Deformation of fire ant rafts under uniform flow
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Yu, Ting-Ying
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Abstract
Fire ants link their bodies together to build rafts. These structures help them survive floods, river flow, and rain. The ability to adapt to changing fluid environments allows fire ants to remain stable on the water surface for weeks. In this study, we record the response of fire ant rafts for 10 hours to uniform flows at 6 cm/s. We observe that raft elongation and stretching downstream are observed in the presence of flow. The deformation is caused by two factors: mechanical passive reaction and the biological active response from fire ants. To investigate these two types of responses separately, we first perform computational fluid-structure-interaction simulations of a pure elastic elliptical raft under uniform flow. The simulation results in a shape with the leading edge compressed and the aspect ratio reduced, which is different from our experimental observation. Thus, by comparing the theoretical passive response to the actual raft's behavior, we further confirmed that the responsive activity of fire ants plays a more critical role in their shape change. In addition, the streamlined shape decreases the fluid pressure by around 40% for the raft under flow. This change in external stress indicates that ants are able to sense the fluid force and make decisions to act in an opposing manner. The findings of this research may provide insights for designing an intelligent swarm robotic system with an active elongating mechanism that helps adapt to fluid flows.
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Undergraduate Research Option Thesis