frequently overlooked features in abaqus - · pdf file · 2011-11-07frequently...
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Frequently Overlooked Features in Abaqus
SIMULIA Great Lakes Regional User Meeting
Oct 12, 2011
Brad Heers
Technical Marketing, Automotive
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A true story…...from the “old days” of CAE
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Looking at Example Problems
Explicit Dynamics for Vehicle Crash Cellphone drop?
Soil mechanics for Civil Engineering Analysis of wet and dirty diapers?
Cohesive elements for fracture analysis Adhesives for food preservation?
Iterative Solver for automotive engines Geomechanics of large oil fields?
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versus today…
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Abaqus 6.11
Contains over 110 new features
Significantly expanded multiphysics
See Release Notes for comprehensive
listing of everything that is new
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Our “Dilemma”
Many new features every Abaqus release Not enough time for SIMULIA to talk about every feature
Not enough time for users to read every Example Problem
CAE has become “mission-critical” and very busy This is good for our personal employment
But does not provide enough time to “imagine new uses”
What are the “Really Useful Features” Or at least some of them?
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Discussion Topics
Elements
Solution Sequences and Solution Features
Performance and Efficiency
Contact
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Discussion Topics
Elements
Solution Sequences and Solution Features
Performance and Efficiency
Contact
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C3D10I: General-Purpose Tetrahedral Element
I = “Improved Surface Stress” Not Incompatible Modes
Integration points at the corner nodes Thus stresses are calculated directly on the surface
Removes extrapolation issues
Removes need for membranes for stress recovery
Improved bending response
Slight performance degradation relative to C3D10
Good in contact with surface to surface formulation
Introduced in Abaqus 6.9
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C3D10I: General-Purpose Tetrahedral Element
Key features Provides accurate surface stress predictions
Suitable for bending-dominated problems
Handles incompressible material behavior
Works well with contact
Some added computational expense
Benefit Simplifies element selection
C3D10IC3D10M
Analytical solution:
38,400 psi
C3D10I matches
analytical solution
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Elastoplastic knuckle
C3D10I: General-Purpose Tetrahedral Element
Note no extrapolation
error in stress contour plot
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C3D10I: General-Purpose Tetrahedral Element
Copper rod impact Good agreement with Abaqus/Explicit results (Benchmark manual).
C3D10M cannot complete simulation.
Initially no Lagrange Multipliers present. As material starts to flow
plastically they are created.
Initial configuration 40μs 80μs
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C3D4H: First Order Hybrid Tetrahedron
Improved element formulation Reformulated the volumetric constraint
Reasonable element choice for certain problems with
extreme deformations: Overloaded bushings
Surface wrinkling
Allows one to extend to high-deformation problems in
/Standard analyses This is still a linear tetrahedron
Important to first compare against a quadratic element mesh
Improved in Abaqus 6.7
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C3D4H: First Order Hybrid Tetrahedron
First-order hybrid tetrahedron Improved C3D4H formulation avoids
volumetric locking in compressible
and nearly incompressible materials
More robust in geometrically
nonlinear highly confined regions
Courtesy of Freudenberg Forschungsdienste KG and
Vibracoustic GmbH & Co KG
Contact PD Dr.-Ing. Herbert Baaser,
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Connectors
Some specific usage that is often overlooked…
Bushing Connectors Very sophisticated 6 degree of freedom coupling
Cross-coupling terms can be dependent and co-dependent
Connectors as kinematic constraints Far superior to MPCs
o Better convergence
o Ability to extract forces, moments and other outputs directly
o No artificially high residuals
Introduced in Abaqus 6.1, progressive enhancements
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Discussion Topics
Elements
Solution Sequences and Solution Features
Performance and Efficiency
Contact
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Implicit Dynamics
Very good for certain quasi-static problems in
which the timescale is measured in seconds
but statically unstable Rubber tracks
Belt drives
“Snap-fit” problems
Keyword: “*DYNAMIC, Application=… ” quasi-static (for aggressive damping in quasi-static models)
moderate dissipation (for moderate damping—”dynamic”
problems for which contact does not need most accurate
precision)
transient fidelity (for most accurate solution—truly “dynamic”
problems)
Introduced in Abaqus 6.9EF
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Implicit Dynamics
Important to check whether model is “static” at the end of
a quasi-static analysis
A good debugging tool for problematic static analyses Dynamic solution may give insight to the static difficulties
Often a good “standard practice” tool for well-understood
quasi-static problems Often a superior solution to quasi-static problems currently being run in
/Explicit
Considerations for usage
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FromNastran: Nastran Translator to Abaqus
Translator from Nastran bdf to Abaqus inp Goal is to replicate equivalent mechanics as defined in runnable Nastran
model
Strong focus on automotive models initially This has been enhanced over subsequent releases
Focused on major Nastran sequences SOL 101, 103, 108, 111
“Customizable” for user and/or company needs Achieved via command line or environment file options
Introduced in Abaqus 6.2; enhanced every release
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Unsymmetric Solver
Often necessary for certain problems Finite sliding contact problems
o Curved surfaces and friction often lead to unsymmetric terms
o Friction forces often give rise to significant unsymmetric terms
Large deformation problems with “follower loads” (pressures, etc.)
Unsymmetric solver is more expensive than symmetric
solver for each pass However, often there are fewer passes for an unsymmetric solve, resulting
in faster runs
Unsymmetric often will solve analyses for which symmetric solver cannot
converge
Long-time feature which is not often appreciated
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Discussion Topics
Elements
Solution Sequences and Solution Features
Performance and Efficiency
Contact
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AMS Available to All Users
Large-scale eigensolver delivered as part of Abaqus Available as SMP parallel
Capable of solving 10M+ dof, 10K+ modes Highly-competitive performance
Also applicable for smaller models (500Kdof, 500 modes)
Good for nearly all Abaqus linear dynamics procedures
Introduced in 6.6, available with no charge as of 6.10
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Linear Dynamics
Very efficient when compared to other solvers Very strong serial capability
Near-linear SMP scaling for large problems
Compatible with Abaqus nonlinear analyses Able to capture pre-loading and manufacturing effects
Contains all known commercial damping models for structural dynamics Including frequency-dependent damping and stiffness
Includes structural-acoustics in one code
Rewritten over the last several releases of Abaqus
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Exterior Node and Element Output
Typically only surface output is needed Maximum stresses and strains
“Envelope” of displacements
Available as a parameter for output requests *ELEMENT OUTPUT, EXTERIOR
*NODE OUTPUT, EXTERIOR
Especially for large cast continuum models (powertrain),
this may result in significantly less output
ODB File Size Reduction! (Abaqus 6.10EF)
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Output at time intervals in Standard
Output at critical time intervals Can enforce time intervals or at nearest time intervals
Saves trouble of dividing into multiple steps
Keyword: “*TIME POINTS”
Example use-case: “Load to 10 KN, and monitor at every
1 KN interval” Without time points, this requires 10 distinct steps
With time points, this is a single step
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Discussion Topics
Elements
Solution Sequences and Solution Features
Performance and Efficiency
Contact
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Penalty Contact
Default for finite sliding surface to surface contact
Penalty=nonlinear may help convergence for some types
of problems
“Structural contact” (for transferring loads)—scaling this
down can lead to better convergence
A useful modification for certain contact problems
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Contact Improvements: No need for C3D10M
C3D10M was originally designed to give better contact
results over the C3D10 element These elements were more expensive and incompatible with other 2nd
order elements
Do not work with embedded elements
Improvements in contact make these elements generally
unnecessary in Abaqus/Standard Previous contact issues for C3D10 have been addressed through contact
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Surface Smoothing in Contact
Important when contact pressure accuracy is important
Improves accuracy and convergence for certain simply
geometries Spherical shapes in contact
Cylindrical shapes in contact
Generated automatically in Abaqus/CAE when geometry
is available
Introduced in Abaqus 6.8
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Surface Smoothing in Contact
Axisymmetric geometries often require accurate
contact pressure predictions Bolts, pins, pistons, cylinders, …
Geometry corrections can improvement accuracy Automatically applied in Abaqus/CAE
Example: Cone-shaped interface
Without correction With correction
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General Contact
Can be used to define ALL contact in the model (similar
to Explicit) Some computational overhead with this approach
Also effective when used in conjunction with contact
pairs on a “pair-by-pair” basis Define contact pairs that are critical, and automatically utilize latest
algorithms
Edge contact is now available in general contact
Available in /Standard since 6.9EF
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And now, a bold prediction…
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Bold Prediction
GPGPU Scalability is boring… But sometimes really powerful things ARE boring
Consider the 4.5 Mdof model Total run time ~ 2x faster vs. 4 core
Abaqus 6.11 “Future Overlooked Feature”
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0.5
1
1.5
2
2.5
3
0.9 1.1 1.4 1.5 3.1 4.5
Speedup
4 cores vs. 4 cores + GPU
Problem size in MDOF
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GPGPU Scalability
Economic implications of this speedup
With a 4 core analysis (using 8 tokens) as baseline…
To run 2x faster on “default” hardware would require 8-12 core in hardware + 12-14 tokens
+100-150% hardware cost and +50-88% token cost of baseline
To run 2x faster on with GPGPU chip would require 4 core + 1 GPGPU in hardware + 9 tokens
~+100% hardware cost and ~+10-15% token cost of baseline
It is necessary to consider these implications in future IT
decisions
Example use case (very problem-dependent!)
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GPGPU Scalability
Looking at this on a per-job basis…
To run 2x number of jobs on “default” hardware would
require Equivalent or slightly-higher hardware cost
75-90% of token cost as baseline (10-25% savings per run)
To run 2x number of jobs with GPGPU chip would
require Equivalent hardware cost
55-60% of token cost as baseline (40-45% savings per run)
…another way of looking at this same data
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Summary
Each Abaqus release averages >100 new features
Many very powerful features are not widely utilized Especially “industry-specific” features
Some ideas to help “discover” additional features Talk to your local office—describe the engineering problem
o Rather than simply describing keywords
Speak to your colleagues (especially the newer users)
Talk to Abaqus users outside your industry and domain
o Sometimes their “old features” may be your “new features”
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Thank you!