Meeting Abstract
Undulatory motion of the body is the dominant mode of locomotion in fishes, and numerous studies of body kinematics and muscle activity patterns have provided insights into the mechanics of swimming. However, it has not been possible to investigate how key parameters such as the extent of bilateral muscle activation affect propulsive performance due to the inability to manipulate muscle activation in live, freely-swimming fishes. We manufacture and utilize a set of actively-controlled pneumatic actuators attached to a flexible foil to gain insight into undulatory locomotion and mechanisms for body stiffness control. Two soft actuators were attached on each side of a flexible panel with stiffness comparable to that of a fish body. To study how bilateral contraction can be used to modify axial body stiffness during swimming, we ran a parameter sweep of actuator contraction phasing and frequency (Jusufi, Vogt, Wood, Lauder, 2016). Thrust production by the soft pneumatic actuators was tested at cyclic undulation frequencies ranging from 0.3Hz to 1.2Hz in a recirculating flow tank at flow speeds up to 28cm/s. Overall, this system generated more thrust at higher tail beat frequencies, with a plateau in thrust above 0.8Hz. Self-propelled speed was found to be 0.8 foil lengths per second or circa 13cm/s when actuated at 0.55Hz. We find this active pneumatic model is capable of producing substantial trailing edge amplitudes with a maximum excursion equivalent to 1.4 foil lengths, and of generating considerable thrust. Altering the extent of bilateral co-contraction in a range from 17% to -22% of the cycle period showed that thrust was maximized with some amount of simultaneous bilateral co-contraction of approximately 3% to 6% of the cycle period (p<0.05). This experimental platform provides a new physical model for studying aquatic propulsion with active control of undulatory kinematics. Body-caudal shape changes facilitated by soft actuators could enhance maneuverability in burst-type responses.
