Trans RINA, Vol 154, Part A2, Intl J Maritime Eng, Apr-Jun 2012
4.2 EFFECT OF AREA OF DAMAGE OPENING ON COMPARTMENT WATER LEVELS
The area of the damage opening was varied from 50% up to 100%, as shown in Table 2, to investigate what influence this has on the flow of water into the compartments and provide experimental data for the purpose of validating numerical codes. Note that 100% damage was assumed to be the full
length of damage
opening multiplied by a height of damage opening up to the static waterline for the design draught. In Table 2, the top of each diagram corresponds approximately to the waterline.
The water levels in the centre tank on the starboard side (2Centre-S12) are plotted as functions of time in Figure 6.
Here the levels all rise very quickly, with only the
result for the 50% damage opening (Run P1_R21) being slightly slower. All reach the same approximate equilibrium position, as this wave probe is in the free flooding space close to the damage opening. This small effect that the 50% damage opening has on the filling rate can also be seen in Figure 9, where the water levels within tank 2Centre-S12 at time t = 10s are plotted. At this point in time, the water level is about 3mm lower than the cases where at least 85% of the damage area is open.
The water levels in the two compartments on the 2nd deck on the port side (2Centre-S15 and 2Aft-S11) are plotted as functions of time in Figures 7 and 8 respectively. With the exception of the smallest damage opening (Run P1_R21, 50%) these results are very similar for the forward of these two compartments (2Centre-S15).
For the aft compartment on the 2nd Deck (2Aft-S11) the damage opening had a slight influence on when the water first reached the wave probe, with the water level taking slightly longer to reach the wave probe when the area of the damage opening was reduced. The damage opening appears to have affected the water level in tank 2Aft-S11 for both the 50% and 85% damage opening cases as they are lower than the 100% case, as can be seen in Figure 9. It should be noted that in all these cases there was a reduction in damage opening area at the aftermost part of the damage opening (thus the incoming water had further to travel to this aft compartment).
4.3 EFFECT OF WAVES ON COMPARTMENT WATER LEVELS
The water levels in compartments 0Fwd-S06, 2Aft-S11, 2Centre-S12, 2Centre-S15 and 2Fwd-S16 from a test in calm water are compared against results from a test in regular beam seas with nominal wave height of 50mm and wave frequency of 0.9Hz, see Figures 10 to 14, respectively. For all these tests the damage opening is facing the oncoming waves and the model is fixed at level heel.
As expected, the incident waves cause the water level in the compartments to also oscillate, which generally occurs at wave frequency, although the variation in water elevation is more complicated due to wave reflection and refraction within the compartments. The magnitude of the oscillations in water level tends to be greatest within those compartments that have more direct access to the damage opening. For example, wave oscillations of up to approximately 40mm occur within compartment 2Centre-S12, which is fully exposed to the damage opening, whereas this reduces to as low as approximately 10mm for 2Centre-S15 and 5mm for 2Aft-S11 (the incident wave
height was 50mm). Both of these
compartments are located on the port side of the model where the waves need to travel through open doors and adjoining compartments.
Of particular note, there appears to be a build up, or ‘set- up’, of water inside each of the compartments on the 2nd Deck. The result of this is that the mean equilibrium water level in the regular beam sea cases is higher than the equivalent calm water case. This is particularly noticeable for the two compartments on the port side, 2Aft-S11 and 2Centre-S15.
Further calm water and beam sea tests were conducted with the model at fixed heel angles of 5 and 10 degrees (both to starboard – i.e. towards the damage, which is facing the oncoming waves). Figure 15 presents a cross- plot of the equilibrium water levels as a function of heel angle. As can be seen, a set-up in water level of similar magnitude occurs at both port-side compartments (2Aft- S11 and 2Centre-S15) at each of the three fixed heel angles (0, 5 and 10 degrees).
However, this set-up appears to reduce at 5 degrees of heel and is not present at all for 10 degrees of heel for the wave probe located along the model centreline (2Fwd- S16) and the probe on the starboard side near the damage opening (2Centre-S12). This reduction in water level set-up at these two locations appears to be approximately linear with increasing
heel angle. Note that the
equilibrium water level during the regular beam sea tests is assumed to be the mean of the oscillations.
Further investigation is required to determine what effect wave frequency and/or wave height may have on these results.
As can be seen in Figure 10, there is very little difference between the calm water and regular beam sea cases for the tank 0Fwd-S06. Water entering this tank does so through a down-flooding hatch so the water level does not oscillate in the same manner as the compartments on the 2nd Deck. Thus, the results in regular beam seas appear to be similar to those from the equivalent calm water tests.
A-58
©2012: The Royal Institution of Naval Architects
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62