Coupled states of flapping flags

Experiments concerning the oscillatory motion of thin flexible filaments lying in flowing soap films have shown particularly interesting phenomena. For example, when two such "flapping" filaments were introduced to the flowing soap film the filaments oscillated in-phase (asymmetry) or in anti-phase (symmetry) depending only on their mutual separation. We have been able to numerically simulate these experiments and provide some additional data on how the interaction changes when the filament separation is varied. Our results show that the fundamental frequency is dominant (single mode) and that the oscillation consists of an asymmetric system for small separations. For larger separations of about one half of the filament length, the fundamental frequency is again dominant although the system exhibits symmetric motion in this case. However, the filaments appear to pass through a domain for which the oscillation is possibly quasi-periodic for intermediate values of the mutual separation. In addition, initial investigations suggest that the frequency of oscillations of the system is greater by approximately 30% for larger separations than for smaller separations. We note that an increase of similar magnitude was also observed in experiment. (C) 2003 Elsevier Ltd. All rights reserved.