Systematic investigations to determine speed-dependent sway forces and yaw torques caused by the bank effect when a ship passes approach channels
From BAWiki
Author: K. Uliczka
Boundary conditions
The model tests to determine the speed-dependent sway forces and yaw torques that are generated by the Bernoulli flow effects (also known as the bank effect in nautical circles) and that act on a ship, not least depending on the passing clearance between ship and embankment, were conducted in BAW-DH’s shallow water basin (length approx. 100 m, width approx. 35 m, max. water depth 0.7 m) in 1:40 scale in accordance with Froude’s model laws. The results of the tests from the hydraulic model have been scaled up accordingly and are given as prototype-size.
This meant that, in addition to the schematic embankments to be investigated, a corresponding guidance system (rail system with triangular guide arm) had to be installed via which the model ship could be guided and the sway and yaw acting on the ship could be measured with a redundant setup. A photograph of the system installed together with a schematic illustration of the effective sway forces and yaw torques recorded is shown in Figure 1.
The model ships were activated via wireless remote control and were self-propelled (propeller drive) with a hard trim. Their freedom of lateral movement (sway force, yaw torque) was restricted by the guide arm, while they were free to move vertically (squat and trim). The friction caused by the guide carriage against the rail system was offset by means of a separate air-propeller drive.
The chart in Figure 2 is a simplified schematic illustration of the guidance and measurement system as well as the configuration of the measurements. A scales for six degrees of freedom had been installed at the toe of the member on board the ship to record the sway forces and yaw torques. Redundantly installed force sensors in the hull and on the guide carriage provided additional measurement and checking of the results from the central scales.
Table 1 lists the ship units investigated together with their dimensions, the block coefficient and the water depths traversed. The under-keel clearance at rest UKCR had been set at 10%, 15% and 20% of the draught (1.1 < h/t < 1.2).
| Designation | Beam b [m] | Length lpp [m] | Draught t [m] | Block coefficient cB [-] | Water depths h [m] | UKCR f(t) [%] |
| PPM55 | 55.0 | 360 | 14.5 | 0.689 | 16.0/16.7/17.4 | 10/15/20 |
| PM32 | 32.2 | 280 | 11.9 | 0.671 | 13.1/13.7/14.3 | 10/15/20 |
| MG32 | 32.2 | 225 | 11.9 | 0.845 | 13.1/13.7/14.3 | 10/15/20 |