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Numerical analysis of jacket foundations: a coupled shell-
beam approach.
Annabel Lush
MScR Student, Computational Mechanics Group,
School of Engineering and Computing Sciences.
Supergen Wind 2: 7th Training Seminar, 4th September 2013.
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Jacket Foundations
IMAGES - web
2 Images: www.ship-technology.com; www.rwe.com
∂
Foundation Design Competition
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Suction Bucket
Monopile
Twisted Jacket Gravity Structure
Suction Bucket Tripod
Images: www.energyengineering.co.uk
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Inward Battered Guide Structure
IBGS – a twisted-jacket foundation designed by Keystone Engineering.
• 20% CAPEX reduction.
• Compact design – 2x more jackets per transportation vessel.
• Supports turbines ≥ 5MW.
4 Image: www.keystoneengr.com
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IBGS Installation Process
5
(I) (II) (III)
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Research Aims
I. Develop a bespoke analysis tool to model the IBGS, using the Finite Element Method.
II. Understand and improve the approach for coupling beam and shell finite elements to achieve a rapid analysis capability.
III. Understand the structural behaviour of the IBGS and highlight design modifications if appropriate.
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Preliminary Analysis
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To understand the general structural behaviour of the IBGS using beam elements.
Photo: www.carbontrust.com
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3D Beam Element
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Linear beam element: 3 translations and 3 rotations per node.
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Beam vs. Brick Elements
A cantilever with an end point load.
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Element type Beam Brick
No. of elements 1 100
No. of DOF 12 1212
Deflection (mm) - 0.1905 - 0.1905
∂
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A B
C
∂
Combined axial/bending stresses (MPa) per load case:
Preliminary Analysis – Results (I)
Jacket-leg Fxx Fyy Fzz Mxx Myy Mzz
A 74 - 113 - 2 5 5 - 7
B - 133 - 76 - 2 3 3 - 7
C 63 121 - 2 - 4 - 4 - 7
A 142 59 - 4 3 - 1 - 22
B - 69 - 120 - 4 1 2 - 22
C - 69 123 - 4 - 1 2 22
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60° twist
0° twist
x
y
z
∂
12 Data: UpWind Report 2011 (Table 6.5)
∂
Combined axial/bending stresses (MPa) per load case:
Preliminary Analysis – Results (II)
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60° twist
0° twist
Jacket-leg Fxx Fyy Fzz Mxx Myy Mzz
A 15 - 11 - 24 47 - 58 - 7
B - 27 - 8 - 24 31 109 - 7
C 13 12 - 24 - 45 - 82 - 7
A 28 6 - 36 27 - 19 - 22
B - 14 - 12 - 36 14 48 - 22
C - 14 12 - 36 - 13 - 48 22
x
y
z
∂
Preliminary Analysis – Results (II)
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Total combined axial and bending stresses.
60° twist 0° twist
A - 38 B 74
C - 133
A - 16
B - 22
C - 77
∂
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x
y
z
Pile height 5-60m
Jacket height 30m IBGS
height
Nacelle height
Water surface
Image: www.timesdispatch.com
∂
Preliminary Analysis – Results (III)
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60° twist
0° twist
Pile height (m)
L2-norm of nacelle
displacement (mm)
∂
Creating a more detailed model
Shell elements used to give detail of stresses at joints:
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MITC9 shell element: 3 translations (not shown) and 2 rotations per node (β1, β2).
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Coupling of beam and shell elements is enforced by:
• reducing the system to be solved, and
• developing relationships to link the shell and beam DOF.
Creating a more detailed model
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∂
Coupled Analysis
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• To examine the stresses at each joint.
• To assess the influence of the jacket twist on these stresses.
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Observations
I. Removing the twist in the IBGS increases the stiffness under the analysed loads cases.
II. An efficient method is employed in the coupled analysis.
III. The analysis tool developed could be used to optimise other tubular structures.
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∂
Further Research Directions
Extend analysis code to include:
• dynamic analysis,
• soil-pile interaction,
• effects of scouring, and
• greater detail around structural joints through using continuum elements on fillets.
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∂
This research was conducted under the Dong Energy
Durham University Partnership, with supervision from
Dr William Coombs, Professor Jon Trevelyan and
Professor Roger Crouch (City University).
Email: [email protected]
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