introduction and global analysis brasil japan cooperative

Celso P. Pesce

Professor of Mechanical Sciences

PhD in Ocean Engineering,

MSc Marine Hydrodynamics, Naval Architect

[email protected]

LMO - Offshore Mechanics Laboratory

Escola Politécnica

University of São Paulo

Brazil

Risers – Flexible Pipes and Umbilicals

Introduction and Global Analysis

Brasil – Japan Cooperative Courses

Risers

junta

flexível

riser de aço

bóia

intermediária

poita

enrijecedores de

flexão

TLPFPSO

flutuadores

restritor de

curvatura

flexible joint

Steel catenary

riser

Bending

restrictors

Subsurface buoy Floaters

Bending stiffener

Lazy-wave riser

Weight anchor

Flexible pipe Flexible pipes

• Umbilical cables: control signals,

electrical power, fluid injection to the

submarine equipment at the well

head.

• Flexible pipes: conveying oil, gas,

from the well head to the production

floating system or to another storage

and offloading vessel after

processing.

Hystoric and trends

• ‘70s – fixed platforms:

• ‘80s – Semi-submersible

platforms and TLP’s

• ‘90s: TLP’s, SPARS

• 2000s: FPSO’s, TLP’s, Mono

Column, Semi-subs

• Umbilicals and steel risers

(static)

• Umbilicals and flexible pipes

(dynamic)

• Umbilicals, flexible pipes and

steel catenary risers (dynamic)

• Umbilicals, mixed systems, riser

towers (dynamic)

Catenary Risers

• Loading: environmental action:

• direct (current, waves) and

• indirect, driven by the floating

system.

• Mechanical failures: overloading,

fatigue, localized damage (impact),

collapse, corrosion, welding,

flexible joints, bending stiffeners,

connections, etc...

• Environmental action has a

stochastic nature.

TDP

“FAR”“NEAR”

terminação

HYDRAULIC

CONTROL

ELECTRICAL

CONTROL CABLE

DYNAMIC ELECTRO-HYDRAULIC UMBILICAL

CHEMICAL

INJECTION

ELECTRICAL POWER

CABLE

OPTICAL FIBRE CABLE

DYNAMIC POWER-OPTICAL UMBILICAL

Typical Umbilical Cables

Integrated Steel Tubed Umbilicals (STU)

Typical Flexible Pipe

by F. Toni

Typical failure modes

• Helical tendons rupture – under traction and internal pressure;

• Internal carcasses collapse – under external pressure, squeezing and

crushing;

• Wear and fatigue of metallic components;

• Helical armour layers instabilities (birdcaging and lateral buckling)

• Leakage of plolymeric layers due to aging, chemical atack, degradation;

• Extreme bending efforts, caused by flexural-torcional instabilities (loops)

during laying operations or during fabrication/storage;

• Thermal expansion and sudden variation of bending stiffness;

• Gas permeation in the anular region – corrosion.

• Creeping of polymeric layers;

• Hoses colapse; copper strands fatigue and kinking (umbilicals);

• Others....


Minimum Bending radius Tests

Bending on a wheel


4’’ flexible pipe:

pressure armor

and carcass

under crushing

tests


Flexible pipe collapse modesexternal pressure, squeezing


Corrosion due to annular gas

permeation

partial pressure with time in

annulus #3

CH4

H2S


Instabilities of flexible pipes

birdcaging Lateral buckling


Umbilical crushing

Facts

• Long lengths and low

tensioning:

• High axial rigidity and low

bending stiffness:

• Geometrically nonlinear

boundary conditions:

• Dynamic perturbations:

➢ Global mechanics dominated by

geometric stiffness (tension);

➢ Dynamic equations numerically

rigid (several distinct frequencies

coexisting);

➢ Local analysis necessary at hot

spots (TDZ, Top, floaters)(;

➢ Global dynamics can be linearized

and end effects corrected a

posteriori.

Global Analysis Approaches

• A complete design procedure deals with many (inter-related)

aspects of the dynamic response caused by FPU motions and

ocean currents, assessing their impact on ULS and FLS, as:

– first-order wave motions and slow-drift motions (wave and wind);

– VIV, wake-interference and clashing;

– dynamic instabilities;

– non-linear boundary conditions at:

• TDA;

• Hang-off.

• Design procedures rely on exhaustive mathematical modeling

and demand a huge computational effort.

• Even though, many (isolated) fundamentals aspects are not yet

fully understood.

• There are at least three different time-scales in the catenary

riser dynamic structural problem:

– The first one is dominated by axial rigidity, giving rise to relatively

small periods of oscillation.

– The second one is related to the catenary or geometric rigidity.

– The third one is of a local nature and is due to the local flexural

rigidity effects.

• Such a diversity of time-scales can lead to serious limitations

concerning numerical integration methods by rendering dynamic

equations mathematically stiff.

• Even the starting problem, to determine the static configuration,

can pose serious numerical difficulties, as the flexural rigidity

effect is confined and dominant just inside small regions close to

the ends, the TDP (touch-down point) and the upper end-fitting

or close to other regions of high curvatures.


Conventional

• Numerical integration of the

nonlinear static equilibrium

equations;

• Nonlinear dynamic analysis

around the static equilibrium in

time domain;

Huge computational times.

Expedit

• Numerical integration of the

nonlinear static equilibrium

equations;

• Linear dynamic analysis around

the static equilibrium in

frequency domain;

• Local nonlinear correction

through boundary-layer

techniques at hot spots.


• Time Domain (TD) schemes are strongly recommended (API-

2RD ) for/as:

– comprehensive treatment of the fully nonlinear hydro-elastic

problem;

– extreme environmental conditions, large displacements, tension

coupling, nonlinear loading, foundation modelling;

– transient events: pull-in/pull-out/disconnecting operations, loss of

FPU station-keeping ability, mooring-system failures;

– a reference for equivalent frequency-domain analysis.

• Frequency Domain (FD) schemes are used for speeding-up

design procedures:

– TDA nonlinear boundary condition should be considered

consistently through asymptotic methods; Aranha et al (1997) and

Pesce and Martins (2004).

– ‘Equivalent’ linear spring modeling is not consistent and must be

consciously exercised vs TD simulations.



• Numerous numerical methods have been discussed and

implemented in the last two decades; see, e.g., Leira and

Remseth (1985), Larsen (1992) …. Silveira and Martins (2003).

CDM HBM WTM NWM

Initial Procedures * * *** ***

Stability * *** *** ***

Accuracy ** ** *** ***

Flexibility * * ** ***

Speed *** *** * **

Numerical methods; a qualitative comparison.

(***: better evaluation); Silveira and Martins (2003)

CDM: Central Difference method

HBM: Houlbolt

WTM: Wilson-Theta

NWM: Newmark

Computational CodesPOLIFLEX 2D and 3D

Dynamics in FD


Environmental loading

Direct

• Current:

– Drag

– VIV

• Waves:

– Mean drag;

– Dynamic loading

Indirect

• Motion imposed at top by FPU:

– In the wave frequency range;

– In low frequency range due to:

• waves;

• current;

• wind;

• DP systems.

Interactions

Moored Semi-Submersible Production Platform

Turret-mooring FPSO

Orcina

Spread-mooring FPSO

6 Azimuth Thrusters

2700kW

+459kN / -293kN

DP-FPSO

Wave Spectrum

0 0.2 0.4 0.6 0.8 1 1.2 1.40

1

2

3

4

5

6

7

8

9

10

Frequência (rad/s)

Densid

ade E

spectt

ral (m

2/r

ad/s

)Pierson-Moskowitz

JONSWAP

TP=11,4s e HS=5,5m

−=

4

0

5

2

4

5exp.)(

gS O

4

0

2

216

5 SO H

g=

( ) )2/(exp

4

0

5

220

220

4

5exp.)(

−−

−=

gS O

( ) ln.287,01.16

5 4

0

2

2−= sO H

g

=

0

0

09,0

07,0

Wind spectrum

10-2

10-1

100

0

5

10

15

20

25

30

35

40

Frequência (rad/s)

De

nsid

ad

e E

sp

ectr

al (

m2/s

) Occhi-ShinHarris

6

52

2862...1146)(

−

+=

VVCSV

Harris

Occhi-Shin

g

V

FVVS

2610).69750()(

−+=

Wind speed sample

0 200 400 600 800 10000

5

10

15

20

25

30

Tempo (s)

Ve

locid

ad

e d

o V

ento

(m

/s)

0 200 400 600 800 10000

5

10

15

20

25

30

Tempo (s)V

elo

cid

ad

e d

o V

ento

(m

/s)

Harris Occhi-Shin

Wind force and moment coefficients (OCIMF)

0 20 40 60 80 100 120 140 160 180-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

Ângulo de Incidência (graus)

Cv

x

Condição: Cheio

Condição: Lastro

0 20 40 60 80 100 120 140 160 1800

0.2

0.4

0.6

0.8

1


Cv

y

Condição: Cheio

Condição: Lastro

0 20 40 60 80 100 120 140 160 180-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15


Cv

n

Condição: Cheio

Condição: Lastro

lateral longitudinal

yaw

FPU Motions due to waves

1000 1100 1200 1300 1400 1500 160099

100

101

102

103

Sw

ay

(m)

Baixa Freq.Total

1000 1100 1200 1300 1400 1500 160044

44.5

45

45.5

46

Ya

w (

gra

us)

1000 1100 1200 1300 1400 1500 1600-0.5

0

0.5

Ro

ll (g

raus)

Tempo (s)

First and second-order wave forces

VLCC 100% loaded; Sea state: Tp=11,4s e Hs=5,5m

Low frequency motions caused by second order

forces due to waves

rmsjPOjPO

jrmsjPO

txtx

dRAOStx

),(866,1),(

),().(2),(

0max0

0

0

2

0

=

=

=

++=n

i

jijiijijPO RAOphasetRAOStx1

02

00 ))),((cos(),()(2),(

Typical RAO - Surge

Typical RAO - Sway

Typical RAO - Heave

Typical RAO - Roll

Typical RAO - Pitch

Typical RAO - Yaw

Selection of Environmental Conditions

Facts

• Described by joint PDFs;

• Multi-directional seas;

• Huge number of combinations

and incidences.

Enormous computational

time, turning analysis

procedures cumbersome

Approach

• Selection of a certain number of

environmental combinations,

related to the particular station

keeping system (spread

mooring, Turret, DP);

• Local sea – wind correlation;

• Prelimanry analysis in

frequency domain

• Selected analysis cases in time

domain.

Relation between Significant Wave Height and Wind Speed


Relation between peak period and significant wave height


Depth: 1200m

100 year Storm:

Hs=7.2m

Hmax=13.9m

Tp=14.2s

100 year Current

V=1,95m/s at surface level

profile according to table 4

310m

185m

20m

FPSOturret

Shell-BC10


Sea States

Preliminary analysis

Lazy-wave extreme conditions analysis

Current Profile

Preliminary Study: 60 Cases

Case 1

Heading: 45o NV

N

EW

S

umbilical

Current

Sea

Swell


Case 2

Heading: 74 o NV

N

EW

S

umbilical

Current

Sea

Swell


Case 3

Heading: 100o NV

N

E

W

S

umbilical

Current

Sea

Swell


Case 4

Heading: 225o NV

N

EW

S

umbilical

Current

Sea

Swell


Case 5

Heading: 0 o NV

N

EW

S

umbilical

Current

Sea

Swell

VIV

Gioria et al.

VIV

• Fundamental findings and their impact in riser

dynamics:

– Reynolds number dependence;

– mass ratio dependence;

– effect of coupled stream and cross-wise

vibrations and bifurcations of shedding patterns;

– persistent vibration at high reduced velocities at

very low mass ratio.

• Still challenging riser dynamics:

– multi-modal (in and out-of-plane) simultaneous

excitation in sheared flow.

– curvature effects;

– stream and cross-wise sub-harmonic resonance;

– coupling of VIV with dynamics in other time-

scales;

– VSIV – VIV induced by FPU motions

– supressors and hydrodynamic loading.

Less important to

flexible pipes and

umbilical, due to high

structural damping

Acknowledgements

TPN

FLUID-STRUCTURE INTERACTION AND

OFFSHORE MECHANICS LABORATORY

introduction and global analysis brasil japan cooperative

Documents