Date of Award
Master of Science in Ocean Engineering
Measuring the performance of hydrophones in submarine and surface ship towed arrays at low frequencies in the Leesburg test facility (Okahumpka, FL) is achieved using ambient noise as a calibration source. The preferred method of calibration that relies on a known, repeatable sound source is not implemented because the equipment capable of generating sound at such low frequencies does not currently exist.
This project examines the feasibility of implementing a moving magnet actuator (MMA) as the motor force in a very low frequency (VLF) underwater acoustic projector. MMAs have the potential to advance low frequency projector technology by providing large linear displacements and large force outputs in a small package. To explore this potential, three methods of investigation are performed in this study: analytical modeling, numerical modeling, and experimental testing. Analytical modeling is performed in Matlab using fundamental equations for a simple acoustic point source. Numerical modeling is represented as a fluid-structure interaction (FSI) problem and is solved using the finite element program Abaqus. Experimental testing is conducted by placing a load on a Bose MMA to simulate the mass of the VLF projector’s water displacement.
Analytical and numerical modeling efforts estimate a projector source level of over 125 dB// 1 μPa @1m at 1Hz and over 180 dB// 1 μPa @1m at 30Hz. The experimental efforts find that the Bose MMA operates at displacements necessary to achieve sound pressure levels calculated from the analytical and numerical models. This study indicates that an MMA is a suitable force generator for the VLF projector and explores future work necessary for VLF projector design, manufacture, and operation.
Wallin, Brenton, "Implementation of Moving Magnet Actuation in Very Low Frequency Acoustic Transduction" (2017). Open Access Master's Theses. Paper 1017.