A drillship is an exceptional vessel to be capable of drilling of new oil or gas wells, and carrying out maintenance or completion work in deep water. The drillship also has ability to take aboard much more variable loads and save the time of sailing between oil fields worldwide than Semi-submersible rig. Sometimes, it is required from design specifications that a drillship is to be designed to be satisfactory to several fields at the same time to maximize such advantages. This paper describes results of the comparative study on fatigue life of a drillship, which was developed by DSME, operating for both GoM (Gulf of Mexico) and Brazil sectors. It was assumed in the calculation that the drillship spends 80% of her life in On-site (GoM and/or Brazil sector) and other percentage in transit condition. Screening works for choosing fatigue sensitive locations such as moon pool corners, discontinuous areas, topside module foundations, etc., were performed referring to the local strength analysis. A whole ship model along with every topside module was generated and the very fine meshes with thickness by thickness as per DNV RP-C203 were embedded therein. Stress RAOs of critical hotspot locations of the drillship were directly obtained through its motions from 3D potential-theory-based analysis, i.e. DNV WADAM. In the analysis, wave scatter diagrams given by BMT were used. As results of the study, it was found that Brazil sector gives comparatively worse results to the drillship in terms of fatigue endurance and finally, Brazil sector was decided in calculating fatigue lives of the drillship as a representative sea state. The fatigue life was computated based on spectral fatigue analysis by means of DSME’s in-hose tool (i.e. D-SFAS, DSME Spectral Fatigue Analysis System).

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