NSWC/WOL ¥R 76-155 



Calculation of Depth, y , of Bottom of Cavitation. Given 



Equations C6a, b, c the problem of determining PNEG reduces to 

 determination of the depths y and y of the top and bottom of the 

 cavitation. To determine y we plotted, as a function of the charge 



weight W, values of y calculated from PNEG-values measured on the 



c 1 



1973 Chesapeake Bay Test Program using Equation C6c. The equation.* 



y = 4.4 W 0,3 (C7) 



c 



where W is the explosive weight in pounds pentolite and y is in 

 feet was used to approximate these measurements. 



Calculation of Depth, y , of Top of Cavitation. The top 



(beginning) of the cavitation region was taken as the point on the 

 reflected ray where the reflected shock first lowered the absolute 

 pressure to the vapor pressure of the water. To calculate y we use 

 the linear superposition of the direct and surface-reflected pressure 

 waves , 



P S UM (t) = P D (t) + PR (t) (C8) 



The direct wave, p (t) , is given by equations C2 , 3, 4. The 

 reflected wave, p (t) , can also be calcuated using Equations C2, 3, 4 

 provided one makes the substitutions "-k" for "k" and "R, " (slant 

 range from image) for "R". To determine y we then solve for the 

 point on the reflected ray path where 



*Equation CT gives a crude empirical fit to the PNEG-values measured on the 1973 

 test program. It was used out of necessity to make kill probability calculations 

 used to design the 1975 test program hut has not been re-evauluated using those 

 and other available PNEG-measurements. 



C-6 



