Experimental And Simulation Study On The Propulsion Performance Of A Carp-Like Robotic Fish

As one of the significant aspects for human beings to exploit the oceans, it is a direct route to learn from marine creatures, such as the swimming fish, which are with the abilities of fast swimming speed and elegant maneuver. In this thesis, inspired from carps, which are common living fish in fresh water, a robotic fish is designed and built. This robotic fish is configured with a easily disassembling caudal fin, of which we can assemble with the fins of different shapes and materials. Based on this platform the fins with three different shapes and two materials are investigated, with the attentions paid to their performances of propulsion. We note that the robotic fish moorings at its nose for all the experimental cases. It is revealed that in general the flexible caudal fins produce more stable thrust when varying their flapping amplitudes and frequencies. When selecting medium to high values of frequency, for the caudal fins with high aspect ratios, the rigid fin can produce larger thrust than its flexible counterpart, while for the fins with lower aspect ratios, the flexible fin can produce larger thrust. Moreover, the Computational Fluid Dynamics (CFD) code FLUENT is employed to investigate in detailed flow field. First, the robotic fish is simplified to a two-dimensional mode with the symmetry profile extracted to represent the fish. The lateral force coefficients and the drag/thrust coefficients are investigated, which accord qualitatively with the experiments, and thus the self-propelled speed of the fish is deduced. And the vortical contours and the pressure contours are studied, which provides a more detailed way for us to understand the flow field around the robotic fish. Second, three-dimensional simulations are performed on a sole caudal fin. The different thrusts, lateral forces and the thrust-to-lateral-force ratios for two different shapes are reported. The results show that for the same kinematic parameters the tuna fin can produce smaller lateral force in terms of its peak value and time averaged value, while larger thrust-to-lateral-force ratio, implying a higher efficiency. We thereby conclude that the tuna fin can achieve more stable and high efficiency propulsion.As a first robotic fish in our laboratory, though the present research is very preliminary, it has established a solid foundation for potential more comprehensive investigation in the future.