Dynamics of Ocean Buoys and Athlete Motion for Energy Harvesting

Abstract

Small scale energy harvesting has become a prevalent area of study over the last decade. These harvesters are used in a wide range of applications, including the powering of remote sensors for structural health in buildings or bridges, tsunami, submarine and wildlife detection in the ocean, as well as general motion analysis of systems. Though many designs have been created to harvest energy for these purposes, the nonlinear dynamics of both the harvester and, when applicable, its housing (i.e. buoy casing) are widely ignored. Because of this, a significant amount of available power is lost through the limitations of linear designs.The first part of this dissertation gives an overview of commonly used linear energy harvesting designs and gives a brief explanation of the limitations of a linear design. Both a simple inertial and linearized magnet-coil model are analytically and numerically studied. This sets the stage for improvement of energy harvesters to operate at a wider range of frequencies by including the inherent nonlinearities of the harvester and/or its environment.In the second part, the nonlinear dynamics of ocean buoys of standard, fundamental shapes (spherical and cylindrical) due to wave loading is studied. Experimental, as well as numerical and analytical analysis is performed on these designs. Also given is a description of common wave-loading devices that can be used in a laboratory setting (wavemakers), as well as for the specific device used to obtain experimental data. Additionally, a simple dynamical system is excited by the buoy motion, which is used to calculate the power available if the system was used as an energy harvester.The last part of this dissertation looks at the nonlinear dynamics of human motion, with a focus on running events. Analysis is performed on running subjects in order to determine the amount of energy available, as well the frequencies where the most energy is available. This information is then used to recreate the motion numerically, which makes it possible to design a simple energy harvester that operates efficiently in such an environment. This harvester is used to power a timing mechanism that gives frequent and useful information about the athlete's position and speed.