Dissertations and Theses

Date of Award


Document Type



Mechanical Engineering

First Advisor

Yiannis Andreopoulos

Second Advisor

Niell Elvin


Energy-harvesting, Vortex-induced vibration, Piezoelectric sensor, Flexible beam, Tunability


Due to the battery lifespan limitation and the need for periodical replacement, energy-harvesting is an actual alternative as a power source for low power devices in some special areas. And among them, the piezoelectric energy-harvesting, which converts mechanical (vibration) into electric energy, is the fastest development one in recent years.

In our current work, a piezoelectric harvester with a finite length cylinder fixed to one end of a flexible thin beam, is the research object in an incoming flow in the CCNY wind tunnel. We report on the efforts to improve the state-of-the-art harvester, called reconfigurable harvester, which has functions of changing its length (aspect ratio, AR) and mass discretely or continuously so that it can be kept always in resonance. At first, experiments on single-cylinder harvester are carried out under changing aspect ratio (3.77-4.89) and additional mass (0-20 mg) discretely or continuously, respectively, to show its features of energy-harvesting output. Then concurrently changing AR and mass, i.e., tunability, are performed to show its improvement in piezoelectric output voltage (power) and lock-in span, for example, its output voltage amplitude increases about 30% to that of its reference state without tuning, and even increases more than 15% to the peak amplitude of the entire reference case. Then, similarly to single-harvester, double harvesters experiments are implemented under three typical distances (contact, small and decoupling gap) by changing AR and additional mass of one. Its piezoelectric output voltage (power) and lock-in span generally have much more increase than that of single-harvester. Its tunability through changing AR and additional mass is also similar to that of single-harvester, which can improve output voltage (power) and broaden its lock-in span.

Owing to the complicated three-dimensionality and huge computing cost, the Van der Pol ODE system describing the VIV of cylinder-type harvester is still a feasible and economical method. Mix model coupling the acceleration, velocity and displacement model of structure acting on vortex shedding wake, is a possible way to extend their applicability to finite length cylinder harvester or higher amplitude oscillation. A good agreement with the experimental shows its feasibility by using this mix model. Likewise, the ODE systems of double-cylinder and mass-changeable harvester are deduced with mix model, respectively. Their numerical results are also in good agreement with the experimental. The other method decreasing computing cost is the reduced-order model (ROM), it was concisely introduced and its equations to double-cylinder harvester was derived for further work in the future.



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