485ac - viv
TRANSCRIPT
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VIV Application toDeepwater Risers
Steve Leverette
Atlantia Offshore Limited
December 2-3, 2003
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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
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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.
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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
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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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
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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
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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
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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
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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Riser Response to Currents
Types of Risers:
TTR - top tensioned riser
SCR - steel catenary riser
Flexible riser
HCR - highly compliant
FSR - free standing riser
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Riser Response to Currents
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
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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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Riser Response to Currents
Buoyancy, cladding, strakes, etc
Touchdown point
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KingKong riser with Buoyancy
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Riser Response to Currents
Static response
Vessel Offset
Increased drag due to VIV
Interference analysis
Touchdown trench effects
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Riser Response to Currents
Dynamic response Modal analysis (string, beam models)
Bending vs axial modes
Finite versus infinite transmission models
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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
Relativeposition,x/L
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
Relativeposition,x/L
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
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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
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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.
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Riser Response to Currents
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
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Historical Shear7, Clift Formulation
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Pre-lock-in, Lock-in, Lock-out
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Dynamic
Response
Power Balance
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Power Balance
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Riser Response to Currents
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Riser Response to Currents
In-line vs
transverse
Single-mode vs
Multi-mode
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Riser Response to Currents
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
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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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
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Fatigue
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(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
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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
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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Tendons in VIV
OTC Paper
Leverette, Rijken, Thompson, Dooley
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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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The FIX
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Shel l Global Solut ions
Fairings for drilling riser
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Fairings for TLP tendon
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Fairings in moonpool
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Half strakes for pipelines
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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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Analysis Methods and Programs
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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Riser Response to Currents
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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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Analysis Methods and Programs
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
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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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
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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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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
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Trenching
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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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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)
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Re=100k
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Re=600k
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Re=4MM
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Grid for cylinder
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Strip theory approach to riser
modeling (J. Kallinderis)
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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
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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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MEMBER OF THE IHCCALAND GROUP
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
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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
MEMBER OF THE IHCCALAND GROUPATLANTIA OFFSHORE LIMITED
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.
MEMBER OF THE IHCCALAND GROUPATLANTIA OFFSHORE LIMITED
( )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)
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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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MEMBER OF THE IHCCALAND GROUP
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
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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.
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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< > =
MEMBER OF THE IHCCALAND GROUPATLANTIA OFFSHORE LIMITED
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
= =
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Consider a simple slab flow problem
first to illustrate the example of limited
power-in length.
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MEMBER OF THE IHCCALAND GROUP
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
MEMBER OF THE IHCCALAND GROUPATLANTIA OFFSHORE LIMITED
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.
MEMBER OF THE IHCCALAND GROUPATLANTIA OFFSHORE LIMITED
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=
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Jump to DS 6402 presentation
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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
MEMBER OF THE IHCCALAND GROUPATLANTIA OFFSHORE LIMITED
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
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
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