Predicting the vibration discomfort of standing passengers in transport

It has previously been assumed that the vibration discomfort of standing people can be<br/>estimated using the same procedures developed from for seated people. In this thesis, the<br/>discomfort of standing people exposed to vibration was investigated to improve understanding<br/>of the mechanisms responsible for discomfort and construct a model that may be used<br/>to predict the discomfort of standing railway passengers.<br/>The first of five experiments using the method of magnitude estimation and 6-s periods<br/>of vibration investigated how the discomfort of standing subjects exposed to fore-and-aft,<br/>lateral, and vertical sinusoidal vibration depends on the frequency of vibration. From the<br/>judgements of 12 subjects at each of the 16 preferred one-third octave centre frequencies<br/>from 0.5 to 16 Hz, frequency weightings were constructed for each direction. For vertical<br/>vibration, the weighting was similar to that recommended in standards, but the weightings<br/>for fore-and-aft and lateral vibration differed from that previously assumed. Horizontal<br/>vibration caused loss of balance at frequencies less than about 3 Hz, and it caused discomfort<br/>in the legs at higher frequencies. Vertical vibration caused discomfort in the upper body. To<br/>adjust the frequency weightings according to differences in sensitivity between directions,<br/>the second experiment with 12 subjects compared the discomfort caused by 4-Hz sinusoidal<br/>vibration in the fore-and-aft, lateral, the vertical directions. It was found that sensitivity<br/>was greater for fore-and-aft vibration than lateral vibration at frequencies less than 4 Hz<br/>and weightings were determined to assist the evaluation vibration in all three directions.<br/>The third experiment investigated the extent to which postural supports used by standing<br/>train passengers (vertical bar, shoulder support, and back support) affect discomfort caused<br/>by fore-and-aft and lateral vibration in the range 0.5 to 16 Hz. Supports that created a<br/>new path for the transmission of vibration to the upper-body increased discomfort over the<br/>range 4 to 16 Hz.<br/>The fourth experiment investigated how the root-mean-square method, the basic evaluation<br/>method in current standards but known to underestimate the discomfort caused by<br/>motions containing occasional peaks, could be modified for the evaluation of non-sinusoidal<br/>vibration. Using 1-Hz and 8-Hz random vibrations with a range of crest factors it was found<br/>that the discomfort of standing subjects was better predicted with an exponent around 3,<br/>rather than an exponent of 2 implicit in r.m.s. averaging. The final experiment determined<br/>a method for predicting the discomfort of tri-axial vibration. The cube root of the sum<br/>of the cubes of the discomfort caused by the single-axis components gave good estimates<br/>of the total discomfort for both 1-Hz and 4-Hz tri-axial vibration. Since it was found in<br/>the first experiment that the discomfort was generally proportional to the acceleration at<br/>the power 0.7. these results suggest that the root-sum-of-squares of the accelerations gives<br/>good estimates of the total discomfort for tri-axial vibration .<br/>The results of all experiments were combined in an empirical model for predicting the<br/>discomfort of standing people exposed to 6-s periods of vibration. It is concluded that there<br/>are two distinctly different mechanisms responsible for vibration discomfort when standing:<br/>postural instability and body vibration. Postural instability is dominant with horizontal<br/>vibration at frequencies less than about 3 Hz, whereas body vibration is dominant with<br/>vertical vibration and with horizontal vibration at frequencies greater than about 3 Hz.<br/>The discomfort of standing people is similar to the discomfort of seated people for vertical<br/>vibration, but fundamentally different with horizontal vibration due to postural instability<br/>at low frequencies and vibration attenuation in the legs at higher frequencies

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2011

Author dc:creator

• Thuong, O.

Advisor dc:contributor.advisor

• Griffin, M.J.