Session: 20-17-01: Rising Stars of Mechanical Engineering

Paper Number: 173205

Collective Hydrodynamics of Robotic Fish 

Group locomotion in animals, particularly in aquatic species such as fish, often serves critical biological functions, including predator avoidance, enhanced navigation, and increased endurance. A long-standing hypothesis is that schooling behavior in fish may confer hydrodynamic benefits, potentially improving swimming efficiency through fluid-mediated interactions. However, experimentally isolating and quantifying these effects in live animals presents significant challenges, due to the complexity and variability of biological systems. While numerous computational, analytical, and biological studies have attempted to address this question, many open questions remain unanswered, particularly regarding the role of coordination and spatial arrangement in modulating these interactions.

To address this gap, we present a reduced-order, biomimetic experimental model designed to investigate the role of multi-body hydrodynamic interactions in collective swimming. Our setup consists of a rotational array of robotic fish that swim in a circular path around a central axis. Each robotic fish executes a prescribed tail flapping motion, while its translational swimming speed emerges naturally from the resulting hydrodynamic forces, rather than being externally imposed. The system is mechanically driven by a single electric motor connected via a series of shafts and gears, enabling precise and synchronized control of the kinematic inputs across multiple robotic fish. In this study, we focus on the two-fish configuration, with the swimmers positioned diametrically opposite each other on the circular path to ensure balanced loading and maximal interaction.

We conduct a systematic exploration of the parameter space by varying the amplitude and frequency of tail flapping, the phase difference between the two swimmers, and their spatial separation. Particle Tracking Velocimetry is employed to reconstruct time-resolved three-dimensional flow fields, providing insight into vortex structures, wake interactions, and energy transfer mechanisms between the swimmers. Concurrently, we measure the electrical power input required to drive the tail mechanisms, enabling calculation of the cost of transport for each tested condition. To corroborate and extend our experimental findings, we also perform complementary numerical simulations that reproduce the flapping kinematics and environmental conditions observed in the lab.

Our results show that the two-fish system exhibits enhanced swimming efficiency compared to an isolated swimmer across a broad range of operating conditions. Notably, we find that synchronized tail motion amplifies this effect, whereas increasing the phase difference between the swimmers toward 180 degrees generally leads to diminished performance. These observations highlight the critical role of temporal coordination in optimizing hydrodynamic benefit.

Overall, our work provides a novel experimental and computational framework for studying multi-body fluid interactions in collective swimming. These findings offer new insights into the physics of group locomotion and inform the design of bio-inspired robotic systems for autonomous underwater applications.

Presenting Author: Hassan Masoud Clemson University

Presenting Author Biography: Dr. Masoud is a Dean's Associate Professor in the Department of Mechanical Engineering at Clemson University. He holds a Ph.D. in Mechanical Engineering from the Georgia Institute of Technology and completed postdoctoral research under the joint supervision of Michael Shelley at the Courant Institute of Mathematical Sciences, New York University, and Howard Stone in the Department of Mechanical and Aerospace Engineering at Princeton University. Masoud leads the Complex Fluids and Active Matter Lab, where he and his team employ the tools of applied mathematics and experimental techniques to fundamentally understand the interaction of fluid flows with dynamically changing boundaries across a wide range of lengths and time scales. Their objective is to integrate this fundamental understanding with engineering principles to tackle pressing technological and societal challenges. Dr. Masoud is a recipient of the NSF CAREER Award and currently serves as an Editorial Board Member and Associate Editor of the Journal of Engineering Mathematics.

Authors:

Muhammad Usman Clemson University
Hassan Masoud Clemson University