Sea transport is rapidly increasing and Very Large Container Ships (VLCS) are built. They are more flexible and their natural frequencies can fall into the range of the encounter frequencies in an ordinary sea spectrum. Such conditions are not covered by the present Classification Rules for ship design and construction. So, structure design of VLCS is at the margin of the rules. Therefore, the wave induced hydroelastic response of VLCS becomes an imperative issue for improving the Classification Rules and ensuring ship safety. This paper is dealing with the methodology of hydroelasticity investigation, based on mathematical model which includes structural, hydrostatic and hydrodynamic submodels assembled in hydroelastic one. Special attention is paid to restoring stiffness in hydrostatic submodel. The modal superposition method is used, and ship natural modes are determined by the advanced beam theory which includes shear influence on torsion. Contribution of transverse bulkheads to hull stiffness is analysed. 1D FEM model is verified by correlating dry natural vibrations with those obtained from 3D FEM model. Validation of the hydroelastic mathematical model is done by comparison with results from model test of a flexible segmented barge. Application of the developed numerical procedure is illustrated in case of a very large container ship.
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