The technical challenges for the structural design of the new ultra deepwater generation of drillships are optimized hull designs that include greater functionality, flexibility and operational efficiency. Compared with traditional design, some drillship structural designs may not include crude oil storage capacity and the vessel is likely to have less deck area. In addition, they are generally free of equipment on deck and are more compact with an increased integrated hull and drilling system arrangement. This calls for a comprehensive and practical procedure for drillship structural design and verification.
This paper describes an advanced design and analysis procedure to address the strength and fatigue requirement which is applicable to all types of drillship structures. With the presumption of unrestricted service operations, the study evaluates structural strength of the drillship in different operating environments (e.g., transit, normal drilling, severe storm), under a variety of operating scenarios and transit conditions. Site-specific conditions with specified probabilities are considered for fatigue evaluation. The presented procedure includes initial prescriptive scantling assessment, comprehensive finite element strength assessment, fatigue assessment, strength and fatigue criteria.