Development and enhancement of various mechanical oscillators for application in vibrational energy harvesting

McRobb, Malcolm (2014) Development and enhancement of various mechanical oscillators for application in vibrational energy harvesting. PhD thesis, University of Glasgow.

Abstract

The context of this thesis surrounds the development and study of the effectiveness of three mechanical-to-electrical energy converter concepts that are based upon oscillatory systems with a view of discovering techniques to enhance their normal functioning throughputs.

The field of energy harvesting has experienced significant growth over recent years with the increased popularity of portable electronic devices and wireless sensors. However, with demand, so too rises the need for increased operating lifetimes not only for extended use for some personal devices, but also to reduce the frequency of periodic battery replacements for remote sensors that may be deployed in potentially hazardous environments.

In light of this need, the proceeding chapters will discuss the development of three conceptual energy harvesters. The first is based upon a simple Euler strut that is intended to harvest known steady-state periodic vibrations applied axially to the beam. The assumption here is that the periodic vibrations would arise from ambient conditions, whether naturally occurring or as a form of waste energy from man-made structures. This concept has built into it the facility to apply a static axial pre-load with which, it will be shown, can be used to passively enhance the energy throughput of the device.

However, it will also be shown that the periodic concept has an inherent sensitivity to excitation frequencies, where even minor shifts can result in significantly reduce outputs. To this end, the second harvester was proposed to relieve this limitation by instead harvesting stochastic inputs. With this in mind, the new concept is again based upon a simple and realisable Euler strut but with the stochastic input applied laterally to the supporting structure. By retaining the facility to apply both static and dynamic axial loads, it will be shown that the cumulative effects of the deterministic and stochastic input can be manipulated to actively enhance the throughput of this system also. However, given the active nature of this form of control that will consume work during its implementation, an approach for ensuring that the net energy will be reduced by this additional work will be discussed. In this way, a conservative estimate of the harvestable energy may be made.

The final energy harvester to be discussed is based upon a planar pendulum that can integrate mechanical accelerations out of the full three degrees of freedom realisable by planar constructs. This begins with the development of a suitable approach to applying rotational excitations to the device, followed by the development of a set of loading terms used to represent the resistive torque that would be exerted upon the system by a suitable power take-off device. This is followed by a comprehensive parameter study of the proposed concept with a mindset towards optimising the operational performance of the device.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Absolute frame of reference, Body frame of reference, Coupled excitations, Decoupled excitations, Deterministic, Dynamic axial load, Enhanced energy throughput, Euler strut, Fourier series approximation, Harmonic solutions, Harvestable energy, Instantaneous power, Mechanical oscillator, Nonlinear, Numerical simulations, Operational bandwidth, Periodic excitation, Planar pendulum, Power take-off, Pre-curvature, Principle parametric resonance, Rectified response, Response trajectory, Rotational excitation, Static axial load, Stochastic resonance, Translational excitation, Torque, Vibrational energy harvesting
• Subjects: T Technology > TJ Mechanical engineering and machinery
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Cartmell, Professor Matthew and Margaret, Professor Lucas
• Date of Award: 2014
• Depositing User: Dr Malcolm McRobb
• Unique ID: glathesis:2014-4851
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 23 Jan 2014 10:40
• Last Modified: 23 Jan 2014 12:13
• URI: https://theses.gla.ac.uk/id/eprint/4851