where 



T = peak spectral period 



f = peak spectral frequency = — 



Parameters a and y are calculated as 



a = 157.9 e 2 

 Y = 6614 e'- 59 



. - A 



4L 



(13) 



where 



i/ s = significant wave height 



L p = wavelength for waves at peak frequency 



The parameter eis a significant wave steepness. The parameter y, called the 

 peak enhancement factor, controls the sharpness of the spectral peak. 



Although the JONSWAP spectrum 

 was developed primarily for actively 

 growing wind waves, it can be used with 

 appropriate choice of yto approximate 

 any single-peaked spectrum including 

 old swell which has travelled a great 

 distance from the generation area 

 (eg. Goda 1985) (Table 9). 



The angular spreading function in 

 Equation 10 is described by the 

 commonly used expression 



D(6) = G(s) cos 2 



( e -e„ 



Table 9 

 Guidance for 

 Choosing y 



Wave Condition 



Y 



Growing sea 



3.3 



Old swell 



8-10 



(14) 



where 



G(s) = normalizing function 



s = constant- valued spreading parameter 



Chapter 4 Numerical Model 



49 



