airbag folding with radioss pre-...
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Dmitri Fokin , EHTC 2009, Copyright © 2008 Altair Engineering, Inc. All rights reserved. 1
Altair Product Design
Dmitri Fokin
Airbag Folding with Radioss Pre- Simulation
3 November 2009European HTC Ludwigsburg, Germany
[email protected]+49 711 6208184
Dmitri Fokin , EHTC 2009, Copyright © 2008 Altair Engineering, Inc. All rights reserved. 2
FE Airbag model
Geometrical folder
Folding pre-simulation with Radioss
Conclusions
Content
Dmitri Fokin , EHTC 2009, Copyright © 2008 Altair Engineering, Inc. All rights reserved. 3
FE Airbag model
Dmitri Fokin , EHTC 2009, Copyright © 2008 Altair Engineering, Inc. All rights reserved. 4
- Airbag geometry (closed volume)- Meshed airbag surface with account of folding- Fabric material and FE property- Internal airbag contacts- Method for airbag simulation (uniform pressure, ALE, finite volume method)
FE Airbag model: general
300 mm
99 mm
straps
Fold 5
Fold 8
Fold 1
Fold 2
border of the airbag (gas
leakage)Fold 7
Fold 6
Fold 4
Fold 3
99 mm
102 mm
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Definition of airbag model is Material definition for the airbag fabric (orthotropic, elasto- plastic materials, no resistance by compression)
/MAT/FABR_A/1MAT_FABRIC # Init. dens. Ref. dens.6.83000000000000E-07 0.0
0.47 0.0 0.47 0.0 0.050.002 0.002 10.00.2 0.2
1 1 0.05 0.05
FE Airbag model: fabric materials and properties
Dmitri Fokin , EHTC 2009, Copyright © 2008 Altair Engineering, Inc. All rights reserved. 6
Definition of airbag model is Material definition for the airbag fabric (orthotropic, elasto- plasticmaterials, no resistance by compression)
/MAT/FABR_A/1MAT_FABRIC # Init. dens. Ref. dens.6.83000000000000E-07 0.0
0.47 0.0 0.47 0.0 0.050.002 0.002 10.00.2 0.2
1 1 0.05 0.05
Property definition for the airbag fabric (membrane, no bending stiffness)
/PROP/SH_FABR/1airbag_thickness # Ishell Ismstr
4 0 0.1 0.1 0.1 0.1
1 0 0.3 0.0 00.0 1.0 0.0 0 00.0 90.0 0.3 0.0 1
FE Airbag model: fabric materials and properties
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Internal contact for airbag fabric components (prescribed contact gap and contact stiffness)
/INTER/TYPE7/2Internal Contact
8 7 1 0 25 0 0 00.0 0.00.0 0.00.1 0.0 0.3 0.0 0.0
000 0 0.0 0.0 0 0 0.0 0
/INTER/TYPE11/1Internal Contact EE
10 10 1 0 25 00.1 0.0 0.203 0.0 0.0
000 0 0.0 0.0 0.0
FE Airbag model: internal contact
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Inflator model: position of injectors, jet directions, gas consistence, massflow rates, gas temperature, time to fire, airbag solver (uniform pressure, finite volume)
/MONVOL/AIRBAG/1Airbag# Isur
7# Scal_T Scal_P Scal_S Scal_A Scal_D
0 0 0 0 0# Mu Pext Tphi
0 1.013E-4 295.0# Gammai cpai cpbi cpci
1.4 926 0 0# Njet
1# Gamma cpa cpb cpc
1.325 1168 .4274 0# Imass Iflow Smass Itemp Stemp Isensor
77 1 .001 84 1 1# Ijet N1 N2 N3
0 0 0 0# Nvent
0
FE Airbag model: solver and inflator
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Unfolded FE airbag (reference geometry)
FE Airbag model: airbag folding
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FE Airbag model: airbag folding
Unfolded FE airbag (reference geometry)
Black box= Airbag Folder
Transformation of airbag geometry
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FE Airbag model: airbag folding
Unfolded FE airbag (reference geometry)
Black box= Airbag Folder
Folded FE airbag
Transformation of airbag geometry
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FE Airbag model: airbag folding
Unfolded FE airbag (reference geometry)
Black box= Airbag Folder
Folded FE airbag
Geometrical folder
- Translate
- Rotate
- Scale
- Non-linear transformation
Transformation of airbag geometry
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FE Airbag model: airbag folding
Unfolded FE airbag (reference geometry)
Black box= Airbag Folder
Folded FE airbag
Geometrical folder
- Translate
- Rotate
- Scale
- Non-linear transformation
Transformation of airbag geometry
Pre- simulation of the folding process using an explicit solver (Radioss)
-Exact simulation of the folding process
-Simulation of a simplified folding process
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FE Airbag model: airbag folding
Unfolded FE airbag (reference geometry)
Black box= Airbag Folder
Folded FE airbag
Geometrical folder
- Translate
- Rotate
- Scale
- Non-linear transformation
Transformation of airbag geometry
Com
bine
d fo
lder Pre- simulation of the folding process
using an explicit solver (Radioss)
-Exact simulation of the folding process
-Simulation of a simplified folding process
Dmitri Fokin , EHTC 2009, Copyright © 2008 Altair Engineering, Inc. All rights reserved. 15
Element sizes, fold thickness and fold layout must be adjustedsuch that certain requirements are met: i.e.
• Package space requirements (final size of folded airbag)
• Requirements for numerical stability (element quality, time step, intersection and penetration free)
• Requirements for model validity (reliable folding deformation)
FE Airbag model: folding requirements
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Geometrical folder
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Simple fold consist of:
Non-knick elements (regions BCD and B´C´D´)
Knick elements (regions AB, A´B´, DE, ´D´E´)
Following rules are important by airbag meshing for further simple folding
1. Only one element should lie in the knick regions AB, A´B´, DE, ´D´E´
2. Elements in the knick and non-knick region should have approximately same size
A B
C
DE
A´ B´C´
D´E´f O
BA C D E
A´ B´ C´ D´ E´d
OBefore folding
After folding
Geometrical folder: simple fold
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Initial data:
Distance between layers, d
Fold height, f
Element size to knick
Elliptic elongation
Thickness increase coefficient
Output data:
Average distance between layers on the knick
Node displacements for corresponding folding step
Calculation of fold parameters ( 3 variants)
Geometrical folder: simple fold
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Step 1
BA C D E
A´ B´ C´ D´ E´d
Direction of displacement
Geometrical folder: four step algorithm
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Move nodes CC´ vertically by the value of “node
displacement for step 2”
BA
C
D E
A´ B´
C´
D´ E´
Step 2
Direction of displacement
Geometrical folder: four step algorithm
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Step 3
Result of rotation:
BA
C
DE
A´ B´C´
D´E´
Rotate all these nodes over node C by 180 grad
BAC
D E
A´ B´
C´
D´ E´
Center of rotation is the node on the lower surface of the airbag
Geometrical folder: four step algorithm
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Step 4
BA
C
DE
A´ B´C´
D´E´Rotate node C´ about node C by 90 grad
BA
C
DE
A´ B´C´
D´E´
Result of rotation
Geometrical folder: four step algorithm
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Geometrical folder: four step algorithm
Elements deform during folding
A B
C
DE
A´ B´C´
D´E´f O
D
BA C D E
A´ B´ C´ D´ E´d
OBefore folding
After folding
Inside elements (B‘C‘, C‘D‘) will be shorter
Outside elements (BC, CD) will be longer
Volume of the folded airbag has changed
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Geometrical folder: reference geometry
Unfolded FE airbag (reference geometry)
Initial strains in the folded airbag fabric
Folded FE airbag
/REFSTA# reference geometryAIRBAG02.ref
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300 mm
99 mm
straps
Fold 5
Fold 8
Fold 1
Fold 2
border of the airbag (gas
leakage)Fold 7
Fold 6
Fold 4
Fold 3
99 mm
102 mm
Geometrical folder: fold planning
Geometrical folder requires exact „planning“ of the airbag geometry: fold lines should be present in the geometry before meshing
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Fold plan for „Branch“ programm
Provides a detailed airbag “fold plan” for further manual airbag folding. Allows to control important characteristics of the airbag: minimal element size, thickness of the folded airbag etc. (Branch programm L.Fredriksson)
Geometrical folder: fold planing
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Airbag folder is a part of the Hyperworks
Types of fold:
- Simple fold
- Open fold
- Tuck folds
- Rolling
Important feature:
Airbag geometry is folded and then meshed!
Geometrical folder: Hypercrash folder
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Folding pre-simulation with Radioss
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Radioss runnable inputdeck with unfolded airbag, materials, contacts etc. but w/o airbag card
Folding pre-simulation with Radioss
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Fold planFOLD 2
0.0 10.0-1000.0 1000.0 0.0 1000.0
0.0 297.864 0.0 296.864-10.7 6.0 1.2 -0.0005 0
FOLD 3 (sym to 2)0.0 10.0
-1000.0 1000.0 -1000.0 0.00.0 -297.864 0.0 -296.864-10.7 6.0 1.2 -0.0005 0
Radioss runnable inputdeck with unfolded airbag, materials, contacts etc. but w/o airbag card
Folding pre-simulation with Radioss
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Fold planFOLD 2
0.0 10.0-1000.0 1000.0 0.0 1000.0
0.0 297.864 0.0 296.864-10.7 6.0 1.2 -0.0005 0
FOLD 3 (sym to 2)0.0 10.0
-1000.0 1000.0 -1000.0 0.00.0 -297.864 0.0 -296.864-10.7 6.0 1.2 -0.0005 0
Fold script generates Radioss inputdeck for folding
Radioss runnable inputdeck with unfolded airbag, materials, contacts etc. but w/o airbag card
Folding pre-simulation with Radioss
Dmitri Fokin , EHTC 2009, Copyright © 2008 Altair Engineering, Inc. All rights reserved. 32
Fold planFOLD 2
0.0 10.0-1000.0 1000.0 0.0 1000.0
0.0 297.864 0.0 296.864-10.7 6.0 1.2 -0.0005 0
FOLD 3 (sym to 2)0.0 10.0
-1000.0 1000.0 -1000.0 0.00.0 -297.864 0.0 -296.864-10.7 6.0 1.2 -0.0005 0
Fold script generates Radioss inputdeck for folding
Radioss runnable inputdeck with unfolded airbag, materials, contacts etc. but w/o airbag card
Folding pre-simulation with Radioss
Radioss simulation
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Folding pre-simulation: principal scheme
Rotated nodes Fixed nodes
Oo
Fold (deformable nodes)
Rotation center
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Folding pre-simulation: principal scheme
Rotated nodes Fixed nodes
Fixed nodes
Rotated nodes
Oo
90o
Fold (deformable nodes)
Rotation center
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Folding pre-simulation: principal scheme
Rotated nodes Fixed nodes
Fold (deformable nodes)
Fixed nodes
Rotated nodes
Rotated nodes
Fixed nodes
Oo
90o
180o
Fold (deformable nodes)
Rotation center
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Folding pre-simulation: principal scheme (video)
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Folding pre-simulation: blade scheme (video)
Rotated elements are deformable and trapped between two rigid blades by a contact
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Folding pre-simulation: knife scheme (video)
All airbag elements are deformable. Folding is carried out by moving rigid knives
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Altair training airbagElement edges follow folding lines4 symmetrical folds
Folding pre-simulation: complete run
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Mesh rotated by 30 grad. Fold lines are parallel to mesh direction
Element edges follow folding lines Arbitrary fine mesh
Folding is mesh independent
Folding pre-simulation: three different meshes
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Fold lines introduced in the mesh Arbitrary fine mesh
Folding pre-simulation: airbag deployment
The airbags have same shape and fold plan but different mesh. Airbag deployment is similar
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- Radioss model for folding is generated automatically
- No intersections and minor penetrations in folded airbag due to sensitive Radioss contacts
- Final size of airbag is predicted before folding starts
- Transfer from unfolded state (reference geometry) to folded is physically consistent (internal material forces and contact forces provide physically reliable strains in the airbag fabric during the folding)
- Folding method is mesh independent
- Folded mesh can be used for any solver (RADIOSS, DYNA)
Folding pre-simulation: some notes
Dmitri Fokin , EHTC 2009, Copyright © 2008 Altair Engineering, Inc. All rights reserved. 43
Example: passenger airbag folding
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Example: description
Mesh 100000 elementsAverage element size 5mmSimulation time 2h
Upper view
Lower view
Side view
Inflator
Housing
Airbag surface- typical 3D T-shape form
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Example: fold plan
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Example: fold plan
First step: symmetrical zig zag side folds
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Example: fold plan
First step: symmetrical zig zag side folds
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Example: fold plan
Second: lower rolls
Second step: lower rolls
First step: symmetrical zig zag side folds
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Example: fold plan
Second: lower rolls
Second step: lower rolls
Third step: upper roll
First step: symmetrical zig zag side folds
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Example: fold plan
Second: lower rolls
Second step: lower rolls
Third step: upper roll
Fourth step: press in housing
First step: symmetrical zig zag side folds
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Example: inputdecks
#RADIOSS STARTER/BEGINAIRBAG01
51 0/MAT/FABR_A/1MAT_FABRIC ……/PROP/SH_FABR/1airbag_thickness……/INTER/TYPE7/2Internal Contact……/INTER/TYPE11/1Internal Contact EE ……/END
Model of unfolded airbag
FOLD 20.0 10.0
-1000.0 1000.0 0.0 1000.00.0 270.000 0.0 269.0001
1.0 6.0 1.2 -0.00101 0FOLD 3 (sym to 2)
0.0 10.0……FOLD 15
70.0 80.0-1000.0 1000.0 -1000.0 1000.0-21.0 0.0 -20.0 0.0
11.0 6.0 1.2 -0.00101 1
END
Fold plan
FOLD SCRIPT
#RADIOSS STARTER/BEGINAIRBAG01
51 0###include FOLD00_0000.inc#include FOLD01_0000.inc##
/MAT/FABR_A/1MAT_FABRIC ……/PROP/SH_FABR/1airbag_thickness……/INTER/TYPE7/2Internal Contact……/INTER/TYPE11/1Internal Contact EE ……/END
Model of unfolded airbag with folding includes
# FOLD 2 START/SENSOR/TIME/ 200000T= 0.000
0.000…….#enddata
Fold includes
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Example: folding of a passenger airbag (video)
Mesh 100000 elementsAverage element size 5mmSimulation time 2h
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Example: fit passenger airbag in housing (video)
Mesh 100000 elementsAverage element size 5mmSimulation time 15min
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Example: deployment of the passenger airbag (v)
Mesh 100000 elementsAverage element size 5mmUniform pressure, Simulation time 0.5h
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Promising technology for numerical airbag folding
Easy to implement in HW
No need of additional explicit solver for folding simulation
Radioss model for folding is generated automatically
Simulation delivers a reliable strains in the folded airbag
Folded mesh can be used for any solver (RADIOSS, DYNA)
Conclusions
Dmitri Fokin , EHTC 2009, Copyright © 2008 Altair Engineering, Inc. All rights reserved. 56
Thank you for the attention!