The boundary acoustic impedance effects of a towing tank underwater sound radiation induced by a steel cylinder continuous vibration

In this study, it was found the characteristics of the boundary was an important factor to the accuracy of measurements and simulations for underwater radiation in a towing tank. Measurements and FEM simulations of the radiation sound field were conducted. In the measurements, two types of continuous vibration were performed in the towing tank which are: A 250 Hz/500 Hz speaker continuous noise and a 45 Hz machine continuous running were used to generate vibrations in a submerged steel circular cylinder. The experiment was conducted to vibrate the watertight cylinder and to measure the underwater sound field, which was significantly impacted by reflections from the tank walls. FEM simulations of radiation sound field were evaluated to compare with the experimental results.The experimental measurements and underwater sound field simulations were consistent with each other at 45 Hz and 250 Hz. The simulation and experiment was slightly larger in the 500 Hz case. The quantitative result was the verification of the measurement and simulation of radiated sound in water. Furthermore, the qualitative result was the simulations investigated the factors affecting the towing tank's boundary effects. Tests of alternative impedances of the walls showed that the wall impedance had strong effects on the underwater sound field. Another boundary effects were investigated by changing the source(the cylinder) direction showed that the wall interference effect was stronger when the cylinder was oriented towards the wall than towards the watercourse. Finally, tests of the source frequencies from 20 Hz to 500 Hz showed that higher frequencies generated stronger boundary interference effects in the underwater sound field than did lower frequencies.