Analyses of biodynamic responses of seated occupants to uncorrelated fore-aft and vertical whole-body vibration

Abstract

The apparent mass and seat-to-head-transmissibility response functions of the seated human body were investigated under exposures to fore-aft (x), vertical (z), and combined fore-aft and vertical (x and z) axis whole-body vibration. The coupling effects of dualaxis vibration were investigated using two different frequency response function estimators based upon the cross-and auto-spectral densities of the response and excitation signals, denoted as H 1 and H v estimators, respectively. The experiments were performed to measure the biodynamic responses to single and uncorrelated dual-axis vibration, and to study the effects of hands support, back support and vibration magnitude on the body interactions with the seatpan and the backrest, characterised in terms of apparent masses and the vibration transmitted to the head. The data were acquired with 9 subjects exposed to two different magnitudes of vibration applied along the individual xand z-axis (0.25 and 0.4 m/s 2 rms), and along both the-axis (0.28 and 0.4 m/s 2 rms along each axis) in the 0.5 to 20 Hz frequency range. The two methods resulted in identical single-axis responses but considerably different dual-axis responses. The dual-axis responses derived from the H v estimator revealed notable effects of dual-axis vibration, as they comprised both the direct and cross-axis responses observed under single axis vibration. Such effect, termed as the coupling effect, was not evident in the dual-axis responses derived using the commonly used H 1 estimator. The results also revealed significant effects of hands and back support conditions on the coupling effects and the measured responses. The back support constrained the upper body movements and thus showed relatively weaker coupling compared to that observed in the responses without the back support. The effect of hand support was also pronounced under the fore-aft vibration. The results suggest that a better understanding of the seated human body responses to uncorrelated multi-axis whole-body vibration could be developed using the power-spectral-density based H v estimator.

An active head–neck model in whole-body vibration: Vibration magnitude and softening

“…The results showed that the transmissibility graphs of this work have in general similar characteristics to those by Fard et al (2004) and Mandapuram et al (2011), with minor differences due to the subject's constraint conditions and the location of the output point on the subject's head (DeShaw and Rahmatalla, 2011;Paddan and Griffin, 1992). However, the experimental and the model transmissibility graphs showed some values that are different than 1 in frequency close to 0 Hz.…”

“…While experimentations may provide significant insight into human biodynamics during vibration Griffin, 1988, 1998;Rahmatalla et al, 2010;Rahmatalla and DeShaw, 2011a;Mandapuram et al, 2011;Madakashira-Pranesh, 2011), computer human models (Boileau et al, 1997;Griffin, 2001) may present less expensive tools with a potential for evaluations that go beyond the experimentation's allowable ethical limits and would help in the development of more effective vibration suspension systems. Still, due to the complexity of the motion in whole-body vibration (WBV) (Griffin et al, 1979), the nonlinearity, and the involuntary muscle activation of the human body (Nawayseh and Griffin, 2005;Wang et al, 2010;Hinz et al, 2010), advances in predictive computer human modeling become a challenging issue.…”

Energy Absorption of Seated Body Exposed to Single and Three-Axis Whole Body Vibration

“…The power along an individual axis, however, is similar to that obtained under single-axis of vibration. This is caused by the relatively small coupling effect of multi-axis vibration, as reported in the APMS responses [27,28].…”

“…The forces along the three translational axes at the two body-seat interfaces (buttocks-seat pan and the upper body-backrest) were measured when exposed to single as well as three-axis whole-body vibration. The experimental setup used in this study was identical to that used for characterization of apparent mass and reported in [26,27]. Briefly, a rigid seat and a steering column were installed on a 6-DOF whole-body vibration simulator (IMV Corp.) at the National Institute of Occupational Safety and Health, Japan.…”

Comprehensive Measurement in Whole-Body Vibration

“…Additionally, all cross-coupled motions should be near zero at frequencies close to zero. Comprehensive measurement in whole-body vibration extremely close for vertical input/output transmissibilities (Zz) but seems to be much more variable in the fore-aft (Xx) and lateral transmissibilities (Yy) [6,7,9,10]. This could be due to the posture conditions, the involuntary lowfrequency motions of the head, and because the resonance transmissibility in these directions tends to be at low frequencies (below 2.0 Hz).…”