Peterson 
and solid particles, and (3) record both bubble size and spatial di- 
stribution in a large liquid volume instantaneously. A mathematical 
analysis of the complete holographic process for bubbles and solid 
particles is given in Appendix A. The schematic representation of 
the holographic equipment at the water tunnel is shown in Figure 8. 
The resulting holograms obtained in these studies recorded the 
bubbles and solid particles contained within a liquid volume 5 cm in 
diameter and 15 cm long. A small magnified view of a hologram 
for 2-25 wm diameter wires and many bubbles and solid particles, 
is shown in Figure 9. As shown in Figure 10, typical exposure du- 
ration was 10 nanoseconds, The hologram is then used to produce 
the 3-dimensional image of the contents of the original volume. This 
volume was scanned with a traveling microscope and the size and 
location of the bubbles and solid particles recorded. Figures 11 and 
12 show the appearance of a bubble and a solid particle as the micro- 
scope is moved away from the focussed position. For the optics u- 
sed in these studies, it was determined both analytically and experi- 
mentally that 25 um diameter was the smallest bubble size that 
could be reliably distinguished from a solid particle for the optical 
configuration used. Smaller bubbles could have been distinguished 
if different optics had been used but a sacrifice in the fluid volume 
recorded would have been necessary. The smallest size possible 
would have been approximately 10 um diameter because of the na- 
ture of this type of holographic process. Conclusions to be made 
later in this paper will show that the additional effort to measure 
smaller sizes was not merited. Typical bubble and solid particle 
size distributions are shown in Figure 13. 
A comparison can be made between the number of measured 
bubbles calculated to strike the body and the total dissolved gas con- 
tent of the water. This is shown in Figure 14 along with the corre- 
sponding go, and the headform material. High speed photography has 
shown that for a dissolved gas content referred to test section pres- 
sure, afar. , of 1.45 and o; = 0.61, approximately 1000 tran- 
sient hemispherical cavities per second were visible on the headform. 
However, when a/a-.= 0.22 and go, = 0.48 and there were only 
on the order of 10 visible hemispherical cavities per second on the 
headform. These observations are in general agreement with the cal- 
culated number of bubbles that would strike the body. The most si- 
gnificant result apparent in Figure 14 is that for changesin a/g TS 
around the saturation condition, very large changes in free gas con- 
tent will occur with very little change in oj . It appears that al- 
though 9; is less than \Spmin , the visible cavities do not produ- 
ce a significant amount of noise when they collapse. The small diffe- 
rence noted between metallic and plastic bodies is attributed to the 
1140 
