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Abstract: Many severe ship accidents in the past were caused by a large water ingress followed by the progressive flooding of the watertight integrity of the ships and finally resulted in the sinking and total loss of the vessels. These accidents show a high demand for a better understanding of the flooding of ships with the help of numerical methods. This would allow to avoid such accidents in the future and to find new designs with an increased capability to withstand flooding. The circumstances of the accidents, which involve flooding are difficult to understand due to the complexity of the inner subdivision and the large number of resulting flooding paths. Hence, a fast numerical simulation method is developed in this thesis to analyse and predict such flooding events. The validation of the method comprises the comparison with experimental results from three test cases of a model test and the re-investigation of three severe ship accidents, which have been carefully investigated before: The accident of the European Gateway, the Heraklion and the Estonia. The results obtained with the new method in these applications are very promising. A quasi-static approach in the time domain is chosen to compute the flooding of the inner subdivision and the resulting equilibrium floating position at each intermediate time step. The flooding paths are modelled with the help of directed graphs. The water fluxes through the openings are computed by a hydraulic model based on the Bernoulli equation. Large and partly flooded holes are taken into account, as well as conditional openings like breaking windows or the flooding through completely filled compartments. The effect of air compression can be taken into account as well if this is required for a certain case. After the determination of the new flood water distribution and the corresponding filling levels in each compartment, the resulting equilibrium floating position is computed. The simulation ends, either if the intermediate floating position does not change any more or if all buoyancy reserve is lost and the ship starts to submerge below the sea surface. The method is developed within the ship design system E4, which ensures a consistent data model and allows the direct coupling with existing and new methods. All essential effects are taken into account without unnecessarily increasing the complexity of the model as this would lower the performance of the simulation method. The method enables the user to study many flooding scenarios within a short period, for example to investigate the influence of watertight doors that were left open.