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Research Papers: Piper and Riser Technology

Slug Flow and Waves Induced Motions in Flexible Riser

[+] Author and Article Information
Arturo Ortega

Centre for Ships and Ocean Structures CeSOS,
Norwegian University of Science and
Technology NTNU,
Trondheim 7491, Norway;
Sección de Ingeniería Mecánica,
Pontificia Universidad Católica del Perú PUCP,
Av. Universitaria 1801,
San Miguel Lima 32, Perú
e-mail: aortegam@pucp.edu.pe

Ausberto Rivera

Centre for Ships and Ocean Structures CeSOS,
Norwegian University of Science and
Technology NTNU,
Trondheim 7491, Norway
e-mail: ausberto.r.medina@ntnu.no

Carl M. Larsen

Centre for Ships and Ocean Structures CeSOS,
Norwegian University of Science and
Technology NTNU,
Trondheim 7491, Norway
e-mail: carl.m.larsen@ntnu.no

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 16, 2016; final manuscript received August 18, 2017; published online October 6, 2017. Assoc. Editor: Qing Xiao.

J. Offshore Mech. Arct. Eng 140(1), 011703 (Oct 06, 2017) (9 pages) Paper No: OMAE-16-1126; doi: 10.1115/1.4037842 History: Received October 16, 2016; Revised August 18, 2017

Flexible risers provide optimum solutions for deep water offshore fields. Reliable dynamic analysis of this kind of slender structure is crucial to ensure safety against long time fatigue failure. Beyond the effects from wave loads, the influence from transient internal slug flow on the slender structure dynamics should also be taken into account. In this study, two coupled in-house codes were used in order to identify and quantify the effects of an internal slug flow and wave loads on the flexible riser dynamics. One code carries out a global dynamic analysis of the slender structure displacements using a finite element formulation. The other program simulates the behavior of the internal slug flow using a finite volume method. The slug flow is influenced by the dynamic shape of the riser, while the time varying forces from internal slug flow plus external waves will influence the shape. Hence, a fully coupled analysis is needed in order to solve the coupled problem. By means of the distributed simulation, these two programs run synchronously and exchange information during the time integration process. A test case using hydrodynamic forces according to the linear Airy wave theory coupled with an internal unstable slug flow was analyzed and the results shown amplification of the dynamic response due to the interaction between the two load types, effects on the effective tension caused by the internal two-phase flow, and influence on the internal slug flow caused by the wave-induced response.

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References

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Figures

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Fig. 1

Fluid particle traveling along a curved pipe segment

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Fig. 2

Slug and bubble regions in the slug tracking model

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Fig. 3

HLA federation used in this work

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Fig. 4

Catenary static riser configuration

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Fig. 5

Effective and true tension distribution after static analysis

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Fig. 6

Time history of internal flow inlet pressure

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Fig. 7

Time history of outlet holdup

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Fig. 8

Time history of outlet liquid flow rate

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Fig. 9

Time history of outlet gas flow rate

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Fig. 10

Time history of effective top tension

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Fig. 11

Time history of ΔX/D displacements—slug flow case

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Fig. 12

Time history of ΔY/D displacements—slug flow case

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Fig. 13

Time history of ΔX/D displacements—regular waves case

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Fig. 14

Time history of ΔY/D displacements—regular waves case

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Fig. 15

Time history of ΔX/D displacements—slug flow combined with regular waves

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Fig. 16

Time history of ΔY/D displacements—slug flow combined with regular waves

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Fig. 17

Maximum values of horizontal displacement recorded during time integration

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Fig. 18

Minimum values of horizontal displacement recorded during time integration

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Fig. 19

Maximum values of vertical displacement recorded during time integration

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Fig. 20

Minimum values of vertical displacement recorded during time integration

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Fig. 21

Displacement on plane of node at middle of riser

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