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Materials

Numerical and Analytical Modeling of Unbonded Flexible Risers

[+] Author and Article Information
A. Bahtui

School of Engineering and Design, Brunel University, London UB8 3PH, UKali.bahtui@brunel.ac.uk

H. Bahai

School of Engineering and Design, Brunel University, London UB8 3PH, UKhamid.bahai@brunel.ac.uk

G. Alfano

School of Engineering and Design, Brunel University, London UB8 3PH, UKgiulio.alfano@brunel.ac.uk

J. Offshore Mech. Arct. Eng 131(2), 021401 (Mar 26, 2009) (13 pages) doi:10.1115/1.3058700 History: Received March 20, 2008; Revised July 11, 2008; Published March 26, 2009

This paper presents an analytical formulation and a finite element analysis of the behavior of multilayer unbonded flexible risers. The finite element model accurately incorporates all the fine details of the riser that were previously considered to be important but too difficult to simulate due to the significant associated computational cost. All layers of the riser are separately modeled, and contact interaction between layers has been accounted for. The model includes geometric nonlinearity as well as frictional effects. The analysis considers the main modes of flexible riser loading, which include internal and external pressures, axial tension, torsion, and bending. Computations were performed by employing a fully explicit time integration scheme on a parallel 16-processor cluster of computers. Consistency of simulation results was demonstrated by comparison with those of the analytical model of an identical structure. The close agreement gives confidence in both approaches.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

A typical six-layer unbonded flexible riser

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Figure 2

Sign conventions of a layer

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Figure 3

Geometry of a helix

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Figure 4

Side view of a single layer before and after deflection

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Figure 5

Meshed version of six-layer unbonded flexible riser

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Figure 11

Torque versus axial rotation at the top reference point

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Figure 12

Radial-stress contour plot for a cross section at the middle of the riser under bending loading (Pa)

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Figure 13

Axial-stress contour plot for a cross section at the middle of the riser under bending loading (Pa): (a) outer helix layer and (b) inner helix layer

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Figure 14

Bending moment versus curvature

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Figure 15

Theoretical prediction and experimental measurements of the bending moment-curvature reported in Ref. 5

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Figure 16

Slipping between adjacent layers

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Figure 17

Maximum contact pressure contour plot (Pa)

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Figure 18

Percentage of energy dissipation to the strain energy

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Figure 10

Axial-stress contour plot for a cross section at the middle of the riser under torsional loading (Pa)

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Figure 9

Hoop-stress contour plot for a cross section at the middle of the riser under torsional loading (Pa)

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Figure 8

Axial force versus displacement at the top reference point

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Figure 7

Axial-stress contour plot for a cross section at the middle of the riser under tensile loading (Pa)

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Figure 6

Detailed geometry of riser (cross-sectional view)

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