ml structural mechanics simulation june 2011
DESCRIPTION
fea analisissimulationTRANSCRIPT
© 2011 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary© 2011 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary
Structural Mechanics Simulation (CSM using finite element analysis)
Mark Leddin
ANSYS UK
© 2011 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary
Agenda
• Structural Mechanics Simulation (CSM using finite
element analysis)
- Structural integrity performance for
complex structures and sub-structures
- Seismic assessment
- Geotechnical engineering
- Thermal bridging
Fluid-Structure-Interaction (FSI)
- Blast loading and structural response
- I-beam structural integrity under thermal loading
© 2011 ANSYS, Inc. All rights reserved. 3 ANSYS, Inc. Proprietary© 2011 ANSYS, Inc. All rights reserved. 3 ANSYS, Inc. Proprietary
Structural integrity performance for complex structures and sub-
structures
© 2011 ANSYS, Inc. All rights reserved. 4 ANSYS, Inc. Proprietary
ANSYS Mechanical FEA Suite
• Founded in 1970, ANSYS have been
developing generic Mechanical FEA software
for 40 years
• Originally developed for the nuclear industry,
quality was paramount in its design, now
in accordance with ISO quality controls
• ANSYS FEA has the broadest range of
capabilities in the market-place, with
technologies for:
– Linear & Nonlinear (geometric/material)
analyses
– Static, frequency-domain & time-domain
– 0-D to 3-D elements
– Isotropic, anistropic, layered materials
– ....
© 2011 ANSYS, Inc. All rights reserved. 5 ANSYS, Inc. Proprietary
Product/Technology Description
ANSYS
DesignSpace
ANSYS
Structural
ANSYS
Professional NLT
ANSYS
Mechanical
Linear Structural
Steady State Thermal
Linear Structural
Steady State Thermal
Transient Thermal
Linear Dynamics
Linear Structural
Non-Linear Structural
Linear Dynamics
Nonlinear Dynamics
Linear Structural
Non-Linear Structural
Linear Dynamics
Nonlinear Dynamics
Steady State Thermal
Transient Thermal
Acoustics
Direct Coupled
Solver Technology
ANSYS
Professional NLS
Linear Structural
Steady State Thermal
Nonlinear Structural
Linear Dynamics
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Analysis Methods & Solvers
Technology Components
Geometry & Mesh
Materials
Boundaries & Loads
Solution
Post-Processing
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ANSYS Structural Mechanics
• Geometry
– Direct CAD Links
• Connect to real CAD models
and create true parametric
analysis
– Create analysis geometry
• Geometry clean-up
• Simplification
• Create Shell & Beam
geometry
– Work with imported files
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Analysis Methods & Solvers
Elements Technology
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Analysis Methods & Solvers
Materials Modeling
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ANSYS Structural Mechanics
Solvers
• Structural / Thermal /
Acoustics / ... / Coupled
• Linear / Nonlinear
• Implicit / Explicit
• Evolving to keep pace
with hardware
developments• Multi-core
• 32 & 64 bit
• Clusters
• GPU
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ANSYS Structural Mechanics
• Postprocessing
• Stress, Strain,
Deformation, Creep,
Contact, Reactions.....
• Images
• Tabular data Excel
• Movie files
• Automated report
generation
© 2011 ANSYS, Inc. All rights reserved. 12 ANSYS, Inc. Proprietary
Submodelling
Submodeling is a finite element
technique that you can use to
obtain more accurate results in
a particular region of a model.
A finite element mesh may be
too coarse to produce
satisfactory results in a given
region of interest. The results
away from this region,
however, may be satisfactory
Jackup Rig
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Base model – Beam Elements
Typical structure that is modelled using
beam elements.
Locally high load at deck to leg
interface.
Load applied in example:
Wind load as nodal forces.
Deck interface as point constraint.
Gravity.
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Shell model for detailed study
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Integral Method
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Seismic assessment
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Spectrum analysis
Deterministic:
• Response Spectrum
• Single-Point Response Spectrum
• Multi-Point Response Spectrum
• Dynamic Design Analysis Method
Probabilistic:
• Random vibration
• Power Spectral Density (PSD)
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Description & Purpose
• It is common to have a large models excited by transient loading.
– e.g., building subjected to an earthquake
– e.g., electronic component subjected to shock loading
• The most accurate solution is to run a long transient analysis.
– “Large” means many DOF. “Long” means many time points.
– In many cases, this would take too much time and compute resources.
• Instead of solving the (1) large model and (2) long transient together, it
can be desirable to approximate the maximum response quickly.
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Description & Purpose
Idea: solve the (1) large model and (2) long transient separately and
combine the results.
Large model
Long transient
Large model
Mode extraction
↓
Mode shapes
Small model
Long transient
↓
Response spectrum
Combined solution
Fast, approximateFull solution
Slow, accurate
Large model
Long transient
Transient Analysis Response Spectrum Analysis
© 2011 ANSYS, Inc. All rights reserved. 20 ANSYS, Inc. Proprietary
Generating the Response Spectrum
ω = 30 Hz
S = 95 m/s2
ω = 50 Hz
S = 138 m/s2
ω = 70 Hz
S = 86 m/s2
© 2011 ANSYS, Inc. All rights reserved. 21 ANSYS, Inc. Proprietary
Spectral Regions
• Two frequencies can often be identified on a response spectrum
– This divides the spectrum into three regionsmid
frequency
high
frequency
low
frequency
fSP
frequency at peak response
(spectral peak)
fZPA
frequency at rigid response
(zero period acceleration)
1. Low frequency (below fSP)
• periodic region
• modes generally uncorrelated
(periodic) unless closely spaced
2. Mid frequency (between fSP and fZPA)
• transition from periodic to rigid
• modes have periodic component and
rigid component
3. High Frequency (above fZPA)
• rigid region
• modes correlated with input frequency
and, therefore, also with themselves
ZPA
© 2011 ANSYS, Inc. All rights reserved. 22 ANSYS, Inc. Proprietary
Mode Combination
Whereas the SRSS method takes the following form,
The CQC and ROSE methods introduce a double sum and a correlation
coefficient.
Each method has a formula for the correlation coefficient, ε, which
is based on the frequency and damping of modes i and j
is designed to vary between 1 (fully correlated) and 0 (uncorrelated)
2
1
1
2
N
i
iRR
2
1
1 1
2
1
1
ROSECQC
N
i
N
j
jiij
N
i
N
ij
jiij RRRRRkR
© 2011 ANSYS, Inc. All rights reserved. 23 ANSYS, Inc. Proprietary
Spectrum analysis
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Spectrum analysis -
Static pre-stress
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Spectrum analysis –
Modal analysis
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Spectrum analysis –
RS loading
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Spectrum analysis –
Results
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Geotechnical
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Drucker-Prager Plasticity
• Drucker-Prager (DP) plasticity is applicable to granular (frictional) materials such as soils, rock, and concrete.
• Unlike metal plasticity, the yield surface is a pressure-dependent von Mises surface for DP:
where sy is a material yield parameter, sm is the hydrostatic pressure, seqv is von Mises stress, and b is a material constant.
• Plotted in principal stressspace, the yield surface isa cone.
s1
s2
s3
s1 s2 s3
y
eqv
mF ss
bs 3
3
© 2011 ANSYS, Inc. All rights reserved. 30 ANSYS, Inc. Proprietary
• Cap Drucker-Prager plasticity model applicable to
– Simulation granular materials such as soils
– Powder compaction simulation
– The model has also been utilized for modeling pressure-dependent
plasticity of polymers
• The model is a new addition to the existing Extended Drucker-
Prager model
– Introduce cap for both tension and compression
– Include cap hardening
– Include shear envelope hardening
Cap Drucker-Prager Model
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Cap Drucker-Prager Model
Soil excavation analysis using EDP model with Cap
Displacement Plot Plastic Strain Plot
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Concrete Model
• The concrete material model in ANSYS can
be used to model brittle materials, such as
concrete, rock and ceramics.
– Both cracking and crushing failure modes
are included.
– Prior to failure, behavior is assumed to be
linear elastic. However, plasticity and/or
creep may be combined with concrete to
provide nonlinear behavior prior to failure.
– This constitutive model is meant for low
tensile strength but high compressive load
carrying capability.
– A “smeared” reinforcement can be
specified via real constants along three
element coordinate directions, or discrete
reinforcements can be separately added
via LINK or COMBIN elements.
© 2011 ANSYS, Inc. All rights reserved. 33 ANSYS, Inc. Proprietary
Drucker-Prager Plasticity and Concrete
... Concrete Model
• The concrete material can be combined with other nonlinearities:
– Plasticity and creep may be included with concrete. Usually, multilinear elastic or
Drucker-Prager plasticity is used for concrete. Note that the plasticity yield
surface must lie inside the concrete failure surface, otherwise no yielding will
occur.
– The concrete failure surface as plotted in principal stress space is shown on right.
Hence, the
yield surface associated
with any other nonlinear
material behavior (i.e.,
plasticity) must lie inside
of the concrete failure
surface. Otherwise, the
material will completely
fail and never yield.
– Adjustments to stresses
due to plasticity are
performed prior to the
cracking/crushing checks.
© 2011 ANSYS, Inc. All rights reserved. 34 ANSYS, Inc. Proprietary
ANSYS Procedure for Concrete
• After solution, cracks can be plotted:
Other items such as the
status (unfailed, crush,
open crack, closed
crack), crack orientation
angles, and rebar
solution, can also be
obtained.
In the plot on right, note
that crack orientation
and plane are plotted
per integration point.
© 2011 ANSYS, Inc. All rights reserved. 35 ANSYS, Inc. Proprietary
Recent Innovation
New Coupled Pore-Pressure
Mechanical Solids
Fluid flow through porous media
Single phase, based on extended Biot-
consolidation theory
Benefits
Allows for modeling of fluid pore
pressure in soils and biomedical
materials
Applications
Bone and prosthetic implants
Foundation and excavation analysis
Geological, Oil & Gas industryImage Courtesy of Archus Orthopedics
Model Courtesy of
© 2011 ANSYS, Inc. All rights reserved. 36 ANSYS, Inc. Proprietary© 2011 ANSYS, Inc. All rights reserved. 36 ANSYS, Inc. Proprietary
Thermal Bridging
© 2011 ANSYS, Inc. All rights reserved. 37 ANSYS, Inc. Proprietary
Study to compare to EN ISO 10211-1:1995
• Thermal bridges in building construction -- Heat
flows and surface temperatures -- Part 1: General
calculation methods
• 3D Geometry
© 2011 ANSYS, Inc. All rights reserved. 38 ANSYS, Inc. Proprietary
3D Case
• Mesh
– 20 noded hexahedral
• Options:
– Low order elements
– Tetrahedrals
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3D Case
• Boundary conditions
• Alpha 20°C with 5 W/m. °C
• Beta 15°C with 5 W/m. °C
• Delta 0°C with 20 W/m. °C
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3D Case
• Results
© 2011 ANSYS, Inc. All rights reserved. 41 ANSYS, Inc. Proprietary
3D Case – results comparison
BS ANSYS Difference Difference rounded Difference %
U 12.9 12.909 0.009 0.0
V 11.3 11.279 -0.021 0.0
W 16.4 16.363 -0.037 0.0
X 12.6 12.554 -0.046 0.0
Y 11.1 11.074 -0.026 0.0
Z 15.3 15.241 -0.059 -0.1
Alpha 46.3 46.109 0.191 0.4
Beta 14 13.904 0.096 0.7
Gamma 60.3 60.013 0.287 0.5
© 2011 ANSYS, Inc. All rights reserved. 42 ANSYS, Inc. Proprietary© 2011 ANSYS, Inc. All rights reserved. 42 ANSYS, Inc. Proprietary
FSI
Blast Loading on
Structures – Explicit
Dynamics
© 2011 ANSYS, Inc. All rights reserved. 43 ANSYS, Inc. Proprietary
Because…
► no equilibrium iteration needed
► no convergence problems in highly nonlinear problems
► material failure and erosion easy to realize
► high frequencies are naturally resolved because of
small time steps
► fast solving of system of equations highly scalable in
parallel mode
► implicit-explicit switching capability for efficienty
Why Explicit?
hypervelocity impact
blast in urban environment
ceramic impact
drop testsheet metal forming
ship collision
Ima
ge
s c
ou
rtesy C
ran
field
Univ
ers
ity (D
CM
T,U
K)
© 2011 ANSYS, Inc. All rights reserved. 44 ANSYS, Inc. Proprietary
ANSYS® AUTODYN®
Ground Shock Urban Blast
Pipe bomb Façade Response
Contact Charge
© 2011 ANSYS, Inc. All rights reserved. 46 ANSYS, Inc. Proprietary
Blast Effects on Structures
• Euler-Lagrange coupling
– Euler Blast Solver
– Deforming structures (solids, shells, beams)
– Fluid (air) vents through openings generated by blast
• Example Application
– Explosion inside masonry structure
© 2011 ANSYS, Inc. All rights reserved. 47 ANSYS, Inc. Proprietary
AUTODYN Simulations of a
Brick Store House
• 3 charge sizes
– 24 kg
– 8 kg
– ~ 1 kg
• Two Configurations
– With a reinforced
concrete roof
– Open at the top
• 2 m x 2 m x 2 m
Jon Glanville, Rich Thayer
Century Dynamics Limited
Craig Hoing, Ian Barnes
DOSG
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24 kg Trial (with concrete roof)
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Structural Response
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• Euler-Lagrange Coupling
– Lagrange solvers used for vehicle and soil
– Euler solver for the air blast
– Combined blast and fragment (soil) loading
Blast Effects on Structures
• Example Application
– Mine blast
© 2011 ANSYS, Inc. All rights reserved. 52 ANSYS, Inc. Proprietary
In Kabul suicide car bomber rammed bus killing
4 and wounding 29.
Almost all injuries attributed to flying shards of
glass.
To reduce the hazards of flying glass shards,
the German Defense Ministry is assessing
various safety concepts for bus windows using:
Full-scale bus experiments
AUTODYN simulations
Test in Large Blast Simulator
Standard glazing Polycarbonate Glazing
• Example Application
– Blast on windows/glazing
Blast Effects on Structures
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Blast Effects on Structures
• Air Blast modeled using the Euler Blast solver
• RPG casing (fragments) and wing box components modeled using Lagrange solvers
• Euler-Lagrange coupling used for the blast loading
• Lagrange contact and erosion used for the fragment loading
Courtesy FhG-EMI, Germany
• Example Application
– Blast and fragmentation loading of composite wing
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• Procedure (Stage 1)
– Static structural implicit
used to apply gravity
loading
• Example Application
– Bomb blast on bridge
10 м
5 м
1000 kg TNT
FE Model of the Bridge
Courtesy EMT-R, Russia
Stresses
Vertical Displacements
Implicit to Explicit
© 2011 ANSYS, Inc. All rights reserved. 55 ANSYS, Inc. Proprietary
• Example Application
– Bomb blast on bridge
• Procedure (Stage 2)
– Transfer model and results
to AUTODYN
– Add Euler-FCT, used to
represent air and explosive
– Blast-Structure Interaction
(FSI) solve in AUTODYN
– Determine bridge damage
Courtesy EMT-R, Russia
Damage
Blast Wave Propagation
Implicit to Explicit
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Courtesy EMT-R, Russia
Implicit to Explicit
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FSI
I-beam structural integrity
under thermal loading
© 2011 ANSYS, Inc. All rights reserved. 58 ANSYS, Inc. Proprietary
Description
• Illustrates the setup and simulation of a
simplified fire in a room, and its effect on the
roof structure as time progresses up to 1 hour.
• The simulation uses ANSYS Fluid-Structure
Interaction (FSI) capability to solve for:
– Air and heat flow within the room
– Thermal radiation
– Heat conduction within the structures
– Structural deformation of the support beams
under thermal and mechanical loading
– Elasto-plastic material behaviour
© 2011 ANSYS, Inc. All rights reserved. 60 ANSYS, Inc. Proprietary
Geometry
• The room is L-shaped, and open only at one end.
• It is about 8m long, and 2.5m high.
• The ceiling is supported by the walls, and 3 steel I-beams.
• The ‘fire’ is positioned on the floor towards the closed end
of the room (idealized simply as a source of hot air).
Open End
4 m
4 m
4 mFire position
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Project Schematic
• Project is setup in Workbench
– FSI (2-way coupled) simulation is created by:
• Adding a Transient Structural analysis
• Right-clicking on Setup and selecting:
– Transfer Data to New -> Fluid Flow (CFX)
– Geometry is shared between physics
– Setup and solution information is transferred
too
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Geometry
• Multibody parts created, with solid bodies for the
fluid (air) and solid geometry.
– The appropriate bodies can be active or suppressed depending
on which physics you are working with.
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Material Properties
• Structural Properties defined in Engineering Materials
– Property tables entered as functions of temperature
© 2011 ANSYS, Inc. All rights reserved. 66 ANSYS, Inc. Proprietary
Structural Setup
• Frictional Contact added under Connections
– Surface-to-Surface contact between
beams and ceiling.
• Contact offset of 1cm to allow air flow
between surfaces if they separate
– Edge(node)-to-Surface between
beams and fixed support emulating
wall beneath.
– Augmented Lagrange formulation.
– Normal stiffness factor together with
appropriate „pinball‟ radius applied
to give efficient contact convergence.
© 2011 ANSYS, Inc. All rights reserved. 67 ANSYS, Inc. Proprietary
Structural Setup
• Loads and Constraints are added to model
– Gravity added
– Zero vertical displacement at ceiling edges and at beam supports
(wall support)
– Rigid body dof constraints (for stability)
– Large pressure load added to top surface to simulate effect of
upper storey presence.
© 2011 ANSYS, Inc. All rights reserved. 68 ANSYS, Inc. Proprietary
Structural Setup
• Analysis Settings added for coupled simulation
– Single step end time = 30s
– Timestep defined by single substep
– Large Deflection = on, for non-linear solution
– Direct solver chosen (should be sparse)
• Fluid-Solid Interfaces added for external surfaces of
beams, and lower surface of ceiling.
– Numbered 1 to 4 (beams are 1-3, and ceiling is no.4)
– These will match to corresponding CFD boundaries for fluid-solid
data transfer
• Nominal Solution fields added to results
– Total Deformation, Equivalent Stress,
and Contact Tool
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CFD Setup in CFX
• Domain Physics, Boundary Conditions, and Fluid-
Structure Control setup in CFX-Pre
– Transient Simulation of 1hr, with 30s timesteps.
• Fluid-Structure coupling will occur every timestep
– Single „air‟ fluid material used, with Ideal Gas equation for density
and full buoyancy effects.
© 2011 ANSYS, Inc. All rights reserved. 72 ANSYS, Inc. Proprietary
CFX Setup
• Domain Physics
– Mesh Deformation initialised to allow for structural movements
– Shear Stress Transport model used to include turbulent effects
– Thermal Energy model added to allow heat transport
– Monte Carlo thermal radiation model included
• Grey spectral model
• Boundary-specific emisivity
• Fluid-Solid Interface Boundaries
– No-slip walls set up at all beams surfaces, and ceiling
– Total Force Density passed to ANSYS, and Displacement received
– Wall Heat Flux passed to ANSYS, and Temperature received
© 2011 ANSYS, Inc. All rights reserved. 74 ANSYS, Inc. Proprietary
Simultaneous Coupled Solution
• CFX Solver Manager used to start CFX and ANSYS
Mechanical solvers
– MFX framework used to communicate data between solvers
using sockets
– Solver Manager allows simultaneous solution monitoring from
both solvers
– Simulation takes about 2 days to solve
© 2011 ANSYS, Inc. All rights reserved. 75 ANSYS, Inc. Proprietary
Simultaneous Coupled Solution
CFD Residuals
FEA ResidualsCoupling
Residuals
FEA Output CFD Output
Temperature
Probes
Displacement
Probes
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Processing with CFD-Post
• Simultaneous processing of Fluid and Structural results
– Structural Stress
– Structural Displacement
– Temperature of both air
and solid structures
– Air velocity distribution
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Processing with CFD-Post
• Examine Beam displacement with time– Beams and ceiling slowly droop into domain. This is due to thermal expansion, and a
reduction in the stiffness due to temperature and plasticity effects.
© 2011 ANSYS, Inc. All rights reserved. 78 ANSYS, Inc. Proprietary
Processing with CFD-Post
• Examine Beam temperature– Examine distribution across beam, and relative contributions of convective and
radiative heat flux, at a point in time.
© 2011 ANSYS, Inc. All rights reserved. 79 ANSYS, Inc. Proprietary
Post-Processing with ANSYS
• Examine potential for structural failure– Beams and ceiling can be examined for stress and plastic strain, to see when and
where failure may occur.
© 2011 ANSYS, Inc. All rights reserved. 80 ANSYS, Inc. Proprietary
Conclusions
• ANSYS can solve the complete fluid-structure-
thermal interaction scenario of a fire in an enclosed
room.
• It has the tools to include complex geometric and
physical details.
• The coupled software has not been tested for the
collapse process itself, and difficulties are
specifically anticipated in sustaining two-way
coupling during impact between structures during
the collapse (if that occurs).
• However, the coupled software is able to analyze
events up to collapse, and the structural software can
analyze the collapse.
© 2011 ANSYS, Inc. All rights reserved. 81 ANSYS, Inc. Proprietary
Overall Conclusions
• Wide range of proven technology
– Elements
– Materials
– Solvers
• Choice of FSI methodlogy
– Fully coupled
– Iterative
• One common platform taking advantage of
– Robust meshing
– Bi-directional CAD