Six wave periods were tested: 2.61, 3.75, 5.60, 7.87, 11.33, and 

 16.01 seconds. For each of these periods three wave heights, ranging 

 from approximately 1.1 to 3.7 feet, were investigated. Water depth varied 

 slightly from 14.02 to 14.30 feet. 



Analysis was limited to that portion of a run which contained unre- 

 flected waves, yet the waves had built up to a uniform height. This number of 

 eligible waves varied from 1 to 8, as determined by the tank length and the 

 wave period (or velocity). The theoretical limits were confirmed by the 

 wave records. Simultaneous recordings of each individual wave were matched 

 up for comparison. Figure 2 is an example of corresponding wave records. 



Three identical runs were made for each condition of wave height and 

 period, and measurements were averaged in order to assure a consistency in 

 results. Table 1 summarizes averaged tabulations for each wave condition 

 by showing an average bottom-to-surface pressure fluctuation ratio for 

 each wave condition and for each means of comparison. Table 1 also indicates 

 the maximum and minimum ratio for each wave condition as found from the 

 analysis of each individual wave. Figure 3 presents these data in graphical 

 form. 



A summary curve was also obtained by averaging all pressure ratios 

 for each wave period regardless of wave height, gage location or means of 

 comparison. This curve is compared with a theoretical curve in Figure 4. 



A review of the comparison curves in Figure 4 indicates that measured 

 ratios differ from theoretical ones only for wave periods of about 4 through 

 13 seconds. Correction factors for the test periods within this range are: 

 1.12 for 5.60 seconds, 1.17 for 7.87 seconds and 1.08 for 11.33 seconds, 

 giving an average of 1.12; in general agreement with that of the University of 

 California. 



Further investigation of the experimental data revealed, in general, 

 that as the wave height decreased the pressure gage response increased 

 (particularly for the longer wave periods). This indication can be seen 

 in Figure 5. Apparently wave heights (or steepness) can also affect deter- 

 mination of the true pressure attenuation. 



* "Investigation of Underwater Pressure Records and Simultaneous Sea Surface 

 Pattern", H. R. Seiwell, Woods Hole Oceanographic Institution, 1947. 



"Sub-Surface Pressures due to Oscillatory Waves", R. G. Folsom, Transactions, 

 American Geophysical Union, Vo. 28, No. 6, p. 875, December 1947. 



29 



