Effective seat-to-head transmissibility under combined-axis vibration and multiple postures (original) (raw)
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March
The low frequency vibration transmitted to the body can affect the comfort, performance, and health of humans. In this paper, the effect of variations in posture and vibration magnitude on the head motion in three translational axes (fore-and-aft, lateral and vertical) has been studied with a vertical seat vibration. Thirty healthy male subjects were exposed to random vibration with three vibration magnitudes of 0.4, 0.8, and 1.2 m/s2 rms over the frequency range of 1–20 Hz. The results are analysed in terms of seat-to-head-transmissibility (STHT) for the head motions in two seated postures (backrest and leaning forward on table). The measurement of the head motion was made with an apparatus (bite-bar) specifically developed for this purpose. The measured responses to a single axis seat vibration have also shown notable cross-axis responses in both vertical and fore-and-aft axes for both postures. The crossaxis fore-aft and vertical STHT responses showed single peak near 5 Hz in bot...
Journal of Low Frequency Noise Vibration and Active Control, 2018
An experimental study has been conducted on the vibration simulator, developed as a mockup of a railway vehicle. In this paper, the effect of variations in the posture and vibration magnitude on head motions in three translational directions (fore-and-aft, lateral and vertical) are studied with seat vibration in fore-and-aft direction. Thirty healthy male subjects are exposed to random vibration with three vibration magnitudes of 0.4, 0.8 and 1.2 m/s 2 r.m.s. over the frequency range 1-20 Hz. The data results are analyzed in terms of seat-to-head transmissibility (STHT) in two sitting postures; backrest and forward lean. Vibration measurements of the head motions are made with an apparatus (bite-bar). The study confirms that the measured responses to single fore-and-aft axis vibration have shown notable cross-axis responses. An increase in the excitation magnitude consistently revealed a decrease in the response peak magnitude and the corresponding resonant frequency, particularly in the presence of a back support. Such non-linear behavior has been interpreted as a non-linear softening effect in the muscle tension under increasing intensity of vibration. The use of a back support significantly alters the biodynamic responses of the seated body, which is attributable to the constraint due to the backrest support.
The effects of posture on seat-to-head Whole-body vibration transmission
2008
Five male subjects were exposed to root-mean-square whole-body vibration (WBV) acceleration levels ranging from 0.011m/s 2 to 0.615m/s 2 while seated on a vibration simulator. During the WBV exposure, subjects adopted 5 unsupported trunk flexion/extension positions (15, 10, 0,-10 and-15, ±2.5 degrees from vertical), and 4 hip flexion positions (-10, 0, 10, and 20 degrees from the horizontal). WBV measurements were taken with a tri-axial accelerometer at the buttock/seat interface and the head. Hydrostatic weighing was also conducted to determine the subject's adipose content. Adipose content of the individual had no significant relationship with the seat-to-head transmission of vibration. Vibration exposures at 4Hz had significantly more transmission than vibration exposures at 6.3Hz. Vibration exposures in the Zaxis (vertical) had significantly more vibration transmission than vibration exposures in the X-(front-to-back) and Y-axes (left-to-right). A significant interaction was also found between trunk position, frequency and axis of exposure.