Trans RINA, Vol 152, Part A4, Intl J Maritime Eng, Oct-Dec 2010


The time histories for water levels in the equipment room and the store are presented in Figure. 27 and 28. The notable differences between the measurement and the calculations in the early stages are caused by the water accumulation between the stiffeners in the bottom of the rooms. The numerical model does not contain these structural details. Thus the floodwater is calculated to accumulate on the forward end of the empty store in the beginning of the flooding, resulting in a slight over- estimation of both the trim and heel angles. This effect is slightly compensated by the slower flooding with the rough estimations for the input data. However, the overall correspondence between the measurements and the simulation is good.


4.4 STABILITY AFTER FLOODING


After the test with the side tank flooding, an inclining experiment was conducted, using movable weights on the upper deck. The damage hole was left open. The righting lever curve for the final condition after the flooding was calculated with the NAPA software. The lost buoyancy method was used.


The results are presented in Figure. 29. The measurement points fit very well in the calculated curve. The difference in the metacentric height is less than 0.01 m, which is clearly within the accuracy limits of the measurement.


calculated measured


0.01 0.02 0.03


−0.03 −0.02 −0.01 0


Figure 5.


The applied successful.


test arrangement Flooding was proved to be very


“damage hole” could be easily closed. Therefore, several tests could be performed within a short


well-controlled and the time. On the


other hand the damage size was small, resulting in fairly slow flooding. The ship had a relatively good initial stability, and thus the maximum heeling angle was rather small, even in an asymmetric flooding case. Yet the changes in the floating position were significant, especially in the two-compartments flooding case.


Comprehensive measurements and video recordings were used to validate a state-of-the-art flooding simulation tool. The calculation predicts very well the progress of the floodwater and the motions of the ship, even with very rough estimations of the permeabilities and the pressure losses in the openings.


When real permeabilities and proper discharge coefficients are applied, the results match even better. Taking into account the above mentioned uncertainties in the modelling of the


especially the permeabilites and structural details, it can be concluded that


the correspondence


numerical simulation results and the measurements is as good as in the validation study with a scale model of a box-shaped barge, [9].


It should be noted that in the presented tests the damage hole was rather small. Thus the effect of its discharge coefficient is much more notable than in the case of a large damage extent. Furthermore, the valve between the SB side tank and the equipment room acts as a bottleneck since the effective pressure head is rather low throughout the flooding process. Consequently the simulation results are sensitive to the applied discharge coefficient for this opening.


The comparison of experiments and simulations clearly shows that the simplified approach of Bernoulli's theorem is accurate enough for modelling progressive flooding inside a damaged ship, if the applied discharge coefficients


are realistic. Furthermore, the air −5 29: −4 −3 Heel [deg] Calculated righting lever CONCLUSIONS


Although large ships have been intentionally sunk in order to establish artificial reefs and diving attractions, [13], systematic experimental research on progressive flooding in full-scale has not been reported in open literature. Contrary to the artificial reef projects, the presented full-scale tests allowed detailed measurements and


recordings inside the flooded compartments. Moreover, the experiments could be easily repeated.


curve and


measurements from the inclining test with flooded side tank


−2 −1 0


compression in a tank with restricted ventilation level can be modelled very realistically with the assumption of perfect gas and Bernoulli’s equation for compressible fluid.


6. ACKNOWLEDGEMENTS


The authors would like to express their sincere gratitude to all persons who were involved in the flooding tests. The project has received funding from Tekes (the Finnish Funding Agency for Technology and Innovation) and STX Europe


Turku Shipyard, which is gratefully


acknowledged. Mikael Stening from Water Resources Laboratory of Aalto University provided the valuable data on pressure losses in various openings. Finally, Turkka Jäppinen from Finnish Naval Research Institute is thanked for arranging the opportunity for the tests.


discharge coefficients, and between the


A-206


©2010: The Royal Institution of Naval Architects


Righting lever [m]


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