Trans RINA, Vol 153, Part A1, Intl J Maritime Eng, 2011 Jan-Mar
Section 4.1 You mention that ‘some difference’ is found between simulated and measured levels (at the start of the flooding). I understand that this can be caused by the stiffeners (we have found some quite serious effects caused by these) but I cannot conclude that from the plots.
Section 4.2 sudden increase of heel at t~900 sec I think this only applies to the ‘rough’ simulation. The other simulation result is quite good. If that is the case can it than be caused by the stiffeners? Or were these modeled in the ‘’detailed’ simulation?
Section. 4.3 What could be the reason for the better results for the heel angle when using the ‘rough’ coefficients? What were the approximate volumes of each compartment? This can give a better idea of the relative importance of a level difference in relation to the heel. The interesting thing is that at t~1500 sec the differences between the measured levels and the ‘rough’ and ‘detailed’ levels is approximately the same. Hence in the simulations the same weight (and location of cog) was predicted. Or does the difference relate to the ‘chaotic’ properties of the flooding
process (small, initial differences can results in quite different outcomes).
Section. 5 I think that it is difficult to draw the conclusion that the effect of a Cd mismatch with a small damage hole is larger than when a large damage hole is used. A large damage hole will, on the other hand, introduce
all kinds of other
phenomena that will not be captured by the (current) simulation tools.
Lots of questions which might not all be relevant for the paper. Nevertheless, I am interested in your comments.
M Schreuder, Chalmers University of Technology, Sweden
I would like to commend the authors on this conspicuous and bold project. It was a pleasure to read the paper from start to end and I learned that the experiments were also very thorough and ambitious.
In the simulation set up you used two different accuracies in modelling two parameters, the discharge coefficients and the permeabilities. I think the presentation of the corresponding simulation results are quite enlightening and could be used as a guide for similar simulations. However in the presentation of the results you do not separate the parameters. Do you have any comment on the relative impact on the results of these parameters in the “rough estimation” and “detailed analysis” respectively?
You have also in the results detected and to some extent quantified the influence of structural members, usually not accounted for in scale models. Even if this influence is not very surprising and also quite small in your test cases, I think your findings are quite unique and also principally important.
©2011: The Royal Institution of Naval Architects
Since you already have a numerical representation of the geometry and other properties of the tested ship, I think it would be of interest to do simulations of a geometrically scaled model, in order to isolate the influence of Boyle’s law. Maybe you have already done similar simulation comparisons, proposal?
or have any other comments to this
D Spanos, National Technical University of Athens, Greece
Thank authors for their paper which provides background information to the software
computing of intermediate stages of damaged ships.
developments in the flooding of the
The power of computer simulation for the analysis of intermediate and progressive flooding was pointed out during the investigation of the sink accident [5] when the feasibility to simulate large complicate arrangements was proved. The simulation method enables to determine the likely flooding scenario and the
final flooded ship condition that is connected to a specific damage opening.
The presently applied theoretical model deals specifically with quasi-static conditions, thereof the software is properly validated in calm water and slow flooding through the small damage opening.
In this framework the flooding problem may be well determined by the set of input parameters those of discharge coefficients and permeability of the flooded spaces. Any uncertainty on the data obviously affects the computed results. The presented results appear sensibly sensitive while still stable to the data variations. Nevertheless when higher accuracy is required, this can be achieved with special assessment of the parameters, like it was done in the course of the present validation work. Thereby using refined data a good correlation between the demonstrated.
calculations and the experiments
In reference to the discharge coefficients for the second valve, which was located between the side tank and the equipment room, it remains unresolved whether the estimated large difference was due to discharging into water or air, or due to pressure head small or large, or due to both factors. To the degree that the pressure head contributes to this difference, this would rather be attributed to the theoretical flow model, which explicitly takes into account the pressure head, instead of attributing the full difference to the discharge coefficient.
It would be also clarifying to which extent the vertically variable permeability was applied in the validation tests and what were the improvements from such detailed description.
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