Where,  is the total pressure variation during the experiment.  is the total injected mass, which can be derived from the mass of propellant in the pyrotechnic inflator and the chemical reaction.

2.2 Outgoing mass determination^[3]

2.2.1 Isenthalpic model

Venting or the expulsion of gas from the volume, the status is assumed to be isenthalpic. The flow is also assumed to be unshocked, coming from a large reservoir and through a small orifice with effective surface area.

Conservation of enthalpy leads to velocity  at the vent hole.  The Bernouilli Equation is then written as:

3 Airbag Definition

This section deals with airbags model implemented into RADIOSS code. There are several ways and methods to model an airbag with the “Monitored Volume” option, and uniform pressure classical method is commonly used, the keyword and brief description shown below.

ü  Line 2:Isur defines airbag surface.

ü  Line 5, 6: Definition of initial gas properties inside airbag

ü  Line 7: Njet defines the number of injectors

ü  Line 8, 9: Definition of gas injection information, include gas properties, gas flow, temperature and sensor information, which is validated during Tank Test.

ü  Line 11: Number of Vent

ü  Line12-14: Definition of vent properties include vent area, out flow equation, scale coefficient, which are often validated by verification test. Outgoing mass determinations of Isenthalpic and Chemkin model have different definition.

FVMBAG type airbag of RADIOSS may be used for Out Of Position(OoP) situation where the gas flow effects must be taken into account.

4 RADIOSS Application

A specific series of airbag tests are conducted to help validate the modeling of side airbag, Drop tower test is commonly used to correlate airbag characteristics of airbag module in a controlled environment. The following is a successful example that simulated by RADIOSS, the set-up and acceleration result of impactor are shown in Figure 2, the acceleration data has similar output.

Figure 3 illustrates the kinematics comparison of the simulation with test result of the model, its kinematics sequency from the side view was captured corresponding to physical test view and the comparisons show very good correlation.

After airbag component validation, the airbag model can be applied in the airbag restraint system level simulation to evaluate the occupant performance.