Le Mihauti 



motions depends upon the phase with which the bubble reaches the 

 surface. Depending upon the depth of the burst, these may include 

 a well-formed hollow column, a very high, narrow jet, or a low, 

 turbulent mound, followed by development of a prominent base surge. 

 The duration of this "initial" disturbance may be quite great, starting 

 from the first appearance of a mound as the bubble nears the free 

 surface, to the collapse, under gravity, of the water thrown upwards. 

 Base surge of plumes are not related to shock interaction. These 

 phenomena are ultimately manifested by a system of water waves 

 radiating from the location of the explosion. 



If the water is of uniform depth, the wave system will have 

 circular symmetry. Most of the energy of the explosion goes Into 

 the shock wave and local turbulence; only a small amount (10% at 

 the most) actually appears in the ensuing water wave system. 



As a result of its complicated origin, the initial disturbance 

 comprises a broad, irregular spectrum. Since deep water is a 

 dispersive medium, as the waves travel outwards, they will become 

 sorted according to frequency; the longer waves running ahead, and 

 the shorter waves trailing behind. A curve of wave period versus 

 time at any distant location, therefore, will monotonically decrease. 



In general, the energy distribution among the frequencies 

 generated will not be uniform; the spectrum will be peaked near a 

 frequency corresponding to a wave length which is a small multiple 

 of the radius of the central disturbance. 



At a fixed distance r from the explosion, if one measures 

 the maximum amplitude ^Ifpax °^ ^^^ envelope of the water waves 

 generated by a given yield W as a function of burst depth, curves 

 having the general shape shown in Fig, 1 will be obtained. These 

 curves have two characteristic peaks. 



UPPER CRITICAL DEPTH 



.LOWER CRITICAL DEPTH 



DEPTH OF DETONATION 



Fig. 1 A schematic illustration of the relationship 

 between wave amplitude, range, depth-of- 

 burst, and yield 



72 



