filter and slow scan. Experience with the system has shown that 

 most seakeeping analyses may be made at slow scan with a 5-cps filter. 

 An exception to this is the usually narrow roll spectrum which suggests 

 using a 2-cps filter with slow scan. 



One further analysis constant to be considered is the averaging 

 time constant. This is a memory medium that controls the length of 

 time, in the past history of the excursion of the filter through the 

 frequency range, that the analog computer will consider amplitudes in 

 its averaging duties. The time constant is adjustable in the range of 

 0.1 to 100 seconds and should be at least as long as the loop time, to 

 utilize all the data in the loop. The longer the time constant, 

 however, the greater the range of amplitudes that will be averaged. 

 A time constant of 3.5 seconds has been used successfully with seakeeping 

 data. 



The effect of creating a discontinuity in the record, where it is 

 spliced into a loop, is to introduce spurious information in the signal 

 that manifests itself as spikes in the energy spectrum. These spikes 

 will appear at the fundamental of the new frequency created by the splice 

 and at its harmonics. If the record is long and/or the filter wide 

 and/or the time constant long, the splice effect will be reduced. There 

 is no appreciable evidence of the splice effect in any of our analyses 

 to date. 



Since only about half the 0-to250-cps oscillator frequency range 

 contains energy, analyses usually take 5 or 10 minutes, depending on 

 whether slow or fast scan is applied. 



14 



