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DNV Recommended Practice on DNV Recommended Practice on Modelling and Analysis of Marine Operations Underwater Technology Conference 2008 Bergen 4-5 June 2008 Arne Nestegård & Tormod Bøe Det Norske Veritas

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Page 1: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

Page 2: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

Page 3: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

Page 4: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

Page 5: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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.

Slide 5June 4th 2008

Page 6: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

Page 7: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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.

Page 8: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

CFD Analysis of Protection Structure

Vertical force on forward bucket

Slide 8June 4th 2008

Page 9: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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.

Slide 9June 4th 2008

Page 10: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

Slide 10June 4th 2008

Page 11: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

πζ−

⋅⎟⎟⎠

⎞⎜⎜⎝

⎛⋅=

Slide 11June 4th 2008

Page 12: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

Slide 12June 4th 2008

wwave surface zone

Page 13: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave 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

Slide 13June 4th 2008

p aw = vertical water particle accelerationat water depth, d

Page 14: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

Slide 14June 4th 2008

force contributions from each main item

Page 15: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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.

Slide 15June 4th 2008

Page 16: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

Slide 16June 4th 2008

LEA /

Page 17: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

Slide 17June 4th 2008

Page 18: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

Towing operations

Submerged tow of objects attached to vessel

Submerged tow of objects attached to towed buoy

Slide 18June 4th 2008

Page 19: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

Slide 19June 4th 2008

Page 20: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

Slide 20June 4th 2008

04 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9

Hs [m]

Page 21: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

Slide 21June 4th 2008

Page 22: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

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

Page 23: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

Slide 23June 4th 2008

Page 24: DNV Recommended Practice onDNV Recommended … - Arne Nestegård.pdf · Supplement to DNV Rules for Planning ... Carried out by Det Norske Veritas in ... 3 Lifting through wave zone

Slide 24June 4th 2008