Global Analysis of Floating Structures – M.H. Kim

Global Analysis of Floating Global Analysis of Floating Structures – M.H. KimStructures – M.H. Kim

WINPOST ProgramWINPOST Program 3-D Coupled Analysis3-D Coupled Analysis

Hull – BEM (3-D panel)Hull – BEM (3-D panel) Moorings & Risers – FEM (EI included)Moorings & Risers – FEM (EI included)

– Taut/Catenary MooringTaut/Catenary Mooring– Top Tensioned, CR, or Flexible RisersTop Tensioned, CR, or Flexible Risers

Time & Frequency Domain ModelsTime & Frequency Domain Models Simultaneous Solution of Integrated SystemSimultaneous Solution of Integrated System Convergence Fast Convergence Fast

Single & Multi-Body ProblemsSingle & Multi-Body Problems GUI InterfaceGUI Interface


WINPOST ProgramWINPOST Program EnvironmentEnvironment

Non-Parallel Waves, Winds, CurrentsNon-Parallel Waves, Winds, Currents Uni-direction & Directional Irregular WavesUni-direction & Directional Irregular Waves Dynamic WindsDynamic Winds Up to 3 CurrentsUp to 3 Currents

Verification & ApplicationsVerification & Applications TLPTLP Classic & Truss SparClassic & Truss Spar FPSOFPSO

Turret – Moored FPSOTurret – Moored FPSO

Elements (half)

Body: 1843

Free Surface: 480

WINPOST vs. MARIN FPSO WINPOST vs. MARIN FPSO Model TestsModel Tests

Vessel Motions Unit Mean Stdv Max

Surge total at turret m -38 11 -61 Sway at turret m 14 3 28 Heave at turret m 0 2 8 Roll deg 0 2 5 Pitch deg 0 1 4 Yaw deg 16 2 27

Mooring Tension

Line#2 total kN 1651 170 2149 Line#8 total kN 884 180 1774

Riser Top Tensions

Liquid prod. (#13) kN 1299 181 2653 Water injection (#22) kN 2252 276 4179 Gas export (#25) kN 528 129 1395

25-50 %

<25 %

> 50 %

Percentage Differences based on data in Wichers (2001)

Multi-Body InteractionMulti-Body InteractionOTRC FPSO + Shuttle Tanker OTRC FPSO + Shuttle Tanker

(Tandem Moored @ 30m)(Tandem Moored @ 30m)


WINPOST ProgramWINPOST Program 3-D Coupled Analysis3-D Coupled Analysis

Hull – BEM (3-D panel)Hull – BEM (3-D panel) Moorings & Risers – FEM (EI included)Moorings & Risers – FEM (EI included)

– Taut/Catenary MooringTaut/Catenary Mooring– Top Tensioned, CR, or Flexible RisersTop Tensioned, CR, or Flexible Risers

Time & Frequency Domain ModelsTime & Frequency Domain Models Simultaneous Solution of Integrated SystemSimultaneous Solution of Integrated System Convergence Fast Convergence Fast

Single & Multi-Body ProblemsSingle & Multi-Body Problems GUI InterfaceGUI Interface


WINPOST ProgramWINPOST Program EnvironmentEnvironment

Non-Parallel Waves, Winds, CurrentsNon-Parallel Waves, Winds, Currents Uni-direction & Directional Irregular WavesUni-direction & Directional Irregular Waves Dynamic WindsDynamic Winds Up to 3 CurrentsUp to 3 Currents

Verification & ApplicationsVerification & Applications TLPTLP Classic & Truss SparClassic & Truss Spar FPSOFPSO

Turret – Moored FPSOTurret – Moored FPSO

Elements (half)

Body: 1843

Free Surface: 480

WINPOST vs. MARIN FPSO WINPOST vs. MARIN FPSO Model TestsModel Tests

Vessel Motions Unit Mean Stdv Max

Surge total at turret m -38 11 -61 Sway at turret m 14 3 28 Heave at turret m 0 2 8 Roll deg 0 2 5 Pitch deg 0 1 4 Yaw deg 16 2 27

Mooring Tension

Line#2 total kN 1651 170 2149 Line#8 total kN 884 180 1774

Riser Top Tensions

Liquid prod. (#13) kN 1299 181 2653 Water injection (#22) kN 2252 276 4179 Gas export (#25) kN 528 129 1395

25-50 %

<25 %

> 50 %

Percentage Differences based on data in Wichers (2001)

Multi-Body InteractionMulti-Body InteractionOTRC FPSO + Shuttle TankerOTRC FPSO + Shuttle Tanker

Side-by-Side MooredSide-by-Side Moored-

PlanPlan Develop CFD method for unsteady separated flow and Develop CFD method for unsteady separated flow and

added mass and damping coefficients about 2-D hull in roll added mass and damping coefficients about 2-D hull in roll motions motions

Use 2-D coefficients (evaluated at different hull stations) to Use 2-D coefficients (evaluated at different hull stations) to adjust the FPSO roll coefficients predicted by WAMITadjust the FPSO roll coefficients predicted by WAMIT

Extend 2-D method to predict the fully 3-D unsteady Extend 2-D method to predict the fully 3-D unsteady separated flow and coefficients about the FPSO hull with separated flow and coefficients about the FPSO hull with the bilge keelsthe bilge keels

Validate with other methods and experimentsValidate with other methods and experiments

FPSO Roll PredictionFPSO Roll Predictionand Mitigation (S.A. Kinnas)and Mitigation (S.A. Kinnas)

ObjectiveObjective Develop accurate computationally efficient model to Develop accurate computationally efficient model to

predict the hydrodynamic coefficients in roll for a FPSO predict the hydrodynamic coefficients in roll for a FPSO hullhull

Investigate effectiveness of bilge keels (size, shape, Investigate effectiveness of bilge keels (size, shape, location across and extent along the hull) on roll mitigationlocation across and extent along the hull) on roll mitigation

FPSO Hull Motions: FPSO Hull Motions: Heave & Roll Coordinate SystemHeave & Roll Coordinate System

Description of boundary conditions on a hull moving at the free surface

Grid used for the heave motionresponse for a rectangular hull form

Computational Domain

Kinematic BC

Far Boundary

u=v=0

v body • n = q fluid•n

Dynamic BC =0

Hull

Bilge Keel Details

Oscillating Flow Past a Flat PlateOscillating Flow Past a Flat Plate

Grid for Oscillating Flat Plate

u = - Um ← u = 0 →

Axial velocity and streamlines predicted by Euler solver at instant t=0 & T/4 for oscillating flow (-UmCos(ωt)) past a flat plate


Comparison between Euler solver, Navier-Stokes solver and experimental data from Sarpkaya, 1995


Euler Navier Stokes Sarpkaya

Euler Navier Stokes Sarpkaya

Cd Cm

Numerical Results: Heave MotionNumerical Results: Heave Motion

Comparison of the added mass and damping coefficients with Newman(1977) for B/D=2 & No bilge keel

Convergence of force histories with increasing grid density

B/D = 2 Fr x D = 1.5

130 30 cells

220 60 cells

310 70 cells

Predicted Roll Added Mass & Damping Coefficients for Different Bilge Keels

Flow Field Around HullFlow Field Around Hull

StatusStatus Developed CFD model to solve the Euler Developed CFD model to solve the Euler

equations around a 2-D hull subject to heave equations around a 2-D hull subject to heave and roll motionsand roll motions

Validated for a flat plate subject to an Validated for a flat plate subject to an oscillating flow. Euler results comparable to oscillating flow. Euler results comparable to those from Navier-Stokes and in reasonable those from Navier-Stokes and in reasonable agreement to experimental dataagreement to experimental data

Demonstrated that modelDemonstrated that model Can describe free surface effects by comparisons Can describe free surface effects by comparisons

with potential flow results for a 2-D hull in heavewith potential flow results for a 2-D hull in heave Results are practically grid independentResults are practically grid independent Can describe unsteady separated flow around a Can describe unsteady separated flow around a

plate in oscillating flow and around the bilge keel of plate in oscillating flow and around the bilge keel of a 2-D hull subject to roll motionsa 2-D hull subject to roll motions

Can predict expected increase in added mass and Can predict expected increase in added mass and damping coefficients with increasing bilge keel sizedamping coefficients with increasing bilge keel size

Future WorkFuture Work Continue validation of 2-D Hull method with other methods Continue validation of 2-D Hull method with other methods

and existing experimentsand existing experiments

Develop method to integrate the 2-D Hull results into Develop method to integrate the 2-D Hull results into WAMIT (“2-1/2 D” model)WAMIT (“2-1/2 D” model)

Use 2-1/2 D to assess effects of various bilge keel designs Use 2-1/2 D to assess effects of various bilge keel designs on motionson motions

Plan & analyze further experiments to validate modelsPlan & analyze further experiments to validate models

Develop fully 3-D methodDevelop fully 3-D method assess accuracy of the 2-1/2 D modelassess accuracy of the 2-1/2 D model Basis for refined analysis of keel designsBasis for refined analysis of keel designs Include the effects of the bilge keel “lift”Include the effects of the bilge keel “lift” Basis for more complete models in the future (e.g., non-Basis for more complete models in the future (e.g., non-

linear free-surface effects, turbulence)linear free-surface effects, turbulence)

MMS JIP Polyester RopeMMS JIP Polyester Rope GoalsGoals

Development of a rationale mitigation Development of a rationale mitigation strategy and guideline for dealing with strategy and guideline for dealing with damaged polyester ropedamaged polyester rope

Installation & In-service damageInstallation & In-service damage Mitigation strategies could includeMitigation strategies could include

InstallationInstallation– Immediate replacementImmediate replacement– Periodically monitor for possible replacement later Periodically monitor for possible replacement later

In-ServiceIn-Service– Replace ASAP (continue operations, curtail, or shut-Replace ASAP (continue operations, curtail, or shut-

in?)in?)– Periodically monitor for possible replacement laterPeriodically monitor for possible replacement later

Support API RP process to develop RPSupport API RP process to develop RP

MMS JIP Polyester RopeMMS JIP Polyester Rope

Length Effect TestsLength Effect Tests - - potential influence of potential influence of length effects on tests of damaged ropes length effects on tests of damaged ropes (small-scale rope) (small-scale rope)

Damaged Full-Scale Rope TestsDamaged Full-Scale Rope Tests – quantify – quantify the influence of damage on full-scale ropes the influence of damage on full-scale ropes (main focus)(main focus)

Verification TestsVerification Tests - verify results of - verify results of Damaged Full-Scale Rope Tests with Damaged Full-Scale Rope Tests with limited tests on longer full-scale ropeslimited tests on longer full-scale ropes

Four RopesFour Ropes

Bexco CSL Whitehill MarlowBexco CSL Whitehill Marlow

Damaged Rope Test ProgramDamaged Rope Test Program

Test

Break Strength

(T)

Nominal Diameter

Length (m)

L/D Test Site # Tests

35 36 mm (1.5 in)

2 60

35 36 mm (1.5 in)

23 560 Length Effect

35 36 mm (1.5 in)

35 1000

Lloyds Beal 24

Damaged Full-Scale

Ropes 700

178 mm (7 in) 10 60

SES CSL

26

Verification 700

178 mm (7 in)

100 560 Holloway/Lowrey 4

2 m sample with midspan damage

23 m sample with damage near splice



Length Effect Tests

Simulated Rope DamageSimulated Rope Damage

Figure 6

Damage Level 2

Figure 5

Damage Level 1

~7 in. Diameter

ResultsResults

Residual strength of damaged ropeResidual strength of damaged rope Rope behaviorRope behavior

Damage level vs. residual rope strengthDamage level vs. residual rope strength Residual strength vs. rope/splice Residual strength vs. rope/splice

constructionconstruction Scale effects on residual strengthScale effects on residual strength Effect of length on residual strength Effect of length on residual strength Effect of damage location on residual Effect of damage location on residual

strengthstrength Data to validate numerical model of Data to validate numerical model of

damaged ropedamaged rope

Documents

Global Analysis of Floating Structures – M.H. Kim