Breaking Stokes' reversibility through nonlinear hydrodynamic interactions

When well-separated rigid objects in a viscous fluid are subjected to an alternating drive, their net translation vanishes due to Stokes' reversibility. We study the breaking of reversibility through nonlinear hydrodynamic interactions, brought about by an intrinsic response of the objects to the drive. The responsiveness may arise, for example, from changes in the objects' shapes or their positions in an external potential. This nonlinear effect may be used to concentrate or disperse an assembly of particles in the limit of zero Reynolds number using an alternating drive. We demonstrate it in a simple simulation of forced flexible objects.