E. J. Richards, J. L. Willis, and D. J. M. Williams 295 
DIAMETER » 20FEET 
WALL THICKNESS 21:5 INE 
N« N° OF CIRCOMFERENTIAL WAVES 
c+ 4984 FT/SEC 
200 
FREQUENCY ~ C.P.S 
C2} 
co 860252 «128-6 62.8 ANB 314 25.1 20-9 18-0 (S7 
AXIAL WAVELENGTH -FT 
Fig. 15.18. Frequencies of vibration of submarine hull. 
etc., and may well involve coupling with other panels which will tend to reduce 
the radiation. All that can be said at this stage is that panel vibration can be a 
major contributor to the radiated noise from a submarine and that careful 
studies of the detailed vibratory modes of typical parts of the structure, with the 
techniques we have used [7, 8] on the Caravelle and Comet, would be well worth 
while. 
15.4.6. Self-Noise 
Boundary-layer pressure fluctuations also provide the level of self-noise 
against which underwater listening devices have to act. This can be calculated 
from the level of the pressure fluctuations, 0.006 g, and from the area over which 
these pressures are correlated. This information is available from our experi- 
ments and can be used to estimate the self-noise in the various applications. 
Obviously the self-noise will depend on the free-stream velocity outside the 
boundary layer and will, of course, be much reduced if the flow at that point is 
laminar. If this level has been sufficiently reduced, then presumably the back- 
ground level will be that of the noise radiated from adjacent surfaces with their 
higher free-stream velocities and turbulent boundary-layer conditions. It seems 
wise, therefore, to place the listening area in a low-speed laminar region as 
far away as possible from the free-flow turbulent boundary layer further down- 
stream. 
A type of body design comes to mind in this context which is based on ex- 
perimental work widely discussed in aeronautical circles some years ago. It is 
