621 



A FURTHER INVEST16AT0N INTO THE DOME ANALYSIS 



METHOD OF DETERMINING THE DEPTH OF 

 UNDERWATER EXPLOS.JNS 



R. A. Shaw 



Marine Aircraft Experimental Es tablivhroent 

 Scotland . 



April 1942 



Sunm g ry . 



The dome snalysis methoo of aeoth oeterminat Ion has Been checked by the analysis of records 

 oDiained with charges at known deothSi It ras been found In aoDlyln9 the method that while the 

 calculated death Is genernlly In fair asreement w'th the true deoth, the agreement Is Imcroved If 

 allowance Is made for the dome shaoe and the Initial olume characteristic of the particular exoloslon. 

 When a correction for these factors Is aoalled, the depth determined by the dome analysis method 

 should not be In errcr by rrore than 101 and will generally be '/ery much closer to the true deoth. 

 The relation which has been found between 3ome ano clume suggests that the formation of both is 

 dependent on the characteristics of the oressure pulse set uo by the explosion. This should appear 

 In the pressure records and an attempt will be made to relate the pressure results to the done and 

 plume charactsrist Ics. 



Introduction . 



^ method of determining the depth of a charge exploding underwater from an analysis of the 

 spray dome which appears on the surface over the exploding charge was described in a orevious 

 report. The method has now oeen checkeo by an anrilysis of some cine recoros of underwater exolosions 

 at known Depths. ^ery clcs-^ agreement Is found between the calculated and the known depth in many 

 Instances but a few examoles where the methoo is as much as 20 - 25i in error have occurreo. 



It was observed In the first report on the method that vi^ry large variations in initial ocme 

 velocity coulo 05 cotained under apparently similar conditions. This is ccnfirmeJ by the present 

 results but It has new been observed also that thess variations .'.re assxiated with variations In 

 the initial velocity of the plume. Further, the dome itself, even in calm water, is not so regular 

 In form as "as at first thought. Some domes are found to be higher at thr centre, and some higher 

 at the rim than woulo follow if they were generated in strict proportion to the (cosine)^ law used 

 In the done iwalysls method. 



It has now been found that when the original dome analysis methoo is in error in calculating 

 the deoth, the error can be related tc the surface chencmena o.s i whole. This has been done ^y 

 assigning oome anj olune factors in each instance. The 3:me factor is the graoient of the calculatea 

 3eoth along the Jjme raolus, an: the olume factor Is siroly the ratir zf the mean initial velocity 

 ;f the oome ?.t its centre. A correction Involving these twr factors has been fjunc; anr when this 

 Is apoliec t. th!- Jecth calculate: tiy the original oome analysis meth:3, very cl:se agreement with 

 the known Oeoths is .-Otalnec. 



The effect of this is that when the true depth is unknown the deoth can oe calculated with 

 fair accuracy by the dome analysis method if a correction In terms of these facttrs is applied. 



The overall range of charge weight in the results conside'red is from 160 to 1,000 lb. and 

 of deoth from 15 to 10 feet.. The tests include some in which the charges were fired on the sea 

 bottom. 



The symbols used in the text are Oefineo oelow:- 



(i) Charge 



Weight k lb. 



depth at detonation J ft. 

 aeoth calculated oy original 



oome analysis nietnc- : ft. 

 calcjlat'i -i-'th =ft"r => 



correction for Ocm? and plur.e factors 3c ft, 



(i!) 



