DESIGNING FIBER OPTIC DYNAMIC RISER CABLES FOR FOR OFFSHORE - - PowerPoint PPT Presentation

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DESIGNING FIBER OPTIC DYNAMIC RISER CABLES FOR FOR OFFSHORE - - PowerPoint PPT Presentation

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conference & convention enabling the next generation of networks & services DESIGNING FIBER OPTIC DYNAMIC RISER CABLES FOR FOR OFFSHORE APPLICATIONS Jon Steinar Andreassen Nexans Norway conference & convention enabling the next

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SLIDE 1 enabling the next generation of networks & services

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DESIGNING FIBER OPTIC DYNAMIC RISER CABLES FOR FOR OFFSHORE APPLICATIONS

Jon Steinar Andreassen

Nexans Norway

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Presenter Profile

Jon Steinar Andreassen graduated from the University of Trondheim with a degree in physical electronics in 1985. He joined STK, now Nexans Norway in 1986. His work has been related to research and development of

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fibre optic cables, with special emphasis on reliability issues and cables for specialty applications. Jon Steinar Andreassen R&D Project Manager Email: Jon-Steinar.Andreassen@Nexans.com Tel: (+47) 22886226 Mobile Tel: (+47) 95995176

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Outline

  • Introduction
  • Dynamic versus Static Applications
  • Design Phases for Dynamic Cables

– Initial Design – Initial Design – Dynamic Analysis – Prototype Manufacturing and Testing

  • Components and Interfaces
  • Summary
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Introduction

  • Drivers for separate FO riser cables for
  • ffshore industry

– Communication needs

  • Platforms or FPOs connected to communication

networks networks

– Fibre optic sensing and monitoring systems

  • Deep water = Dynamic riser cables

– Different design criteria compared to seabed deployed cables – Extensive engineering and development

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Dynamic versus Static Applications

  • Static subsea cables

– Loads during deployment and repair

  • NOTS (48hours) – NTTS (1hour)
  • Low cycle fatigue
  • Low cycle fatigue
  • Dynamic subsea cables

– Cyclic loads over entire operational life

  • Site specific dynamic conditions
  • High cycle fatigue
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Design Phases – Initial Design

  • Fundamental client input

– Functional requirements – Site data

  • Configuration
  • Configuration

– Free hanging catenary – ”Lazy wave” configuration

  • Subsea layout

– Adjacent riser cables – Weight / Dimension criteria

  • Water depth / Seabed conditions
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Design Phases – Initial Design

  • Proposed design

– Structural analysis

  • Global parameters

– Axial stiffness – Axial stiffness – Bending stiffness – Torsional stiffness

– Local stress analysis

  • Cable capacity curve

– Material characteristics

  • Fatigue strength / S-N curves

OD 64 mm Weight , air 144 N/m Weight , seawater 110 N/m Weight / Diameter 1700 N/m2

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Design Phases – Initial Design

  • Global

parameters

Elongation / Torque vs Axial Load Elongation / Rotation vs Axial Load Axial Stiffness 270 MN Bending Stiffness (No load) ∼1 kN·m2 Torsional Stiffness (No load) ∼135 N·m2

  • 0,5
  • 0,45
  • 0,4
  • 0,35
  • 0,3
  • 0,25
  • 0,2
  • 0,15
  • 0,1
  • 0,05
0,025 0,05 0,075 0,1 0,125 0,15 0,175 0,2 0,225 0,25 100000 200000 300000 400000 500000 600000 700000 Rotation [deg/m] Strain [%] Axial Load [N] Strain Rotation 5 10 15 20 25 30 35 40 45 50 0,025 0,05 0,075 0,1 0,125 0,15 0,175 0,2 0,225 0,25 100000 200000 300000 400000 500000 600000 700000 Reaction Torque [N·m] Strain [%] Axial Load [N] Strain Torque

Elongation / Torque vs Axial Load (Fixed ends) Elongation / Rotation vs Axial Load (One end free)

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Design Phases – Initial Design

  • Cable capacity curve

– Limited by local stress in any layer

500 600

Capacity - Yield Average, Yield

100 200 300 400 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 Axial Load [kN] Curvature [1/m]

Average, Yield 80% utilization

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Design Phases – Initial Design

  • S-N curves

– 2,3mm OD laser welded steel tube (AISI 316)

1000

) log( ) log( ) log( σ ∆ ⋅ − = m a N

N : # cycles to failure

100 10000 100000 1000000 10000000 Stress Range [MPa] Number of Cycles to Failure ´08 20degC ´08 20degC runout ´08 65degC ´08 65degC runout ´09 65degC ´09 65degC runout

N : # cycles to failure Log(a), m : curve fit parameters ∆σ : stress range

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Design Phases - Analysis

  • Inputs

– Cable characteristics – Waves and currents conditions

  • Meteorological/Oceanographic data

(Metocean)

”Far” ”Near”

(Metocean)

– Floater movements

  • Response Amplitude Operator (RAO)
  • Analysis for

– Load scenarios – Fatigue life – Interference

”Far” ”Near” Bouyancy Modules
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Design Phases - Analysis

  • Global Analysis

– Establish load cases – Combinations of waves and currents

”Far” ”Near” ”Transverse”

and currents – Typical extreme case:

  • 100 year wave
  • 10 year current profile
  • ….and vice versa
  • ”all” directions
”Cross” Offset Riser Cable Current Wave

– >Tension / Curvature

Within 80% capacity for extreme

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Static x-z configuration

  • rd.

Static x-z configuration

rd.

Design Phases - Analysis

  • Extreme condition analysis

– Floating platform, North Sea – 350m water depth

Hang-off movement, ”near”

X-coord.

z-coord

Original hang-off position Hang-off movement, ”far”

X-coord.

z-coord

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Design Phases - Analysis

  • Extreme condition analysis

– Tensile load along cable

”Near” ”Far”

100 200 300 400 500 600 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 Axial Load [kN] Curvature [1/m] Capacity - Yield Average, Yield 80% utilization

”Near” ”Far”

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Design Phases - Analysis

  • Extreme condition analysis

– Curvature along cable

0.6 0.7

maximum dyn

0.6 0.7

static

100 200 300 400 500 600 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 Axial Load [kN] Curvature [1/m] Capacity - Yield Average, Yield 80% utilization

0.1 0.2 0.3 0.4 0.5 0.6 100 200 300 400 500 600 700

Length coordinate (m) Total curvature (1/m) maximum dyn static minimum dyn ”Far”

0.1 0.2 0.3 0.4 0.5 0.6 100 200 300 400 500 600 700

Length coordinate (m) Total curvature (1/m)

static maximum dyn minimum dyn ”Near”

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Hang-off movement, ”transverse”

Static y-z configuration

Design Phases - Analysis

  • Interference analysis

– Ensure no contact with adjacent risers – Extreme conditions

  • Configuration envelopes
Original hang-off position Hang-off movement, ”transverse”
  • Configuration envelopes

(”Y-Z”)

– Structural data on ”neighbours” – Match hydrodynamic properties

  • Weight/Diameter ratio
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Design Phases - Analysis

  • Fatigue analysis

– Establish wave scatter diagram (Period L0)

  • Distribute loads into ”blocks”
  • Wave heights/periods - Number of waves – Directions
  • Wave heights/periods - Number of waves – Directions

– Establish load cycle diagram (Period L0) – Total fatigue damage (Period L0)

  • Palmgren-Miner

– Fatigue life

( )

∑ ∑

= =

∆ ⋅ = =

k i k i m i i i i

n a N n D

1 1

1 σ

D L Lf =

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Design Phases - Prototype

  • Manufacturing and Testing

– Verify processing – Verify all mechanical properties of the cable – Fatigue test parameters determined from – Fatigue test parameters determined from fatigue analysis

  • Equivalent fatigue damage to operational life
  • Safety factor
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Components and Interfaces

  • Close interaction, cable and components

– Pull-in and hang-off arrangements – Topside interface

  • Bend stiffener / Bellmouth
  • Bend stiffener / Bellmouth
  • Inclination angle

– Bouyancy modules – Seabed anchor system

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Summary

  • Dynamic cables require

– comprehensive engineering and analysis

  • Global parameters
  • Local stress – High cycle fatigue resistance
  • Local stress – High cycle fatigue resistance

– dynamic analysis

  • Load scenario – Fatigue life – Interference

– full prototype qualification programme – close interaction with components during development

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2010

enabling the next generation of networks & services

conference & convention

Pacifico Convention Plaza Yokohama & InterContinental The Grand Yokohama 11 ~ 14 May 2010 www.suboptic.org The 7th International Conference & Convention

  • n Undersea Telecommunications
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