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Research Papers: Piper and Riser Technology

Finite Element Analysis of Flexible Pipes Under Axial Compression: Influence of the Sample Length

[+] Author and Article Information
Eduardo Ribeiro Malta

Department of Naval Engineering,
University of São Paulo,
São Paulo 05539-080, Brazil

Clóvis de Arruda Martins

Department of Mechanical Engineering,
University of São Paulo,
São Paulo 05508-010, Brazil

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received October 28, 2015; final manuscript received July 25, 2016; published online September 21, 2016. Assoc. Editor: Myung Hyun Kim.

J. Offshore Mech. Arct. Eng 139(1), 011701 (Sep 21, 2016) (9 pages) Paper No: OMAE-15-1114; doi: 10.1115/1.4034379 History: Received October 28, 2015; Revised July 25, 2016

In order to study the axial compressive behavior of flexible pipes, a nonlinear tridimensional finite element model was developed. This model recreates a five layer flexible pipe with two tensile armor layers, an external polymeric sheath, an orthotropic high strength tape, and a rigid inner core. Using this model, several studies were conducted to verify the influence of key parameters on the wire instability phenomenon. The pipe sample length can be considered as one of these parameters. This paper includes a detailed description of the finite element model itself and a case study where the length of the pipe is varied. The procedure of this analysis is here described and a case study is presented which shows that the sample length itself has no practical effect on the prebuckling response of the samples and a small effect on the limit force value. The postbuckling response, however, presented high sensitivity to the changes, but its erratic behavior has made impossible to establish a pattern.

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References

Figures

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Fig. 1

The multilayered structure of a flexible pipe. Courtesy of Fernando Toni.

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Fig. 2

Lateral tensile armor buckling (Braga and Kaleff [2])

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Fig. 3

Radial tensile armor buckling (Braga and Kaleff [2])

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Fig. 4

General aspect of the mesh (with shell thickness)

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Fig. 5

One side of the model was clamped (external layers removed for tensile armor visualization)

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Fig. 6

A displacement was applied on the axial direction, while the other degrees-of-freedom were constrained

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Fig. 7

Side view of the polymeric layer showing the “sleeves”

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Fig. 8

Stress versus strain curve for high density polyethilene

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Fig. 9

Stress versus strain curve for high strength tape

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Fig. 10

Two pitches long sample, the moment before instability. Stresses in MPa.

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Fig. 11

Two pitches long sample, after instability. Stresses in MPa.

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Fig. 12

Two pitches long sample. Force reaction versus axial relative deformation for each layer.

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Fig. 13

Two pitches long sample. Resultant reaction versus axial relative deformation.

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Fig. 14

2.5 pitches long sample, the moment before instability. Stresses in MPa.

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Fig. 15

2.5 pitches long sample, after instability. Stresses in MPa.

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Fig. 16

2.5 pitches long sample. Force reaction versus axial relative deformation for each layer.

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Fig. 17

2.5 pitches long sample. Resultant reaction versus axial relative deformation.

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Fig. 18

Three pitches long sample. Lateral instability on the outer tensile armor. Stresses in MPa.

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Fig. 19

Three pitches long sample. Lateral instability on the inner tensile armor. Stresses in MPa.

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Fig. 20

Three pitches long sample. Force reaction versus axial relative deformation for each layer.

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Fig. 21

Three pitches long sample. Resultant reaction versus axial relative deformation.

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Fig. 22

3.5 pitches long sample. Lateral instability on the inner tensile armor. Stresses in MPa.

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Fig. 23

3.5 pitches long sample, outer tensile armor on the frame prior to instability. Stresses in MPa.

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Fig. 24

3.5 pitches long sample. Both armor layers during instability. Stresses in MPa.

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Fig. 25

3.5 pitches long sample. Force reaction versus axial relative deformation for each layer.

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Fig. 26

3.5 pitches long sample. Resultant reaction versus axial relative deformation.

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Fig. 27

Four pitches long sample. Lateral instability on the outer tensile armor. Stresses in MPa.

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Fig. 28

Four pitches long sample. Lateral instability on the inner tensile armor. Stresses in MPa.

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Fig. 29

Four pitches long sample. Force reaction versus axial relative deformation for each layer.

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Fig. 30

Four pitches long sample. Total force reaction versus axial relative deformation.

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Fig. 31

Comparison between yielding times for each layer

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Fig. 32

Reaction force x axial relative deformation curve for all five model variants

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Fig. 33

Comparison between different machines

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