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Significance Fish and birds moving in groups are thought to benefit from hydrodynamic or aerodynamic interactions between individuals. To better understand these effects, we devise a robotic “school” of flapping swimmers whose formations and motions come about from flow interactions. Surprisingly, we find that the flows naturally generated during swimming can also prevent collisions and separations, allowing even uncoordinated individuals with different flapping motions to travel together. Other benefits include freeloading by a “lazy” follower who keeps up with a faster-flapping leader by surfing on its wake. More generally, our study provides complete maps linking flapping motions to group locomotion, which is needed to test whether flow interactions are also exploited by animals.
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Mapping Spatial Patterns to Energetic Benefits in Groups of Flow-coupled Swimmers
Abstract The coordinated motion of animal groups through fluids is thought to reduce the cost of locomotion to individuals in the group. However, the connection between the spatial patterns observed in collectively moving animals and the energetic benefits at each position within the group remains unclear. To address this knowledge gap, we study the spontaneous emergence of cohesive formations in groups of fish, modeled as flapping foils, all heading in the same direction. We show in pairwise formations and with increasing group size that (1) in side-by-side arrangements, the reciprocal nature of flow coupling results in an equal distribution of energy re-quirements among all members, with reduction in cost of locomotion for swimmers flapping inphase but an increase in cost for swimmers flapping antiphase, and (2) in inline arrangements, flow coupling is non-reciprocal for all flapping phase, with energetic savings in favor of trailing swimmers, but only up to a finite number of swimmers, beyond which school cohesion and energetic benefits are lost at once. We explain these findings mechanistically and we provide efficient diagnostic tools for identifying locations in the wake of single and multiple swimmers that offer op-portunities for hydrodynamic benefits to aspiring followers. Our results imply a connection between the resources generated by flow physics and social traits that influence greedy and cooperative group behavior.
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- Award ID(s):
- 2100209
- PAR ID:
- 10609563
- Publisher / Repository:
- bioRxiv
- Date Published:
- Format(s):
- Medium: X
- Institution:
- eLife
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Posted Content:
- https://doi.org/10.1101/2024.02.15.580536
