engleski

Effective stiffness of the engine room structure in large container ships

Very large container ships are rather flexible due to the large deck openings. Therefore, hydroelastic stress analysis is required as a basis for a reliable structural design. In the early design stage, the coupling of the beam model with a 3D hydrodynamic model is rational and preferable. The calculation is performed using the modal superposition method, so natural hull modes have to be determined in a reliable way. Therefore, the advanced thin-walled girder theory, which takes the influence of shear on both bending and torsion into account, is applied for calculating the hull flexural and torsional stiffness properties. A characteristic of very large container ships is the quite short engine room, whose closed structure behaves as an open hold structure with increased torsional stiffness due to the deck effect. The paper deals with the calculation of its effective torsional stiffness parameters by utilizing the energy balance approach. Also, estimation of distortion of transverse bulkheads, as a result of torsion and warping, is given. The procedure is checked by the 3D FEM analysis of a ship-like pontoon. Such a modified beam model of the engine room structure can be included in the general beam model of a ship hull for the need of hydroelastic analysis, where only a few first natural frequencies and mode shapes are required. For practical use in the preliminary design stage of ship structures, the simplicity of the beam model presents an advantage over 3D FEM models.

Container ship; Engine room structure; Torsion; Warping; Distortion; Thin-walled girder; Analytical solution; FEM; Hydroelasticity

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