SURFACE REFLECTION AND CAVITATION 



191 



image law just stated has to be modified; for, sea 

 water is apparently incapable of sustaining a tension 

 of any appreciable magnitude, and cavitation will 

 therefore set in at any point where the pressure be- 

 comes negative. At short ranges, therefore, the pres- 

 sure-time curve for a shock wave and its reflection 

 usually looks like the full line in Figure 10, instead 

 of following the dotted curve as it would if there 

 were no cavitation. 



Experiments on explosion waves in sea water'" 

 strongly suggest that the water begins to cavitate as 

 soon as the pressure becomes negative, and that the 

 cavitation can develop sufficiently rapidly to prevent 

 negative pressures from persisting even as long as 

 10 Msec. This is to be expected if there are even a few 

 tiny bubbles in the water. A theory of the propaga- 

 tion of cavitation fronts has been given by Ken- 

 nard.*'''^ 



