APPENDIX B - POWER SPECTRAL ESTIMATES 

 OF IN SITU PRESSURE FLUCTUATIONS 



A. General 



One of the variables the Submarine Systems Section attempted to record was 

 pressure fluctuation, as measured by a Wiancko differential pressure gauge. This 

 gauge was mounted on the sail with the diaphragm parallel to the deck of the sub- 

 marine (Fig. 1). Thus, when the submarine hovered at a keel depth of 100 feet, the 

 gauge's rubber diaphragm was actually 60 feet below the surface. 



Total pressure change occurring at the diaphragm of the differential pressure 

 gauge of the hovering submarine will be composed of, (1) pressure change due to 

 surface wave motion, (2) linear motions of the submarine (heave, sway, and surge), 

 and (3) angular motions (roll, pitch, and yaw). 



Pressure changes at the gauge due to surface wave motion alone are independent 

 of the submarine's relative heading. Total motion of the submarine, hence total 

 pressure change associated with the submarine's motion, is definitely a function of 

 relative heading. Even under stationary wave conditions, power spectra of the 

 Wiancko recordings will, in general, be different for different relative headings. 



B . Spectral Estimates of Filtered Signals 



The problem of recording pressure fluctuations on the hovering REDFIN was 

 complicated by the limited dynamic range of the Wiancko differential pressure gauge. 

 To prevent damage to the gauge, a relief valve eliminates differential pressure in the 

 interior chamber of the gauge when the dynamic range of the gauge Is exceeded . A 

 typical in situ pressure recording is shown in Figure Bl . The small oscillations are 

 pressure changes due to surface wave motion and linear and angular components of the 

 submarine motion. The very long "period" oscillations are associated with the slowly 

 changing dive angle of the hovering submarine. The amplitude ratio of the large to 

 small oscillations Is about 20 to 1 . This highly compressed recording represents approxh 

 mately 8 minutes of recording . Many of the Wiancko pressure recordings were charac- 

 terized by breaks or "jumps" which occurred when the amplitude of the long-period 

 oscillations became too large. When this happened, the relief valve would relieve 

 the differential pressure momentarily, and the recording would begin anew at the 

 center of the chart. 



Power spectra of the recording shown in Figure Bl were estimated by the wave 

 analyzer system at the Hydrographic Office and are shown in Figure B2. In Figure B2, 

 three different estimates are superimposed to show the effect of filtering. Curve A is 



57 



