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Ole Jan Nekstad, Product Director Sesam3 December 2012
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SesamTM
40 years of success
Efficient engineering of topside structures
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Efficient engineering of topside structures
� Save man-hours and increase quality by using the latest available capabilities in concept technologies for- Structure modelling- Deadweight loads- Environmental loads- Forces, stresses, deflections- Beam/plate code checking- Fatigue from wave or wind- Refined fatigue- ULS, FLS, ALS
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
Topside structures (including modules, flare booms, bridges)
� On jacket- Often members only
� On floater- Often plates and stiffeners and members
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© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Common challenges in design
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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The importance of the Sesam design loop
40-60% of engineering time often spent in evaluation
How fast can you do it over again?
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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How can Sesam GeniE help you to design a topside structure
Structure
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Structure modelling
� Easy to facilitate the range from small to large and complex
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Structure modelling
� Combine detailed models ina global model- FE results, SCF for beam fatigue,
plate fatigue
FE shell
FE beam
Plates
Beam
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
Structure modelling
� Make the complete model in Sesam GeniE- Beams, plates, trusses, double beams, segmented
members, auto creation of tubular joints, connections
- Automatic model update when inserting, deleting, moving, copying- The model topology is always updated, hence major
changes in the model may easily be performed
- You may be become more productive by using scripting and parametric modelling
- Several engineers can work on parts of the topside and merge prior to analysis- Result evaluation may also be performed on same parts
- Same model and loads may be used for several loading conditions
� Re-use data and continue modelling in GeniE- Older Sesam models- Sacs, StaadPro, StruCad3D, Ansys
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© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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How can Sesam GeniE help you to design a topside structure
Deadweight loads
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Deadweight loads
� From structural mass x gravity
� From point masses x gravity
� Blanket loads (evenly distributed mass)
� Equipments
� Specific pressure loads, point or line loads
� Mass of ice x gravity (same as marine growth for jacket)
� Compartment loads
� Temperature loads
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Deadweight loads
� When jack-up is in “fixed structure” modus. Easy to define compartment loads- Content and filling degree is enough to compute the acting pressures in the walls
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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How can Sesam GeniE help you to design a topside structure
Environmental loads
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Topsides/modules on jackets or floaters
� Topside on jackets- All is done inside Sesam GeniE- Wind, current, wave- Morison theory- Deterministic, stochastic, time domain- Non-linear pile/soil analysis normally included
� Topside on floaters- Opt. 1 - Integrated: Results from Sesam HydroD
(hydrodynamic frequency or time domain analysis) imported into Sesam GeniE
- Opt. 2 - No load transfer: Accelerations and deflections are computed in Sesam HydroD and used as basis for load-cases in Sesam GeniE
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Option 1: Topsides/modules on floaters
� Waves give deformations and stresses in topsides and modules- These are converted to deterministic loads
before import to Sesam GeniE
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Option 2: Topsides/modules on floaters
� Deformations and accelerations used to define load cases in Sesam GeniE- Accelerations constant or centripetal (from Sesam HydroD)- Deformations from global structural analysis (used as prescribed displacements in GeniE)
� Sp1: 2mm
� Sp2: 3mm
� Sp3: 5mm
� Sp4: 2mm
CentripetalAcceleration
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Topsides/modules on jackets
� Codes of practice specify different safety factors for structural mass on various parts of the structure
� Sesam GeniE can work with different load factors for structure mass by using a utility script as found on the Sesam GeniE SnackPack- I.e. Force = acceleration x mass x load factor
Lower level loads from mass x acceleration (x & z-dir)
Upper level loads from mass x acceleration (z-dir)
Rotational accelerationHarmonic induced wave
motion
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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How can Sesam GeniE help you to design a topside structure
Results assessment
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Efficient engineering – typical steps
� First assessment- Forces, stresses and deflections
� Code checking- Check against prescriptive standards
� Member re-design- Evaluate the effect of modifying section
properties or code check parameters- Often many attempts – depends on the
engineer’s experience
� Design iteration- A complete re-run of all to document the
re-design
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Beam forces and stresses
� Forces and stresses in 2D view as well as tabular
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Check deflection ratio against AISC levels
� Allowable deflection ratio 180, 240, 360 and scanning all load cases
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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How can Sesam GeniE help you to design a topside structure
Code checking of members & stiffened panels
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Code checking in GeniE - members
� Supporting- API WSD 2002/AISC ASD 2005- API WSD 2005/AISC ASD 2005 (API: 2007, 2010 updates)- API LRFD 2003/AISC LRFD 2005 (withdrawn by API)- NORSOK 2004/Eurocode 3 1993 (EC: 2008, 2009, 2010 updates)- ISO 19902 2007/Eurocode 3 1993 (EC: 2008, 2009, 2010 updates)- DS 412/449
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Document code check results
� Graphically – complete model
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Document code check results
� Graphically – parts of structure only
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Efficient redesign of members
� Redesign (“design iterations”)- Step1: Preliminary results when
modifying section, material, stiffener spacing or buckling length parameters- Note: The loads and stiffness
are not updated
- Step2: Commit changes to model- Step3: Re-run analysis and code
check- Reports may be automatically
re-created
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Redesign – single members
� Select a capacity member for redesign
� Modify parameters- Preliminary results automatically computed
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SesamTM
3 December 2012
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Redesign – single members
� Look at all details (Full Table)- Shown with colour coding
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SesamTM
3 December 2012
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Redesign – multiple members
� Select capacity members for redesign
� Modify parameters- Preliminary results automatically computed
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Redesign – segmented beams
� Before and after
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SesamTM
3 December 2012
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Redesign – re-run all from one command
� The “Run All” command will- Update structure from members- Run analysis- Generate code check loads (positions)- Execute code check
� Recreation of a report
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Code checking of stiffened panels
� Create panels- Panels are independent of analysis and finite
element mesh
� Three different options to define panels- Min Box finds the smallest idealised rectangular
panel possible enclosing the possibly non-rectangular structural region
- Max Area Moment is an alternative algorithm finding the major axis based on calculation of area moment of inertia of the surface. This algorithm will also work for irregular panel shapes
- CSR Tank Default is the algorithm usually used when doing a CSR Tank (PULS) code check
Min Box
Max Area Moment
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Code checking of stiffened panels – ships and offshore
� Code checking according to PULS (DNV RP-C201.2)- Linear and non-linear
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Code checking of stiffened panels - offshore
� Yield check of plates – based on membrane stress- Includes a safety factor S
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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How can Sesam GeniE help you to design a topside structure
Multiple analysis
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Multiple analysis
� Multiple analysis in same project- E.g. Lifting, transport, in-place- Varying parameters
- Structure- Boundary conditions- Load cases
The “master” model
Lifting Condition Transport Condition In_place Condition
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Multiple analysis – graphic results
� Different results at your finger-tips- Bending moments shown
Lifting Condition
Transport Condition
In_place Condition
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Multiple analysis – code check results
� Different results at your finger-tips- API WSD and default settings used in example below
Lifting Condition
Max Uf = 2.51
Transport Condition
Max Uf = 1.85
In_place Condition
Max Uf = 4.58
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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Multiple analysis
� Frigg TCP2 MSF removal
Transportation
Lifting Condition
MSF: Main Support Frame
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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How can Sesam GeniE help you to design a topside structure
Fatigue
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
Fatigue of topsides
� Sesam supports 3 options- Deterministic fatigue (regular waves, time domain wave load
analysis)- More accurate wave loads (any theory and proper drag)- Simple and straight forward
- Stochastic fatigue (spectral wave load analysis)- Structural dynamics and better coverage of environmental
conditions- Prior to fatigue analysis partial damage may be set
- Time domain fatigue (irregular waves, time domain wave load analysis) – also known as Rainflow Counting Fatigue (RFC)- Wave loads to instantaneous free surface (also for irregular
sea states)- Non-linear pile soil effects
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© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
Fatigue of topsides
� Include a refined shell model (finite element model) in the global model for the purpose of computing stresses, SCF’s for beam fatigue or direct shell fatigue
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Use the GeniE SnackPack to autoconvert from beam to shell
© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
Fatigue of topsides
� Results can be used to derive SCF for use in traditional beam fatigue
� Results can be used to do fatigue of shells – FE size same as thickness and should be as quadratic as possible
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© Det Norske Veritas AS. All rights reserved.
SesamTM
3 December 2012
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