### Meeting Abstract

**58.2** Thursday, Jan. 5 **Understanding undulatory locomotion in fishes using an inertia-compensated flapping foil robotic device** *WEN, Li*; LAUDER, G.; Harvard University; Harvard University* liwen@oeb.harvard.edu

Recent advances in understanding fish locomotion with robotic devices have included the use of flapping foil robots that are self-propelled and in which the thrust forces during swimming average to zero when summed over an entire flapping cycle. But, instantaneous forces are not zero throughout the undulating cycle, and thus the center of mass of the flapping foil does not oscillate in a manner similar to that of freely-swimming live fishes. We have designed a new robotic system that can produce controlled upstream-downstream motion for swimming flexible foils. A linear motor oscillates the flapping robot which is mounted on a low-friction air bearings. We conducted experiments using a flexible foil with a length of 15 cm and a height of 6.8 cm (modulus=1.66 GPa), actuated in heave ±1.5cm at the leading edge at a frequency of 1.5Hz. The imposed linear motion profile is a sine wave function and the linear oscillating frequency was set to double the flapping frequency at 3Hz. We varied the linear amplitude from 0.1 mm to 1 mm, and varied the phase between the foil heave and linear motion. Three forces and three torques were measured simultaneously during self-propulsion. The results showed that a phase of 260-270° produced the minimum force fluctuations. Furthermore, the addition of a linear amplitude of 0.5mm added an inertial component that sums with the net axial force produced by the foil so that force fluctuation is minimal. The summation of forces induced by the added linear motion and forces generated by flapping produces the equivalent of a true freely-swimming foil with appropriate center of mass oscillation.