Meeting Abstract
Fishes swim through the water by passing undulatory waves down their body. To better understand the mechanics of fish locomotion, we fabricated a passive, compliant model from 3-D scans of a rainbow trout (Onchorynchus mykiss, 18 cm body length) that could generate thrust-producing undulatory movements when actuated. We used a mechanical controller capable of simultaneously actuating translation (lateral heave) and rotation (yaw) of the model independently from a single actuation point located near the head. We monitored the swimming kinematics of the model with high speed video while simultaneously recording the locomotor forces and torques on the mounting rod with a six-axis force transducer. A sine wave was used to drive both heave and yaw at 2.5Hz. We measured the thrust production and propulsion efficiency of the model while systematically changing the phase angle between heave and yaw at a single flow speed (0.5 body lengths per second). The model exhibited a variety of bending movements depending on the phase angle: no bending at 0°, a travelling undulatory wave at 90° – 180° and a standing wave at 270°. Minimum and maximum thrust values were generated at phase angles of 0° and 180°, respectively. Thrust production was positively correlated with the tail beat amplitude. The model was most efficient at phase angles between 120° and 180°, which, unlike previous studies with hydrofoils, generated thrust throughout the entire tail beat cycle. Our results highlight the remarkable importance of phase angle as an actuation parameter in establishing efficient undulatory locomotion.
