Presentationof a simplified methodfor the crashworthinessof offshore wind turbine jacketsT i m o t h é e P i re ( U L g , F R I A fe l l ows h i p )

H e r vé L e S o u r n e ( G e M / I C A M )

L o ï c B u l d g e n ( U L g )

P h i l i p p e R i g o ( U L g )

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Context•More and larger wind farms

•Closer to traffic lanes(passengers and commercials)

•Need of maintenance

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Collision riskanalysis

Probability Damage

[offshorenergytoday.com] [northnorfolknews.co.uk]

[maritimejobs.org]

Context•Several wind turbinesupporting structurures :• Monopile

• Tripod

• Jacket

• Floating

•Finite elements : accurate but time demanding

•Need for a faster method for pre-design stage :Continuous Elements Method

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[boem.gov], [smulders-hoboken.com]

Deformation modes

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State of art•Only local crushing taken into account

•Good results for low energy impacts

•Model too rigid in case of large energy impacts

•Other deformation modes have to be added

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Displacement [m]

Resultant force

SE LS-DYNA

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SE LS-DYNA

[BULDGEN L., LE SOURNE H., PIRE T., Extension of the Super-Elements Method to the Analysis of a Jacket Impacted by a ship, Marine Structures, 2014, vol. 38, pp. 44 – 71]

Global deformation

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SE LS-DYNA

-2

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SE LS-DYNA

Local crushing : model

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[BULDGEN L., LE SOURNE H., PIRE T., Extension of the Super-Elements Method to the Analysis of a Jacket Impacted by a ship, Marine Structures, 2014, vol. 38, pp. 44 – 71]

Local crushing : developments•Local crushing• Rings

𝐸𝑏 = 2𝑚0

𝑉𝐵𝑅2

+1

𝑅2−

1

𝑅1𝑉𝐹 +

𝐹

𝐸

χ1𝑑𝑙 + 𝐷

𝐹

χ2𝑑𝑙

• Generators

𝐸𝑚 θ, δ = 𝑛0 −ξ2

ξ1

ε𝑚 θ, δ, 𝑦 𝑑𝑦 = 𝑛0 δ1

ξ1+1

ξ2𝑤 θ, δ

𝜕𝑤

𝜕δ

• Total

𝑃𝑙 δ 𝑎 δ =

𝑖

𝐸𝑖

•Three-hinges mechanism

𝑃𝑔 δ =𝐿1 + 𝐿2𝐿1𝐿2

1 + ξ𝑡 𝑀0 1 −𝑁 δ 2

𝑁02 + 𝑁(δ) δ − δ𝑡 cos γ𝑡

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Local crushing : results

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Punching : model

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[HSIEH J.-R., Analytical formulations for ship-offshore wind turbine collisions, Master thesis, Nantes : ICAM (EMSHIP Erasmus Mundus Master Course), 2015, 104 p.]

Punching : results

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Buckling : model

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Buckling : developments•Hinges 1-3

𝐸𝐻,1−3 = 2𝑚0 0

π/2𝜕α

𝜕θ𝑅𝑑θ θ

•Hinge 2

𝐸𝐻,2 = 4𝑚0 0

π/2𝜕α

𝜕θ𝑑𝑠𝑑θ θ

•Membrane effect

𝐸𝑀 = 4𝑛0 0

𝐻

0

π/2

ε𝑑𝑠𝑑β𝑑𝑧

= 4𝑛0 θ

π𝑅 0

𝐻

𝐿α2 𝑑𝑧

•Total

𝑀 θ =

𝑖

𝐸𝑖

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1

3

2

βR

Lα

Buckling : results

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0,000E+00

5,000E+06

1,000E+07

1,500E+07

2,000E+07

2,500E+07

0,000E+00 5,000E-02 1,000E-01 1,500E-01 2,000E-01 2,500E-01 3,000E-01

Mo

men

t [N

m]

Theta [-]

SE LS-DYNA

0,000E+00

5,000E+05

1,000E+06

1,500E+06

2,000E+06

2,500E+06

3,000E+06

3,500E+06

4,000E+06

0,000E+00 5,000E-02 1,000E-01 1,500E-01 2,000E-01 2,500E-01 3,000E-01

E [J

]

Theta [-]

SE LS-DYNA

Complete algorithm

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Complete model : scenario•Colliding ship :• Non-bulbous OSV

• 6000 tons (added mass included)

• 5m/s initial speed

• 75 MJ kinetic energy

•Impact point• On a leg, between two nodes

• Perpendicular to one plan

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Complete model : results

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SE LS-Dyna

Complete model : comparison•Better accuracy for large energy impact

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StateofArt LS-Dyna SE

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Conclusions•Short computation time : ≈ 5 minutes (instead of ≈10h for FE)

•Good accuracy in results : difference of max. 10% in terms of energy

•Still needs more validation tests

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Good tool for pre-design stage

Acknowledgements

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FRIA fellowship – Federal governement of Belgium

Financial support for the PhD research : Development of acode based on the continuous elements method to analysethe ship impact on the jacket of an offshore windturbine

MSC Software Corporation

Technical support to the use of the softwarePatran and Nastran to create numerical modelsand perform finite element analyses.

Thank you

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