Effects of pendulum orientation and excitation type on the energy harvesting performance of a pendulum based wave energy converter

Abstract With global electricity requirements due to increase in the coming years and growing pressure to reduce dependence on fossil fuels, universal demand for renewable energy is projected to grow. Marine energy, including wave energy, is an active research area, with potential to meet future energy demands, due to its high energy density. With a view to using a pendulum system in a floating object to extract energy from ocean waves, this paper analyses the effects of pendulum orientation and excitation type on the system’s dynamics. Three excitation scenarios, surge, heave and dynamic tilt of the floating object, with various pendulum orientations, were analysed and simulated. Both linearised and nonlinear systems were investigated with the former providing insight into the nonlinear system’s behaviour. Effects of pendulum orientation on power output potential differs significantly with excitation type and pendulum properties. While expected peak power output is observed at the resonant frequency and twice the resonant frequency under direct and parametric excitations respectively for both systems, the linearised system also exhibits regions of instability. These instability regions under parametric excitations were investigated with consideration for energy harvesting applications. Theoretical and experimental findings revealed that dynamic tilt excitations can be utilised for broadband energy harvesting at the expense of the peak power output. While peak average power output for these excitations for the considered system parameters is relatively low, 1 W versus 12.5 W for heave excitation, the bandwidth is very broad and starts from 0 rad/s frequency if tilt excitation amplitude is above 1.1 rad.