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

Fore-and-aft and dual-axis vibration of the seated human body: nonlinearity, cross-axis coupling, and associations between resonances in the transmissibility and apparent mass
Fore-and-aft and dual-axis vibration of the seated human body: nonlinearity, cross-axis coupling, and associations between resonances in the transmissibility and apparent mass
© 2018 This study examined how the apparent mass and transmissibility of the human body depend on the magnitude of fore-and-aft vibration excitation and the presence of vertical vibration. Fore-and-aft and vertical acceleration at five locations along the spine, and pitch acceleration at the pelvis, were measured in 12 seated male subjects during fore-and-aft random vibration excitation (0.25–20 Hz) at three vibration magnitudes (0.25, 0.5 and 1.0 ms−2 r.m.s.). With the greatest magnitude of fore-and-aft excitation, vertical vibration was added at 0.25, 0.5, or 1.0 ms−2 r.m.s. Forces in the fore-and-aft and vertical directions on the seat surface were measured to calculate apparent masses. Transmissibilities and apparent masses during fore-and-aft excitation showed a principal resonance around 1 Hz and a secondary resonance around 2–3 Hz. Increasing the magnitude of fore-and-aft excitation, or adding vertical excitation, decreased the magnitudes of the resonances. At the primary resonance frequency, the dominant mode induced by fore-and-aft excitation involved bending of the lumbar spine and the lower thoracic spine with shear deformation of tissues at the ischial tuberosities. The relative contributions to this mode from each body segment (especially the pelvis and the lower thoracic spine) varied with vibration magnitude. The nonlinearities in the apparent mass and transmissibility during dual-axis excitation indicate coupling between the principal mode of the seated human body excited by fore-and-aft excitation and the cross-axis influence of vertical excitation. Relevance to industry: Understanding movements of the body during exposure to whole-body vibration can assist the optimisation of seating dynamics and help to control the effects of the vibration on human comfort, performance, and health. This study suggests cross-axis nonlinearity in biodynamic responses to vibration should be considered when optimising vibration environments.
Biodynamics, Dual-axis excitation, Nonlinearity
0169-8141
58-65
Zheng, Guangtai
e881f56c-5420-450b-afb7-288c67a634cd
Qiu, Yi
ef9eae54-bdf3-4084-816a-0ecbf6a0e9da
Griffin, Michael J.
24112494-9774-40cb-91b7-5b4afe3c41b8
Zheng, Guangtai
e881f56c-5420-450b-afb7-288c67a634cd
Qiu, Yi
ef9eae54-bdf3-4084-816a-0ecbf6a0e9da
Griffin, Michael J.
24112494-9774-40cb-91b7-5b4afe3c41b8

Zheng, Guangtai, Qiu, Yi and Griffin, Michael J. (2019) Fore-and-aft and dual-axis vibration of the seated human body: nonlinearity, cross-axis coupling, and associations between resonances in the transmissibility and apparent mass. International Journal of Industrial Ergonomics, 69, 58-65. (doi:10.1016/j.ergon.2018.08.007).

Record type: Article

Abstract

© 2018 This study examined how the apparent mass and transmissibility of the human body depend on the magnitude of fore-and-aft vibration excitation and the presence of vertical vibration. Fore-and-aft and vertical acceleration at five locations along the spine, and pitch acceleration at the pelvis, were measured in 12 seated male subjects during fore-and-aft random vibration excitation (0.25–20 Hz) at three vibration magnitudes (0.25, 0.5 and 1.0 ms−2 r.m.s.). With the greatest magnitude of fore-and-aft excitation, vertical vibration was added at 0.25, 0.5, or 1.0 ms−2 r.m.s. Forces in the fore-and-aft and vertical directions on the seat surface were measured to calculate apparent masses. Transmissibilities and apparent masses during fore-and-aft excitation showed a principal resonance around 1 Hz and a secondary resonance around 2–3 Hz. Increasing the magnitude of fore-and-aft excitation, or adding vertical excitation, decreased the magnitudes of the resonances. At the primary resonance frequency, the dominant mode induced by fore-and-aft excitation involved bending of the lumbar spine and the lower thoracic spine with shear deformation of tissues at the ischial tuberosities. The relative contributions to this mode from each body segment (especially the pelvis and the lower thoracic spine) varied with vibration magnitude. The nonlinearities in the apparent mass and transmissibility during dual-axis excitation indicate coupling between the principal mode of the seated human body excited by fore-and-aft excitation and the cross-axis influence of vertical excitation. Relevance to industry: Understanding movements of the body during exposure to whole-body vibration can assist the optimisation of seating dynamics and help to control the effects of the vibration on human comfort, performance, and health. This study suggests cross-axis nonlinearity in biodynamic responses to vibration should be considered when optimising vibration environments.

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Transmissibility_and_Apparent_Mass Revised YQ - Author's Original
Restricted to Repository staff only until 24 October 2020.
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More information

Accepted/In Press date: 27 August 2018
e-pub ahead of print date: 24 October 2018
Published date: 1 January 2019
Keywords: Biodynamics, Dual-axis excitation, Nonlinearity

Identifiers

Local EPrints ID: 428233
URI: https://eprints.soton.ac.uk/id/eprint/428233
ISSN: 0169-8141
PURE UUID: c254d021-ba44-43f4-a716-da128cdc07a6
ORCID for Michael J. Griffin: ORCID iD orcid.org/0000-0003-0743-9502

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Date deposited: 15 Feb 2019 17:30
Last modified: 17 Jul 2019 01:22

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Author: Guangtai Zheng
Author: Yi Qiu

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