Laboratory tests on the predictability of the natural frequencies of oscillation in special U-ducts

The aim of this work is to verify the methodology tocalculate the natural oscillation frequencies of the REWEC2device (REsonant Wave Energy Converter realization N.2). Thischeck is fundamental because the performance of the REWEC2devices is based on their capabilities to work in resonance withthe incoming waves. Several tests on a small-scale model of awave energy absorber were conducted. In order to measure thenatural oscillation frequency of the plant, unforced oscillations ofthe water in the vertical duct and in the chamber, were induced.These oscillations were produced by a rapid pressure drop of theair in the upper caisson, opening the valve that links the caissonwith the atmosphere quickly.A pressure transducer measured the pressure in the uppercaisson, whereas a second transducer, placed in the plenumchamber, measured the fluctuation of pressure produced by theoscillations of the free water surface inside the chamber. Thefrequency of these unforced oscillations was compared to thefrequency foreseen by the mathematical model.The good agreement carried out between the experimental testsand the theoretical results, has validated the methodologyproposed.