Numerical Study Of The Airbag Deployment And Interaction With The Environment

The airbag deployment is a very complicated process with the gas flowing, the large non-linear deformation of flexible material, fluid structure coupling and the interaction with the exterior environment mentioned. It has very important significance to reveal the cushion mechanism and evaluate the safety during the airbag operations by studying the airbag deployment.In the development of an airbag, in constrast to the expensive and long period experimental tests, the low cost, high effectiveness and good flexiblity numerical simulation is more popular. The computations are opetrated to improve the accuracy by developing all kinds of airbag models. The main terms influencing the numerical accuracy include the description of inflating gas model, the treatment of flexible material with large deformation and rotation, the building of the airbag initial mesh, the response of environmental structure and so on. In this thesis, according to these reasons, the Arbitrary Lagrangian-Eulerian (ALE) is applied to analyze the airbag deployment. The details are as following:1. The point source model is introcued to the ALE method by defining the locations, areas, direction vectors of orifices of the inflator. It can describe the gas flow inside the airbag in detail, and it lays the foundation for the accurate solution of the airbag deployment and the impact calculation. At present, there are two inflation models mainly used for simulating the inflator. One is based on the thermodynamic equations, and the gas pressure is loaded on the airbag surface uniformly to calculate the airbag deployment. It is assumed that the pressure inside the airbag is uniform at any time. In this model, the gas flow statement cannot present. The other one is based on ALE method. It has a significant improvement on the gas flow description compared with the uniform pressure (UP) model. However, in this simplified inflator model, only single gas is mentioned and the jetting characteristics and directions of the orifices are ignored.2. The FE model of the airbag is another important part for improving the simulation accuracy. For a flatten airbag model, it can be meshed based on the geometry directly. However, for the complicated and wrinkled initial airbag statement, a simplified model is applied usually. The simplification deviated from the test statement will result in the decrease of calculation accuracy. In this thesis, according to the drooping wrinkled airbag test statement, the 3D designed unfolding shape of the airbag is taken as the initial statement. The dynamic relaxation is adopted to obtain the airbag initial mesh by loading the gravity inversely. The results indicate that the well-built initial airbag statement is highly consistent with the test in unfloding shape, pressure and impact load. Furthermore, the analysis of variance (ANOVA) is operated to find the factors affecting the airbag deployment efficiency according to design of experiment (DOE) method. The significance of factors which have impact on the pressure peak and peak time is given.3. The accuracy of airbg external environment is also very necessary to ensure the accurate solution of airbag deployment. The thermoplastic airbag case will rupture under the impact load of the airbag deployment, and the failure parameters are very important to reflect the material fracture characteristics. The quasi-static test of thermoplastic material cannot describe the complicated mechanical behavior. In this thesis, the strain rate dependent thermoplastic material property is obtained by the tension test under different loading speed. Furthermore, the impact test data is chosen as design space, the failure parameters as variables, the numerical results as response, and the mean square error between test and numerical results as the objective function, the parameter identification is applied to obtain the failure parameters inversely. And the failure parameters are validated by the additional test. It solves the strain rate dependent thermoplastic fracture problem.4. In the closed space, it is very difficult to solve the large deformation and rotation response of the flexible material in fixed and moving boundary. By using airbag technology and the computation of non-linear dynamics, the high frequency dynamic response of flexible material during gas compression/inflation can be solved. In this thesis, the rupture of hydraulic accumulator diaphragm under the pulsating hydraulic pressure is calculated based on the CV method. The mechanical response of flexible surface under alternative dynamic load is obtained. The analysis indicates that the residual strain of rubber material causes local wrinkle and stress concentration. By decreasing the surface area of diaphragm, the local wrinkle can be eliminated, and the stress degree can be improved significantly. In addition, in the multi-stage rocket, the stage separation period uses the gas pressure between the two stages to implement the separation. Duiring the separation process, the motion and coupling of the stages and the flexible linking material are very difficult to solve. The common analysis ignores the friction and runout of the flexible material. In this thesis, the closed chamber between two stages can be regarded as an airbag. Applying the CV method, the characteristics of airbag deployment and the stages'motion are present.5. The working environment of the airbag is very complicated. Excluding the external structural environment, the water environment is mentioned some time. For the airbag cushion in water, it is a coupling problem of three phases, including:gas, liquid and structure, and it makes the problem more complicated. In this thesis, by combining the airbag technology and the application of ALE method, the numerical simulation of the airplane landing on the sea surface with an airbag cushion is analyzed. Based on the results, the load characteristics of the airbag and link are obtained, and it gives a valuable reference for the strength design of the airbag and link's material.