Biodynamic Response Analysis of a Seated Human Occupant with Back Support Under Vertical Vibration

The seated body exposed to vertical vibration exhibits considerable motions in the saggital plane, which cause considerable interactions of the upper body with the backrest support. The biodynamic responses of the seated body have been mostly evaluated on the basis of body interactions with the seat pan. This study investigates the dynamic interactions of the seated body exposed to vertical vibration at the two driving-points, formed by the upper body-backrest and buttock-pan interfaces in terms of force-motion relationships. Laboratory measurements were performed to characterize the dynamic interactions in terms of apparent masses at the two driving-points under white noise random vibration of different magnitudes and a track-measured random vibration in the 0.5-40 Hz frequency range. The experiments were performed with 24 adult (12 male and 12 female) subjects seated in a rigid seat, designed following the automotive seat geometry, with upper body supported against an inclined backrest. The vertical and fore-aft forces developed at the body-pan and body-backrest interfaces, respectively, were measured to determine the apparent mass responses at both the driving-points. The results clearly revealed significant dynamic interactions of the upper body with the back support. The results also showed considerable influences of the vibration magnitude, body mass and the subjects' hands position on the measured biodynamic responses, while the gender effect was marginal.