Assessing the performance of flexible barrier subjected to impacts of typical geophysical flows: a unified computational approach based on coupled CFD/DEM

Flexible barriers have been increasingly used in the mitigation of destructive geophysical flows, including rock avalanches, debris avalanches, debris flood, muddy debris flows as well as muddy flows. No rigorous analytical tools are available for the design of flexible barriers to resist a wide spectrum of geophysical flows of different natures and over a broad Froude-number range. Responses of a flexible barrier to the impacts of geophysical flows are known to be exceedingly complicated, involving intricate multi-body, multi-phase interactions, mass exchange and transportation and energy transformation/dissipation which are challenging for both numerical and physical modelers. To investigate the complex interactions between channelized geophysical flows and a non-uniform flexible barrier, a unified hydro-mechanical modeling framework was developed based on the coupled computational fluid dynamics and discrete element method (CFD/DEM). Five typical geophysical flows were modeled, for instance, a muddy debris flow was considered as a mixture of a continuous viscous fluid phase and a discrete phase consisting of gap-graded frictional particles. A permeable flexible barrier consisting of deformable meshes, cables and energy dissipators was modeled by applying the DEM accounting for connections and contact in a realistic manner. The coupled CFD/DEM model was well validated by experimental data in the literature. Based on the simulations, we examined the dynamics of flow-barrier interactions, energy dissipation mechanism, regime quantification, peak-static load ratio, momentum reduction and the correlations between flow Froude number/solid fraction and the impact mechanism transitions. It was observed that the peak-static load ratio in a flexible barrier increases while the barrier-induced momentum reduction of overflow decreases with increasing flow Froude-number. The analyses of the peak-static load ratio showed that rock avalanches generate the largest one and muddy flows generate the lowest one. For the first time, the impact mechanism transitions from pile-up to run-up for five geophysical flows impacting on a non-uniform flexible barrier were quantitatively identified according to the approaching flow dynamics and solid fraction. (The study was supported by RGC/HK under T22-603/15N and GRF#16205418.​)