Effect of seat surface angle on forces at the seat surface during wholebody vertical vibration
Abstract
Twelve male subjects have been exposed to wholebody vertical random vibration so as to investigate the effect of seat surface angle, vibration magnitude and contact with a backrest on the 'vertical apparent mass' (calculated from forces normal to the seat surface and vertical acceleration) and 'foreandaft crossaxis apparent mass' (calculated from forces parallel to the seat surface and vertical acceleration). At each of four seat surface angles (0°, 5°, 10°, and 15°), the subjects were exposed to four vibration magnitudes (0.125, 0.25, 0.625, and 1.25 m s ^{2} rms) in the frequency range 0.2515 Hz. The 'vertical apparent mass' and 'foreandaft crossaxis apparent mass' on the seat surface suggested resonances in the vicinity of 5 and 4 Hz, respectively. At all seat angles, both with and without a backrest, the resonance frequency in the 'vertical apparent mass' was greater than the resonance frequency in the 'foreandaft crossaxis apparent mass'. Within subjects, the two resonance frequencies were not correlated in any condition. Seat angles up to 15° had a negligible effect on the 'vertical apparent mass' but a considerable effect on the 'foreandaft crossaxis apparent mass' on the seat surface, where 'crossaxis apparent mass' increased with increasing seat angle. At all seat angles, increasing the vibration magnitude decreased the resonance frequency in both directions. The least significant decrease in resonance frequency with increasing vibration magnitude occurred in the 'foreandaft crossaxis apparent mass' at the maximum seat angle of 15°. At low frequencies, the backrest reduced the forces in both directions, with the reduction greatest in the 'foreandaft' direction. The 'foreandaft crossaxis apparent mass' at resonance was correlated with subject mass and subject stature.
 Publication:

Journal of Sound Vibration
 Pub Date:
 June 2005
 DOI:
 10.1016/j.jsv.2004.06.038
 Bibcode:
 2005JSV...284..613N