EVALUATION OF NOISE REDUCTION COATINGS: EXPERIMENTAL DESIGN

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Authors
  1. Hamm, C.A.
Corporate Authors
Defence Research Establishment Atlantic, Dartmouth NS (CAN);Guigne International Ltd, Paradise NFLD (CAN)
Abstract
A small scale method for evaluating the effect of damping the decoupling coatings on the noise radiated from metallic structures into water has been investigated. The method involved mechanically exciting a semi-submerged plate, and measuring the sound radiated into a reverberant tank. The effectiveness of a particular damping or decoupling material was judged in terms of the difference in radiated noise from coated and uncoated plates. The interpretation of this noise reduction spectrum proved to be difficult, since modal frequencies shifted with the added mass of the coatings or as result of the effect of the decoupling layer. Thus, the noise reduction spectrum was not a smooth function of frequency, as one might expect based on the material properties of a coating. A fourth order polynomial fit to the noise reduction spectrum clearly showed the expected trends for a closed cell foam decoupling material, with approximately 18 dB reduction at 2000 Hz. For damping materials, a more appropriate figure of merit was found to be the integrated noise reduction spectrum over a wide frequency band. It was suggested that improvements to the small scale measurement method could be made by measuring the radiated sound power using a near field intensity probe.
Keywords
Decoupling
Report Number
DREA-CR-96-417 — Contractor Report
Date of publication
01 May 1996
Number of Pages
73
DSTKIM No
96-02588
CANDIS No
499041
Format(s):
Document Image stored on Optical Disk;Hardcopy

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