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The natural ocean/river currents energy can be harvested using Flow Induced Motion (FIM) phenomena. The effect of damping-ratio and mass-ratio on Flow Induced Motion energy harnessing of a square cylinder are numerically investigated for Reynolds number 15500 < Re < 232000 (0.2 m/s < flow velocity <3.0 m/s). Four typical regions can be observed in the Flow Induced Motion responses, including Vortex Induced Vibration (VIV) Initial Branch, Vortex Induced Vibration Upper Branch, Vortex Induced Vibration-Galloping Transition and Galloping. Results indicate that as the velocity increases, the number of vortices shed per cycle increases, and the harnessed power increases without upper limit. The energy conversion efficiency increases up to the highest value until the Vortex Induced Vibration upper branch. Then, it starts decreasing and tends to a relatively small value in the galloping region. Increasing mass-ratio will shorten the velocity range of Vortex Induced Vibration. High damping-ratio has a negative impact on oscillation amplitude, but provides a boost for energy harnessing. In all tests, the power (143 W) is considerable at damping-ratio = 0.6. As the damping-ratio reaches up to 0.8 (nearing critical damping), galloping will no longer occur. [ABSTRACT FROM AUTHOR]

Vortex-induced oscillations offer a potential means to harness hydrokinetic energy even at low current speeds. In this study, we consider a novel converter where a cylinder undergoes angular oscillations with respect to a pivot point, in contrast to most previous configurations, where the cylinder undergoes flow-induced oscillations transversely to the incident free stream. We formulate a theoretical model to deal with the coupling of the hydrodynamics and the structural dynamics, and we numerically solve the resulting nonlinear equation of cylinder motion in order to assess the performance of the energy converter. The hydrodynamical model utilizes a novel approach where the fluid forces acting on the oscillating cylinder are split into components acting along and normal to the instantaneous relative velocity between the moving cylinder and the free stream. Contour plots illustrate the effects of the main design parameters (in dimensionless form) on the angular response of the cylinder and the energy efficiency of the converter. Peak efficiencies of approximately 20% can be attained by optimal selection of the main design parameters. Guidelines on the sizing of actual converters are discussed. [ABSTRACT FROM AUTHOR]