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2.2.2 Frequency characteristic comparison
A Nyquist locus was found to check the frequency characteristic of the system by using the control coefficients. Kx, Kp and Kd of each display and Nyquist loci are shown in Fig. 4. The following became clear from Fig. 4
Fig.4 Nyquist Locus
L=100m
L=280m
a. ship's length 100m
・Phase margins decrease to order of NO. Support, Heading (heading display), Lateral Deviation (lateral deviation display) and Turn Rate (turn rate display).
・The difference in NO. Support of the phase margin maximum and Turn Rate of the phase margin minimum is small.
b. ship's length 280m
・Phase margins decrease to order of "Heading", "Lateral Deviation", "No Support" and "Turn Rate".
・The difference in phase margins between "Turn Rate" and the other are remarkable.
・The difference in "Heading" of the phase margin maximum and "Turn Rate" of the phase margin minimum is large.
2.2.3 The comparison of the rudder response characteristic of the ship by steering
Changes in time series of tracks, which were derived from the numerical simulation using control coefficients in section 2.2.1, are shown in Fig. 5. And, comparison with changes in time series of tracks derived from the numerical simulation using normalization control coefficients are shown in Fig.6.
Fig.5 Tracks
Average L=100m Tracks
Average L=280m Tracks
Furthermore, lateral deviations are shown in Fig. 7 and Fig. 8. The following becomes clear from these figures.
a. ship's length 100m
・Average lateral deviations decrease to order of "No Support", "Heading", "Lat. Dev." and "Turn Rate".
・Normalized increases the amounts of overshoot more than Turn Rate when Turn Rate is compared Normalized (normalization coefficient). Then, Normalized of the average lateral deviation as well is larger than Turn Rate.
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