/MONVOL/GAS
Block Format Keyword Describes the perfect gas monitored volume type.
Format
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

/MONVOL/GAS/monvol_ID/unit_ID  
monvol_title  
surf_ID_{ex}  I_equi  
Ascale_{t}  Ascale_{P}  Ascale_{S}  Ascale_{A}  Ascale_{D}  
$\gamma $  $\mu $  T_{relax}  T_{ini}  ${\rho}_{i}$  
P_{ext}  P_{ini}  P_{max}  V_{inc}  M_{ini}  
N_{vent} 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

surf_ID_{v}  A_{vent}  I_{deleted}  
T_{vent}  $\text{\Delta}{P}_{def}$  $\text{\Delta}t{P}_{def}$  
fct_ID_{t}  fct_ID_{P}  fct_ID_{A}  Fscale_{t}  Fscale_{P}  Fscale_{A} 
Definitions
Field  Contents  SI Unit Example 

monvol_ID  Monitored volume
identifier (Integer, maximum 10 digits) 

unit_ID  Unit Identifier (Integer, maximum 10 digits) 

monvol_title  Monitored volume
title (Character, maximum 100 characters) 

surf_ID_{ex}  External surface
identifier. 1 (Integer) 

I_equi  Thermodynamic equilibrium
flag. 3
(Integer) 

Ascale_{t}  Abscissa scale factor for
time based functions. Default = 1.0 (Real) 
$\left[\text{s}\right]$ 
Ascale_{P}  Abscissa scale factor for
pressure based functions. Default = 1.0 (Real) 
$\left[\text{Pa}\right]$ 
Ascale_{S}  Abscissa scale factor for
area based functions. Default = 1.0 (Real) 
$\left[{\text{m}}^{2}\right]$ 
Ascale_{A}  Abscissa scale factor for
angle based functions. Default = 1.0 (Real) 
$\left[\text{rad}\right]$ 
Ascale_{D}  Abscissa scale factor for
distance based functions. Default = 1.0 (Real) 
$\left[\text{m}\right]$ 
$\gamma $  Ratio of specific
heat. (Real) $\gamma =\frac{{C}_{p}}{{C}_{v}}$ 

$\mu $  Volumetric
viscosity. Default = 0.01 (Real) 

T_{relax}  Relaxation time. 10 (Real) 
$\left[\text{s}\right]$ 
T_{ini}  Initial
temperature. Default = 295K (Real) 
$\left[\text{K}\right]$ 
${\rho}_{i}$  Initial mass density
inside the monitored volume. (Real) 
$\left[\frac{\text{kg}}{{\text{m}}^{\text{3}}}\right]$ 
P_{ext}  External
pressure. (Real) 
$\left[\text{Pa}\right]$ 
P_{ini}  Initial
pressure. (Real) 
$\left[\text{Pa}\right]$ 
P_{max}  Maximum pressure. 5 Default = 10^{30} (Real) 
$\left[\text{Pa}\right]$ 
V_{inc}  Incompressible
volume. (Real) 
$\left[{\text{m}}^{3}\right]$ 
M_{ini}  Initial (gas)
mass. (Real) 
$\left[\text{kg}\right]$ 
N_{vent}  Number of vent
holes. (Integer) 

surf_ID_{v}  Vent holes area surface
identifier. 8 (Integer) 

A_{vent}  if surf_ID_{v} ≠ 0:
scale factor on vent hole area Default = 1.0 (Real) 

if surf_ID_{v} = 0: vent
hole area. Default = 0.0 (Real) 
$\left[{\text{m}}^{2}\right]$  
I_{deleted}  if surf_ID_{v} ≠ 0 if I_{deleted} = 0: area of surface surf_ID_{v} is considered for venting 

if
I_{deleted} =
1: area of deleted elements inside surface surf_ID_{v} is considered for
venting. (Integer) 

T_{vent}  Start time for
venting. Default = 0.0 (Real) 
$\left[\text{s}\right]$ 
$\text{\Delta}{P}_{def}$  Pressure difference to
open vent hole membrane
$\text{\Delta}{P}_{def}={P}_{def}{P}_{ext}$
. (Real) 
$\left[\text{Pa}\right]$ 
$\text{\Delta}t{P}_{def}$  Minimum duration pressure
exceeds P_{def} to
open vent hole membrane. (Real) 
$\left[\text{s}\right]$ 
fct_ID_{t}  Porosity vs time function
identifier. (Integer) 

fct_ID_{P}  Porosity vs pressure
function identifier. (Integer) 

fct_ID_{A}  Porosity vs area function
identifier. (Integer) 

Fscale_{t}  Scale factor for
fct_ID_{t}. Default = 1.0 (Real) 

Fscale_{P}  Scale factor for
fct_ID_{P}. Default = 1.0 (Real) 

Fscale_{A}  Scale factor for
fct_ID_{A}. Default = 1.0 (Real) 
Comments
 surf_ID_{ex} must be defined using segments associated with 4nodes or 3nodes shell elements (possibly void elements), and not with /SURF/SEG.
 The volume must be closed and the normals must be oriented outwards.
 By default, I_equi =0 assumes that the volume to be filled by the gas will not increase. If the volume increases, the P_{ext} pressure will not be reached. If the volume increases when inflated, use I_equi =1 or 2 and define the initial temperature and initial gas density.
 Abscissa scale factors are used to
transform abscissa units in airbag functions, for example:
(1) $$\text{F}(t\prime )={\text{f}}_{t}\left(\frac{t}{{\mathit{Ascale}}_{t}}\right)$$where, t is the time and ${\mathrm{f}}_{t}$ is the function of fct_ID_{t}.(2) $$\text{F}(P\prime )={\text{f}}_{P}\left(\frac{P}{{\mathit{Ascale}}_{P}}\right)$$Where, $P$ is the pressure and ${\mathrm{f}}_{P}$ is the function of fct_ID_{P}.
 When P_{max} is reached, the pressure is reset to external pressure and venting has no effect.
 Vent hole membrane is deflated if T > T_{vent} or if the pressure exceeds P_{def} while more than $\text{\Delta}t{P}_{def}$ .
 vent_holes_surface =
${A}_{\mathit{vent}}\cdot A\cdot {\text{f}}_{A}\left(\frac{A}{{A}_{0}}\right)\cdot {\text{f}}_{P}(P{P}_{\mathit{ext}})$
Where,
 A
 Area of surface surf_ID_{v}
 A_{0}
 initial Area of surface surf_ID_{v}
 ${\mathrm{f}}_{A}$
 Function of fct_ID_{A}
 ${\mathrm{f}}_{P}$
 Function of fct_ID_{P}
Functions ${\mathrm{f}}_{P}$ = fct_ID_{P} are assumed to be equal to 1, if they are not specified (null identifier).
Function ${\mathrm{f}}_{A}$ fct_ID_{A} is assumed as: ${\text{f}}_{A}\left(\frac{A}{{A}_{0}}\right)=1$ if it is not specified.
 If surf_ID_{v} ≠ 0 (surf_ID_{v} is defined) the vent hole area is
computed as:
vent_holes_area = ${A}_{\mathit{vent}}\cdot A\cdot {\text{f}}_{A}\left(\frac{A}{{A}_{0}}\right)\cdot {\text{f}}_{t}(t)\cdot {\text{f}}_{P}(P{P}_{\mathit{ext}})$
If surf_ID_{v} = 0 (surf_ID_{v} is not defined).
vent_holes_area = ${A}_{\mathit{vent}}\cdot {\text{f}}_{t}(t)\cdot {\text{f}}_{P}(P{P}_{\mathit{ext}})$
Where, A
 Area of surface surf_ID_{v}
 ${\mathrm{f}}_{A}$
 Function of fct_ID_{A}
 ${\mathrm{f}}_{t}$
 Function of fct_ID_{t}
 ${\mathrm{f}}_{P}$
 Function of fct_ID_{P}
Functions ${\mathrm{f}}_{t}$ = fct_ID_{t} and ${\mathrm{f}}_{P}$ = fct_ID_{P} are assumed to be equal to 1, if they are not specified (null identifier).
Function ${\mathrm{f}}_{A}$ = fct_ID_{A} is assumed as:
${\text{f}}_{A}\left(A\right)=A$ if it is not specified.
 For tire modeling, pressure in the
tire is:
(3) $${P}_{tire}={P}_{ini}{P}_{ext}$$So, P_{ext} and P_{ini} have to be defined.
 Pressure will be applied linearly from P_{ext} at time t=0 to P_{ini} at time t=T_{relax}.