suc brasil 2012 : sesam for topsides

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


SesamTM

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Topside structures (including modules, flare booms, bridges)

� On jacket- Often members only

� On floater- Often plates and stiffeners and members

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Common challenges in design


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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?


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How can Sesam GeniE help you to design a topside structure

Structure


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Structure modelling

� Easy to facilitate the range from small to large and complex


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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


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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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Deadweight loads


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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


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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


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Environmental loads


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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


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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


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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


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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


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Results assessment


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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


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Beam forces and stresses

� Forces and stresses in 2D view as well as tabular


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Check deflection ratio against AISC levels

� Allowable deflection ratio 180, 240, 360 and scanning all load cases


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Code checking of members & stiffened panels


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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


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Document code check results

� Graphically – complete model


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Document code check results

� Graphically – parts of structure only


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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


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Redesign – single members

� Select a capacity member for redesign

� Modify parameters- Preliminary results automatically computed


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Redesign – single members

� Look at all details (Full Table)- Shown with colour coding


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Redesign – multiple members

� Select capacity members for redesign

� Modify parameters- Preliminary results automatically computed


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Redesign – segmented beams

� Before and after


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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


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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


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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


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Code checking of stiffened panels - offshore

� Yield check of plates – based on membrane stress- Includes a safety factor S


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Multiple analysis


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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


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Multiple analysis – graphic results

� Different results at your finger-tips- Bending moments shown

Lifting Condition

Transport Condition

In_place Condition


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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


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Multiple analysis

� Frigg TCP2 MSF removal

Transportation

Lifting Condition

MSF: Main Support Frame


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Fatigue


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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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SesamTM

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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


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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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Safeguarding life, property and the environment

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suc brasil 2012 : sesam for topsides

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