It is well known that the riser VIV responses are affected by many parameters including the Reynolds number, surface roughness, strakes, fairings, 3D sheared currents and ambient turbulence. In order to provide accurate analyses of the VIV phenomena, the Finite-Analytic Navier-Stokes (FANS) numerical method has been employed in conjunction with a chimera domain decomposition approach to investigate the complex deepwater riser VIV induced by various current profiles. As noted earlier, the FANS method has been successfully used for VIV analysis of smooth and roughened risers in uniform currents. In this research, the method has been further extended for the prediction of VIV responses of deepwater risers under both the uniform and sheared current profiles. The simulation results were compared with available experimental data to assess the accuracy of the CFD predictions.
In order to extend the predictive capability of the FANS code from relatively short 3D risers with L/D ~ 10 to long 3D risers with L/D ~ 1,000, the following numerical investigations have been performed and summarized in this report:
- development of modal solver for riser finite element motion equation,
- development of direct solver for riser finite element motion equation,
- 2-D simulations of flow past a fixed riser at high Reynolds numbers,
- 2-D simulations of flow past a forced motion riser at high Reynolds numbers,
- 3-D simulations of flow past a horizontally positioned riser in uniform current,
- 3-D simulations of flow past a horizontally positioned riser in shear current,
- 3-D simulations of flow past a vertically positioned riser in uniform current,
- 3-D simulations of flow past a vertically positioned riser in shear current,
- validation of FANS simulation results with experimental data, and
- comparison of FANS results with numerical results obtained by commercial codes.
The simulation results clearly demonstrate the capability of the FANS code for accurate prediction of VIV responses of deepwater risers under uniform and sheared currents.