# Monitored Volume Time Step

An "AIRBAG1" time step is estimated into the Engine, but this time step will never control the time step during the run. If that is the case, it means there is a non-physical airbag definition in the input deck.

## Element Time Step Control

- /DT/AIRBAG
- Defines $\text{\Delta}{T}_{sca}$ and $\text{\Delta}{T}_{\mathrm{min}}$ for airbags
- /DT/FVMBAG
- Defines $\text{\Delta}{T}_{sca}$ and $\text{\Delta}{T}_{\mathrm{min}}$ for Finite Volume Method airbag

/DT/FVMBAG is only used for monitored volumes type /MONVOL/FVMBAG1. The $\text{\Delta}{T}_{sca}$ and $\text{\Delta}{T}_{\mathrm{min}}$ can be defined to insure stability and a minimum time step size by triggering additional finite volume merges when the FVMBAG1 entity penalizes the computation. /DT/FVMBAG/1 is used to merge finite volumes when $$dt<\text{\Delta}{T}_{min}$$.