- u - 265 



where p is the hydrostatic pressurt. Insertion of numerical values shows that in the majority of 

 cases this effect is one to be reckoned with. (it is prevented from being of importance for the 

 infinite plate by the fact that the mass of unrt drea of plate and reconstituted water is infinite). 

 It is emphasised that this effect is distinct from both the impact of cavltated water that we have 

 been studying and also from any effects due t3 bubble oscillations, though it is hydr:dynamicany 

 akin to both of these. 



Discussion of results . 



The conclusion that cavitation is an important factor in producing damage in thin pTales is 

 in agreement with Klrkwood's(5) work, and the investigation for a very thick plate has shown that 

 cavitation may make an appreciable contribution even in this extreme case. There is, however, a 

 serious discrepancy, in that Kirkwood(3) finds that nearly ell the energy Is absorbed by the plate, 

 wMreae we have arrived at a factor of the order of |. If all the energy is to be absorbed, then 

 we must have the velocities of the plate and the velocities of the cavitated water just arriving at 

 the reloading front equal, and this is definitely not possible according to the equations we have 

 obtained. The cause of the discrepancy may lie in the distinction that Kirkivood(>) draws between 

 the over-damped and under-damped cases.. This cannot be unaerstooJ without access to his full theory. 

 In this report all practical cases start ay being over-Oamped (owing to the radiation term /O C Ji) 

 but become unJer-Jarapea 5irectly cavitation sets in. The present Investigation gives reasonable 

 grounds for hoping that satisfactory rules for assessing the importance of the efffct from an 

 engineering point of view will eventually be found without a prohibitive amount of numerical work. 

 The next step is clearly to try and work out some methods of assessing the effect u" edges and 

 stiffeners, and of oblique incidence of the pressure— pulse. 



Conclusion. 



Kirkwood's general conclusion that cavitation contributes largely to damage of thin plates 

 has been substantiated, and application of the theory to a thick plate indicates that the effect is 

 appreciable even here. The conclusion that nearly all the energy that would otherwise bi radiated 

 away can be rsi'.bsorb'ed by this cavitation mechanism is not igreed with, as it is believed that a 

 certain amount of loss at collision is inevitable. It is not possible to decide the question 

 experimentally, because the effect of the edges is unknown. 



References . 

 (l) Taylor. 



(2) 



(3) 

 (") 

 (5) 

 (6) 

 (7) 

 (8) 



(») 



"The pressure and impulse of submarine explosion waves on plates". 



"The distortion under pressure of a diaphragm which is clamped along 

 its edge and stressed beyond the elastic limit." 



U.S. Report U.E. 10. 



Phys, Rev. March 1943. 



Taylor Model Basin Report 511. 



Taylor Model Basin Report 527, 



U.S. Reports u.F. 18 ana 19. 



G..Charlesworth "Deflection-time curves, at the centre of box-moJel plates, result 



Taylor. 



Klrkwood. 

 Kennard. 

 Kennard. 

 Kennard. 



from underwater explosions", 

 Taylor Model Basin Ropcrt R.2ii8. 



ng 



