Date of Award

2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical and Aerospace Engineering

Committee Chair

Gang Wang

Committee Member

Kader Frendi

Committee Member

D. Brian Landrum

Committee Member

Q.H. Ken Zuo

Committee Member

Wenzhang Huang

Subject(s)

Piezoelectric devices., Electric resonators., Vibration., Fluid dynamics.

Abstract

Harvesting energy using piezoelectric transduction has focused on vibration-based types that rely on ambient vibrations. The challenge is to identify a consistent vibration source which is essential for uninterrupted power. Wind energy can provide a reliable and sustained source of vibration to achieve these energy harvesting goals if flow-induced vibration on piezoelectric structures is carefully explored. In this dissertation, flow-induced vibration on piezoelectric structures is investigated based on the galloping piezoelectric energy harvester (GPEH) concept. A GPEH is composed of a cantilevered piezoelectric beam with a tip bluff body. Self-excited vibration is induced when the tip bluff body is subjected to airflow. Then, the piezoelectric materials can convert the mechanical energy into electrical energy. In order to understand the underlying physics, nonlinear coupled aero-electro-mechanical models are developed in which both geometric and material nonlinearities are considered. Dimensionless formulation is adopted so that it is convenient to conduct scaling and performance comparison of different galloping piezoelectric devices. Analytical approximate approach is employed to solve the nonlinear coupled equations using the Krylov-Bogoliubov method. This ensures that system parameters such as galloping velocity, limit cycle oscillation (LCO) amplitude, transient period, and harvested energy are determined accordingly and presented in an explicit form. Additionally, numerical studies are conducted using COMSOL Multiphysics. Several GPEH prototypes were fabricated. The baseline prototype is composed of a bimorph piezoelectric cantilever beam with a square cross-section bluff body. Subsequently, improved designs including addition of an impact bump stop to improve fatigue life and a bio-inspired tip bluff body borrowed from tubercles on flippers of the humpback whale. Comprehensive tests were conducted in a subsonic wind tunnel to determine system damping, electrical response, and LCO amplitude data. An optimal bump stop configuration was determined from tests that showed a significant reduction in LCO amplitude but with less effect on harvested voltage. Also, results from tests with the bio-inspired bluff body reveal the protuberances can be used as a passive control scheme to tune galloping velocity which hitherto depended on system damping and the shape of the bluff body cross-section. Moreover, measured data was used to validate model predictions. Finally, an airflow sensor prototype was developed to demonstrate an application of the GPEH concept. In summary, flow-induced vibration on piezoelectric structures is characterized in which model predictions on the GPEH were validated by experimental data with good agreement. It is expected that the current findings will advance the state-of-the-art of piezoelectric energy harvesting and lead to an innovative airflow sensor system.

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