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Use of the FTSS Modular Crash Dummy Models in Frontal Occupant Simulation

Legal and consumer crash tests use crash dummies as the key measurement device in the assessment of crash severity. The dummies are complex assemblies in themselves, and sophisticated DYNA FE models are available, with a significant amount of validation testing to support them. In a large vehicle crash model, the dummy is typically responsible for 10-20% of the CPU time, and there is no strong motivation to reduce its size; in fact, the tendency is to make the dummy models more complex, and the latest versions have undergone a significant refinement, which has increased the CPU time needed to run the dummy on its own by a factor of 2. If the size of the vehicle crash model is reduced, however, the proportion of CPU time taken by the dummy increases, and can constitute 90% of the total. Recent developments in the use of DYNA for frontal occupant modelling at Jaguar Land Rover require a significant reduction in overall run-time, and the standard full dummy models impose a limit on the reduction that can be achieved. For this reason, simpler dummy models have been created by FTSS, which allow the selection of the full, sophisticated representation, where maximum fidelity of measurement is necessary, but provide a simpler model, where this is adequate. The model is constructed using a modular structure, allowing any combination of complex and simple dummy parts to be assembled, and ensuring that geometry, joint configurations and output references are maintained. A set of component validation comparisons has been made at FTSS and Jaguar Land Rover between the simple and complex models, to demonstrate the degree of approximation inherent in the new models. Additionally, a comparison has been made in vehicle sled models to demonstrate the usefulness of the approach. The CPU requirement has been compared, using a number of configurations of dummy and vehicle models. The validation results show that the simple models are a valid representation of the dummy in areas where the detail of the local behaviour is not required. In many areas the simple model can also provide adequate dummy measurements. There is scope for further development of the simple dummy parts, but the modular nature allows current limitations to be avoided, through the use of the fine model, where the application requires it. The CPU demands of the dummy model can be significantly reduced, allowing the demands of the smaller vehicle crash models to be met. Additionally, the criteria for usability, such as maintenance of geometry, and of positioning configuration are fulfilled.

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