Numerical investigation of three-dimensional hull girder ultimate strength envelope for an ultra large container ship

Ultra large container ship (ULCS) structures feature large deck openings and low torsional rigidity. It is essential to accurately evaluate the maximum loading carrying capacity of ship structures. When the ship sails at an oblique heading in rough sea, the horizontal and torsional moments may approach or even exceed the magnitude of vertical bending moment. In such cases, hull girder ultimate strength assessment of container ships under load combinations comprising of vertical bending moment, horizontal bending moment and torsion is necessary in their structural design stage. In this paper, special attentions are thus paid to the hull girder ultimate strength of an ULCS (i.e., a typical 10,000 TEU container ship) subjected to combined three load components mentioned above, which is also a common load case in ships and ship-shaped offshore structures and it is assumed that the three kinds of main loads can be combined each other freely. A series of nonlinear finite element analyses (NFEA) is carried out. Effects of fabrication related initial imperfections are investigated in the present study. Based on the computed numerical results, the 3D hull girder ultimate strength envelope considering initial deformation and incorporating the interaction relationships among three kinds of load components mentioned above is established.