Influence Of Grain Properties On Jumps During Free Surface Granular Flows

Abstract

Granular flows may feature liquid and gaseous states despite their solid composi¿on. They can also dissipate significant amounts of energy through internal collisions and fric¿onal contacts. In many real-world scenarios, strong varia¿ons in the free surface and internal proper¿es of the granular flow occur upon impac¿ng an obstacle or facing a change in the slope. This thesis studies these changes at slow and fast regimes, referred to as subcri¿cal and supercri¿cal, respec¿vely.

Changes in the surface of supercri¿cal flows are examined in the context of granular jumps, which commonly occur when a fast and dilute flow experiences an abrupt slowdown, producing an increase in density and height to compensate for the velocity loss. Granular jumps typically occur during the retainment of avalanches and landslides by structures for which es¿ma¿ng their final height becomes relevant to prevent an overflow. To address this, this work studies a wide range of granular jumps using discrete element method (DEM) simula¿ons to study the flow characteris¿cs that influence the final height of the flow.

Regarding the subcri¿cal flow regime, the changes in the free surface are studied experimentally using a conveyor belt setup, where a granular mass is displaced towards an obstacle, crea¿ng a heap in the free surface upon impact. The surface varia¿ons and internal velocity fields are studied using x-ray radiography from two perpendicular direc¿ons.

The results from these setups address a significant gap in understanding the changes in the free surface of granular flows at different flow regimes.