Cracking of submerged beds

TL;DR

This study explores how projectile impacts cause crater formation and gas release in submerged beds of hydrophobic particles, revealing unique scaling laws and the role of the granular skin in the impact process.

Contribution

It introduces a new understanding of impact dynamics in submerged hydrophobic granular beds, highlighting the formation of a granular skin and its cracking behavior.

Findings

Crater morphology follows different scaling laws than dry beds.

Gas release volume depends on impact velocity, bed depth, and water column depth.

Granular skin provides rigidity and influences impact outcomes.

Abstract

We investigate the phenomena of crater formation and gas release caused by projectile impact on underwater beds, which occurs in many natural, geophysical, and industrial applications. The bed in our experiment is constructed of hydrophobic particles, which trap a substantial amount of air in its pores. In contrast to dry beds, the air-water interface in a submerged bed generates a granular skin that provides rigidity to the medium by producing skin over the bulk. The projectile's energy is used to reorganise the grains, which causes the skin to crack, allowing the trapped air to escape. The morphology of the craters as a function of impact energy in submerged beds exhibits different scaling laws than what is known for dry beds. This phenomenon is attributed to the contact line motion on the hydrophobic fractal-like surface of submerged grains. The volume of the gas released is a function of multiple factors, chiefly the velocity of the projectile, depth of the bed and depth of the water column.