Qualitative and Quantitative Comparisons between Spar and Semi-Submersible Platforms

Spars and semisubmersibles are two floating platforms commonly used in offshore deepwater exploration and production. However, currently lack of studies are available to comparatively evaluate the two platforms under similar cost range. This study compares the hydrodynamic motions of a truss spar and a semisubmersible under similar cost and wave environment. The platforms were numerically modelled using the radiation/diffraction software HydroSTAR. The response amplitude operators (RAO) were obtained for surge, heave and pitch respectively. The findings indicate the responses for the truss spar are generally lower than the semisubmersible, with the exception for the peak heave and pitch RAO. At 1000 m, the percentage difference of the peak surge RAO for spar and semisubmersible is 0.005%; heave RAO for semisubmersible is 34% of the spar’s value; and pitch RAO for semisubmersible is 79% of the spar’s value. Additionally, the semisubmersible achieved its peak RAO at a higher frequency for the heave and pitch. The findings proved that overall the spar’s dynamic responses are better for the majority of wave frequencies.