Summary
Objective
Vortex-induced vibration (VIV) is an important issue in the design of deepwater riser systems, including drilling, production and export risers. The VIV can produce a high level of fatigue damage in a relatively short period of time for risers exposed to severe current environments. The wake interference between various risers in the same riser array may also lead to collisions between adjacent risers. Suppression devices, such as helical strakes or fairings may be needed to prevent unacceptable levels of fatigue damage. Reliable computational fluid dynamics (CFD) tools are needed to accurately analyze the VIV phenomenon and ensure safe riser operation under various flow conditions. The objective of this research is to focus on the development of advanced CFD capabilities for improving the prediction of riser VIV responses at high Reynolds number and under three-dimensional sheared currents.
Introduction
There is an increasing need for advanced modeling tools for riser design, particularly in the area of vortex-induced vibrations (VIV). The riser VIV responses are affected by many parameters including the Reynolds number, surface roughness, strakes, fairings, 3D sheared currents and ambient turbulence. The Finite-Analytic Navier-Stokes (FANS) numerical method will be employed in conjunction with a chimera domain decomposition approach to investigate the complex riser vibrations induced by the 3D sheared currents. The FANS method has been successfully used in the first phase of the project for VIV analysis of smooth and roughened risers with two-degree-of-freedom (DOF) motions. In the proposed research, the method will be further extended to assess the effects of Reynolds numbers, surface roughness, ambient turbulence, and highly sheared 3D currents on riser VIV responses. The performance of VIV suppression devices such as helical strakes and fairings will also be evaluated. The simulation results will be compared with available experimental data to assess the performance of various turbulence models for VIV predictions.
Benefits to MMS & Industry
The CFD results will provide a detailed understanding of the VIV phenomenon for deepwater riser systems including the effects of Reynolds number, surface roughness, and 3D sheared currents. These information can be used by MMS and industry to ensure safe design and operation of risers under severe current environments.
Deployment of Results
The CFD results will be synthesized for smooth and roughened risers under various operating conditions. This will provide designers a better understanding of the complex VIV phenomenon, and provide insight and a basis for designing to minimize VIV fatigue damage.
Project Organization and Timing
The project was initiated in 2003 and will be completed in three years. During Phase 1 (2003-2004) of the project, a CFD code was developed for time-domain simulation of single riser VIV under steady currents. In Phase 2 (2004-2005) tasks focused on the simulation of multiple riser interactions and the evaluation of vortex-suppression devices. In Phase 3 (2005-2006), the CFD code will be extended for time-domain simulation of riser VIV in highly sheared 3D currents.
Related Publications
Pontaza, J.P., Chen, H.C. and Reddy, J.N, “A Local-Analytic-Based Discretization Procedure for the Numerical Solution of Incompressible Flows,” International Journal for Numerical Methods in Fluids, Vol. 49, pp 657-699, October 2005.
Pontaza, J.P., Chen, C.R. and Chen, H.C., “Simulations of High Reynolds Number Flow Past Arrays of Cylinders Undergoing Vortex-Induced Vibrations,” Proceeding, 15th International Offshore and Polar Engineering Conference (ISOPE-2005), Vol. II, pp. 201-207, June 19-24, 2005, Seoul, Korea.
Pontaza, J.P., Chen, H.C. and Chen, C.R., “Numerical Simulations of Riser Vortex-Induced Vibrations,” Proceedings, SNAME Maritime Technology Conference & Expo and Ship Production Symposium, October 19-21, 2005, Houston, Texas.
Pontaza, J.P. and Chen, H.C., “Numerical simulations of circular cylinders outfitted with vortex-induced vibrations suppressors,”Proceeding, 16th International Offshore and Polar Engineering Conference (ISOPE-2006), San Francisco, California, USA.
Pontaza, J.P. and Chen, H.C., “Three-dimensional numerical simulations of circular cylinders undergoing two degree-of-freedom vortex-induced vibrations,” Proceedings, 25th International Conference on Offshore Mechanics and Arctic Engineering (OMAE-2006), Hamburg, Germany.
Huang, K. and Chen, H.C., “Ultra Deepwater Riser Interference Analysis by Using a Time Domain Simulation Approach with VIV Effect,” Proceedings of D.O.T. XVIII (2006) Conference, Unlocking Deepwater Assets through Technology, November 28-30, 2006, Houston, Texas.
Huang K., Chen, H.C., and Chen, C.R., “Deepwater Riser VIV Assessment by Using a Time Domain Simulation Approach,” OTC 18769, Offshore Technology Conference, 30 April – 3 May 2007, Houston, Texas, USA.
Huang, K., Chen, H.C. and Chen, C.R., “Time-Domain Simulation of Riser VIV in Sheared Current,” OMAE 2007-29363, Proceedings of the 26th International Conference on Offshore Mechanics and Artic Engineering, June 10-15, 2007, San Diego, California, USA.
Pontaza, J.P., Menon, R.G. and Chen, H.C., “Three-Dimensional Numerical Simulations of Flow Past Smooth and Rough/Bare and Helically Straked Circular Cylinders, Allowed to Undergo Two Degree-of-Freedom Motions,” OMAE 2007-29366, Proceedings of 26th International Conference on Offshore Mechanics and Artic Engineering, June 10-15, 2007, San Diego, California, USA.
Huang, K. Chen, H.C. and Chen, C.R., “Riser VIV Analysis by a CFD Approach,” Proceedings of the 17th International Offshore and Polar Engineering (ISOPE) Conference, Lisbon, Portugal, July 1-6, 2007.
Pontaza, J.P. and Chen, H.C., “Three-Dimensional Numerical Simulations of Circular Cylinders Undergoing Two Degree-of-Freedom Vortex-Induced Vibration,” ASME Journal of Offshore Mechanics and Arctic Engineering, Vol. 129, No. 3, pp. 158-164, August 2007.
Huang, K., Chen, H.C. and Chen, C.R., “A Three Dimensional CFD Approach for Deepwater riser VIV Simulation,” Proceedings of 9th International Symposium on Fluid Control, Measurement and Visualization (FLUCOME), Tallahassee, Florida, September 17-19, 2007.
