What is it about?
In nature, fish and other aquatic animals often swim together in groups, adjusting their timing and movements to become more efficient. Inspired by this, we studied how two flexible robotic fins, each free to move on its own, can swim more efficiently when they coordinate their motion. Using computer simulations, we found that adjusting the phase difference, or the timing between the two fins’ movements, can help the follower fin use less energy or generate more thrust by taking advantage of the water flow created by the leader. This shows how flexible propulsors can “communicate” through the surrounding fluid to achieve better performance as a group, without needing direct control. These findings could help improve the design of future underwater robots, drones, or sensor systems that operate in swarms.
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Photo by Thuỷ Nguyễn on Unsplash
Why is it important?
While many studies have examined individual flexible fins or externally constrained models, little is known about how multiple freely moving flexible fins interact and cooperate. This work is among the first to numerically demonstrate that collective propulsion efficiency can be significantly enhanced through hydrodynamic interactions between self-propelled flexible bodies, without any direct mechanical or control-based communication. By identifying optimal phase differences and spatial arrangements, this study provides timely insights for the development of energy-efficient, swarm-based underwater robotic systems. These findings are particularly relevant for the future design of autonomous aquatic vehicles and bio-inspired collective locomotion strategies.
Perspectives
Working on this study was a truly rewarding experience, as it brought together my long-standing interest in bio-inspired propulsion and collective locomotion. This research allowed me to explore how simple mechanical interactions, without explicit communication or control, can give rise to complex and efficient group behavior. I found it especially meaningful to observe how flexible structures, when left unconstrained, naturally form energy-saving patterns through phase-mediated interactions. I hope this work contributes to expanding the understanding of emergent behavior in soft robotics and inspires further developments in swarm-based autonomous underwater vehicles.
Young Dal Jeong
Chosun University
Read the Original
This page is a summary of: Phase-mediated interactions on collective locomotion of two unconstrained self-propelled flexible fins, Physics of Fluids, August 2025, American Institute of Physics,
DOI: 10.1063/5.0279894.
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