Locomotion of flexible filaments

Interaction of fluid and filaments is studied by means of three-dimensional Direct Numerical Simulation to reveal the locomotion ubiquitously exhibited by animals and vegetations. The filaments are assumed to be thin and flexible and are modelled using immersed boundary methods. A reduced integration scheme is adopted when computing the interaction forces between the fluid and filaments to improve the stability of the algorithm. After examining the vibration of a single filament in the fluid flow, multiple filaments with various initial layouts are tested. In the side-by-side arrangement, synchronization of filament motions via the oscillation of the fluid flow is observed and the deformation of the filaments are substantially suppressed by the neighbouring filaments. Such synchronization and suppression effects are much weaker in the tandem arrangement. As the rigidity of the filament increases, the synchronized motion changes from two-dimensional (in-plane) vibrations to three-dimensional (out-of-plane) rotations, during which the interactions between neighbouring filaments or sections of each individual filament become critical.