This paper presents a Truss Semisubmersible (Truss Semi) design optimized to meet the post-Katrina Gulf of Mexico (GoM) environment criteria, with global performance correlated in 1:50 scale model tests in a wave basin. A conventional semisubmersible with a ring pontoon is facilitated with heave plates supported by the truss structure to increase heave natural period. The size of the semisubmersible hull and the configuration of the heave plates are optimized through frequency domain analysis to minimize the vertical motion enough to allow the dry trees to accommodate top tensioned production risers. The system includes eight production top tension risers (TTRs) connected to the production deck and a single drilling riser connected to the drilling deck. All of the TTRs are connected through the hydro-pneumatic tensioner system. One gas export and one oil export steel catenary riser (SCR) export the oil and gas to the storage facility. Structures designed for this deepwater area (4,300 ft) of the central Gulf of Mexico (GoM) must be designed to meet newly proposed environmental criteria [1]. The optimized Truss Semi was tested in the Offshore Technology Research Center (OTRC) model basin, to confirm the global performance, such as motion, air gap and loads on the heave plates. The numerical predictions correlate well with the model test results.

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