Pneumatic and similar breakwaters

Abstract

The process of calming waves by injecting air bubbles beneath the surface has been known to civil engineers for nearly 50 years. It has been little used for its results have been erratic, its method of working was unknown and its effect could not be predicted. The investigation described in this paper has shown that the surface currents set up by air injection, and the distribution of the water velocity within the currents, can be matched by currents set up by water jets, and that the two currents so matched have almost the same wave-damping effect whether they are set up by water jets or by air. It is concluded that the bubbles as such have at most a very small effect on the wave motion. It is found that waves of small amplitude are stopped in the way predicted theoretically, but that as the amplitude increases the surface current necessary to stop waves of a given length increases.