Trans RINA, Vol 153, Part A1, Intl J Maritime Eng, 2011 Jan-Mar


especially when the valve is not fully submerged. The applied values for the simulation (detailed analysis) were selected from these measurements, based on the most long-term flow conditions during the flooding tests. This was based on the video footage from the flooded compartments.


Dr Spanos and Mr Ypma asked for a clarification on the modelling of


permeability. All permeabilities were


considered to be constant, although the applied software can deal with variable permeabilities. Only in the pump room the large tanks were modelled as separate (impermeable) rooms. Thus all machinery was included in the permeability.


Mr Ypma and Mr Schreuder noted the effect between the of


stiffeners, especially in the two-compartment case. The stiffeners and the brackets were not included in the detailed model. In fact, the room geometries were exactly the same; the only difference


rough


estimation and the detailed analysis was in the applied permeabilities and discharge coefficients. Figure. 4a and Figure. 7 give an idea of


the web frames and other


stiffeners in the ship. These structures affect the details of the flooding process, especially when the water level in the flooded room is low. However, the authors believe that these details usually have only a minor effect on the stability of the ship and on the progress of flooding to the other compartments.


Regarding Dr Corrignan’s comments on water level figures and conclusions in the text,


the paper contains


only examples of the water level measurements. The locations of all sensors are shown in Figure. 7. The presented observations and conclusions, e.g. on the effect of stiffeners, are however based on all measurement data and visual observations from the video footage.


Mr Ypma and Dr Khaddaj-Mallat also asked about measurement accuracies and uncertainty analysis. The accuracy of heel and trim angles is about 0.02. The water heights were measured through


pressure with an accuracy of about 1 % or better. The largest uncertainty is related to the correct modelling of the sensor location. Thus


Dr Corrignan and Mr Ypma raised a question on the measurement of flow velocity in the damage opening. A paddle wheel transducer was used. The measurement point was not in the centre of the pipe, but close to the perimeter of the pipe, whereas the calculated


velocities are averaged over the pipe area. Thus direct comparisons are not reasonable. As mentioned in the text, the


velocities is questionable.


Mr Ypma also asked about the effect of air compression in the side tank flooding case. With full ventilation in the tank the time-to-flood is about 10 seconds shorter. Mr Schreuder made an interesting suggestion on studying the scale effects by numerical calculations in scale. Since scaling of the numerical ship model is a rather laborious task, it remains a future research subject.


hydrostatic the maximum error is


considered to be about 5.0 cm. Some measurements were also checked against the video recordings. All water levels are presented as vertical distance between the water level and the sensor. Full uncertainty analysis was not considered to be necessary for the purpose of the study.


Mr Ypma pointed out the difference between simulations of the two-compartment flooding case. The equal water levels do not directly indicate equal volumes since the heeling angle can be different. In this case the results are quite sensitive to the discharge coefficient of the second valve. Yet in general small changes in the input data did not have major effect on the output. The stiffeners in the bottom of the store room are considered to be the biggest


Dr McTaggart asked about the size of the damage hole. It is believed that a larger opening could have caused larger transient heeling angle if the “damage creation” would have been rapid. Due to structural and practical reasons, the used damage hole was the largest possible. In response to Mr Ypma and Dr Valanto, the conclusion that discharge coefficient is less important for large damage openings is based on the fact that


in that


situation the damaged room is flooded rapidly and the smaller internal openings then become the “bottle necks” for the floodwater. Consequently, the authors believe that the evaluation of discharge coefficients damage openings might not be very feasible.


for realistic


The authors agree with Dr Corrignan that the presented conclusions on the applicability of Bernoulli’s theorem may not be directly extended to flooding cases with significant sloshing. However, as Dr Taggart noted, for this ship type the sloshing is likely not an important


reliability of the measurement with low


reason for the unexpected result that the simulation with rough estimations


has pipe, a better correlation to


measurements. Regarding the comparison of rightfully pointed out


the


both Dr Corrignan and Dr Khaddaj-Mallat that


flow velocity in the air the flow regime changes


during the flooding process. As described in the text, the presented air flow velocities in Figure. 15 are not fully comparable. Dr Corrignan noted that the power-law equation can be applied for velocity profile of turbulent flow. The Reynolds number at the maximum measured velocity is about 105. Thus the peak flow velocity is in fact quite well estimated with the Bernoulli’s equation for compressible flow. However, as Dr Khaddaj-Mallat noted, the Reynolds number will decrease and eventually the flow regime will become laminar near the final condition. Dr Corrignan also asked about the decision to ignore air compression in the other compartments. These rooms were vented through large open hatches.


In


addition, no peaks were observed in the measurements of over-pressure in these rooms.


flow


©2011: The Royal Institution of Naval Architects


A-67


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