Quantifying supine human discomfort in off-road whole-body vibration

This work presents a new methodology to quantify supine human discomfort during transport when multi-axis whole-body vibration (WBV) and shocks are present. The methodology employs a new scheme to normalise the reported discomfort. Twenty-six human subjects were tested under different off-road conditions and their reported discomforts collected. The paired Wilcoxon signed-rank method was used to investigate the significant differences (p < 0.01) between different track sections on the normalised reported discomfort from the subjects. Analyses based on ISO 2631-1 showed weak correlation with the reported discomfort when significant lateral motions existed. The results with the new formulation showed that discomfort is highly correlated with the vibration dose value at the head of the supine human during WBV (p < 0.001). These results are consistent with previous published work showing that discomfort based on motion at the head-neck region comprises more than 70% of the reported discomfort during supine transport under multiple-axis WBV.Practitioner summary: There are shortcomings in the current approaches to quantifying discomfort of supine humans in multi-axis whole-body vibration where lateral motions are excessive. This study revealed that reported discomfort is strongly related to the vibration dose value at the head of supine subjects rather than the input motion to the body.Abbreviations: WBV: whole-body vibration; RMS: root-mean square; VDV: vibration dose value; PSD: power spectral density; RDn: reported discomfort; NDn: normalized discomfort; : discomfort scaling coefficient; aw(t): frequency-weighted acceleration; wRMS: weighted root-mean square; Aw: weighted root-mean square acceleration; Aw,p: point weighted root-mean square acceleration; Wd: frequency-weighting factor; Wk: frequency-weighting factor; kx: weighed acceleration multiplying factor in x-direction; ky: weighed acceleration multiplying factor in y-direction; kz: weighed acceleration multiplying factor in z-direction; CV: coefficient of variation; VDVp: point vibration dose value; SD: standard deviation; pVTV: point vibration total value.