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5. MANEUVERABILITY ON UNSTABLE SHIPS TO CONTROL THEIR POSITIONS
It has been verified that the control law enables to estimate human steering on unstable ships. Using the constants written in Table 3 and Table 4, we have carried out the numerical simulations. The results have been substituted for the regression equations shown in Fig.14 〜 Fig.17. The handling results which a normal human will conduct have been estimated.
The estimated handling results are shown in Fig.18 〜 Fig.21. The horizontal axis indicates the length of a ship and the vertical axis indicates the loop width in each figure. The symbol "●" indicates mean value of the handling result by the mariners and the value is written near the symbol. Each of the solid lines indicates an estimated contour line. The number with brackets indicates the value of the contour line.
Fig.14 |
The relation between human control and numerical simulation on maximum lateral deviation |
Fig.15 |
The relation between human control and numerical simulation on mean lateral deviation |
Fig.16 |
The relation between human control and numerical simulation on maximum rudder angle for checking turn |
Fig. 17 |
The relation between human control and numerical simulation on proportion of rudder angle for checking turn |
As Figure 18 and Figure 19 show, both the estimated lateral deviations increase with increasing length of a ship. In case of 100-meter ship and 150-meter ship, both the lateral deviations are almost fixed value in spite of increasing the loop width, whereas, in case of 240-meter ship and 300-meter ship, both the lateral deviations increase with increasing loop width. As Figure 20 and Figure 21 show, in case of the small ships, the mariners can control a position of the ship by using large ladder angles even if the loop width increases, whereas, in case of the large ships, when the loop width becomes large, the same control as a ship with small loop width can not be performed even if mariners take a large rudder angle. This result indicates that larger unstable ships have worse ability for position control.
Figure 20 and Figure 21 also show that the estimated maximum rudder angle for checking turn and the estimated proportion of the rudder angle for checking turn increase with increasing length of a ship and the loop width. As Figure 20 shows, especially in the area of 30° or more, the rudder angle exceeds the limitation. Under the condition, mariners have no margin for avoiding other vessels or for meeting disturbance. Even if the area is from 25° to 30°, the rudder angle may reach the limitation if there is a strong wind or a current.
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