Finite element study on vibration behavior of the human head in an upright sitting posture under fore-aft whole-body vibration.

To quantify the response characteristics of varying positions of the human head in an upright sitting posture under fore-aft whole-body vibration, modal and random response analysis in 0-20 Hz was conducted on a previously created whole-body finite element model with detailed anatomical structure. The study revealed two main peaks in the transmissibility of the seat to the head, with direct-axis peak frequencies of 0.76 and 2.74 Hz, respectively, and cross-axis peak frequencies of around 2.9 and 5.3 Hz, respectively. Moreover, the direct-axis peaks decreased from the top of the head to four sides, with the first peak decreasing by 21% (from 3.44 to 2.73) and the second peak decreasing by 74% (from 2.88 to 0.76). The maximum and minimum values of cross-axis peaks in the sagittal plane were located at the forehead and crown, respectively, and the maximum value (2.1) was 5.8 times the minimum value (0.36). Although the peak frequencies of vibration transmissibility of the seat to different positions of the head were the same under fore-aft whole-body vibration, the amplitudes of transmissibility varied greatly. Therefore, there were significant differences in vibration measurement and vibration comfort evaluation at different positions of the head.