Enhancing power extraction in bottom-hinged flap-type wave energy converters through advanced power take-off techniques

Abstract

The linear and non-linear dynamics of a bottom-hinged, flap-type wave energy converter in response to regular waves were studied through computational simulations to assess the performance of power take-off techniques and enhance the power extraction. The computational model was developed in Comsol Multiphysics using its Multibody Dynamics Module and was carefully validated. The hydrodynamic coefficients are from the linear wave theory. To avoid damages to the device, especially in extreme sea conditions, a brake mechanism is used to limit the amplitude of flap oscillations. With that limit imposed, we show that the optimum damping coefficient proposed in the literature for power take-off does not actually lead to an optimum power extraction for a range of wave frequencies. Over that range, the brake mechanism becomes engaged, leading to a significant energy loss. We propose new power take-off techniques that avoid the engagement of the brake, yet keep the amplitude within the specified range. They are proposed for both the linear and non-linear flap dynamics, and their efficacy is demonstrated for several flap geometries. The proposed techniques enhance the power extraction by as high as 600% (linear) and 19% (non-linear), in the latter case by minimizing the energy loss due to brake.