Since 1960 in Japan, accidental injury has been the leading cause of the death of children. The number of injuries that require hospitalization is estimated to be 20-175 times more than the number of deaths. In addition, the number of injuries that need visits to the doctor is estimated to be 1900-15,800 times more than the number of deaths. Thus, accidental injury to children is a health concern. Effective countermeasures against such accidents are required for accident prevention and mitigation. Currently, much accident data about children have been collected by Advanced Industrial Science and Technology. Using these data, such accident data statistics as type, location, and the region of the body injured in the accident have been studied. However such information is often fragmented. For instance, although injured body regions and locations where the accidents occurred are available from the data, how the accidents and injuries actually occurred often remains unclear. Therefore, suggesting effective countermeasures and evaluating their effectiveness is occasionally difficult. In this study, we simulated accident reconstruction to understand accident situations and to propose and evaluate effective countermeasures. A multi-body child human model was constructed and used for this simulation. Its geometry was based on the geometry of an adult polygon model. The joint characteristics and contact stiffness of this child human model were calculated by scaling the adult characteristics from the literature. Such physical characteristics as the mass, the position of the center of gravity, and the moment of inertia were calculated by volume on the assumption that humans have uniform density. This child human model's biofidelity was evaluated by a series of impact test simulations that represented the evaluation with a Q3 dummy. Using this validated child human model, we reconstructed accidents based on accident data. Such accident situations as child's posture were identified and reconstructed by an optimization technique. As a result, a multi-body child hum an model was reconstructed based on the height and weight data of injured children taken from the accident data. The mass ratio of each body segment and the child human model's geometry were evaluated. The results clearly show that each body segment of the child human model has reasonable geometry and mass ratio. In addition, most impact simulations showed reasonable biofidelity of the child human model, although the result of the thoracic impact simulation indicated that the child human model has a stiff thorax. The child human model's posture and location where the accidents occurred were identified by an optimization technique. The injured region and the injury index estimated by accident simulation agreed well with the accident data.
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