Effects of sitting postures on biodynamic response of seated occupants under vertical vibration

The biodynamic response characteristics of 13 male and 14 female seated subjects, exposed to vertical vibration, are characterized under different postural conditions. The measurements are performed for a total of 36 different sitting postural configurations realized through variations in hands position (in lap and on steering wheel), three seat heights (510, 460 and 410mm), and seat design factors involving two different pan orientations (0° and 7.5°) and three different back support conditions (no support, and support with vertical and inclined backrest). The measured data, expressed in terms of the vertical apparent mass (APMS), are analyzed to study the effects of sitting posture on the biodynamic response under whole-body vertical vibration. Owing to the complex dependence of apparent mass response on the body mass, the statistical analyses are performed with body mass as a covariant. The results suggest that the hands in lap posture yields larger primary resonant frequency and considerably higher APMS magnitude response in the vicinity of primary resonant frequency than the hands on the steering wheel posture, when the back is supported with an inclined backrest. The apparent mass magnitudes at frequencies above the primary resonance tend to increase when the back is supported irrespective of the hands position. A higher seat height yields higher peak magnitude response which is attributed to relatively larger portion of the body mass supported by the seat, while the influence of seat pan inclination is observed to be negligible for range of inclination investigated. Relevance to industry The apparent mass of seated occupants exposed to whole body vibration yields significant information on human response to vibration, and forms the basis for developing analytical models representing the seated human body, and for potential applications in assessment of coupled occupant system and design of automotive seat. The knowledge of influence of various design and operating factors, and some of the anthropometric factors is vital to realize better seat design.