Hydrodynamics of multiple self-propelled flapping flexible plates

Inherent hydrodynamic mechanism for aggregates of active swimmers has attracted significant attention. We here study the collective behavior of multiple self-propelled flexible plates by means of the numerical simulation of fluid-structure interaction, which are driven by sinusoidally oscillating motions of identical frequency and amplitude at the leading-edges of the plates. Both fast mode with compact configurations and slow mode with sparse configurations were observed. The Lighthill conjecture that orderly configuration may emerge passively from hydrodynamic interactions was verified with multiple plates. The whole group may consist of subgroups and individuals with regular separations. Hydrodynamic forces experienced by the plates near their multiple equilibrium locations are all springlike restoring forces, which stabilize the orderly formation and maintain group cohesion. For the cruising speed of the whole group, the leading subgroup or individual plays the role of 'leading goose'.