Effects of posture and vibration magnitude on seat to head transmissibility during exposure to fore-and-aft vibration

Abstract

An experimental study has been conducted on the vibration simulator, developed as a mockup of a railway vehicle. In this paper, the effect of variations in the posture and vibration magnitude on head motions in three translational directions (fore-and-aft, lateral and vertical) are studied with seat vibration in fore-and-aft direction. Thirty healthy male subjects are exposed to random vibration with three vibration magnitudes of 0.4, 0.8 and 1.2 m/s 2 r.m.s. over the frequency range 1-20 Hz. The data results are analyzed in terms of seat-to-head transmissibility (STHT) in two sitting postures; backrest and forward lean. Vibration measurements of the head motions are made with an apparatus (bite-bar). The study confirms that the measured responses to single fore-and-aft axis vibration have shown notable cross-axis responses. An increase in the excitation magnitude consistently revealed a decrease in the response peak magnitude and the corresponding resonant frequency, particularly in the presence of a back support. Such non-linear behavior has been interpreted as a non-linear softening effect in the muscle tension under increasing intensity of vibration. The use of a back support significantly alters the biodynamic responses of the seated body, which is attributable to the constraint due to the backrest support.

Effects of seat back height and posture on 3D vibration transmission to pelvis, trunk and head

“…A reduced perturbation signal magnitude resulted in increase main response peak gains in all perturbation directions for head and trunk, accompanied with higher peak frequencies (Table 1a). Previous studies found similar non-linear effects of seat vibration magnitude (Bhiwapurkar et al, 2016;Bhiwapurkar, Saran and Harsha, 2019;Nawayseh and Griffin, 2003). These findings were explained by non-linear muscle yielding in response to increasing motion magnitudes (Nawayseh and Griffin, 2003;Matsumoto and Griffin, 2002).…”

Examining the Impact of Rotated Neck and Trunk Postures on Vertical Seat-to-Head Vibration Transmissibility and Self-Reported Discomfort

“…The term posture in the WBV literature is used loosely [8], where it can mean changes in pelvic rotation/tilt [19,20], tension in the spine [10], use of a backrest support [21,22], use of armrests [18,23], slouching [24], flexed and extended trunk and hip positions [25], and rotated trunk and neck positions [12,17,18,26,27]. In a study using nine different pelvis and spine postures, there were peaks in apparent mass at 5 and 10 Hz and peaks in seat-to-pelvis pitch transmissibility at 12 Hz [20].…”

“…The STHT has been measured in laboratory experiments simulating WBV exposure from a dozer machine [23] and railway vehicle [21]. In the dozer study, two sitting postures were used: one with the subject sitting in a standard posture supported by the seat back, and the second in a forward back-unsupported posture, where the arms were on their laps and their feet on a foot pedal while using the armrests or grasping the steering wheel [23].…”

Modeling and parameter identification of seated human body with the reference vector guided evolutionary algorithm

“…Three biodynamic response functions were usually used to analyze the vibration characteristics of human body -seat to head transmissibility (STHT), apparent mass (AM), and mechanical impedance (MI) respectively. [7][8][9][10][11][12] In order to analyze the vibration of human body and improve ride comfort of vehicle, various models have been built to describe the vibration response characteristics of human body. [13][14][15][16] Lumped parameter model is a typical, simple method to analyses vibration responses of seated human body.…”