The influence of the magnitude of vibration on the prediction of vibration discomfort

Abstract

The discomfort caused by the whole-body vibration of seated persons depends on the magnitude, frequency, direction, and duration of the vibration. Many legacy studies have investigated how the four main attributes of whole-body vibration influence discomfort and these have led to standardised methods for evaluating vibration to predict discomfort. The aim of the research in this thesis was to investigate the application of the methods when predicting discomfort caused by multi-axis and multiple-frequency vibration. The first experiment investigated discomfort caused by pitch oscillation of a rigid seat with and without a backrest. Seated participants used magnitude estimation to indicate their discomfort during sinusoidal vibration at frequencies from 0.5 to 5 Hz. At frequencies greater than 1.0 Hz, the discomfort and the rate-of-growth of discomfort was greater with the backrest. At frequencies less than 1.0 Hz, the discomfort and the rate-of-growth of was similar in both seating conditions. The second experiment investigated discomfort caused by six-axis vibration recorded in a road vehicle. Participants used the method of paired comparisons to judge differences in discomfort between six vibration conditions obtained by modifying the recorded vibration. Two scenarios involved reductions of either 50% or 100% in the vibration magnitude in each of five axes (fore and-aft, lateral, vertical, roll, or pitch) and a control motion. No statistically significant differences in discomfort were found when reducing the vibration magnitude in any single axis prompting further investigation into the method of combining motions when predicting vibration discomfort. The third experiment investigated how vibration discomfort depends on the frequency and magnitude of translational vibration. Seated participants judged the discomfort produced by sinusoidal vibration from 1.0 to 10 Hz using magnitude estimation. It was found that the rate-of growth of discomfort varied between directions and frequencies of vibration, resulting in different equivalent discomfort contours at different magnitudes. Horizontal vibration at magnitudes lower than those used when developing the current standards were judged more uncomfortable than vertical vibration at frequencies greater than the 3.15 Hz equivalence frequency. The final experiment investigated the prediction of vibration discomfort caused by combinations of different directions and different frequencies of vibration. Using magnitude estimation, seated participants judged the discomfort of single-axis, dual-axis, and tri-axial translational motions (one-octave bandwidth random motions centred on 2.0, 4.0, or 8.0 Hz). In addition, participants judged the discomfort caused by multiple-frequency single-axis motions in each of the three axes. It was found that when using ‘power summation’ of subjective measures of components in a complex motion, the power required to predict the discomfort depends on the rate-of-growth of discomfort. The findings from the four experiments show that the rate-of-growth of discomfort is crucial when attempting to predict discomfort caused by individual vibration components, multiple frequency vibration, and multi-axis vibration. The rate-of-growth of discomfort is highly dependent on the frequency and direction of vibration, so the inter-axis equivalence between vibration in different directions changes when the magnitude changes. Single frequency weightings and axis multiplying factors cannot provide good predictions of vibration discomfort over a wide range of vibration magnitudes. Different frequency weightings and different axis multiplying factors are required for different magnitudes of vibration.

More information

Identifiers

ORCID for James Arnold: orcid.org/0000-0003-1987-515X

ORCID for Ying Ye: orcid.org/0000-0002-7721-5451

Catalogue record

Export record