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.

The defined surface must be closed (the normal to shell elements must be all oriented outward, as shown in 図 1. The shell normal must be oriented outside the volume. It is possible to reverse the shell normals for a given property set (by entering a negative property number). Dummy properties (/PROP/TYPE0) and materials (/MAT/TYPE0) can be used.

図 1. Tire Model: Volume Closed
There are five types of MONITORED VOLUME:
  1. AREA Type: volume and surface output (post processing option, no pressure)
  2. PRES Type: user function defining pressure versus relative volume
  3. GAS Type: adiabatic pressure volume relation. P ( V V i n c ) γ = C s t with γ = c p c v
  4. AIRBAG Type: Single airbag P V = n R T = m r T

    P = ρ r T = ρ ( c p c v ) T = ( γ 1 ) ρ c v T = ( γ 1 ) E V

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

Same basic equations:

Typical use of monitored volume is for tire, fuel tank, airbag.
  • 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.