Nonlinear analysis of a piezoelectric energy harvester in body undulatory caudal fin aquatic unmanned vehicles

Abstract

Body caudal fin (BCF) locomotion aquatic unmanned vehicles (AUVs) are making critical transitions to full autonomous systems but have challenge in endurance. Therefore, engineering solutions need to be found to maximize the mission capability of these systems. The body actuation of these AUVs offers a platform for a piezoelectric energy harvester to scavenge electrical energy from the mechanical motion. The motion of the animals which these AUVs are inspiring from can be represented in a spatio-temporal function with different envelope constraints to represent an Anguilliform, Subcarangiform, Carangiform, and Thunniform motion. A better approximation of the strain is accounted for by considering the higher-order nonlinear terms due to the large deformation of these systems. Gibbs function is utilized to better approximate the nonlinear constitutive relations of the piezoelectric material. Parametric studies are carried out to investigate how the nonlinear strain and nonlinear piezoelectric material properties affects the performance of the BCF energy harvesters under each motion for various length and placement conditions. The results show that considering the higher-order strain is needed due to the underestimation of the harvested power when linear assumptions are employed for these types of undulatory motion. It is shown that assuming that load resistance, Ropt≈1/Cpω, over-approximates the resistance for the nonlinear piezoelectric material model. This analysis shows the importance of including the nonlinearities due to the piezoelectric material and large deformations in order to accurately estimate the levels of the harvested power and its optimal configuration.