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5. SIMULATION STUDY
5.1 Test ships and bank passages
Two ships have been selected for the study, a 172 m long Ropax vessel with a design speed of 28 knots and a conventional 250 m long single screw tanker. Their main dimensions are listed in Table 3. Both ships are dynamically modelled for simulations in SSPA general manoeuvring and seakeeping program SEAMAN II. The manoeuvring characteristics of the respective ship are documented in Appendix A in the form of 35 circles.
Table 3 Test ship parameters
| Ship parameter |
Unit |
Ropax |
Tanker |
| Length between perpendiculars |
m |
172.2 |
250.0 |
| Beam |
m |
28.4 |
46.0 |
| Draught, fore |
m |
6.6 |
16.0 |
| Draught, aft |
m |
6.6 |
16.0 |
| Displacement |
m3 |
19 609 |
150 000 |
| Long. center of gravity rel L/2 |
m |
-5.01 |
3.00 |
| Total rudder area |
m2 |
2×28.0 |
1×76.0 |
| Design speed |
knots |
28.0 |
17.0 |
| Propeller diameter |
m |
5.30 |
8.5 |
| Pitch ratio |
- |
1.30 |
0.68 |
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The test program of the simulated cases is shown in Table 4. As shown in Fig.1, three different bank configurations are selected for the study,
1. Bank 1 - A vertical bank.
2. Bank 2 - A 14° sloping bank.
3. Bank 3 - A vertical bank connected to a 10 m wide and 2m deep flooded bank.
The test program was run for each ship and for each of the three bank alternatives. The test program was covered for each of three mathematical models:
1. Mod 1 - SSPA old model [5]
2. Mod 2 - SSPA new model
3. Mod 3 - Ch'ng et al model [9]
At these simulations the ship was forced to move parallel to the bank with constant speed and zero rudder angle.
To achieve the speeds given in Table 4, the propeller load coefficients CT as given in Table 5 were used. The decreasing CT values with increasing speed in Table 5 depends on the automatic engine setting used in the simulations, which was not able to estimate the steady state propeller rpm/pitch setting corresponding to the chosen speed good enough.
Complete simulation results are presented in Appendix A at the end of the paper. A selection of results is presented below in diagram form.
Table 4 Simulation test program
| Case No |
Water depth ζ=T/(h-T) |
Ship Speed (knots) |
Bank distance parameter η=B/y |
| 1 |
0 |
6 |
1.5 |
| 2 |
0 |
6 |
1.0 |
| 3 |
0 |
6 |
0.5 |
| 4 |
0 |
9 |
1.0 |
| 5 |
0 |
9 |
0.5 |
| 6 |
0 |
12 |
1.0 |
| 7 |
0 |
12 |
0.5 |
| 8 |
5 |
6 |
1.5 |
| 9 |
5 |
6 |
1.0 |
| 10 |
5 |
6 |
0.5 |
| 11 |
5 |
9 |
1.0 |
| 12 |
5 |
9 |
0.5 |
| 13 |
5 |
12 |
1.0 |
| 14 |
5 |
12 |
0.5 |
| 15 |
10 |
6 |
1.5 |
| 16 |
10 |
6 |
1.0 |
| 17 |
10 |
6 |
0.5 |
| 18 |
10 |
9 |
1.0 |
| 19 |
10 |
9 |
0.5 |
| 20 |
10 |
12 |
1.0 |
| 21 |
10 |
12 |
0.5 |
| 22* |
5 |
6 |
1.5 |
| 23* |
5 |
6 |
1.0 |
| 24* |
5 |
6 |
0.5 |
| 25* |
5 |
9 |
1.0 |
| 26* |
5 |
9 |
0.5 |
| 27* |
5 |
12 |
1.0 |
| 28* |
5 |
12 |
0.5 |
| Note |
* is the
case without propeller load |
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Table 5 Propeller load coefficients CT
| Water depth(m) |
Ship speed
(knots) |
Propeller load coefficient |
| Ropax |
TanKer |
Ropax |
Tanker |
| 100 |
100 |
6 |
0.71 |
1.61 |
| 100 |
100 |
9 |
0.55 |
1.54 |
| 100 |
100 |
12 |
0.51 |
1.47 |
| 7.92 |
19.2 |
6 |
3.62 |
5.65 |
| 7.92 |
19.2 |
9 |
3.23 |
5.31 |
| 7.92 |
19.2 |
12 |
2.98 |
3.13 |
| 7.26 |
17.6 |
6 |
4.36 |
6.60 |
| 7.26 |
17.6 |
9 |
3.71 |
5.72 |
| 7.26 |
17.6 |
12 |
3.50 |
3.10 |
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5.2 The effect of different bank configurations
In Fig.16 - Fig.19, the total CY and CN coefficients of both ships passing three bank alternatives at a distance y=B and at a water depth 20% larger than the respective ship's draught are presented.
The diagrams are based on the depth Froude number, Fnh, and they show the force and moment coefficients for the two ships tested. The two ships provide very similar values, indicating that the form or fullness of the ship is not of great importance.
Fig.16 Ropax - at B/y=1.0, h/T=1.2
Fig.17 Ropax - at B/y=1.0, h/T= 1.2
Fig.18 Tanker - at B/y=1.0, h/T=1.2
Fig.19 Tanker - at B/y=1.0, h/T=1.2
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