Caisson breakwaters embodying an OWC with a small opening—Part I: Theory

We deal with the problem of a caisson breakwater embodying an OWC which is connected to the sea through a small opening. Waves cannot enter this OWC and the oscillations of the water column are due to the wave pressure on the small opening. The problem is solved through two alternative approaches. First alternative: we assume that the plant generates a progressive wave which is superimposed on the standing wave yielded by the reflection of the incident wave. Second alternative: a priori before the breakwater there may be every periodic waveform with the given frequency and a mean energy flux smaller than (or equal to) the mean energy flux of the incident waves, and we look for the waveform satisfying the equations of wave–OWC interaction, and giving the largest value of Φ¯/E¯ (mean energy flux/mean energy per unit surface). In some cases the solutions obtained through the two alternative approaches prove to be coincident with each other. In other cases the solution giving the largest value of Φ¯/E¯ proves to be a sum of two standing waves with phase angles in space and time. In these cases (sum of two standing waves) the plant may absorb up to the 100% of the incident wave energy.