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Transmission of vibration through backrests and apparent mass of the back during whole-body fore-and-aft vibration

Transmission of vibration through backrests and apparent mass of the back during whole-body fore-and-aft vibration
Transmission of vibration through backrests and apparent mass of the back during whole-body fore-and-aft vibration

Knowledge of the transmissibility of seats and the biodynamic responses of a seated person exposed to fore-and-aft vibration are very limited despite extensive research in the vertical direction.  This thesis aims to extend understanding of the transmissibility of backrests and the apparent mass of the back during whole-body fore-and-aft excitation.

A series of experiments has measured the transmissibility of backrests and the apparent mass of the back of seated persons exposed to whole-body fore-and-aft vibration.  In most experiments, twelve male subjects were exposed to random fore-and-aft vibration in the frequency range 0.25 Hz to 20 Hz at five inclination magnitudes: 0.1, 0.2, 0.4, 0.8 and 1.6 ms-2 r.m.s.  The effects of backrest inclination, seat-pan inclination, push force at the feet and fore-and-aft position of the footrest on both the transmissibility of backrests and the apparent mass of the back were investigated.  The influence of different foam thickness on the transmissibility of a foam backrest was also investigated.

The transmissibility of a car seat backrest and a foam backrest showed a principal resonance frequency around 5 Hz, which coincides with the principal resonance frequency of the apparent mass of the back.   It is suggested that the resonance frequency of the backrest transmissibility is related to the mode of vibration of the body at the principal resonance – a mode of the entire body involving combined bending in the thoracic spine and pitching of the pelvis and the upper body.

The fore-and-aft transmissibility of both backrests varied significantly between 2 and 10 Hz when measured at five vertical locations at the backrest above the seat surface, although the resonance frequencies showed little change.  The variation in the transmissibility may have arisen from relative movement along the spinal column caused by the different modes of vibration of the body at the principal resonance during fore-and-aft excitation.

The apparent mass of the back was significantly non-linear with vibration magnitude.  The non-linearity of the body is suggested to have greatly influenced the non-linearity in the transmissibility of backrest with vibration magnitude.

University of Southampton
Abdul Jalil, Nawal Aswan
a5a361ed-9384-4ba1-9b1e-1b3b2fe504b1
Abdul Jalil, Nawal Aswan
a5a361ed-9384-4ba1-9b1e-1b3b2fe504b1

Abdul Jalil, Nawal Aswan (2005) Transmission of vibration through backrests and apparent mass of the back during whole-body fore-and-aft vibration. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Knowledge of the transmissibility of seats and the biodynamic responses of a seated person exposed to fore-and-aft vibration are very limited despite extensive research in the vertical direction.  This thesis aims to extend understanding of the transmissibility of backrests and the apparent mass of the back during whole-body fore-and-aft excitation.

A series of experiments has measured the transmissibility of backrests and the apparent mass of the back of seated persons exposed to whole-body fore-and-aft vibration.  In most experiments, twelve male subjects were exposed to random fore-and-aft vibration in the frequency range 0.25 Hz to 20 Hz at five inclination magnitudes: 0.1, 0.2, 0.4, 0.8 and 1.6 ms-2 r.m.s.  The effects of backrest inclination, seat-pan inclination, push force at the feet and fore-and-aft position of the footrest on both the transmissibility of backrests and the apparent mass of the back were investigated.  The influence of different foam thickness on the transmissibility of a foam backrest was also investigated.

The transmissibility of a car seat backrest and a foam backrest showed a principal resonance frequency around 5 Hz, which coincides with the principal resonance frequency of the apparent mass of the back.   It is suggested that the resonance frequency of the backrest transmissibility is related to the mode of vibration of the body at the principal resonance – a mode of the entire body involving combined bending in the thoracic spine and pitching of the pelvis and the upper body.

The fore-and-aft transmissibility of both backrests varied significantly between 2 and 10 Hz when measured at five vertical locations at the backrest above the seat surface, although the resonance frequencies showed little change.  The variation in the transmissibility may have arisen from relative movement along the spinal column caused by the different modes of vibration of the body at the principal resonance during fore-and-aft excitation.

The apparent mass of the back was significantly non-linear with vibration magnitude.  The non-linearity of the body is suggested to have greatly influenced the non-linearity in the transmissibility of backrest with vibration magnitude.

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Published date: 2005

Identifiers

Local EPrints ID: 465887
URI: http://eprints.soton.ac.uk/id/eprint/465887
PURE UUID: ca3bae2d-6d70-42b1-b5fb-f3171a988a8b

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Date deposited: 05 Jul 2022 03:27
Last modified: 16 Mar 2024 20:25

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Author: Nawal Aswan Abdul Jalil

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