Trans RINA, Vol 152, Part A4, Intl J Maritime Eng, Oct-Dec 2010
model and test procedure are provided in Macfarlane and Renilson, 2010.
A rectangular shaped damage opening was located on the starboard side of the ship model. When intact, this opening was sealed using a taut latex membrane.
A very rapid damage opening scenario was simulated by puncturing the taut membrane using blades attached to a pneumatic ram that was operated by a remote switch. Puncturing the membrane in this way resulted in the loss of the latex patch within 1/25th second (one video frame), leading to a very rapid damage event.
3. 3.1
EXPERIMENTAL SET UP INSTRUMENTATION
The water surface elevation within specified tanks was measured using wave probes. A total of seven wave probes were included to measure the water levels in the following compartments: 0Fwd-S06; 2Aft-S11; 2Centre-S12; 2Centre-S15; 1Aft-S17; and 1Centre-S23. The locations of these are indicated on Figure 5 by: ‘WP’. Two video cameras were deployed; one internal camera located onboard the ship model to view the flooding of the compartments and one external camera to view the entire model.
The motion of the fully unconstrained model was measured in all six degrees of freedom by a non-contact digital video tracking system (Qualisys). The calibration of this system utilises a series of 16 permanent reference markers that have been surveyed into position around the basin. The capabilities and operation procedures of this system are described in detail in Qualisys (2008). A set of active markers were installed on the model to allow the Qualisys system to track the model’s motion. These four white spherical markers can be seen in Figure 3.
3.2 UNCERTAINTY The following levels of uncertainty were estimated:
• Model dimensions = breadth and draught ±1.0 mm and for length ±1.5 mm
• Model displacement = ±100 grams • Model KG = ±1.0 mm • Model roll radius of gyration = ±3.0 mm • Model pitch radius of gyration = ±2.0 mm • Water surface elevation = ±2.0 mm • Measurement of roll and pitch = ±0.1 degrees
3.3 TEST PROCEDURE
For all the runs the model was in calm water and at zero forward speed. The water depth in the basin was monitored daily and fixed at 800 mm.
Prior to the commencement of each test run approximately 3 seconds of data was collected while the system was static. This provided a ‘zero’ position for each instrument which was subtracted from the data to provide absolute values. For the Qualisys system, recording of
the model motions was triggered to coincide with the recording of the wave probe data.
On completion of data acquisition the model was removed from the basin, the water was emptied from all tanks and carefully dried and a new latex membrane fitted over the damage opening prior to setting up for the next run.
Once the model was prepared and
located, the basin was allowed to return to a calm state before the next run was begun.
4. TEST PROGRAM
Five runs were conducted to determine the repeatability of the
process, and three additional runs were
conducted at different KG values to investigate the effect of KG on the results. Note that only valid runs of relevance to this work are reported here.
5. RESULTS AND DISCUSSION 5.1
REPEATABILITY
A comparison of the results from five runs with the same nominal particulars gives a good indication of the repeatability of
the process. In this case the KG remained constant at 173mm.
The results from these runs are compared in Figures 7 to 13. Note that in all cases time t = zero seconds is the point at which damage has been initiated.
It should be noted that all results are given in model scale.
5.1(a) Roll angle
The roll angle as a function of time for each of these runs is shown in each of the plots (right axis), as well as in Figure 7. As can be seen, for each of these runs the damage causes an initial positive heel
angle (to
starboard), followed by a negative heel angle (to port) and finally the model rolls back to starboard again and settles at its equilibrium heel angle without an overshoot.
The initial motion is very similar for all the runs, with the initial heel angle to starboard being almost the same for all five runs. Even the small unsteadiness in the roll as the model starts to roll back to the upright is similar in all these runs. However, the extreme angle to port (away from the damage) is different in the five different runs, and the roll angle as a function of time from that point onwards is different, until the model settles at approximately the same equilibrium angle to
finally
A-210
©2010: The Royal Institution of Naval Architects
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