Download - Recommendations for Airbag Numerical Simulation with Uniform and Variable Gas Pressure using RADIOSS
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Innovation Intelligence®
Recommendations for Airbag Numerical
Simulation with Uniform and Variable Gas
Pressure using RADIOSS
2014 European Altair Technology Conference
June, 25 2014
Francis Arnaudeau
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Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
Agenda
• Motivation for FVM
• RADIOSS Input
• New features in V12 & V13
• Vent Holes & Porous Surfaces
• Examples
1. Driver AirBag
2. Passenger AirBag
3. Side AirBag
4. Curtain AirBag
• Conclusion
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Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
INTRODUCTION
First airbag models have been made with the assumption of uniform
pressure (UP)
Uniform Pressure assumption is not accurate enough in:
• Out of position configurations (OOP)
• Side impacts
• Curtain airbags CAB
• SAB
• Opening of airbag cover (e.g. passenger airbags PAB)
Solution: take into account gas flow, in particular for the first
milliseconds of the airbag deployment
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RADIOSS FVM
EULER CONSERVATION EQUATIONS COMPRESSIBLE INVISCID FLOW
(Mass)
(Momentum)
(Energy)
PERFECT GAS EOS
0).(
u
t
0).(
f
puu
t
u
0).().(
fupueu
t
e
ep )1(
4
2
32 TCT
CTCTCTCCC pf
pe
pdpcpbpap
vp CC / RCC pv
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RADIOSS INPUT
• /MONVOL/AIRBAG, /MONVOL/COMMU, /MONVOL/FVMBAG
• No new developments
• /MONVOL/AIRBAG1, /MONVOL/COMMU1, /MONVOL/FVMBAG1
• Injected gas are defined in separated input : /MAT/GAS
• /MAT/GAS/PREDEF
• /MAT/GAS/MASS
• /MAT/GAS/MOLE
• /MAT/GAS/CSTA
• Injectors are defined in separated input : /PROP/INJECT
• /PROP/INJECT1
• /PROP/INJECT2
• Porous fabric
• Loss heat flow
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RADIOSS INPUT - FVM
Internal gas mesh
• Automatic Mesher : input a frame and # of volumes in each direction
• Solid 3D elements : Brick, Pentahedron or Tetrahedron
• Can be performed on a closed reference geometry (iref)
Merging parameters
• cgmerg , cnmerg
• Can be modified in Engine run : /FVMBAG/MODIF [v12.0.202]
• Merge can be activated with Dtmin input keyword /DT/FVMBAG [v12.0.202]
Other inputs can be default
Internal surfaces : diffusers, tethers, inflators Isurfi
• Works only with solid elements gas mesh (tetra, hexa <=> HyperMesh)
• Injectors on Internal surfaces [v12.0.202]
• Can be porous, porosity input in fabric material law
Remaining input identical to UP Airbags
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RADIOSS INPUT – FVM - AUTOMESH
Define a Frame (O, V1, V2, V3)
Define boxes (N1, N2, N3)
Generate points at the intersection of the boxes and the bag
Generate Finite Volumes
(polyhedra)
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RADIOSS INPUT - FVM
• AVAILABLE FV IN /GRBRIC INPUT
• Hexahedron /BRICK
• Tetrahedron /TETRA4
• Pentahedron
• Triangular prism /PENTA6
/BRICK N1,N2,N3,N1,N4,N5,N6,N4
• Pyramid [v14] /BRICK N1,N2,N3,N4,N5,N5,N5,N5
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RADIOSS INPUT - FVM – Internal surfaces
Injection
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RADIOSS - New in Versions 12 & 13
• Contact : /INTER/TYPE23 [v12.0.210]
• Fully integrated quad membrane (Batoz)
• Lost Heat Flow
• Hconv [v12.0.210]
• Air flow through vent holes inside the bag [v13.0]
• UP Airbags
• /MONVOL/COMMU1 [v12.0.202]
• /EREF/SHELL /EREF/SH3N [v12.0.210]
• Leakage models /LEAK/MAT [v12.0]
• /MONVOL/AIRBAG1 Nporsurf
• FVM Airbags
• /FVMBAG/MODIF [v12.0.202]
• /DT/FVMBAG [v12.0.202]
• Leakage models /LEAK/MAT [v13.0.210]
• /MONVOL/FVMBAG1 Nporsurf
• Injectors on Internal surfaces Isurfi [v12.0.202]
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RADIOSS INPUT : AIRBAG FOLDING
• Folding with a RADIOSS pre-simulation
• Contact type 7 + 11 => no intersections
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EXAMPLE 1 : DRIVER AIRBAG
• FOLDED WITH HYPERCRASH
• BAG CONTACT TYPE 7 + 11
• FVM
• Automatic mesher on reference geometry
• 3583 polyhedrons
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Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
EXAMPLE 1 : DRIVER AIRBAG
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Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
EXAMPLE 1 : DRIVER AIRBAG
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Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
EXAMPLE 1 : DRIVER AIRBAG
• UP – FVM ( bag contact type 7 + 11)
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EXAMPLE 1 : DRIVER AIRBAG
• Windows 1 CPU : Intel(R) Core(TM) i7-4900MQ CPU @ 2.80GHz (x86_64)
• Final simulation time 150ms
• Ratio FVM/UP : 1.71
Bag Contact
Type
Elapsed Dt Average
UP 7+11 3h 3’ 0.497ms
FVM 7+11 5h 12’ 0.495ms
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EXAMPLE 2 : PASSENGER AIRBAG
• FOLDING THE BAG WITH RADIOSS
The 3D passenger airbag (PAB) is meshed on it reference geometry using
HyperMesh. Rigid surfaces and the airbag box are added around the meshed airbag.
Displacement is imposed the top of the rigid surface to push the bag in its box. A
depression is applied in the airbag.
Imposed
displacement
Airbag mesh
Rigid surface (offset of
the PAB mesh)
Airbag
box (rigid)
Monitored volume with
negative pressure)
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EXAMPLE 2 : PASSENGER AIRBAG
• Model description
• The folded geometry of the bag is extracted from the RADIOSS ascii output file (.sta)
• The initial geometry of the airbag is used as reference (/REFSTA or /XREF)
• The option "zerostress" is activated in order to remove stress in the airbag coming
from the differences between the initial and reference shape of the elements.
• The airbag model is integrated in the car
Airbag box
(deformable) IP cover (with
rupture)
Car environment (rigid)
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EXAMPLE 2 : PASSENGER AIRBAG
• Two models are made:
• A Uniform Pressure (UP) model is made with Monitored Volume type AIRBAG1
• The gas is meshed with 26304 tetrahedrons and a Finite Volume model (FVM) is
made with Monitored Volume type FVMBAG1
Gas
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EXAMPLE 2 : PASSENGER AIRBAG
• UP : « ibag » influence (bag with contact type 7 + 11)
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EXAMPLE 2 : PASSENGER AIRBAG
• UP : bag contact type influence
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EXAMPLE 2 : PASSENGER AIRBAG
• UP - FVM (contact type 23 and ibag=1)
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EXAMPLE 2 : PASSENGER AIRBAG
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Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
EXAMPLE 2 : PASSENGER AIRBAG
![Page 25: Recommendations for Airbag Numerical Simulation with Uniform and Variable Gas Pressure using RADIOSS](https://reader035.vdocuments.mx/reader035/viewer/2022081715/54139c7c8d7f7299698b4680/html5/thumbnails/25.jpg)
Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.
EXAMPLE 2 : PASSENGER AIRBAG
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EXAMPLE 2 : PASSENGER AIRBAG
• Windows 1 CPU : Intel(R) Core(TM) i7-4900MQ CPU @ 2.80GHz (x86_64)
• Final simulation time 150ms
• Ratio FVM/UP : 3.72
Bag Contact
Type
Ibag Elapsed Dt Average
UP 7+11 0 1h 34’ 0.887ms
UP 7+11 1 1h 9’ 0.888ms
UP 23 1 1h 2’ 0.883ms
FVM 23 1 3h52’ 0.538ms
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EXAMPLE 3 : SIDE AIRBAG
• Injection is made in an internal diffuser which
must be taken into account by the gas flow
• Input an internal surface « isurfi »
• Automatic gas mesher is not compatible with
internal surface
• Mesh the gas with HyperMesh
• « cgmerg & cnmerg » set to 1.e-10 in STARTER
input
• « cgmerg & cnmerg » to be given in ENGINE
input : /FVMBAG/MODIF
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EXAMPLE 4 : CURTAIN BAG
MESH#1 ON INITIAL GEOMETRY
639 FV
NB1= 61
NB2= 24
1
2
1 volume !
NB2 is too small
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EXAMPLE 4 : CURTAIN BAG
MESH#2 MESH ON REFERENCE GEOMETRY
991 FV
NB1= 50
NB2= 50
1
2
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EXAMPLE 4 : CURTAIN BAG
MESH#2 MESH ON REFERENCE GEOMETRY
991 FV
NB1= 50
NB2= 50
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EXAMPLE 4 : CURTAIN BAG
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HINTS
UP&FVM
No initial intersections
Contact : type7 + type11
FVM
Perform a preliminary UP run (AIRBAG1 or COMMU1)
Injection velocity : input sound speed at injection temperature
If internal surfaces
• Use Tetra mesh
• Start merging in the Engine run (to avoid initial merging of FV on both sides of an
internal surface)
• Injection of gas occurs in the opposite direction of the normal
Unstable gas flow computation
• Reduce time step with Dtscale (/DT/FVMBAG)
• Increase Dtmin (/DT/FVMBAG)