Hydrodynamic investigation on a three-unit oscillating water column array system deployed under different coastal scenarios

Abstract

To harvest the available wave power in marine areas as much as possible, the deployment of arrays of oscillating water columns (OWCs) is promising and a preferred scheme. In the present work, by making full use of the advantages of Computational Fluid Dynamics (CFD) technique in capturing the complex and variable flow field characteristics in the interaction process between the OWC array and nonlinear waves, an array system with three cylindrical OWC units aligned in line was numerically investigated. The numerical model was verified against the experimental tests, including the scenarios wherein an isolated cylindrical OWC and multiple cylindrical OWC devices, respectively, were located in a wave flume. To avoid the improper configuration that may cause inefficiency, and give full play to the superiority of the array configuration in wave power extraction, the performance of the OWC array deployed under different coastal scenarios, including deployed offshore, located in front of and embedded into a straight coast, was quantitatively compared. The effects of the transverse spacing between the sub-units in the array on the wave power capture width ratio were examined. The results indicate that among the three layout scenarios, the case of being embedded into a straight coast is the most preferred scheme as the coast effect and the array effect both can impose a constructive interaction between the OWC units, especially under a relatively larger transverse spacing condition. The scheme of being located in front of a straight coast has a certain extent of ineffectiveness due to the triggered total reflection phenomenon on the windward side of structures under a specific wave condition, which was also proved by establishing a theoretical model based on the potential flow theory. There is a location criterion for identifying the zero-value of the capture width ratio, thus inappropriate deployment when located in front of a straight coast that may cause inefficiency can be prevented. Compared to the case that an isolated OWC device is embedded into a coast, the superiority of the array system can be demonstrated when the transverse spacing is designed as a relatively larger value.