1887
Volume 30 Number 6
  • E-ISSN: 1365-2478

Abstract

A

Source strength of an airgun array may be increased by:

  • —  utilizing higher pressure,
  • —  increasing total array volume,
  • —  employing more guns,
  • —  improving gun efficiency.

One measure of gun efficiency is “specific source strength”, *, defined as source strength per unit quantity of air used. Typical units are MPa m/l. Most developments are directed toward increasing gun pressure and/or gun volume to increase source strength of the array. These efforts require that more air compressors be installed onboard the ship. Consequently, a larger ship may be needed for the additional compressors, guns, and auxiliary equipment.

A development program was initiated in 1976 to increase source strength of the array without using a larger ship. New guns were designed and built—one for 41.4 MPa and 7.37 liter (6000 p.s.i./450 in3) operation and another with 13.8 MPa and 4.92 liter (2000 p.s.i./300 in3) capability. Experiments were conducted with these new guns (and existing guns) over a range of pressures from 13.8 to 41.4 MPa (2000 to 6000 p.s.i.).

Design of the new guns was aided by a mathematical model. The model relates physical dimensions of the airgun to acoustic pressure in the water. It consists of four nonlinear differential equations relating

  • —  shuttle motion,
  • —  bubble pressure,
  • —  chamber pressure,
  • —  bubble radius.

The last equation is the “free‐bubble‐oscillation equation” and represents the ideal case of a pressurized bubble released instantaneously in water. The three other equations modify this ideal case; the four equations together model an airgun of the type manufactured by Bolt Associates, Inc.

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2006-04-27
2020-03-31
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References

  1. Giles, B. F. and Johnston, R. C.1973, System approach to airgun array design, Geophysical Prospecting21, 77–101.
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  • Article Type: Research Article
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