/DT/FVMBAG/Iflag

Engine Keyword Time step for control for Finite Volume Method airbag.

Format

Field	Contents	SI Unit Example
`Iflag`	Finite volume merge flag. = 0 or blank (Default) The finite volume is merged, if the time step < airbag volume < 10 * the minimum volume defined in global merge, /FVMBAG/MODIF. = 1 The finite volume is merged, if time step < $Δ T_{\min}$ . = 2 The finite volume is merged, if time step < $Δ T_{\min}$ . The time step computation is defined by the flag `L_type`. 2
$Δ T_{s c a}$	Scale factor on time step. Default = 0.9 (Real)
$Δ T_{\min}$	Minimum time step. (Real)
`Lambda`	Stability factor. Default = 0.01 (Real)
`L_type`	Time step computation method. = 1 Characteristic length of FVM mesh (computed during Starter). = 2 (Default) Characteristic length is computed from cubic root of the volume.
`Monvol_ID`	Monitored volume identifier. (Integer)

The $Δ T_{s c a}$ and $Δ T_{\min}$ can be defined to ensure stability and a minimum time step size by triggering additional finite volume merges when the FVMBAG entity penalizes the computation.
When using /DT/FVMBAG/2, time step is computed as:(1)
$Δ T = Δ T_{s c a l} \frac{Δ x}{|u - w| + c}$

Where,

$u$

Gas velocity.

$w$

Polyhedron velocity.

$c$

Speed of sound.

$Δ x$

Characteristic length.

The soothing factor is applied using $Δ T \leftarrow \min (Δ T, Δ T_{o l d} (1 + λ))$ .