title: Impact on soft sand: void collapse and jet formation.
abstract: Very fine sand is prepared in a well-defined and fully decompactified state by letting gas bubble through it. After turning off the gas stream, a steel ball is dropped on the sand. On impact of the ball, sand is blown away in all directions ("splash") and an impact crater forms. When this cavity collapses, a granular jet emerges and is driven straight into the air. A second jet goes downwards into the air bubble entrained during the process, thus pushing surface material deep into the ground. The air bubble rises slowly towards the surface, causing a granular eruption. In addition to the experiments and the discrete particle simulations we present a simple continuum theory to account for the void collapse leading to the formation of the upward and downward jets.
authors.affiliation: Faculty of Science and J. M. Burgers Centre for Fluid Dynamics, University of Twente, 7500 AE Enschede, The Netherlands.
authors.forename: Detlef
authors.initials: D
authors.lastname: Lohse
authors.forename: Raymond
authors.initials: R
authors.lastname: Bergmann
authors.forename: René
authors.initials: R
authors.lastname: Mikkelsen
authors.forename: Christiaan
authors.initials: C
authors.lastname: Zeilstra
authors.forename: Devaraj
authors.initials: D
authors.lastname: van der Meer
authors.forename: Michel
authors.initials: M
authors.lastname: Versluis
authors.forename: Ko
authors.initials: K
authors.lastname: van der Weele
authors.forename: Martin
authors.initials: M
authors.lastname: van der Hoef
authors.forename: Hans
authors.initials: H
authors.lastname: Kuipers