Research Papers: Piper and Riser Technology

Prototype Reynolds Number Vortex-Induced Vibration Tests on a Full-Scale Rigid Riser

[+] Author and Article Information
Decao Yin

Trondheim NO-7052, Norway
e-mail: decao.yin@sintef.no

Halvor Lie

Trondheim NO-7052, Norway

Rolf J. Baarholm

Stjørdal NO-7500, Norway

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 April 27, 2017; final manuscript received July 26, 2017; published online September 14, 2017. Assoc. Editor: Luis V. S. Sagrilo.

J. Offshore Mech. Arct. Eng 140(1), 011702 (Sep 14, 2017) (11 pages) Paper No: OMAE-17-1069; doi: 10.1115/1.4037538 History: Received April 27, 2017; Revised July 26, 2017

Slender offshore structures in deep water subjected to currents may experience vortex-induced vibrations (VIV), which can cause significant fatigue damage. Extensive experimental researches have been conducted to study the VIV in the past several decades. However, most of the experimental works have small-scale models and relatively low Reynolds number (Re)—“subcritical” or even lower Reynolds number regime. There is a lack of full understanding of the VIV in prototype Re flow regime. Applying the results with low Re to a full-scale riser with prototype Re might have uncertainties due to the scaling effects. In addition, the surface roughness of the riser is also an important parameter, especially in critical Re regime, which is the case for prototype risers. In the present study, two full-scale rigid riser models with different surface roughness ratios were tested in the towing tank of MARINTEK in 2014. Stationary tests, pure crossflow (CF) free oscillation tests, and forced/controlled motion tests were carried out. Several conclusions could be made: The drag coefficient is dependent on the Re number and surface roughness ratio. At critical and supercritical flow regimes, the displacement amplitude ratio is less sensitive to Re than that at lower Re. The displacement amplitude ratio in subcritical flow regime is significantly larger than that in critical and supercritical flow regimes. Two excitation regions for the ‘smooth riser’ and one excitation region for the “rough riser” are identified.

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Fig. 1

Principle sketch of MARINTEK's towing tank

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Fig. 2

Principle sketch of MARINTEK's full-scale VIV test rig: (a) side view, (b) top view of free vibration setup, and (c) top view of forced vibration setup

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Fig. 3

Photo of the test rig with smooth riser model

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Fig. 4

Illustration oscillation orbits with different phase angles when the towing directions are opposite

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Fig. 5

Rough surface modeled by sandpaper, k/D = 1.0 × 103

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Fig. 6

Decay test in air, without riser model, Tn = 2.62 s, damping ratio is 1.3%

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Fig. 7

Decay test in air, without riser model, Tn = 5.82 s, damping ratio is 3.6%

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Fig. 8

Test matrix of forced motion tests

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Fig. 9

Drag coefficients from stationary tests

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Fig. 10

Strouhal number from stationary tests

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Fig. 11

Anom/D versus Ur at prototype Re

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Fig. 12

Smooth cylinder CF VIV response at subcritical Re: (a) Anom/D versus Ur and (b) oscillation frequency to still water natural frequency ratio

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Fig. 13

Calculated peak response amplitude ratio by modified Griffin plot [3]. *, Re=2.16×105, k/D=5.3×10−5, ○, Re=3×105, k/D=5.3×10−5, ×, Re=4×105, k/D=5.3×10−5, +, Re=6×105,k/D=5.3×10−5, Δ, Re=2×105, k/D=1.0×10−3, □ , Re=4×105,k/D=1.0×10−3.

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Fig. 14

Fluctuating lift (C′L) and drag (C′D) coefficients, and mean lift (CL) coefficient, the Transition in shear layer (TrSL), Transition around separation (TrS) and Transition in boundary layer (TrBL) regimes [17,18]

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Fig. 15

Oscillation frequency versus still water natural frequency

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Fig. 16

Free oscillation test on the smooth riser, k/D=5.3×10−5, Re=3×105, Ur=7: (a) time histories of lift force and CF displacement, (b) time histories of towing speed and selection of two time windows, (c) power spectral density (PSD) of Ydisp in TW1, and (d) PSD of Ydisp in TW2

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Fig. 17

Plot of contour curves for CF excitation coefficient in an amplitude ratio—nondimensional frequency map, k/D=5.3×10−5,Re=4×105. Data points are marked with blue dots.

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Fig. 18

Plot of contour curves for CF excitation coefficient in an amplitude ratio—nondimensional frequency map, k/D=1.0×10−3,Re=4×105. Data points are marked with blue dots.

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Fig. 19

Drag coefficients of all forced motion VIV tests

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Fig. 20

Drag coefficients of two series of forced oscillation tests of smooth riser, k/D=5.3×10−5, Re=4×105




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