Fig. 7.13. Photograph of a semisubmersible model (scale 1/90). 
(From Oda, Yamanouchi, et al.5%) 
Figures 7.14~7.17>° show the results of frequency response analysis of the model 
seakeeping data as heave, relative wave height, pitch, and surge in irregular waves deter- 
mined by the AR model fitting technique for the same offshore semisubmersible. These 
data were analyzed as a one—input/one—output vector process, although, if we like, we 
can analyze them as a one—input/multiple—output vector AR process. The orders of AR 
models fitted to these systems are marked on each of the figures. 
Figure 7.16 is concerned with the same response under the same conditions as Fig. 
7.12. From these results, we can find the same characteristics of AR—model fitting tech- 
niques. All the spectra and the frequency responses are much smoother and follow well 
the rapid changes with the frequency. These tendencies are more clearly indicated by Fig. 
TUS: 
In Fig. 7.18 the response characteristics of heave, relative wave height, pitch, and 
surge are shown expanded in the important range of response frequencies for 6-24 sec- 
ond periods for a full—scale structure. The results obtained by the AR model fitting and 
B-T methods are shown with results of experiments in regular waves in the tank. The 
figures show rather surprisingly how well the results from the AR model fitting technique 
follow the minor changes of the response in amplitude as well as in phase relations ob- 
tained in experiments with the regular harmonic waves of several frequencies. 
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