31 



449 



The diaphragm bulges outward at time (2> possibly 

 due to impulse received when cavitation closes up. 



The bending wave reaches center and all motion 

 ceases temporarily. 



The jerky motion of material appears in the flat 

 central region of the diaphragm, shown by broken 

 lines, possibly due to vibrations in a layer of 

 water left on undersurface of diaphragm. 



i_i 



LJ_,J 



C3/^ 



t \ ! 



Diaphragm I millisecond 

 after Initiation of f^flotion 



Diaphragm at Time t. 



Diaphragm at Time tj 



. Bending Wove 



,Diophragm at Time t^ 



Bending Wave 

 Diaphragm of Time t^ 



Bending Wave 



, Diaphragm at Time t 



The diaphragm acquires uniform initial velocity. 

 Cavitation takes place between reflected shock 

 wave and diaphragm. 



■ Diophraqm at Initiai 

 / Instont of Motion 



t t t t ! / 1^ 



a c o o c e> o o o ^ o o o^ — Cavitation Region 



~ Reflected Shock Wove 



Figure 23 - Various Stages of Motion of a Diaphragm 



As soon as the diaphragm begins to move, a bending wave, carryinf!: 

 the news of the retarding presence of the edge, travels radially Inward to- 

 ward the center, as In Figure 23. The material in the central region of the 

 diaphragm. Interior to this bending wave, continues to move with almost its 

 initial uniform velocity until the wave reaches it. Near the center a small 

 but definite Jerking motion is superimposed on this velocity, as seen in the 

 typical displacement-time curves In Figures 2Ua and 2Ub, of the center spots 

 on the diaphragms. In general, there seem to be four separate pauses, occur- 

 ring at times t^, t ^' , <„", and t^. The material in the central region re- 

 gains sufficient velocity, after times t^ and t^ , and in about one-half to 

 two-thirds of the cases after time t^' , to more than make up for the velocity 

 lost at these times. That Is, in this region up to time t ^' , and in about 



