Simultaneous energy harvesting and gust alleviation for a multifunctional wing spar using reduced energy control laws via piezoceramics
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The increasing need for lightweight structures in Unmanned Aerial Vehicle (UAV) applications raise issues involving gust alleviation. Here we examine the gust alleviation problem using a self-sensing, self-charging, and self-actuating structure. The basic idea is that the wing itself is able to harvest and store energy from the normal vibrations during flight along with any available sunlight. If the wing experiences any strong, unexpected wind gust, it will sense the increased vibration levels and provide vibration control to maintain its stability. In this paper, a multifunctional wing spar is designed, which integrates a flexible solar cell array, piezoceramic wafers, a thin film battery and an electronics module into a composite structure. This multifunctional wing spar therefore carries on the functions of energy harvesting and storage, as well as the functions of gust alleviation via piezoelectric materials. The piezoceramic wafers act as sensors, actuators, and harvesters. The global modulus and stiffness of this multifunctional wing spar are estimated using both the rule of mixtures and the cross section transformation method. These values are then used in an Euler-Bernoulli cantilever beam model of the multifunctional spar. The first two dominant modes are predicted analytically for the distributed parameter model. The finite element method is employed to confirm the analytical eigenvalues estimation. Special attention is given to the self-contained gust alleviation with the goal of using harvested energy. The gust signals are generated using a Gaussian white noise source n (t) ∼ N (0,1) fed into a linear filter, with the required intensity, scale lengths, and power spectral density (PSD) function for the given flight velocity and height. The Dryden PSD function is implemented for atmospheric turbulence modeling. The recently developed reduced energy control law is combined with a positive strain feedback controller to minimize the actuation energy and the dissipated heat energy. Positive feedback operation amplifiers (op-amps) and voltage buffer op-amps are implemented for two dominant mode gust disturbance controls. This work builds off of our previous research in self-charging structures and holds promise for improving UAV performance in wind gust alleviation. © 2011 by ASME.
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