Porosity

The isenthalpic model is also used for porosity. In this case, one can define the outgoing surface by:(1)

$$A_{OUT}=\lambda f(A)g(P)h(t)$$

Where,

$A$

Area of the specified surface

$\lambda$

Scale factor

$P$

Pressure of the gas

$t$

Time

The second model integrated in Radioss is called the Chemkin model, in which the mass flow due to the porosity is computed by:(2)

$$\dot{m}=A_{vent}u{\rho }_{airbag}$$

Where, $u$ is the user-defined function, represented as:(3)

$$u=f\left(P-P_{ext}\right)$$