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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