Frequently Overlooked Features in Abaqus

Transcription

1 Frequently Overlooked Features in Abaqus SIMULIA Great Lakes Regional User Meeting Oct 12, 2011 Brad Heers Technical Marketing, Automotive 1

2 A true story...from the old days of CAE 2

3 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? 3

4 versus today 4

5 Abaqus 6.11 Contains over 110 new features Significantly expanded multiphysics See Release Notes for comprehensive listing of everything that is new 5

6 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? 6

7 Discussion Topics Elements Solution Sequences and Solution Features Performance and Efficiency Contact 7

8 Discussion Topics Elements Solution Sequences and Solution Features Performance and Efficiency Contact 8

9 C3D10I: General-Purpose Tetrahedral Element Introduced in Abaqus 6.9 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 9

10 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 Analytical solution: 38,400 psi C3D10I matches analytical solution C3D10M 10 C3D10I

11 C3D10I: General-Purpose Tetrahedral Element Elastoplastic knuckle Note no extrapolation error in stress contour plot 11

12 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 12

13 C3D4H: First Order Hybrid Tetrahedron Improved in Abaqus 6.7 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 13

14 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, 14

15 Connectors Introduced in Abaqus 6.1, progressive enhancements 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 15

16 Discussion Topics Elements Solution Sequences and Solution Features Performance and Efficiency Contact 16

17 Implicit Dynamics Introduced in Abaqus 6.9EF 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) 17

18 Implicit Dynamics Considerations for usage 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 18

19 FromNastran: Nastran Translator to Abaqus Introduced in Abaqus 6.2; enhanced every release 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 19

20 Unsymmetric Solver Long-time feature which is not often appreciated 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 20

21 Discussion Topics Elements Solution Sequences and Solution Features Performance and Efficiency Contact 21

22 AMS Available to All Users Introduced in 6.6, available with no charge as of 6.10 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 22

23 Linear Dynamics Rewritten over the last several releases of Abaqus 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 23

24 Exterior Node and Element Output ODB File Size Reduction! (Abaqus 6.10EF) 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 24

25 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 25

26 Discussion Topics Elements Solution Sequences and Solution Features Performance and Efficiency Contact 26

27 Penalty Contact A useful modification for certain contact problems 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 27

28 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 2 nd 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 28

29 Surface Smoothing in Contact Introduced in Abaqus 6.8 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 29

30 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 30

31 General Contact Available in /Standard since 6.9EF 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 31

32 And now, a bold prediction 32

33 Bold Prediction Abaqus 6.11 Future Overlooked Feature 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 Speedup 4 cores vs. 4 cores + GPU Problem size in MDOF 33

34 GPGPU Scalability Example use case (very problem-dependent!) 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 tokens % hardware cost and % 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 34

35 GPGPU Scalability another way of looking at this same data 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) 35

36 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 36

37 Thank you! 37