NSWC/WOL TR 76-155 



(2) Regions of less than 50% kill — since they encompass 

 a tremendous volume of water — make a major contribution to the 

 total number of fish killed by an underwater explosion. 



These two features are examined further in Sections 4.2 and 4.3. 



4.2 KILL PROBABILITES AS A FUNCTION OF DEPTH FOR DIFFERENT 

 SIZED FISH 



Figure 4.2.1 shows the variation of predicted kill-probability 

 with fishes' depth at a fixed horizontal range for different fish 

 corresponding to three different sized swim bladders. The predicted 

 kill-probability is obtained from calculated Z-values, e.g., 

 Table 4.1.1, using Equation 3.2.1 (dashed line in Figure 3.2.2). The 

 approximate length of Striped Bass corresponding to the equivalent 

 bladder radii of the bladder oscillation calculations was calculated 

 from 



Bladder Radius = >Q42 (4.2.1)* 



Fish Length 



For the two larger sized fish in Figure 4.2.1 the maxima 

 occurring at about 7 and 11 meters depth, respectively, are caused by 

 surface cut-off occurring at the first half-cycle of bladder 

 oscillation. At shallower depths the bladder does not have time to 

 respond fully to the positive portion of the explosion wave; while 

 coincidence of the first half-cycle and surface cut-off amounts to 

 a resonance between the oscillatory response and the driving pressure 

 field outside. Thus, at shallow depth the larger fish are in effect 

 protected from harm by their swim bladders; while at the resonance 

 depth their swim bladders "do them in." 



*The value .042 is 80% of that experimentally measured from a sample of 3 

 Stripped Bass. The value 80% represents a guess at the correction to go 

 from measured radius to equivalent computation radius for this fish. 



57 



