Progress Reports: June 2006 December 2005 June 2005 December 2004 June 2004 December 2003
CFD Simulation OF Riser VIV
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 & 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.
ANTICIPATED NUMBER OF PHASES: 3
PROJECT PLAN FOR PHASE 3 (2005-2006):
Scope and Plan: The primary focus of this phase is to generalize the CFD code for time-domain simulation of riser VIV in 3D sheared currents. The following tasks are planned.
Riser VIV
1. Parallelize CFD Code - The CFD code will be parallelized to speed up the computation using multiple processors. This will allow us to simulate flow past a long riser with reasonable computer run times.
2. Fixed 3D cylinder in uniform current – For Re > 188.5, the 2D simulation is known to overpredict the drag force since the cylinder wake becomes 3D due to a secondary instability of the vortex street. Simulations will be performed first for a fixed 3D cylinder in uniform current to investigate the spanwise coherence and frequencies of the forces for both the smooth and rough 3D cylinders.
3. Fixed 3D cylinder in shear currents – Simulations will then be performed for a fixed cylinder in 3D sheared current. The spanwise coherence structure and the time history of drag and lift forces will be analyzed and compared with the uniform current results.
4. Riser VIV simulations in uniform current – Riser VIV will be investigated for a rigid long cylinder (5~20 diameter in length) undergoing two-DOF motion in uniform current to better understand spanwise coherence and frequencies of the drag and lift forces.
5. Riser VIV simulations in sheared currents – Riser VIV simulations will also be performed for a rigid long cylinder undergoing two-DOF VIV motion in 3D sheared currents to better understand spanwise coherence and frequencies of the drag and lift forces.
Hydro-elastic behavior of risers
6. Couple CFD code to CABLE3D program - The CFD code will be coupled with the CABLE3D mooring/riser finite element code to determine the hydro-elastic behavior of the risers. The forces and moments obtained from the CFD code will be incorporated into the CABLE3D program to determine the six-DOF riser motion.
7. Coupled CFD/CABLE3D simulations of riser VIV – Simulations will be performed for a very long riser undergoing six-DOF VIV motion. The riser will be divided into a number of cylindrical elements, and 2D simulations will be performed to determine the forces and moments acting on each riser segment. The predicted forces and moments will be coupled with CABLE3D program to determine the riser VIV motion in uniform current as well as in shear currents.
8. Riser analyses - Comparisons will be made between 2D (uniform current) and 3D (sheared currents) results to assess the effects of 3D current on riser VIV. Simulations will be analyzed to determine modal responses and damping. Results will be compared to data or analyses from other sources.
9. Prepare Final Report – A final report will be prepared to summarize the theoretical formulation, numerical method, and simulation results for riser VIV.
Anticipated Milestones & Results: It is anticipated that the CFD simulations will provide detailed flow field and motion history for risers subjected to 3D sheared currents. The performance of various turbulence models for riser VIV applications will also be evaluated. The results will be disseminated through interim progress reports and the end-of-phase final report.
PRINCIPAL INVESTIGATORS AND OTHERS INVOLVED IN THE PROJECT:
PI’s: Hamn-Ching Chen, Chia-Rong Chen and Richard S. Mercier
Others: Juan P. Pontaza
Date: May 2006
Project Name: CFD Simulation of Riser VIV
MMS Project: 481 TO Numbers: 74521/35983
Principal Investigators: Hamn-Ching Chen, Chia-Rong Chen and Richard S. Mercier
Estimated Completion Date: October 30, 2006 – Current Phase
Project Description:
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. VIV 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 riser VIV responses are affected by many parameters including the Reynolds number, surface roughness, strakes, fairings, 3D sheared currents and ambient turbulence. In this project, an advanced Navier-Stokes numerical method will be developed in conjunction with a chimera domain decomposition approach to assess the effects of Reynolds numbers, surface roughness, ambient turbulence, and highly sheared 3D currents on riser VIV responses. The simulation results will be compared with available experimental data to assess the performance of various turbulence models for VIV predictions.Progress:
We have successfully performed three-dimensional simulations of two degree-of-freedom VIV using Large Eddy Simulation (LES). The simulations were performed for low aspect ratio cylinders L/D = 3.0 with periodic boundary conditions using up to 2 million grid points with fine spanwise grids near the surface of the cylinder. The computations were performed in parallel using our newly developed capabilities. In practice, aspect ratios can easily exceed L/D = 100, and for such cases the computational resources required for a full viscous flow simulation would be prohibitively expensive. Our current focus is in developing a quasi-three-dimensional VIV simulation program, where the riser is modeled as an elastic structure which can deform axially and transversely. We have developed a finite element model of the structure, which we model as a “fluid-conveying beam”. Along equally spaced sections of the structure we place “two-dimensional flow planes”, where we solve for the viscous flow around the cross section of the structure. At each time step the forces exerted by the oncoming fluid are computed around the structure’s cross-section on each of the planes, which serves as the input load to the finite element model of the structure. Once the displacement field of the structure has been determined using our finite element model, the position of the structure’s cross-section is updated on each of the flow planes. Simulations of two degree-of-freedom VIV motions for uniform and sheared currents for L/D > 100 will be performed using this new capability.Recent Publications:
1. 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.
2. 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.
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Date: December, 2005Project Title: Deepwater Riser VIV Project – CFD Simulation of Riser VIV
MMS Project: 481 TO Numbers: 74521/35983
PI: Hamm-Ching Chen, Chia-Rong Chen, Richard Mercier
COTR: S. Buffington
Estimated Completion Date: October 30, 2006
Project Description:
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. VIV 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 riser VIV responses are affected by many parameters including the Reynolds number, surface roughness, strakes, fairings, 3D sheared currents and ambient turbulence. In this project, an advanced Navier-Stokes numerical method will be developed in conjunction with a chimera domain decomposition approach 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 investigated. The simulation results will be compared with available experimental data to assess the performance of various turbulence models for VIV predictions.
Progress:
The developed Reynolds-Averaged Navier-Stokes (RANS) numerical solution method has been extended to the three-dimensional case and the code has been parallelized. The workload is distributed among processes by assigning to each process an arbitrary number of grid blocks such that the load is balanced across processes. Three-dimensional numerical simulations of flows past a fixed circular cylinder have been performed using close to 1.5 million grid points and the load distributed among multiple processors. For the range of Reynolds number considered, it has been established that a Large Eddy Simulation (LES) is appropriate and a turbulent eddy viscosity Smagorinsky model has been implemented. Simulations were performed for low aspect ratio cylinders with L/D = 3.0 using periodic boundary conditions. These conditions are sufficient to qualitatively capture the spanwise effects of the three-dimensional flow field. Simulations of two degree-of-freedom VIV motions for the three-dimensional cylinders are underway. Some limited two-dimensional simulations of a cylinder outfitted with a fairing were performed, allowing for three degree-of-freedom (x, y, ?) VIV motions and zero torsional damping.
Recent 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.
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Date: May 9, 2005
Project Title: Deepwater Riser VIV Project – CFD Simulation of Riser VIV
MMS Project: 481 TO Numbers: 74521/35983
PI: Hamm-Ching Chen, Chia-Rong Chen, Richard Mercier
COTR: A. Konczvald
Estimated Completion Date: August 31, 2006
Project Description: 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 riser VIV responses are affected by many parameters including the Reynolds number, surface roughness, strakes, fairings, 3D sheared currents and ambient turbulence. In this project, an advanced Navier-Stokes numerical method will be developed in conjunction with a chimera domain decomposition approach 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 investigated. The simulation results will be compared with available experimental data to assess the performance of various turbulence models for VIV predictions.
Progress: The developed Reynolds-averaged Navier-Stokes (RANS) numerical solution method has been parallelized and two-dimensional simulations have been carried out in as many as 10 processors working in parallel. The speed-up scales linearly with the number of processes provided suitable load-balance is specified. The workload is distributed among processes by assigning to each process an arbitrary number of grid blocks such that the load is balanced across processes. Computations were performed for fixed cylinders in tandem arrangement for a wide range of Reynolds numbers. In addition, numerical simulations of pairs of smooth circular cylinders, in tandem and side-by-side arrangement, undergoing two-degree-of freedom VIV were performed at a transitional Reynolds number. VIV simulations were also performed for a four-cylinder array configuration: a square-shaped array and a diamond-shaped array (see Figure 1). The simulation results show complex time-dependent interaction among multiple cylinders undergoing VIV. Two-dimensional and three-dimensional simulations with vortex-shedding suppression devices are underway.
Reports & Publications:
Pontaza, JP, Chen, C.R. and Chen, H.C. “Chimera Reynolds-averaged Navier-Stokes simulation of vortex-induced vibrations of circular cylinders.” Proceedings: Civil Engineering in the Oceans VI Conference, Baltimore, Maryland, October 2004.
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, 2005, accepted.
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, Seoul, Korea, June 2005.
Pontaza J.P., Chen, H.C. and Chen, C.R. “Numerical simulations of riser vortex-induced vibrations.” Proceedings: SNAME, Houston, TX, October 2005.
Pontaza J.P. and Chen, H.C., “Numerical Simulations of Circular Cylinders Undergoing Two Degree-of-Freedom Vortex-Induced Vibrations at a High Reynolds Number.” Journal of Fluids and Structures, submitted.
Date: December, 2004
Project Title: Deepwater Riser VIV Project – CFD Simulation of Riser VIV
MMS Project: 481 TO Numbers: 74521/35983
PI: Hamm-Ching Chen, Chia-Rong Chen, Richard Mercier
COTR: J. McNeilEstimated Completion Date: August 31, 2006
Project Description: 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 riser VIV responses are affected by many parameters including the Reynolds number, surface roughness, strakes, fairings, 3D sheared currents and ambient turbulence. In this project, an advanced Navier-Stokes numerical method will be developed in conjunction with a chimera domain decomposition approach 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 investigated. The simulation results will be compared with available experimental data to assess the performance of various turbulence models for VIV predictions.
Progress: A Reynolds-averaged Navier-Stokes (RANS) numerical method has been developed for time-domain simulation of riser VIV under steady currents. In the present study, a chimera domain decomposition approach is employed for time-domain simulation of single and multiple risers involving arbitrary VIV motions. In this approach, the riser grid blocks are completely embedded in background rectangular grids representing the ambient water to simplify the grid-generation process for arbitrary riser motions. In addition, local grid refinement can be easily implemented to improve the boundary layer and wake resolution around the risers without significant increase in the overall computing time. Calculations were performed for both smooth and rough circular cylinders undergoing two degree-of-freedom (DOF) VIV motion at high Reynolds numbers. In addition, large eddy simulations (LES) of three-dimensional vortex shedding were also performed to provide a better understanding of the coherent structure in the spanwise direction of 3D risers. In order to facilitate more efficient simulations of riser array interactions and 3D risers with vortex-suppression devices, a multi-processor parallelization of the CFD code is currently being implemented to speed up the computation linearly with the number of processors.
Reports & Publications:
Pontaza J.P., Chen H.C., Reddy J.N., “A local-analytic-based discretization procedure for the numerical solution of incompressible flows.” International Journal for Numerical Methods in Fluids, 2004; submitted.
Pontaza J.P., Chen, C.R. and Chen, H.C. “Chimera Reynolds-averaged Navier-Stokes simulation of vortex-induced vibrations of circular cylinders.” Proceedings: Civil Engineering in the Oceans VI Conference, Baltimore, MD, October 20-22, 2004.
Date: June 2004Project Name: CFD Simulation of Riser VIV
Project Number: 481 Task Order: 74521
Principal Investigators: Hamn-Ching Chen, Chia-Rong Chen and Richard S. Mercier
Estimated Completion Date: October 31, 2006
Project Description: Vortex-induced vibration (VIV) is an important issue in the design of deepwater riser systems, including drilling, production and export risers. 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. Riser VIV responses are affected by many parameters including the Reynolds number, surface roughness, strakes, fairings, 3D sheared currents and ambient turbulence. An advanced Navier-Stokes numerical method is being developed in conjunction with a chimera domain decomposition approach 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 investigated. The simulation results will be compared with available experimental data to assess the performance of various turbulence models for VIV predictions.
Progress: A Reynolds-averaged Navier-Stokes (RANS) numerical method has been developed for time-domain simulation of 2D riser VIV under steady currents. The hydro-elastic behavior of the 2D risers is solved using a bi-linear oscillator model. In the present study, a chimera domain decomposition approach is employed to simplify the grid-generation process for single and multiple risers involving arbitrary VIV motions. In this approach, the riser grid blocks are completely embedded in background rectangular grids representing the ambient water. The riser grids are allowed to undergo arbitrary translational and rotational motions with respect to the fixed background grids without tedious grid regeneration at every time step. In addition, local grid refinement can be easily implemented to improve the boundary layer and wake resolution around the risers without significant increase of the overall computing time. Calculations were performed for both smooth and rough circular cylinders undergoing two degree-of-freedom (DOF) VIV motion in steady currents. The method is currently being generalized to incorporate a near-wall second-moment turbulence closure model to evaluate the effects of Reynolds stress anisotropy for riser VIV predictions.
Reports & Publications:
Pontaza, P., Chen, C.R. and Chen, H.C., “Chimera RANS Simulation of Vortex-Induced Vibrations of Circular Cylinders,” Civil Engineering in the Oceans VI Conference, Baltimore, Maryland, October 20-22, 2004.
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Date: December 2003
Project Name: CFD Simulation of Riser VIV
TEES Project Number: 32558-65540 MMS Task Order: 74521 MMS Project Number: 481
Principal Investigators: Hamn-Ching Chen, Chia-Rong Chen and Richard S. Mercier
Estimated Completion Date: August 2006
Project Description:
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 riser VIV responses are affected by many parameters including the Reynolds number, surface roughness, strakes, fairings, 3D sheared currents and ambient turbulence. In this project, an advanced Navier-Stokes numerical method will be developed in conjunction with a chimera domain decomposition approach 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 investigated. The simulation results will be compared with available experimental data to assess the performance of various turbulence models for VIV predictions.
Progress:
A Reynolds-averaged Navier-Stokes (RANS) numerical method is currently being generalized for time-domain simulation of 2D riser VIV under steady currents. The hydro-elastic behavior of the 2D risers is solved using a bi-linear oscillator model. In the present study, a chimera domain decomposition approach is employed to simplify the grid-generation process for single and multiple risers involving arbitrary VIV motions. In this approach, the riser grid block is completely embedded in the background rectangular grids representing the ambient water. The riser grid is allowed to undergo arbitrary translational and rotational motions with respect to the fixed background grids without tedious grid regeneration at every time step. A general grid-interface conservation technique is employed to enforce the conservation of mass and momentum across adjacent grid block boundaries. In addition, local grid refinement can be easily implemented to improve the boundary layer and wake resolution around the risers without significant increase of the overall computing time. Calculations have been performed for a smooth cylinder undergoing two degree-of-freedom (DOF) VIV motion in steady currents. The method is currently being generalized to include the effects of surface roughness.
Reports & Publications: None
