Performance assessment of a parametric-resonance wave energy converter: change of instability intensity going from regular to irregular waves

Parametric resonance, rather than a risk, can be leveraged to broaden the response bandwidth of a wave energy converter, potentially increasing energy availability at the power take-off shaft. Using a nonlinear Froude-Krylov force model, particularly suitable for axisymmetric and prismatic floaters, the paper focuses on a pendulum-based device purposely designed to experience a beneficial type of parametric instability. This study specifically investigates the intensity and triggering effects of parametric resonance under regular and irregular wave conditions. It is shown that, although with a notable reduction in intensity, the potential of parametric resonance as an enabling factor to improve energy extraction is significant also with panchromatic waves.