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

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 generation of networks & services Presenter Profile Jon Steinar Andreassen graduated from the University of Trondheim with a degree in Place physical electronics in 1985. He joined STK, picture now Nexans Norway in 1986. His work has here been related to research and development of 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

conference & convention enabling the next generation of networks & services 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

conference & convention enabling the next generation of networks & services Introduction • Drivers for separate FO riser cables for offshore 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

conference & convention enabling the next generation of networks & services 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

conference & convention enabling the next generation of networks & services 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

conference & convention enabling the next generation of networks & services Design Phases – Initial Design • Proposed design – Structural analysis • Global parameters – Axial stiffness – Axial stiffness – Bending stiffness – Torsional stiffness OD 64 mm – Local stress analysis Weight , air 144 N/m Weight , seawater 110 N/m • Cable capacity curve N/m 2 Weight / Diameter 1700 – Material characteristics • Fatigue strength / S-N curves

conference & convention enabling the next generation of networks & services Design Phases – Initial Design • Global Axial Stiffness 270 MN parameters ∼ 1 kN·m 2 Bending Stiffness (No load) ∼ 135 N·m 2 Torsional Stiffness (No load) Elongation / Torque vs Axial Load Elongation / Torque vs Axial Load Elongation / Rotation vs Axial Load Elongation / Rotation vs Axial Load (Fixed ends) (One end free) 0,25 50 0,25 0 0,225 45 0,225 -0,05 0,2 40 0,2 -0,1 0,175 35 0,175 -0,15 Reaction Torque [N·m] Rotation [deg/m] 0,15 30 0,15 -0,2 Strain [%] Strain [%] 0,125 25 0,125 -0,25 0,1 20 0,1 -0,3 0,075 15 0,075 -0,35 Strain Strain 0,05 Torque 10 0,05 -0,4 Rotation 0,025 5 0,025 -0,45 0 0 0 -0,5 0 100000 200000 300000 400000 500000 600000 700000 0 100000 200000 300000 400000 500000 600000 700000 Axial Load [N] Axial Load [N]

conference & convention enabling the next generation of networks & services Design Phases – Initial Design • Cable capacity curve – Limited by local stress in any layer 600 Capacity - Yield 500 Average, Yield Average, Yield 80% utilization 400 Axial Load [kN] 300 200 100 0 0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 Curvature [1/m]

conference & convention enabling the next generation of networks & services Design Phases – Initial Design • S-N curves – 2,3mm OD laser welded steel tube (AISI 316) log( ) log( ) log( ) = − ⋅ ∆ σ N a m 1000 N : # cycles to failure N : # cycles to failure Log(a), m : curve fit Stress Range [MPa] parameters ∆ σ : stress range 100 10000 100000 1000000 10000000 Number of Cycles to Failure ´08 20degC ´08 20degC runout ´08 65degC ´08 65degC runout ´09 65degC ´09 65degC runout

conference & convention enabling the next generation of networks & services Design Phases - Analysis • Inputs – Cable characteristics ”Near” ”Far” – Waves and currents conditions • Meteorological/Oceanographic data (Metocean) (Metocean) – Floater movements • Response Amplitude Operator (RAO) ”Near” ”Far” • Analysis for Bouyancy Modules – Load scenarios – Fatigue life – Interference

conference & convention enabling the next generation of networks & services Design Phases - Analysis • Global Analysis – Establish load cases ”Transverse” ”Far” ”Near” – Combinations of waves and currents and currents – Typical extreme case: ”Cross” • 100 year wave • 10 year current profile Wave Offset Current Riser Cable • ….and vice versa – >Tension / Curvature • ”all” directions Within 80% capacity for extreme

conference & convention enabling the next generation of networks & services Design Phases - Analysis • Extreme condition analysis – Floating platform, North Sea – 350m water depth Static x-z configuration Static x-z configuration ord. z-coord rd. z-coord Hang-off movement, ”near” Hang-off movement, ”far” X-coord. X-coord. Original hang-off position

conference & convention enabling the next generation of networks & services Design Phases - Analysis 600 • Extreme condition analysis Capacity - Yield 500 Average, Yield 80% utilization 400 Axial Load [kN] 300 – Tensile load along cable 200 100 0 0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 Curvature [1/m] ”Far” ”Far” ”Near” ”Near”

conference & convention enabling the next generation of networks & services Design Phases - Analysis 600 Capacity - Yield 500 • Extreme condition analysis Average, Yield 80% utilization 400 Axial Load [kN] 300 200 – Curvature along cable 100 0 0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 Curvature [1/m] 0.7 0.7 maximum dyn maximum dyn static static 0.6 0.6 0.6 0.6 Total curvature (1/m) static maximum dyn Total curvature (1/m) 0.5 0.5 minimum dyn minimum dyn 0.4 0.4 0.3 0.3 0.2 0.2 0.1 0.1 0 0 0 100 200 300 400 500 600 700 0 100 200 300 400 500 600 700 ”Far” Length coordinate (m) ”Near” Length coordinate (m)

conference & convention enabling the next generation of networks & services Design Phases - Analysis • Interference analysis – Ensure no contact with adjacent risers – Extreme conditions Static y-z configuration • Configuration envelopes • Configuration envelopes Hang-off movement, ”transverse” Hang-off movement, ”transverse” (”Y-Z”) – Structural data on ”neighbours” – Match hydrodynamic properties Original hang-off position • Weight/Diameter ratio

conference & convention enabling the next generation of networks & services Design Phases - Analysis • Fatigue analysis – Establish wave scatter diagram (Period L 0 ) • Distribute loads into ”blocks” • Wave heights/periods - Number of waves – Directions • Wave heights/periods - Number of waves – Directions – Establish load cycle diagram (Period L 0 ) – Total fatigue damage (Period L 0 ) • Palmgren-Miner 1 k n k ( ) ∑ ∑ m = = ⋅ ∆ σ D n i i i N a = 1 = 1 i i i – Fatigue life L = 0 L f D

conference & convention enabling the next generation of networks & services 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

conference & convention enabling the next generation of networks & services 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

conference & convention enabling the next generation of networks & services 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