密度范围较宽条件下，颗粒相运动特性和周液流场同时测量的水下颗粒倒塌过程的测量数据集，为该方向的研究提供了基础数据集和标准算例，进一步讨论了水土相互作用过程中的能量转化机制，提供了水下颗粒滑坡后的长距输运机制的一种解释；结合 CFD-DEM 数值模拟技术，对水下滑坡失稳后阶段水体与土体的耦合作用机制进行实验和数值模拟研究，讨论两个机制与相关参数之间的关系，分析滑坡失稳后阶段两者的相互影响和促进，探寻水下滑坡状态转化的临界参数表达及其规律，在此基础上发展了新的深度积分模型，建立了有实用前景的水下滑坡失稳后演化过程的数值模拟和预测模型，克服了经典模型体系的弊端，为水下滑坡的破坏范围研究提供理论支持、分析方法和基础数据。

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