Trans RINA, Vol 157, Part A3, Intl J Maritime Eng, Jul-Sep 2015
with 0.5 B and 1.0 B as an example, Figure 7 shows the variance of center of mass deviating from the bank for verical and sloped bank. The simulation results clearly indicates that for a constant ship speed, the center of mass deviating from the bank increases as the distance between the ship and the verical sloped bank.
or
According to the simulation results, the more obvious the eddy currents produced at the ship stern, the larger the bank effects on the ship. Figure 8 shows the eddy current phenomenon produced at the stern of Ship 1. When the ship navigated for 50 s, no eddy currents have yet produced at the ship stern; however, the effects of bank suction became increasingly obvious as navigation time increased. As obvious eddy currents
seen in the were figure, produced (in a
counterclockwise rotation) at t = 150 s. In the figure, the ship was influenced by the ship stern eddy current on the port side and its bow deviated towards the center of the navigating channel. Figures 9 and 10 are the pressure variations on the x-y plane 1 m below the surface of water for Ships 1 and 2, respectively, when navigating along
a vertical embankment. Red
represents high pressure zones and blue represents low pressure zones. The figures show that the area between the ship stern and the embankment was a low pressure zone; thus, as navigation time increased, the ship stern increasingly approached the embankment because of bank suction. The pressure waves at the bow moved forward, and the pressure on the starboard side became higher than that on the port side, producing a bank cushion effect and causing course deviation.
4. CONCLUSION
In this study, 3D physical modelling was applied to construct ship models and fluid dynamic computational methods were used to simulate two types of ships navigating in restricted waters for analyzing the induced bank effects. The simulation results revealed that the bank effects produced during the navigation of ships were influenced by the following factors: ship type, draft, under keel clearance, trim, list, navigation speed, water depth, channel geometry, distance to bank(BS), and wind pressure. This study only investigated two types of ships navigating at 3 kn along banks with a BS of 0.5 B and 1.0 B. Under such conditions, obvious bank effects were produced, both bank suction and bank cushion, during ship navigation
in regular restricted waters.
Intense bank effects were observed when the ship was close to the bank and far away from the center of the navigation channel, the channel width was narrow, and the navigation speed was fast. Only fixed water depths were simulated in this study; however, it is a fact that the squat effect also increases the intensity of the bank effects. Ship operators can also take advantage of the characteristics of bank effect to help operate ships when turning in channels.
5. 1.
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