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MEMBER OF THE IHCCALAND GROUP

ATLANTIA OFFSHORE LIMITED

VIV Application toDeepwater Risers

Steve Leverette

Atlantia Offshore Limited

December 2-3, 2003

MEMBER OF THE IHCCALAND GROUPATLANTIA OFFSHORE LIMITED

AgendaIntroduction

Environment

Riser Response to Currents

Fatigue

Tendons

The FIX

Analysis Methods and Programs

Model Tests and Data Sets

Other Issues

Areas of R&D

Industry Experience

Conclusion

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Thanks to:

Thanos Moros, BP Owen Oakley, Jim Stear, Hugh Thompson, Chevron

Kim Vandiver, MIT

Guy Mansour, Atlantia

T. Sarpkaya, Naval Postgraduate School

Don Allen/Li Lee, Shell Global Solutions

Rodney Masters, AIMS


Introduction

Risers and tendons

Steel Catenary Riser: SCR

Top Tensioned Riser: TTR

Flexible Riser

Free Standing Riser: FSRHighly Compliant Riser: HCR

Tendons

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Perspective from the industry:

The offshore industry has been made painfully aware of

what may go wrong, how VIV may affect operations.

The industry is having to be conservative because of

uncertainties in environment and in engineering

prediction tools.

For water depths to 5000, we can proceed with

reasonable solutions. For 10,000, we cannot afford

high levels of conservatism and still afford to makemoney producing oil.


VIV is a resonant feedback

phenomena

Engineering in uncertainty:

Risks not generally in getting

design numbers wrong,

but in not designing for new

phenomena.

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Risks and Cost Impacts

Risers and Tendons represent critical structural and oil

containment systems

Uncertain environment new phenomena being discovered

Uncertain response highly non-linear, stochastic in nature

Failure has high cost


AgendaIntroduction

Environment


Fatigue

Tendons

The FIX



Other Issues

Areas of R&D

Industry Experience

Conclusion

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Environment

Geography

Mode experiment

Types of Ocean Currents

Typical and extreme magnitudes

Durations

Uncertainties, unknowns

Combination with other events Ratio of environmental forces, shallow to deep


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MODE Experiment

WHOI - 1970s

Weather in the Oceans

Fronts, temporal variation

Large scale turbulence

Vertical Structure


Ocean Currents

Tidal Currents (how they exist in deep water)

Loop

Eddy

Storm (wind stress model) Inertial

Slope

Bottom Boundary Current (Sigsby Escarpment)

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Ocean Currents

loop current / eddy current


Cold Core Current Profile

0.0

500.0

1000.0

1500.0

2000.0

2500.0

3000.0

3500.0

0. 000 1. 000 2. 000 3. 000 4.000 5. 000 6.000 7. 000Velocity

Depth-feet

Ocean Currents

Cold Core Eddy

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Inertial and Slope currents

Morpeth

Hurricane Earl

Neptune

Hurricane Georges 1.8 2.2 kts in 2000


Sigsbee Escarpment

Currents

identified frombottom

furrows

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Current profiles

Allegheny

Current Profiles

0.0

500.0

1000.0

1500.0

2000.0

2500.0

3000.0

3500.0

0.000 2.000 4.000 6.000 8.000

Velocity (ft/s)

Depth-

feet

Orig. WarmCore

New WarmCore Profile

New ColdCore Profile


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Environment

Insert DW Currents presentation


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AgendaIntroduction

Environment


Fatigue

Tendons

The FIX



Other Issues

Areas of R&D

Industry Experience

Conclusion



Types of Risers:

TTR - top tensioned riser

SCR - steel catenary riser

Flexible riser

HCR - highly compliant

FSR - free standing riser

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Typical dimensions

4 flowline SCR

4 flowline SCR with 9 buoyancy

21 drilling riser

48 drilling riser with buoyancy

18 export SCR

120 aircans

8 tieback risers


Effects of End Conditions

Taper Joint

Flexjoint

Keel joint

Tensioner/Gimbal

Guide frames

Cantilever wellhead

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PRT at Full Extend, Null, Full Retract

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Buoyancy, cladding, strakes, etc

Touchdown point

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KingKong riser with Buoyancy



Static response

Vessel Offset

Increased drag due to VIV

Interference analysis

Touchdown trench effects

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Dynamic response Modal analysis (string, beam models)

Bending vs axial modes

Finite versus infinite transmission models


TLP production Riser

Modes 1-2,11-12,22-23

TLPProduction Riser Lateral MotionMode Shape

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Mode shape

Relativeposition,x/L

Mode 23

Mode 22

TLP Production RiserLateral Motion Mode Shape

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Modeshape


Mode 11 Mode 10

TLP Production RiserLateral Motion Mode Shape

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Modeshape


Mode1

Mode2

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Typhoon TLP Tendon Lateral Motion Natural Frequency

(Pretension = 1917 kips)

0.0

0.5

1.0

1.5

2.0

2.5

0 2 4 6 8 10 12 14 16 18 20

Mode Number

Frequency,

Hz

Mode No Frequency, Hz

1 0.090

2 0.1803 0.271

4 0.363

5 0.456

6 0.552

7 0.650

8 0.750

9 0.853

10 0.959

11 1.069

12 1.183

13 1.301

14 1.423

15 1.549

16 1.680

17 1.816

18 1.957

19 2.10320 2.255


Illustration of SCR Inplane Modes

-3.0E-04

-2.0E-04

-1.0E-04

0.0E+00

1.0E-04

2.0E-04

3.0E-04

4.0E-04

0 500 1000 1500 2000 2500

Node Number

Cur

vature(1/ft)

Mode 1

Mode 5

Mode 10

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-2250 -1750 -1250 -750 -250 250 750

LOCAL-3 AXIS ; VP=(0.00,0.00,1.00)

-

500

0

500

1000

1500

2000

2500

LOCAL-1AXIS

Mean Position

Mode No. 32

-2250 -1750 -1250 -750 -250 250 750-500

0

500

1000

1500

2000

2500

LOCAL-3 AXIS ; VP=(0.00,0.00,1.00)

Mean Position

Mode No. 2

LOCAL-1AXIS

Examples of SCR Mode Shapes

MEMBER OF THE IHCCALAND GROUPATLANTIA OFFSHORE LIMITEDIllustration of Axial Modes Influence

0.0E+00

1.0E-03

2.0E-03

3.0E-03

4.0E-03

5.0E-03

6.0E-03

7.0E-03

8.0E-03

0 50 100 150 200 250

In-plane Mode Number

MaxCurvature(1/ft)

-1000 -500 0 500 1000 1500 2000 2500 3000

LOCAL-3 AXIS ; VP=(0.00,0.00,1.00)

-500

0

500

1000

1500

2000

2500

3000

350

0

LOCAL-1AXIS

MeanPosi tion - G68_mean_2D_XY_110ModeNo.50 - G68_mean_2D_XY_110

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-400 -300 -200 -100 0 100 200 300 400-1

-0.5

0

0.5

1

excitation

-400 -300 -200 -100 0 100 200 300 4000

0.2

0.4

0.6

xresponse

amplitude

Steady Flow Response for an Infinite Beam with

Finite Length Excitation

= 4.5

Standing wave excitation

power inL

Traveling waves

Standing wave response


Matterhorn Production

Risers

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Matterhorn production riser from

main deck


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Jolliet Single Piece Tendon

Provided by

Steve Leverette

Atlantia Offshore Limited

Steel tendons 24 indiameter.



VIV response characterization

Strouhal number, Reduced velocity

Cl (AOD, Re, Vr)

Pre-lockin, Lock-in, lock-out

Power in, versus damping and radiation

Effects of damping on response

Power balance solution

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VIV Characteristics

stf DStU

=

r

st

UV

f D=

Strouhal Number

Reduced Velocity

St=0.2, Vr=5


Historical Shear7, Clift Formulation

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Pre-lock-in, Lock-in, Lock-out


Dynamic

Response

Power Balance

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Power Balance



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In-line vs

transverse

Single-mode vs

Multi-mode



Bending and increased drag effects

Spectral approach to response

Uncertainties in response

Typical hot spots

Types of currents that are problematic

Effect of increased tension (decrease mode,

reduce bending)

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AgendaIntroduction

Environment


Fatigue

Tendons

The FIX



Other Issues

Areas of R&D

Industry Experience

Conclusion


Fatigue caused by VIV

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Fatigue

log N = log a m log

log N = log a m log [ (t/tref)k]

API, AWS

DOE, DnV

1

k

i

i i

nDN=

= Miners rule


Fatigue

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ATLANTIA OFFSHORE LIMITED Fatigue


(Kips)2/Hz

0.01

0.1

1

10

100

1000

10000

100000

fre

quency(Hz)

Allegheny

01/01/0100:00

02/2612:00

04/24 06/1912:00

08/15 10/1012:00

12/06 01/3112:00

Date

Tendon 1

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

orr 03/25/02 17:13:52Confidential Property of Atlantia

One Year of Tension Spectra

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Safety Factors

Depends on application

Typically 3 for structures

Typically 10-20 for risers


Fatigue

Fracture Mechanics

Frequency Sensitivity: mode, curvature, no. cycles

Ways to combine response modes Rainflow

Spectral approach to fatigue (Wirsching, Dirlik)

Sensitivity to assumptions

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AgendaIntroduction

Environment


Fatigue

Tendons

The FIX



Other Issues

Areas of R&D

Industry Experience

Conclusion


Tendons in VIV

OTC Paper

Leverette, Rijken, Thompson, Dooley

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AgendaIntroduction

Environment


Fatigue

Tendons

The FIX



Other Issues

Areas of R&D

Industry Experience

Conclusion


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The FIX


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Shel l Global Solut ions

Fairings for drilling riser


Fairings for TLP tendon

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Fairings in moonpool


Half strakes for pipelines

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AgendaIntroduction

Environment


Fatigue

Tendons

The FIX



Other Issues

Areas of R&D

Industry Experience

Conclusion

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Engineering tools, not simulators

Summary of how they work

Comparisons

Why they vary so much

CFD

Wake models and other approaches

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Flow diagram of

Shear 7 Analysis



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Figure 8: Shear7 4.3 defines a smoothed lift coefficient curve by fitting two parabolas to

three points defined by four user-specified values.

1

2

4

3

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Example Shear7 Analysis


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Shear7, Viva, Vivana, Vivarray

Engineering tools, not simulators

Summary of how they work

Comparisons / Example

Why they vary so much

CFD

Wake models and other approaches

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AgendaIntroduction

Environment


Fatigue

Tendons

The FIX



Other Issues

Areas of R&D

Industry Experience

Conclusion


The LiteratureReview Papers

Parkinson (1974, 1989)

Sarpkaya (1979, 1995)

Griffin and Ramberg (1982)

Bearman (1984)

Pantazopoulos (1994)

Books

Blevin 1990

Chen 1987

Naudascher and Rockwell 1994

Sumer and Fredsoe 1997

Au-Yang 2001

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Recent Model Tests and Data Sets

Deepstar St Johns, CFD, Lake Seneca

Stride (2H Allegheny and model tests)

VIVA

PMB HCR Lake Pend Oreille

BP

Exxon

Shell


AgendaIntroduction

Environment


Fatigue

Tendons

The FIX



Other Issues

Areas of R&D

Industry Experience

Conclusion

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Other Issues

Wake effects, riser arrays

High Re performance of fairings/strakes

Issue of low mass systems, frequencyindependence

Directionality of currents, resulting stresshot spots

Directionality of response amplitude Trenching


Trenching

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AgendaIntroduction

Environment


Fatigue

Tendons

The FIX



Other Issues

Areas of R&D

Industry Experience

Conclusion


Areas of Research and

Development Empirical

CFD

Fairings

JIPs MIT - VIVA MIT - Vandiver JIP and Shear7

Deepstar (ARA CFD, Principia CFD, Lake Seneca, St.Johns)

Several CFD proposals out

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Slides from Chevron (O. Oakley)

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riser undergoing hydro-elastic response; mesh and vorticitycontours in the wake are shown; note the difference in the shed

wake pattern between the nodes and the anti-nodes of the structure


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Vortex Dislocations Visualizations

Remax=1000 R-DNS Simulations

Remax=100 R-DNS SimulationsRe=100 Experiments C.H.K. Williamson (1989)


Re=100k

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Re=600k


Re=4MM

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Grid for cylinder


Strip theory approach to riser

modeling (J. Kallinderis)

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MEMBER OF THE IHCCALAND GROUPATLANTIA OFFSHORE LIMITEDConstant Contours of Spanwise Vorticity (non-dimensional)

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Numerical Modeling

SMC,

..

k-..

k-S-A

S-AS-ASmag

.

none

Turbulence

Model

DESRAN

S

LESDNSCFD

Approach:

CFD = computational fluid dynamics, solution of

Navier-Stokes equations for fluid flow

)(

1)(

0

jjj

ijjj

i

xxxj

xx

i

xx

ij

x

U

UUU

U

=

=

=

DNS direct numerical solver

LES turbulence model spatial

filter representation of turbulence

fluctuations


CFD Spars2dof Modeling Straked Cylinder

No chains, pipes or anodes

S-A turbulence model

Re = 34MM

Navier-Stokes Solution:

URANS - time averaging

LES space averaging

DES RANS in boundary

layer & LES outside

RANS Grid

DES Grid

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ATLANTIA OFFSHORE LIMITED Displacement History

Genesis spar, strakes only

Pressure PressureVelocity Mag.

30 40 50 60 70 80 90 100 110 120-90

-80

-70

-60

-50

-40

-30

-20

-10

0

Eastings(ft)

Northings(ft)

041707SES 04/17/01 07:00:01

DESRANS


Lock-in Slope

Locked in

Lock-out Slope

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Objectives and Challenges for High

Mode Number, Flow-Induced VibrationModel Tests in Sheared Flow

Prof. J. Kim Vandiver

MIT

June 3, 2003


Principal Issues for High Mode Number VIV

Response Prediction

Does lock-in occur at high mode number in

uniform and sheared flow?

What are the statistics of single versus

multi-frequency response in sheared flow?

What are the statistics of in-line and cross-

flow response?

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Principal Issues for High Mode Number VIV

Response Prediction

Do hydrodynamic damping models needimprovement?

What fairing or strake coverage is required

What is the effect of Reynolds number on St, C

Ldamping and suppression effectiveness.


( )6. , Reynolds number

e

DU xR

=

( )2. , Reduced velocityR

v

U xV

f D=

25. ,

2

Modal damping and wave attenuation

ss t t

n

r Land n

m

= =

23. Reduced damping

( )

n n

f in

R

U x L

21. mass ratio

f

m

D

Important dimensionless groups

4. What about

correlation length?

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How is lock-in affected by mass ratio

versus reduced velocity bandwidth?

Is the response different if the wake adjusts itsfrequency to match the cylinder or the natural

frequency adjusts to match the wake.

21. mass ratio

f

m

D

R

v

V( )2. , lock-in bandwidth

f the vibration frequency

R R

v Rc

U xV dV

f D V

= = =

=

MEMBER OF THE IHCCALAND GROUPATLANTIA OFFSHORE LIMITEDA/D versus Reduced velocity (based on

a fixed natural frequency)

mr=34

mr=0.78

R

Rc

V

V

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Castine field experiment in

uniform flow(1981)Uniform flow on short lengths(75 feet)


Site layout

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Cable, pipe and wire rope properties

Cable was PVC plastic tubing with accelerometers,wires, strength members and potting compound,

D=1.25 inches., s.g.=1.4

Pipe was 1.631 inch steel tube with the cable pulled

inside as the measuring instrument. S.g.=2.4

Wire rope was polyethylene coated oceanographicwire, 3x19 construction. D=.28 inches, s.g.=2.5

MEMBER OF THE IHCCALAND GROUPATLANTIA OFFSHORE LIMITEDCastine pipe response, L=75 ft, D=1.63

inches, specific gravity = 2.4

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ATLANTIA OFFSHORE LIMITEDStable lock-in events are aided by isolated

natural frequencies with no overlap.

Pipe, s.g.=2.4

Tension

FrequencyHz

Cable, s.g.=1.4

Ca= 0 and 1.0

MEMBER OF THE IHCCALAND GROUPATLANTIA OFFSHORE LIMITEDAn example from Helland Hansen:Peak frequencies versus time. What is

going on?

From Robit Helland Hansen Report

40

50

60

70

80

90

100

Date[Y

Y-MM-DD]

Power Spe ctra, Helland-Hansen, DACOS 2 (x-acc )

98-05-04

98-05-05

98-05-06

98-05-07

98-05-08

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Wire rope: L=75 ft, D=0.25 inches, specific gravity = 2.6

Steady beating around 6th mode, components 0.6 Hz apart

Reduced velocity bandwidth of +-20%=+-2.6Hz


Does lock-in occur at High Mode Number ?

Increasing Overlap with Mode Number

+/- 20 % Bandwidth

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5

Uniform Flow Speed (m/s)

ModeNumber

Increase in Uniform flow speed Increasing overlap of competing

modes

Reduced velocity bandwidth of +-20% would include many modes.

Can just one respond in a uniform flow? What happens in shear?

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Wire rope: L=900 ft, D=0.280 inches,

specific gravity = 2.5

Nearly uniform flow on a 900 foot long sample.

+- 10% flow variation along the length

Lock-in at 50th mode

Conclusions:

High mass ratio provides stable sharp resonances.

VRbandwidth allows for some spatial tolerance toflow variations. Single frequency dominance ispossible in nearly uniform flows, even at highmode number.


2 2

2

2

Two forms are equal:

8 - Griffin

Vandiver

s et s

f

s ng

f n

mS

D

rS

U

=

=

The role of damping in uniform flow?The role of damping in uniform flow? The reducedThe reduceddamping is a statement of dynamic equilibriumdamping is a statement of dynamic equilibrium ..

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,

A useful property is that:

2 , the equation of an

hyperbola for lines of constant lift coefficie t.n

nL n u

qC S

D< > =


10-2

10-1

100

101

10-2

10-1

100

101

Lift Coe fficie nt in Phas e with Ve loc ity at Loc k-in

Re duced Damping, Sg

Peakres

ponseA/D

Cl =0.01

0.02

0.05

0.10

Cl =0.2

0.5

1.0

Cylinder Data

Cl=2S g*A/D

Peak

Response

(A/D)

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in

,2

,

A flexible cylinder in a n on-uniform flow

with a power-in reg ion of length L has a resonant

m odal response given by:

2 2

In red are 3 key parameters in prediction pro

L n in

n

L nn w n

n u

Cq

D R

UC L

S

= =

u

,

2 2

u 2 2

grams.

They form a dimensionless group S and

Average modal lift coefficient

8 S

L n

n n t n n

w in w in

C

R S M

U L D L

= =


Consider a simple slab flow problem

first to illustrate the example of limited

power-in length.

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ATLANTIA OFFSHORE LIMITEDShroud created a still water damped region

Shroud covers this

length, creates still

water around the

cylinder

Uniform flowpower-in region

U

L

Lin


Example Experimental Data for a Slab

Flow

Tsahalis, D. T.,Experimental Study of the

Vortex Induced Vibrations of a Long Model

Riser Exposed to Uniform and Nonuniform

Steady Flow, Houston, Texas, WesthollowResearch Center, 1985.

Thank you to Shell Global Solutions for

allowing me to publish these results.

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Experiment Details Steel pipe, O.D. = 1.5in(3.81cm)

I.D. = 1.334in(3.39cm)

U= 0.33 to 6ft/s(0.1 to 1.83 m/s) in steps of0.33ft/s(0.1m/s), modes 1 thru 3.

Biaxial accelerometers at 5 points: L/8, L/4,L/2, 5L/8, AND 5L/6.


Shrouds used to simulate slab

flow cases.

Exposed length of cylinder in 7 steps

100%

87.5%

75.0% 62.5%

50.0%

37.5%

25.0%

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Reduced Velocity versus Mode 2, peak A/D

for various fractions of exposure length

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.0 2.0 4.0 6.0 8.0 10.0

Vr, based on vibration frequency

PeakresponseA/D,mod

e2

Lin=25% Lin=25% Lin=37.5% Lin=37.5% Lin=50%

Lin=50% Lin=62.5% Lin=62.5% Lin=75% Lin=75%

Lin=87.5% Lin=87.5% Lin=100% Lin=100% Lin=100%

Delta Vr =0.42

r

v

UV

f D=


Jump to DS 6402 presentation

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AgendaIntroduction

Environment


Fatigue

Tendons

The FIX



Other Issues

Areas of R&D

Industry Experience

Conclusion


Industry Experience(interesting bits of history)

BNOC West of Shetlands

BP Scheihellion experiences

Exxon Brazil

Andaman Sea

West Seno Risers and Tendons

Auger Top Tensioned Sales Riser

Allegheny SCR clashing Allegheny trenching

Matterhorn (effects of cantilevered wellhead, strakes help installation,cold core re-fit)

Typhoon SCR design and cold core issue

Discovery of cold core/submerged current events

Atlantis (and Thunder Horse) Sigsby Escarpment, high bottomcurrents, full straked riser 7200 WD, 12 deg top, ~10,000 for 2export, 6 production

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AgendaIntroduction

Environment


Fatigue

Tendons

The FIX



Other Issues

Areas of R&D

Industry Experience

Conclusions


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Summary and Conclusions

VIV is significant design issue in deep water

Highly non-linear in excitation and in damage

Instability of wake, not easy to predict

Industry addressing problem through many studiesand investigations

Documents

485AC - VIV