Presentation by Pal Dahlberg on Seminar Design of Fixed Structures with DNV Software (April 2012)

1. 1
SesamTM
40 years of success
Sesam for collapse analysis
Pål Dahlberg, Sesam Principal Sales Executive
17 April, 2012

2. Benefits from using Sesam for jackets
New builds covering Manage existing Collapse analysis Modification work
entire life cycle re-analysis models Requalification - all phases
MTO, deflection check, Understand models over time, Extreme conditions, Design of new parts
code check, fatigue produce and view results accidents, fire, explosion Re-design of existing
Same model for all stages – can be shared with other units like the floating department
SesamTM
13 December 2011
© Det Norske Veritas AS. All rights reserved. 2

3. Non-linear analysis
- Re-qualification
- Accidents
- Collapse & large scale deformations
- Fire & explosions
SesamTM
13 December 2011
© Det Norske Veritas AS. All rights reserved. 3

4. The SESAM suite of programs
Packages:
DeepC
Coupled global
response
of moored deep water
floating systems
GeniE
Design of beam and
plate offshore
structures
HydroD
Hydrodynamic
analysis
of ship and floating
offshore structures
SesamTM
13 December 2011
© Det Norske Veritas AS. All rights reserved. 4

5. Our tools – your solutions – your decisions
xml xml
Transportation, launching Transportation, lifting
Deflections, Stresses, Deflections, Stresses,
Code-check, Fatigue Code-check, Fatigue
fem
Non-linear analysis, Linear analysis (wave, pile/soil)
collapse, accidents, Deflections, Stresses,
re-qualifications Code-check, Fatigue, Earthquake
SesamTM
13 December 2011
© Det Norske Veritas AS. All rights reserved. 5

6. Structural analysis & design
 Non-linear analysis
- Accidents: Member yields and changes shape
- Impact, Collision, Explosion, Dropped objects
- Geometry changes significantly
- Lifting operations, cable structures
- Loads depend on structural response
- Wave, current, wind, motions
- Static analysis
- Ultimate strength, Energy absorption
- Dynamic simulation (of real events)
- Collision, explosion, motions
- Environment (wave, buoyancy, stability, wind)
- Foundation
- Pile, soil, spudcan (jack-up)
- Temperature effects
- Changed material properties, Fire
SesamTM
13 December 2011
© Det Norske Veritas AS. All rights reserved. 6

7. Non-linear analysis
 USFOS is a specialized tool for ultimate resistance
evaluation of typical offshore structures
- Increased efficiency
- Better numerical predictions
- Lower threshold for new users to enter complex physics
 The ultimate resistance of a structure is important
for many reasons
- New loading conditions, linear design exceeded, e.g.
- Extreme waves, increased explosion pressure
- Increased platform weight, extra conductors
- Damaged structure (cracks etc) – necessary to repair
immediately?
- Energy absorption performance
- Boat landing, crane operations/dropped objects, vessel
impact etc.
SesamTM
13 December 2011
© Det Norske Veritas AS. All rights reserved. 7

8. Non-linear analysis in Usfos
 Why non-linear
- Linear codes cannot describe ductility
(metal)
- Linear codes cannot account for the
change in geometry for increasing
loads
- Usfos includes “all” physical effects and
predicts the “real” behaviour of a
structure
SesamTM
13 December 2011
© Det Norske Veritas AS. All rights reserved. 8

9. Importing models into Usfos
Model consistency :
GeniE Sacs
Model
Wave loads
Soil
The Sacs input file The GeniE model The Usfos model
SesamTM
13 December 2011
© Det Norske Veritas AS. All rights reserved. 9

10. Importing models to Usfos
 Migration to Usfos
- Detailed model not needed for Collapse analysis
- This model would benefit from a “clean-up”
- Deck plating  Coarse Mesh
- Necessary to get rid of the small gaps
- Beams  One element per physical member
- Enough for detection of buckling & Plastic Hinges (end
nodes + middle of beam)
- Gravity + Explicit Deck Loads + Wave load (to be
exported to Usfos)
- More loads can easily be imported to Usfos, but they
should be relevant for collapse analysis
- Remove Dummy beams  Not relevant for non-linear
analysis
- Wave loads exported from GeniE as explicit loads
- No need to define wave data and hydrodynamic
coefficients in Usfos
SesamTM
13 December 2011
© Det Norske Veritas AS. All rights reserved. 11

11. Importing models to Usfos
 How to do it?
- Start Usfos (Xact) and import the structure and wave load data
SesamTM
13 December 2011
© Det Norske Veritas AS. All rights reserved. 12

12. Collapse analysis
 History Plots
- Global Load vs. Displacement of Control Node (normally a node with large displacements)
- Global Stiffness vs. Step Numbers
SesamTM
13 December 2011
© Det Norske Veritas AS. All rights reserved. 13

13. Collapse analysis
 Displacements  Plastic utilization
SesamTM
13 December 2011
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14. Collapse analysis
 Element forces
SesamTM
13 December 2011
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15. Boat impact
 Boat Impact
- Energy specified by user to be dissipated
- Local Denting of Tube
- Buckling & Plastic Hinges for local Hit Member
- Fracture Criteria based on strains
- In this case when less 0.15
- Global Deformation of the Global Model
SesamTM
13 December 2011
© Det Norske Veritas AS. All rights reserved. 16

16. Boat impact
 History Plots (Global Load = 1, means  Plastic utilisation
Max Impact Energy)
- Shown for control node
SesamTM
13 December 2011
© Det Norske Veritas AS. All rights reserved. 17

17. Safeguarding life, property
and the environment
www.dnv.com
SesamTM
13 December 2011
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