Effects of mooring configurations on the hydrodynamic performance of a floating offshore oscillating water column wave energy converter

Abstract

This paper presents the results of a systematic experimental investigation into the effects of different mooring configurations on the hydrodynamic performance of a 1:36 scaled Oscillating Water Column (OWC) Wave Energy Converter (WEC) model. The OWC WEC was tested in the fixed, free-floating and moored conditions with three different mooring configurations namely a tension leg, a taut mooring with 45O tendons, and a catenary mooring with heavy chains. Detailed analysis included hydrodynamic capture width ratios (CWR), fluid interactions between the OWC chamber and the incident waves, response amplitude operators (RAO), mooring tensions, and turbine damping coefficients. The rigid-body motions of the device had adversely affected the WEC's performance with a substantial decrease in the hydrodynamic CWR occurring between the fixed condition and the floating-moored conditions. The RAOs of surge and pitch were found to be inversely proportional to the CWRs, however, heave motions contributed to power absorption for the taut moorings. Of the floating-moored conditions, the 45O taut mooring was the best performing, followed by the vertical taut and catenary mooring. Both taut-moored conditions exhibited significantly higher mooring tensions than the catenary moored condition. The maximum mooring tensions for the taut-moored conditions correlated with increased CWRs, whereas the maximum tension in the catenary was induced by the maximum heave and pitch RAOs.