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The deep-draft semisubmersible (DDSS) platform is well known due to its favourable vertical motion routine. However, DDSS platforms face a serious challenge in vortex-induced motion (VIM) due to the changing forces of the column. A computational fluid dynamic (CFD) simulation using AcuSolve is conducted to investigate the effect of a twisted-square column with different twisted angles, 0°, 22.5°, 45.0°, 67.5° and 90.0°, on the VIM responses and performance at current incidence angles of 0° and 45°.Platform models at a scale of 1:70 are studied to determine that the alteration of vortex shedding due the separation line at the twisted column expressively influences the mean and fluctuation of hydrodynamic forces and motion. In particular interest is the drag and lift coefficients, surge, sway amplitudes, as well as the yaw motion of the DDSS platform. The simulation was conducted at a velocity of 0.16 m/s.

A numerical study is conducted to determine the Vortex Induced Motion (VIM) effects on Deep-Draft Semi-Submersibles (DDSS). The VIM phenomena is a crucial problem that can cause severe impact on the fatigue life of mooring risers in DDSS. Therefore, a comprehensive numerical simulation is conducted using the Acusolve computational fluid dynamics (CFD) software. Five models of immersed columns with different aspect ratios (ie. 0.6, 0.8, 1.0, 1.2 and 1.4) are numerically investigated under two different incidence angles, which are 0° and 45°. The transverse and in-line vibration amplitude, amplitude of lift force coefficient and vortex shedding are analyzed. The numerical measurements are obtained to see the response of horizontal plane motions, which are transverse, in line and yaw motions. This study with detailed numerical results from parametric data will contribute future studies and the comparisons are made to demonstrate the capability of the present CFD approach.