| Summary: | 博士 === 國立清華大學 === 動力機械工程學系 === 101 === Hula-hoop motion refers to the gyrating of a ring around a human body. This is made possible by the interactive forces between the human body and the moving ring. Inspired by the generic concept of hula-hoop motion, this study proposes a novel motion transformer design that consists of a main mass sprung in one translational direction and a free-spinning mass hinged eccentrically onto the center of the main mass. It is expected that the motion transformer can convert linear reciprocating motion into rotational one and accommodate various power sources, which mainly accompany with the vibrations of the vehicle suspension and machine base as well as the motion of human body.
This thesis aimed at designing an energy-harvesting device that can scavenge energy, especially, from human motion by integrating an electromagnetic generator with a hula-hoop motion transformer. The harmonic and impulsive forces caused by both machine vibration and human motion were investigated, individually.
First, a thorough dynamic analysis of the proposed transformer system with harmonic excitation was conducted in order to characterize the relationships between the various system parameters and the likelihood of hula-hoop motion occurring. The governing equations were derived using Lagrange method. This was followed by a search for steady-state solutions via the Homotopy perturbation method; meanwhile, a direct numerical simulation was performed to verify the correctness of the approximate analysis. The corresponding stability analysis was conducted via Floquet theory. In this manner, the feasibility of the proposed design and the occurrence criteria of hula-hoop motion were assessed. After that, an experimental study confirmed that the dynamic responses were well matched with the numerical simulation. The results imply the possibility of hula-hoop motion over a large set of combinations of excitation frequencies and amplitudes, which are confirmed by not only the dynamic analysis but also the experiment.
Secondly, the transient dynamic analysis was also performed based on the governing equations by applying an impulsive excitation to the main mass, which then created its initial velocity. A direct numerical simulation was performed to verify the correctness of the equations considering the impulsive excitation. Additionally, the occurrence of hula-hoop motion was investigated to find the dynamic matching between the initial conditions and the system parameters of the hula-hoop motion transformer. Moreover, the experimental responses were used to verify both the correctness of the equations considering impulsive excitation and the dynamic responses of the direct numerical integration.
Thirdly, for the generation of energy through electromagnetism, the equations describing the relation between induced voltage and power for the system were derived according to the Faraday theory. Herein, the equation of induced electrical damping was obtained as well, in which the effect of electrical damping was concerned for the system response. Moreover, the responses from the theoretical analysis, numerical simulation, and experiment were in good agreement with one another regarding the accuracy of the equations of the induced voltage and power from the generator.
Finally, the proposed energy-harvesting system was proved to generate power through electromagnetism after integrating the electromagnetic generator with the hula-hoop motion transformer. Specifically, the maximum power that the system can generate is approximately 5 mW when the frequency and amplitude of the external harmonic excitation are 8 Hz and 11.2 N, respectively.
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