/MONVOL/GAS

Block Format Keyword Describes the perfect gas monitored volume type.

Format

(1)	(2)	(3)	(5)	(7)	(9)
/MONVOL/GAS/`monvol_ID`/`unit_ID`
`monvol_title`
`surf_ID`_ex	`I_equi`
`Ascale`_t		`Ascale`_P	`Ascale`_S	`Ascale`_A	`Ascale`_D
$γ$		$μ$	`T`_relax	`T`_ini	$ρ_{i}$
`P`_ext		`P`_ini	`P`_max	`V`_inc	`M`_ini
`N`_vent

Define N_vent vent holes membranes (3 Lines per vent holes membrane)

(1)	(2)	(3)	(5)	(6)	(7)	(9)
`surf_ID`_v	`A`_vent			`I`_deleted
`T`_vent		$Δ P_{d e f}$	$Δ t P_{d e f}$
`fct_ID`_t	`fct_ID`_P	`fct_ID`_A	`Fscale`_t		`Fscale`_P	`Fscale`_A

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. 1 (Integer)
`I_equi`	Thermodynamic equilibrium flag. 3 =0 (Default) Constant volume is used to calculate the mass needed to fill the volume. =1 Increasing volume assumes a constant temperature when calculating the mass needed to fill the volume. =2 Increasing volume uses an adiabatic process (gas temperature can increase) when calculating the mass needed to fill the volume. (Integer)
`Ascale`_t	Abscissa scale factor for time based functions. Default = 1.0 (Real)	$[s]$
`Ascale`_P	Abscissa scale factor for pressure based functions. Default = 1.0 (Real)	$[Pa]$
`Ascale`_S	Abscissa scale factor for area based functions. Default = 1.0 (Real)	$[m^{2}]$
`Ascale`_A	Abscissa scale factor for angle based functions. Default = 1.0 (Real)	$[rad]$
`Ascale`_D	Abscissa scale factor for distance based functions. Default = 1.0 (Real)	$[m]$
$γ$	Ratio of specific heat. (Real) $γ = \frac{C_{p}}{C_{v}}$
$μ$	Volumetric viscosity. Default = 0.01 (Real)
`T`_relax	Relaxation time. 10 (Real)	$[s]$
`T`_ini	Initial temperature. Default = 295K (Real)	$[K]$
$ρ_{i}$	Initial mass density inside the monitored volume. (Real)	$[\frac{kg}{m^{3}}]$
`P`_ext	External pressure. (Real)	$[Pa]$
`P`_ini	Initial pressure. (Real)	$[Pa]$
`P`_max	Maximum pressure. 5 Default = 10³⁰ (Real)	$[Pa]$
`V`_inc	Incompressible volume. (Real)	$[m^{3}]$
`M`_ini	Initial (gas) mass. (Real)	$[kg]$
`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)
`A`_vent	if `surf_ID`_v = 0: vent hole area. Default = 0.0 (Real)	$[m^{2}]$
`I`_deleted	if `surf_ID`_v ≠ 0 if `I`_deleted = 0: area of surface `surf_ID`_v is considered for venting
`I`_deleted	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)	$[s]$
$Δ P_{d e f}$	Pressure difference to open vent hole membrane $Δ P_{d e f} = P_{d e f} - P_{e x t}$ . (Real)	$[Pa]$
$Δ t P_{d e f}$	Minimum duration pressure exceeds `P`_def to open vent hole membrane. (Real)	$[s]$
`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)

Comments

surf_ID_ex must be defined using segments associated with 4-nodes or 3-nodes 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)
$F (t') = f_{t} (\frac{t}{{Ascale}_{t}})$

where, t is the time and $f_{t}$ is the function of fct_ID_t.(2)
$F (P') = f_{P} (\frac{P}{{Ascale}_{P}})$

Where, $P$ is the pressure and $f_{P}$ 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 $Δ t P_{d e f}$ .
vent_holes_surface = $A_{vent} \cdot A \cdot f_{A} (\frac{A}{A_{0}}) \cdot f_{P} (P - P_{ext})$
Where,

A

Area of surface surf_ID_v

A₀

initial Area of surface surf_ID_v

$f_{A}$

Function of fct_ID_A

$f_{P}$

Function of fct_ID_P

Functions $f_{P}$ = fct_ID_P are assumed to be equal to 1, if they are not specified (null identifier).

Function $f_{A}$ fct_ID_A is assumed as: $f_{A} (\frac{A}{A_{0}}) = 1$ 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 = $A_{vent} \cdot A \cdot f_{A} (\frac{A}{A_{0}}) \cdot f_{t} (t) \cdot f_{P} (P - P_{ext})$

If surf_ID_v = 0 (surf_ID_v is not defined).

vent_holes_area = $A_{vent} \cdot f_{t} (t) \cdot f_{P} (P - P_{ext})$

Where,

A

Area of surface surf_ID_v

$f_{A}$

Function of fct_ID_A

$f_{t}$

Function of fct_ID_t

$f_{P}$

Function of fct_ID_P

Functions $f_{t}$ = fct_ID_t and $f_{P}$ = fct_ID_P are assumed to be equal to 1, if they are not specified (null identifier).

Function $f_{A}$ = fct_ID_A is assumed as:

$f_{A} (A) = A$ if it is not specified.
For tire modeling, pressure in the tire is:(3)
$P_{t i r e} = P_{i n i} - P_{e x t}$

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.