TM No. 377 



8.0 m I, and 10.0 m III) display clear double peaks, which are obviously attenuated 

 with depth. 



The 8.0 m I peak at 50 mcps exceeds the 6.0 m I peak; but in the range of the 

 wind wave frequencies (above 150 mcps) the 6.0 m I curve lies consistently above 

 the 8.0 m I curve, as would be expected. 



BBELS-11 Observations - The BBELS-11 observations of 29 and 30 March 1965 were 

 made to study the 2 1 4-hour variation in wave energy at various depths. This aspect 

 of the observations is discussed later in this chapter. 



During the period between 1713 and 2005 on 29 March, sixteen observations were 

 made of the vertical velocity w (using the LIMDUM I system) over a depth range from 

 0.5 meter to 8.0 meters below the mean wave trough level. The vertical separation 

 of the two cylinders was 1.5 meters. «, 



Because of recorder pen failure, only one channel could be used; hence, w was 

 not measured at the two depths simultaneously. Instead, the leads of the upper 

 and lower w meters were alternately connected to the usable recorder channel. 



The results of this sequence of observations (serial 032-0^7) are listed in 

 table IV- 3. The winds varied from E to ENE and averaged about 9-5 m sec -1 . The 

 variances are plotted (crosses) in figure V-20. The distribution of C^ "*- is very 

 similar to that for BBELS-5 and 7. The surface intercept (at 0.0 m) appears to be 

 at about lU00-1500 cm 2 sec -2 . As with BBELS-5 and 7, the exponential attenuation 

 °£ ^uj*" with depth is indicated by the linearity of the log plot. 



The thin envelope of points in figure V-20 indicates that the two different 

 wave meters produce similar wave data under similar wind and wave conditions. 

 Hence, the fundamental designs of the OMDUM II and LIMDUM I systems (even though 

 each has different calibration curves, probably different drag coefficients with 

 respect to wave motions, and different geometries) would seem to be capable of 

 detecting faithfully the gross oscillatory motions in waves. 



BBELS-lU Observations - The BBELS-lU observations were made on 7 June 1965, 

 using the LIMDUM I system (configured as shown in figure 11-17). The purpose of 

 these observations was to measure the vertical velocity component w simultaneously 

 at two vertically separated points in the manner shown by figure TLl-h. For this 

 purpose, the LIMDUM I system did not need to be fastened to the horizontal rod 

 with its north, south, and back guys, as was necessary with the OMDUM systems. 

 The LIMDUM I system was simply suspended by the main support guy and counter- 

 weighted with a bottom pennant attached to six sash weights having a combined 

 weight of about 18 kg. The ducted meters were spaced 2.0 meters apart, and 

 observations were made at various depths. The simultaneous measurements at two 

 different depths supplied particularly good data on how the variance of the wave 

 motion varied with depth. The statistical results of these observations are given 

 in table IV-3. 



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