# Monitored Volume

An airbag is defined as a monitored volume. A monitored volume is defined as having one or more 3 or 4 node shell property sets.

- AREA Type: volume and surface output (post processing option, no pressure)
- PRES Type: user function defining pressure versus relative volume
- GAS Type: adiabatic pressure volume relation. $P{\left(V-{V}_{inc}\right)}^{\gamma}=Cst$ with $\gamma =\frac{{c}_{p}}{{c}_{v}}$
- AIRBAG Type: Single airbag
$PV=nRT=mrT$
$P=\rho rT=\rho \left({c}_{p}-{c}_{v}\right)T=\left(\gamma -1\right)\rho {c}_{v}T=\left(\gamma -1\right)\frac{E}{V}$

- COMMU1 Type: Chambered, communicating, folded airbag (airbag with communications)

Same basic equations:

- For tire use PRES or GAS type monitored volume.
- For fuel tank use PRES or GAS type monitored volume.
- For simple unfolded airbag use AIRBAG type monitored volume.
- For chambered airbag use two ore more COMMU1 type monitored volumes.
- For folded airbag use a set of COMMU1 type monitored volumes.