1 MARINTEK MARINTEK do Brasil Opening Seminar Iberostar Hotel, Rio de Janeiro, April 19, 2007 Recent MARINTEK activities on assessment of Vortex-Induced Vibrations Rolf Baarholm MARINTEK
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MARINTEK do Brasil Opening SeminarIberostar Hotel, Rio de Janeiro, April 19, 2007
Recent MARINTEK activities on assessment of Vortex-Induced Vibrations
Rolf Baarholm MARINTEK
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Today’s presentation
Brief Introduction to VIV problem areasKey VIV activities at MARINTEKExamples of Test Methods and Results from MARINTEK Research
3D tests – Multimode VIV2D tests
Conclusive Remarks
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VIV problem areas
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More specifically…
SPARs/SEMI:Increased global motionsIncreased dragIncreased mooring line tensions
Risers: Reduced fatigue life
Increased axial tension
Increased extreme loads
Increased drag
Increased “diameter” and
drag
2d
d
Increased axial tension
T
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Key VIV Work at MARINTEK
Experimental work in laboratory and large-scale (fjord) testingAnalysis of experimental data (small-, large- & full scale test results) Development of VIV prediction tools
VIVANA (Semi-empirical force model prediction tool)SIMVIV (Simplified response model prediction tool)
Consultant work onMarine risersDeepwater umbilicalsFree spanning pipelines
Strong interaction with the research at the Centre of Excellence on Ship and Ocean Structures (NTNU)
3 PhD students on VIV on pipelines, one post doc.
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Typical VIV tests
2-D Tests (L/D = 10-30)To determine hydrodynamic coefficientsTo study effect of VIV suppression devicesTo study in-line vs cross-flow oscillations
3-D Tests (L/D > 300)To study multimode oscillations in sheared currentTo study effect of VIV suppression devicesTo interaction and clashing in riser arrays
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Multimode VIV in sheared current
Riser:
L= 2000m, D= 0.25 m,
Uc = 4 knots 50th mode
Uc = 2 knots 25th mode
UC f1 f4f3f2 f5
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The Hanøytangen Experiment Set-Up
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Experimental set-up Rotating Rig
The riser is attached to the rotating test rig
Current profile
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NDP High Mode VIV Test in Ocean BasinTest Set-up for Uniform and Sheared Flow
Riser model Clump weight
∇
riser
gondol
riser
gondol
Uniform flow Sheared flow
L=38m
L/D=1400
Bare and straked riser
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PLAY
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Free Span VIV Testing of Static UmbilicalNorsk Hydro Ormen Lange Field
Wires to Fibre Optical sensors
Wires to accelerometers
Umbilical
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NDP Dual riser interaction/clashing
Primary objectives:
Enhance the understanding of the physical mechanisms that drives riser clashingProvide benchmark data for riser interaction/clashing code validation
R1
R2VC
FB1 FB2
FT2FT1
S1 S2
J2J1
Bare and straked risers
With and without bumper elements
Experiments for:
Systematic variation of:Riser spacing Inflow angle
Current velocity (towing velocity)
L=10m
L/D=500
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Straked risers
Riser spacing =10D
Inflow angle = 10deg
Bare risers
Riser spacing=10D
Inflow angle = 5 deg
The videos show the riser behavior at midspan
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Test set-up for 2D test:NDP Systematic Parameter Investigation of the Efficiency of Helical Strakes
Bare riser
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Riser configurations
4 different Pitch/Diameter-ratios (5, 8.8, 13.2, 17.5) 4 different Height/Diameter-ratios (0.1, 0.14, 0.2 and 0.25).2 different pipe diameters (76.1mm and 114.3mm)3 start helical strakes and 4 start helical strakesBare riser
Increasing P/D
Increasing H/D
Phase I : Parametric study of strake configurations
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Model production at the MARINTEK workshop
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P/D=17.5, H/D=0.25
D=0.0761m
PLAY
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0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0 2 4 6 8 10 12 14
Reduced velocity (-)
rms
z/D
[-]
P8.8_H10 P8.8_H14 P8.8_H20
Increasing strake height
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Phase II: NDP Helical Strakes Extended study
Objectives:Investigate the effect of marine growth on cylinders with helical strakesInvestigate the effect of mass ratioInvestigate the effect of strake fin geometry on VIV suppression
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Soft marine growth on a real riser
Soft marine growth (slimy marine grass)
Soft marine growth as modeled
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Hard marine growth on a real riser
Hard marine growth (Shell, wart barnacle, etc.)
Hard marine growth as modeled
100% 60% 100% 35% 10%20%
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Next project
NDP Fairing Study
2D Free Oscillation Tests
2D Fixed Fairing Tests
3D Elastic Riser Model Tests
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Summary
Vortex-induced vibrations is widely occurring phenomenon for deep-water marine risersPotential to cause costly and environmentally damaging fatigue failuresVIV gives large problems for drilling risers in high currentVIV is the major contributor to fatigue of SCRs and TTRsSuppression devices such as helical strakes may reduce the VIV response by more than 95%State-of-the-art semi-analytical prediction tools have limitations
Multi-mode VIVIn-line vibrations
Next generation of prediction tool (Stochastic VIV) is under developmentCFD is immature for VIV simulations