Exploring the multi-functional potential of a Giant-Larvacean-inspired undulating module for fluid pumping and propulsion.*

Aquatic microplastic is a pollution crisis. Current cleaning methods such as tow nets or propeller suction are unideal due to low maneuverability and severe biological intrusion. We present a novel modular robot biomimetically inspired by Giant Larvaceans. A rectangular flexible panel with non-uniform rigidity is positioned in 2D confinement in quiescent water, actively undulated at the anterior, and sustains passive flapping in the posterior portion. An actuation frequency between 0.5 and 9 Hz paired with different bending rigidities was tested, measuring pumping flow rates (Q) and propulsive forces (T) were simultaneously measured. Interestingly, different trends in Q and T were observed with frequency. Particularly, three regimes can be identified for Q, a constant plateau within the frequency range of 2 to 6 times the resonance plus two linear ranges below or above. Two continuously increasing regimes can be identified for T, but separated by distinctive slopes. Phase-averaged vorticity and Lagrangian Coherent Structures show the transitions between regimes are correlated with changes in the wake vortex structure, proving the potential to theoretically model Q by superposition of the panel-motion-induced velocity and vortex-induced velocities. The elongated-body theory validated the propulsive force and drew connections between Q and T. Finally, the robotic prototype shows promising potential to assemble, maneuver, navigate, and multitask for microplastic collecting missions.