DNV Recommended Practice onDNV Recommended …possibility.no/utc2008/ps/C3 - Arne Nestegård.pdf ·...
Transcript of DNV Recommended Practice onDNV Recommended …possibility.no/utc2008/ps/C3 - Arne Nestegård.pdf ·...
DNV Recommended Practice onDNV Recommended Practice on Modelling and Analysis of Marine Operations
Underwater Technology Conference 2008Bergen 4-5 June 2008
Arne Nestegård & Tormod BøeDet Norske Veritas
New DNV Recommended Practice
DNV-RP-H103 M d lli d A l i f M i O tiModelling and Analysis of Marine Operations
Supplement to DNV Rules for Planning
and Execution of Marine Operations
Slide 2June 4th 2008
COSMAR - COSt Effective MARine Operations
Joint Industry Project with the objective to:j
- Develop improved methods and simulation procedures for
Carried out by Det Norske Veritas in cooperation with Marintek/Sintefsimulation procedures for
modelling and analysis of marine operations.
cooperation with Marintek/Sintef
Partners:
- Implement new methods and procedures in DNV R d d P ti (DNV
Partners:
- StatoilHydroRecommended Practice (DNV-RP-H103) to become directly accessible and useful for the industry
- Shell Technology- Petrobras- Acergyindustry. gy- Technip
Slide 3June 4th 2008
Background
Marine operations are involved at all major stages of anMarine operations are involved at all major stages of an offshore field with significant costs
- Transportation, installation, maintenance, repair interventions, p pdecommisioning
Advanced, accurate and reliable numerical methods to establish operational criteria will contribute to more optimized
d t ff ti i tiand cost effective marine operations- Prolonged profitable tail-production, increased exploitation of
petroleum resourcespetroleum resources
Slide 4June 4th 2008
Background (cont)
Advanced modelling of physical effects are available, but the use of such models in numerical simulations of marine operations is not well establishedoperations is not well established.
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DNV RP-H103: Modelling and analysis of marine operations
CONTENTS
1 Introduction
2 General methods of analysis of marine operations
3 Lifting through wave zone - general
4 Lifting through wave zone – simplified methods
5 Deepwater lowering operations
6 Landing on seabed and retrieval
7 Towing operations
8 Weather criteria and availability analysis
Slide 6June 4th 2008
General analysis methods for marine operations
Frequency domain analyses – use of RAOs- Use and limitations/disadvantages use of design waves irregular sea states- Use and limitations/disadvantages, use of design waves, irregular sea states
Time domain analyses- Different formulations. Equations of motion. Use and limitations. Multi-bodyDifferent formulations. Equations of motion. Use and limitations. Multi body
simulations. Impact loads. Snap loads.
Computational Fluid Dynamics- Available methods and tools. Accuracy of local flow description. Accuracy of
global load predictions
Statistics and extremes of marine operationsStatistics and extremes of marine operations- Assessment of extreme response under stationary / non-stationary
conditions. Statistics of snap loads and impact loads
Model tests of marine operations- Oscillation tests to find hydrodynamic coefficients. Wave tests. Tests of the
l t t
Slide 7June 4th 2008
complete set-up.
Lifting through wave zone - general
Hydrodynamic Loads and Load Effects
- Quadratic and linear damping. Dependence on KC-number. Inertia forces due to moving object. Wave
it ti fexcitation forces.
Hydrodynamic coefficients and empirical datap
- Added mass on typical structures (subsea modules). Added mass and damping for ventilated structures. Drag coefficients.
Moonpool Operations- Water kinematics Blocking effects on drag and added mass- Water kinematics. Blocking effects on drag and added mass.
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Lifting through wave zone – simplified methods
The objective of the Simplified Method is to give simple conservative estimates of the
Main assumptions:
give simple conservative estimates of the forces acting on the object in order to verify sufficient crane and rigging capacity.
Main assumptions:
the horizontal extent of the lifted object is jsmall compared to the wave length
vertical motion of object and water dominates j→ other motions can be disregarded
the vertical motion of the object is equal the vertical crane tip motion
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Simplified Method – Examples
Wave kinematicsThe wave amplitude, wave particle velocity and acceleration can be taken as:
Sa H⋅= 9.0ζd24π
gT
zaw
z
d
eT
v2
42
ππ
ζ−
⋅⎟⎟⎠
⎞⎜⎜⎝
⎛⋅=
d24πgT
zaw
z
d
eT
a2
42
2π
πζ−
⋅⎟⎟⎠
⎞⎜⎜⎝
⎛⋅=
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Simplified Method – Hydrodynamic Forces
Slamming impact force
Slamming forces are short-term impulse g pforces that acts when the structure hits the water surface.
AS is the relevant slamming area on the
22wctcs vvvv ++=
AS is the relevant slamming area on the exposed structure part. Cs is slamming coeff.
The slamming velocity, vs :
vc = lowering speedvct = vertical crane tip velocityvw = vertical water particle velocity
at water surface
Varying buoyancy force
at water surface
gVF ⋅⋅= δρρ
gVF ⋅⋅= δρρ
y g y y
Varying buoyancy, Fρ , is the change in buoyancy due to the water surface elevation. 22~
ctawAV ηζδ +⋅=
δV is the change in volume of displaced water from still water surface to wave crest or wave trough.
ζa = wave amplitudeηct = crane tip motion amplitudeÃw = mean water line area in the
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wwave surface zone
Simplified Method – Hydrodynamic Forces
Drag forceDrag forces are flow resistance on submerged g gpart of the structure. The drag forces are related to relative velocity between object and water particles.
22wctcr vvvv ++=
l i /h i ti dThe drag coefficient, CD, in oscillatory flow for complex subsea structures may typically be CD ≥ 2.5.
R l ti l it f d b
vc = lowering/hoisting speedvct = vertical crane tip velocityvw = vertical water particle velocity
at water depth , dA = horizontal projected area
Mass force
Relative velocity are found by : Ap = horizontal projected area
( )[ ] ( )[ ]22M aAVaAMF +++= ρ
“Mass force” defined as a combination of inertia force, Froude-Kriloff force and diffraction force.
M = mass of object in airA33 = heave added mass of object
( )[ ] ( )[ ]3333 wctM aAVaAMF ⋅++⋅+= ρ
Crane tip acceleration and water particle acceleration are assumed statistically independent.
33 jact = vertical crane tip accelerationV = volume of displaced water relative to
the still water levela = vertical water particle acceleration
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p aw = vertical water particle accelerationat water depth, d
Simplified Method – Hydrodynamic ForceThe hydrodynamic force is a time dependent function of slamming impact force, varying buoyancy, hydrodynamic mass forces and drag forces. In the Simplified Method the forces may be combined as follows:Simplified Method the forces may be combined as follows:
22slamhyd )FF()FF(F MD ρ−++=
The structure may be divided into main items and surfacescontributing to the hydrodynamiccontributing to the hydrodynamic force
Mass and drag forces contributions are thencontributions are then summarized :
∑=
iiMM FF ∑=
iiDD FF
i i
FMi and FDi are the individual force contributions from each
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force contributions from each main item
Simplified Method – Slack SlingsThe Slack Sling Criterion.
Snap forces shall as far as possibleSnap forces shall as far as possible be avoided.
The following criterion should beThe following criterion should be fulfilled in order to ensure that snap loads are avoided:
minstatichyd F9.0F −⋅≤ minstatichyd
Fstatic-min = weight before flooding, g gincluding a weight reduction implied by the weight inaccuracy factor.
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Deep water lowering operations
Horizontal offset due to currentx
z
Dynamics of lifted object –eigenperiods and vertical Ueigenperiods and vertical resonance
U
w
q ξ(z)
M d lli f h
FD0
ξL
η
Modelling of heave compensation
W0
L
M
m , EA
LEA
mLAMT
/31
233
0
++= π
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LEA /
Landing on seabed and retrieval
Landing on seabed- Landing impact problem definition- Landing impact problem definition- Physical parameters- Numerical analysis procedure- Application to modules with and
without skirts
Skirt penetration resistanceSkirt penetration resistance
Installation by suction
Levelling by application of suction or overpressure
Retrieval of foundationsRetrieval of foundations
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Towing operations
Submerged tow of objects attached to vessel
Submerged tow of objects attached to towed buoy
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Submerged tow of long slender elements
wave directiontowing direction
X
Zwave directiontowing direction
X
Zwave directiontowing direction
X
Zwave directiontowing direction
X
Z
T i
1200m
Top assembly, Bottom assembly,
X
T i
1200m
Top assembly, Bottom assembly,
X
T i
1200m
Top assembly, Bottom assembly,
X
T i
1200m
Top assembly, Bottom assembly, T i
1200m
Top assembly, Bottom assembly,
X
bottom
wire
Top wire net buoyancy 50 t net buoyancy 30 tbottom
wire
Top wire net buoyancy 50 t net buoyancy 30 tTop wire net buoyancy 50 t net buoyancy 30 tTop wire net buoyancy 50 t net buoyancy 30 tTop wire net buoyancy 50 t net buoyancy 30 t
Top chain Bottom chainTop chain Bottom chainTop chain Bottom chainTop chain Bottom chainTop chain Bottom chain
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Surface tow
M i li iMaximum towline tensionas function of seastate
6000
7000
4000
5000
n [k
N]
L1
L2
2000
3000
Axi
al T
ensi
on 2
L3
0
1000
2000
L1 < L2 < L3
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04 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9
Hs [m]
Weather criteria and availability analysis
Environmental parameters relevant for marine operations- Primary characteristicsPrimary characteristics- Weather routing
Accuracy of environmental datay- Instrumental data- Numerically generated data
Climatic uncertainty- Climatic uncertainty
Weather forecasting - Weather restricted operations / uncertainties of weather forecasts- Weather restricted operations / uncertainties of weather forecasts
Persistence statistics
M it i f th diti dMonitoring of weather conditions and responses
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Summary
A new Recommended Practice; ”DNV RP H103 ModellingA new Recommended Practice; ”DNV-RP-H103 Modelling and Analysis of Marine Operations” is scheduled for October 2008.
The new RP gives guidance on methods and simulation procedures for modelling and analysis of marine operations.
Slide 22June 4th 2008