Influence of the outside air inertia effect on airbag deployment.

There are three common models of the gas infusion process that are currently used for computer airbag simulations. The first simple model states the uniform increase of the pressure in all parts of airbag volume during deployment. A serious drawback of this model is the lack of dynamic effects from incoming gas stream. Partial deficiencies of this mode are overcome by adding 'jet formulation' including dynamic effect of the gas and can be understood as a second model, as commonly used in available commercial codes. The third most advanced model takes into account the variation of inner pressure in time and space inside the airbag. All these models take into account only those physical phenomena that happen inside the airbag. None of them takes into account influence of the external environment. The influence of outside air inertia is clearly seen on both presented examples: a simple 2-D case and a full 3-D model. Effect of outside inertia is proportional to the acceleration of the airbag fabric so is important mainly in initial phases of fabric motion. As a direct result it may be stated that the compressive air wave generated outside the fabric of the bag during the first milliseconds after deployment significantly reduces outside fabric velocity changing both the unfolding and impacted body contact pattern. Nevertheless it seems that identified outside air inertia effect has limited influence on the acceleration pulses transmitted onto impacted body. In contact cases additionally two other factors have to be considered: the initial distance between airbag module and mass properties of impacted body(or body region). Current results indicate that short body-module initial distance and relatively small mass of impacted body might be considered as the conditions in which the outside air inertia influences not only the behaviour of the bag but also level of forces applied on the impacted body.Long time effects are visible in interaction of airbag with relatively light objects like head. For the covering abstract see ITRD E141807.