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Non-linear dual-axis biodynamic response to fore-and-aft whole-body vibration

Non-linear dual-axis biodynamic response to fore-and-aft whole-body vibration
Non-linear dual-axis biodynamic response to fore-and-aft whole-body vibration
Seated subjects have participated in two experiments with fore-and-aft whole-body vibration to investigate dynamic responses at the seat and footrest in the direction of vibration and in other directions. In the first experiment, 12 males were exposed to fore-and-aft random vibration (0.25–20 Hz) at four magnitudes (0.125, 0.25, 0.625, and 1.25 m s?2 rms) while sitting on a seat with no backrest in four postures with varying foot heights to produce differing thigh contact with the seat (feet hanging, feet supported with maximum thigh contact, feet supported with average thigh contact, and feet supported with minimum thigh contact). In the second experiment, six subjects were exposed to three vibration magnitudes (0.125, 0.25, 0.625 m s?2 rms) in the average thigh contact posture, both with and without a rigid backrest. Forces were measured in the vertical, fore-and-aft, and lateral directions on the supporting seat surface (in the first experiment) and in the fore-and-aft and vertical directions at the footrest (in the second experiment).
On the seat, there were three vibration modes in the fore-and-aft apparent mass on the seat at frequencies below 10 Hz in all postures (around 1 Hz, between 1 and 3 Hz, and between 3 and 5 Hz); large vertical forces were dependent on foot support while lateral forces were relatively small. At the feet, the fore-and-aft apparent mass showed a resonance between 3 and 5 Hz, which increased in frequency and magnitude when a backrest was used. The fore-and-aft vibration produced high vertical forces at the footrest. At frequencies below resonance, the backrest reduced vertical and fore-and-aft forces at the footrest. On the seat and the footrest, the forces showed a nonlinear characteristic that varied between postures.
The presence of appreciable vertical forces indicate that during fore-and-aft excitation the body moved in two dimensions. It is concluded that forces in directions other than the direction of excitation should be taken into account when considering biodynamic responses to fore-and-aft whole-body vibration.
0022-460X
831-862
Nawayseh, N.
1b8c9e26-3666-4a16-be48-be0ef4593231
Griffin, M.J.
24112494-9774-40cb-91b7-5b4afe3c41b8
Nawayseh, N.
1b8c9e26-3666-4a16-be48-be0ef4593231
Griffin, M.J.
24112494-9774-40cb-91b7-5b4afe3c41b8

Nawayseh, N. and Griffin, M.J. (2005) Non-linear dual-axis biodynamic response to fore-and-aft whole-body vibration. Journal of Sound and Vibration, 282 (3-5), 831-862. (doi:10.1016/j.jsv.2004.03.044).

Record type: Article

Abstract

Seated subjects have participated in two experiments with fore-and-aft whole-body vibration to investigate dynamic responses at the seat and footrest in the direction of vibration and in other directions. In the first experiment, 12 males were exposed to fore-and-aft random vibration (0.25–20 Hz) at four magnitudes (0.125, 0.25, 0.625, and 1.25 m s?2 rms) while sitting on a seat with no backrest in four postures with varying foot heights to produce differing thigh contact with the seat (feet hanging, feet supported with maximum thigh contact, feet supported with average thigh contact, and feet supported with minimum thigh contact). In the second experiment, six subjects were exposed to three vibration magnitudes (0.125, 0.25, 0.625 m s?2 rms) in the average thigh contact posture, both with and without a rigid backrest. Forces were measured in the vertical, fore-and-aft, and lateral directions on the supporting seat surface (in the first experiment) and in the fore-and-aft and vertical directions at the footrest (in the second experiment).
On the seat, there were three vibration modes in the fore-and-aft apparent mass on the seat at frequencies below 10 Hz in all postures (around 1 Hz, between 1 and 3 Hz, and between 3 and 5 Hz); large vertical forces were dependent on foot support while lateral forces were relatively small. At the feet, the fore-and-aft apparent mass showed a resonance between 3 and 5 Hz, which increased in frequency and magnitude when a backrest was used. The fore-and-aft vibration produced high vertical forces at the footrest. At frequencies below resonance, the backrest reduced vertical and fore-and-aft forces at the footrest. On the seat and the footrest, the forces showed a nonlinear characteristic that varied between postures.
The presence of appreciable vertical forces indicate that during fore-and-aft excitation the body moved in two dimensions. It is concluded that forces in directions other than the direction of excitation should be taken into account when considering biodynamic responses to fore-and-aft whole-body vibration.

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More information

Published date: 2005
Organisations: Human Sciences Group

Identifiers

Local EPrints ID: 28076
URI: http://eprints.soton.ac.uk/id/eprint/28076
ISSN: 0022-460X
PURE UUID: 7820db01-b371-44d9-8e50-1c819cf7dfc8
ORCID for M.J. Griffin: ORCID iD orcid.org/0000-0003-0743-9502

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Date deposited: 28 Apr 2006
Last modified: 15 Mar 2024 07:23

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Contributors

Author: N. Nawayseh
Author: M.J. Griffin ORCID iD

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