Abstract
The flexion-extension motion of the head-neck complex (HNC) in the trunk horizontal (fore-and-aft) vibration was investigated. It was assumed that the motion of the HNC only occurs in mid-sagittal plane. An electro-hydraulic vibrator was used as a source of vibration. The input acceleration and HNC angular velocity were measured whereas the trunk of the seated subject was fixed to the seatback. Accordingly, the acceleration of the vibrator was considered to be equal to that of the trunk. Six subjects took part in the experiment. They were exposed to the random motion at a magnitude of 1.60ms-2rms (root-mean-square) for 50 seconds. The coherence and frequency response function between the HNC angular velocity and the trunk horizontal acceleration were then obtained on 0.5Hz to 10Hz. Averaging the obtained transmissibilities allowed to represent an optimized frequency response corresponding to each of the subjects. It was found that the HNC behavior above 0.8Hz was quasi-linear with a dominant resonance frequency between 0.8Hz and 1.6Hz. The variabilities of the results within and between subjects were investigated. It was further concluded that linear models could describe the HNC so that their orders should be selected in accordance with the frequency response function of the system as well as the objectives of modeling.
