Surface Wave and Transport Dynamics of a Self-propelling Vibrating Robot Fan Boat

Active agents on fluid surfaces can perturb their surroundings by creating waves that can reciprocally affect the agent. Inspired by the rich wave-mediated dynamics of surface-bouncing droplets, we study the motion and wave field dynamics of an 11.7 cm diameter, 8.8 cm tall vibrating robot fan boat moving on the surface of a 4-10 cm deep pool of water. The boat's vibration motor creates outwardly propagating surface waves with frequency range 10-63 Hz; a Schlieren method enables surface wave visualization with submillimeter resolution. Far from boundaries, the boat generates circular waves for frequencies below 42.8 Hz with maximum amplitude 0.6 mm; above 42.8 Hz, the waves gain subharmonic components. In obstacle-laden environments (lattices of posts 16.7 cm apart), the wave field becomes complex, and the presence or lack of vibration strongly affects boat trajectories. Without vibration, the boat pins itself permanently to any obstacle encountered with incident angle less than 34°, often occurring within three collisions; with vibration, the boat displays spontaneous reorientations about obstacles, enabling escapes and producing ballistic motion at all tested timescales. We posit these dynamics are due to both hydrodynamic wave-obstacle and vibratory boat-obstacle interactions.