Hydrodynamic And Mooring Analysis Of A New Concept Production Semi-Submersible With Four Oblique Columns

In recent years, with the increase demand for energy, the exploitationof oil and gas engineering gradually develops from shallow waterextending to deep water. Semi-submersible platforms have been widelyapplied in deep water oil exploitation industry because of their excellentcharacteristics: great performance of stability, small water plane area, thecapacious deck area, preferably payload and so on. Therefore, it issignificative to carry out research on the hydrodynamic performance ofdeep water semi-submersible platform. As the National Offshore Oil981platform has been completed and put into use, it should carry out furtherresearch on deep water semi-submersible production platform.A new concept semi-submersible platform is the research object inthis paper. Different from traditional semi-submersible platform, the newplatform with four oblique columns above the water surface adopts deepdraft design concept. It is expected to work in the South China Sea withthe water depth of1500m. A combination method of model tests andnumerical simulation has been used to investigate the hydrodynamiccharacteristics of the deep water semi-submersible production platform.The hydrodynamic performances of the new concept deep water semi-submersible production platform are perfect. In operationalcondition, the maximum horizontal offset response is54.40m,3.63%ofthe water depth. The maximum heave motion response is2.29m, andheave motions are controlled within3m. In survival condition, themaximum horizontal offset response is106.59m,7.11%of the waterdepth. The maximum heave motion response is7.83m. The maximummooring line tension is10.2MN with the catenary mooring system, thatmeans the minimum safe factor is1.97satisfied the requirements.Compare response results of the semi-submersible productionplatform between catenary mooring system and taut mooring system inoperational and survival condition. The results show that, the heave, rolland pitch motions response of the platform are more severe in tautmooring system than in catenary mooring system. Generally, the kineticperformance of the catenary mooring system is better than the tautmooring system, especially in severe sea conditions.Carry out research about the oblique columns of the new conceptsemi-submersible platform by CFD software, to investigate the effect ofair gas performance. Study results showed that the character of columnshas significantly reduced the wave elevation.