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2.3 Numerical Simulation
Another method to investigate the manoeuvrability at design stage is the numerical simulation. "MView" is used for our simulation study. Fig. 4 shows the predicted spiral loop and height through the numerical simulation. In case of the spiral loop width, it is not easy to find its relationship with the parameter L/U. However, we can find clear tendency between the height of spiral loop and L/U. The increase of L/U causes the decrease of the spiral loop height. What we can also see from Fig. 4 is that, if L/U is similar, smaller ships have the larger spiral loop height.
Fig.4 Spiral-loop characteristics from simulation.
(a) Width of spiral loop
(b) Height of spiral loop
Fig.5 |
Relationship between the overshoot angles and the characteristics of spiral loop from simulation. |
(a) Spiral loop width vs. 1st OVS of 10/10 zigzag
(b) Spiral loop width vs. 2nd OVS of 10/10 zigzag
(c) Spiral loop height vs. 1st OVS of 10/10 zigzag
(d) Spiral loop height vs. 2nd OVS of 10/10 zigzag
Table 3 Correlation coefficients between the overshoot angles and spiral loop and height
| Overshoot angles from simulation |
| Spiral loop |
10°/ 10°Z
1st OVS. |
10°/ 10°Z
2nd OVS. |
20°/ 20°Z
1st OVS. |
| Width |
0.869 |
0.819 |
0.714 |
| Height |
0.571 |
0.411 |
0.735 |
| Overshoot angles from sea-trials |
| Spiral loop |
10°/ 10°Z
1st OVS. |
10°/ 10°Z
2nd OVS. |
20°/ 20°Z
1st OVS. |
| Width |
0.370 |
0.521 |
0.097 |
| Height |
0.560 |
0.398 |
0.219 |
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Fig 5 shows the relationship between the overshoot angles and the spiral widths and heights acquired from numerical simulation. Correlation coefficients between them are summarized in Table 2. We can see strong correlation between the overshoot angles and the spiral loop widths. This reconfirms the fact that the overshoot angles are deeply correlated with the directional stability of a ship, and they can be used as a good index for yaw-checking ability.
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