Sesam Hydrodynamics Training Oct 2012

Hydrodynamic analysis in Sesam DNV Software Seminar for ATKINS Fan Joe Zhang, Sesam Business Development Manager September, 2012

About the Seminar 

I am ZHANG Fan Joe, DNV Software - I do SESAM business development, user courses, etc.



Responsibility for Sesam lies with DNV Software in Houston, USA - DNV Software is a commercial software house in DNV - Serving approximately 150 commercial Sesam customers



Offices in Oslo, London, Houston, Rio de Janeiro, Kuala Lumpur, Kobe, Busan, Beijing, Shanghai, Singapore, Kaohsiung and Hyderabad H yderabad

Hydrodynamic analysis in Sesam September, 2012

Day 1 – Presentations Time

Topic

09:00

Sesam for floaters – an overview

09:30

Hydrostatic and dynamic analysis – The importance of nonlinear analysis

10:30

Break

10:45

An overview of coupled analysis, mooring and riser design

11:30

Q&A

12:00

Lunch

13:00

Air gap analysis – Traditional frequency-domain frequency-domain prediction vs. time-domain analysis

14:00

FPSO full ship analysis – an overview

15:30

Break

15:45

Fatigue assessment of TLP tendons – an overview

16:30

Summary


Day 2 – Examples and Demos Time

Topic

09:00

Recap of first day

09:15

HydroD – Non-linear analysis of a pipe-laying vessel with Morison model

10:30

Break

10:45

HydroD – Non-linear analysis of a semi-submersible with anchors

11:30

Q&A

12:00

Lunch

13:00

DeepC – Pipe-in-pipe analysis

14:00

DeepC – Riser fatigue analysis

15:30

Break

15:45

UmbiliCAD and Helica - Capacity check and detail section fatigue analysis of umbilical

16:30

Summary


Information on www.dnv.com/software

NEW!

Get more information on Sesam


Documentation 

User Manuals -

-

Most manuals in electronic format (pdf) Part of installation -

(C:\Program Files\DNVS)...\SESAM\MANUA Files\DNVS)...\SESAM\MANUALS LS

- Available from Brix Explorer 

Status Lists provide additional information: -



Open through Internet or download, see next page

Reasons for update (new version) New features Errors found and corrected Etc.

Look up and search Status Lists: -

Part of installation -

-

(C:\Program Files\DNVS)...\SESAM\STATUS\status Files\DNVS)...\SESAM\STATUS\status.html .html

Updated Status Lists through Internet, see previous page


Support 

Phone:

+47 6757 8181



E-mail:

[email protected]



Support covers:



-

Guidance in how to use programs to solve problem defined by you

-

Locating and correcting deficiencies (bugs, etc.)

-

Guidance to get around deficiencies, alternatively updated program

To assist you as efficiently as possible we generally need: -

Concise information (have it readily available when calling us)

-

Program input to reproduce problem -

Compress files to reduce size!


Safeguarding life, property and the environment www.dnv.com


SesamTM Continuing 40 years of success The integrated strength assessment system for floating structures Joe Zhang, Sesam BD Manager, DNV Software October, 2012

The Sesam Floating Structure Package 

Linear structural analysis of unlimited size



Hydrostatic analysis including stability code checking



Hydrodynamic analysis



Buckling code check of plates and beams



Fatigue analysis of plates and beams



Coupled analysis, mooring and riser design



Marine operations

The integrated strength assessment system for floating structures October, 2012

A typical workflow 

From modelling to stochastic fatigue - Concept modelling of floaters - Structure analysis model - Hydrodynamic model

- Hydrostatic analysis - Hydrodynamic analysis in frequency domain - Hydrodynamic analysis in time domain - Statistical post-processing of hydrodynamic results - Design wave or direct load approach - Transfer of all loads to analysis

- Structural finite element analysis - Post-processing and code-checking - Global and refined fatigue


Sesam – a fully integrated analysis system 2. Pressure loads and accelerations

1. Stability and wave load analysis

Wave scatter diagram

L o a d

Local FE analysis

t r a n s f e r

5. Local stress and deflection & fatigue

FE analysis

4. Global stress and deflection & fatigue screening The integrated strength assessment system for floating structures October, 2012

3. Structural model loads (internal + external pressure)

Main tools – floating structures package 

GeniE for modelling and structural analysis - Supported by - Patran-Pre, Presel - Sestra - Xtract, Cutres, Submod, Stofat



HydroD for hydrostatics and hydrodynamics - Supported by - Wadam, Waveship, Wasim - Postresp, Xtract



DeepC for installation, mooring and riser analysis - Supported by - Mimosa, Simo, Riflex - Xtract


Model building


Model building in GeniE 

Purpose - Panel and Morison model for use in hydrostatics and hydrodynamics

- Structure model to define compartments and masses for use in hydrostatics and hydrodynamics - Finite element models (FE) for use in structural analysis - The discretization (mesh size) may be different for panel and FE models Hydro models

FE model

Concept model


Structural

Model building in GeniE 

Various analysis models can easily be created from same concept model

Local analysis model e.g. refined mesh size 0.5 m and global mesh size 3 m

Global analysis model e.g. mesh size 3 m


Design load based versus direct analysis 

Design load (aka rule) based analysis - The loads are defined manually including those from hydrostatic or hydrodynamic analysis - Acceleration effects are modelled with centripetal accelerations or loads - The loads are often described in class notifications or codes of practices

- Limited number of loadcases 

F = Static loads + mass x acc

Direct analysis - The loads include hydrodynamic pressure loads - The loads include acceleration loads – hydrodynamic acceleration applied on structural mass, equipment masses and compartment masses - Many loadcases, but more reliable



For both analyses the same concept model is used - Significant savings in modelling time


F = Compartment x acc + mass x acc + hydro-pressure

What you can do with HydroD 

Model environment and prepare input data for hydrostatic and hydrodynamic analysis



Perform hydrostatics and stability computations (including free surface)



Calculate still water forces and bending moments





Perform hydrodynamic computations on fixed and floating rigid bodies, with and without forward speed (hydrodynamic coefficients, forces, displacement, accelerations etc) Transfer hydrostatic and hydrodynamic loads to structural analysis HydroD D1.3-04 Date: 31 May 2005 15:01:34

GZ-Curve

4 3 2 ] 1 m [ Z 0 G 1 2 -

0

50 100 Heel Angle [deg]

150

GLview Plugin not installed. Press here to install plugin The integrated strength assessment system for floating structures October, 2012

Hydrostatic analysis


Hydrostatic analysis 

Typical tasks - Define cross sections - Define loading conditions - Draft, trim, heel - Mass & compartment contents - Auto balancing tools - Balance 3 or more filling fractions - Balance three tanks, keep the others full or empty, minimizing GM

- Flood openings - Weather tight options

- Create and execute stability analysis - Multiple analysis - Wind moment calculations

- Run code checks - Including intact and damaged conditions

- Run allowable vertical centre analysis


Hydrostatic analysis – typical results 

GZ Curve



Moment of force



Openings (envelope)



Cross section data



Hydrostatic data from analysis


Hydrostatic analysis - results 

Create a range of cross sections - Still water force and moment distribution

- Mass and buoyancy separate 

Split moment ? - X moment of a longitudinal cross section


Hydrostatic analysis - results 

Calculations - Metacentre height (dry and wet)

- Free surface corrections - COG (dry/wet) - COB 

Compartments - Volume - Mass - COG - Free surface centre


Code check 

Supported offshore code checks, intact and damaged conditions - NMD

- IMO MODU - ABS MODU - User defined


AVCG/KG analysis 

Allowable Vertical Centre of Gravity (KG) - Uses stability criteria of the selected rule to find allowable VCG (vertical centre of gravity)

- The maximum VCG value that satisfies each criteria is calculated. The minimum of these values is the VCG that satisfies all criteria, this is reported as the ” AVCG min curve”.




Hydrodynamic analysis 

Zero speed - Linear analysis: Wadam - Non-linear analysis: Wasim



Forward speed/current - Linear / non-linear: Wasim


Hydrodynamic analysis 

Hydrodynamic results can be displayed and animated by Xtract



Each frequency/heading combination or time series is animated separately



Very useful for checking of results



Data which can be displayed: - Wave elevation

- Pressure on structural model - Rigid body motion - In addition stresses, beam forces and displacements from finite element analysis


Frequency domain analysis 



The Frequency domain analysis is used to calculate the transfer functions (RAOs) Input is a ”Frequency domain condition” - Direction set - Frequency set - Amplitude (default value 0.1)



Typical tasks (built on hydrostatic model) - Morison sections - Pressure area elements - Off-body points (wave pressure, wave particle velocities) - Define Wadam run - Global response variables - Load transfer


Time domain analysis 

Use time domain analysis to simulate a physical sea state



Can create snapshots of loads



The sea state can be defined by - ”Irregular time condition” - Wind sea (direction, wave spectrum, spreading function) - Swell

- ”Regular wave set” (period, height, phase, direction) - Calm sea


Time domain non-linear analysis 

Effects included in the non-linear analysis - Hydrostatic and Froude-Krylov pressure on exact wetted surface - Exact treatment of inertia and gravity - Quadratic terms in Bernoulli equation - Quadratic roll damping







Morison models important also for floaters with frame structures (e.g. SemiSubs), truss-Spar, pipelaying vessel…

Nonlinear Morison drag force considered in time domain. Better representation of damping. Using incoming wave kinematics, force integrated up to the exact in-coming wave free surface.

GLview Plugin not installed. Press here to install plugin



The importance of Morison models - Calm sea run with 5 degree heel angle. No additional roll damping assigned.

- With Morison model, the roll motion is damped out.

5 4 3 e d u t i l p m a n o i t o M

2 1 0 1 2 3 4 5 -

0

20

Roll - CalmSeaRun_noMorison Roll - CalmSeaRun_Morison


40

60

80

100

120 Time


The importance of roll damping - Roll motion in Oblique wave 5 th order stokes wave (period 12s, wave height 20m), No additional roll damping assigned. - With Morison model, larger response in the beginning stage, but more s tabilized due to damping from stinger. 0 1 8.161


2

1.8471

0 2 4 6 8 0 1 -

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

Time

Roll - Stokes5_Morison

Roll - Stokes5_noMorison


Post processing and load transfer


Statistical post processing 

Postresp is used to perform statistical post processing - Plotting of response variables – RAO (H W ( ω ))2

- Combinations of response variables - Calculating short-term response - Calculating long-term statistics

Heave response The integrated strength assessment system for floating structures October, 2012

Pitch moment

Split moment

Short-term response 

Wave spectra for a range of Tz - SW(ω) - Pierson-Moskowitz

- ISSC - Jonswap - Torsethaugen - Ochi-Hubble - General Gamma

PIERSON-MOSKOWITZ



Response spectra for given wave spectra - Sr( ω ) = SW( ω ) x (HW( ω ))2



Significant response - Long-crested sea

- Short crested sea including wave spreading

Wave spreading The integrated strength assessment system for floating structures October, 2012

Statistical computations 

Short term statistics - For a given duration of a sea state - Compute most probable largest response - Compute probability of exceedance - No. of zero up-crossings

- For a given response level - Compute probability of exceedance

- For a given probability of exceedance - Compute corresponding response level 

Long term statistics - Assign probability to each direction - Select scatter diagram - Select spreading function - Create long-term response



Direct analysis, improved focus on - Ultimate strength (catastrophes) - Fatigue (pollution) - Different environmental conditions - Vessel lifetime



Rule loads do not always give the t he truth - Direct calculations may give different loads - Examples 2000000

- Ultimate strength loads - VBM and VSF

150000

1500000

] m N1000000 k [

100000

] N k [

50000

500000 0

0 0

- Fatigue loads

0. 2

0. 4

0. 6

0. 8

1

0

0.2

0.4

VBM (linear)

- External pressure Rule Direct

Pressure


0. 6

VSF (linear)

0. 8

1


Design load based - Make concept model - Beams, plates, equipment, compartment content

- Create structural model - Compartment loads

- Run analysis - Explicit loads

- Result assessment - Stress evaluation, code checking and rule based fatigue (“simplified fatigue”)

- Refined analysis - Make local details part of global model and re-run



Direct analysis - Make concept model - Beams, plates, equipment, compartment content

- Create panel model - Compartment masses

- Hydrostatic analysis - Hydrodynamic analysis - Structural analysis - Hydro pressure/acceleration p ressure/accelerations s

- Result assessment - Stress evaluation, code checking, stochastic fatigue

- Refined analysis - Make local model and re-run using sub-modelling techniques - Stress evaluation, code checking, stochastic fatigue

- Mooring and riser analysis


Load transfer to structural analysis 

Accelerations



Pressures



Rigid body motions



AddedMass (compartments) - Additional mass from compartment filling in HydroD


Structural analysis


Structural analysis 

Linear structural analysis



General post-processing



Code checking of beams and plates



Global fatigue screening



Refined analysis - Sub-modelling techniques



Refined fatigue analysis

Stresses

Fatigue life The integrated strength assessment system for floating structures October, 2012

Advanced Methods for Ultimate and Fatigue Strength




SesamTM Continuing 40 years of success Hydrostatic and hydrodynamic analysis - The importance of nonlinear analysis Fan (Joe) Zhang, Sesam BD Manager, DNV Software October, 2012

What can you do with HydroD? 

Model environment and prepare input data for hydrostatic and hydrodynamic analysis



Perform hydrostatics and stability computations (including free surface)



Calculate still water forces and bending moments



Perform hydrodynamic computations on fixed and floating rigid bodies, with and without forward speed (hydrodynamic coefficients, forces, displacement, accelerations etc.)



Transfer hydrostatic and hydrodynamic loads to structural analysis HydroD D1.3-04 Date: 31 May 2 005 15:01:34

GZ-Curve

4 3 2 ] 1 m [ Z 0 G 1 2 -

0

Hydrostatic and hydrodynamic analysis - The importance of nonlinear analysis October, 2012

50 100 Heel Angle [deg]

150

Why HydroD? 

Hydrostatics, hydrodynamics in frequency-domain and time-domain



Same model for all the analysis, easy comparison of results from frequency/time-domain



Wizard – Step-by-step guide for the new users



Zero speed to high speed vessels with mono- or multi-hull



First-order, mean second-order and QTF for frequency-domain wave force analysis



Linear or non-linear time-domain wave force analysis

 Automatically

composite load transfer to single structure model



Same statistical post-processing tool for hydrodynamic performance evaluation


Why HydroD?  Anchor

and TLP elements simulation



Multi-body analysis – hydrodynamic, stiffness and damping coupling are included



Compartments modeling – automatically balancing calculation!

 Automatically

composite load transfer to structure model



Nonlinear time-domain analysis – More accurate analysis when regular analysis is not fit for purpose - Wave kinematics instead of wave diffraction - Nonlinear Morison drag force considered in t ime domain - 5th order Stokes wave in particular important in shallow water - Load transfer to instantaneous water surface


The On-line documentation On-line help: Help | Help Topics…


Wizard – Hydrostatics & Stability, Wadam and Wasim Step-by-step guide! Make is much easier for the new users!!


Online Help – getting useful information on time! Light bulbs give detailed information about each input field or button

Book-icons give general information about the dialogue


General environment inputs for all kinds of analysis

 Air





Locations, (one ore more objects)

- Wind profiles (hydrostatic analysis)

- Depth, density, gravity

Directions

- Referring to frequencies, directions, spectrum etc., defined in Directions and Water

- Direction set, directions (hydrodynamic analysis) 

Water - Frequency set, spectrum, current, wave spreading etc. (hydrodynamic analysis)


Easy to reuse in different analysis!

Hydro model – same model in different analysis 

The assembly of all the models to be used in an analysis, including their properties



Definition of models in a multi-body analysis - Reuse existing hydro models

Stability Wasim


Panel model – generated by conceptual modeling tool



The default panel model is a Sesam model (T*.FEM)



Note that a panel model on Wamit (GDF) format can also be used



Symmetry is not valid for hydrostatic/stability analysis



Translation in x or y direction is only valid for models without use of symmetry, i.e. the complete model must be created in the preprocessor


Section model – directly define the section curves



The section model (pln-file) describes the vessel geometry by a set of curves


Mass model – 4 different approaches 

Data may be given in different coordinate systems



Mass & CoG (x, y) may be calculated from the panel model. Other data must be given manually



Directly using structure model as mass model is possible.


New mass calculation for Wadam – much faster!! 

HydroD is now used to calculate the mass matrices for Wadam



For large models with compartments the execution time will be significantly improved



The new mass calculation is more accurate – the elements are now split exactly on the cross sections, not using a point mass cloud.



There are small deviations in the mass calculation compared to the previous method, especially for the sectional mass matrices.

Global response – insignificant deviations Hydrostatic and hydrodynamic analysis - The importance of nonlinear analysis October, 2012

Sectional loads – minor deviations

Sectional loads – single or multiple sections 

Calculating of cross sectional forces and moments



Wadam has a maximum of 25 and Wasim 100 sections



Stability has no limitation on number of sections



Used to valid the load transfer quality


Compartment properties 

Define use of Compartments in the wizard



Define properties from the browser/tool bar


Automatically balancing with two approaches



Adjust the tank filling to match the loading condition



Will try to have tanks full or empty



Select three or more filling fractions and click “ Auto Balance”.



Will try to maximize GM



Need to tune three tanks at the end



Required filling fractions are automatically created as properties



Combinations are tried in ”intelligent” order



“All combinations” may need a long time to finish


Hydrostatic Report – Various data 

GZ curve



Moment of Force -



Righting moment Heeling moment

Cross Section Data



Moment of Force



Openings



Zero crossings are calculated

-



Cross Section Data



Integrals can be calculated

-



Information



Openings



Moment of Force -

-

Distance to waterline Zero crossings

Righting moment Heeling moment


Sectional forces Sectional moments Split into contributions from mass and buoyancy Info: Detailed print, also available on file



Information -

Mass & Buoyancy Centre of flotation Trim moment Detailed print of tank data Similar information from the browser

Hydrostatic Report – Animation  An

animation is created for each hydrostatic analysis, showing the heeling motion of the structure



The animation is displayed by opening the eye in the browser



The animation can be controlled by “Modeling draw style”


Hydrostatic Report – Wind heeling moment 

The computed wind surface may be displayed at a certain heeling angle - The colours are given by drag coefficients



The display may be controlled from ‘Modelling Draw Style’ and ‘ColorPalettes’



Triangles are split against free surfaces/cross-sections to give exact results.


On file Report – Available on both HTML and XML formats


Rule check 

Choose between stability codes for ships and for mobile offshore structures



Column stabilized unit is calculated automatically (changed in HydroD 4.0)





- Stability angles - Righting/heeling ratio - MaxGZ

The rule check report is found under ”Information”

- GZArea - GZ with/out deck




The user defined rule check can be used to check

Stability angles must be defined to create the integration/search ranges

AVCG analysis  Allowable

VCG

- Uses stability criteria of the selected rule to find allowable VCG (vertical centre of gravity) - The maximum VCG value that satisfies each criteria is calculated. The minimum of these values is the VCG that satisfies all criteria, this is reported as the ”AVCG min curve”.

 Allowable

KG

- VCG is reported in the input system - When the keel is at Z=0, AVCG is identical to Allowable KG - Otherwise the keel z coordinate must be subtracted from the AVCG values to get allowable KG.


Hydrodynamic analysis in Sesam 

Zero speed - Linear analysis: Wadam - Non-linear analysis: Wasim



Forward speed/current - Linear / non-linear: Wasim


Hydrodynamic analysis 

Frequency domain - Wave directions - Frequency set - (Amplitude)



Time domain - Irregular waves - Main direction - Wave spectrum - Spreading function

- Regular wave set


Frequency domain analysis 

The Frequency domain analysis is used to calculate the transfer functions (RAOs)



Input is a ”Frequency domain condition” - Direction set - Frequency set - Amplitude (default value 0.1)



Typical tasks (built on hydrostatic model) - Morison sections - Pressure area elements - Off-body points (wave pressure, wave particle velocities) - Define Wadam run - Global response variables - Load transfer


Time domain analysis 

Use time domain analysis to simulate a physical sea state



Can create snapshots of loads



The sea state can be defined by - ”Irregular time condition” - Wind sea (direction, wave spectrum, spreading function) - Swell

- ”Regular wave set” (period, height, phase, direction) - Calm sea


Time domain non-linear analysis 

Effects included in the non-linear analysis - Hydrostatic and Froude-Krylov pressure on exact wetted surface - Exact treatment of inertia and gravity - Quadratic terms in Bernoulli equation - Quadratic roll damping


Post processing and load transfer


Statistical post processing 

Postresp is used to perform statistical post processing - Plotting of response variables – RAO (H W ( ω ))2 - Combinations of response variables - Calculating short-term response - Calculating long-term statistics

Heave response Hydrostatic and hydrodynamic analysis - The importance of nonlinear analysis October, 2012

Pitch moment

Split moment

Short-term response 

Wave spectra for a range of Tz - SW(ω) - Pierson-Moskowitz - ISSC - Jonswap - Torsethaugen - Ochi-Hubble - General Gamma

PIERSON-MOSKOWITZ



Response spectra for given wave spectra - Sr ( ω ) = SW ( ω ) x (H W ( ω ))2



Significant response - Long-crested sea - Short crested sea including wave spreading

Wave spreading Hydrostatic and hydrodynamic analysis - The importance of nonlinear analysis October, 2012

Statistical computations 

Short term statistics - For a given duration of a sea state - Compute most probable largest response - Compute probability of exceedance - No. of zero up-crossings

- For a given response level - Compute probability of exceedance

- For a given probability of exceedance - Compute corresponding response level



Long term statistics - Assign probability to each direction - Select scatter diagram - Select spreading function - Create long-term response


Combinations of response variables 

Built-in combinations - Displacement, velocity or acceleration in specified points (absolute value in any of the x, y or z-directions) - Relative vertical motion (relative to incoming wave) -

CREATE RESPONSE-VARIABLE COMBINED-MOTION

- First and second derivatives



-

CREATE RESPONSE-VARIABLE FIRST-DERIVATED

-

CREATE RESPONSE-VARIABLE SECOND-DERIVATED

General combinations - Specified by user -

CREATE RESPONSE-VARIABLE GENERAL-COMBINATION


Air-gap calculation 

Define an off-body point in HydroD on the surface, ELEV1



Define a point in Postresp with the same X and Y, and Z below deck, PT1



Create combined motion for this point, CM1



Create a general combination CM1-ELEV1



This is relative air-gap

 Absolute

air-gap = Original airgap - relative


Hydrodynamic analysis 

Hydrodynamic results can be displayed and animated by Xtract



Each frequency/heading combination or time series is animated separately



Very useful for checking of results



Data which can be displayed: - Wave elevation - Pressure on structural model - Rigid body motion - In addition stresses, beam forces and displacements from finite element analysis


Comparison of hydrodynamic analysis modules Wadam

Waveship

Wasim

Ships







Offshore structures







Morison model







Forward speed







Global response







Local loads







Non-linear option







CPU consumption








Wasim main features 

3D solver





Rankine panel method



Time domain with optional transformation to frequency domain



No limitations in vessel speed or wave frequency and direction



Global and local responses

 Automatic

load transfer to FEM solver

Sestra


Non-linear extension: - Hydrostatic and Froude-Krylov pressure on exact wetted surface - Exact treatment of inertia and gravity - Quadratic terms in Bernoulli equation - Quadratic roll damping

Comparison of different methods


Quadratic roll damping for Wadam 

Select ”Use stochastic linearization” and ”Use global quadratic coefficient” in the ”Roll damping” section in Wadam.



The global quadratic coefficient is defined by a ”Roll damping” coefficient in the loading condition (defined the same way as for Wasim)


Example of quadratic roll damping 

Global response was calculated for three cases - No roll damping - Linear roll damping - Quadratic roll damping (the damping coefficient is comparable to the linear case)



Roll response:

90 degree wave direction


Morison models in Wasim  Anchor

and TLP elements

- Linear and non-linear analysis - Same model as in Wadam 

Morison 2D-elements and pressure area elements - Non-linear only - Exact handling of viscous drag term - Relative velocity

- “Unlimited” number of sub-elements 

Same procedure as Wadam for load transfer to Morison model - Structural model can be a single superelement


Morison model in Wasim 

Extend Wasim’s capability for floaters with frame structures, truss-Spar, pipelaying vessel…



Nonlinear Morison drag force considered in time domain. Better representation of damping.



Using incoming wave kinematics, force integrated up to the exact in-coming wave free surface.



Verified by comparing with Wajac and Wadam



Morison model in Wasim 5 4 3 e d u t i l p m a n o i t o M

2 1 0 1 2 3 4 5 -

0

20

40

60

80

100

Roll - CalmSeaRun_noMorison Roll - CalmSeaRun_Morison 

Calm sea run with 5 degree heel angle. No additional roll damping assigned.



With Morison model, the roll motion is damped out.


120 Time

Morison model in Wasim 0 1 8.161


2

1.8471

0 2 4 6 8 0 1 -

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

Time

Roll Roll - Stokes5 Stokes5_Mo _Moriso rison n

Roll Roll - Stokes5 Stokes5_no _noMo Moriso rison n



Roll motion in Oblique wave 5th order stokes wave (period 12s, wave height 20m), No additional roll damping assigned.



With Morison model, larger response in the beginning stage, but more stabili zed due to damping from stinger.


Verification of TLP element implementation TLP Hull Draft

31.394

Displacement

51231.3 Diameter

m m^3

19.507

m

Span

60.96

m

Width

9.754

m

Height

8.534

m

COG above sea surface

4.359

m

Total Weight

34580

Ton

Column

Pontoon

Tendon

Drill. Riser

Prod. Riser

12

1

11

1798.72

1867.1

1867.1

m

Top tension

1.104E+07

6.71E+06

3.35E+06

N

Axis stiffness

1.52E+07

4.77E+06

1.07E+07

N/m

Number Length



No motion control is taken in current study. study. The horizontal restoring is from the TLP elements only.



The frequency domain analysis is compared with WADAM, a decay run in calm sea is is done to verify the stability of the system.


WADAM vs WASIM


The motion given initial surge displacement (dis0=0.1, dt=0.15)


The motion given initial heave/pitch velocity (vel0=0.02, dt=0.15)


Tentative conclusion of TLP element testing 

The agreement on Heave/Surge/Sway motion is very good; Differences are f ound at low frequency side in Pitch/Roll/Yaw motion RAOs.



The eigenvalue taken from Wadam list file agree well with the data taken from time series of Wasim calculation.



The Surge/Sway/yaw motion eigenvalues are around 180/180/153



The heave/pitch/roll motion eigenvalues are around 2.9/3.35/3.35



Given small enough time step, the motions in all DOF are decaying.



The most important force contribution from the Morison model is the anchor element and the damping force due to the relative velocity.


Adjustment of the model as for anchor element testing 

Remove all TLP elements, add 12 anchor elements to the previous nodes of tendon elements.



The angle_x are 45, 135, 225, 315 for the middle anchor elements attaching at the bottom of each column. (+/-) 30 leads to angle_x of the side anchor elements.



The parameters of the anchor section and the overall setting-ups are shown in the figures.



Mass model is adjusted accordingly. COG is at (0,0,5) in the global coordinate system.


WADAM vs WASIM





The results with “_1” are those without damping from 2D Morison elements.





The results with “_1” are those without damping from 2D Morison elements.


Stokes 5th order wave – moving into more shallow water 

Only implemented for single harmonic component => Design wave Case I

Case II

d = 10m

d = 10m

H = 2.94m

H = 3.06m

T = 5.30 s

T = 8.69 s


Airy vs. Stokes wave H=10m, T=17.27s, d=50m (left)/30m (right), 180°, U=12.5m/s HydroD D 4.4-03 Date: 25 M ay 2010 17:21:05

HydroD D 4.4-03 Date: 25 M ay 2010 17:10:30

WasimAnalysis

WasimAnalysis 7

6

6

5

5

4

4

3 e d u t i l p m a n o i t o M

3

2

e d u t i l p m a n o i t o M

1 0 1 2 -

2 1 0 1 2 -

3 -

3 -

4 -

4 -

5 -

5 -

200

205

210

215

220

225

230

Incoming wave - Was imActivity_h10 Incoming wave - Wasim Activity_h10_s tokes


235

240

245

250

Time

200

205

210

215

220

Incoming wave - Wasim Activity_h10_d 30 Incoming wave - WasimActivity_h10_stokes_d30

225

230

235

240

245

250

Time

Airy vs. Stokes wave – Heave H=10m, T=17.27s, d=50m (left)/30m (right), 180°, U=12.5m/s HydroD D 4.4-03 Date: 25 M ay 2010 17:19:36

HydroD D 4.4-03 Date: 25 M ay 2010 17:16:38

WasimAnalysis

WasimAnalysis

5 4

3

3

2

2 e d u t i l p m a n o i t o M

1

1

e d u 0 t i l p m 1 a n o i t o 2 M

0 1 2 3 -

3 -

4 -

4 -

5 -

200

205

210

215

220

225

230

235

240

245

250

Time Heave - WasimActivity_h10_stokes

Heave - WasimActivity_h10


200

205

210

215

Heave - Wasim Activity_h10_d 30 Heave - Wasim Activity_h10_s tokes_d30

220

225

230

235

240

245

250

Time

Airy vs. Stokes wave – Vertical Bending Moment H=10m, T=17.27s, d=50m (left)/30m (right), 180°, U=12.5m/s HydroD D 4.4-03 Date: 25 M ay 2010 17:31:32

HydroD D 4.4-03 Date: 25 M ay 2010 17:30:37

WasimAnalysis

e d u t i l p m a d a o l l a n o i t c e S

WasimAnalysis

9 0 0 + e 3

9 0 0 + e 3

9 0 0 + e 2

9 0 0 + e 2

e d u t i l p m a d a o l l a n o i t c e S

9 0 0 + e 1

0

9 0 0 + e 1 -

200

205

210

215

220

225

230

LoadCros section_X_P3 My - Was imActivity_h10 LoadCros section_X_P3 My - WasimActivity_h10_s tokes


235

240

245

250

Time

9 0 0 + e 1

0

9 0 0 + e 1 -

200

205

210

215

220

225

230

LoadC ross ection_X_P3 My - Wasim Activity_h10_d30 LoadC ross ection_X_P3 My - Wasim Activity_h10_stokes_ d30

235

240

245

250

Time

Pressure reduction on parts of vessel 

It is expected that there should be pressure scaling only between the user specified pressure reduction zone in Case III.

wl_pres=1

am=5

wl_pres=1 am=5 [-50m, 50m]


”HydroMesh” - surface meshing for section models 

Improved meshing control – good for models like semi-submersibles



The user can control the splitting of the free surface



Stand-alone application, integrated in HydroD


User controlled surface meshing

Mesh size

Define corner points for the patch


Resulting mesh

User defined mesh with hydro pressure arrows




The mesh is exported as ssg, geo and fem file – can be used for both Wasim and Wadam



FEM file can be used as offbody points for Wadam. (xy plane of Panel model’s coordinate should be on free surface. No translation shall be assigned.)



FEM file can be also used as 2nd order free surface model.

Offbody points for Wadam




Model must be translated to water level at origin



The input file is T7374.FEM – symmetric and in the global coordinate system



Visualization in Xtract showing displacements

Free surface model for Wadam




The input file is T7373.FEM – no symmetry parts



Can be used as free surface model for Wadam Second-order analysis or Wave Drift Damping

Starting Sestra from HydroD 

Sestra can be started - from BRIX Explorer for Sesam - directly from HydroD (new) - Only standard quasi-static analysis

- Load case number listing available (consistent to Xtract loading case numbering)


Side by side configuration – convergence study  Analysis 

by Moss Maritime, Oslo, Norway

Meshes: - Coarse - 2000 elements in total - Medium - 6300 elements in total - Medium/fine - 11000 elements in total - Fine - 14000 elements in total


RAO’s


Single body vs. two bodies at 180°


Excitation forces


Added mass


Damping


Mean drift force


Buoy with moonpool


Free surface generated by HydroMesh


RAOs comparison between Wasim and Wadam

Heave Hydrostatic and hydrodynamic analysis - The importance of nonlinear analysis October, 2012

Pitch

Effects of “internal” free surface on motion (head sea)

Heave


Pitch

Animation of donut forced heave motion



Multi-body additional damping 

For multi-body analysis in frequency domain it is possible to run up to 15 different bodies. We have made such analysis even more powerful by allowing the user to specify an additional coupled damping matrix for the bodies.

Additional damping matrix. This layout shows a 12x12 matrix for 2 bodies


Improved compartment load retrieval 

Compartment load retrieval independent of sub-model - The definition of acceleration and zero pressure reference points allows that a submodel may be independent of a compartment - In other words, a sub-model may contain partial compartments also for load transfer - Flexibility in modelling compartment model and sub-models

Compartments global model


Sub-model at node

Load retrieval from compartments to submodel

User defined pressure reduction region  Apply

a user defined pressure reduction region on a selected part of the vessel

- The the method is only recommended on the part of the vessel which is wall-sided and should thus be controlled by the user - Benefit: User defined in addition to supporting the DNV rules - This option is available for both frequency and time domain analysis

User defined wall-sided part


User defined reference point 

User defined reference point for calculation of results -

-

More flexibility as the reference point can be used for calculation of hydrodynamic results like e.g. motions, forces and RAO’s Applicable for results from both frequency and time domain analysis

Surge 1.4 1.2

e 1 d u 0.8 t i l p 0.6 m A 0.4 0.2 0 4

6

8

0 1

2 1

4 1

6 1

8 1

0 2

2 2

4 2

6 2

8 2

0 3

2 3

Period

Sway 1.4 1.2

Two different reference points

e 1 d u 0.8 t i l p 0.6 m A 0.4 0.2 0 4

6

8

0 1

2 1

4 1

6 1

8 1

0 2

Period


2 2

4 2

6 2

8 2

0 3

2 3

Optimum panel definitions  Automatic

proposal for the number of panels needed for an optimum analysis

- When creating a panel model from a section model - Based on the model dimensions and mesh criteria

Different panels proposed for different model dimensions Hydrostatic and hydrodynamic analysis - The importance of nonlinear analysis October, 2012



SesamTM Continuing 40 years of success Sesam DeepC for deepwater coupled analysis, mooring and riser design Fan (Joe) Zhang, Sesam BD Manager, DNV Software October, 2012

Contents 

DeepC overview



DeepC.Riser – DeepC for riser design



Traditional method vs. coupled analysis approach - Floater/Mooring/Riser Coupling Effects - Coupled Analysis Strategies - Fatigue and code check riser analysis – three approaches - Examples of FPSO, SPAR, TLP and multi-body analysis



New release and on-going development



Demo – SEMI with drilling riser

Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

Global Response & Coupled Analysis


Global Response: Floater Motions


Coupled Analysis Influence on floater mean position and dynamic response due to slender structure restoring, damping and inertia forces 

Main purpose to compute more accurate line/riser response and vessel motion



Covering the range from simple to complex field layouts

Two independent vessels


Three connected vessels

Challenges in the riser design 





Traditional way – De-coupled methodologies. For deep waters the coupling effects of lines relative to platform motions, can be especially significant. It is expected a reduction of the amplification of platform motions compared to decoupled analysis results. The coupled analysis considers the interaction between - the hydrodynamic behavior of the hull, - the structural behavior of mooring lines. - and risers subjected to environmental loads.



For the deep and ultra-deep water scenarios, a steel catenary ris er design adopting prescribed displacements from coupled analyses will provide more realistic and optimum r esults as compared to a more traditional de-coupled analysis.


WF- and LF floater motion characteristics Riser/mooring/floater systems comprise an integrated dynamic system

n o i t o m e g r u S

Mean +LF+WF motion components

time

Complex response to wind, waves and current: 








Wave frequency (WF) response due to wave loading on the floater. Normally not influenced by the slender structures Low frequency response (LF) due to dynamic excitation from wind- and 2nd order wave forces. Horizontal LF is motion governed by resonance dynamics of the riser/mooring/floater system. Damping is essential for prediction of LF motions. Mean offset governed by mean environmental loading and restoring characteristics of the riser/mooring/floater system.

Floater/Mooring/Riser Coupling Effects Influence on floater mean position and dynamic response from slender structure restoring-, damping - and inertia forces. 1) Static restoring from station keeping system as function of floater offset 2) Current loading and its effects on restoring force of mooring and riser system

Restoring

3) Seafloor friction (if slender structures have sea-bottom contact) 4) Damping from mooring and riser system due to dynamics, current etc 5) Hull/riser contact (friction) 6) Additional inertia forces due to mooring and riser system

De-coupled:

1)

accurately accounted for

2), 4), 6)

may be approximated

3), 5)

generally cannot be accounted for

Coupled:


Consistent treatment of all these (6) effects!

Damping Inertia

Coupled analysis: Solution Method 

Non-linear finite element method (large displacements and rotations, small strains)



Vessel modelled as a rigid body (6 DOFs)





All other structural parts modelled with finite elements Floater, moorings and risers solved simultaneously with dynamic equilibrium at each time step.

i M i (t ) x Coupled

 C i

 K i

( x, t ) xi

 F i

(t ),

i



1,6

Rigid body vessel DOFs

i



7, n

Finite element DOFs


(t ) xi

i



1, n

de-coupled

Un-coupled floater motion analysis Floater load model: 

Floater mass and hydrostatic restoring



Hull damping model



1st and 2nd order wave loading



Wind and current loading

Slender structure model:

Un-coupled response model:



Static restoring characteristics



No external loading on slender structures

Solution scheme: 



TD solution of floater motion (6 dof) Restoring force from slender structures applied as non-linear external static force (springs)

Separated assessment of other floater/slender structure c o u p l i n g e f f ec t s required, e.g. : - Damping due to slender structure dynamics - Current loading on slender structures - Inertia forces due to slender structures Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

System and excitation dependent effects, case by case evaluation

Coupled floater motion analysis

Coupled floater slender structure response model









All Co u p l i n g e ff e c t s automatically accounted for, e.g. - Non- linear restoring force - Damping due to slender structure dynamics - Current loading on slender structures - Inertia forces due to slender structures Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012



Floater force model is included in detailed FE models of the complete slender structure system (moorings and risers). Floater, moorings and risers are solved simultaneously in time domain with dynamic equilibrium at each time step. All floater/slender structure coupling effects are automatically accounted for. A rather coarse slender structure model still catching the main coupling effects may be applied to gain computational efficiency Most accurate response model for global performance analysis of moored offshore structures

Coupled Analysis Strategies Advanced vessel model

Vessel Motion Analysis

Simplified slender structure model

Separated floater motion/slender structure analysis

LF & WF vessel motions

(b)

Select vessel motion representation

Establish ‘representative’ offset (mean & LF)

Vessel WF motion RAO

The purpose of coupled analysis is prediction of floater motions





(a)

F &LF vessel motions

Advanced slender structure model of each riser & mooring

A rather coarse slender structure model is applied still catching the main coupling effects (damping/restoring, current loads)





Flexible/efficient approach



Often used in riser design with detailed fatigue analysis

Combined floater motion/ slender structure analysis 

Slender structure analysis

Slender structure analysis 

F slender structure responses

F & LF slender structure responses


Detailed slender structure response is found by subsequent FE analysis considering forced floater motions

Include detailed model of selected slender structures of interest in coupled response model. Simple ‘all in one’ approach

Benefits from coupled analysis FPSO, SPAR, TLP, SEMI, etc.


Global Response Summary: Significance of Low and High Frequency coupling Low Frequency (LF) coupling effects for moored floaters SYSTEM

WATER DEPTH Shallow

Intermediate

Deep

Ultra Deep

FPSO

Small

Moderate

High

High

TLP

----

Small

Moderate

Moderate*

SPAR

----

----

Moderate

Moderate-high*

High Frequency (HF) coupling effects for TLPs only SYSTEM

WATER DEPTH Shallow

Intermediate

Deep

Ultra Deep

FPSO

----

----

----

----

TLP

----

Moderate

High

High*

SPAR

----

----

----

----

*Limited information available Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

Example – coupled analysis of turret moored FPSO 

Experience/examples



Typical coupling effects



System effects

Norne


DeepC Coupled FPSO Model


The importance of coupling effects for turret moored FPSO Surge damping ratio as function of water depth

Mean/dynamic floater offset as function of water depth Dynamic

Mean (static)


Coupled FPSO analysis experience Significant coupling effects identified 

Current loading on slender structures (up to 40 % of total)

Coupled analysis experiences 

Stable numerical performance



Simplified slender structure model can be applied



LF surge damping 20-30% of critical



Computation time = real time



WF response not influenced by coupling effects



Applicable in design analyses



Coupling effects are strongly system dependent 

Modelling is ‘straight forward’ for experienced users

No. of risers and mooring lines - More damping and inertia force



Water depth

Coupling effects are excitation dependent 



Waves and current Needs to be estimated for actual environmental condition


Coupled approach contributes significantly to increased confidence of FPSO motion analyses

Benefits: FPSOs 

Low Frequency (LF) response highly dependent on mooring/riser damping - Mooring and risers may contribute up to 40% of critical damping in extreme sea depending on water depth – automatically included by coupled analysis



Provides consistent design input for mooring lines (intact, damaged, extreme, fatigue) risers (extreme, fatigue) and turret. Norne

Ideal for complex systems involving FPSO, offloading systems and tankers considering both hydrodynamic and mechanical interaction. Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

Example – Coupled Analysis of Spar Platforms 

Experience/examples






System effects


SPAR Platforms 



State of the Art - Function:

DTU and WTU

- Installed since 1996:

10

- Spars under contract:

4

- Water depth:

1,710 m (Devil’s Tower)

- Topside weight :

26,000 t (Holstein)

- No of TTR’s:

20 (Genesis)

- Presence:

GOM and SEA

Challenges - Offshore deck floatover - Worldwide application - Hull VIV


Spar concepts


Important responses from coupled SPAR analysis 

Wave-frequency (WF) surge/sway, heave and roll/pitch



Low-frequency (LF) surge/sway, heave and roll/pitch



Mooring tensions



Riser responses



Push-up/pull-down for air-can supported riser systems



Tensioner stroke for SSVR (Spar supported vertical risers) systems


Spar WF-LF Motion Characteristics

The fairlead position : LF rotation centre

WF rotation centre


Keel surge motion – Coupled/uncoupled


Surge motion at SWL- Coupled/uncoupled


Hull/slender structure coupling effects Coupling effects : Size matters !

Hoover/Diana (1460m) over downtown Houston


DeepC – Coupled classic spar model


DeepC – Coupled Truss Spar Model

Truss Spar Hull

Mooring Lines (16)

Steel Catenary Risers (2)

Top Tensioned Risers (15)


SPAR – Spectra of surge motion, 3000 ft water depth

De-coupled analysis without any damping 200 contribution from moorings/risers

Coupled Uncoupled Modified

De-coupled analysis with best estimate of damping coefficients

y t i 150 s n e d l a r t c e100 p S

Fully coupled analysis – damping automatically incl.

50

0

0

0.05

0.1 0.15 0.2 Angular frequency [rad/s]

0.25

Hurricane condition (H S = 11.9 m, T p = 15.2 s) with risers and current Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

SPAR - Mathieu instability


SPAR - Outfloating and upending of Genesis


SPAR upending analysis

DeepC D2.2-04 Date: 02 Mar 2004 20:45:06

SPAR hull bending moment envelope during upending 6 0 0 + e 3

] m * N k [ y y M t n e m o M

6 0 0 + e 2

6 0 0 + e 1

0

0

20

40

60

80

100

Line Coordinate[m]


120

140

160

180

200

220

Coupled Spar analysis experience Coupling effects, general

Heave Coupling effects



Complex WF/LF motion pattern





Difficult to calibrate de-coupled analysis model





Significant coupling effects identified







Sensitive to water depth and environmental conditions





Coupling effects identified WF heave response (in particular SSVR systems. Otherwise no coupling effects for WF response Reduction in LF standard deviation Surge - Waterline

10-20 %

Surge - Keel

10-35 %

Pitch

15-30 %

Coupled approach essential for deep water Spar analysis


Coupled analysis essential, in particular for SSVR Standard deviation reduced by a factor of 2 compared to uncoupled analyses Stick/slip riser/hull contact model essential Significant contribution from mooring system damping, in particular for conventional chain/wire systems

Coupled analysis experience 

Stable numerical performance



Simplified slender structure model can be applied



Computation time = real time



Modelling is complex but ‘straight forward’ for experienced users

Benefits - SPAR 

Heel motions are of importance for both topside, hull structure and moorings and risers - Coupled analyses tend to reduce maximum pitch angle, which is beneficial



Heave damping sources: - Hydrodynamic potential damping

- Viscous hull damping (strakes, trusses etc.) - Viscous damping from moorings/risers

Neptun e

- Friction damping forces (hull/riser & tensioner)

A coupled analysis can treat all damping contributions consistently! Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

Example – Coupled TLP analysis 

Experience/examples






System effects


Tensioned Leg Platforms 

State of the Art - Function:

DTU

- TLP’s installed:

17

- Water depth:

1,433 m (Magnolia)

- Topside weight:

85,000 t (Heidrun)

- No of TTR’s:

42 (Snorre)

- Presence:

GOM, North Sea & Asia



Challenges



Tether design in wd > 1500 m - Stepped tethers - Pressurized tethers



Riser clashing - More severe for TLP’s - Deepwater req. larger riser spacings


Coupled Response Model of Mini-TLP


TLP - Measured & computed tension spectra


measured

coupled

mean

24.7

26.0

std-tot

0.93

1.0

std-LF

0.16

0.19

std-WF

0.82

0.99

std-HF

0.36

0.29

Fully coupled analysis – analysis – HF damping automatically included

Benefits - Tensioned Leg Platform 







Coupling effects important for Low Frequency (LF) and High Frequency (HF) TLP motions

Coupled analyses predict high damping in LF surge and HF pitch compared to de-coupled analyses Coupled analyses increase HF tendon tension for fatigue waves Coupled analyses decrease HF tendon tension for extreme waves

Coupled analysis can treat all response ranges LF, WF, and HF consistently. Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

SEMI Submersibles State of the Art - Function:

Wet Trees

- Water depth:

2,133 m (Atlantis)

- Topside weight:

42,000 t (Aasgard B)

- No of flexibles:

79 (P-51)

- No of SCR’s:

Several (one Semi, Brazil)

- Presence:

Worldwide

P 52 Roncador

Challenges Hull VIV motions in high current regions - Serious challenges for SCR’s

Shallow draft semis as DTU’s Deck installation for large draft DTU’s Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

Extendable Draft Platform, DTU

Benefits: Semi-submersibles 

For large production semis: - Significant Low Frequency (LF) roll/pitch motions of the same l evel as WF motions



Attractive for design of Steel Catenary Risers (SCR) because: - LF and WF response are treated consistently and available early in the design process



Gust wind induced LF motion/response motion/respon se is easily included

Improved confidence in global response important for SCR design Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

SEMI in Brazilian waters

Modelled/analysed Modelled/analy sed by DNV Rio Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

Coupled analyses – summary 











Coupled analysis is a well established methodology Verified by calibration to model tests and full scale measurements (several publications available) Vital importance for qualification of deep water moored structures Adds confidence to results as compared to traditional de-coupled analyses

Numerical performance (stability/computation time) allows for application in design analyses Modelling is complex but ‘straight forward’ for experienced users


Deepwater Model Basin Limitations Limit: 10 m basin Scale: 1:100  1000 m wd Scale: 1:60  600 m wd

Suitability of using a pit?

10 m

20 m

Limit: 30 m pit Scale: 1:100  3000 m wd Scale: 1:60  1800 m wd Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

Coupled floater motion analyses

Uncoupled floater motions Separate floater motions and mooring/riser response Coupled floater motions Floater and mooring/riser constitutes an integrated dynamic system


RAO

DeepC Overview What is DeepC?


What is DeepC 

The tool in Sesam for riser analysis, mooring analysis and coupled analysis



Modelling of all slender structures



Set-up and execution of time domain analysis with - Riflex and Simo for coupled analysis - Riflex for conventional riser analysis



Statistical post-processing



Fatigue analysis of risers



Combined Loading Code Checking of metallic risers


Why DeepC 

Main purpose to compute more accurate line/riser response and vessel motion - Code checking and fatigue of lines





Covering the range from simple to complex field layouts All Co u p l i n g e f f ec t s automatically accounted for, e.g. - Non-linear restoring force - Damping due to slender structure dynamics - Current loading on slender structures - Inertia forces due to slender structures


Riser & mooring analysis modules in Sesam 

GeniE

Hull modelling



HydroD

Wave-body interaction. Radiation/diffraction and Morison theory



DeepC

Coupled analysis & riser analysis. Non-linear time domain

- Simo Floater forces generation (also used for simulation of marine operations and uncoupled analysis) - Riflex of motions

Finite element program for slender structure analysis and solver for equation



Xtract

Animation of results



Mimosa

Frequency domain de-coupled mooring analysis.


DeepC – The coupled analysis tool DeepC is a package consisting of

DeepC Concept Modeller

DeepC Analysis Engine SIMO

• Fully integrated large body (vessel) interface to the FE solver for coupled analysis

DeepC Analysis Engine RIFLEX

• Fully integrated special purpose FE solver (beams/trusses) for coupled analysis or single riser/mooring analysis.

DeepC Post-processing Engine

• Special purpose post-processing: computation of spectra, envelopes and key statistics from time series results

SIMO and RIFLEX are owned and maintained by Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

How to use DeepC HydroD 

Vessel characteristics: - Force, added mass & damping transfer functions

DeepC 

Modelling & Analysis:

Time series post processing:



- Mooring/risers

- Statistics of forces and motions.

- Environment - Vessel modification (wind & current coefficients, mass etc)

- Filtering (LF, WF) - Response envelopes

- Analysis control

- Code Checking - Fatigue assessment DeepCD2.0-05 Date: 10 Apr2003 10:51:36

Power Spectrum of Oil Offloading Line Tension

0 0 0 0 0 3

0 0 0 0 5 2

0 0 0 0 0 2 m u r t c e p S y t i s n e D y g r e n E

0 0 0 0 5 1

0 0 0 0 0 1

0 0 0 0 5

0

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

Circular Frequency [rad/s]

S0:41204.1, S1:23002.7,S2:14502,S3:10137.2,S4:7653.19,Tz:8.92615,Cutoff:1, Smoothing:7


Results from DeepC 



XY-plots for presentation of time series, response spectra, envelopes etc. with export to MS Excel. Graphical presentation and statistical reporting of fatigue life.



Animation of typical motions and riser/mooring forces.



Full unit support in modeling and results presentation.



Built-in post-processing of time series responses such as forces and displacements: - High-pass/Low-pass filtering - Response spectra - Envelopes - Computation of key statistical parameters - Code checking of metallic risers


Fatigue 



Purpose: Calculate fatigue life and damage of risers or mooring lines. Combines a number of environment conditions, based on discretizations of the scatter diagram - This often requires a high number of analysis to be executed



Rain flow counting


DeepC applications 

FPSOs - Low Frequency (LF) excitation damping. - Slow drift surge/sway motions.



Semi-submersibles - Improved accuracy of steel catenary riser response. - Prediction of LF fatigue contribution.



Spars - Improved modeling of slow drift roll, pitch and heave motions. - Fatigue of tensioned riser systems. - Heave response of classic and truss spars.



TLPs - Incorporate non-linear tether forces and tether dynamics in wave frequency (WF) responses. - Improved accuracy of LF surge and High Frequency (HF) pitch damping predictions.


DeepC handles both single- and multi-floater coupled systems Large volume floaters

Wind

Wave

Current Slender structures


Coupled analysis – Multi-body systems 

Complex multi-body systems



FPSO with spread mooring



Buoy loading systems





Coupled Analyses of Two-body system

Independent Verification of Motion and Slender Structure Responses Dec. 2002 using DeepC DNV Houston Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

Line breakage – Oil offloading buoy Line break simulation Mooring line breaks

DeepC V2.1-01 Date: 02 Sep 2003 14:18:50

Moorin g Line 6 Top tension 0 0 4 1 0 0 2 1 0 0 0 1

] N k [ e c r o F

0 0 8 0 0 6 0 0 4 0 0 2 0 0 0 2 -

0


20

40

60

80

100

120

140

160

180

200

Time [s]

Line breakage – Oil offloading buoy

Line break simulation

Mooring line breaks

DeepC V2.1-01 Date: 02 Sep 2003 14:18:50

Mooring Line 6 Top tension 0 0 4 1 0 0 2 1 0 0 0 1

] N k [ e c r o F

0 0 8 0 0 6 0 0 4 0 0 2 0 0 0 2 -

0

20

40

60

80

100

120

140

160

180

200

Time [s] Release Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

Intact

A Two-Floater system


DeepC solves simultaneously for all responses


Some other examples – SEMI and TLP


DeepC for Riser Design How DeepC helps on riser design? (Separate presentation in day 2)


The DeepC for riser design configuration 

Subset of DeepC - Customized user interface



Single riser (or mooring line) analysis - Modeling of one (or several) lines and environment in DeepC GUI



Line independent vessel motion: - Transfer functions read from file - Time series read from an existing coupled analysis - Time series read from file (measurement, model test, etc.)



Time domain analysis - Riflex



Regular waves - In addition to irregular sea



Main benefit -

Computational speed Fatigue analysis Code checking What-if-scenarios (efficient design iteration)


Riser analysis characteristics 

Slender marine structures - Risers, mooring lines, TLP tendons



Environment - Regular and irregular waves - Arbitrary current profiles



Load models -



External/Internal hydrostatic pressure effects Morison’s equation Loading caused by vessel motion Seafloor contact

Modelling - Nonlinear finite element formulation - Connector elements (ball, joints, hinges) - Non-linear material properties



Results processing - Deformations, stress, code check, fatigue


Riser configuration – Steel Catenary Riser (SCR) Pro’s: 

Floater motions absorbed by change in configuration geometry

Con’s 

Subjected to fatigue loads, particularly in the touchdown zone, due to - platform movements - Vortex Induced Vibrations (VIV) - sea currents.


Riser configuration – Top-tensioned Riser (TTR) 







Pro’s: Vertical risers supported by top tension. Heave compensators allowing for relative riser/floater heave motion. Avoid buckling and excessive bending stress due to platform motion and VIV Reduce drilling and completion costs




Con’s:



Complicated completions



Heavy workover requirements



Requires a platform with good motion response characteristics - Tension Leg Platform (TLP) - Negligible heave (0 to 1 feet) z

- Spar Platform - Small heave (0.5 to 12 feet)

Riser configuration – Free-standing Riser Pro’s 



Decouple the response of the riser tower from that of its associated floater, as well as from the effect of wind-driven seas and swell. Overriding requirement is to provide a credible, long-term assessment of the buoyancy force that stabilizes the tower.

Con’s 



The towers also experience motions induced by current. Hence, the requirement arises to track the structural response of the towers over their lifetime.

Example fields: Total’s Girassol, Exxon Mobil’s Kizomba A and Kizomba B, BP’s Greater Plutonio Block 18 offshore Angola, plus Petrobras’ P-52 offshore Brazil and its five free-standing risers at Cascade Chinook in the Gulf of Mexico. Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

Fatigue and code check riser analysis – Three Approaches Coupled analysis





An efficient option

-

Most accurate results

-

Regular and irregular waves

1. Do the coupled analysis on a global but coarse model (including all slender structures),

-

Most time consuming approach

2. Remove all lines except the riser to analyze,

Uncoupled irregular wave analysis



-

Most common approach used, but results may be sensitive to water depth

-

Vessel motion based on RAO's

-

Less time consuming

Uncoupled regular:



-

Very fast approach and often used for early design purpose

-

Similar to the irregular case during modelling


3. Refine the model (make many local but detailed models), 4. Rerun with time series from the coupled analysis for each local model to perform postprocessing.

Fatigue Analysis 

Fatigue analysis of tubular lines - Based on a coupled or uncoupled analysis

- Nonlinear Time Domain - Rainflow counting - Regular or Irregular waves


Fatigue with multiple scatter discretizations 

Make it much easier to handle direction dependent scatter diagrams!!


Single Riser/Mooring Line Analysis 



Modelling of one (or several) lines and environment in DeepC GUI

Line independent vessel motion: - Transfer functions read from file (coupled or de-coupled) - Time series read from file (typically decoupled analysis) - Time series read from an existing coupled analysis


DeepC – Code checking of risers 



Based on fully coupled analysis or single riser analysis Capacity checking according to - DNV OS F201 - Von Mises Stress (API RP) - ISO 13628-7



Axial stress and bending moments scaled with factors according to - LRFD or WSD - ULS, SLS, ALS


Pipe-in-pipe analysis


DeepC for SURF How DeepC helps on SURF design? (Separate presentation in day 2)


Subsea Umbilicals Risers Flowlines - SURF Umbilicals – Multi-purpose service lines

Flexible riser

Flowlines & pipelines


Subsea installation

New modules in the DeepC package 

UmbiliCAD



Helica



Vivana



FatFree

D / A e d u t i l p m a n o i t a r b i V

CROSS-FLOW

IN-LINE

0.0

2.0

4.0

6.0

U/f 0D 8.0

10.0

Reduced Velocity V


12.0 R

14.0

16.0

Summary Why DeepC?


SESAM – Deep water technical analysis capabilities

MANAGING RISK Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

A customer statement 











DeepC – Coupled Analysis concluding remarks For deep water installations, the riser and mooring systems greatly influence the motions of the floater In deep water floating system design, coupled analysis will be an important and practical tool in combination with de-coupled analysis and model test Coupled analysis approach improves riser and mooring design DeepC treats Coupling Effects in a consistent way and increase the confidence level of vessel motion prediction and riser and mooring design and analysis Quote by Qi Ling, MODEC Houston

Uncoupled+2/3LumpMass 2.0

RegularWaveTestRAOs

750

1.8

WhiteNoiseHs=10.0ft

675

WhiteNoiseHs=17.0ft

1.6

600

FrequencyDomainCoupled Analysis 100-yrHurr.WaveHs=43.5ft

1.4 ) t f 1.2 / t f ( O A R 1.0 e v a e 0.8 H

525 )

d a r / c

e 450 s 2 ^ t f (

375 m u r t c

300 e p

S y g r

0.6

e 225 n

0.4

a 150 W

0.2

75

E e v

0.0

0 0

5

10

15

20

25

30

Period(sec)


Concluding remarks – Why DeepC? 



Coupled analyses essential for some systems Modelling flexibility, easy access to system modification - E.g. Pipe in pipe and flexible joints



Efficient statistical post-processing



Code check on metallic risers









Fatigue analysis with regular/Irregular coupled/decoupled analysis Unsurpassed at solution speed Easy to compare different approaches for doing riser analyses Less documentation of assumptions in coupled analysis



Efficient for design iterations



Scripting facilitate easy reuse and modification



Extensively validated – numerous papers exist


“As the oil and gas fields get deeper, the installations of deepwater

platforms become more challenging. The coupling effects between a floater and it’s moorings become more pronounced

and more important. Sesam is an excellent tool for analysing the interaction between hull, moorings and risers.” Andy Kyriakides, Project Manager, Modec International LLC.


Demo for drilling riser 







Visualization of pipe-in-pipe motion in Xtract Scatter diagrams/discretizations etc. for regular waves Possibility to apply multiple scatter discretizations (e.g. direction dependent) in Fatigue analyses. Parallel execution of analyses




DeepC - Improved confidence in deep water concepts A comparison of frequency- and time-domain air gap analysis Joe Zhang, Sesam Product Management Mayl, 2012

Air gap introduction 





Air gap analysis is crucial during both the conceptual global performance analysis and detail structure design stages.

For existing structures a more precise air gap analysis may be of importance for requalifications when environmental criteria change. Traditional frequency-domain method and statistic extreme values prediction are based on a Rayleigh distribution assumption and linear solution of potential theory. - However, this method generally does not effectively reproduce measurement from model test.

DeepC - Improved confidence in deep water concepts Mayl, 2012

Importance of time-domain air gap analysis 



Compared to an air gap approach by Wadam/Postresp, the DeepC method will also include the contributions from static offset and LF motion in the vertical modes.

Effect of diffracted/radiated waves may be taken into account when doing air gap calculation in DeepC. - Including diffraction/radiation effects is optional. To include, diffraction/radiation free surface elevation must be available on SIF file.







For the vessel in static equilibrium position, i.e. horizontal offset and yaw motion, surface elevation time series is pre-calculated by Simo in the air gap point. At each time step, the actual vertical position of the air gap point on the vessel is evaluated. In cases where the moorings have an important effect on the WF motion, anchor/TLP elements should be used, or stiffness matrix should be modified directly.


Analysis semi-submersible model


Air-gap definition and notation

  = 0 − [  −   ]   = 3  +  ∙ 4() −  ∙  5() 0 = 12.5  DeepC - Improved confidence in deep water concepts Mayl, 2012

Traditional frequency domain analysis using HydroD and Postresp Input

Output

HydroD

HydroD



Panel model (Generated from GeniE)



Location



Direction and wave period set



Off-body points

Postresp 

Specified checking points



Wave spectrum



Duration (10800s)




Added mass and potential damping coefficients



Motion RAOs



Wave elevation

Postresp 

Response spectrum - Standard deviation



Short term statistics - Most probable largest value

Air Gap Extremes ( Hs = 12.0m, Tp = 13.8s, γ = 3.3, Dir = 45˚) 8.521

 ()  = ()  −  () ()   = () 

2 0



 = 2 ln

Most probable largest value

 = .   DeepC - Improved confidence in deep water concepts Mayl, 2012

Basic Inputs and Outputs for DeepC Inputs 

Hydrodynamic coefficients (G1.SIF)

Outputs 

- Added mass and potential damping coefficients - Wave force transfer functions - Water surface elevation transfer functions at specified positions (if disturbed wave needed to be considered) 

Wind and current forces coefficients



Time domain environment conditions



Mooring and riser configurations



Specified checking points






Vertical position of vessel air gap point Surface elevation at air gap point Air gap at specified checking point

Air gap analysis in DeepC (with wave, current and wind)

WIND

CURRENT


Output from DeepC Checking point elevation vs. wave elevation

Air gap time series


Air gap time series at Point 78

 = −.  


Evaluation

• •

Frequency domain analysis can not capture the low frequency part as expected. By including the mean position, the frequency domain analysis could give more accurate statistics.


Conclusion 





Using DeepC time domain air gap analysis, more accurate extremes could be obtained.

In some environment conditions (with wave period close to heave natural period), traditional frequency prediction may lead to a under-estimated air gap result. Compare to frequency domain analysis, average displacements (static off set and LF motion) from coupled analysis have strong effects on the air gap analysis. - Heave, Roll and pitch



It could be an acceptable solution to combine statistically predicted extreme air-gap values and static configuration from coupled analysis.


Considerations 



The air gap point in the vessel frame of reference has radiation/diffraction surface elevation transfer function calculated for a number of wave headings.

If the main wave heading is not coincident with any of the transfer function wave headings, DeepC/Simo will perform an interpolation in between values for t he two adjacent transfer function wave headings. - Note that static offset in the vertical modes is neglected when pre-calculating the surface elevation.



The air gap is obtained as the vertical distance between the air gap point on the vessel and the pre-calculated free surface elevation. - Note that this do not account for any dynamic horizontal motion of the vessel.



Using pre-generated wave kinematics will give statistical results which are practically equal to results based on actual position at each time step.




FPSO Full Ship Analysis Integrated Strength and Hydrodynamic Analysis using Sesam Fan (Joe) Zhang, Sesam BD Manager, DNV Software October 15, 2012

Topics 

Strength assessment of FPSOs and related software from DNV



Global modelling






Ultimate strength analysis



Submodelling



Fatigue analysis

FPSO Full Ship Analysis October 15, 2012

FPSO Package for design and analysis Risk Analysis Safeti Hydrodynamics • Seakeeping • Wave loads HydroD

Topside GeniE

Main scantlings Nauticus Hull

3D Hull modelling GeniE

Fatigue Simplified, Spectral Nauticus Hull Stofat

Turret Local analysis GeniE

Risers DeepC

Mooring Mimosa

Proven solutions in use by major companies around the world FPSO Full Ship Analysis October 15, 2012

SESAM strength assessment analysis system and interfaces Workflow manager Modelling, structural analysis and code check

Stability and wave load analysis

Mooring and riser analysis

GeniE

HydroD

DeepC

Model

Model

Loads

Results

Global analysis 1

Wave load 1

Stability 1

Analysis 1

Global analysis 2

Wave load 2

Stability 2

Analysis 2

Global analysis n

Wave load n

Stability n

Analysis n

Local analysis


Sesam – a fully integrated analysis system 2. Pressure loads and accelerations

1. Stability and wave load analysis


L o a d

Local FE analysis

t r a n s f e r

5. Local stress and deflection & fatigue

FE analysis

4. Global stress and deflection & fatigue screening FPSO Full Ship Analysis October 15, 2012

3. Structural model loads (internal + external pressure)

Sesam Workflow Manager



Key features - Model and file management



Benefits - Automatic re-run of analysis hierarchy to re-produce analysis after model updates - Facilitate alternate engineers to re-run analysis - Documentation/description of models and analysis can be linked into the explorer - Supports best engineering practice and workflow


GeniE 

Key features - Modeller for all hydrodynamic and structural applications within the Sesam system - User interface for FE analysis, post-processing and code checks for both hull, topside and jacket



Benefits - One common model for strength and hydrodynamics - Efficient modelling and code checks within one user environment - Easy to implement updates and changes to geometry and properties - Different level of detailing of FE model derived from one global model by adjusting mesh densities - Mesh automatically adapts to changes in the model


HydroD 

Key features - Hydrostatics and stability calculations - Linear and non linear hydrodynamics



Benefits - Handling of multiple loading conditions and models through one user interface and database - Sharing models with structural analysis - Direct transfer of static and dynamic loads to structural model


Analysis Overview Task

Purpose

Global modelling






ULS analysis



Spectral fatigue analysis

 

Spectral ULS analysis




Input

Make global model for hydrodynamic and strength analysis



Calculate loads for fatigue and ultimate strength



Calculate hull girder strength



Fatigue screening on nominal stress Local fatigue analysis



Calculate long term stress based on spectral method













Output

Ship drawings Loading manual

Global

FE model

Global FE model Wave data



Load files for structural analysis

Global FE model Snap shot load files from HydroD



Ultimate strength results

Global FE model Frequency domain load files from HydroD



Calculated fatigue lives




Long term stress


Purpose

Global modelling






ULS analysis




 





Input


























Output




Global FE model
















Long term stress

Creating the Global Model Model requirements 



Challenges

The global model is used to calculate loads and strength and must represent the actual properties of the ship



Modelling of hull form



Creating compartment and loads

For direct strength calculations essential properties are



Mass tuning

- Buoyancy and weight distribution - Compartment loads - Structural stiffness and strength


Global Modelling with GeniE


Benefits of GeniE for Global Modelling 

One common model for hydrodynamic and structural analysis



Geometry modelling - Advanced surface modelling functions - Re-use data from CAD - Parametric modelling using JavaScript - Use of units



Compartment and loads - Compartments are created automatically - GeniE calculates tank volumes and COG - Loads are generated from compartment fillings and automatically applied to tank boundaries



Mass tuning - Scaling mass density to target mass



Purpose

Global modelling






ULS analysis




 





Input


























Output




Global FE model
















Long term stress

Hydrodynamic Analysis Model requirements 

Hull shape as real ship



Correct draft and trim



Weight and buoyancy distribution according to loading manual



Mass and buoyancy in balance


Challenges 

Obtain correct weight and mass distribution



Balance of loading conditions

HydroD


Benefits of HydroD 

One common program and model for -

Stability calculations Linear hydrodynamic analysis Non-linear hydrodynamic analysis With or without forward speed



Supports composite panel & Morrison models



Support both standalone and integrated analysis - Models can made in HydoD or based on structural models



Loading conditions - Multiple loading conditions by changing compartment contents



Balancing the model - Auto balance of loading conditions by draft and trim or compartment fillings



Built in roll damping module - Stochastic linearization - Quadratic damping



Strong postprocessing and graphical results presentation



Load transfer to FE analysis - Snap shot or frequency domain - With splash zone correction for fatigue



Purpose

Global modelling






ULS analysis




 





Input


























Output




Global FE model
















Long term stress

Ultimate Strength Analysis 

Global structural analysis with load transfer from hydrodynamic analysis



Snap shot load transfer of non linear loads for selected design conditions



Yield and buckling check with PULS



Benefits of global analysis with direct load transfer - Eliminate effect of boundary conditions - Loads applied as a simultaneous set of sea and tank pressures according to the calculated design wave  No need for conservative and/or uncertain assumptions - Integrated buckling check


Design Wave Determination – Example 1. Calculate long term response (100 years return period for FPSO) 

100 years wave bending moment: 2.184E9 Nm

2. Find peak value, phase and corresponding peak period in transfer function 

Peak value:

2.33E8 Nm



Phase angle: ϕresp= 128 deg (relative to incoming wave)



Period:

12 s

3. The design wave is then 

Amplitude

100 year response/peak value 2.184E9/2.33E8*2=18.75 m



Period



Phase:

12 s ϕwave = 360 - ϕresp = 360 – 128 = 232 deg.

Resulting values:

232 deg hogging 52 deg sagging -

Which is sagging and hogging must be evaluated separately


Verify the applied loads 

Reaction forces



Sestra.lis

- Reacting forces “close to zero” compared to the global excitation forces (<~1%) - E.g. stillwater load case Max Fz < mass*g/100


Verification of applied loads 

Visual check using Xtract - Pressure mapping - external and internal pressures - Deflections - Nominal stress level


Verification of applied loads 

Global sectional loads



Cutres

- Cutres calculates and integrates the force distribution of cross sections and is ideal to evaluate the hull girder shear forces and bending moments - Large deviations



Improper load balance

- Small deviations will occur since HydroD only consider vertical loads (mass) from internal tank pressures

- NB! Check position of neutral axis in HydroD sections and Cutres results

Vertical shear force distribution

e c r o f r a e h s l a c i t r e V

0

50

100

150

200

Distance from AP


250

300

350

Vertical bending moment distribution

WASIM CUTRES

t n e m o m g n i d n e b l a c i t r e V

0

50

100

150

200

250

300

350

WASIM CUTRES

Distance from AP

Cutres – main features 

Relevant for long and narrow structures that may be viewed as beams, e.g. ships



Two basic features: - Presentation of stress resultant diagrams for user defined sections through the FE model



Integration of stress resultants over sections and presentation of force and moment graphs along ship axis


Sections created in Cutres


Display section diagram


Still water bending moment


Vertical shear force and bending moment

Postresp: 2.33E8 * 9.375 = 2.18E9 Cutres: 2.207E9


Cross sections positions adjust


PULS – Advanced Buckling & Panel Ultimate Limit State

PULS is a code for buckling and ULS assessments of stiffened and unstiffened panels


Benefits of PULS 

Characteristics

Py

- Higher accuracy than traditional rule formulations and classic buckling theory - Quick and easy-to-use design tool for calculation of ULS capacity

Px

- Valuable information about failure mode and buckling pattern - Effective to evaluate



Benefits

250 Abaqus PULS DNV Rules

- Design optimization with increased control of safety margins

GL Rules

200

) a P

150

M ( 2 1

100

50

0 0

20

40

60

80 2


(MPa)

100

120

140

PULS - Element library



Un-stiffened plate element



Stiffened plate element (S3)



Corrugated plate element (K3)



Stiffened plate element (T1)


PULS Code Check in GeniE 

Buckling capacity panels are automatically generated from the plate and beam concepts



Colour code presentation of Utilization Factors (UF)



Support for multi-core parallel buckling calculations



Numeric and colour code presentation of result



“Worst case” - colour code presentation of the maximum UF from all load cases



Buckling panels can be exported to PULS Advanced Viewer and PULS Excel for further postprocessing


Combination of still water and wave loads results 

Design wave load transfer from Wadam results in separate result cases for static and hydrodynamic loads - RC1 still water load - RC2 wave loads



Create result combination in GeniE - Alternative: Combine results in Prepost


Code check 

Code check according to DNV-RP-C201 Pt 2 (PULS) by “CSR Tank”



Note: Default parameters are according to CSR Tank and must be modified according to the RP


Modified CSR Tank PULS code check 

FPSO ULS 3 hold or global model - Design wave approach with direct load transfer from HydroD or Maximum hogging and Maximum sagging condition (according to DNV-RP-C102, App D) . - Check only longitudinal structure - Method 1 (Ultimate Capacity), according to DNV-RP-C201 Pt 2 (PULS) - Stiffened panel type - Allowable usage factor = 0.8 (loadcase design condition must be harbour or seagoing) - Meshing rules: Gross scantlings, (don’t use co -centric stiffeners).


Code check result



Purpose

Global modelling






ULS analysis




 





Input


























Output




Global FE model
















Long term stress

Simplified vs. spectral fatigue Environment

Wave loads

Stress calculations:

Simplified

Spectral fatigue

Long term rule Weibull distribution

Actual wave scatter diagram and energy spectrum

Rule formulations for accelerations, pressure and moments on 10-4 probability level

Direct calculated loads - 3D potential theory

Rule formulations for stresses.

Load transfer to FE model. Complete stress transfer function.

Rule correlations.

Hotspot stress models for SCF

Fatigue damage calculation:


Based on expected largest stress among 10^4 cycles of a rule long term Weibull distribution

Based on summation of part damage from each Rayleigh distributed sea state in scatter diagram.

Stochastic Fatigue Analysis 

Wave Load Analysis - Input: Global model, wave headings and frequencies - Output: Load transfer functions (RAOs) Direct Load Transfer



Stress Response Analysis - Input: FE models and load file from wave load analysis - Output: FE results file with load cases describing complex (real and imaginary) stress transfer functions (RAOs)



Fatigue Damage Calculation

Stress Transfer Functions

- Input: Stress transfer functions (FE results f ile), wave data


- Output: Calculated fatigue life

Fatigue Life


S-N Fatigue Curves

Typical workflow RAO’s

Hydrodynamic model


•External pressure •Rel. wave elevation • Accelerations •Full load / intermediate/ ballast • ->800 complex lc

Global FE-model RAO’s

Load transfer Global + local FEmodel

Global stress/deflection

Local model boundary conditions


Global structural analysis

Deflection transfer to local model

•External pressure •Internal pressure • Accelerations • Adjusted pressure for intermittent wetted areas

RAO’s

•Global stress/deflections •Entire global model

Global deflections as boundary conditions on local model

Typical workflow

Local stress/deflections

Local structural analysis

Stress distribution for each load case RAO’s

•Local stress/deflections

Local stress transfer functions Notch stress Stress

Geometri c stress at hot spot (H ot spot stress) Geometri c stress Nominal stress

Principal hotspot stress

Stress extrapolation

Hot spot

Scatter diagram

Fatigue calculations

Input •Hot spot location Result •RAO •Principal hot spot stress

Input •Wave scatter diagram •Wave spectrum •SN-curve •Stress RAO •=> Fatigue damage

SN data


Global Frequency Domain Analysis 

Loads from HydroD



Static load case - For verification of load balance and static shear and bending compared to loading manual - Enables automatic calculation of mean stress effect in fatigue calculartions - Enables possibility for to calculate long term extreme loads including static stress



Dynamic load cases - Number of complex dynamic load cases = number of wave headings x number of wave periods (e.g. 12 x 25 = 300)


Pressure reduction zone

Postresp Long Term Prediction

CN 30.7

Zwl


= ¾*5.626E04/(1025*9.81) = 4.196

Load Transfer to Global Model


Fatigue Calculation Program - Stofat 

Performs stochastic (spectral) fatigue calculation with loads from a hydrodynamic analysis using a frequency domain approach



Deterministic fatigue under development



Structures modelled by 3D shell and solid elements

 Assess

whether structure is likely to suffer failure due to the action of repeated loading

 Assessment

made by SN-curve based fatigue

approach  Accumulates

partial damages weighed over sea states and wave directions


POSTPROCESSING

E L I F E C A F R E T N I S T L U S E R

E L I F E C A F R E T N I S T L U S E R L A R U T C U R T S

Stofat

Shell/plate fatigue

Stofat database

Global Screening Analysis 

Fatigue calculations based on nominal stress from global analysis and stress concentration factors



Typical use - Identify fatigue sensitive areas - Determine critical stress concentration factors for deck attachment and topside supports - Determine location of local models and fine mesh areas - Decide extent of reinforcements based on SCF from local analysis


Fatigue Screening Analyses 

Fatigue Damage in Lower Hopper Knuckles - Global screening scaled by results from local analysis Screening Result TBHD Pos. Local Model Result 1.250

1.000

] [ e 0.750 g a m a D e u g i t 0.500 a F

0.250

0.000 100425

120425

140425

160425

180425

Distance from AP [mm]


200425

220425

Global Screening


Local Fatigue Analysis 

Local fine mesh model created from global GeniE model by changing the mesh density in the location of the crack



Hot spot stress RAOs at the location of the crack established by spectral FE calculation



Submodelling techniques is used to transfer the results from the global FE analysis to the boarders of the local model



Fatigue damage/life calculated using Stofat

Local fine mesh model

Concept model with mesh densities Calculated fatigue life FPSO Full Ship Analysis October 15, 2012

Submodelling


Fatigue Strengthening and Screening of Extent 

Soft bracket added in the local model of the stringer at crack location



Re-run sub-model analysis and fatigue calculation to check effect of strengthening proposal



Necessary extent of repair evaluated by fatigue screening of global



Stress concentration factor used in global screening calculated by the ratio of long term stress from local and global analysis

Local model with new bracket

Fatigue results

Results from fatigue screening of global model to evaluate extent of repair FPSO Full Ship Analysis October 15, 2012


Purpose

Global modelling






ULS analysis




 





Input


























Output




Global FE model
















Long term stress

Stochastic ULS Analysis Challenge:

Determine ULS design wave for areas subjected to a combination of different load effects (e.g. turret area) Typical way: Selection of one or several design waves  Uncertainties New solution with Stofat: Spectral stress analysis to determine long term stress distribution directly 

Wave Load Analysis - Input: Global model, wave headings and frequencies - Output: Load transfer functions (RAOs)



Direct Load Transfer

Stress Response Analysis - Input: FE models and load file from wave load analysis - Output: FE results file with load cases describing complex (real and imaginary) stress transfer functions (RAOs)



Long Term ULS Load Calculation - Input: Stress transfer functions (FE results file), wave data

Stress Transfer Functions


- Output: Calculated long term stress

Long term stress FPSO Full Ship Analysis October 15, 2012

Stofat – Features and Benefits 

Features - Stochastic fatigue calculations based on wave statistics - Supports all common wave models - Predefined and user defined S-N curves - Option for implicit mean stress correction (by static load case)

- Statistical stress response calculations - Calculation of long term stress and extreme response including static loads

- Graphical presentation of fatigue results and long term stress directly on FE model



Calculated fatigue damage by nominal stress and user defined SCF for an LNG carrier

Benefits - Unique functionality for spectral fatigue and stochastic long term stress and extreme response calculations - Flexible – support all your needs - Transparent – all calculation steps can be documented Calculated long term stress amplitude (left) and fatigue damage (right) for the hopper knuckle in an oil tanker


Local fatigue check result


Benefits of Sesam for Advanced Analysis 

Complete system – Proven Solution - Cover your needs for strength assessment of ship and offshore structures - 40 years of DNV experience and research put into software tools



Concept modelling - Minimize modelling effort by re-use of models for various analysis - Same concept model can be used for global & local strength analysis, stability, linear and non-linear hydrodynamic hydrodynamic analysis



Same system for offshore and maritime structures - Minimizes the learning period and maximizes the utilisation of your staff

 Process, file and analysis management by Sesam Explorer




SesamTM Conitnuing 40 years success Nonlinear analysis of a pipe-laying vessel with Morison model Fan (Joe) Zhang, Sesam BD Manager, DNV Software October 16, 2012

Contents 

Pipe-laying vessel parameters



Time domain analysis settings - Wasim - Morison Model - Motion Control springs - Mass activity

- Setup activity 

Morison model in time-domain analysis



Comparison of different wave theories

Nonlinear analysis of a pipe-laying vessel with morison model October 16, 2012

Main parameters Pipe-laying vessel parameters

Characteristic length

162.4

m

Gravity

9.8

m/s^2

Density of sea water

1025.0

Kg/m^3

Water line Z coordinate

0.0

m

Period

12

s

Height

20

m

Direction

135

deg

Mass

5.1e7

kg

X-COG

4.3

m

Y-COG

0

m

Z-COG

0

m

RX

14.01

m

RY

46.5

m

RZ

45.51

m

General

Incoming wave parameters

Mass data

Radius of gyration


GLview P Plugin lugin not installed. Press here to install plugin

Wasim Wizard 

Set up the steps of the wizard, other features may be added later, if necessary - Time domain - Morison Model - Motion Control springs - Mass activity - Setup activity


Define Morsion Crossection


Define Section Model


Section model mesh


Mesh on the free surface


Morison model in Wasim (Calm Sea, Original Roll=5 deg)

Calm sea run with 5 degree heel angle. No additional roll damping assigned. With Morison model, the roll motion is damped out.


Morison model in Wasim

T=12 s, H=20 m, Dir=135 deg No additional roll damping assigned.

With Morison model, larger response in the beginning stage, but more stabilized due to damping from stinger.


Airy vs. Stokes wave – Wave

Depth = 50 m


Depth = 30 m

Airy vs. Stokes wave – Heave

Depth = 50 m


Depth = 30 m

Airy vs. Stokes wave – Roll

Depth = 50 m


Depth = 30 m

Airy vs. Stokes wave – Roll moment

Depth = 50 m


Depth = 30 m



SesamTM Conitnuing 40 years success Comparison of linear and nonlinear analysis of a Semi-submersible with anchors Fan (Joe) Zhang, Sesam S esam BD Manager, DNV Software October 16, 2012

Contents 

Semi-submersible parameters



Frequency domain analysis - Using Wadam - Section Model - Stochastic drag - Anchor elements



Time domain analysis - Using Wasim - Wave spectrum - Mass activity - Setup activity



Comparison - Frequency vs. time domain - Linear vs. nonlinear method


Main parameters Semi-submersible Main Parameters

General

Wave spectrum

Mass data

Radius of gyration

Anchor sections sections

Characteristic Length

80.46

m

Gravity

9.8

m/s^2

Density of water

1025

kg/m^3

Water line Z coordinate

31.394

m

Water depth

Infinite

Significant wave height Hs

12

m

Peak period Tp

16

s

Mass

5.11e7

kg

X

0

m

Y

0

m

Z

31.76

m

RX

35.66

m

RY

35.66

m

RZ

42.80

m

Pre-tension

1.79e6

N

Vertical stiffness

1e4

N/m

Horizontal stiffness

1.5e4

N/m

40

deg

Angle sea surface surface Nonlinear analysis of a pipe-laying vessel with morison model October 16, 2012


Wadam Wizard 

Set up the steps of the wizard, other features may be added later, if necessary - Frequency domain - Section Model - Stochastic drag - Anchor elements


Define Morsion Crossection


Define Section Model


Section model mesh


Motions RAOs from frequency domain analysis


Wasim Wizard 

Following features are selected - Time domain

- Wave spectrum - Mass activity - Setup activity


Wave surface mesh created by ‘Automatic surface meshing’

Free surface mesh generated by WasimMesh does not give satisfactory results. Nonlinear analysis of a pipe-laying vessel with morison model October 16, 2012

Create free surface mesh by HydroMesh


Refine the free surface mesh 



The way to improve the mesh is to split the free surface into patches of as regular shape as possible.

This is done by creating split lines.


Refine the free surface mesh


Comparison of Wadam and Wasim (linear and nonlinear)


Comparison of linear and nonlinear analysis in Wasim


Comparison of linear and nonlinear analysis in Wasim




SesamTM Continuing 40 years of success DeepC for pipe-in-pipe analysis Fan (Joe) Zhang, Sesam BD Manager, DNV Software October, 2012

Industry example – Subsea TTRD operations on the Åsgard Field 





The Åsgard field : 16 templates, 56 wells. Åsgard A production started May 1999 Well P-4H - started production 2001. - Closed 2005



Subsea TTRD operations 2010 -

Whipstock was set at 3900 m MD Sidetrack drilled to approx 5700 m MD Total length of sidetrack 1800 m Source: Drilling Contractor Magazine


Example: DeepC riser analysis – TTRD 

TTRD: Through Tubing Rotary Drilling - Drilling and workover mode



Water depth: 310m



Workover mode: -

Hs: 2m, 4m, 6m Tp: 8s, 10s, 12s, 14s Seven vessel offsets Calculation of load utilization

Diverter

Low pressure riser

Flex joint

Telescopic joint inner barrel

Telescopic joint outer barrel

SBOP

UTSJ

High pressure riser

Merlin Riser

LTSJ

EDP LRP XT


DeepC model of the TTRD system Tension frame

Drill Floor Elevation (RKB)

Coiled tubing stack Telescopic joint Riser tensioners

HP Workover riser Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

DeepC model of the TTRD system Tension frame legs

Surface flow tree Drill floor (RKB)

Coiled tubing stack Slick joint Diverter and Flex joint Telescopic Joint Extension pipe (inside telescopic joint)


Structural utilization. Statistical post-processing. 

Post-processing to establish utilization - Module : Combined Loading Analysis


Final result of analysis: Operating Limitations Example : Coiled tubing mode. 10ksi internal pressure

e v a w t s n a H c t , i f i h n i g g e i S h

Vessel offset Sesam DeepC for deepwater coupled analysis, mooring and riser design October, 2012

Demo for drilling riser – simplified workshop 







Visualization of pipe-in-pipe motion in Xtract Scatter diagrams/discretizations etc. for regular waves Possibility to apply multiple scatter discretizations (e.g. direction dependent) in Fatigue analyses. Parallel execution of analyses


Single Drilling Riser Analysis 

Simulate a single drilling riser with pipe-in-pipe contact applied in a Semisubmersible platform and conduct time-domain analysis and evaluate the results with animation; - In this demo the analysis will be de-coupled, in which the motion of SEMI are calculated based on RAO functions from HydroD/Wadam analysis. - Pipe-in-pile contact is simulated by stiffness between inner and outer risers. - Results will be checked both in DeepC GUI and animation in Xtract.


Fatigue analysis 



For the present riser configuration, fatigue is not a problem of great concern. The shortest fatigue lives are found in the splash zone, and therefore only the upper part of the outer riser is included in the Fatigue Analyses. - In order to have more “interesting” fatigue results for this demo, we have modified the fatigue properties, by introducing thinner walls and higher Stress Concentration Factors to reduce Fatigue life.



In DeepC version V4.5-04 or higher, regular scatter is available. This alternative uses regular waves (wave height and period) which are quicker to compute.


Code check 



The Code Check which is set up in the workshop is based upon vonMises stress formulation. The analyses are set up to get some resemblance with the code API 16Q.



In this code the yield is set to 358 MPa, corresponding to 52.000 psi.



API 16Q has two modes: Drilling mode and non-drilling mode. - In drilling mode the allowed utilization factor is 40%. - in non-drilling mode the allowed utilization factor is 67%. - We have used 0.4 (40%) in this workspace.


Define the environment


Cross sections parameters


Slender structure modeling Totally the outer riser consists of 24 segments


Pipe-in-pipe contacts


Responses under irregular waves

DeepC V4.6-08 Date: 15 Oct 2012 21:18:10

L41_DrillRiser_Outer_DRO_18_Element_1_Te

6 0 0 + e 8 . 1 ] N [ e c r o F

6 0 0 + e 5 7 . 1

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

Time [s]

L41_DrillRis er_Outer_DRO_18_Eleme nt_1_Te - Mean: 1772816 .785, Std: 2875.7310 54, Min: 1743157 , Max: 180414 8.75, Start: 0, End: 199.5, Step: 0.5 DeepC V4.6-08 Date: 15 Oct 2012 21:18:26

200

L41_DrillRiser_Outer_DRO_18_Element_1_Mx

0 1 ] m * N [ e c r o F f O t n e m o M

0

-5.863

0 1 0 2 -

0

10

20

30

40

50

60

70

80

90

100

110

120

130

L41_DrillRis er_Outer_DRO_18_Elemen t_1_Mx - Mean: -4.728001134 , Std: 6.07571419 4, Min: -22.6324996 9, Max: 9.36987972 3, Start: 0, End: 199.5, Step: 0.5


140

150

160

170

180

190

200 Time [s]

Define properties for fatigue analysis


Environment condition for fatigue analysis


Fatigue analysis result

DeepC V4.6-08 Date: 15 Oct 2012 22:25:38

Fatigue L ife 0 1 0 + e 1 ] s r a e Y [ e f i L e u g i t a F

0 0 0 0 0 1

230

240

250

260

270

280

290

300

310

320

330

Line Coordinate[m] FatigueIrr1-L41_DrillRiser_Outer


FatigueReg1-L41_DrillRiser_Outer

Properties for code check analysis


Combined loading code check result

DeepC V4.6-08 Date: 15 Oct 2012 22:56:59

CombinedLoading Results 1 . 1 1 9 . 0 8 . 0 r o t c a f n o i t a z i l i t U

7 . 0 6 . 0 5 . 0 4 . 0 3 . 0 2 . 0 1 . 0 0

230

240

250

CL_AnaReg_T17x5_dir0-L41_DrillRiser_Outer-Sample CL_AnaReg_T10x5_dir0-L41_DrillRiser_Outer-Sample


260

270

280

290

300

CL_AnaReg_T17x5_dir45-L41_DrillRiser_Outer-Sample CL_AnaReg_T10x5_dir45-L41_DrillRiser_Outer-Sample

310

320

330

Line Coordinate[m]



Umbilical Design Using UmbiliCAD and Helica

Fan Joe Zhang, Business Development Manager, Americas 03 August, 2012

Introduction to UmbiliCAD 

UmbiliCAD® by UltraDeep - A cross-section design, drawing and modeling tool

- Drawing contains all material properties - Calculates mass, weights, axial, bending and torsion stiffness - Stress capacity calculation - Analythical methodolgy for stiffness and stress capacity calculation - Tube sizing according to DNV-OS-F101 and ISO 13628-5 - Module for reel capacity calculation - Module for bill of material - DXF export to other CAD tools - Module for Helica calculations - Plugin capability

Umbilical Design 03 August, 2012

UmbiliCAD Power cable/umbilical


Steel tube umbilical

Control umbilical

Why UmbiliCAD? 

No need to be an advanced draftsman



Early cross section analysis – first results within hours in stead of days - Linear analysis with no stick/slip

Capacity Curve

1200

100% Utilisation

1100

80% Utilisation

1000 900 ] N k [ n o i s n e T

800 700 600 500 400 300 200 100 0.0 0.0


0.04

0.08

0.12

0.16 0.2 0.24 Curvature [1/m]

0.28

Introduction to Helica 

Helica™ by DNV - A cross-section stress analysis tool

- Short-term fatigue analysis - Long-term fatigue analysis - a tailor-made software for cross-sectional analysis of flexible pipes and umbilicals - Load-sharing between elements considering axis-symmetric analysis - Calculation of cross-sectional stiffness properties (axial, torsion and bending stiffness) - Helix element bending performance analysis to describe stresses in helix elements during bending considering stick/slip behaviour due to interlayer frictional forces.


Helica 

Cross-sectional load sharing analysis - Load-sharing between elements considering axis-symmetric analysis

- Calculation of cross-sectional stiffness properties (axial, torsional and bending stiffness) - Helix element bending performance analysis to describe stresses in helix elements during bending considering stick/slip behaviour due to interlayer frictional forces 

Short-term fatigue analysis - To assess the fatigue damage in a stationary short-term environmental condition considering fatigue loading in terms of time-series of simultaneous bi-axial curvature and effective tension produced by global dynamic response analysis - Helica uses results from DeepC as the response database for time domain global dynamic analysis as loading



Long-term fatigue analysis - To assess the long-term fatigue damage by accumulation of all short -term conditions vr

v

x


v

Helica 

Cross-sectional bending characteristics - Relative motion between layers/components

- Friction, stick/slip behaviour (Tension dependent) - Moment/curvature hysteresis - Non-linear amplitude dependent - Above effects automatically accounted for

t n e m o M

Curvature Umbilical Design 03 August, 2012

UmbiliCAD and Helica Bundle 





UmbiliCAD and Helica is a bundeled software UmbiliCAD exports cross section geometry and material properties to Helica, set up load cases, and build the model for analysis. Helica can be run from mbiliCAD and results and plots can be presented in UmbiliCAD The Helica model can also be exported and run manually in Helica for batch processing.


Demo Case Umbilical Component and Crosssection Design


Cross-section


Parameter Ou ter Diameter

Value Unit 143.1 [mm]

Mass Empty

30.8

[kg/m]

Mass F illed

32.6

[kg/m]

Mass Filled An d Flood ed

35.2

[kg/m]

Submerged Weight Empty Su bmerg ed Weigh t Filled

14.3 16.1

[kgf/m] [kgf/m]

Submerged Weight Filled And Flooded

18.7

[kgf/m]

Sp ecific Weigh t Ratio

2.1

[- ]

Su bm . Weigh t. Dia. Ratio

130.8 [kgf/m^2]

Ax ial Stiffn ess Bend ing Stiffn ess

431.5 [MN] 24.9 [kNm^2]

Bend ing Stiffn ess (friction free)

15.0

Torsion Stiffn ess

148.6 [kNm^2]

Tension /Tor sion Factor

-0.02 [deg/m/kN]

[kNm^2]

The Dynamic Umbilical Design Process


CLIENT Function.list

Functional Requirements

Cross-section

Component Design

Standards and Codes

drawing

(UmbiliCAD)

(ISO 13628-5)

Mechanical Properties

Cross-section Design (UmbiliCAD & Helica)

Capacity Curves

Local Analysis (Helica)

Global Design and Analysis (DeepC Riflex)

Global Analysis

Global Extreme Analysis

Global Fatigue Analysis

Global Fatigue

Report

(e.g. 100 year hurricane

(Full scatter diagram

Analysis Report

DeepC Riflex)

DeepC Riflex)

Local Fatigue Analysis

Local Fatigue

(e.g. in BS, sag, hog etc.

Analysis Report

Helica)


Component and Cross-section Design 

Using UmbiliCAD and Helica


Local Analysis 

Using Helica - Compute cross sectional properties

Helix position: 270.0000 600

Parameter

Value Unit

Outer D iameter Mass Empty Mass Filled

133.2 [mm] 35.9 [kg/m] 39.4 [kg/m]

Mass Filled And Flooded

42.4

[kg/m]

Submerged WeightEmpty

21.6

[kgf/m]

Submerged WeightFille d Submerged WeightFilled And Flooded

25.1 28.1

[kgf/m] [kgf/m]

Specific Weight Ratio

3.0

[-]

Sub m. Weight. Dia. Ratio AxialStiffness

210.8 [kgf/m^2] 677.3 [MN]

Bending Stif fness Bending Stiffness (friction free) Torsion Stif fness

21.3 16.7 27.5

[kNm^2] [kNm^2] [kNm^2]

Tension/Torsion Facto r

0.00

[deg/m/kN]

CapacityCurve

500

100% Utilisation 80% Utilisation

450 400

500

350 s s e r t s x i l e h l a t o T

] N300 k [ n o250 i s n e200 T

400 300 200

150 100

100

50 0 -0.0004 -0.0003 -0.0002 -0.0001

0

0.0 001 0.0 002 0.0003 0.0 004

Curvature


0.0 0 .0

0 .0 4

0 .0 8

0 .1 2

0 .1 6 0 .2 0 .2 4 0 .2 8 Curvature [1/m]

0 .3 2

Global Design and Analysis 

Using DeepC Riflex - Coupled or de-coupled analysis Wave loading

Forced floater motions

Non-linear load model

Non-linear structure


Global Analysis 

Using Helica to get capacity curve - The capacity curve presents all load combinations that result in the specified maximum allowable equivalent stress due to: - Tension - Pressure - Bending - Torsion

- All cross-section members are considered Bend stiffener region


Local Fatigue Analysis 

Using Helica



Load sharing analysis - Axi-symmetrical analysis to establish tension in each element - Bending analysis including the hysteretic, friction induced stick/slip behavior of the helix elements


Local Fatigue Analysis – Short-term fatigue analysis 



Purpose of the analysis is assessment of fatigue damage in a stationary shortterm environmental condition Specification of: -



Helix element Longitudinal locations Helix positions/hot-spots SN-curve

Helix stresses calculated: - Stick/slip friction due to bending - Bending about local axis - Stresses due to tension (from axisymmetrical analysis)



Rainflow cycle counting



Fatigue damage calculation


s s e r t s e u g i t a F



 t

- Fatigue stress time series

Time

Stress range

Local Fatigue Analysis – Long-term fatigue analysis 



Purpose of the analysis is to assess the long-term fatigue damage by accumulation of all short-term conditions Required input: - Fatigue results for all short-term conditions - Probability of each short-term condition


Size of problem – numerical performance 

270 TD simulations with 1 hour duration (20.000 time steps)



Rectangular tensile armours, 4 hot-spots



12 helix locations





Fatigue damage calculated at 76 locations along riser (including bend stiffener area)

y

yl

Total of 985.000 1 hour stress time series generated by cross-sectional analysis

xl 

Computation time – standard single core lap-top Model

Total

Per case

Tube, no friction

0.38 hours

5 seconds

Helix, no friction

3.8 hours

50 seconds

Helix with friction

5.8 hours

77 seconds

Global TD analyses not included in computation time


x

Example

Local Fatigue Analysis


Analysis process 

Calculate cross section parameters - Mass/weight in UmbiliCAD

- Axial, bending and torsion stiffness from Helica 

Global analysis using DeepC - Riflex - Inpmod - Riser definition – Cross section parameters from first step - Environment definition – wave heights, current etc. with corresponding direction

- Riflex – Stamod - Static analysis

- Riflex – Dynmod - Dynamic analysis 

Short-term fatigue analysis using Helica



Long-term fatigue analysis using Helica



Design of umbilicals is also based on ULS – this is part of UmiliCAD/Helica analysis, but not covered in this presentation


Lay-out of the riser

27 Environment conditions


Step 1 Create cross-sections and calculate mass properties 

UmbiliCAD will do both


Parameter

Value Unit

Outer Diameter

117.0 [mm]

Mass Empty

23.0

[kg/m]

Mass Filled Mass Filled An d F loo ded

26.5 28.7

[kg/m] [kg/m]

Su b merg ed Weig ht Emp ty

12.0

[kgf/m]

Su b merg ed Weig ht Filled

15.5

[kgf/m]

Su b merg ed Weig ht Filled An d Floo d ed

17.7

[kgf/m]

Sp ecific Weight Ratio Su b m. Weigh t. Dia. Ratio

2.6 [- ] 151.1 [kgf/m^2]

Ax ial Stiff n ess

476.3 [MN]

Ben d in g Stiff n ess

29.0

[kNm^2]

Ben d in g Stiff n ess ( fr ictio n fr ee)

23.7

[kNm^2]

Tor sion Stiff n ess Ten sion /Tor sio n Factor

43.5 0.00

[kNm^2] [deg/m/kN]

Step 2 Calculate stiffness using Helica


Step 3 Run global response analysis using Riflex 

For a fatigue analysis, responses under multiple environment conditions (wave scatter) may be analyzed. Batch executions are normally used. ( run-riflex.bat )



Motion RAOs of the vessel will also be used. ( trafile.tra)



In this example, the analysis setup contains 27 weather directions.

Inpmod.inp Stamod.inp Dymod.inp

Trafile.tra


run-riflex.bat

executing…

Capacity curve vs. time-domain time series 

Responses should be within the 80% or 100% capacity curves


Step 4 Run fatigue analysis using Helica 

Calculate short term fatigue for critical area for each of the bins. - In this example the critical areas are the BS area of SDTube2 and SDTube4 (inner layer of cross section).





When all bins are completed, fatigue is accumulated and long term fatigue is calculated by Helica. Following input files are normally needed: - Helica Fatigue analysis input file (BSSDTube2_fat_ana.inp) - Helica Cross Section (helica.inp, could be generated by Helica) - Fatigue setup, (where to calculate fatigue etc (BSSDTube2_fat_geo.inp) - Fatigue probabilities (fat_conditions.inp) - SN curves (SN-lib.inp)


Helica fatigue analysis input file 

Defining the parameters used in Helica fatigue analysis, e.g. - Analysis time window - Helix element positions - If friction will be considered - Etc.

Here ‘2’ means friction will be considered using updated contact force.


Long term fatigue histograms

Case19_layer3_compone nt1_location11_hotspot5


Summary – Why UmbiliCAD and Helica? 

To facilitate the deepwater challenge

1)

:

- “Increased importance of higher order cross -sectional effects” - Tension/radial displacement coupling - Internal friction

- “These effects may considerably affect dynamic umbilical performance i n deep waters” 

Main benefits - No need for specialist competence in a CAD system – drawings, cross sectional properties and early design capacity curves made in hours instead of days - Outstanding numerical performance gives answer in days instead of weeks - Extreme design – capacity curves for entire cross -section in compliance with applicable design codes - Fatigue stress analysis of helix elements considering stick-slip behaviour in bending - Calculation of consistent fatigue stresses by direct application of global response time series from DeepC as external loading - Short-term fatigue life calculation capabilities including Rain-flow cycle counting - Long-term fatigue life calculation capabilities including assessment of long- term stress cycle distribution

1)

Ref.: OTC 17986:2006: “Predicting, Measuring and Implementing Friction- and Bending Stresses in Dynamic Umbilical Design”, Ekeberg et.al.) Umbilical Design 03 August, 2012

Sesam Hydrodynamics Training Oct 2012

Recommend Documents