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Global Analysis of Floating Structures – M.H. Kim

WINPOST Program 3-D Coupled Analysis Hull – BEM (3-D panel) Moorings & Risers – FEM (EI included) Taut/Catenary Mooring Top Tensioned, CR, or Flexible Risers Time & Frequency Domain Models Simultaneous Solution of Integrated System Convergence Fast Single & Multi-Body Problems

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Global Analysis of Floating Structures – M.H. Kim

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  1. WINPOST Program 3-D Coupled Analysis Hull – BEM (3-D panel) Moorings & Risers – FEM (EI included) Taut/Catenary Mooring Top Tensioned, CR, or Flexible Risers Time & Frequency Domain Models Simultaneous Solution of Integrated System Convergence Fast Single & Multi-Body Problems GUI Interface Global Analysis of Floating Structures – M.H. Kim

  2. Global Analysis of Floating Structures – M.H. Kim WINPOST Program • Environment • Non-Parallel Waves, Winds, Currents • Uni-direction & Directional Irregular Waves • Dynamic Winds • Up to 3 Currents • Verification & Applications • TLP • Classic & Truss Spar • FPSO

  3. Turret – Moored FPSO Elements (half) Body: 1843 Free Surface: 480

  4. WINPOST vs. MARIN FPSO Model Tests Percentage Differences based on data in Wichers (2001) <25 % 25-50 % > 50 %

  5. Multi-Body InteractionOTRC FPSO + Shuttle Tanker (Tandem Moored @ 30m)

  6. WINPOST Program 3-D Coupled Analysis Hull – BEM (3-D panel) Moorings & Risers – FEM (EI included) Taut/Catenary Mooring Top Tensioned, CR, or Flexible Risers Time & Frequency Domain Models Simultaneous Solution of Integrated System Convergence Fast Single & Multi-Body Problems GUI Interface Global Analysis of Floating Structures – M.H. Kim

  7. Global Analysis of Floating Structures – M.H. Kim WINPOST Program • Environment • Non-Parallel Waves, Winds, Currents • Uni-direction & Directional Irregular Waves • Dynamic Winds • Up to 3 Currents • Verification & Applications • TLP • Classic & Truss Spar • FPSO

  8. Turret – Moored FPSO Elements (half) Body: 1843 Free Surface: 480

  9. WINPOST vs. MARIN FPSO Model Tests Percentage Differences based on data in Wichers (2001) <25 % 25-50 % > 50 %

  10. Multi-Body InteractionOTRC FPSO + Shuttle TankerSide-by-Side Moored -

  11. FPSO Roll Predictionand Mitigation (S.A. Kinnas) • Objective • Develop accurate computationally efficient model to predict the hydrodynamic coefficients in roll for a FPSO hull • Investigate effectiveness of bilge keels (size, shape, location across and extent along the hull) on roll mitigation Plan Develop CFD method for unsteady separated flow and added mass and damping coefficients about 2-D hull in roll motions Use 2-D coefficients (evaluated at different hull stations) to adjust the FPSO roll coefficients predicted by WAMIT Extend 2-D method to predict the fully 3-D unsteady separated flow and coefficients about the FPSO hull with the bilge keels Validate with other methods and experiments

  12. Dynamic BC =0  Far Boundary u=v=0 Hull Kinematic BC ComputationalDomain v body• n = q fluid•n FPSO Hull Motions: Heave & Roll Coordinate System Bilge Keel Details Description of boundary conditions on a hull moving at the free surface Grid used for the heave motion response for a rectangular hull form

  13. Oscillating Flow Past a Flat Plate Grid for Oscillating Flat Plate

  14. Oscillating Flow Past a Flat Plate Axial velocity and streamlines predicted by Euler solver at instant t=0 & T/4 for oscillating flow (-UmCos(ωt)) past a flat plate u = - Um← u = 0 →

  15. Cd Euler Navier Stokes Sarpkaya Oscillating Flow Past a Flat Plate Comparison between Euler solver, Navier-Stokes solver and experimental data from Sarpkaya, 1995 Cm Euler Navier Stokes Sarpkaya

  16. Numerical Results: Heave Motion Comparison of the added mass and damping coefficients with Newman(1977) for B/D=2 & No bilge keel

  17. Convergence of force histories with increasing grid density 130 30 cells 220 60 cells B/D = 2 Fr x D = 1.5 310 70 cells

  18. Predicted Roll Added Mass & Damping Coefficients for Different Bilge Keels

  19. Flow Field Around Hull

  20. Status • Developed CFD model to solve the Euler equations around a 2-D hull subject to heave and roll motions • Validated for a flat plate subject to an oscillating flow. Euler results comparable to those from Navier-Stokes and in reasonable agreement to experimental data • Demonstrated that model • Can describe free surface effects by comparisons with potential flow results for a 2-D hull in heave • Results are practically grid independent • Can describe unsteady separated flow around a plate in oscillating flow and around the bilge keel of a 2-D hull subject to roll motions • Can predict expected increase in added mass and damping coefficients with increasing bilge keel size

  21. Future Work • Continue validation of 2-D Hull method with other methods and existing experiments • Develop method to integrate the 2-D Hull results into WAMIT (“2-1/2 D” model) • Use 2-1/2 D to assess effects of various bilge keel designs on motions • Plan & analyze further experiments to validate models • Develop fully 3-D method • assess accuracy of the 2-1/2 D model • Basis for refined analysis of keel designs • Include the effects of the bilge keel “lift” • Basis for more complete models in the future (e.g., non-linear free-surface effects, turbulence)

  22. MMS JIP Polyester RopeGoals • Development of a rationale mitigation strategy and guideline for dealing with damaged polyester rope • Installation & In-service damage • Mitigation strategies could include • Installation • Immediate replacement • Periodically monitor for possible replacement later • In-Service • Replace ASAP (continue operations, curtail, or shut-in?) • Periodically monitor for possible replacement later • Support API RP process to develop RP

  23. MMS JIP Polyester Rope • Length Effect Tests -potential influence of length effects on tests of damaged ropes (small-scale rope) • Damaged Full-Scale Rope Tests – quantify the influence of damage on full-scale ropes (main focus) • Verification Tests - verify results of Damaged Full-Scale Rope Tests with limited tests on longer full-scale ropes • Four Ropes Bexco CSL Whitehill Marlow

  24. Damaged Rope Test Program

  25. Length Effect Tests 2 m sample with midspan damage 23 m sample with midspan damage 23 m sample with damage near splice 35 m sample with midspan damage

  26. Simulated Rope Damage Figure 5 Damage Level 1 ~7 in. Diameter Figure 6 Damage Level 2

  27. Results • Residual strength of damaged rope • Rope behavior • Damage level vs. residual rope strength • Residual strength vs. rope/splice construction • Scale effects on residual strength • Effect of length on residual strength • Effect of damage location on residual strength • Data to validate numerical model of damaged rope

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