Sinusoidal vertical motion of a sonobuoy suspension – Experimental data and a theoretical model

Mouvements verticaux sinusoïdaux du mécanisme de suspension de la bouée acoustique – Données expérimentales et modèle théorique

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Authors
  1. Chapman, D.M.F.
  2. Kezele, D.B.A.
Corporate Authors
Defence R&D Canada - Atlantic, Dartmouth NS (CAN);Sparton of Canada Ltd, London ONT (CAN)
Abstract
To isolate its acoustic sensor from the large vertical motions of the buoy at the ocean surface, a typical sonobuoy employs a low-pass mechanical filter comprising a bungee cord (spring) and a damper disk (hydrodynamic added mass and damping). If the system were to behave as a driven simple harmonic oscillator, the transfer function of vertical motion would roll off at 40 dB/decade above resonance; however, experimental systems of this sort exhibit a rolloff of approximately 30 dB/decade. Experiments have shown that the inertia coefficient CI and the drag coefficient CD of a circular disk in sinusoidal motion are in fact not constants, but depend on the dimensionless ratio of amplitude of motion to disk diameter, A/d. Incorporating this concept, the simple harmonic oscillator model has been enhanced to produce an iterative model for the transfer function of the bungee/disk system that agrees well with experimental data. Well above resonance, the model simplifies to an expression giving a 27 dB/decade rolloff.

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Keywords
sonobuoys, suspension, ocean waves, resonance, drag coefficent, hydrodynamic add
Report Number
DRDC-ATLANTIC-TM-2008-121 — Technical Memorandum
Date of publication
01 Jun 2008
Number of Pages
36
DSTKIM No
CA032039
CANDIS No
531045
Format(s):
Electronic Document(PDF)

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