Causes of Excessive Volatility in Bellhop Transmission Loss

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Authors
  1. McCammon, D.
Corporate Authors
Defence R&D Canada - Atlantic, Dartmouth NS (CAN);McCammon Acoustical Consulting, Waterville NS (CAN)
Abstract
This study has examined the factors that control the ray amplitude as a function of range in the Bellhop Gaussian beam method of computing transmission loss (TL). These factors are the Gaussian weighting function and its standard deviation, the boundary losses and the beam width. For the single case tested here, it was determined that the beam width, a ray-traced quantity, was responsible for the large volatility of the transmission loss with range. And, more specifically, the amount of change in the sound speed (SP) gradient at the start of each SP layer was controlling the beam width. There were no simple remedies to the volatility of the beam width discovered in this study. For example, employing a larger number of sound speed points to reduce the gradient change between each layer did not change the result, but it did adversely impact the run time. Range and frequency averaging were tested, and for this test case, only range averaging was effective in reducing the TL volatility.

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Report Number
DRDC-ATLANTIC-CR-2011-054 — Contractor Report
Date of publication
01 Oct 2011
Number of Pages
40
DSTKIM No
CA036888
CANDIS No
536627
Format(s):
Electronic Document(PDF)

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