Fish-Inspired Propulsion through a Water-Air Interface

Archer fish are capable of accurately jumping for aerial prey from a stationary aiming position directly below the water’s surface. This jumping behavior may provide a bioinspired strategy for water-exit in underwater vehicles, especially in sensitive environments where other thrusters (e.g., high-pressure water jets) may be too disruptive. However, any engineered implementation of this behavior relies on the ability to simplify, replicate, and optimize archer fish-inspired propulsion using a mechanical system. In particular, flapping flexible plates and hydrofoils are commonly-used simplified mechanical models of fish locomotion. This project aims to use these models to understand why the archer fish changes the timing and size of each tailbeat as it leaves the water and how to optimally execute similar kinematic variations.

We use experimental models to determine how changing the amplitude and timing of each propulsive “tailbeat” affects cumulative propulsion during water-exit. Is it better to execute faster, smaller-amplitude motions or larger, sweeping ones? How does the optimal motion vary with the size and flexibility of the actuator? Can we time each motion such that a beneficial interaction with the wake of the previous tailbeat is achieved? At what point during water-exit does force production reach diminishing returns, where so little of the plate or foil is underwater that additional “tailbeats” do not significantly contribute thrust?

Our efforts to answer these questions include designing and prototyping mechanisms to replicate the kinematics of jumping fish and analyzing the forces and flow patterns produced by these mechanical models using high speed imaging, dye visualization, six axis force sensing, and particle image velocimetry. In Fall 2024, we will focus on collecting and analyzing force sensor and high-speed imaging data to better understand the role of the water's surface on propulsive performance.

Research will take place during the Fall and Spring semesters for academic credit. Paid summer positions are available; summer offers will be made in the Spring semester.

Essay Prompt (~paragraph length): Why are you interested in working on this research project? What will you bring to the project and what do you hope to learn? Please also submit the names of two HMC professors as references who can comment on your work habits.