381 



cases studied, and the motion Is upward for all charges over 1/2 pound. The 

 horizontal motion diminishes with an increasing size of charge in the cases 

 studied at all charges over l/2 pound. 



Finally, a rough estimate is made of the effect of the migration 

 upon the pressure that is generated in the water by the recompression of the 

 gas globe; curves are shown in Figure ly on page 28. A migratory displace- 

 ment equal to one-third of the maximum radius R2 decreases the peak pressure 

 by about one-third, whereas a displacement equal to ^2 reduces the peak pres- 

 sure to one-tenth of its value for zero migration. The impulse, however, is 

 much less affected by the migration. 



Important cases remain to be taken up, in particular those in which 

 the distance from the wall is less than 2i?2. ^i^cl in which the charge lies be- 

 tween two rigid surfaces, like the ground and a ship's bottom. 



The conditions for exact similitude with respect to migration can 

 not be reconciled with those governing the flow of destructive energy from a 

 charge to a target, as applied in the nominal theory of TMB Report U92 (11 ). 

 The application of model tests of migration effects to the prediction of full- 

 scale phenomena is therefore subject to correction for scale effect and any 

 direct expansion from a very small scale to full scale, without full know- 

 ledge of the scale effects, may lead to erroneous conclusions. The exact 

 formulation of the scale effect corrections will form the subject of further 

 work. 



