In this study, we investigate the efficiency of a novel energy converter that exploits vortex-induced motions of a cylindrical body. The converter comprises a rigid circular cylinder supported by an arm such that it can perform angular oscillations with respect to a pivot point while held perpendicular to an incident fluid current. Two configurations are considered in which the pivot point is located either upstream or downstream of the oscillating cylinder. We simulate the angular response of the cylinder via the torque balance using an analytical hydrodynamic model that includes fluid damping due to drag, fluid inertia due to added mass, and fluid excitation due to vortex shedding in the cylinder wake based on the instantaneous relative velocity between the moving cylinder and the uniform fluid current. A simplified version of the equation of motion with linearized terms indicates that the drag force on the cylinder modifies the stiffness and thereby the natural frequency of the system. We performed simulations of the vortex-induced motion of the cylinder by numerically integrating the full nonlinear equation of motion in order to study the effects of the mechanical parameters. The amplitudes of angular response obtained from simulations with the present model compare satisfactorily with experimental data from the literature. The results for a structure-to-fluid density ratio of 5 show that there is an optimal value of the damping ratio of 0.1 that maximizes the power-extraction efficiency, which reaches approximately 11%. It is also shown that the peak efficiency is attained at different arm lengths for the two configurations studied.
Optimal Damping for Energy Extraction From Drag-Aided Vortex-Induced Motions
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Malefaki, I, & Konstantinidis, E. "Optimal Damping for Energy Extraction From Drag-Aided Vortex-Induced Motions." Proceedings of the ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. Volume 10: Ocean Renewable Energy. Madrid, Spain. June 17–22, 2018. V010T09A012. ASME. https://doi.org/10.1115/OMAE2018-78394
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