Time dependency of whole-body vibration discomfort

The current International Standard (ISO 2631, 1978) on whole-body vibration defines a complex relation between discomfort arid duration of vibration exposure. There are doubts concerning the accuracy of this relation and there are difficulties and dangers in its application to some non-steady-state conditions. This paper compares the ISO time-dependency with those based on root mean square (rms) and root mean quad (rmq) averaging of levels over time. [The rmq averaging procedure is based on experimental studies reported by Griffin and Whitham (1980) J. Acoust. Soc. Am. 68, 1277-1284.] It is shown that although the rmq procedure was developed from studies involving only short duration vibration, it defines a time dependency which may be acceptable for much longer periods.</p

Measuring vibration on soft seats

Two experiments have been conducted to assess a method of measuring the whole-body vertical vibration experienced by persons seated on soft seats. The method utilises a transducer mount located between the seat and the body. Comfort contours obtained on hard flat seats are shown to be applicable to measurements made within a firm bar or plate placed on a cushion beneath the ischial tuberosities of a seated subject. However, since some mounts alter seat transmissibility a firm plate (SIT-BAR) contoured to cause seat compression similar to that produced by the buttocks is recommended for some applications.</p

Discomfort produced by impulsive whole-body vibration

This paper reports four whole-body vibration experiments conducted to determine the effects of “pulse” duration and combinations of “pulses” of vibration on human discomfort. The first experiment investigated the variation in discomfort with vibration duration for the frequencies 4, 8, 16, and 32 Hz and durations from one cycle of motion to 4 s. The second experiment extended the results for 8-Hz vibration to durations up to 32 s. The third experiment involved complex motions with one predominant frequency and root mean square acceleration level but differing peak levels. The final experiment investigated the effect of vibration duration at different vibration frequencies. The results of the first two experiments conflict with previous reports of a short finite integration time for human response to vibration. The data are used to devise a procedure for predicting the discomfort of the motions used in the third experiment. The procedure which is based on a “root-mean-quad” unit: rmq = [T– fToa4(t) dt]1/4 indicates that motions of the same frequency and same rms level will cause greater discomfort with increasing peak levels. The predictions are in good general agreement with the experimental results. Possible uses of the rmq unit are discussed.</p

Six axis vehicle vibration and its effects on comfort

The vibration in vehicles has been measured in three translational axes and three rotational axes at the passenger/seat interface and on the floor beneath the seat. The level, frequency and direction of vehicle vibration was shown to depend upon vehicle type, vehicle speed and road condition. Vibration associated with vehicle suspension, engine and seat characteristics can be identified. Comparison of vehicle vibration levels obtained within each axis with discomfort levels obtained in the laboratory implied that, in the vehicles investigated, vibration in the translational axes produced greater discomfort than vibration in the rotational axes. Vertical vibration appeared to produce greater discomfort than fore-and-aft, lateral, roll, pitch or yaw vibration.</p