studied, the "integral of energy" mode of operation is often used. Here 

 the average square energy of the frequency components are added to pro- 

 vide a monotonic nondecreasing function (curve which never goes down) 

 whose maximum (asymptotic) value is a measure of the total energy in 

 the seakeeping record. 



The output of the analog computer is applied to an X-Y plotter. 

 The net result of analysis is a graphical display on 8^-in. X 10-in. 

 paper of the output of one of the operational modes as ordinate, and 

 frequency (magnified by speed-up ratio) as abscissa. 



Figure 3 illustrates the most frequently used operational modes. 

 Both the density function (spectrum) and the distribution function (inte- 

 grated spectrum) relate to the same input data. It will be noted that the 

 rate of change of the distribution function corresponds well with the ups 

 and downs of the density function, as expected from the integration pro- 

 cess involved. The maximum value of the cumulative distribution function 

 is, as stated, a measure of the total energy and is therefore equivalent 

 to the integral of the density function, or to the area it represents 

 on the X-Y plotter. 



Several analysis constants require discussion before the subject 

 is closed. The width of the filter determines the resolution of the 

 energy spectrum. A narrow filter provides fine detail but is a relatively 

 poor estimate because fewer frequency components are averaged. Conversely, 

 a wide filter provides good estimates but poor resolution. A priori 

 knowledge of the shape of the spectrum is helpful in filter selection. 



12 



