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Isogeometric Analysis
in LS-DYNA
Liping Li, Attila P. Nagy, Dave J. Benson | Livermore Software Technology
Corporation
Stefan Hartmann | DYNAmore GmbH
Outline
Isogeometric Analysis – motivation
The importance of geometry
Analysis enhancements
Selected applications
Future developments and challenges
Isogeometric Analysis – motivation
The importance of geometry
Analysis enhancements
Selected applications
Future developments and challenges
2
Isogeometric Analysis – motivation
Reduce effort of geometry conversion from CAD into a suitable
mesh for FEA
Isogeometric
same description of the geometry in the design (CAD) and the analysis
CAD Geometry Design
FE Mesh
Analysis Optimization
CAD Geometry Design
NURBS
Analysis Optimization
3
Outline
Isogeometric Analysis – motivation
The importance of geometry
Analysis enhancements
Selected applications
Future developments and challanges
4
NURBS Shell
5
Shell formulations
Reissner-Mindlin - with and without rotational DOF
Kirchhoff-Love
Blended - selective addition of rotational DOFs
Consistent or lumped mass matrix
Integration schemes
Standard or uniformly reduced Gaussian quadrature
Patch-wise reduced Gaussian quadrature (quadratic NURBS only)
Designed quadrature rules (trimmed elements only)
Uniformly sized interpolation elements
Improved keyword format for trimmed shells
Trimming loops are represented by NURBS curves
Topology preserving - backward compatibility with CAD
Trimming is a generic capability - user defined Splines
*DEFINE_NURBS_CURVE
*ELEMENT_SHELL_NURBS_PATCH_TRIMMED_TITLE
NURBS Shell
6
Shell formulations
Reissner-Mindlin - with and without rotational DOF
Kirchhoff-Love
Blended - selective addition of rotational DOFs
Consistent or lumped mass matrix
Integration schemes
Standard or uniformly reduced Gaussian quadrature
Patch-wise reduced Gaussian quadrature (quadratic NURBS only)
Designed quadrature rules (trimmed elements only)
Uniformly sized interpolation elements
Improved keyword format for trimmed shells
Trimming loops are represented by NURBS curves
Topology preserving - backward compatibility with CAD
Trimming is a generic capability - user defined Splines
*DEFINE_NURBS_CURVE
*ELEMENT_SHELL_NURBS_PATCH_TRIMMED_TITLE
Trimmed NURBS Shell *ELEMENT_SHELL_NURBS_PATCH_TRIMMED
$# npeid pid npr pr nps ps 1 1 665 3 319 3
$# wfl form int nisr niss imass
0 0 0 -2. -2. 0 $# r1 r2 r3 r4 r5 r6 r7 r8
… trimming loop 1
$# c1 c2 c3 c4 c5 c6 c7 c8
1 2 3 4 ...
*DEFINE_NURBS_CURVE $# id n p peri type wfl
1 78 3 0 1 1
$# t1 t2 t3 t4 t5 t6 t7 t8 0.000000 0.000000 0.000000 0.000000 0.031701 0.039515 0.040491 ...
$# r s - w 0.000000 0.000000 0.875000
CAD
0
-2.
7 *ELEMENT_SOLID_NURBS_PATCH (no trimming capability)
Standard trivariate tensor product formulation
Lack of mesh generators is a limitation
Standard Gaussian quadrature
Interpolation elements
Contact, boundary conditions, and post-processing
NURBS Solid
8
Analysis suitable geometry (ASG) is unlikely to be prepared by the designer
Lack of support in the de facto industry standard CAD softwares
Plenty of work on the CAGD CAE interface
LSPrepost: import IGES file to create ASG.
CAD to ASG
9
Cross-field optimized or approximated trimmed NURBS Elysium Co., Ltd. . Honda Motor Co., Ltd.
~600 patches approximated by a single trimmed NURBS patch
LS-DYNA keyword output
CAD to ASG
10
T-splines, U-splines
Coreform LLC . Ford Motor Co., Inc.
*INCLUDE_TRANSFORM
Bézier Extraction Format - Shell
11
Truncated hierarchical T-splines
Carnegie Mellon University . Honda Motor Co., Ltd.
*INCLUDE_TRANSFORM
Bézier Extraction Format - Solid
12
Watertight CAD models B Urik, UT Austin LS-DYNA modal analysis
Novel CAD Solutions
Outline
Isogeometric Analysis – motivation
The importance of geometry
Analysis enhancements
Selected applications
Future developments and challanges
13
14 *CONSTRAINED_NODE_TO_NURBS_PATCH_SET
*LOAD_NURBS_SHELL_ID
Quadratic NURBS under vertical point load
Boundary conditions
Prescribed motions, e.g. spot welds - penalty formulation
Point, distributed, and pressure loads
Display of section forces
Shells and solids
Improved stable time step estimates
Trimmed and untrimmed elements
Consistency and performance
SMP, MPP, and hybrid
Recent Features and Improvements
15
*MAT_022 or *MAT_COMPOSITE_DAMAGE
*MAT_033 or *MAT_BARLAT_ANISOTROPIC_PLASTICITY
*MAT_USED_DEFINED_MATERIALS etc.
Directional dependent material models Anisotropic elasticity
Anisotropic plasticity
User defined materials
List of available materials is steadily increasing
Constitutive Models
Outline
Isogeometric Analysis – motivation
The importance of geometry
Analysis enhancements
Selected applications
Future developments and challanges
16
17
Aerospace
Jet engines and blades
Foreign object impact
Automotive
Crashworthiness
Metal stamping and other manufacturing processes
Noise, vibration, and harshness (NVH)
Fluid-structure interaction (FSI)
Biomedical
Cardiovascular modeling
Industrial Focus
18
IGA and combined FEA with IGA Ford Motor Co., Inc.
Front rigid barrier sled test
35 mph against 450 kg rigid fixture
Steel crash can
trimmed NURBS
Y Chen et al., LS-DYNA UC, 2016
regular mesh
Crashworthiness
19
Rigid upper die Blank
Rigid binder Rigid lower punch
Draw-bead radius: ~4mm
NUMISHEET 2005 benchmark in 2017
Average element size: ~4 mm (draw-bead driven)
Patch-wise reduced integration rule (biquadratic patch)
Al5182-0 - piecewise linear plasticity (*MAT_024)
Uniform initial blank thickness: 1.6 mm
Thickness update during analysis
No adaptive refinement
MPP
FEA baseline model Fully integrated shell with assumed strain formulation
Average element size ~2 mm
Metal Stamping
20
FEA 3h 41m
IGA 2h 12m
Comparison of Results
21
NURBS Shell Model
Full Guass integration rule
Piecewise linear plasticity (*MAT_024)
FEA baseline model Fully integrated shell with assumed strain formulation
Frequency Domain: SSD
22
IGA:1444 47s
Comparison of Results
FEA:1444 6s
FEA:5776 23s
FEA:12996 54s
23
IGA:1444 47s
Comparison of Results
FEA:1444 6s
FEA:5776 23s
FEA:12996 54s
FEA
IGA
24
Chevrolet Camaro
with Facundo del Pin
Fluid-Structure Interaction
Outline
Isogeometric Analysis – motivation
The importance of geometry
Analysis enhancements
Selected applications
Future developments and challenges
25
26
Pre-processing
Analysis suitable geometry (ASG) is unlikely to be prepared by the draftsmen/designer
Generating (an editable) ASG is essential and necessary - meshing is analysis dependent
Accommodate ASG in the new STEP standard
Analysis
Rethink and enable existing FEA capabilities for IGA - 9M+ lines of code in LS-DYNA
Coupling of patches/parts (shell to shell and shell to solid)
Adaptive mesh refinement
Further enhance support for geometric input
Increase efficiency - SMP, MPP, and hybrid
Continue coupling with different formulations, e.g. FEA (mostly done), acoustics, EM, ICFD,
meshless, etc.
Post-processing
Enhance field rendering capabilities in LS-PrePost
Future Challenges
Thank you!