4 -l-^Klj) (.. 



where, H = significant wave height 

 (jj = modal frequency 

 In order to generate a family of spectra, the probability function which 

 governs the modal frequency for a given significant wave height was estab- 

 lished from statistical analysis of available data, and a total of nine 

 modal frequencies were derived as a function of significant wave height 

 (Ochi 1978) . The values of these modal frequencies are given in Table 1 

 together with the weighting factor assigned to each frequency. Examples of 

 the family of wave spectra for significant wave height of 3.0 m (9.8 ft) 

 and 9.0 m (29.5 ft) are shown in Figures 5 and 6. 



2. Six-Parameter Wave Spectra Family 



In order to cover a variety of wave spectra associated with the growth 

 and decay of a storm including the existence of swell, the six-parameter 

 family consisting of eleven members for a specified significant wave height 

 was derived (Ochi 1976). It is given by. 



i 







/4A,.r 



/ 'U'\ 



^^ 



V4 > 



e 



[^ j 



0.^-'^^' 







(5) 



where, j = 1, 2 stands for the lower and higher frequency components 



respectively 



H = significant wave height 



(jj = modal frequency 



\ = shape parameter 



The values of six-parameters, H^,H„, tjj^,cj„, A,, and A„ are given 



in Table 2 as a function of sea severity (significant wave height). The 



weighting factor for the most probable spectrum is 0.50, and is 0.05 for 



all other spectra of the family. Examples for the family of wave spectra 



for significant wave height of 3.0 m (9.8 ft) and 9.0 m (29.5 ft) are 



shown in Figures 7 and 8. 



97 



