Validation of Gasflow Airbag Simulation Methods

For challenging cases such as airbag deployment in out of position scenarios, airbag simulation technology is being continuously enhanced. The airbag internal pressure can be calculated in different ways. The traditional scheme uses the assumption that the airbag internal pressure is uniform at any given time. This so-called Uniform Pressure (UP) method is efficient and accurate for In-Position frontal impact scenarios, when the occupant-airbag interaction takes place after the airbag is almost fully deployed, and over a relatively long time-span. However, in Out-of-Position scenarios, there is strong interaction between occupant and airbag during the airbag deployment phase and during deployment, the airbag pressure is strongly non-uniform.

Complex gas flow (GF) models such as Coupled Lagrangean-Eulerian (CLE) methods and Mesh Free (MF) methods enable a physical description of the gas flow. This paper presents verification of the MADYMO gasflow method using relatively simple analytical references as well as realistic folded and unfolded airbag load cases.

• For predictive airbag simulations accurate input data is needed including inflator properties, folding pattern, permeability, fabric and environment parameters.
• An adapted gasflow formulation is supplied, which eliminates through flow while gasflow cells may cross fabric layers. This formulation improves physical accuracy while limiting CPU demands.
• Fundamental tests like the 1D shock tube and the Emery test show good correlation. This proves the ability of MADYMO gasflow to predict shock waves.
• The application range of the “multichamber” option for gasflow has been extended by an improved formulation of the flow between chambers for high gas flow velocities.
• In tank test validation good correlation is obtained using gasflow. On airbag pendulum tests with folded and unfolded airbags, gasflow provides an improved prediction in particular for the initial inflation phase.
• Gasflow simulation results can be obtained from an overnight run.