滑坡–堵江–涌浪灾害链模拟的DEM–CFD耦合分析方法及其应用

Coupled DEM–CFD Method for Landslide–river Blockage–impulse Wave Disaster Chain Simulation and its Application

滑坡–堵江–涌浪灾害链的演化过程涉及复杂的滑坡–河流相互作用。为了真实再现这一演进过程,本文提出了一种扩展的离散元法(DEM)与计算流体动力学(CFD)耦合数值方法,通过在局部平均DEM–CFD耦合方法中引入流体体积法(VOF)建立了一套能够描述河流自由水面演化的扩展DEM–CFD耦合数值框架,实现了对滑坡涌浪形成及传播过程的追踪;并提出了一种新的局部孔隙率计算方法即虚拟球模型,来克服网格颗粒临界尺寸比的限制,从而实现复杂地形建模要求;进一步通过多个典型算例验证其准确性和有效性。在此基础上,开展了滑坡–堵江–涌浪灾害链演化模拟,并应用至白格滑坡坝形成过程复演,深入分析了滑坡–河流动态演化过程及耦合作用机理。结果表明:所提出的方法能够准确模拟滑坡–河流相互作用;滑坡–河流–河谷地形的耦合作用驱动了灾害演化,滑坡体驱动了涌浪的传播,而河流则增加了滑坡体的动能耗散,且对其沉积过程在河流流向上产生相反影响;模拟得到的白格滑坡运移路径、沉积形态及涌浪侵蚀面积与实地调查结果吻合度较高,成功再现了2018年10月11日白格滑坡堵江事件。本文所提出的扩展DEM–CFD耦合数值方法为深入研究滑坡–堵江–涌浪灾害链演化机制提供了有力的数值工具,对于灾害预测及防灾减灾策略的制定具有一定的参考价值。

The intrusion of landslides into a river can block the river and induce surge waves. The evolution of the landslide–river blockage–surge wave disaster chain involves complex landslide–river interactions. To reproduce it realistically, an extended coupled discrete element method(DEM) and computational fluid dynamics(CFD) numerical method is proposed in this research: the VOF model is introduced to track the evolution of river free surface;a virtual sphere model is proposed to overcome the limitation of the critical size ratio of the mesh and particle;and the model is verified by several typical cases. Based on this, the simulation of the landslide–river blockage–surge wave disaster chain was carried out to reproduce the formation process of the Baige landslide-induced river damming, and the dynamic evolution process and interaction mechanism of landslide–river dynamics are investigated comprehensively. The results show that the proposed method can accurately simulate the landslide–river interaction during the evolution of landslide–river blockage–surge wave disaster chain;the landslide mass drives the propagation of surge waves, while the river significantly increases the kinetic energy dissipation of the landslide mass and has opposites effect on the deposition of the landslide along the flow directions;the simulated migration path, deposit morphology and wave erosion area of the Baige landslide are in good agreement with the field survey results, and the method successfully reproduces the October 11th, 2018 Baige landslide. The extended coupled DEM–CFD method proposed in this research provides a robust numerical tool for the understanding of the river blockage and impulse wave evolution mechanism, as well as the prediction of the disaster evolution process, which is of reference value for the of disaster emergency response and disaster mitigation strategies.