Each flake is a small sphere that is dragged along by the liquid and sinks through it. At low Reynolds number the Stokes drag is F = 6πμ r v, so the flake relaxes towards the local liquid velocity with time constant τp = 2ρp r²/(9μ) while settling at vt = 2(ρp − ρf) g r² / (9μ). The simulation integrates dv/dt = (u − v)/τp − vt/τp, where u is the swirling liquid velocity set up by a shake.
The swirl decays viscously with τf = R²/(ν j²) (j = 2.405 is the first zero of J0, a standard estimate for a bounded container), so a thicker liquid (glycerine mixture) calms down much sooner and flakes fall more slowly. The Stokes law holds only while the particle Reynolds number Re = 2 r vt/ν stays below about 0.5, which the readout flags.
Honest simplifications: the liquid motion is a prescribed decaying swirl rather than a Navier-Stokes solution, flakes do not interact or feel buoyant turbulence, the globe is a 2D slice, and wall bounces are simple reflections.