21 



209 



Figure 8a - Before the Explosion Figure 8b - After the Explosion 



Figure 8 - Photographs showing a Shock Wave forming in Bubbly Water 



Equation [25]. In this statement, the wave length as it exists in homogene- 

 ous water is meant. If the effective length of the shock wave is actually 

 comparable with the bubble wave length, the reflection should be materially 

 increased by resonance effects, and at the same time the wave in the bubbly 

 water should be heavily damped, in consequence of the scattering of the in- 

 cident wave. If the length of the shock wave is progressively decreased, 

 however, until it becomes several times smaller than the bubble wave length, 

 the reflection should fall off rapidly, and as the shock wave is further 

 shortened both reflection and scattering should tend toward small values. 



The statements regarding high reflection are conditioned by the 

 assumption that cavitation does not occur. As stated in the previous section, 

 cavitation occurring in the homogeneous water lying next to the bubbly layer 

 may decrease the reflection or markedly alter its character. 



The part of the incident energy that is not reflected but enters 

 the bubbly water is gradually scattered by the bubbles as the waves progress; 

 this process accounts for the progressive weakening of the waves. In real- 

 ity there will be also a certain dissipation of energy due to friction and 

 heat conduction, but estimates indicate that this dissipation ought to be 

 comparatively small. 



