COMMU1 Type

The airbag simulation used by Radioss adopts a special uniform pressure airbag. Hence, regardless of the state of inflation or shape, the pressure is uniform.

Perfect gas law and adiabatic conditions are assumed. Injected mass and temperature are defined as a time function. A sensor can define the inflate start time.

Deflation of vent hole is available after reaching a pressure ( P d e f ) or time ( T d e f ) criteria.


Figure 1. Chambered Airbag Schema
The key assumptions are:
  • Uniform airbag pressure kinetic energy is negligible
  • Adiabatic conditions
The airbag simulation must include:
  • Injection of energy and mass
  • Bag mechanics (that is, unfolding, expansion, membrane tension, impacts, ...)
  • Exhaust through vent holes

This option is used to simulate chambered airbags and may be used to unfold an airbag.

Each COMMU1 type monitored volume works like an AIRBAG type monitored volume with possible vent communication with some other monitored volume of COMMU1 type. A chambered airbag is therefore modeled with two or more COMMU1 type monitored volumes.

Each monitored volume can have an inflater and an atmospheric vent hole.

Monitored volume 1 can communicate with monitored volume 2 with or without communication from 2 to 1. Communicating area, deflation pressure or time from 1 to 2 can be different from corresponding values from 2 to 1. It is thereby possible to model a valve communication.

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Mass Injection

Same equations as for AIRBAG type monitored volume are used. Refer to Mass Injection.

Venting

Same equations as for AIRBAG type monitored volume are used. Refer to Venting Outgoing Mass Determination.

The mass flow rate is given by:(1) m ˙ o u t = ρ v e n t A v e n t u = ρ ( P e x t P ) 1 γ A v e n t u MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKf MBHbqefqvATv2CG4uz3bIuV1wyUbqedmvETj2BSbqefm0B1jxALjhi ov2DaebbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8 qqaqFr0xc9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9 q8qqQ8frFve9Fve9Ff0dmeaacaGacmGadaWaaiqacaabaiaafaaake aaceWGTbGbaiaadaWgaaWcbaGaam4BaiaadwhacaWG0baabeaakiab g2da9iabeg8aYnaaBaaaleaacaWG2bGaamyzaiaad6gacaWG0baabe aakiaadgeadaWgaaWcbaGaamODaiaadwgacaWGUbGaamiDaaqabaGc caWG1bGaeyypa0JaeqyWdi3aaeWaaeaadaWcaaqaaiaadcfadaWgaa WcbaGaamyzaiaadIhacaWG0baabeaaaOqaaiaadcfaaaaacaGLOaGa ayzkaaWaaWbaaSqabeaadaWccaqaaiaaigdaaeaacqaHZoWzaaaaaO GaaGPaVlaadgeadaWgaaWcbaGaamODaiaadwgacaWGUbGaamiDaaqa baGccaWG1baaaa@5C9F@
The energy flow rate is given by:(2) E ˙ o u t = m ˙ E ρ V = ( P e x t P ) 1 γ A v e n t u E V MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKf MBHbqefqvATv2CG4uz3bIuV1wyUbqedmvETj2BSbqefm0B1jxALjhi ov2DaebbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8 qqaqFr0xc9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9 q8qqQ8frFve9Fve9Ff0dmeaacaGacmGadaWaaiqacaabaiaafaaake aaceWGfbGbaiaadaWgaaWcbaGaam4BaiaadwhacaWG0baabeaakiab g2da9iqad2gagaGaaiaaykW7daWcaaqaaiaadweaaeaacqaHbpGCca WGwbaaaiabg2da9maabmaabaWaaSaaaeaacaWGqbWaaSbaaSqaaiaa dwgacaWG4bGaamiDaaqabaaakeaacaWGqbaaaaGaayjkaiaawMcaam aaCaaaleqabaWaaSGaaeaacaaIXaaabaGaeq4SdCgaaaaakiaaykW7 caWGbbWaaSbaaSqaaiaadAhacaWGLbGaamOBaiaadshaaeqaaOGaam yDaiaaykW7daWcaaqaaiaadweaaeaacaWGwbaaaaaa@5864@

These mass and energy flux are removed from the current volume and added to the communicating volume at next cycle.

Supersonic Outlet Flow

Same equations as for AIRBAG type monitored volume is used. Refer to Supersonic Outlet Flow.

Jetting Effect

Same explanation as for AIRBAG type monitored volume is used. Refer to Jetting Effect.

Reference Metric

Same explanation as for AIRBAG type monitored volume is used. Refer to Reference Metric.

COMMU1 Type Examples

Example: Communication between the 2 Volumes

Volume 1 communicates with volume 2 and vice-versa.

Monitored volume 1 communicates with monitored volume 2 with or without communication from 2 to 1. The communicating area, deflation pressure or time from 1 to 2 can be different from the corresponding values from 2 to 1. It is thereby possible to model a valve communication.


Figure 2. Communication between the 2 Volumes

Example: No Communication between 2 and 3

Volume 1 communicates with volume 2 and volume 2 with volumes 1 and 3, but there is no communication from 3 to 2.

Two COMMU1 type monitored volume communications can have common nodes or common shell property sets but this is optional.

To model a folded airbag, one COMMU1 type monitored volume is used for each folded part. The boundary between two folded parts is closed with a dummy property set (fictitious property). The pressure in each folded part will be different and the area of communication will increase during inflation. With this model, the volume with inflater will inflate first and before than folded parts (better than "jetting" model).


Figure 3. No Communication between 2 and 3

Example: Monitored Volume with Communication Coefficient

Volume 1 and volume 2 with common property set.


Figure 4. Monitored Volume with Communication Coefficient

Example: Folded Airbag