Effects of Inter-Subject Variability and Vibration Magnitude on Vibration Transmission to Head during Exposure to Whole-Body Vertical Vibration

Abstract

In this paper, the effect of inter-subject and intra-subject variabilities on transmission of vibration through seated human subjects is discussed using experimental results. The experimental study targeted three representative postures (backrest, erect, and forward lean on table) while performing sedentary activities and under three magnitudes (0.4, 0.8, 1.2 m/s 2 rms) of vertical vibration. The frequency range considered is 1 Hz-20 Hz as representative of those likely prevailing in wide range of vehicles. The data sets are investigated in terms of STH (seat-to-head) and BTH (back support-to-head) transmissibilities and phase differences, and respective coherences under the magnitudes and postures undertaken. In addition to determining the effect of different frequencies, subjective readings were collected at vertical backrest support postures at representative frequencies using the Borg CR 10 comfort scale. The responses show significant variations in transmissibility and phase among all of the subjects. In all postures, the mean STH transmissibility increases with increasing vibration magnitude at body resonance frequency, which lies approximately between 4.5 Hz and 6 Hz. Resonance in STH transmissibility of erect and forward lean on table posture visibly tends to shift to a lower frequency with increasing vibration magnitude. The subjective reading obtained, in terms of discomfort level, match with experimental data sets and provides evidence that human body resonance frequency or discomfort zone is around 5 Hz. Therefore, it might be concluded that the inclusion of vibration magnitude, posture, and inter-subject variabilities in the prediction of seat biodynamic response is essential. The development of biodynamic models and design of seat should include the variation of STH and BTH transmissibility and phase in different possible postures under different vibration magnitude.

Seat-to-Head Transmissibility and Reading\\ Discomfort of the Seated Subjects Exposed to Whole Body Vibration

“…There is a decrease in resonance frequency with an increase in vibration magnitude, which is also evident in many previous studies. 7,17,19 This shows the nonlinear softening characteristics of three human body under the exposure of vibration.…”

“…where a head (f ) is acceleration at the head, and a seat (f ) acceleration at the seat. A large number of experimental studies 6,7,11,17,18,21,22,25 have focused on the transmissibility of vibration to various parts of the human body, such as seat-to-head, pelvis, lumber/cervical, etc., with a broad range of experimental conditions. Griffin and Whitham have observed the significant effect of individual variability on transmissibility of WBV through the seated subjects.…”

Tooth Base Geometrical Variability Effect on the Vibration Behavior of the Stator

“…The mesh convergence analysis was performed to determine the appropriate mesh size, and the validity of a model is determined if the relative difference between two successive meshes is less than 1%. 26,31 Mesh 4 satisfied this criterion for the first three natural frequencies and was thus used in this study. Moreover, as recommended by Mahjudin et al 26 and Yin et al, 31 the optimal mesh (M4) in the nominal configuration is suitable for the variability analysis.…”

“…26,31 Mesh 4 satisfied this criterion for the first three natural frequencies and was thus used in this study. Moreover, as recommended by Mahjudin et al 26 and Yin et al, 31 the optimal mesh (M4) in the nominal configuration is suitable for the variability analysis.…”