Response of a Vibrating Plate in a Fluid 



c) The Panel Response Field 



Measurements were made of the power spectral density and 

 cross -correlation of the displacement. Typical results are shown 

 in Figs. 4 and 5 for a pressure differential of 14 psi. The static 

 deflection of the panel was 0.06 inches at the center, and the dynamic 

 deflection was small in comparison with its thickness. 



The displacement spectral density at the center of the panel 

 show pronounced spikes , the lowest frequency of which corresponds 

 to the lowest mode of the panel. The accuracy beyond a frequency of 

 3100 Hz was poor due to the spatial resolution of the capacitance 

 transducer, and therefore the spectrum beyond 3100 Hz was ignored. 



Space-time correlation measurements were made along the 

 panel centerline from x = x' = 3 in, y = y'= 3 in, at one -inch inter- 

 vals up to a maximum separation of 6 in. The cor'relogram indicates 

 a convected feature with a phase velocity ± Ucp = 770 ft/sec. This 

 convection velocity corresponds to that found in the previous experi- 

 ment using the same arrangements, except that no shock was present 

 [Maestrello 1968] . 



S 10 



X = X' = 0.5 ft. 



y = y' = 0.25 fi- 



M =3.03 

 e 



Press. Dlff. Ap = 



14 psl 



1700 1900 2100 2300 2500 2700 



FHEQUKNCY Hz 



2900 3100 3300 



Fig. 4. Displacement Spectral Density 



483 



