| Popis: |
The practical application of currently standardised methods of evaluating wholebody vibration assumes the discomfort caused by a combination of frequency components can be predicted using time averaging methods, such as the rootmean-square, r.m.s., or vibration dose value, VDV. This study investigated whether the discomfort produced by random vibration depends on the frequency of the vibration (three bands of octave-bandwidth random vibration with frequencies in the range 1.4 to 11.3 Hz) or the direction of vibration (fore-and-aft, lateral, or vertical). The study was conducted with frequency-weighted vibration magnitudes in the range 0.40 to 0.78 ms-2 r.m.s. Eighteen subjects provided magnitude estimates of their discomfort when exposed to single and multiple bands of the octave-bandwidth random whole-body vibration. With each of the three directions of vibration, the linear sum of the magnitude estimates of the discomfort overestimated the discomfort caused by the combination of 2 or 3 bands, whereas the magnitude estimate of discomfort caused by the worst band underestimated the discomfort caused by the combination of 2 or 3 bands. Over all the vibration stimuli investigated, the optimum power for summating magnitude estimates to predict vibration discomfort was 2.54, with no statistically significant differences between frequencies or directions of vibration. It is explained that the optimum power for summating vibration magnitudes differs from the optimum power for summing magnitude estimates of vibration discomfort, because vibration discomfort is not usually linearly related to the magnitude of vibration and the rate of growth of vibration discomfort varies with the frequency and the direction of vibration. |
