Effect of kinematics and physical properties of caudal fin on performance of a robotic fish

In this work, we built a Robo-physical model to study the effect of various physical, geometrical, and kinematic parameters of fin on performance. The model can swim along a large circular path continuously to carry extensive experiments. We examined 12 fins in total, which were a combination of 3 different shapes, 3 flexibilities, and uniform or tapered thickness for a particular shape. Each fin was tested with 4 different frequencies and two different amplitudes of oscillation. The results of 96 trials revealed: 1) for any frequency of oscillation there is optimal flexibility that minimizes the cost of transportation. 2) The swimming speed linearly varies with the tail tip velocity. 3) Rectangular fin with the same aspect ratio is more efficient compared to the remaining two shapes 4) Uniformly thick fins require less work and torque while a tapered fin generates more speed. Furthermore, a numerical model was developed using panel method and free vortex sheet. We used this model to find the optimum phase offset between heave and pitch motion in a freely swimming fish and compared that to a tethered fish model. The results were significantly different for tethered and freely swimming cases.