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CFD For Offshore Applications

CFD For Offshore Applications






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    CFD For Offshore Applications CFD For Offshore Applications Presentation Transcript

    • CFD for Floating Systems
      • Bob Gordon
      • Granherne Americas, Inc.
    • Outline
      • Overview of CFD
      • Present Offshore Industry Use of CFD
      • Applications
    • Overview of CFD
      • What is CFD?
      • Brief History
      • Overview of CFD Methods
      • Validation & Verification
    • Fluid Dynamics
      • Theoretical
        • Analytical Solutions (Heyday in 19 th & early 20 th 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
    • 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
    • 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 ~10 0 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 ~10 5 GFlop )
    • 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
    • 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
    • Offshore Industry Use of CFD
    • 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
    • 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
    • Riser VIV SOURCE: C.H.K. Williamson, Cornell U.
    • DeepStar/MIT Lake Seneca Tests 2004 SOURCE: K. Vandiver, MIT
    • 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
    • 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, l c .
      SOURCE: A. H. Techet, MIT
    • SOURCE: BP
    • VIV Suppression SOURCE: BP, GlobalSantaFe, Shell
    • 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
      SOURCE: A. H. Techet, MIT
    • Wave Slamming
      • 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
    • 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
      SOURCE: Diamond Offshore Drilling
    • Damage from Hurricane Waves SOURCE: Dave Wisch, Chevron
    • Damage from Hurricane Waves SOURCE: Dave Wisch, Chevron
    • 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
    • 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
    • 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
    • Comparisons with Lab Data SOURCE: OMAE2006-92124
    • 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
      SOURCE: OMAE2005-67238
    • Mesh SOURCE: OMAE2005-67238
    • VIM Results SOURCE: OMAE2005-67238
    • Wave Impact - Idealized Case SOURCE:OTRC 11/05A156
    • 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
      SOURCE: OMAE2005- 67097
    • Tank Sloshing Observed and predicted wave profile SOURCE: CD-adapco
    • Tank Sloshing Validation SOURCE: CD-adapco
    • 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