Upload
rahul-m
View
219
Download
1
Tags:
Embed Size (px)
DESCRIPTION
Advanced FE Analysis
Citation preview
Experience that DeliversExperience that Delivers
Advanced post-processing of FE Analyses: 3D sub-modelling for subsea pipelines
Graham Viecelli
AOG Focus on TechnologyPerth Convention & Exhibition Centre, 20th February 2014
1
Sub-modelling for pipelines
2
• Identify the peak stress & strain (tensile and compressive) plus stress ranges at the girth weld – governing location for design
• Account for:– All potential temperature and pressure loads during installation, pre-start-
up, operation and decommissioning– Coatings, field joints, CRA clad or liner material– In-line structures (TEE, WYE, reducer, valves, anchors etc) – External factors (pipe-soil interaction, trawling interaction, counteracts,
other pipelines, anchors, dropped objects)– Any other case-specific issues that influence the pipeline structural
response
Subsea pipeline design
3
• Simple geometry – a pipe is just a cylinder after all!
• Homogeneous material – only the steel pipe is structural
• Flanges, TEE’s, WYE’s, buckle arrestors, reducers only affect the submerged weight
• Stress and strain concentration can be accounted for later by applying factors
Design assumptions
4
Numerical representation of a pipeline
Element features• Based on Timoshenko ‘shear flexible’
non-linear beam theory
• Consists of 2 nodes with 6 degrees of freedom, a single integration point and at least 8 section points around the pipe circumference
• Fully validated element response against numerous experimental tests within the limits of non-linear beam theory
PIPE31H beam element
Nodes
Integration PointSection Points
12
3Illustration of a PIPE31H beam element indicating the location of the integration point and section points
5
• Simple geometry – a pipe is just a cylinder after all!– What about the weld? Field joints? Misalignment or ovality?
• Homogeneous material – only the steel pipe is structural– What about CRA liner/clad, thick insulation or CWC?
• Flanges, TEE’s, WYE’s, buckle arrestors, reducers only affect the submerged weight– Thick, dense structures are also incredibly stiff…
• Stress and strain concentration can be accounted for later by applying factors– True, but what about ovalisation or local deformation
› Will high bending strains affect the fluid flow? › Can you pass a pig through the pipe under design operating conditions?› Do conservative SCF / SNCF influence the ECA results?
Design assumptions
6
3D pipeline design problems
Typical design approach• Assume simplified geometry
- Full cohesion between layers- No weld geometry at field joint
• Assume simplified loads- Pure axial or bending, not both- Internal pressure on pipe wall
only, end cap force only applied at ends
• Ignore operational configuration- Initial conditions include; straight
pipe, virgin material
Calculating strain concentration
Or wrinkling of lined pipe
7
How can sub-modelling help?
BMW Crash testing• An initial analysis is performed
including the whole car
• Many simplifications are included to reduce the model complexity and analysis run-time
• Smaller sections are analysed using sub-modelling to confirm the behaviour in the global analysis
• Even the passengers can be modelled!Taken from “Migration of Crash
Simulation Software at BMW”, 2005
Global model/analysis
Sub-model
8
How can sub-modelling help?
Airbus A380 design and testing• The design process for this aircraft
represented a step-change in design challenges
• Experimental testing was prohibitively expensive – design relied heavily on numerical modelling
• Multiple analysis levels (global models and sub-models) were used to obtain the aircraft structural response
Airplane components
Taken from AIRBUS Central Entity, 2005
9
1. Using a coarse model of the pipeline, perform a ‘global’ analysis(The global analysis defines the overall structural response of the pipeline)
2. Smaller sections of pipe may be analysed using sub-models – each sub-model is ‘driven’ by the output of the global analysisThe sub-model is a more accurate representation of the pipe section, and may include additional materials and/or geometry as required.
3. Multiple sub-model analyses may be performed on the same global analysis
4. A sub-model analysis can also be used as a global analysis
Sub-modelling overview
10
Sub-Model analysis sequence
• 3D sub-model is driven by the output from the global analysis:o Nodal displacements and rotation
oro Nodal forces and moments oro Combination of the above
• Additional details may be added:o Geometric featureso Additional materialso Local loadso In-line structures
Glo
bal p
ipel
ine
mod
el
11
Sub-model advantages & limitations
• Advantages:o Greater accuracy in stress and straino Include geometric and material interactionso Can be performed many times on the same global analysiso Computationally cheap
• Limitations:o The global analysis must be an adequate representation of the structural
response (i.e. the stiffness of the sub-model should reasonably match the same section in the global model)
12
Sub-model applications
Design considerations• Initial global analysis defines the
overall pipeline structural response
• First sub-model allows 3D visualisation of the stress and further sub-modelling
• Second sub-model captures the weld geometry and material properties
• Third sub-model can recreate test specimens for model / material calibration and testing
Multiple sub-models
Sub-model 3
Global analysisSub-model 1
Sub-model 2
13
Sub-model applications
Figure illustrates the stress distribution 12m either side of the apex of a lateral buckle
Design considerations• Stiffness of the CWC is captured in
the global analysis
• Field joints are also included as regions devoid of concrete.
• No need for SNCF!! Strain output from global analysis already captures increase due to presence of coatings.
• 3D analysis computationally ‘cheap’, analysis time for single load cycle < 1.5 hours.
Apex of a lateral buckle with CWC
14
Sub-Model AnalysisGlobal Analysis
Animation illustrates the strain distribution 12m either side of the apex
Apex of a lateral buckle with CWC
Sub-model applications
15
Sub-model applications
Figure illustrates the stress distribution 3m either side of the apex of a lateral buckle
Design considerations• Misalignment not included in global
analysis.
• Stress concentration can now be based on known (as built) pipe geometry under design conditions; can compare with analytical calculation in DNV-OS-F101.
• 3D analysis computationally ‘cheap’, analysis time for single load cycle < 10 minutes.
Pipe-joint misalignment
Pipe-joint misalignment
16
Applications
Design considerations• Sub-model can be used to
assist in buckle arrestor design.
• Increase confidence in the ability of a buckle arrestor to halt propagating buckles under a variety of design conditions.
Buckle arrestor design
17
Installation case study
Global analysis Sub-model analysisModel overview
18
Installation case study
Global analysis Sub-model analysisInitiate a local buckle
19
Installation case study
• Local buckle initiated in the sub-model only
• Sub-model boundary conditions from the global analysis provide support to the pipeline during this unstable process
• Buckle propagation measured to be faster than 200 m/s!
20
Installation case study
Global analysis Sub-model analysisBuckle propagation ends near the stinger
Propagating
21
Installation case study
• Cut view of the pipeline as (approximately) viewed from the end of the stinger
• The local buckle propagates up the catenary, eventually running out of steam as it approaches the stinger
22
Installation case study
Global analysis Sub-model analysisBuckle arrestor stops buckle progression
Propagating
23
Installation case study
• As viewed downstream from the buckle arrestor
• The local buckle propagates down the catenary and along the laid pipeline until it reaches the buckle arrestor. Propagation is then halted by the buckle arrestor – a satisfactory design!
24
• Sub-modelling is an established method for obtaining highly accurate results from finite element analyses
• Sub-model analyses are fast and stable, and offer the most efficient method for modelling a 3D pipeline under all operational loads
• Wood Group Kenny has developed an ABAQUS GUI plug-in capable of sub-modelling pipeline FEA. Model development is fast, accessible to non-FEA engineers and capable of performing many different pipeline design analyses.
AcknowledgementsDavid Timmins, Rotger Jost, Terry Griffiths & Andrew Rathbone
Further questions:[email protected]
Summary