Decreasing the radiated acoustic and vibration noise of both prop-driven and buoyancy-driven autonomous underwater vehicles

Abstract

Our previously published results from decreasing the radiated acoustic and vibration noise of a mid-size, prop-driven autonomous underwater vehicle (AUV) show self noise levels recorded at sea by an AUV-mounted hydrophone array that are at, or below, typical background ocean noise levels across the frequency band above 200 Hz. The remaining noise below 200 Hz is primarily vibration induced. The modifications required to achieve this 20–50 dB reduction in propulsion and steering system noise levels will be reviewed in this talk. In addition, at-sea measurements of the acoustic noise radiated by the large (30 L) buoyancy engine on a 20-ft wing span flying wing autonomous underwater glider are presented. Whereas a prop-driven system operates continuously, the buoyancy-driven propulsion system has a very low duty cycle of a few percent; it is on only for about 3 min during each dive cycle. Onboard self noise from the glider's internal fluid-based roll control system far exceeds that from an aileron-based system. However, the former system provides control authority at or near neutral buoyancy. [Work supported by the Office of Naval Research and BP.]