24 



10 



/ 



/ 

 I 



I 



I 



Charge I 

 • I 



1 

 I 

 \ 

 \ 



\ 



V 



Water 



Air 



Cavitation 



Cavitation at the Plate: 

 The Free-Flight Phase 



It has repeatedly been ob- 

 served that cavitation occurs near the 

 interface between water and a solid, 

 when tension develops in the water be- 

 hind a reflected shock wave. See, for 

 example. Figure 15- If cavitation 

 were to occur at the interface and 

 there only, as in Figure 8, Just as 

 the increment of pressure due to the 

 wave sank to zero, the plate would 

 leave the water at the time T„ with 

 the velocity v„ given by Equation [7]; 

 see Figure 5- In reality, cavitation 

 cannot occur until the pressure sinks 

 at least to the vapor pressure of the 

 liquid, and it may not begin until a lower pressure is reached. Hence in 

 practice a short phase of negative acceleration would intervene and the plate 

 would leave the water, with a velocity somewhat less than v„; for example, at 

 the time T' in Figure 5- Many initial velocities agreeing with this deduc- 

 tion from theory have been observed at the Taylor Model Basin. A streak pho- 

 tograph illustrating the sudden acquisition of velocity by a plate is repro- 

 duced in Figure 9- 



\ 



Figure 8 - Schematic Illustration of 



Deflection of a Plate with Cavitation 



Only at the Plate 



The broken ciirve represents the front of the 

 reflected shock wave. 



Diapliragm 



Spots 



0.5 I 



Time in milliseconds 



Figure 9 



A Streak Photograph Showing Impulsive Acceleration 

 of a Diaphragm by a Shock Wave 



The streaks were made by light from 5 spots, one on the center of the diaphragm, two others half way 

 to the edge, and two on the supporting rim. The line of view was at 30 degrees to the plane of the 

 diaphragm. The streaks were made from left to right. The sudden bend terminating the straight portion 

 of each streak indicates an impulsive acquisition of velocity by the diaphragm. 



