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EXPLOSIVE LOAD ON UNDERWATER STRUCTURES 

 AS MODIFIED BY BULK* CAVITATION 



ABSTRACT 



Whereas cavitation is most commonly observed at the interface be- 

 tween water and a solid surface, there are Indications that it may also occur 

 in the midst of a mass of water. Such cavitation may modify the action of 

 explosive pressure waves upon structures. This is possible wherever reflec- 

 tion of the wave gives rise to tension in the water. An extension of hydro- 

 dynamical theory to cover such cases is described in this report. 



It is shown that cavitated regions should be formed through the 

 propagation of breaking-fronts moving at supersonic velocity. The cavitation 

 should usually take the form of small bubbles continuously distributed, rath- 

 er than of large voids. Subsequently the cavitation will be destroyed as the 

 boundary of the cavitated region contracts and acts as a closing-front. The 

 relevant mathematical formulas are cited. 



Similitude relations are discussed, and the theory is applied to a 

 plane wave falling normally upon a plate, and to the explanation of the dome 

 that is formed over large charges exploded in the sea. 



INTRODUCTION 



The study of the behavior of ship structures when loaded by an un- 

 derwater explosion is a major project at the David W. Taylor Model Basin. 

 Good progress has been made toward an understanding of the pressure field 

 in open water, with all boundaries well removed, and to this extent the 

 groundwork has been laid for defining load. Important gaps still exist in 

 this line of information, however. The energy balance is still incomplete, 

 so that it is not yet possible to say what fraction of the explosive energy 

 is made available in the first cycle of pulsation of the gas globe. It is, 

 therefore, still impossible to evaluate the effect of the displacement of 

 the gas globe which may put its center at a point nearer the target at the 

 end of the first cycle than at its beginning. Questions of this sort have 

 led others also to conclude that sound fundamental data are still most 

 necessary (1 ) .** 



Questions relating to the properties of the target, as distinguished 

 from the load which the explosion puts on the target, are set aside for sepa- 

 rate consideration. It may be assumed that in this report the load is treated 



This term is rather new; it mill be defined and discussed in the report. 

 Numbers in parentheses indicate references on page 25 of this report. 



