Kim and Mevciev 



If statistical information is available on characteristic wave 

 period and significant wave height 



A = miHyjf/T* 



4 

 B = 691/T 



where T = 27rm /m 



m = variance or area under spectrum, ft 



mi - first moment of spectrum about „ - axis, ft 2 /see 



Data suggest that T^ can be taken as the observed characteristic 

 period. The Seakeeping Committee should study further the use of the 

 proposed two parameter spectral formulation." 



This formulation is based on work of Pierson and Moskowitz.[l7j 



The statistics of the response are related to the area under the 

 response spectrum, where, assuming that the amplitudes of response 

 records are narrow-banded and follow Rayleigh distributions, the 

 average apparent response (crest-to-trough) is 



x = 2.5 Ve (3) 



x 



the average of the one-third highest responses, or "significant" res- 

 ponse, is 



(x) l/q = 4.oVe~ (4) 



1/3 x 



and the average of the one-tenth highest responses is 



(X) 1/10 -5-1^ <5) 



where 



00 



E = /la (w)| 2 Sj.Mdw (6) 



x J Q ' x i f 



is the variance, or area under the spectral density curve, oc (oj) is 

 xhe frequency response function (transfer function) describing response 

 in the x* n mode of motion to a sinusoidal wave excitation, and S (co) 

 is the input (wave) spectral density. 



It is possible to express responses to the ITTC (or Pierson- 

 Moskowitz) sea spectra in dimensionless form, applicable to any size 



802 



