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Research Papers: Piper and Riser Technology

Influence of Sea Current on Stabilization of Moments and Forces in Risers

[+] Author and Article Information
Iwona Adamiec-Wójcik

Faculty of Management and Transport,
University of Bielsko-Biala,
Willowa 2,
43-309 Bielsko-Biala, Poland
e-mail: i.adamiec@ath.bielsko.pl

Lucyna Brzozowska

Faculty of Management and Transport,
University of Bielsko-Biala,
Willowa 2,
43-309 Bielsko-Biala, Poland
e-mail: lbrzozowska@ath.bielsko.pl

Stanisław Wojciech

Faculty of Management and Transport,
University of Bielsko-Biala,
Willowa 2,
43-309 Bielsko-Biala, Poland
e-mail: swojciech@ath.bielsko.pl

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the Journal of Offshore Mechanics and Arctic Engineering. Manuscript received January 15, 2019; final manuscript received April 15, 2019; published online May 17, 2019. Assoc. Editor: Jonas W. Ringsberg.

J. Offshore Mech. Arct. Eng 141(6), 061701 (May 17, 2019) (15 pages) Paper No: OMAE-19-1004; doi: 10.1115/1.4043541 History: Received January 15, 2019; Accepted April 16, 2019

One of the important aspects in the design of floating, production, storage, and offloading (FPSO) systems is to ensure a fairly constant load on risers despite the base motion caused by sea waves. The paper presents the authors’ own formulation of the finite segment method for dynamic analysis of risers and its application to the solution of a dynamic optimization problem. This task consists in defining vertical displacements of the top of the riser which compensate horizontal movements of the vessel or platform caused by sea waves. Compensation involves stabilizing the bending moment in the risers or the force in the connection of the riser and the wellhead. The model takes into account the influence of the sea by means of Morison equations. Different sea current profiles are considered. Calculation of vertical displacements of the top of the riser is carried out in order to stabilize the force or the bending moment for a defined function of horizontal displacements of the riser.

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References

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Figures

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Fig. 1

Discretization of a link: (a) primary division and (b) secondary division

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Fig. 2

Slender link after bending: (a) the link and (b) parameters of the element

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Fig. 4

Hydrodynamic force

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Fig. 5

Constraint reactions at points A0 and AE

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Fig. 6

Configuration analyzed: (a) catenary riser and (b) vertical riser

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Fig. 7

Sea currents analyzed: (a) case C1 and (b) case C2

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Fig. 8

Current influence on the shape of the riser

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Fig. 9

Current influence on bending moments

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Fig. 10

Courses of M(t, s*) for cases C0, C1, and C2

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Fig. 11

Courses of F0 for cases C0, C1, and C2

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Fig. 12

Motion in direction of axis x of the top of the catenary riser: (a) displacement 0 and (b) velocity x~˙0

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Fig. 13

Initial approximation B1: (a) moment M(s*,t) and (b) force F0(t)

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Fig. 14

Initial approximation B2: (a) moment M(s*,t) and (b) A0(t)=0

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Fig. 15

Case B1: (a) courses of function 0(t); yb, initial course; y0, after optimization and (b) courses of moment M(s*,t); Mb, initial course; M0, after optimization

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Fig. 16

Case B2: (a) courses of function 0(t); yb, initial course; y0, after optimization and (b) course of moment M(s*,t); Mb, initial course; M0, after optimization

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Fig. 17

Case B1 with sea current 1.1 m/s: (a) courses of function 0(t); yb, initial course; y0, after optimization and (b) course of moment M(s*,t); Mb, initial course; M0, after optimization

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Fig. 18

Case B2 with sea current 1.1 m/s: (a) courses of function 0; yb, initial course; y0, after optimization and (b) course of moment M(s*,t); Mb, initial course; M0, after optimization

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Fig. 19

Courses of (a) horizontal displacement 0 and (b) velocity x~˙0 of the top of the riser

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Fig. 20

Initial (t = 0) position of the riser: (a) step I, (b) step II, and (c) shape of the riser

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Fig. 21

Case B1/C0: (a) courses of function 0(t); yb, initial course; y0, after optimization and (b) course of force FE(t); FEb(t), initial course; FEO(t), after optimization

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Fig. 22

Case B2/C0: (a) courses of function 0(t); yb, initial course; y0, after optimization and (b) course of force FE(t); FEb(t), initial course; FEO(t), after optimization

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Fig. 23

Case B1/C2: (a) courses of function 0(t); yb, initial course; y0, after optimization and (b) course of force FE(t); FEb(t), initial course; FEO(t), after optimization

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Fig. 24

Case B2/C2: (a) courses of function 0(t); yb, initial course; y0, after optimization and (b) course of force FE(t); FEb(t), initial course; FEO(t), after optimization

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Fig. 25

Scheme of the procedure which enables the model to be used in control

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