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Vertical and dual-axis vibration of the seated human body: nonlinearity, cross-axis coupling, and associations between resonances in transmissibility and apparent mass

Vertical and dual-axis vibration of the seated human body: nonlinearity, cross-axis coupling, and associations between resonances in transmissibility and apparent mass
Vertical and dual-axis vibration of the seated human body: nonlinearity, cross-axis coupling, and associations between resonances in transmissibility and apparent mass
The vertical apparent mass of the human body exhibits nonlinearity, with the principal resonance frequency reducing as the vibration magnitude increases. Measures of the transmission of vibration to the spine and the pelvis have suggested complex modes are responsible for the dominant resonance during vertical excitation, but the modes present with dual-axis excitation have not been investigated. This study was designed to examine how the apparent mass and transmissibility of the human body depend on the magnitude of vertical excitation and the addition of fore-and-aft excitation, and the relation between the apparent mass and the transmissibility of the body. The movement of the body (over the first, fifth and twelfth thoracic vertebrae, the third lumbar vertebra, and the pelvis) in the fore-and-aft and vertical directions (and in pitch at the pelvis) was measured in 12 male subjects sitting with their hands on their laps during random vertical vibration excitation (over the range 0.25–20 Hz) at three vibration magnitudes (0.25, 0.5 and 1.0 m s?2 rms). At the highest magnitude of vertical excitation (1.0 m s?2 rms) the effect of adding fore-aft vibration (at 0.25, 0.5, and 1.0 m s?2 rms) was investigated. The forces in the vertical and fore-and-aft directions on the seat surface were also measured so as to calculate apparent masses. Resonances in the apparent mass and transmissibility to the spine and pelvis in the fore-and-aft and vertical directions, and pitch transmissibility to the pelvis, shifted to lower frequencies as the magnitude of vertical excitation increased and as the magnitude of the additional fore-and-aft excitation increased. The nonlinear resonant behaviour of the apparent mass and transmissibility during dual-axis vibration excitation suggests coupling between the principal mode associated with vertical excitation and the cross-axis influence of fore-and-aft excitation. The transmissibility measures are consistent with complex modes contributing to motion of the body at the principal resonance: pitch motions of the upper thoracic and lumbar spine, and vertical and fore-aft motion of the pelvis and spine. The mode varies with the magnitude of vertical and fore-and-aft excitation.

0022-460X
5880-5894
Zheng, G.
dcdb031e-fb26-4b7d-9b83-66e71a7d0cbf
Qiu, Y.
ef9eae54-bdf3-4084-816a-0ecbf6a0e9da
Griffin, M.J.
24112494-9774-40cb-91b7-5b4afe3c41b8
Zheng, G.
dcdb031e-fb26-4b7d-9b83-66e71a7d0cbf
Qiu, Y.
ef9eae54-bdf3-4084-816a-0ecbf6a0e9da
Griffin, M.J.
24112494-9774-40cb-91b7-5b4afe3c41b8

Zheng, G., Qiu, Y. and Griffin, M.J. (2012) Vertical and dual-axis vibration of the seated human body: nonlinearity, cross-axis coupling, and associations between resonances in transmissibility and apparent mass. Journal of Sound and Vibration, 331 (26), 5880-5894. (doi:10.1016/j.jsv.2012.07.029).

Record type: Article

Abstract

The vertical apparent mass of the human body exhibits nonlinearity, with the principal resonance frequency reducing as the vibration magnitude increases. Measures of the transmission of vibration to the spine and the pelvis have suggested complex modes are responsible for the dominant resonance during vertical excitation, but the modes present with dual-axis excitation have not been investigated. This study was designed to examine how the apparent mass and transmissibility of the human body depend on the magnitude of vertical excitation and the addition of fore-and-aft excitation, and the relation between the apparent mass and the transmissibility of the body. The movement of the body (over the first, fifth and twelfth thoracic vertebrae, the third lumbar vertebra, and the pelvis) in the fore-and-aft and vertical directions (and in pitch at the pelvis) was measured in 12 male subjects sitting with their hands on their laps during random vertical vibration excitation (over the range 0.25–20 Hz) at three vibration magnitudes (0.25, 0.5 and 1.0 m s?2 rms). At the highest magnitude of vertical excitation (1.0 m s?2 rms) the effect of adding fore-aft vibration (at 0.25, 0.5, and 1.0 m s?2 rms) was investigated. The forces in the vertical and fore-and-aft directions on the seat surface were also measured so as to calculate apparent masses. Resonances in the apparent mass and transmissibility to the spine and pelvis in the fore-and-aft and vertical directions, and pitch transmissibility to the pelvis, shifted to lower frequencies as the magnitude of vertical excitation increased and as the magnitude of the additional fore-and-aft excitation increased. The nonlinear resonant behaviour of the apparent mass and transmissibility during dual-axis vibration excitation suggests coupling between the principal mode associated with vertical excitation and the cross-axis influence of fore-and-aft excitation. The transmissibility measures are consistent with complex modes contributing to motion of the body at the principal resonance: pitch motions of the upper thoracic and lumbar spine, and vertical and fore-aft motion of the pelvis and spine. The mode varies with the magnitude of vertical and fore-and-aft excitation.

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Published date: December 2012
Organisations: Human Sciences Group

Identifiers

Local EPrints ID: 354930
URI: http://eprints.soton.ac.uk/id/eprint/354930
ISSN: 0022-460X
PURE UUID: e7eec8e8-1766-417e-b456-0d303de91df2
ORCID for M.J. Griffin: ORCID iD orcid.org/0000-0003-0743-9502

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Date deposited: 23 Jul 2013 10:36
Last modified: 27 Apr 2022 07:25

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Contributors

Author: G. Zheng
Author: Y. Qiu
Author: M.J. Griffin ORCID iD

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