Sesam - A Complete System for Strength Assessments of Fixed Structures

Pål Dahlberg, Principal Sales Executive, DNV Software

April 2012

SesamTM 40 years of success

A complete system for strength assessments of fixed structures

© Det Norske Veritas AS. All rights reserved.

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Efficient engineering of fixed structures

Save man-hours and increase quality by using the latest available capabilities in concept technologies for

- Structure modelling

- Loads & Environment modelling

- Forces, stresses, deflections

- Local models in global model

- Beam code checking

- Design iterations including redesign of members

- Fatigue

- Launching and upending

Fixed structures

- Jackets, Jack-Ups, Bridges, Flare-booms….


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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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Closing the design loop – our strength

Efficient data transfer from initial modelling through

analysis, results processing and code checking

- “How long time does it take from modelling to first result?”

Efficient member code check iterations

- “What is the effect of modifying a section or code check

parameters without re-running complete analysis?”

Efficient update of model based on code check iterations

- “How long time does it take to re-generate a code

check-report based on a full re-run of model and analysis”


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How can Sesam help you – Making a model in GeniE Structure


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From modelling to stochastic fatigue

- Linear structural analysis of unlimited size

- Hydrodynamic and pile/soil analysis

- Code check of beams and joints

- Fatigue and earthquake analysis

- Gust wind fatigue included

- Non-linear analysis (push-over)

- Launching & upending analysis

Overall capabilities for fixed structures


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The Sesam Jacket Package

Packaged to meet your needs

- Topside, equipments, flare booms, bridges...

- Supporting structure (hydrodynamic and structural)

- Pile/Soil (non-linear)

Based on Morison equation

- Wave, current, wind

- Deterministic or stochastic

Code checking, fatigue, result presentation,

re-design, design reporting, push-over (non-linear),

launching

GeniE is the main tool – supported by

- Sestra, Wajac, Splice, Framework, Usfos, Installjac


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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

The SESAM suite of programs


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Application domains of GeniE

Jackets


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Application domains of GeniE


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The benefit of concept technology

Dynamic adjustment of can, stub, cone and gap when

modifying chord or brace properties

seen from above


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GeniE uniqueness – structure modelling

Parametric modelling – define variables in script files

4.27E07 3.58E07

Wizard for GeniE scripting_rev1.xls


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Demo-time Make a local shell joint in a jacket model


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Demo case – The base model

Structure (jacket beams only), piles, soil, environment


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Some typical results viewed in the plug-in component

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http://www.glview.com/plugin



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The selected joint will be converted to a shell model

- Beam model: Max deformation is 0.825 mm


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Max axial stresses

469 kpa at 1 m

480 kpa at 0 m


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Demo case – Convert beams in joint to shells

Mesh density of shell 0.125 meter


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Deformations correspond to pure beam model


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The stresses differ from pure beam model – as expected


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Some typical results viewed in the plug-in component

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Demo case – speed!

Question becomes – how long time does it take

to convert the beam joint to a shell model and

re-run analysis?

- 1 day

- 1 hour

- 30 min?

- 15 min?

- 10 min?

You can start your stop watches now

- …..and not using a predefined special purpose build

script for this case….

http://www.online-stopwatch.com/full-screen-stopwatch/


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How can Sesam help you – Making a model in GeniE Loads


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The benefit of concept technology

Load or mass definitions

from equipments

- Automatic

- Always in balance

- Load patterns – footprints

- Load patterns – primary or

secondary beams

Traditional load or mass

definitions

- Point loads

- Line loads

- Pressure loads

- Point mass

- Temperature loads

- Prescribed displacements


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GeniE uniqueness – load application

Easy to apply loads to complex shapes


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Hydrodynamic analysis slender structures

Hydrodynamic analysis of stationary vessels

- Morison equation on beam model

- Several wave theories (Airy, Stoke 5th, Dean stream

function, Cnoidal and Newwave) including the current

- Wind included in deterministic analysis or separately

Results

- Deterministic load calculation in time domain

- Calculation of force transfer in the frequency domain

- Time domain simulation of loads for a given short

term sea-state

- Global responses including rigid body motions and

sectional forces/moments

- Pressure and accelerations

- The loads are automatically used by subsequent

structural analysis


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Pile/soil analysis

Non-linear analysis

Soil modelling

- Scour

- Soil types sand and clay

- P-Y, T-Z and Q-Z curves

- Standards and user defined

- Soil curves

- Soil data

- Soil sub-layers

Pile

- Modelling

- Characteristics

- Seabed scour


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How can Sesam help you – Making a model in GeniE Analysis


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Structural analysis & design

Linear static and dynamic analysis

- Unlimited in size using standard hardware for large problems

Stress and deflection assessments

- Efficiently combine results, scan results and present

results for large models with many loadcases

Code checking yields utilisation factors

- Beams according to API/WSD & AISC, API/LRFD & AISC,

Norsok & Eurocode, ISO and DS

- Stiffened and un-stiffened plates according to API,

DNV RP C201.1, NPD and PULS (DNV RP C201.2)

Fatigue life

- Deterministic (real waves) and stochastic approach (unit

waves with load transfer functions) for beams

- Stochastic approach for plates

- Gust wind fatigue for beams


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Local analysis

Characteristic t x t


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How can Sesam help you – Result assessment Beam deflections and stresses


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Beam stresses

2D graphs, scanning and envelopes

- Print to report

Single load case

Envelope (max/min)


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Beam deflections

2D graphs, scanning and envelopes

- Print to report

Envelope (max/min)

Single load case


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How can Sesam help you – Result assessment Code checking of beams and joints


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Code checking jackets/jack-ups/topsides

Approach

- Make capacity manager(s)

- Define members and/or joints

- Specify code of practice, loadcases and

code check settings

- Compute code checking forces

- Run code check

- Reporting – graphically or text based

- Re-design of members

- Re-run all to update mass and stiffness


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Supporting beam and tubular joint

code check standards

- API WSD 2002 (incl. AISC 2005)

- API WSD 2005 (incl. AISC 2005)

- API LRFD 2003 (incl. AISC 2005)

- NORSOK 2004 (incl. Eurocode 2005)

- ISO 19902 2007 (incl. Eurocode 2005)

- DS 412 / 449



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Create & modify joint capacity members

Used in punching shear


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Demo case

- Topside member code checking

- Jacket tubular punching shear check


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How can Sesam help you – Result assessment Fatigue


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Principles for fatigue - basics

Miner’s rule of cumulative damage gives a usage factor (interaction ratio)

Fatigue life = target fatigue life / usage factor

Framework fatigue analyses

- Deterministic according to American Welding Society (AWS)

- Many waves stepped through structure

- Static (or dynamic) linear analysis

- Stochastic (or spectral) according to Vugts & Kinra

- Frequency domain wave load analysis

- Quasi-static or dynamic frequency domain analysis

- Rainflow counting (new in Sesam 2011 )

- Regular or irregular wave load time series

Which method to use?

- Your decision

fatigue


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Principles for fatigue – SCF’s

3 SCFs for each hotspot

- Axial stress – SCFax

- In-plane bending stress – SCFby

- Out-of-plane bending stress - SCFbz

Type of SCFs

- DEFINE FATIGUE-CONSTANTS … - Global SCFs where no other SCFs assigned

- Minimum SCFs when parametric formulae used

- ASSIGN SCF JOINT … - LOCAL / GLOBAL

- PARAMETRIC: Efthymiou, Kuang, Wordsworth, Lloyds, Smedley

& Fisher

- ASSIGN SCF MEMBER … - LOCAL / GLOBAL

- Parametric: BUTT-WELD / CONE-TRANSITION

in-plane

bending

out-of-plane

bending

axial force

x z

local beam

coordinate system


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Deterministic fatigue

Wajac

- Several wave directions

- Several waves (any theory) for

each direction

- Each wave stepped through

structure (non-linear drag)

Sestra

- Structural analysis

- Loads = directions waves steps

- No other loads (*)

Framework

- Maximum stress difference for each

wave gives stress range

- Environmental data:

long term wave height distribution

determines number of cycles

stress

stress range:

S = max. diff.

wave directions

waves: theory + height + length

steps

H

Hi

log N ni

(*) Utility tool – DetSfile - converts “regular loads” to “wave loads”


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Stochastic fatigue

Framework

- Each wave direction given probability

- Wave statistics defined and assigned to directions:

- Create scatter diagram - long term distribution of wave

heights vs. zero up-crossing

- Assign wave spectrum to scatter diagram

- Create wave spreading function and assign to scatter

diagram

Wajac

- Several wave directions

- Several frequencies (linear harmonic waves) for each direction

- Linearization of drag

Sestra

- Quasi-static or dynamic analysis

- Loads = directions wave frequencies

- Complex loads and complex results

wave directions

waves: harmonic, unit height

1


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Stochastic fatigue

Unit waves, different frequencies / directions

Demands linearity wave height / wave force

- Linear harmonic Airy wave

- Linearization of drag (FD = ρ (D/2) Cd vn |vn|)

- Linearization of variable submergence: max!

- Choose between two linearization methods:

- Equivalent linearization

- Linearization with respect to wave height

- No contribution from current to loads

Distributed loads (load transfer functions) transferred to

structural analysis for all waves

Frequency domain complex loads

Prepares for quasi-static or dynamic structural analysis

(Sestra) and stochastic fatigue analysis (Framework)

1

1


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Deterministic & Stochastic Fatigue

Some pro’s and con’s

Deterministic

- More accurate wave loads (any theory and proper drag), but many load cases

- Together with piles and soil

- Simple and straight forward

- Often used to establish the general acceptability of fatigue resistance or screening to identify

most critical details to be considered in stochastic approach

Stochastic

- Structural dynamics and better coverage of environmental conditions

- Prior to fatigue analysis partial damage may be set

- More preparation of input needed – need to run eigenvalue analysis to determine quasi-static

approach or not

- Natural periods higher than 3 sec. -> use dynamic


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How can Sesam help you – What is unique about us?


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Our value proposition and uniqueness

Closing the design loop by modern concept modelling and work process tools

- Quick modelling

- Local model in global model

- Scripting/parametric models

- Changes during design

- One model – many analyses

- Interaction with hydro

- Advanced hydrodynamics

- Beam/plate code checking

- Beam/plate fatigue

- Non-linear pushover

- Reporting


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“Keppel chose Sesam software for its user-friendliness

and technical reliability as well as cost-effectiveness.”

Paul Liang, Section Manager, Engineering Division Keppel O&M.


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Safeguarding life, property

and the environment

www.dnv.com

Sesam - A Complete System for Strength Assessments of Fixed Structures

Technology

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