557 



MBASUREMENT OF BUBBLE PULSE PH5N0MENA,, III 

 RADIUS AMD PERIOD STUDIEi; 



I. INTRODUCTION 



In •117 study of tha mechanism and energetics of an underwater explosion, 

 one is inevitably led to a realization of the very considerable amounts of 

 energy inherent in the bubble of explosion product gases. Since the total 

 damage done by an underwater explosion is caused by both the shock wave and 

 the subsequent bubble pulses, these effects must be separated for a proper 

 understanding of the mechanisms involved. To determine the exact quantities 

 of energy present at various stages of the explosion and to find the amount 

 of useful energy is a task of great aagnitude. In this report are presented 

 data which were gathered in an attempt to evalioate the energy in the bubble. 



One of the easiest measurements to make is the measurement of the 

 periods of oscillation of the bubble, that ir le time intervals between 

 successive minima in the bubble radius. Th6se are referred to as the first 

 bubble period, second bubble period, and so on. The length of the bubble 

 period is related to the energy left after the passage of the shock wave by 

 the equations discussed below. In general, it may be said that the longer 

 the period, the greater the energy. However, it is necessary to have 

 additional information — specifically, the eqxiation of state of the product 

 gases — before an exact calculation of the total energy can be made. 



A second measure of the energy may be obtained from a study of the 

 maximum and minimum radii of the bubble. Photographs of the bubble at 

 various stages of its oscillation show that the outline of the bubble is 

 rather clearly delineated up to the first meiximum, but that it is somewhat 

 less clear at subsequent maxima, and is completely obscured by carbon 

 streamers in the water at the minima. Since the bubble radii at the minima 

 have not been measui-ed, it is not possible to obtain a good value of the 

 energy from radius measurements alone. By a combination of radius and 

 period measxirements , however, an attack can be mads on a more precise 

 calculation of the energy in the bubble. 



This report presents a compilation of data obtained in a rather extensive 

 program of bubble period and radius measurements. -^j 2/ Those appear to bo the 

 most complete and accurate data of this sort available at the present time. 

 Using these meas\irementg , calculations of energy and other parameters 

 appearing in the bubble equations have been carried out. 



II. EXPERIMENTAL METHODS 



1. Bubble Periods 



Periods were measured^) by recording oscillographicedly the signal from 

 a piezoelectric gauge exposed to the shock wave eind bubble pulses. The 

 pressure changes were recorded on moving film simultaneously with a 1 kc 

 timing wave. 



