Research activities in the Norwegian Deepwater ProgrammeConference on CeSOS Highlights and AMOS Visions

Rolf Baarholm, Statoil6/5/2013

− Norwegian Deepwater Programme

− VIV characterization and prediction

− VIV mitigation

− Marine growth

− Concluding remarks

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Outline of presentation

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www.L2S.no www.ndwp.org

• NDP is an organisation of the deep water licences awarded in 15th round (1996) in the Norwegian Sea. Later extended to include 16th 17th 18th 19th 20th and 21st round deepwater licences. About MNOK 400 in projects investment since start. 2012 budget MNOK 24.0.

• The objective is to join forces and carry out cost effective preparations for safe and efficient drilling and field development.

• The program phases are: Phase 1 (1996-2000), Phase 2 (2001-2005), Phase 3 (2006-2008), Phase 4 (2009-2012) and agreed Phase 5 (2013-2016).

• 2012 members: Statoil , Norske Shell, Chevron, Suncor , ENI, Total, and BP.

PL215PL217 PL218

PL210

PL207 PL208

PL209

15th Round

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Norwegian Deepwater Programme

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Environment

Metocean

Seabed Subsea

Riser & Mooring

NDP Riser & MooringObjectives

• Development and verification of design tools

• Development of Guidelines or Recommended Practices

• Bring extended knowledge into engineering companies

• Make the results available to the end users in a transparent format

Focus areas

• Norwegian Sea

• Water depths: 1200-1500 m

• Harsh environment

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VIV in the Norwegian Deepwater Programme

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NDP Riser & Mooring expenditure year 2000From NDP Riser & Mooring

Brochure for 1997-1999.

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NDP funded experimental VIV projects at MARINTEK

Year Project Client

19981999199919992003200320042005200620072011

Clashing criteria and VIVAnalysis full-scale drilling riser VIV experimentVIV in current and floater motions Clashing energy and VIVDual riser clashing testsHigh mode VIV model testsFaired 3D riser VIV test, effectiveness and instability Parametric 2D tests of strakes2-D strake riser VIV test, extended study (with marine growth)NDP Fairing study, pendulum tests, fixed 2D tests, 3D elastic testsVIV riser tests (bare, straked, fairings)*

NDPNDPNDPNDPNDPNDPNDPNDPNDPNDPSHELL/NDP*

* Test funded by Shell and analysis funded by NDP

Understanding VIV phenomenon

• Analysis of full-scale field measurements

• Analysis of Hanøytangen experiments

• NDP high mode VIV experiments at MARINTEK

• Analysis Shell high mode VIV

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NDP High Mode VIV Test in Ocean Basin3D tests with 38m long riser model, dia=27mm

riser

gondol

riser

gondol

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CF and IL fatigue vs. tow speed for bare riser in uniform flow

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Max. fatigue damage vs. tow speed

1.00E-11

1.00E-10

1.00E-09

1.00E-08

1.00E-07

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

0.00 0.50 1.00 1.50 2.00 2.50

Velocity [m/s]

D [1

/yrs

] Bare17.5D0.25D5D0.14D

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Analysis of Shell VIV tests• Similar set-up as for the NDP high mode tests

• Three different pipes tested: L/D = 3800, 1085, 333

• Various suppression devices/coverage

• Marine growth and pipe roughness

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Ref: Halvor Lie et al, “COMPREHENSIVE RISER VIV MODEL TESTS IN UNIFORM AND SHEARED FLOW”, OMAE2012-84055

Compliant: fn < fviv

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NDP Analyses 2012-2014• Modal analysis

• Wavelet analysis

• Estimation of hydrodynamic forces and hydrodynamic coefficients

• Spatial variation in VIV response

• Stability of fairings response

• Response overlap – Reynolds number effects

• Damping regions and power-in regions

• Explore responses with various mitigation devices

• Analysis of higher order responses

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VIV Suppression

Success factors for VIV suppression devices:• Suppress vortex induced vibrations effectively (VIV)

• Avoid global instability (galloping)

• Low drag forces

• Ease of handling (short cord length, low weight, potential pre-installation)

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Suppression devices

• Helical strakes

• Fairings

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Suppression devices

• Helical strakes

• Fairings

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Helical strakes

• Several R&D test campaigns

• Parametric model tests 2D

• Flexible riser tests 3D

• Full scale testing at high Re

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Parametric 2D test of helical strakes

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Straked riser (P/D=17.5, h/D=0.25)

Bare riser

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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

Example: effect of strake height

xRMS / D

Increasing strake height

Reduced velocity, Vr =U / fn D

20% of D

10% of D

14% of D

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Coverage = 52%

Coverage = 82%

Coverage = 100%Coverage = 75%

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• Do we need to clean?

• If so, WHEN?

But, what about marine growth?

Pictures from BP: Marine growth on risers fitted with helical strakes

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Modeled Marine GrowthSoftHard

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Effect of hard marine growth

Cross-flow vibrations

Hard marine growthStraked cylinder 17.5D/0.25D

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

5.00 7.00 9.00 11.00 13.00 15.00 17.00 19.00

Reduced velocity (-)

rms(

z)/D

0% growth10% growth20% gorwth35% growth60% growth100% growth

xRMS / D

Reduced velocity, Vr =U / fn D

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Hard35Hard35

Hard20Hard20

Hard60Hard60

Hard100Hard100

100%60%

100%,

50% Cov

35%10% 20%

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Effect of soft marine growth

Cross-flow vibrations

Soft marine growthStraked cylinder 17.5D/0.25D

0.000

0.100

0.200

0.300

0.400

0.500

0.600

5.00 7.00 9.00 11.00 13.00 15.00 17.00 19.00

Reduced velocity (-)

rms(

z)/D

0% growth10% growth20% growth35% growth60% growth100% growth

xRMS / D

Reduced velocity, Vr =U / fn D

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NDP Fairing studyObjectives:

• Study the dynamic behavior of several fairing geometries with respect to transverse and rotational motion

• Develop and qualify catalogue ready fairing for production and drilling risers.

Focus on drag reduction, suppression of vortex induced vibrations and instability motion onset

Fairing

Riser

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Low Re-number fairings tests• Elastically mounted rigid cylinder: pendulum tests

• Fixed cylinder: cavitation tunnel tests

• Flexible cylinder: towing tank tests

10 different profiles tested

Results: New VERY good fairings

Max CF RMS strain

Max IL RMS strain

Great success:

• New fairings with very good performance

But:

• Needed to be tested at higher Re-number in order to verify the performance at full scale conditions

Fairing 3 Fairing 4

Fairing 4 Fairing 3

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Instability of Faired Riser, 3 D Test

Fairing

Riser

Comparative Fairing Study - Stability Analysis

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Increased damping

Stable

Unstable

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Flutter theory

Finding:We can construct unconditionally stable fairings by moving CoGforward of mid-point of riser (EC)

Fairing 1 Fairing 2

Fairing 3 Fairing 4

Fairing 6Fairing 5

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High Re-number fairings tests on 15” pipe Oceanic Consulting Corporation, St. John’s

Single pipe tests

Tandem pipe tests:• Fairing downstream of straked riser• Fairing downstream of fairing

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Single pipe tests Tandem pipe tests

Drag coefficient of downstream pipeDrag coefficient

Cross-flow amplitudeCross-flow amplitude of downstream pipe

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A successful program

- Has benefited from the active and open

participation of all members.

- Has enabled strengths of the various

companies to be effectively combined.

- Strengthened cooperation between Academia,

R&D institutes and operators

- Provides a sound foundation to build on.

Selected references

Huse E., Kleiven G. and Nielsen F.G. “Large Scale Model Testing of Deep Sea Risers”, OTC 8701, 1998

Baarholm R. and Lie H. (2005) “ Systematic parametric investigation of the efficienyof helical strakes”, Deep Offshore Technology Conference

Skagset K. and Baarholm R (2008) “Effect of marine growth on an elastically mounted circular cylinder”, OMAE2008-57586

Baarholm R. and Skagset K. (2008) “Modelling and characterization of articifialmarine growth”, OMAE2008-57587

Trim A.D., Braaten H., Lie H. and Tognarelli M. (2005) ”Experimental Investigation of vortex-induced vibration of long marine risers”, J. Fluid and Structures.

Lie H et al (2012) “Comprehensive riser VIV model tests in uniform and sheared flow”, OMAE2012-84055

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Research activities in the Norwegian Deepwater Programme

Rolf BaarholmPrincipal ResearcherE-mail rolbaa@statoil.comTel: +4748045296

www.statoil.com

6/5/2013