Wave data were analyzed in two ways. A down-crossing analysis was per- 

 formed on the time series of water elevations as well as spectral analysis using a 

 Fast Fourier Transform (FFT). For spectral analysis, the fundamental frequency, 

 or a/, was 0.00098 Hz (1/1020 s). Forty frequency bands were averaged to 

 produce the spectral density estimates. The downcrossing analysis produced the 

 calculated parameters shown in Table 3. 



Table 3 || 

 Calculated Wave Parameters from Downcrossing Analysis || 



Parameter Name 



Description 



ETABAR 



Average water level 



ETAMIN 



Minimum water surface elevation 



ETARMS 



Root-mean-square water surface elevation 



ETAMAX 



Maximum water surface elevation 



ETASD 



Standard deviation of water surface elevation 



RHOHH 



Correlation between wave heights 



RHOHT 



Correlation between heights and periods 



HMIN 



Smallest wave height 



HMAX 



Largest wave height 



HEAR 



Average wave height 



H 1/3 



Significant wave height, average of highest 33 percent of wave 

 heights 



H 1/10 



Average of highest 10 percent of wave heights 



H 1/20 



Average of highest 5 percent of wave heights 



H 1/100 



Average of highest 1 percent of wave heights 



TEAR 



Average wave period 



T 1/3 



Significant wave period, average period of highest 33 percent of 

 waves 



T1/10 



Average wave period of highest 1 percent of wave heights 



T1/20 



Average wave period of highest 5 percent of wave heights 



T 1/100 



Average wave period of highest 1 percent of wave heights 



WEIBULL ALPHA 



For Rayleigh distribution of wave heights, alpha = 2 and 

 beta = 0.5. Truncation of higher vi/ave heights due to break- 

 ing increases alpha. 



WEIBULL BETA 



NO. OF WAVES 



Number of weaves in record 



H (P = 0.5) 



(P = probability) 



Median wave height 



T (P=0.5) 



Median wave period 



The FFT or single channel frequency domain analysis was performed over the 

 entire 20,400 data points (a/=0.05 sec). In the analysis the mean was removed 

 and a cosine square taper applied over 10 percent of the data at the beginning and 

 end of the data record. The spectral parameters calculated are listed in Table 4. 

 Zero-moment wave heights, peak frequencies, and mean velocities for 12 cases 



Chapter 3 Experirrient Procedures and Data Analysis 



13 



