Transcript 2003 UGM: Modelling Contact

OrcaFlex
- Modelling Contact
Clearance Models
• Seabed clearance (from line centreline at a
node)
• Line clearance (between segment centrelines)
• Line contact clearance (between segment
outer surfaces)
• Clearance may be all you need if contact is
forbidden
• Use dummy lines to mark “no-go” areas like
moonpool edges
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OrcaFlex User Group 2003
Slide 1 of 8
OrcaFlex
- Modelling Contact
Contact Models
• Seabed contact (with line centreline at a
node)
• Solid contact (with line centreline at a node)
• Line clash contact (between segment outer
surfaces)
• All linear elastic + linear damping (inward
motion only)
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OrcaFlex User Group 2003
Slide 2 of 8
OrcaFlex
- Modelling Contact
Contact Example - #1
• Roll-on/roll-off contact over an arch using
solids
• Slowly varying contact – contact force is
insensitive to contact stiffness and is therefore
reliable
• Fine segmentation needed in contact region
• Small changes can give different static
solutions
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OrcaFlex User Group 2003
Slide 3 of 8
OrcaFlex
- Modelling Contact
Contact Example - #2
• Sliding contact – riser guide modelled using a
hollow solid
• Contact occurs at centreline – hole represents
“rattle space”
• High solid stiffness gives a lot of rattling
contact; lower stiffness is more realistic
• Riser rests first on one side then the other –
contact force is a representative result
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OrcaFlex User Group 2003
Slide 4 of 8
OrcaFlex
- Modelling Contact
Contact Example - #3
• Sliding contact – riser guide modelled using
line clashing
• Contact occurs at segment OD – guide line
spacing chosen to give the same rattle space
as before
• High contact stiffness needed to prevent one
line cutting through another
• Force results similar to previous model
• OrcaFlex 8.4 will include a new Clash report
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OrcaFlex User Group 2003
Slide 5 of 8
OrcaFlex
- Modelling Contact
Contact Example - #4
• Dynamic clashing between risers –
hammer/anvil example
• 2 versions – 5m and 2m segments
• How to characterise the initial impact – force,
impulse, energy…?
• Use of clash report to determine impact
sequence, then time histories for closer
investigation
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OrcaFlex User Group 2003
Slide 6 of 8
OrcaFlex
- Modelling Contact
Contact Example - #5
• More complex example – re-entry of a
releasable buoy to an FPSO
• Ship structure represented as a network of
lines
• Buoy represented as a single fat line for clash
purposes
• Shows a series of rattling impacts during reentry
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OrcaFlex User Group 2003
Slide 7 of 8
OrcaFlex
- Modelling Contact
Contact Example - #6
• Using links to model contact – example from
OrcaLay
• Applicable where contact point is predictable
with no slip
• Long links avoid small errors due to axial
movement (strain) of pipe
• Solids (Shapes) used for illustration only –
zero stiffness
www.orcina.com
OrcaFlex User Group 2003
Slide 8 of 8