Effects of frequency, magnitude, damping, and direction on the discomfort of vertical whole-body mechanical shocks

Abstract

The discomfort of seated subjects exposed to a wide range of vertical mechanical shocks has been studied experimentally. Shocks were produced from responses of single degree-of-freedom models with 16 fundamental frequencies (0.5–16 Hz) and four damping ratios (0.05, 0.1, 0.2 and 0.4) to half-sine force inputs. Shocks with a damping ratio of 0.4 were presented with both polarities. Each type of shock was presented at five unweighted vibration dose values (0.35–2.89 m s −1.75). The magnitude estimates of 15 subjects to all 400 shocks showed that the rate of growth in discomfort (the exponent in Stevens’ power law) decreased with increasing shock frequency from 0.5 to 4 Hz. Equivalent comfort contours showed greatest sensitivity from 4 to 12.5 Hz. At lower magnitudes, variations in discomfort with frequency were similar to weighting W b in British Standard 6841. At higher magnitudes, low frequencies were judged relatively more uncomfortable than predicted by this weighting. There were small but statistically significant differences in discomfort associated with variations in damping ratios and shock direction. It is concluded that the frequency dependence of discomfort produced by vertical shocks depends on shock magnitude, but for shocks of low and moderate discomfort, the current evaluation methods are reasonable.