Global Performance Analysis of Deep Draft Semi-Submersible Designed for Standard GOM Application

A deep draft semi-submersible hull has been developed by SHI (Samsung Heavy Industries) and Williams as a standardization concept which can support the topside structures up to the facility weight for the specific level of daily oil production in GOM (Gulf of Mexico). The designed hull has the optimized dimensions of pontoon and column which secure the sufficient level of GM for the stability and ballast capacity for coping with the weight change of topside structures. The hull form also has the good global motion in waves to be able to use the SCR (Steel Catenary Riser) as a deep draft semi-submersible concept. Two hull forms are designed to have 4 columns with two different cross sections and the conventional ring pontoon. The compartmentation and basic hydrodynamic analysis are performed at the hull sizing stage to achieve the sufficient stability and the motion performance as well. The mooring systems are also designed for two different water depths of 1000m and 3000m as a standard design concept of hull including mooring lines. To verify the feasibility of the proposed hull concept with regard to the hydrostatic/hydrodynamic characteristics and mooring line design, the numerical global performance analyses are carried out. Hydrostatic stability is investigated for intact and damage condition of operational loading condition and the proper tank compartments are verified under the given topside weight and the environment condition in GOM. The global motion is validated for all the possible combinations of wave, wind, current for a site in central GOM. Through the frequency-domain analysis and quasi-static time-domain analysis as well, the essential items such as the maximum offset, mooring line tension/fatigue, air-gap and the extreme acceleration at topside are examined and confirms that the certain design criteria of Semi FPU (Floating Production Unit) operation are satisfied. The possibility of SCR usage is also investigated with the fully coupled time domain analysis using the preliminary design of risers and confirms that the designed hull form has the suitable hydrodynamic characteristics to permit the minimum motion performance for SCR in the sense of extreme load and fatigue life.