基于固-液耦合作用的泥石流冲击机理研究

The debris flow impact load is an important component of the debris flow dynamic properties. Meanwhile, the estimated impact load is the basis of the protective structure design. The obstacle of understanding the debris flow-structure interaction is not from the properties of protective structures, but from the diversity and complexity of two-phase debris flows themselves. Currently, the debris flow load models are mostly semi-empirical. Specifically, there have to be certain formulae or empirical parameters for certain types of debris flows, e.g., diluted debris flows and viscous debris flows. The essential reason is the lack of understanding of debris impact mechanisms, especially the effects of solid-fluid coupling on the dynamics of debris flows. In this study, the methodology adopted includes theoretical analysis, flume impact tests, and two-phase numerical simulation (CFD-DEM). The main variable of the physical tests is the solid fraction of debris flows. The objectives are to determine the key dimensionless number that depicts the behavior of solid-fluid coupling and to reveal the mechanisms of debris impact on protective structures. A newly-developed load model which covers the spectrum of diluted debris flows and viscous debris flows will be proposed. Research outcomes of this study will shed light on the complex dynamic properties of debris flows. Furthermore, research outcomes will facilitate the optimization of protective structures and the development of a sustainable mountainous area.

泥石流冲击荷载是泥石流动力特性的重要组成部分，也是泥石流防护结构的设计依据。泥石流冲击防护结构问题的复杂之处不在于防护结构的特性，而在于泥石流作为一种两相流体本身的多样性和复杂性。目前的泥石流冲击荷载模型多为半经验性质，具体表现为针对不同类型的泥石流，如固相含量不同的稀性和粘性泥石流，通常采用不同的荷载计算公式或者不同的经验参数。其本质原因在于对泥石流冲击机理的认识不清，尤其是固-液耦合作用对泥石流动力特性的影响。本项目采用理论分析、水槽实验、计算流体力学与离散元耦合的数值方法等手段，以固相含量为主要变量，以微观层面的固-液耦合作用为主线，提取固-液耦合作用的无量纲数学表达，研究泥石流的冲击机理，构建涵盖稀性和粘性泥石流的冲击荷载模型。研究成果可以提高对泥石流动力特性的认识，同时对优化防护结构型式和实现山区可持续发展具有重要现实意义。

泥石流冲击荷载是泥石流防护结构设计的重要参数，也是验证泥石流动力学理论模型的可靠严谨的手段。但是目前的泥石流应用方面的研究（包括冲击力等）均把两相的泥石流当作单相流体来对待，忽略了其中的固液耦合作用对动力学特性的影响。本项目通过理论分析、水槽实验和数值模拟等综合研究手段，以体积固相浓度为主要变量，以微观层面的固-液耦合作用为主线，系统地研究了体积固相浓度对泥石流冲击行为的影响和两相流流态对泥石流动力学行为的调控，通过实验结果验证了Vertical jet 和 Momentum jump两种理论模型的适用性及适用范围（宏观的Froude数Fr=3-4为阈值）；最后，从动量和能量角度论证了泥石流冲击刚性和柔性结构的冲击动力学特性。研究成果提高了对泥石流动力特性的认识，赋予了冲击荷载模型清晰的物理意义；对优化防护结构型式具有重要现实意义。