A nonlinear biodynamic model of helicopter seat: ATD system exposed to vertical impact for predicting the risk of injury in airworthiness certification

In helicopter crashes, occupants endure instantaneous vertical impact forces, which can lead to injuries. To accurately forecast the dynamic response of occupants in such scenarios, this study presents an impact dynamics model for the seat–ATD system and a parameter identification method based on experimental data. A nonlinear dynamics model of the ATD–seat system is developed to simulate the dynamic response during vertical impacts. Impact experiments are conducted, and parameters are optimized according to the experimental data. A comparison of the simulation results with the experimental results shows errors consistently below 10%, indicating the practicality of the proposed model. Furthermore, a sensitivity analysis of the model parameters is performed to identify the most and least sensitive factors affecting lumbar spine force. Finally, three existing models are selected for comparison across three replicate experiments. The proposed model shows the lowest average error, which is 1.11% less than the error shown by the state-of-the-art models in the field. Furthermore, the model presented in this study enhances predictive accuracy during the 0 ms–30 ms ascending phase of the lumbar spine force curve. In conclusion, we introduce an optimization-based dynamic simulation framework that integrates a nonlinear biomechanics, multibody dynamics, ATD-seat interaction, and foot–ground contact. The established biodynamic model is a valuable tool for evaluating the effects of impact loads on the injury risk of the ATD. The validated model can be used for analyzing spinal injury risk and predicting the motion of the head, chest, and pelvis caused by vertical impact.