Nonlinear wave loads on a stationary cylindrical-type oscillating water column wave energy converter

Abstract

Based on the potential flow theory, a second-order Higher-Order Boundary Element Method model is developed to simulate hydrodynamic loads and pressure on a stationary cylindrical-type oscillating water column (OWC) wave energy converter. Quadratic pneumatic damping and additional viscous damping are introduced to simulate the effects of the power take-off and the viscous dissipation inside the chamber, respectively. The proposed model is verified against a carefully instrumented scaled experiment. The effects of the chamber geometry and the wave environment on the hydrodynamic loads of the OWC device are then explored using the validated model. The resonance excited by the second-order wave component is observed with the fundamental frequency being half of the natural frequency. This resembles a sloshing mode and leads to a significant increase in hydrodynamic pressure and surge force as well as pitch moment. The effects of the second-order waves cannot be ignored under the action of the low-frequency long waves. In addition, the surge force and the pitch moment are not sensitive to the variation in the orifice opening ratios, while the heave force increases with the opening ratio at a resonant heave frequency.