Study on the Ultimate Strength of Semi-submersible Platform Considering the Effect of Accommodation Structures Available to Purchase

Structure design technology based on the limit state is becoming the mainstream technology. It is significant for carrying out researches on the Ultimate Limit State (ULS) for semi-submersible drilling platform. The author of this paper has conducted researches on the finite element analysis technology of semi-submersible drilling platform by the ABAQUS finite element package and proposed the engineering numerical techniques for ultimate strength of semi-submersible platform. In order to simplify the problem, the structures and equipments on the upper hull deck are omitted. This will significantly affect the reliability of the result. So, the influence of the accommodation structure on the ultimate strength of the semi submersible platform was studied. Based on the previous research results, the deformation modes and ultimate bearing capacity, under the load modes due to split force between pontoons, longitudinal shear force and torsion moment about transverse horizontal axis, were analyzed by the non-linear finite element code ABAQUS respectively. The comparison between the platform without accommodation was made from the progressive buckling, including the stress distribution, strain distribution, deformation modes and the bearing load. Then, the different designs of general arrangement for accommodation were put forward. By comparative studies, the structural optimization design and the recommendation for the semi-submersible drilling platform were put up. Lastly, considering the significant change in the stiffness of the connection between accommodation and upper hull, the fatigue crack is easily generated in the joints under wave loading. The damage deformation mode and the ultimate strength under above load modes of semi-submersible drilling platform with failure crack were calculated. Further, the comparative analysis between the damaged structure and the intact structure was performed, and the effects of crack on ultimate strength were discussed.