To help in design efforts of a full airbag impact actuation system for the Mars Gravity Biosatellite Program a simple MATLAB simulation has been written to give a better understanding of airbag impact dynamics. This simulation was then compared with a series of tests to determine the influence of vent radius on the behaviour of the system.
A MATLAB simulation was constructed to model the behavior of a simple airbag impact attenuation system. The model consisted of a simple spherical airbag being squeezed under a virtual mass of 75kg, simplified airbag volume equations during the compression and ideal gas assumptions to reduce the complexity of the code. The simulations investigate the effect from varying parameters such as the burst pressure, vent radius, initial velocity and initial airbag pressures on the pressure and deceleration behaviour of the system. Venting was the most important aspect of the simulation and while mathematical manipulations could give formulas for venting, the actual venting rates were
dependant on the discharge coefficient which can only be determined experimentally.
Impact attenuation tests on airbags with 15mm, 17.5mm, 20mm and 25mm radius vents were conducted. For this a test rig and airbag were constructed, with the test rig constructed into a flat circular plate of mild steel 3mm thick, with a smaller plate at the centre welded to a vertical support column. The airbag was made from sailcloth Nylon coated in a polyurethane sealant. The airbag was constructed from six ‘orange peel’ sections sewn together using a three line prayer seam. The seams were sealed using a liquid silicone sealant.
It was found that the discharge coefficient varied with the vent size and relationships were obtained correlating both the pressure and decelerations of the test rig with the simulations.