Collision Study of Rigid Ships with a Deformable Offshore Wind Turbine Jacket Structure Andres Barrera

La Spezia, Italy

February 17, 2014

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CHARGEOL Project • Project for the foundations of renewable marine energy.

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Focus of study:

• Risk of Collision.

• Understanding seabed behavior.

• Scouring issues.

• Better understanding of load response of the

structures.

Objectives • General:

Develop Numerical Basis for the Simplified Calculation Tool.

• Specific:

Characterizing the sensitivity of the jacket to:

Gravity Loads/Tower

Ship Type

Velocity/Collision Angle/Impact height

Determine Resultant Force Distribution

Comparison to simplified calculation tool

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Offshore Wind Turbine Jacket • Latticed Steel Structure.

• Developed from Oil and Gas Industry.

• Used in renewable wind industry up to depths of 45 m.

• Lower production costs than monopile structures.

• Weakness in welded nodes.

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Ship Models

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Displacement: 132797 tons

Added Mass: 6639 tons Displacement: 5000 tons

Added Mass: 250 tons

SIMULATIONS CARRIED OUT

Crude Oil Carrier Simulations

6 simulations.

Sensitivity of the structure to variation in impact location (leg-brace joint), speed and angle.

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• Sensitivity to Gravity Loads

2 m/s and 6 m/s simulations performed.

• Determination of Critical Scenario (Leg-Brace Joint).

• Sensitivity to OWT Tower

Leg Collision 6 m/s with tower

• Study of Resultant Force Transmission

Leg Collision, single impact location 6 m/s

• Comparison with Simplified Calculation Tool

Leg Collision, single impact location 2 m/s

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Sensitivity to Gravity Loads

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2 m/s Without Gravity Loads

2 m/s With Gravity Loads

Gravity Loads Without Gravity

Resultant Force Transmission

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-2.00

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

0.000 1.000 2.000 3.000 4.000 5.000 6.000

Resu

ltan

t F

orc

e (

MN

)

Penetration (m)

565

558

530

536

566

532

562

564

558_2

Simplified Tool Comparison

• 2 m/s leg section single impact point

10

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

0 0.5 1 1.5

Resu

ltan

t F

orc

e (

KN

)

Penetration (m)

Simplified

LS_DYNA

Conclusions I • High Energy (Tanker):

High energy collisions at brace joint are sensitive to variation in collision angle.

Leg impact is more detrimental to jacket in high energy scenarios.

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Conclusions II • OSV Simulations

Leg impact more detrimental to jacket.

High sensitivity to collision angle; initial rupture of leg at 2 m/s.

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Gravity loads did not affect shock response of structure at 2 and 6 m/s.

Coupling between the tower, platform and transition piece cannot be simplified.

Legs are more sensitive to local deformation than braces are to bending or buckling failure.

Up to penetration of 0,58 m, simplified tool in accordance with simulation, error for internal energy and crushing force below 20%.

Further Work

• Better definition of connectivity between the OWT tower, the platform, transition piece and jacket.

• Additional OSV simulations varying collision height and impact location.

• Additional comparisons to simplified tool with different velocities, impacting ship section geometries (leg and stem).

• Simulations that account for soil/structure interaction.

• Detailed study of buckling of braces for analytical tool.

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