User Group Meeting – Houston, October 24, 2006

Design Challenges for Terra Nova and RJS-409 Projects

Agenda

• Roll damping due to mooring and risers in deep water

• Snap loads during pull-in of disconnectable turret mooring

Roll Damping – System Description

• FPSO Ciodade do Rio de Janeiro

• Water Depth = 1370m

• Vessel = 362 kDWT

• Spread mooring system, 18 mooring lines, 10 bow, 8 stern

• 34 Flexible risers, simple catenary configuration

Roll Damping – Problem Definition

• Maximum Allowable 100-year roll angle = 10 deg

• 100-year beam sea: Hs = 6.7m; Tp = 11.4s

• Natural period in roll varies with draft from 10.6s to 14.1s

• Bilge keels: 1.5m wide; 205m long (66% Lbp)

Model Tests, scale 1:60 at Marintek, Norway

Movie

Roll Damping - Approach

• Model tests of FPSO in horizontal mooring– Max Roll Ballast = 11.1 deg

– Max Roll Full = 6.1 deg

• 3D diffraction analysis (HOBEM)– First order wave forces

– Added mass

– Potential damping

• OrcaFlex calculation of vessel roll response using 6D calculated motions

OrcaFlex Calculations

Configuration Max Roll

(deg)Horizontal Mooring 11.2

Actual 18-leg mooring 9.7

Mooring + Risers 8.5

Effect of mooring and risers on max roll

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Snaploading in pull-in line

• Terra Nova FPSO

• Water depth = 95m

• No disconnection in 100-yr storm (Hs = 16m)

• Disconnect for ice berg > 100,000 mt

• Reconnect in Hs = 3.5m

• Full DP system with 5 azimuthing thrusters 5MW each

Terra Nova FPSO

Mooring & Risers

Terra Nova FPSO and Spider Buoy

Model Tests

• Institute for Marine Dynamics

• Scale 1:44

• Instrumented winch

• Full DP system

• Snaploading in pull-in line during reconnect tests

Snaploading from model test

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OrcaFlex Model

• FPSO – Vessel

• Spider Buoy – 6D Buoy

• Mooring Lines

• Risers

• Alternative Model with springs

• 2 Types of analysis– Constant length

– Variable length

All line model

X Y

Z30 mTime: 23.7050s

Model with equivalent springs

X Y

Z30 mT ime: 50.0240s

Comparison of 3-spring to all-line model

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OrcaFlex simulation vs Model test results

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Effect of shock absorber

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