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Recent ship damages underline the importance of an accurate intact and damage stability analysis. The stability of ships is presently determined by applying quasi-static methods, neglecting dynamic effects; for flooding scenarios, flow calculations are not carried out either. In general, for damage cases, water dynamics inside the compartment affect ship motions. It has been observed that some kind of vessels could experience large roll motions due to the sudden water ingress after damage. In this article, a non-linear tool for damage stability evaluation is presented, including water dynamics in a flooded compartment. In particular the transient stage of flooding is investigated. The flooded water has been treated using the lumped mass approach. A new method has been developed and applied in this article in order to model the water motions: the freesurface is assumed to be no more horizontal but dependent on ship and flooded water accelerations. The developed method is intended to be an intermediate approach between the quasi-static method (uncoupled) and fully coupled method. In coupling the flooded water motions with ship motions, no more unknowns are introduced: only ship lateral acceleration is used to determine the freesurface inclination of the flooded water. A valuation is carried out, comparing the numerical result from the simulations with the experimental studies on a barge model. Additional applications are carried out on the free roll motion of the TNK tanker model.

The motions of a flooded ship in waves are difficult to evaluate. They are affected by complex phenomena involving ship and floodwater dynamic interactions. Several numerical methods have been proposed to estimate the dynamic behavior of a damaged ship in waves. In this article, a fast simulation tool is developed to tackle the problem, aiming at a simplified method with an acceptable accuracy of the results. A novel approach in simulating floodwater effects on ship motions is presented. The method allows modeling the floodwater motions (seen as lumped mass) out of phase from ship motions. This technique is based on the basic fluid mechanics knowledge for a liquid in a uniformly accelerated tank. The study intends to analyze the behavior of a flooded ship in regular beam waves, for compartment fillings that involve shallow and intermediate fluid depths. The nonlinear model for the roll damping moment of a ship is implemented. An attempt to model viscous effects in the floodwater dynamics is proposed and applied. Two sets of applications are carried out on two different hull models. The comparisons of the intact and of the flooded ship responses in waves are conducted and discussed.

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