Multibody Modeling of Direct and Cross-Axis Seat to Head Transmissibility of the Seated Human Body Supported with Backrest and Exposed to Vertical Vibrations

Drivers of the road and off-road vehicles are continuously exposed to low-frequency whole-body vibration of significant magnitudes arising from tire/track-terrain interactions. The human body models reported in the literature for analyzing these are usually of lumped parameter category having only a few degrees of freedom. Most of them are also one-dimensional models, i.e., they allow an analysis of vibration only in the vertical direction. The highly complex motion that the human body is subjected to in real life requires at least a two-dimensional model. This paper presents a multibody human body model of 12 degrees of freedom that represents a seated human with backrest support. The motion has been assumed to occur in only the sagittal plane allowing vibration analysis in two dimensions. The modeling of the interconnection of masses using rotational and translational springs and dampers and the contact with backrest gives a better simulation of forces transmitted to the upper and lower torso. A sensitivity study to find the effect of critical model parameters on the frequencies of peak moduli helps in identifying the section of the human body which should be given appropriate support for improving comfort. This can lead to the re-design of the seat by considering the effect on different sections of the human body. This is expected to be a better approach than the current practice of considering the overall effect on the human body.