Inflation of the Sphere 



The kind of gas used for inflation will be dictated somewhat 

 by where and how the pneumatic source is used. In shallow- 

 water applications, most of the experiments were conducted 

 using conventional Navy issue carbon dioxide cylinders of 

 different sizes. For deep submersion work the problem is 

 more involved, since carbon dioxide is very temperature - 

 sensitive. In these applications compressed air at around 

 2000 psi was used. In order to obtain rupture a certain 

 differential pressure must be achieved depending upon the 

 elastic material used. 



Inflation of pneumatic spheres or tubes might also be 

 accomplished by an explosive gas, with the rupture induced 

 by application of a spark. Since there is a marked difference 

 between the broad-band sound produced by a chemical 

 explosive alone and the almost monofrequency effect of the 

 pneumatic source, it would appear that a combination of the 

 two might well produce a substantial low-frequency output. 

 However, this possibility has not been explored at NEL, as 

 considerable study of chemical explosives as sound sources 

 has already been performed elsewhere. 



THEORETICAL DISCUSSION 



Frequency Control 



The frequency of the pneumatic sound source can be 

 closely controlled. Although it is dependent to some degree 

 on characteristics of the basic sphere, it is more conven- 

 iently dependent on the hydrostatic pressure to which it is 

 subjected at the time of bursting. The composite effect of 

 diameter and wall thickness is evident by comparing the 

 data on figures 27, 2 8, and 29, which are plots of frequency 

 vs. depth for three different sizes of spheres, all made of 

 Reeves Rubber Company Mix No. 3015. 5. It has been 

 found that other rubber mixes influence the frequency 

 characteristic of a given sized sphere, probably because of 

 differences in elasticity. 



50 



