engleski

Application of 1D FEM & 3D BEM hydroelastic model for stress concentration assessment in large container ships

Ultra Large Container Ships (ULCS) have relatively lower torsional stiffness and higher speed, compared to the other merchant ships. Due to their specifi c design and operational characteristics, natural frequencies of ULCS can fall into the range of encounter frequencies of ocean wave. So, their structural design should be based on hydroelastic analysis. In this paper an outline of an earlier developed hydroelastic model, comprised of a sophisticated beam structural model and a 3D panel hydrodynamic model, is given. The sophisticated beam model includes shear influence on both bending and torsion, contribution of transverse bulkheads to hull stiffness as well as an appropriate modelling procedure of relatively short engine room structure. The model represents a reliable numerical tool for determination of ship global hydroelastic response in frequency domain, by the modal superposition method and here a possibility of its extension for stress concentrations assessment, as a prerogative for fatigue damage calculation, is shown. The procedure is illustrated within the numerical example which includes complete hydroelastic analysis of an 11400 TEU container ship. The transfer functions of sectional forces are determined and compared to the rigid body response. Further on, modal displacements at selected cross-sections are calculated, and then they are spread to the fore and aft contour of a fi ne 3D FEM substructure model. Finally, the stress concentrations in the considered structural detail are obtained. The validation of the sophisticated beam model is done by correlation analysis with the dry natural vibration response of the fi ne mesh 3D FEM model. Global and local hydroelastic responses are compared with those calculated by the fully coupled 3D FEM + 3D BEM hydroelastic model and acceptable agreement is obtained.

Beam model; Container ship; Hydroelasticity; Springing; Stress concentrations

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