Inspired by music-playing harmonicas that create tones via oscillations of reeds when subjected to air blow, this paper entails a concept for microwind power generation using flow-induced self-excited oscillations of a piezoelectric beam embedded within a cavity. Specifically, when the volumetric flow rate of air past the beam exceeds a certain threshold, the energy pumped into the structure via nonlinear pressure forces offsets the system’s intrinsic damping setting the beam into self-sustained limit-cycle oscillations. The vibratory energy is then converted into electricity through principles of piezoelectricity. Experimental and theoretical results are presented demonstrating the feasibility of the proposed concept.
First and foremost, I thank God for all the blessings he bestowed on me during my life, and for giving me such a great opportunity, along with the patience and enthusiasm necessary to complete this Ph.D dissertation. Secondly, I especially thank my Thesis advisor, Dr. Mohammed F. Daqaq, for his invaluable support and advice throughout my time in Clemson. I am very blessed to have him as a friend and a mentor. I thank him for patiently teaching me innumerable lessons pertinent to research and also for motivating and inspiring me towards new possibilities of life. Without his thorough guidance, the completion of this work would not have been possible.
This paper develops and validates an aero-electromechanical model which captures the nonlinear response behavior of a piezoelectric cantilever-type energy harvester under combined galloping and base excitations. The harvester consists of a thin piezoelectric cantilever beam clamped at one end and rigidly attached to a bluff body at the other end. In addition to the vibratory base excitations, the beam is also subjected to aerodynamic forces resulting from the separation of the incoming airflow on both sides of the bluff body which gives rise to limit-cycle oscillations when the airflow velocity exceeds a critical value. A nonlinear electromechanical distributed-parameter model of the harvester under the combined excitations is derived using the energy approach and by adopting the nonlinear Euler–Bernoulli beam theory, linear constitutive relations for the piezoelectric transduction, and the quasi-steady assumption for the aerodynamic loading. The resulting partial differential equations of motion are discretized and a reduced-order model is obtained. The mathematical model is validated by conducting a series of experiments at different wind speeds and base excitation amplitudes for excitation frequencies around the primary resonance of the harvester. Results from the model and experiment are presented to characterize the response behavior under the combined loading.
This paper investigates employing a nonlinear restoring force to improve the performance of flow energy harvesters (FEHs). To that end, a galloping FEH possessing a quartic potential energy function of the form V ¼ 1 2 ly 2 þ 1 4 cy 4 is considered. This potential function is used to model either a softening (l > 0, c < 0), hardening (l > 0, c > 0), or bi-stable (l < 0, c > 0) restoring force. A physics-based model of the harvester is obtained assuming piezoelectric transduction and a quasi-steady flow field. The model is validated against experimental data and used to obtain a closed-form solution of the response by employing a multiple scaling perturbation analysis using the Jacobi elliptic functions. The attained solution is subsequently used to investigate the influence of the nonlinearity on the performance of the harvester and to illustrate how to optimize the restoring force in order to maximize the output power for given design conditions and airflow parameters. Specifically, it is shown that for similar design parameters and equal magnitudes of l, and c, a bi-stable energy harvester outperforms all other configurations as long as the inter-well motions are activated. On the other hand, if the motion of the bi-stable harvester is limited to a single well, then a harvester incorporating a softening nonlinear restoring force outperforms all other configurations. Furthermore, when comparing two FEHs incorporating the same type of restoring force at the optimal load and similar values of l, then the FEH with the smaller c is shown to provide higher output power levels. V C 2015 AIP Publishing LLC.
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