Gd 
Nn 
VO 
901 
Expand (e,) as far as first order terms in r/e and expand 1/r 
about the. centere of the two orifices. 0 is then calculated 
to be 
(92) Fi = Bo pee ee oy 
where se is the distance between centers. When R/s = 0.25, the 
error in Fio due to the expansion of 1/r is estimated at not more 
then 0.5% and that due tc the exnension of (a) is believed to be 
not more than 0.1% for a 0.5 millisec vulee. 
T T e I Vv R d_ Blo 
An estimate of the thicknese of en immovable rigid block may 
be made es follows. Assume that the incident wave is vlene, 
and that the block is infinitely wide as well as rigid; that is, 
neglect diffraction at its edges. Then the separate relief forces 
contributed by the front and back surfaces are equal and proportional 
to the velocity of the block, and the equation of motion is 
- £/6 
(10.1) (ppd) zZ = ah, c ~ape 2 
where 
density of block, 
thickness of block, 
disvlacement of block, 
peak nressure of incident wave, 
decay constant of incident wave. 
® FUN pw 
wne wo 
We calculete the velocity of the baffle from (10,1) and then 
the relief pressure from (19.2). The result may be exvressed as 
2 iva 
