/MONVOL/COMMU1
Block Format Keyword Describes multichambered airbag with hybrid input of injected gas. This keyword is similar to /MONVOL/COMMU (Obsolete), but has more flexible input.
 Gas materials can be specified in separate /MAT/GAS cards
 Injector can be specified in separate /PROP/INJECT1 for injector
 Scaling of communication area between airbag chambers as function of time or relative pressure is possible
Format
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

/MONVOL/COMMU1/monvol_ID/unit_ID  
monvol_title  
surf_ID_{ex}  H_{conv}  
Ascale_{t}  Ascale_{P}  Ascale_{S}  Ascale_{A}  Ascale_{D}  
mat_ID  $\mu $  P_{ext}  T_{0}  I_{equil}  I_{ttf} 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

N_{jet} 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

inject_ID  sens_ID  I_{jet}  node_ID_{1}  node_ID_{2}  node_ID_{3} 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

fct_ID_{Pt}  $fct\_I{D}_{P\theta}$  $fct\_I{D}_{P\delta}$  Fscale_{Pt}  $Fscal{e}_{P\theta}$  $Fscal{e}_{P\delta}$ 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

N_{vent}  N_{porsurf} 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

surf_ID_{v}  I_{form}  A_{vent}  B_{vent}  vent_title  
T_{start}  T_{stop}  $\text{\Delta}{P}_{def}$  $\text{\Delta}t{P}_{def}$  I_{dtPdef}  
fct_ID_{t}  fct_ID_{P}  fct_ID_{A}  Fscale_{t}  Fscale_{P}  Fscale_{A}  
fct_ID_{t'}  fct_ID_{P'}  fct_ID_{A'}  Fscale_{t'}  Fscale_{P'}  Fscale_{A'} 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

surf_ID_{ps}  Iform_{ps}  Iblockage  surface_title  
T_{start}  T_{stop}  $\text{\Delta}{P}_{def}$  $\text{\Delta}t{P}_{def}$  I_{dtPdef} 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

C_{ps}  Area_{ps}  fct_ID_{cps}  fct_ID_{aps}  Fscale_{cps}  Fscale_{aps} 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

fct_ID_{v}  Fscale_{v} 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

N_{bag} 
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

bag_ID  surf_ID_{c}  $\text{\Delta}{P}_{Cdef}$  A_{com}  T_{com}  $\text{\Delta}t{P}_{Cdef}$  
fct_ID_{Ct}  fct_ID_{CP}  Fscale_{Ct}  Fscale_{CP} 
Definition
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. (Integer) 

H_{conv}  Heat transfer coefficient.
23 (Real) 
$\left[\frac{\text{W}}{{\text{m}}^{\text{2}}\text{K}}\right]$ 
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) 
$\left[\text{m}\right]$ 
mat_ID  Material identifier for
initial gas (/MAT/GAS). (Integer) 

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

P_{ext}  External
pressure. (Real) 
$\left[\text{Pa}\right]$ 
T_{0}  Initial
temperature. Default = 295K (Real) 
$\left[\text{K}\right]$ 
I_{equil}  Initial thermodynamic
equilibrium flag.
(Integer) 

I_{ttf}  Time shift flag. Only
active when at least one injection sensor is specified.
Determines time shift for venting, porosity and communication
options when injection starts at a Time to Fire specified in a sensor.
(Integer) 

N_{jet}  Number of
injectors. (Integer) 

inject_ID  Injector property
identifier. (Integer) 

sens_ID  Sensor
identifier. (Integer) 

I_{jet}  Jetting flag.
(Integer) 

node_ID_{1}, node_ID_{2}, node_ID_{3}  Node identifiers N_{1}, N_{2}, and N_{3} for jet shape definition. (Integer) 

fct_ID_{Pt}  Identifier of the function
number defining
$\text{\Delta}\mathrm{P}(t)$
. (Integer) 

$fct\_I{D}_{P\theta}$  Identifier of the function
number defining
$\text{\Delta}\mathrm{P}(\theta )$
. (Integer) 

$fct\_I{D}_{P\delta}$  Identifier of the function
number defining
$\text{\Delta}\mathrm{P}(\delta )$
. (Integer) 

Fscale_{Pt}  Scale factor for
fct_ID_{Pt}. Default = 1.0 (Real) 
$\left[\text{Pa}\right]$ 
$Fscal{e}_{P\theta}$  Scale factor for
$fct\_I{D}_{P\theta}$
. Default = 1.0 (Real) 
$\left[\text{Pa}\right]$ 
$Fscal{e}_{P\delta}$  Scale factor for
$fct\_I{D}_{P\delta}$
. Default = 1.0 (Real) 
$\left[\text{Pa}\right]$ 
N_{vent}  Number of vent
holes. (Integer) 

N_{porsurf}  Number of porous
surfaces. (Integer) 

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

I_{form}  Formulation flag.
(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) 
$\left[{\text{m}}^{2}\right]$  
B_{vent}  If
surf_ID_{v} ≠ 0:
scale factor on impacted vent hole area. Default = 1.0 (Real) 

If
surf_ID_{v} = 0:
B_{vent} is reset
to 0 for vent hole area. Default = 0.0 (Real) 
$\left[{\text{m}}^{2}\right]$  
vent_title  Vent hole
title. (Character, maximum 20 characters) 

T_{start}  Start time for
venting. Default = 0 (Real) 
$\left[\text{s}\right]$ 
T_{stop}  Stop time for
venting. Default = 10^{30} (Real) 
$\left[\text{s}\right]$ 
$\text{\Delta}{P}_{def}$  Pressure difference to
open vent hole membrane. $\text{\Delta}{P}_{def}={P}_{def}{P}_{ext}$ Default = 0 (Real) 
$\left[\text{Pa}\right]$ 
$\text{\Delta}t{P}_{def}$  Minimum duration pressure
exceeds P_{def} to
open vent hole. Default = 0 (Real) 
$\left[\text{s}\right]$ 
I_{dtPdef}  Time delay flag when
$\text{\Delta}{P}_{def}$
is reached:
(Integer) 

fct_ID_{t}  Porosity versus time
function identifier. (Integer) 

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

fct_ID_{A}  Porosity versus 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) 

fct_ID_{t'}  Porosity versus time
function identifier during contact. (Integer) 

fct_ID_{P'}  Porosity versus pressure
function identifier during contact. (Integer) 

fct_ID_{A'}  Porosity versus impacted
surface function identifier during contact. (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) 

surf_ID_{ps}  Porous surface identifier
(ignored if Iform_{ps}
= 0). (Integer) 

Iform_{ps}  Porosity formulation.
(Integer) 

Iblockage  Block leakage flag, if
contact (Iform_{ps} > 0).
(Integer) 

surface_title  Porous surface
title. (Character, maximum 20 characters) 

C_{ps}  Scale factor on leakage
area (Iform_{ps}
=0). (Real) 

Area_{ps}  Leakage area
(Iform_{ps}=0). (Real) 
$\left[{\text{m}}^{2}\right]$ 
fct_ID_{cps}  Function identifier
defining
C_{ps}(t),
ignored if C_{ps} is
not equal to zero. (Integer) 

fct_ID_{aps}  Function identifier
defining
Area_{ps}(PP_{ext}), ignored if
Area_{ps} is not
equal to zero. (Integer) 

Fscale_{cps}  Scale factor for
fct_ID_{cps}. Default = 1 (Real) 

Fscale_{aps}  Scale factor for
fct_ID_{aps} Default = 1 (Real) 
$\left[{\text{m}}^{2}\right]$ 
fct_ID_{v}  Outflow velocity function
identifier, Chemkin model. (Integer) 

Fscale_{v}  Scale factor on
fct_ID_{v}. Default = 1.0 (Real) 
$\left[\frac{\text{m}}{\text{s}}\right]$ 
N_{bag}  Number of communicating
airbags. (Integer) 

bag_ID  Airbag identifier. 20 (Integer) 

surf_ID_{C}  Communicating surface
identifier. (Integer) 

$\text{\Delta}{P}_{Cdef}$  Pressure difference to
open communication surface membrane. (Real) 
$\left[\text{Pa}\right]$ 
A_{com}  Communicating surface, if surf_ID_{C} = 0.  $\left[{\text{m}}^{2}\right]$ 
Scale factor on surface,
if surf_ID_{C} ≠
0. Default = 1.0 (Real) 23 

T_{com}  Start time for
communication. (Real) 
$\left[\text{s}\right]$ 
$\text{\Delta}t{P}_{Cdef}$  Minimum duration pressure
difference exceeds
$\text{\Delta}{P}_{Cdef}$
to open communication surface
membrane. (Real) 
$\left[\text{s}\right]$ 
fct_ID_{Ct}  Communicating surface
versus time function identifier. (Integer) 

fct_ID_{CP}  Communicating surface
versus relative pressure function
identifier. (Integer) 

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

Fscale_{CP}  Scale factor for
fct_ID_{CP}. Default = 1.0 (Real) 
Comments
 The airbag external surface should be built only from 4 and 3 noded shell elements. The airbag external surface cannot be defined with /SURF/SEG, nor with /SURF/SURF, if a subsurface is defined in /SURF/SEG.
 The volume must be closed and the normals must be oriented outwards.
 Abscissa scale factors are used
to transform abscissa units in airbag functions, for example:$$\text{F}(t\prime )={\text{f}}_{t}\left(\frac{t}{{\mathit{Ascale}}_{t}}\right)$$Where,
 $t$
 Time
 ${\mathrm{f}}_{t}$
 Function of fct_ID_{t}
$$\text{F}(P\prime )={\text{f}}_{P}\left(\frac{P}{{\mathit{Ascale}}_{P}}\right)$$Where, $P$
 Pressure
 ${\mathrm{f}}_{P}$
 Function of fct_ID_{P}
 Pressure and temperature of external air and the initial pressure and temperature of air inside of airbag is set to P_{ext} and T_{0}.
 The characteristics of the gas initially filling the airbag (temperature and pressure) must be defined (no default) and must be equal for each communicating airbag.
 Initial thermodynamic equilibrium
is written at time zero (I_{equil} =0) or at beginning of jetting
(I_{equil} =1), based on the following
equation with respect to the volume at time zero, or the volume at beginning of
jetting:$${P}_{\mathit{ext}}V=R\frac{{M}_{0}}{{M}_{i}}{T}_{0}$$
Where, ${M}_{0}$ is the mass of gas initially filling the airbag, ${M}_{\mathrm{i}}$ is the molar mass of the gas initially filling the airbag, and $R$ is the gas constant depending on the units system given the in /BEGIN card. For example in SI system:
$$R=8.314\frac{J}{\mathit{mole}\cdot K}$$  If jetting is used, an additional
$\text{\Delta}{P}_{jet}$
pressure is applied to each element of the
airbag:$$\Delta {P}_{\mathit{jet}}=\Delta \text{P}\left(t\right)\cdot \Delta \text{P}\left(\theta \right)\cdot \Delta \text{P}\left(\delta \right)\cdot \text{max}\left(\mathbf{n}\xb7\mathbf{m},0\right)$$
Function $\text{\Delta}P\left(t\right)$ is automatically shifted by time given in sensor, which activates injection.
 With m being the
normalized vector between the projection of the center of the element upon
segment (N_{1} and N_{3}) and the center of the element;
$\theta $
the angle between vectors
MN_{2} and m (in degrees),
$\delta $
is the distance between the center of the element and
its projection upon segment (N_{1} and N_{3}).The projection of a point upon segment (N_{1} and N_{3}) is defined as the projection of the point in direction MN_{2} upon the line (N_{1} and N_{3}) if it lies inside the segment (N_{1} and N_{3}). If this is not the case, the projection of the point upon segment (N_{1} and N_{3}) is defined as the closest node N_{1} or N_{3}.
with M between of N_{1} and N_{3}
 If node_ID_{3} = 0, node_ID_{3} is set to node_ID_{1} and the dihedral shape is reduced to a conical shape.
 If
fct_ID_{v} = 0:
isenthalpic outflow is assumed, otherwise Chemkin model is used and outflow
velocity is:$$v={\mathit{Fscale}}_{v}\cdot {\text{f}}_{v}\left(P{P}_{\mathit{ext}}\right)$$Where, ${f}_{v}$ is the function of fct_ID_{v}.
 Isenthalpic model
Venting or the expulsion of gas from the volume is assumed to be isenthalpic.
The flow is also assumed to be unshocked, coming from a large reservoir and through a small orifice with effective surface area, A.
Conservation of enthalpy leads to velocity, u at the vent hole. The Bernouilli equation is then written as:
(monitored volume) $\frac{\gamma}{\gamma 1}\frac{P}{\rho}=\frac{\gamma}{\gamma 1}\frac{{P}_{\mathit{ext}}}{{\rho}_{\mathit{vent}}}+\frac{{u}^{2}}{2}$ (vent hole)
Applying the adiabatic conditions:
(monitored volume) $\frac{P}{{\rho}^{\gamma}}=\frac{{P}_{\mathit{ext}}}{{{\rho}_{\mathit{vent}}}^{\gamma}}$ (vent hole)
Where, $P$ is the pressure of gas into the airbag and $\rho $ is the density of gas into the airbag.
Therefore, the exit velocity is given by:
$${u}^{2}=\frac{2\gamma}{\gamma 1}\frac{P}{\rho}\left(1{\left(\frac{{P}_{\mathit{ext}}}{P}\right)}^{\frac{\gamma 1}{\gamma}}\right)$$For supersonic flows the outlet velocity is determined as described in Supersonic Outlet Flow in the Theory Manual.
The mass out flow rate is given by:
$${\dot{m}}_{\mathit{out}}={\rho}_{\mathit{vent}}*\mathit{vent}\_\mathit{holes}\_\mathit{surface}*u=\rho {\left(\frac{{P}_{\mathit{ext}}}{P}\right)}^{\frac{1}{\gamma}}*\mathit{vent}\_\mathit{holes}\_\mathit{surface}*u$$The energy flow rate is given by:
$${\dot{E}}_{\mathit{out}}={\dot{m}}_{\mathit{out}}\frac{E}{\rho V}={\left(\frac{{P}_{\mathit{ext}}}{P}\right)}^{\frac{1}{\gamma}}*\mathit{vent}\_\mathit{holes}\_\mathit{surface}*u\frac{E}{V}$$Where, $V$ is the airbag volume and $E$ is the internal energy of gas into the airbag.
 Chemkin model$${\dot{m}}_{\mathit{out}}=\rho \cdot \mathit{vent}\_\mathit{holes}\_\mathit{surface}\cdot {\text{f}}_{v}\left(P{P}_{\mathit{ext}}\right)\cdot {\mathit{Fscale}}_{v}$$
Where, $\rho $ is the density of the gas within the airbag and ${f}_{v}$ is the function of fct_ID_{v}
 Isenthalpic model
 Vent holes area is computed as
follows:$$vent\_holes\_area\text{}={A}_{vent}\cdot {A}_{non\_impacted}\cdot {\mathrm{f}}_{t}\left(t\right)\cdot {\mathrm{f}}_{P}\left(P{P}_{ext}\right)\cdot {\mathrm{f}}_{A}\left(\frac{{A}_{non\_impacted}}{{A}_{0}}\right)$$ $$+{B}_{\mathit{vent}}\cdot {A}_{\mathit{impacted}}\cdot {\text{f}}_{{t}^{\prime}}\left(t\right)\cdot {\text{f}}_{{P}^{\prime}}\left(P{P}_{\mathit{ext}}\right)\cdot {\text{f}}_{{A}^{\prime}}\left(\frac{{A}_{\mathit{impacted}}}{{A}_{0}}\right)$$
With impacted surface:
$${A}_{\mathit{impacted}}=\sum _{e\in {S}_{\mathit{vent}}}\frac{{n}_{c}\left(e\right)}{n\left(e\right)}{A}_{e}$$and nonimpacted surface:$${A}_{\mathit{non}\_\mathit{impacted}}=\sum _{e\in {S}_{\mathit{vent}}}\left(1\frac{{n}_{c}\left(e\right)}{n\left(e\right)}\right){A}_{e}$$where for each element e of the airbag materials ${n}_{c}\left(e\right)$ means the number of impacted nodes among the $n\left(e\right)$ nodes defining the element and ${A}_{e}$ is the area of element e.
And,
A_{0} is the initial area of surface surf_ID_{v}
${\mathrm{f}}_{t}$ , ${\mathrm{f}}_{P}$ and f_{A} are functions of fct_ID_{t}, fct_ID_{P} and fct_ID_{A}
f_{t'}, f_{P'} and f_{A'} are functions of fct_ID_{t'}, fct_ID_{P'} and fct_ID_{A'}
 Functions fct_ID_{t'} and fct_ID_{P'} are assumed to be equal to 1, if they are not specified (null identifier).
 Function
fct_ID_{A'} is assumed as:
${\text{f}}_{{A}^{\prime}}\left(A\right)=A$ if it is not specified.
 To account for contact blockage of vent holes and porous surface area, flag I_{BAG} must be set to 1 in the correspondent interfaces (Line 3 of interface TYPE7 or TYPE23). If not, the nodes impacted into the interface are not considered as impacted nodes in the previous formula for A_{impacted} and A_{non_impacted}.
 Vent holes and interchamber components should be included into the airbag (chamber) external surface.
 When there is no sensor which activates gas injection, the vent holes and porosity becomes active, if time T becomes greater than the T_{start} or if the pressure P exceeds P_{def} value longer than the time given in $\text{\Delta}t{P}_{def}$ .
 When at least one of the
injectors is activated by the sensor, then activation of venting, porosity and
communication options is controlled by
I_{ttf}.
T_{inj} is the time of the first injector to be activated by the sensor.
I_{inj} = 0:Venting, Porosity Communication Activation When $P>\text{\Delta}{P}_{def}$ longer than the time $\text{\Delta}t{P}_{def}$ , or $T>{T}_{start}$ When $P>\text{\Delta}{P}_{Cdef}$ longer than the time $\text{\Delta}t{P}_{Cdef}$ , or $T>{T}_{com}$ Deactivation T_{stop} N/A Time dependent functions No shift No shift I_{ttf} = 3:Venting, Porosity Communication Activation When $T>{T}_{inj}$ and $P>\text{\Delta}{P}_{def}$ longer than the time $\text{\Delta}t{P}_{def}$ , or $T>{T}_{inj}+{T}_{start}$ When $T>{T}_{inj}$ and $P>\text{\Delta}{P}_{Cdef}$ longer than the time $\text{\Delta}t{P}_{Cdef}$ , or $T>{T}_{inj}+{T}_{com}$ Deactivation ${T}_{inj}+{T}_{stop}$ N/A Time dependent functions Shifted by ${T}_{inj}+{T}_{start}$ Shifted by ${T}_{inj}+{T}_{com}$ All other related curves are active when the corresponding venting, porosity or communication option is active.
The variety of I_{ttf} values comes from historical reasons. Values I_{ttf}=1 and 2 are obsolete and should not be used. Usual values are I_{ttf}=0 (no shift) or I_{ttf}=3 (all relative options are shifted by T_{inj}).
 Leakage by porosity
formulations; the mass flow rate flowing out is computed as:
 Iform_{ps} = 0
${\dot{m}}_{\mathit{out}}={A}_{\mathit{eff}}\sqrt{2P\rho}{Q}^{\frac{1}{\gamma}}\sqrt{\frac{\gamma}{\gamma 1}\left[1{Q}^{\frac{\gamma 1}{\gamma}}\right]}$
(Isentropic  Wang
Nefske)
with
$$Q=\frac{{P}_{\mathit{ext}}}{P}$$and ${A}_{\mathit{eff}}={C}_{\mathit{ps}}\cdot {\mathit{Area}}_{\mathit{ps}}$ or ${A}_{\mathit{eff}}={\text{C}}_{\mathit{ps}}(t)\cdot {\text{Area}}_{\mathit{ps}}(P{P}_{\mathit{ext}})$
Note that the effective venting area A_{eff} does not vary with different airbag fabric materials.
 Iform_{ps} > 0, the effective venting area A_{eff} is computed according to the input in the /LEAK/MAT input for fabric materials of TYPE19 or TYPE58.
 Iform_{ps} = 1 ${\dot{m}}_{\mathit{out}}={A}_{\mathit{eff}}\sqrt{2P\rho}{Q}^{\frac{1}{\gamma}}\sqrt{\frac{\gamma}{\gamma 1}\left[1{Q}^{\frac{\gamma 1}{\gamma}}\right]}$ (Isentropic  Wang Nefske)
 Iform_{ps} = 2
${\dot{m}}_{\mathit{out}}={A}_{\mathit{eff}}\rho v(P{P}_{\mathit{ext}})$
Where, v is the outflow gas velocity (Chemkin)
 Iform_{ps} = 3 ${\dot{m}}_{\mathit{out}}={A}_{\mathit{eff}}\sqrt{2\rho (P{P}_{\mathit{ext}})}$ (Graefe)
 Iform_{ps} = 0
${\dot{m}}_{\mathit{out}}={A}_{\mathit{eff}}\sqrt{2P\rho}{Q}^{\frac{1}{\gamma}}\sqrt{\frac{\gamma}{\gamma 1}\left[1{Q}^{\frac{\gamma 1}{\gamma}}\right]}$
(Isentropic  Wang
Nefske)
 If leakage blockage is activated,
Iblockage=1, the effective venting area is modified
as:$${A}_{\mathit{eff}}={A}_{\mathit{non}\_\mathit{impacted}}$$
A_{non_impacted} is nonimpacted surface. 11
The blockage will be active only if flag I_{BAG} is set to 1 in the concerned contact interfaces (line 3 of interface TYPE7 and TYPE23).
 It is not allowed to combine /MONVOL/COMMU and /MONVOL/COMMU1 cards in one multichambered airbag. However, in the same model it is possible to use different multichambered airbags (based on /MONVOL/COMMU or /MONVOL/COMMU1) for each airbag.
 When there is no sensor which activates gas injection, the communication surface is open if T > T_{com} or if the pressure exceeds $\text{\Delta}{P}_{Cdef}$ during more than $\text{\Delta}t{P}_{Cdef}$ . 17
 Communication surface,
S_{com} is computed as:
 if surf_ID =0,$${S}_{\mathit{com}}={A}_{\mathit{com}}\cdot {\text{f}}_{\mathit{Ct}}\left(t\right)\cdot {\text{f}}_{\mathit{CP}}\left(\Delta P\right)$$
 if surf_ID > 0 and Area is the surface of surf_ID,$${S}_{\mathit{com}}={A}_{\mathit{com}}\cdot \mathit{Area}\cdot {\text{f}}_{\mathit{Ct}}\left(t\right)\cdot {\text{f}}_{\mathit{CP}}\left(\Delta P\right)$$
Where, $\text{\Delta}P$ is the pressure difference between the chambers and ${f}_{Ct}$ and ${f}_{CP}$ are functions of fct_ID_{Ct} and fct_ID_{CP}
 if surf_ID =0,
 The lost heat flow is given
by:$$\dot{\text{Q}}\left(x,t\right)={H}_{\mathit{conv}}\cdot \text{Area}\left(x,t\right)\cdot \left(\text{T}\left(x,t\right){T}_{0}\right)$$