Degree Candidacy: Doctor of Philosophy in Mechanical Engineering
Date: Tuesday, July 22, 2014
Time: 2:00 PM
Location: 215 EIB
Advisor: Dr. Mohammed Daqaq
Committee Members: Dr. Ardalan Vahidi, Dr. Gang Li, and Dr. Richard Figliola
Title: Investigation of Concurrent Energy Harvesting from Ambient Vibrations and Wind
In recent years, many new concepts for micro-power generation have been introduced to harness wasted energy from the environment and maintain low-power electronics including wireless sensors, data transmitters, controllers, and medical implants. Generally, such systems aim to provide a cheap and compact alternative energy source for applications where battery charging or replacement is expensive, time consuming, and/or cumbersome.
Within the vast field of micro-power generation, utilizing the piezoelectric effect to generate an electric potential in response to mechanical stimuli has recently flourished as a major thrust area. Based on the nature of the ambient excitation, piezoelectric energy harvesters are divided into two major categories: the first deals with harvesting energy from ambient vibrations; while the second focuses on harvesting energy from aerodynamic flow fields such as wind or other moving fluids. This Dissertation aims to investigate the potential of integrating both sources of excitation into a single energy harvester. To that end, the Dissertation presents reduced-order models that can be used to capture the nonlinear response of piezoelectric energy harvesters under the combination of external base and aerodynamic excitations; and provides approximate analytical solutions of these models using perturbation theory. The analytical solutions are used, subsequently, to identify the important parameters affecting the response under the combined loading and to develop an understanding of the conditions under which the combined loading can be used to enhance efficacy and performance. As a platform to achieve these goals, the Dissertation considers two energy harvesters; the first consisting of a piezoelectric cantilever beam rigidly attached to a bluff body at the free end to permit galloping-type responses, while the second consists of a piezoelectric cantilever beam augmented with an airfoil at its tip. The airfoil is allowed to plunge and pitch around an elastic axis to enable flutter-type responses. Theoretical and experimental studies are presented with the goal of comparing the performance of a single integrated harvester to two separate devices harvesting energy independently from the two available energy sources.
It is demonstrated that, under some clearly identified conditions, using a single piezoelectric harvester for energy harvesting under the combined loading can improve its transduction capability and the overall power density. Even when the wind velocity is below the cut-in wind speed of the harvester, i.e. galloping or flutter speed, using the integrated harvester amplifies the influence of the base excitation which enhances the output power as compared to using one aeroelastic and one vibratory energy harvesters. When the wind speed is above the cut-in wind speed, the performance of the integrated harvester becomes dependent on the excitation's frequency and its magnitude with maximum improvements occurring near resonance and for large base excitation levels.