Underwater sound transmission through water tunnel barriers

Abstract

In hydrodynamic test facilities with flowing water, receiving hydrophones are commonly placed behind a solid barrier to reduce flow noise from buffeting and turbulence. However, acoustic waves from the sound sources under study, such as cavitation bubbles, may propagate through the barrier as compression or shear waves, and the presence of the second wave type distorts signals recorded by the hydrophones. Such distortion depends on the structural characteristics of the barrier and the source-receiver geometry, and it may lead to sound-source detection and localization errors. This presentation describes results from a combined experimental and computational effort to understand the sound transmission characteristics of plastic and metal barriers typically used in water-tunnel testing. The experiments were conducted in a 1.0-meter-deep and 1.07-m-diameter cylindrical water tank using a single sound projector, a receiving array of 16 hydrophones, and impulsive (100 micro-second) signals having center frequencies from 30 kHz to 100 kHz. Computations intended to mimic the experiments are completed with the wave number integration software package OASES. Together the computations and experiments allow the most important barrier parameters to be identified. Dependencies of the received signal on the barrier parameters are presented. [Supported by NAVSEA through the Naval Engineering Education Center.]