A fully coupled Fluid Structure Interaction model for assessing ship hard grounding dynamics

Ship grounding accidents continue to dominate ship casualty statistics and may lead to oil spills, vessel capsize following serious flooding, significant asset damage and loss of human life. To date, the influence of grounding events on ship safety as implemented in the IMO Safety of Life at Sea (SOLAS) regulatory instrument is based on limited accident statistical datasets. The development of improved ship safety standards requires rapid and reasonably accurate models for use in structural integrity rules and damage stability regulations. This is also important within the context of the development of risk control options and future decision support systems. The goal of this research has been to study the influence of ship hard grounding dynamics by combining principles of marine hydrodynamics, structural crashworthiness and their impact on ship damage stability in a way that is useful within the context of ship design for safety. To achieve this the thesis proposes a rapid Fluid Structure Interaction (FSI) model for the idealization of ship hard grounding dynamics under realistic operating conditions. The model developed is used to demonstrate how existing databases may be updated to account for the influence of deterministic damage extents of passenger vessels following hard grounding. The thesis claim is supported by three internationally peer-reviewed journal publications. Publication-I presents a rapid 6-DoF time domain maneuvering model with a conventional rudder propeller that may be of single or twin-screw configuration. For the twin-screw vessel, a reference method that accounts for the change in the hydrodynamic assumption of hull forces is presented. Maneuvering motions are validated against existing model-scale experiments. Publication-II proposes an FSI model. The approach combines internal and external mechanics and investigates the effect of plate split angle variations at multiple rock penetration depths. The model accuracy is validated by comparisons against 3D LS-DYNA MCOL commercial software simulations. Publication-III uses the FSI model to estimate probabilistic extents of damage following the grounding of a passenger ship under real environmental conditions. The method utilizes Monte Carlo simulations to generate the ship operating parameters and the conical rock profile which is then used as an input to the FSI model. The major findings of this thesis are as follows: (1) the rapid 6-DoF maneuvering model presented provides well-validated ship trajectories and the time history of ship motions. The model idealizes well external hydrodynamic actions; (2) the plate tearing angle formed during the contact of hull bottom with a conical rock is dependent on ship motions and the depth of penetration of the rock into the hull. The assumption of constant plate split angle should be ignored; (3) the rapid coupling algorithm significantly reduces computational time and with sufficient accuracy predicts structural deformations and damage extents; (4) Damage extents predicted by the new method and review of historical data indicate that ship damage lengths are larger than those suggested in existing accident databases. The model yields marginally lower estimates for damage width and penetration.