Application of an advanced beam theory to ship hydroelastic analysis

Modern sea transport requires building of Very Large Container Ships (VLCS), which are relative flexible structures. Bearing in mind this fact, and taking into account the speed of VLCS, it is obvious that their natural frequencies could fall into the range of the encounter frequencies in an ordinary sea spectrum. Present Classification Rules for ship design and construction don’t cover such conditions completely. This encourages scientists and engineers to develop more powerful and reliable tools for the analysis of ship behavior in seas and to improve the Rules. Hydroelastic analysis of VLCS seems to be appropriate solution for this challenging problem. Methodology of hydroelastic investigation is based on mathematical model which includes structural, hydrostatic and hydrodynamic submodels which are assembled into hydroelastic one. The hydroelastic problem can be solved at different levels of complexity and accuracy. It is obvious that the best way is to consider 3D FEM structural model and 3D hydrodynamic model, but this approach would be too expensive, especially in preliminary design stage. At this level it would be more appropriate to couple 1D FEM model of ship hull with 3D hydrodynamic model. In this paper, the emphasis is given on the advanced beam model which includes shear influence on torsion as an extension of shear influence on bending, and contribution of transverse bulkheads to hull stiffness. Beside structural model, hydrostatic and hydrodynamic submodels, as constitutive parts of hydroelastic model are briefly described. Verification of proposed numerical procedure is done by correlation analysis of the simulation results and the measured ones for flexi-ble barge, for which the test results are available in the literature. Numerical example, which includes com-plete hydroelastic analysis of 7800 TEU container ship, is also given. In this case, validation of 1D FEM model is checked by correlation analysis with the vibration response of the fine 3D FEM model. The obtained results confirm that advanced thin-walled girder theory is a reasonable choice for determining wave load effects on VLCS, in preliminary design stage.