Change of Seat-to-Head Transmissibilities at Two-Hour Intervals with and without Whole-Body Vibration

Abstract

Human exposure to whole body vibration (WBV) affects the change of human sensory system such as discomfort and human fatigue. To investigate these cause-effect relationships, we examined if the human dynamic property changes due to with and without vibration. The aim of this study is to investigate the change of the seat-to-head transmissibility at two-hour intervals for "with vibration" condition, and compared the results with those obtained for "without vibration" condition. A preliminary study explored the change of seat-to-head transmissibility at two-hour intervals, in which the subjects were not exposed to whole-body vibration. In this study, eight male subjects performed a car driving simulation while exposed to vertical vibration for two hours. Transmissibilities were measured once before and once immediately after the driving simulation. While they played the driving simulation on a screen, they were exposed to vertical random vibration (0.2-0.3 m/s 2 in r.m.s.) in the 1-30Hz frequency range. The transmissibility was evaluated in the root-mean-square value (T_rms), which is introduced in order to assess the amplitude of transmissibility within the frequency range of interest (2-20 Hz). The results show that T_rms of "after" two-hour driving for "with vibration" appear to become smaller than that of "before" driving. On the other hand, when T_rms's of "before" and "after" were compared for "without vibration", no significant difference was observed. Moreover, by comparing the distribution of damping ratio for "with vibration" with that for "without vibration", no significant difference appeared.