A nonlinear biodynamic model of seated human body exposed to vertical vibration with sensitivity analysis

The nonlinearity observed in the apparent mass of a seated human body exposed to vertical vibration demonstrates a decrease in resonance frequency as the vibration magnitude increases. However, there is a dearth of appropriate models that accurately capture this nonlinear biodynamic response. Furthermore, the impact of different properties of human body parts on this nonlinearity remains unexplored. This paper presents a model that effectively characterizes the nonlinearity in the apparent mass of a seated human body subjected to vertical vibration.The proposed model incorporates the legs, thighs, pelvis, torso, head, and viscera as key components. Nonlinear springs are employed to simulate the dynamic interactions between the human body and the seat, as well as the connection between the viscera and the pelvis/torso. To validate the model, vertical in-line and fore-and-aft cross-axis apparent masses were measured at the seat pan for 11 subjects without backrest contact, using three different vibration magnitudes (0.4, 0.6, and 1.0 m/s2 r.m.s.).A comprehensive global sensitivity analysis was conducted with the calibrated model to identify the factors that have the greatest influence on the biodynamic response. The results revealed that the stiffness of the soft tissues beneath the thighs, the mass of the thighs, and the mass of the torso were the three most influential parameters affecting the apparent mass. When considering the degree of nonlinearity in the apparent mass, the stiffness of the soft tissues beneath the thighs and the mass of the torso contributed the most.The proposed model holds significant potential for studying the nonlinear biodynamic responses of vehicle drivers and passengers. It provides a valuable tool for gaining insights into the intricate dynamics of human body vibration and can contribute to the development of improved seating systems and enhanced ride comfort in vehicles.