DESIGN IMPROVEMENTS OF AN UNDERWATER LOW FREQUENCY PROJECTOR BASED ON CLARINET ACOUSTICS

Open Access
Author:
Koh, Veronica Wei
Graduate Program:
Acoustics
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 07, 2017
Committee Members:
  • Stephen C. Thompson, Thesis Advisor
  • Daniel A. Russell, Committee Member
  • Thomas B. Gabrielson, Committee Member
Keywords:
  • Underwater
  • Acoustics
  • Clarinet
  • Low Frequency Projector
Abstract:
Low frequency (ka<<1) underwater projectors are desired for long range sonar applications and oceanography due to their low absorption losses. However, their inherent design constraints often lead to large size and high cost. This thesis discusses several design improvements made to a prototype of a low cost low frequency underwater projector based on clarinet acoustics. First, a new pressure chamber was designed and built to improve water sealing, ease of assembly, as well as interface with a larger diameter pipe to reduce occurrence of cavitation. Lab measurements of the improved prototype were made using both PVC and aluminum based resonators, with two different reed configurations and tested at different blowing pressures. Analysis of measurement results showed how playing frequency varied with blowing pressure and resonator type. In particular, intermodulation products generated at high blowing pressures resulted in perception of a large drop in playing frequency. Distortion of the sound generated was also calculated and shown to increase at higher blowing pressures. Second, improvements in the equivalent circuit model of the underwater clarinet were made by including effects of pressure chamber impedance and elastic wall. The chamber and resonator impedances were first modeled using COMSOL Multiphysics. Two-resonance and four-resonance equivalent circuit models were then derived to fit the acoustic impedances measured in COMSOL. Overall system impedance analysis and time domain simulation of the improved model were also performed. Results from the improved model provided explanation for the trends observed during measurements. Finally, a combination of measured sound pressure level and modeling was used to predict sound pressure level in the far field. The efficiency in converting input pneumatic power to acoustic power was also estimated using the model. By varying different design parameters in the model, the trade-offs between these parameters and the performance of the underwater clarinet were also discussed.