The vortex-induced motions (VIM) of deep draft semi-submersible platforms have been challenging engineering issues because of its impact to the fatigue life of mooring and riser systems. This paper presents numerical studies on the vortex-induced motions (VIM) of a deep draft semi-submersible. Numerical simulations are performed by using an improved delayed detached eddy simulation (IDDES). VIM amplitudes for in-line (surge), transverse (sway) and yaw motions and hydrodynamic force coefficients are obtained for different current incidence angles. The sensitivity analyses on grids and time step sizes are carried out to ensure convergences of the computational results. Comparisons with experimental data demonstrate the capability of the present numerical model. It is observed that the transverse motions for 22.5° current incidence are larger than those for 0° and 45° current incidences. The mean drag force coefficients for these simulated current incidence angles tend to grow as the transverse motion amplitudes increase. In addition, parametric studies have also been performed to examine the effects of the column corner radius on VIM.

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