This study is to develop a biomechanical model of human on a seat with backrest for evaluating the vehicular ride quality. In describing the human body motion, four biomechanical models are discussed: 1 DOF (degree-of-freedom) model mainly describes the z-axis motion of the hip, and 2 and 3 DOF models describe the z-axis motion of the hip and head while 9 DOF model we proposed includes the motions of the floor, hip, back, and head to describe the whole-body vibration in a sitting posture with backrest support.
To validate the proposed model, we measured the accelerations at the hip, back, and head of 10 subjects with the floor under vertical vibration excitation. From this measurement, three transmissibilities for each subject were obtained. We also measured the parameters including the material property of seat cushion, joint positions of human body, and the contact positions between human body and seat, while the other parameters such as stiffness and damping at the hip, back, and head were determined by matching the model transmissibilities to the experimental ones. The 9 DOF model shows good matching for transmissibility at the both first 4.2 Hz mode and second 7.7 Hz mode. The comparison of the experimental data with those simulated using 1, 2, 3, and 9 DOF models shows that 9 DOF model provides the best description of the experimental results.
Relevance to industry: The mechanical response of human body can be predicted reasonably well using our 9 DOF biomechanical model. Thus we may estimate the dynamic ride quality of a vehicle if the floor vibration data are available, which will help in designing vibration isolator such as seat.