Ellis 



Fig. 9 - Bubble collapsing at approximately one maximum 

 diameter from the wall showing initial elongation normal 

 to. wall and subsequent jet formation (5000 frames/sec; 

 actual size) 



Fig. 10 - Collapse of a bubble touching a wall (to the left) 

 and in a vertical hydrostatic pressure gradient. The jet 

 axis angle is about midway between vertical and the normal 

 to the wall (5000 frames/sec; 2X). 



bubbles in a pressure gradient and that jets occurring during collapse due to 

 solid wall proximity were sometimes much thinner than could be treated by the 

 perturbation theory of Naude' and Ellis. In addition, theoretical considerations 

 showed that for many deformable shapes such as may be assumed by bubbles, 

 the kinetic energy of the liquid may advantageously be written in terms of bubble 

 deformation rates and speed of the centroid. In this way the importance of mo- 

 mentum conservation and the Kelvin impulse in considering cavitation damage 

 mechanisms become more apparent. It appears that there are many more fac- 

 tors to be considered in studying the hydrodynamics of actual cavitation damage 

 than have been considered in the spherically symmetric case. One oversimpli- 

 fied but intuitively satisfying point of view is to regard a bubble moving toward 



146 



