SUMMARY OF COMPUTATIONAL FORMULAS USED FOR THE HURRICANE CARLA 

 WAVE SPECTRA 



Twelve pieces of record at various time 

 chosen for analysis. Each piece consisted 

 level elevations taken at a time increment 

 these records was NAt = 13.65 minutes long 

 ment would be Af = 1/NAt = 0.00122 sec."^. 

 this choice is f^y = l/2At = 1/0.4 = 2.5 s 



period of 0.4 second. Energy in waves with 

 would thus be aliased into lower frequencie 

 spectra produced little evidence of much en 

 frequency. 



s in the storm (Table 1) were 

 of N = 4,096 values of water 

 of At = 0.2. Thus, each of 

 The frequency scale incre- 

 The Nyquist frequency for 

 ec."-^ which corresponds to a 

 periods smaller than 0.4 second 

 s. An examination of the final 

 ergy past this selected Nyquist 



Table 1. Hurricane Carla data analyzed. 



Date 



Time 



Data code 



8 Sept. 1961 



0600 



6877 





1200 



6878 





1800 



6879 



9 Sept. 1961 



0000 



6880 





0600 



6881-1 





0620 



6881-2 





1200 



6882 





1500 



6883 





1800 



6884 





2100 



6885 



10 Sept. 1961 



0000 



6886-1 





0020 



6886-2 



The 4,096 water level elevations were transformed by the fast Fourier 

 transform algorithm to yield Fourier coefficients, for 0<m<N: 



4,095 



A„ = At Z n„ e 

 n=0 



-i2TTmn/N 



(29) 



The spectral lines were then computed from 



P(fm) = |Am|2/(819.2) , 



(30) 



when |A^| denotes the complex modulus of A^ . The spectral density was 

 estimated by a moving average of the spectral lines: 



p(fj = Z wj p(fm-i]/ ^ Wj , 



(31) 



16 



