72 58 



(2a) cavitation and reloading: 



In tests on steel diaphragms p/p^ = 1/7.83, while a/h is of the order of 100 

 and I lies between 5 and 10. For such values, in the absence of cavitation, 

 E somewhat exceeds £■„. In the case of cavitation without reloading, the fac- 

 tor x' ^ ranges from 1/11 to l/l7> so that E is only a third or a quarter of 

 E^; the reloading by the water will then probably increase E to something be- 

 tween £„/2 and 2E^. In some cases it may happen that E = f^„. 



Thus, although exact formulas are not easy to obtain, it can at 

 least be said that the observed rough proportionality of the deflections of 

 many diaphragms or similar structures to WyR, or at least to the square root 

 of the energy In the incident wave, and the approximate equality of the plas- 

 tic work to the incident energy, stand in fair harmony with analytical expec- 

 tations. 



To sum up, the analytical results suggest that the major factor 

 controlling damage 



1 . should be the maximum pressure for relatively small structures, 

 whose swing time and diffraction time are both small as compared with the 

 time constant of the incident wave; 



2. should be the incident impulse when the swing time of the target 

 is much greater than the time of action of the pressure, provided cavitation 

 does not occur; 



5. may be something nearly proportional or even equal to the Incident 

 energy in some intermediate cases, or when cavitation occurs. 



PART 5- ANALYSIS OF A FEW DATA ON DIAPHRAGMS 



The application of the preceding formulas to recent observations 

 made at the Taylor Model Basin will be discussed in the report on those ob- 

 servations. Two other sets of test data, reported by the Bureau of Ships, 

 will be discussed here. 



MODUGNO GAGES 



The data published by the Bureau of Ships on Modugno gages (19) are 

 in partial agreement with the theoretical expectations set forth here. 



The diameter of the gages was 1 inch for the diaphragm itself and 

 2.6 Inches overall. Thus the diffraction time T^ would be 0,008 millisecond 

 for the diaphragm or 1.3/59 = 0.022 millisecond for the entire gage. 



