Laboratory modelling of nonlinear power take-off damping and its effects on an offshore stationary cylindrical OWC device

The accurate evaluation of the wave energy conversion of oscillating water column (OWC) wave energy converter has consistently plagued scholars. In this paper, an original and well-validated test platform is proposed for exploring the flow characteristic of a nonlinear power take-off (PTO) damping, with which a more accurate and stable measurement of captured energy is obtained in the laboratory modelling. This study utilizes ten orifices to comprehensively investigate the impact of the PTO damping on an offshore stationary cylindrical OWC device. The joint effect of the PTO damping with wave height (Hi) or draft of OWC (Dr) is examined. The damping coefficient Cf = 10350 is found to be the optimal damping coefficient, in terms of both the peak wave energy conversion and the efficient bandwidth. It is revealed that the variations of the PTO damping can regulate the effect of Dr and Hi on wave energy conversion. An appropriate reduction in PTO damping can alleviate the weak energy output caused by the increased Dr and Hi. The effect of increased Hi on wave energy conversion could be judged by the size relation of the maximum and minimum values of internal pressure data.