300 - « - 



It is seen from Figure 1 that the effect of a baffle is to increase the deflection very 

 considerably above that of the infinite plate which, as Figure 2 shows, is due to the increased net 

 pressure on the piston due to diffraction. For the finite baffle, the non-compress ive approximation 

 results in an averaging out of the effects of diffraction from the baffle and region beyond. when 

 compressibility is allowed for as Fn equation (t), the first effects of diffraction on the piston arc- 

 due only to the baffle which results in larger deflections in the earlier stages than in the non- 

 compressive case. Table 1 shows that the energy ratios for the finite baffle are of the same order 

 of magnitude as observed in box model experiments, which is not the case for either the infinite plate 

 or infinite baffle. The form of the net pressures in Figure 2 indicates that cavitation is unlikely 

 to occur at box model plates for bubble waves even whi,n the plate is not deflected initially. 



Piston Deflected InitxalLy . 



Using equations (l6), (l6), (l7) and (l8), the ratios of energy absorbed to energy incident on 

 the piston have been calculated for numerical values of the constants listed in the previous section. 

 It has also been assumed that the movement of the bubble towards the target is the same as the 

 calculated value for a 1 oz. charge towards a rigid disc. The results are shown in Figure 3, the 

 energy ratio being plotted as ^ function of the distance of the charge from the piston. 



It is seen that the non-compressive case leads to lower values of the ratio than equation (l5). 

 This is because neglect of compressibility results in lower pressures on the piston in the earlier 

 stages of its mot ion. 



The magnitude of the energy ratio is in reasonable agrerment with observation in view of the 

 approximations involved. It may be concluded that the observed tncrgy ratio is due to the diffraction 

 effects arising from the presence of the flange round the target plate. 



Reference . 



(l) Notes on the motion of a finite plate due to an underwater explosion. 



