Non-linear Viscous and Friction Effects on a Heaving Point Absorber Dynamics and Latching Control Performance

Abstract Linear modelling approaches are widely applied to predict the hydrodynamics of wave energy conversion systems. One main weakness is that the linearisation near the equilibrium point removes the effects of some important non-linear phenomena, like viscous and friction forces, and hence exaggerates the excursion and power productivity of wave energy conversion devices. This work focuses on the modelling of the viscous and friction forces and their effects on the dynamics and latching control performance of a heaving cylindrical point absorber. A 1/50 scale buoy has been constructed and tested in a wave tank to determine the profile of the viscous and friction forces. Non-linear models concerned with the viscous or/and friction effects are proposed, simulated and compared with wave tank tests. A non-predictive latching control is evaluated and the simulation shows that the viscous and friction effects decrease the controlled buoy excursion and power conversion efficiency significantly.

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