Shake it till it moves

All students and staff welcome.

Speaker

Dr James (Jian) Guan, University of Hull

Abstract

Put a tray of liquid on a shaker, and things start to move on their own. In 2005, oil droplets were discovered to "walk" across a vibrating bath, surfing on their own waves. For over twenty years, no one could get a solid particle to do the same. Rough surfaces, awkward wetting, and badly matched fluid properties kept scrambling the bouncing rhythm a particle needs to resonate with the waves beneath it.

In this talk, I show how millimetric glass beads can walk along the interface between two immiscible liquids, and explain how added mass, viscous drag, and density ratios shape their motion. We then flip the problem on its head: instead of a solid bouncing on a fluid, what about a bubble in a shaken fluid? I reveal a new symmetry-breaking mechanism in which bubbles "gallop" by coupling their shape oscillations. They swim by flexing their bodies and using inertia rather than shedding vortices, so they keep going even where viscous swimming fails. Depending on the settings, they move in straight lines, orbit, or run and tumble.

From bead herds to bubble couriers that transport cargo, sort, and clean surfaces, I'll show how a little vibration can create surprisingly lifelike behaviour, with implications for microfluidics, soft robotics, heat transfer, and active matter.

Refreshments

Meet at 16.30 outside the lecture theatre for tea and cakes prior to the talk.