Nonbreaking Wave Forces on Multiresonant Oscillating Water Column Wave Power Caisson Breakwater

Abstract

Experimental measurements of in-line wave forces on a 1:50 scale model of an array of multiresonant oscillating water columns (MOWCs), a free-standing wave energy caisson, are reported. Wave forces on a vertical wall were measured and compared with Sainflou’s and Goda’s formulas, which serve as base for studying wave forces on an MOWC array. A range of hydrodynamic parameters with different damping of the OWC chamber and center-to-center (c/c) spacing were used. In general, the force on the MOWC caisson array is twice that of the vertical wall for maximum damping of the OWC chamber. Reduction of damping of the OWC air chamber reduces the force on the array of caissons by 35–60% of the force on a vertical wall. It is found that shoreward force magnitude is greater than seaward. For spacing of 2–3 times the harbor width, the OWC array acts like a perforated breakwater, experiencing 60% of wave forces on the vertical wall, while for a c/c spacing range of 4–5, it behaves like a vertical wall. Incorporation of an air pressure release by pass system for the OWC chamber is recommended, as this will reduce in-line wave forces on a caisson array to a range of about 35–40%. The nonlinear response of the OWC on wave forces warrants the use of a numerical model and further investigation.