WAVE PRESSURE DISTRIBUTIONS ON A U-OWC BREAKWATER: EXPERIMENTAL DATA VS CFD MODEL

U-OWCs are Wave Energy Converters belonging to the family of Oscillating Water Column. The interaction betweenwaves and a U-OWC breakwater produces an unknown pressure distribution on the breakwater wall, due to the motioninside the plant. In order to evaluate the force acting on a U-OWCbreakwater produced by regual waves, we carried outan experiment in a 2D numerical flume. The computational domain is equipped by a piston-type wavemaker, in the leftextremity side and a U-OWC breakwater on the opposite side. The water-air interaction is taken into account by meansof the Volume Of Fluid (VOF) model implemented in the commercial CFD code Ansys Fluent. Both air and waterflow fields are assumed to be unsteady and are computed by solving the Reynolds-Averaged Navier-Stokes (RANS)equations. In the numerical model, air is considered as an ideal gas, in order to take into account the compressibilityinside the plenum chamber. Results were compared with a theoretical model on a traditional vertical breakwater andexperimental results obtained through an experiment directly at sea, off the beach of Reggio Calabria, in the easterncoast of the Straits of Messina (Southern Italy). As observed in the physical experiment at sea, the pressure distributionare strongly influenced by the absorption of the plant. Indeed, in case of high performace of the U-OWC, we found adeformation of the pressure distribution in respect to the theoretical one, expecially near the outer opening of the plant.This deformation produces a lower in line force on the structure.