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Preliminary calculations of the response of the DIFIS concept

Preliminary calculations of the response of the DIFIS concept. Gilbert Damy ( Hydrodynamic group ) Daniel Priour ( Fishing Technology group ) Peter Davies ( Materials & Structures group ). IFREMER Brest Centre. Aim: to get a first idea of the stability of the riser tube. Two Methods used:

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Preliminary calculations of the response of the DIFIS concept

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  1. Preliminary calculations ofthe response of the DIFIS concept Gilbert Damy (Hydrodynamic group) Daniel Priour (Fishing Technology group) Peter Davies (Materials & Structures group) IFREMER Brest Centre

  2. Aim: to get a first idea of the stability ofthe riser tube • Two Methods used: • Deeplines software, FE analysis • In-house FE software FEMNET

  3. Current profile, knots 50m 2.5 0 100 Tons Buoyancy (20 m high) 2.5 100 m 1.5 200 m 1.0 800 m 2 m diameter riser (Undeformable) 3500m 12 anchor lines Diameter 80m 0 Input for analyses:

  4. 1. Deepline analysis www.principia.fr/eng/logiciels/deeplines/ Global Analysis of Risers, Moorings and Flowlines

  5. Deformed line shape 100 T buoyancy

  6. Depth

  7. 100 T buoyancy Buoy pulled down from –50 to >-400 m depth ! Depth

  8. Horizontal offset, 100T buoyancy Buoy lateral movement 1.4 km ! Depth

  9. Same analysis but with 1000 Ton buoyancy (1000m3) Still 320 m offset

  10. 2. FE Model of flexible structures (D. Priour, 1999, Commun. Numer. Mech Engng, 15, p755-763). Depth 3000 m, same 100T buoyancy Applied uniform 1.1 m/s current profile (chosen to give same offset as Deeplines) FEMNET software. Uses triangular elements to model dome, to examine how it deforms.

  11. Deformed shape, Plan view

  12. Horizontal offset around 1200m for 3000m depth (matched to Deeplines)

  13. Dome deformed shape Opening in dome turns towards current Riser tube flattening ? Local design critical depends on local loading and current profile. Max. tension in anchor lines up to 50 tons even with 12 anchors.

  14. Preliminary conclusions • Need very high buoyancy to stabilize riser tube • but this increases cable tensions and anchor loads. • Can multiply anchors, but requires time to install. • Alternative anchoring concept ? Have other preliminary design calculations been performed to validate DIFIS concept ? Discussion with SENER urgently required to clarify feasibility of this type of system.

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