Strong ocean currents flowing past bluff offshore structures such as semisubmersibles and tension-leg platforms (TLP) can instigate large amplitude vortex-induced motion (VIM). This can lead to significant fatigue loads on the mooring system and its attachments. Simulating this problem numerically is of particular interest to the offshore industry in order to determine design loads and to avoid or suppress motion and vibration of the structure. But despite this being a classical flow problem, it remains a major numerical challenge, particularly at high Reynolds numbers where most offshore platforms operate. The difficulty arises from the strong nonlinear nature of the governing Navier-Stokes equations and the unsteady turbulent nature of the physical flow itself.
This study was therefore conducted to identify best practices for using Computational Fluid Dynamics (CFD) to estimate the loads imposed by uniform currents past a stationary bluff body (representing a semisubmersible column). Several Reynolds numbers were chosen to cover the subcritical, transcritical, and supercritical flow regimes. Two Reynolds-Averaged Navier-Stokes (RANS) software packages were used, the open source code OpenFOAM and the commercial code STAR-CCM+.
Verification of the numerical model and validation of results against published experimental test data is presented and the implications discussed. The paper provides several key elements that should be considered when modeling a uniform current past bluff body at high Reynolds number.