Global Analysis of Floating Structures

1
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
• GUI Interface

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)
lt25
25-50
gt 50
5
Multi-Body InteractionOTRC FPSO Shuttle Tanker
(Tandem Moored _at_ 30m)
6
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
• GUI Interface

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)
lt25
25-50
gt 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

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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
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Oscillating Flow Past a Flat Plate
Grid for Oscillating Flat Plate
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Oscillating Flow Past a Flat Plate
Axial velocity and streamlines predicted by Euler
solver at instant t0 T/4 for oscillating
flow (-UmCos(?t)) past a flat plate
u - Um ?
u 0 ?
15

Oscillating Flow Past a Flat Plate
Comparison between Euler solver, Navier-Stokes
solver and experimental data from Sarpkaya, 1995
Cm
Euler Navier Stokes Sarpkaya
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Numerical Results Heave Motion
Comparison of the added mass and damping
coefficients with Newman(1977) for B/D2 No
bilge keel
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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
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Flow Field Around Hull
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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

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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 Rope Goals

• 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

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Damaged Rope Test Program
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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
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Simulated Rope Damage
Figure 5 Damage Level 1
7 in. Diameter
Figure 6 Damage Level 2
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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