Oasys LS-DYNA Environment 8.1 VOLUME 3 ... - Oasys Software

Oasys LS-DYNA Environment: User Guide (Version 8.1)
*AIRBAG_WANG_NEFSKE
$ SID ][ SIDTYP ][Rbody ID][ V scale][ P scale][ V init ][mass dmp][ SPSF ]
1 1 0 1.0 1.0 0.000E+00 5.000E+01 0.7
$ Cv ][ Cp ][ Temp ][LC temp ][LC mflow][tank vol]
8.5e8 1.1e9 800 1
$ C23 ][ LCC23 ][ A23 ][ LCA23 ][ CP23 ][ LCCP23 ][ AP3 ][ LCAP23 ]
1.0 1500.
$P ambint][rho amb ][ G conv ]
1.009E-01 1.200E-12 1.000E+00
$ IOC ][ IOA ][ IVOL ][ IRO ][ IT ][ LCBF ]
*SET_PART_LIST
1
1 5
$
$ ====================== LOAD CURVES ======================
$
*DEFINE_CURVE
1
$ massflow into airbag
$ Time (s) mass flow rate (kg/s)
0.00000E+00 0.00000E+00
0.010000 1.8e-3
0.040000 0.0
0.10000 0.0
Note:
! The easiest way to specify the elements that make up the airbag is with a part list, referred to
on card 1, first entry.
! Some damping is recommended (card 1, last two entries).
! Always define GC as 1.0 (card 3, 3rd entry)
! Cp, Cv, T and the mass flow rate normally come from a tank test analysis programme which
back-calculates these parameters from the pressure time-history in the tank.
! The mass flow rate is defined as a function of time using a curve as in the example. The units
are Tonne/sec in this example. It typically peaks at about 2E-3 Tonne/sec.
FOLDING AIRBAGS
Although real airbags are initially folded, it is not always necessary to use a folded mesh when
simulating them. With in-position occupant studies, the airbag is usually fully inflated by the time
the occupant contacts it, so that the unfolding process has little effect on occupant interaction.
Unfolded or partially folded meshes are easier to create and use than fully folded meshes. Apart
from the extra time required to fold an airbag mesh, additional CPU time is needed to analyse
them due to the finer mesh and internal contact.
Initially unfolded airbags are typically flat discs, with a spacing of around 1.0mm between the
front and back layers. In such cases the occupant’s arms may be initially penetrating the outer
regions of the airbag. One way of avoiding initial contact is by introducing a small number of
initial folds so that the arms are outside the airbag. For example, there might be a 90 degree
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