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

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designing fiber optic dynamic riser cables for offshore
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DESIGNING FIBER OPTIC DYNAMIC RISER CABLES 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 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 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 fibre optic cables, with special emphasis on reliability issues and cables for specialty applications.

Place picture here

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 – 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

– 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
  • 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

– 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 – 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

‐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) Axial Stiffness 270 MN Bending Stiffness (No load) 1 kN·m2 Torsional Stiffness (No load) 135 N·m2

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Design Phases – Initial Design

  • Cable capacity curve

– Limited by local stress in any layer

100 200 300 400 500 600 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 A x i a l L

  • a

d [ k N ] Curvature [1/m]

Capacity ‐ Yield Average, Yield 80% utilization

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Design Phases – Initial Design

  • S-N curves

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

100 1000 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

) log( ) log( ) log(      m a N

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

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Design Phases - Analysis

  • Inputs

– Cable characteristics – Waves and currents conditions

  • Meteorological/Oceanographic data

(Metocean)

– Floater movements

  • Response Amplitude Operator (RAO)
  • Analysis for

– Load scenarios – Fatigue life – Interference

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Design Phases - Analysis

  • Global Analysis

– Establish load cases – Combinations of waves and currents – Typical extreme case:

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

– >Tension / Curvature

Within 80% capacity for extreme

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Hang‐off movement, ”near”

Static x-z configuration

X-coord.

z-coord.

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

Static x-z configuration

X-coord.

z-coord.

Design Phases - Analysis

  • Extreme condition analysis

– Floating platform, North Sea – 350m water depth

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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 A x i a l L
  • a
d [ k N ] Curvature [1/m] Capacity ‐ Yield Average, Yield 80% utilization
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Design Phases - Analysis

  • Extreme condition analysis

– Curvature along cable

0.1 0.2 0.3 0.4 0.5 0.6 0.7 100 200 300 400 500 600 700

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 0.7 100 200 300 400 500 600 700

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

static maximum dyn minimum dyn ”Near”

100 200 300 400 500 600 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 A x i a l L
  • a
d [ k N ] Curvature [1/m] Capacity ‐ Yield Average, Yield 80% utilization
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Original hang‐off position Hang‐off movement, ”transverse”

Static y-z configuration

Design Phases - Analysis

  • Interference analysis

– Ensure no contact with adjacent risers – Extreme conditions

  • 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

– 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 

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 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
  • 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

– dynamic analysis

  • Load scenario – Fatigue life – Interference

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

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2010

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

enabling the next generation of networks & services

The 7th International Conference & Convention

  • n Undersea Telecommunications

conference & convention

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