16 



243 



14 



13 



12 



10 9 8 7 6 5 4 



Distance from Plote in feet 



4000 



3000 o 



2000 



1000 



-Pk 



-1000 



■2000 



Figure 11 - Distributions of Pressure behind a Plate at Successive 

 Instants of Time, in the Absence of Cavitation 



Figure 11, on the other hand, shows the instantaneous distribution 

 of pressure in the water adjacent to the plate, plotted against the distance 

 from the plate. The distances shown in the figure correspond to 300 pounds 

 of TNT; for 1 ounce they would be 1/17 as great. The curves are calculated 

 by Equation [19] where t + x/c is positive, and by Equation [12] elsewhere. 

 Curve A shows the distribution of pressure at the instant at which the pres- 

 sure wave first reaches the plate (( = 0). Curve B shows the distribution 

 0.2 millisecond later (( = 0.0002); at this time the reflected wave has ad- 

 vanced 1 foot from the plate. Curves C, D, E, F refer similarly to times 

 about 0.4, 0.8, 1.6, 2.U milliseconds after the arrival of the incident wave. 

 Curve F serves also to represent the final form of the reflected wave; the 

 incident wave has by this time completely disappeared. 



These figures will be modified by the occurrence of cavitation in a 

 way that depends upon the laws governing the cavitation. 



Cavitation may occur at the plate. It may occur as soon as the 

 pressure sinks to the hydrostatic pressure p^; this will be at the instant 

 marked (j in Figure 10. In this case the plate leaves the water with a ve- 

 locity equal to v^^^ as given by Equation [1?]. and the curve for the pres- 

 sure on the plate in Figure 10 coincides with the axis of zero pressure from 

 the time (j onwards. An alternative pqssibillty, however, is that cavitation 

 may not begin until a lower pressure p^' is reached, at a later time such as 

 that marked tj In Figure 10. In this case the plate leaves the water at the 

 time ^2 with a velocity less than v ^^^ . The pressure on the plate after «2 

 will then be the constant cavity pressure p^. If p^ = p^', the curve will 

 extend horizontally from the point t^, as shown by the lower of the broken 



