Structural response of a ship in severe seas considering global hydroelastic vibrations

In this paper, a consistent structural analysis procedure to estimate the global and local load effects considering symmetric and anti-symmetric hydroelastic vibrations in high waves is proposed. The procedure consists of motion analysis followed by a structural analysis. First, a system equation of motion by modal approach is set-up and solved in the time domain. In the load evaluations, not only linear but also nonlinear forces such as quadratic component in Bernoulli's theory and body nonlinearity due to the fluctuation of wetted surface, which might have high priority from the viewpoint of structural analysis, are considered by using three-dimensional potential theory. The accuracy of the structural analysis results depends upon the consistency between the models employed in each analysis as well as the accuracy of the analysis at each stage itself. In order to maintain the consistency, the mass terms and the modal forces are evaluated based on the FE model of the whole ship in which all the mass properties are included, and also on modal analysis results on the same model. Then, the inertia forces and pressure distributions at selected time steps are statically applied on to the FE model considering dynamic amplification effects arising from the flexible modes. The procedure is applied to a large container ship. Local and global effects are evaluated. Fluctuating component in torsional mode, or springing in torsion is found.