Periodic solutions for three sedimenting spheres

Abstract
Exact periodic solutions are found for the relative motion of three spheres sedimenting in a Stokes fluid. Nearby solutions are found to be nearly periodic for a long time. Existence of the exact periodic solutions is proved using the point‐particle approximation and symmetry properties of Stokes equations. Numerical simulations for finite‐sized particles are performed using a method of multipole expansions.