/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_IDex I_equi                
Ascalet AscaleP AscaleS AscaleA AscaleD
γ μ Trelax Tini ρ i
Pext Pini Pmax Vinc Mini
Nvent                  
Define Nvent vent holes membranes (3 Lines per vent holes membrane)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
surf_IDv Avent     Ideleted        
Tvent Δ P d e f Δ t P d e f        
fct_IDt fct_IDP fct_IDA   Fscalet FscaleP FscaleA

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_IDex 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)

 
Ascalet Abscissa scale factor for time based functions.

Default = 1.0 (Real)

[ s ]
AscaleP Abscissa scale factor for pressure based functions.

Default = 1.0 (Real)

[ Pa ]
AscaleS Abscissa scale factor for area based functions.

Default = 1.0 (Real)

[ m 2 ]
AscaleA Abscissa scale factor for angle based functions.

Default = 1.0 (Real)

[ rad ]
AscaleD Abscissa scale factor for distance based functions.

Default = 1.0 (Real)

[ m ]
γ Ratio of specific heat.

(Real)

γ = C p C v

 
μ Volumetric viscosity.

Default = 0.01 (Real)

 
Trelax Relaxation time. 10

(Real)

[ s ]
Tini Initial temperature.

Default = 295K (Real)

[ K ]
ρ i Initial mass density inside the monitored volume.

(Real)

[ kg m 3 ]
Pext External pressure.

(Real)

[ Pa ]
Pini Initial pressure.

(Real)

[ Pa ]
Pmax Maximum pressure. 5

Default = 1030 (Real)

[ Pa ]
Vinc Incompressible volume.

(Real)

[ m 3 ]

Mini Initial (gas) mass.

(Real)

[ kg ]
Nvent Number of vent holes.

(Integer)

 
surf_IDv Vent holes area surface identifier. 8

(Integer)

 
Avent if surf_IDv0: scale factor on vent hole area

Default = 1.0 (Real)

 
if surf_IDv = 0: vent hole area.

Default = 0.0 (Real)

[ m 2 ]
Ideleted if surf_IDv0

if Ideleted = 0: area of surface surf_IDv is considered for venting

 
if Ideleted = 1: area of deleted elements inside surface surf_IDv is considered for venting.

(Integer)

Tvent 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 Pdef to open vent hole membrane.

(Real)

[ s ]
fct_IDt Porosity vs time function identifier.

(Integer)

 
fct_IDP Porosity vs pressure function identifier.

(Integer)

 
fct_IDA Porosity vs area function identifier.

(Integer)

 
Fscalet Scale factor for fct_IDt.

Default = 1.0 (Real)

 
FscaleP Scale factor for fct_IDP.

Default = 1.0 (Real)

 
FscaleA Scale factor for fct_IDA.

Default = 1.0 (Real)

 

Comments

  1. surf_IDex must be defined using segments associated with 4-nodes or 3-nodes shell elements (possibly void elements), and not with /SURF/SEG.
  2. The volume must be closed and the normals must be oriented outwards.
  3. By default, I_equi =0 assumes that the volume to be filled by the gas will not increase. If the volume increases, the Pext 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.
  4. Abscissa scale factors are used to transform abscissa units in airbag functions, for example:(1)
    F ( t ) = f t ( t Ascale t )
    where, t is the time and f t is the function of fct_IDt.(2)
    F ( P ) = f P ( P Ascale P )

    Where, P MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbbG8FasPYRqj0=yi0dXdbba9pGe9xq=JbbG8A8frFve9 Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacaWGqbaaaa@3733@ is the pressure and f P is the function of fct_IDP.

  5. When Pmax is reached, the pressure is reset to external pressure and venting has no effect.
  6. Vent hole membrane is deflated if T > Tvent or if the pressure exceeds Pdef while more than Δ t P d e f .
  7. vent_holes_surface = A vent A f A ( A A 0 ) f P ( P P ext )
    Where,
    A
    Area of surface surf_IDv
    A0
    initial Area of surface surf_IDv
    f A
    Function of fct_IDA
    f P
    Function of fct_IDP

    Functions f P = fct_IDP are assumed to be equal to 1, if they are not specified (null identifier).

    Function f A fct_IDA is assumed as: f A ( A A 0 ) = 1 if it is not specified.

  8. If surf_IDv0 (surf_IDv is defined) the vent hole area is computed as:

    vent_holes_area = A vent A f A ( A A 0 ) f t ( t ) f P ( P P ext )

    If surf_IDv = 0 (surf_IDv is not defined).

    vent_holes_area = A vent f t ( t ) f P ( P P ext )

    Where,
    A
    Area of surface surf_IDv
    f A
    Function of fct_IDA
    f t
    Function of fct_IDt
    f P
    Function of fct_IDP

    Functions f t = fct_IDt and f P = fct_IDP are assumed to be equal to 1, if they are not specified (null identifier).

    Function f A = fct_IDA is assumed as:

    f A ( A ) = A if it is not specified.

  9. For tire modeling, pressure in the tire is:(3)
    P t i r e = P i n i P e x t

    So, Pext and Pini have to be defined.

  10. Pressure will be applied linearly from Pext at time t=0 to Pini at time t=Trelax.