Energy harvesting using ship motions applying a gimballed pendulum system as an energy conversion mechanism

Abstract

This research describes a novel methodology of assessing the mechanical power contributed by the multiple-degree-of-freedom dynamics of a ship in waves concerning the directional responses of the ship oscillatory motions. It is motivated by the limited understanding of the potential use of wave energy harvesting using wave-induced ship motions, and the quantitative assessment of the ship motions energy in the real sea has never been explored. By adopting the seakeeping analysis and the statistical technique as the standard wave spectrum, therefore, the contributed mechanical power of a ship in a sea state can be quantified. It is found that the magnitude of mechanical power of a ship in waves varies proportionally to the ship scale, but the power is contributed by the different dynamic determinants depending on the scale or size of the ship. Importantly, it is also discovered that the number of the involved degree-of freedoms is able to magnify the mechanical power of a ship in waves that is available to be harvested. Typically, the wave energy harvesting system onboard a marine vessel is designed to operate in a limited degree-of-freedom. This contrasts to the dynamics of a floating ship in the variance real sea condition as it could lose to potential to harvest more energy. Consequently, the concept of using a multiple-degree of-freedom system as a 2-axis gimballed pendulum mechanism has recently been introduced. However, its dynamics has never been investigated as a multiple-degree-of-freedom system. Therefore, the research examines the dynamics of a gimballed pendulum system in an aspect of an energy conversion mechanism regarding its directional responses and applies it as an onboard energy conversion mechanism for ship motions energy harvesting. Moreover, in this thesis, a novel numerical model of a gimballed pendulum system is indicated which is validated by a set of experimental testings of a prototype of a gimballed pendulum energy harvester based on the directional harmonic excitations on a motion simulator. At the sufficient angle, the gimballed pendulum created coupled motions between two referenced pivots. Outside resonance, the coupled motions are small and are found to be beneficial in the simultaneous power generations by the pivots. At resonance, the motions are more significant. Also, the coupling relationships between the two referenced rotational axes become more influential which diminishes the pendulum responses compared to when it performs as a single-degree-of-freedom system at the identical disturbance. This behaviour can be numerical and experimentally confirmed. However, the numerical prediction of the coupled pendulum motions at around resonance has been found to be inaccurate compared to the experiment. This is because of the simplified assumption that is made to form the equations of motion using geometric coupling relationships of two inertial perpendicular pendulum dynamics around two horizontal axes (2-DOF). Yet, with the potential asymmetric inertial properties between the gimballed pivots, the determination of the equations of motion which are included all DOFs is theoretically complex and not straightforward. iv Then, the gimballed pendulum system has been applied onboard a ship model as the numerical and experimental investigations have been carried out. Based on the result, it shows that the multiple-degree of-freedom ship dynamics offers the potential to generate more energy that reflects the simultaneous power generations by the coupled motions of the gimballed pendulum. Also, this proves that the energy harvesting using ship motions applying a gimballed pendulum as an energy conversion mechanism is practicable.

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Identifiers

ORCID for Philip Wilson: orcid.org/0000-0002-6939-682X

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