DESCRIPTION OF THE SEADAC 



1 . GENERAL 



The SEADAC is associated with one specific aspect of seakeeping data 

 reduction, that of converting time histories of random variables into 

 some form of spectral density presentation. The basic functions of the 

 system are summarized as follows: 



1. Preparation. 



2. Analysis. 



3. Storage. 



To get a clear general picture of the operation of the system, see 

 Figure 1. The raw data are transmitted from the transducers (T) to the 

 tape recorder in the field and are brought to the laboratory on reels of 

 magnetic tape. Each reel may contain the data from many runs (experiments) 

 and each run may comprise as many as 14 channels of information on the 

 tape. These data are usually recorded at 1-7/8 ips (inches per second). 

 The first operation involves playing the data back, on a reel recorder, 

 at a speed 32 times greater than the original recorded speed (that is, 

 60 ips)and re-recording the sped-up signal on the loop record'er at 1-7/8 

 ips. At the same time, the signals on eight of the channels are recorded 

 on 8-channel chart paper at 5 ram/sec. A second chart paper recording 

 will be required if more than eight channels of information were recorded 

 originally. The original data are coded so that runs are easily 

 separated. The paper records are divided into separate runs, labeled 

 properly for indent if icat ion, and put into a binder in the form of a 

 book. Figure 2 shows a typical page from such a book. 



