The role of seat geometry and posture on the mechanical energy absorption characteristics of seated occupants under vertical vibration

Abstract The power absorption characteristics of 27 male and female seated subjects, exposed to vertical vibration in the 0.5–40 Hz frequency range, are characterized under different sitting postures. 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), seat heights (510, 460 and 410 mm), and seat design factors involving pan (0° and 7.5°) and backrest (0° and 12°) orientations, and different back support conditions. The measured data, expressed in terms of the vertical absorbed power density, are analyzed to study the effects of sitting posture on the biodynamic response under whole-body vertical vibration. An indirect method of computing absorbed power from the apparent mass response is formulated and validated using the directly measured absorbed power data. The measured data were analyzed to study the dependence of vibration energy absorption on various factors related to anthropometry (body mass, fat and mass index), seat geometry and sitting postures. The strong linear dependence between the absorbed power and the body mass and body mass index were revealed over the frequency range considered. The results clearly validate that the power absorption strongly depends upon the magnitude of whole-body vibration. Both the absorbed power near the primary resonance and the total power increase nearly quadratically with the exposure level. The hands in lap sitting posture yields to higher power absorption, irrespective of the back support condition. The sitting with a backrest reduces the energy dissipation at low frequencies and increases the energy absorption at frequencies above resonance, irrespective of the hands position, while the influence of seat pan inclination is negligible within the range of angles investigated. Relevance to industry The biodynamic responses of seated occupants exposed to whole-body vibration have been mostly investigated in terms of apparent mass characteristics, which show negligible contributions due to exposure level. Considering that the severity of vibration exposure is related to the level and duration of exposure, the apparent mass responses cannot be used for assessment of the associated risks. Alternatively, the absorbed power characteristics of the seated vibration exposed occupants show strong dependence on the level of exposure. Moreover, the absorbed power response characteristics could be applied to obtain an estimate of the cumulative energy dissipated by the exposed body over a given exposure duration. The absorbed power can thus serve as a measure for assessing the health and safety risks associated with exposure to whole-body vertical vibration. The energy dissipation by the vibration-exposed body is further influenced by the sitting posture and seat design factors. The knowledge of the seat design factors and some of the anthropometric factors on the energy dissipation is thus vital to realize better seat designs.