Ming-Shun Chang 
coming from the North bank and waves coming simultaneously from 
both banks. Both regular and irregular waves were generated. The 
periods of the regular waves were 1.6, 2.0, 2.5, and 3.0 seconds. 
These wave periods correspond to waves with angular resolution of 
less than 10 degrees upto 90 degrees. The irregular waves were 
generated from available random seaway tapes. These wave trains 
had average wave periods ranging from 1.6 to 3.0 seconds. 
Sonic probes operating at a frequency of 200 KH were mount- 
ed approximately 20 inches above the still water surface. These 
devices can measure the instantaneous water surface elevations with 
great accuracy. From the digitized records, cross spectra were 
calculated for all irregular waves. Wave amplitudes and wave phases 
were calculated for the regular waves by means of Fourier trans- 
forms. The directional wave spectra were then obtained by the use of 
Equation (2. 8). 
Some resulting directional wave spectra measured from the 
linear array are shown in Figures 8 through 16. Figures 8 through 
11 are for regular waves and Figures 12 through 16 are for irregular 
waves. The curves for regular waves represent the directional spec- 
tra obtained under several different conditions such as different 
wave-maker dome air pressures, which are indicated in terms of 
blower rpm, different directions, which are designated by N or 
W for waves generated at the North and West banks, respectively, 
and different wave combinations. The coordinates of the figures are 
the normalized wave vector components in the direction parallel to 
the array, and the normalized spectrum density 
S(k 34) 
S*(k) 34) 156 goat 
where S, (4) is the average of the one-dimensional spectrum den- 
sities obtained by the five probes. Since S(k, ;w) is approximated by 
a ninth order Fourier series, the normalized spectrum density 
S*(k,;w) should be less than 9,5 as previously discussed, The theo- 
retical maximum value of S*(k, ;w) depends on the wave conditions. 
If a wave of a given frequency were generated at only one bank, 
S*(k, ;w) should have a maximum value of 9.5 in the direction in 
which it was generated, For other directions, it will be less than 
9.5 . The actual value depends on the combination of the wave am- 
plitudes generated at the two banks. The regular wave results as 
shown in the figures agree with this theoretical value very well regard- 
less of the wave frequencies, wave amplitudes and the presence of 
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