CFD for Floating Systems.pdf
- 1. CFD for Floating Systems Bob Gordon Granherne Americas, Inc.
- 2. 2 Outline Overview of CFD Present Offshore Industry Use of CFD Applications
- 3. 3 Overview of CFD What is CFD? Brief History Overview of CFD Methods Validation & Verification
- 4. 4 Fluid Dynamics Theoretical • Analytical Solutions (Heyday in 19th & early 20th Century) • Potential Flow • Many analytical solutions, including nonlinear equations (Airy, Stokes, Kelvin, Lamb, Korteweg and de Vries, Stoker, …) • Viscous Flow • Very few analytical solutions (Stokes, Poiseuille, Blasius, Ekman, …) • Theory of Turbulence (Reynolds, 1889 ->) Experimental • Many advances in laboratory and field instrumentation continue to appear (e.g., Particle Image Velocimetry, Acoustic Doppler Current Meters) Computational • Many advances continue in physical models, algorithms, software (parallelization) and computing hardware • Advances in CFD depend on good experimental data for verification
- 5. 5 Why CFD? Real world flows are too complex to be addressed solely by theory or experimentation • Nonlinear • Complicated Geometry • Coupled (Heat & Mass Transfer, Chemical Reaction, Fluid-Structure Interaction) • Turbulent
- 6. 6 Some Historical Milestones 1922 - L. F. Richardson developed first numerical weather prediction system using finite differences calculated by hand (Humans ~10-9 GFlop) 1946 - J. von Neumann develops program for ENIAC to calculate hydrogen bomb explosion (ENIAC ~10-6 GFlop) 1965 - Harlow & Welch develop the MAC method at LANL; first successful technique for incompressible flows (CDC 6600 ~10-3 GFlop) 1981 - Spalding (ICL & CHAM) develops the first commercial CFD code - PHOENICS (CRAY X-MP ~100 GFlop) 2002 - NASA Pegasus5 CFD code is used by Boeing to design the Sonic Cruiser aircraft with much reduced reliance on wind tunnel tests (IBM BlueGene ~105 GFlop)
- 7. 7 Components of a Numerical Solution Method Mathematical Model • Incompressible vs. Compressible, Laminar vs. Turbulent, 2D vs. 3D, etc Discretization Method • Finite Difference, Finite Volume, Finite Element Coordinate System • Cartesian, Orthogonal and Non-orthogonal Curvilinear, etc Numerical Grid • Structured, Block-structured, Unstructured Finite Approximations • Accuracy vs. speed Solution Method • Time stepping for transient; Iteration schemes for steady state Convergence Criteria
- 8. 8 Validation & Verification As with all Engineering Analysis codes, it is essential that the model (i.e., code, conceptual modeling assumptions, and input data) be verified and the predicted results be validated Validation ~ Solving the right equations • Compare against measured data • Compare against benchmark analytical and/or numerical solutions Verification ~ Solving the equations right • Check convergence with mesh and time step refinement • Make sure that numerical errors are sufficiently small
- 9. 9 Offshore Industry Use of CFD Oil Companies Chevron 9 Shell 5 Petrobras 4 BP 2 ExxonMobil 2 Service Co. & Consultants Technip 8 Marintek 5 Marintek 3 Principia 2 SBM 1 BPP 1 Force 1
- 10. 10 Enabling Technology Physical Models • Turbulence Models (DNS, LES, RANS) • Heat & Mass Transfer, Multi-Phase Flows, Combustion Algorithms • Finite Element & Volume Methods • Grids • Moving Grids • Arbitrary Lagrangian-Eulerian Methods (ALE) • Level Set Methods • Sliding Grids • Chimera Grids Software • Parallelization Hardware • Low Cost, High Performance Parallel Computing Architectures • Clusters • Grids
- 11. 11 Some Offshore Problem Areas of Interest for CFD Fluid-Structure Interaction • Vortex-induced vibrations of risers • Vortex-induced motions of floating platforms Flow Around Vessel Hulls and Superstructure • Wind and current forces Slam and water impact loading Sloshing in Tanks
- 12. 12 Riser VIV QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. SOURCE: C.H.K. Williamson, Cornell U.
- 13. 13 DeepStar/MIT Lake Seneca Tests 2004 QuickTimeª and a YUV420 codec decompressor are needed to see this picture. SOURCE: K. Vandiver, MIT
- 14. 14 Classic VIV Catastrophe If ignored, these vibrations can prove catastrophic to structures, as they did in the case of the Tacoma Narrows Bridge in 1940. SOURCE: A. H. Techet, MIT
- 15. 15 VIV in the Ocean Non-uniform currents effect the spanwise vortex shedding on a cable or riser. The frequency of shedding can be different along length. This leads to “cells” of vortex shedding with some length, lc. SOURCE: A. H. Techet, MIT
- 16. 16 QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. SOURCE: BP
- 17. 17 VIV Suppression QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. SOURCE: BP, GlobalSantaFe, Shell
- 18. 18 Platform Vortex-Induced Motions Same phenomenon as Riser VIV Vortex-induced motion amplitudes (A) for a Spar can up to 1.5 times the Platform Diameter (D), if no VIV suppression is used Motion is typically in a Figure 8 pattern Magnitude of A/D is velocity dependent QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. SOURCE: A. H. Techet, MIT
- 19. 19 Wave Slamming QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. Basic Physics • Drag forces: caused by viscosity resulting in flow separation • Inertia forces: related to the acceleration of the incident flow and the modification of the incident wave pattern by the member. • Slam forces: occur when a wave engulfs a member causing a volume of water to be decelerated (conservation of fluid momentum) Progress has bee made in predicting loads using CFD SOURCE: MARINTEK
- 20. 20 Surface Blow-Out Preventer (SBOP) Uses high pressure casing riser Allows wells to be drilled quickly Has been used in areas with relatively calm weather Industry is looking to extend to harsher climates Wave impact is a critical issue QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. SOURCE: Diamond Offshore Drilling
- 21. 21 Damage from Hurricane Waves QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. SOURCE: Dave Wisch, Chevron
- 22. 22 Damage from Hurricane Waves QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. SOURCE: Dave Wisch, Chevron
- 23. 23 Wind Forces Typical industry practice for offshore platform design is to determine wind loads from scaled wind tunnel tests Changes during design or after installation may require revision to wind loads CFD is being used to determining effects of changes SOURCE: Force Technology
- 24. 24 Example Applications Vortex-Induced Vibration of a Long Riser Vortex-Induced Motion of a Spar Wave Slamming Tank Sloshing Drag on a Riser Fairing Wind Loads
- 25. 25 VIV of a Long Riser Work performed by Chevron Comparisons made against high quality lab data from Norwegian Deepwater Program Fully 3D simulations for a riser with L/D=1400. This is a world record! Procedure was to find the coarsest mesh that yields the required accuracy SOURCE: OMAE2006-92124 Riser Configuration Elevation View of Mesh
- 26. 26 Comparisons with Lab Data QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. SOURCE: OMAE2006-92124
- 27. 27 VIM of a Spar Work performed by Chevron Tow tests made of 1:46 scale model of Genesis spar Care was taken to include appurtenances in both physical & numerical models QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. SOURCE: OMAE2005-67238
- 28. 28 Mesh QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. SOURCE: OMAE2005-67238
- 29. 29 VIM Results QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. SOURCE: OMAE2005-67238
- 30. 30 Wave Impact - Idealized Case QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. SOURCE:OTRC 11/05A156 QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture.
- 31. 31 Wave Slamming on GBS Deck Work performed by Marintek Wave basin model of Statfjord GBS at 1:54 scale Deck instrumented to record wave impact loads Excellent agreement with CFD calculation QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTimeª and a TIFF (Uncompressed) decompressor are needed to see this picture. SOURCE: OMAE2005- 67097
- 32. 32 Tank Sloshing Tank Sloshing Observed and predicted wave profile QuickTimeª and a Cinepak decompressor are needed to see this picture. SOURCE: CD-adapco
- 33. 33 Tank Sloshing Validation Tank Sloshing Validation SOURCE: CD-adapco
- 34. 34 Summary CFD has become a “mainstream” engineering tool for many industrial applications • Appropriate for initial studies • Appropriate to interpolate and extrapolate measurements Adoption in the Offshore Oil & Gas industry is growing rapidly