On the calculation of cross-flooding time

Abstract

Asymmetric flooding in a damaged ship is a dangerous situation. Cross-flooding ducts are used to provide the necessary equalization across the ship in order to decrease the heeling angle. The elapsed time for this passive counteraction depends on the arrangement of the ducts and the tanks. In addition the air pipes have a significant effect since air must be vented from the flooded tanks. This paper presents CFD calculations, applied to obtain the discharge coefficient of the whole cross-flooding duct, as well as for assessing the pressure losses for air flow in two typical air pipe designs. The results are combined in order to study their final effect on the time to equalize the asymmetric flooding. Calculations are performed by using both simplified approaches and time-domain simulation. The results indicate that small inaccuracies in the applied coefficients have only a minimal effect on the results. Thus the use of simplified methods for determination of the applied discharge coefficients seems to be justified. However, the use of CFD and time-domain simulations may be necessary for exceptional arrangements. The results also indicate that neither the scale 1:3 nor the inlet pressure height has significant effect on the discharge coefficient.