Modeling Wind Shielding for FPSO Tandem Offloading using CFD

Bob Gordon, GranherneSatpreet Nanda, CD-adapco

Presentation Outline

• FPSO Tandem Offloading• Examples of Shielding in Offshore Applications• Wind Tunnel Tests for Tandem Offloading• Preliminary CFD Results• Summary

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FPSO Tandem Offloading

• FPSO can be spread or turret moored– If turret moored, FPS orients into wind,

wave and current• Tanker approaches under its own

power and moors (with work boat assistance) to FPSO using hawsers

• FPSO & Tanker are in close proximity during offloading and both change draft

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Turret Moored FPSO

Effects of Shielding

• FPSO shields tanker from environment– Impacts tanker’s maneuverability

during approach– Impacts separation distance while

connected

• Relative headings of the vessels can vary significantly during offloading due to shielding, effects of current, or fish-tailing

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Spread Moored FPSO

Collisions and Near Misses During Tandem Offloading in North Sea 1996-2000

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Source: UK HSE Offshore Technology Report 2000/086

Examples of Shielding in Offshore Applications

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Truss Spar Platform

Multiple Riser Towers

Grouped Single Line Risers

Velocity Reduction due to Shielding

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From van Walree and Willemsen, 1988

Wind Tunnel Tests

• Part of MARIN’s Offloading Operability JIP

• Tests performed at DNW in 2003• Model scale was 1:250• Barge-shaped FPSO model and

shuttle tanker• Measurement of unshielded wind

and current forces• Measurement of wind velocities

behind the FPSO• Measurement of shielded forces

for validation of shielding model8

Use of CFD to Model Wind Tunnel Tests

• Collaborative effort between MARIN, Granherne/KBR and CD-adapco

• Surface geometry models prepared by MARIN• MARIN using in-house code and Granherne

using STAR-CCM+• Granherne calculations performed in the blind• Comparisons will be made against model test

data and between CFD codes• Goal is to present joint paper at OMAE 2010

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Vessel Characteristics

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450 m

Position of Vessels Relative to Incident Wind & Velocity Profile

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Wind

Velocity Profile

V/V10

Z/Z10

Surface Mesh

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Volume Mesh

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1.44 Million Cells

SST k-omega turbulence model

y+ wall treatment

Speed Contours in Horizontal Plane

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Z=5m

Z=30m

A A

A A

B

B

Speed Contours in Vertical Plane

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A A

B B

Streamlines

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Pressure Contour

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Drag and Lift on Tanker

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Tandem Arrangement (450 m separation)

Shuttle Tanker Only

Wind Tunnel Measurement

OCIMF

DRAG LIFT

Summary

• Tandem offloading operations are sensitive to weather conditions

• Accurate simulation of tandem offloading is difficult due to wind shielding

• Wind loads on the shuttle tanker vary with relative wind direction, distance from FPSO and orientation relative to FPSO

• Wind tunnel testing is limited due to relatively small number of configurations that can be tested

• Preliminary CFD results indicate good agreement with wind tunnel data (but little shielding for case investigated)

• CFD can provide a suitable means to augment wind tunnel test data

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Acknowledgement

• Thanks to Dr. Arjen Koop of MARIN for collaborating in this endeavor and for providing the vessel geometry models

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