Acoustic wave propagation in air‐bubble curtains in water—Part I: History and theory

Abstract

Air bubbles in water increase the compressibility several orders of magnitude above that in bubble‐free water, thereby greatly reducing the velocity and increasing attenuation of acoustic waves. The effect of air bubbles in water on acoustic wave propagation was studied extensively during World War II as part of an overall effort to apply underwater sound in submarine warfare. Currently, air bubble curtains are used to prevent damage of submerged structures (e.g., dams) by shock waves from submarine explosives. Also, air‐bubble curtains are used to reduce damage to water‐filled tanks in which metals are formed by explosives. Since World War II, research has progressed less feverishly in government and university laboratories. Published results of laboratory experiments generally confirm theoretical velocity and attenuation functions and demonstrate that these quantities are dependent principally upon frequency, bubble size, and fractional volume of air. Below the bubble resonant frequency and in the frequency range of marine energy sources, acoustic wave velocity is essentially independent of frequency and bubble radius, being well below the velocity in bubble‐free water. In this frequency range, attenuation increases with increasing frequency, decreasing bubble radius, and increasing fractional air volume.