November 8, 2019

Keeping Passengers Safe with Airbag Simulation

Automobiles are continually becoming safer as new features and technologies are developed.…
Clare Scott

Automobiles are continually becoming safer as new features and technologies are developed. One of the most important safety developments in the history of vehicle development dates back commercially only to the 1970s: the airbag. These inflatable cushions deploy when a vehicle strikes another car or other large object, protecting the driver and front-seat passenger from hitting the interior and windows. A crash sensor triggers non-harmful (or non-toxic) gas, contained within the cushions, to expand, placing a soft barrier between the occupants and the hard surfaces.

Airbags have become much more advanced than they were at first invention. They are typically built into the steering wheel, dashboard, doors and roof of a vehicle and are one of two types: front-impact or side-impact. Front-impact airbags can be particularly advanced, determining with how much power to inflate based on not only the severity of the crash but the seat occupant’s size and seat position.

The airbags must inflate rapidly, before the occupant hits them, and then deflate just as rapidly to absorb the occupant’s energy. Ensuring that the airbags deploy with the proper speed, force and direction is a complex task that requires careful modeling and detailed simulation.

Abaqus includes three methods for modeling airbags: a uniform pressure method (UPM); Coupled Eulerian-Lagrangian method (CEL); and Lumped Kinematic Molecular (LKM) method. UPM controls the pressure uniformly in the fluid cavity, and can control the sequence of inflation using a multi-chambered fluid cavity and the fluid exchange between the cavities. CEL realistically simulates gas flow by coupling the gas flow in the Eulerian domain with the airbag behavior in the Lagrangian domain. This is useful for the early stages of deployment. LKM is based on kinetic gas theory and uses a particle-based method, modeling lumped gas molecules as rigid particles. This method is particularly useful for highly sophisticated airbags with narrow passages for high-speed inflating gas.

Side-impact curtain airbags are particularly challenging, as they are larger and need to be inflated in a shorter period of time. Side-impact curtain airbags are tightly rolled to fit into the narrow area of the side roof, which means that the fast-moving gas needs to push its way through very narrow passages. All three methods of airbag modeling may be used in simulating side-impact curtain airbags and the users can select the method that fits best for their purpose. The computational cost is in the order UPM, LKM, CEL. LKM and CEL are used in the early stage of deployment since they can replicate the gas behavior more precisely. Once it is fully deployed, they can switch to UPM to compute the interaction between the occupants and interior or windows at lower computational cost.

Airbag simulation is an important part of overall crashworthiness simulation, which models an occupant’s safety in a potential crash situation. These simulations need to be performed early in the vehicle’s design process, as well as quickly so that the development of the vehicle is not interrupted or delayed.

To learn more about simulation of airbags and other features of crashworthiness, check out the webinar Crashworthiness Simulations | Recent Advances in Abaqus/Explicit with HPC. It can be accessed here.

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