A document by Yong Kong. Click on the document to view its contents.

A document by Yong Kong. Click on the document to view its contents.

A document by Yong Kong. Click on the document to view its contents.

Multiphase geophysical flows impacting slit-check dams can create jammed and mobilized domains, which partially govern the overspreading, energy-breaking, and trapping dynamics. This study presents systematic numerical simulations of debris flows, debris avalanches, and rock avalanches against single-slit structures with narrow, medium, and broad openings, using the coupled computational fluid dynamics and discrete element method (CFD-DEM). A typical debris flow is treated as a mixture of discrete particles (by DEM) and a continuous slurry (by CFD). This model well captures essential physics observed in experiments. We show how flow materials, dynamics, and barrier filters alter the impact-induced jammed and mobilized domains that possibly affect the energy-breaking efficiency. Our results reveal that flow materials (wet versus dry) and dynamics (slow versus fast) jointly drive the hazardous overspreading dynamics, while slit openings dominate the trapping patterns, including clogging with domes, blockage, and self-cleaning.

Geophysical flows impacting a flexible barrier can create complex flows and solid-fluid-structure interactions, which are challenging to quantify and characterize towards a unified description. Here, we examine the common physical laws of multiphase, multiway interactions during debris flows, debris avalanches and rock avalanches against a flexible barrier system using a coupled computational fluid dynamics and discrete element (CFD-DEM) method. This model captures essential physics observed in experiments and fields. The bi-linear, positive correlations are found between peak impact load and Fr or maximum barrier deflection, with inflection points due to the transitions from trapezoid-to triangle-shaped dead zones. Our findings quantitatively elucidate how flow materials (wet versus dry) and impact dynamics (slow versus fast) control the patterns of the identified bi-linear correlations. This work offers a physics-based reference and insights for improving widely-used impact solutions for geophysical flows against flexible barriers.

Flood retention lakes (RLs) are widely employed in rural-urban catchments with low impacts on the natural environment. While hydrologic models have been commonly applied to evaluate RLs’ performances, insights are lacking over the consequences of a wide climatic variability, particularly those corroborated by 2D hydrodynamic models. Thus, this study aims to conduct a systematic catchment-scale evaluation of RL effectiveness; blueprinted RLs with various geographic configurations are also considered in addition to the individual RL. A 2D hydrodynamic model is verified to be capable of simulating flood events in the rural-urban catchment interacted with RLs. Under a wide range (1- to 15- hour duration and 1- to 100-year return period) of rainstorm scenarios, the RL has a satisfactory performance within an L-shaped band in the frequency-duration diagram. The L-shaped band coincides with moderate return periods (10- to 25- year) and large durations (> 6 hours) or small durations (< 4 hours) and large return periods (> 25-year), whereas different criteria yield different optimal combinations. With the increase of event size, 4 typical stages of RL-river interactions are characterized, which projects the catchment-scale performances. Blueprinted RLs with distributed and parallel connections mitigate larger areas of inundation in sub-watersheds than aggregated and series ones. Upstream controls are less effective than downstream controls under moderate events while the relation is reversed for extreme events. Critical changing factors concerning RL-river interactions and spatiotemporal rainstorm variabilities prompt comprehensive considerations of both local-scale RL configurations and catchment-scale climate characterizations.