Bio-inspired aquatic propulsion using piezoelectric effect

Underwater propulsion of fishes have inspired many biomimetic structures. Generally, the bio-inspired structures mimics the flapping behaviour of various control surfaces/fins in fishes. The present study mimics the flapping behaviour using a piezoelectric structure. The system is analyzed as a fluid structure interaction problem. The dynamic behaviour of a cantilever beam surrounded by a bounded fluid domain open at top is analyzed. The structure is modeled as a Euler-Bernoulli beam and the fluid is modeled using potential flow theory. The influence of domain size on the wet natural frequencies of the system was analyzed. The dimensions of the fluid domain wherein the variation in wet natural frequencies becomes insensitive were determined. The influence of added mass on the wet natural frequency was parametrized based on Non-dimensional Added Mass Increment (NAVMI) factor. The NAVMI factors were observed to be relatively higher for lower wet modes of the structure. Therefore, the peizo-beam was analyzed by exciting the lower wet modes. The thrust generated at different excitation frequencies were determined using tip velocity of the cantilever beam following Lighthill's analogy. The results from the study indicated that higher propulsive thrust was produced for lower modes of excitation of the structure.