I25r 



7804260916 

 Hs= 12.5cm 



<;t)U 



1 



7803281500 



200 



- 



Hs - 15.5 cm 

 Op --3.45 



150 



- 





100 



■ A 



( 



50 

 n 



\V 



u , 



250 



200- 



150 



100 



50 



0.25 0.50 0.75 1.00 1.25 

 f (Hz) 



Run ID Code = 7803281403 

 Hc= 17.2 cm 



On=5.54 



0.25 



0.50 

 f (Hz) 



75 



.00 



0.25 



0.50 0.75 

 f (Hz) 



.00 



1.25 



Figure 4. Sample incident laboratory wave spectra. 



The zero up-crossing method was also used to analyze wave records. In this 

 method the height of an individual wave is defined as the difference in extreme 

 water elevations (maximum level minus minimum level) between two successive 

 points in time where the water level up-crosses the mean water level. The 

 period associated with that wave is the time between up-crossings . This type 

 of analysis is useful for examining wave characteristics such as wave height, 

 period, or joint wave height-period distributions. Zero up-crossing results 

 may also be used to describe wave grouping (Rye, 1974). A high level of wave 

 grouping means that there is a strong probability that a wave of approximately 

 the same height will follow the previous wave (i.e., large waves are followed 

 by large waves and small waves are followed by small waves). In this study the 

 autocorrelation of zero up-crossing wave heights is used to quantify the amount 

 of wave grouping. The wave gage records seaward of the test structure are 

 somewhat contaminated by reflected waves, depending on the amount of reflection, 

 so the autocorrelation of incident wave heights, pj, is taken as the average 

 wave height autocorrelation of the three gage records seaward of the structure. 



18 



