A study of the suspension-seat-occupant system dynamics under tri-axial translational vibration

Abstract

Most previous studies on the biodynamic response and the seating dynamics were limited to single axial excitations. How the suspension-seat-occupant system behaves in the multi-axial vibrational environment is less reported. The objective of this study is to advance the understanding of the effect of the excitation magnitude and the backrest inclination angle on the biodynamic response of the seated human body and the transmissibility of the suspension seat with tri-axial translational excitation. An experimental study was carried out with single-axial excitations at various magnitudes up to 1.0 ms-2 (r.m.s.) to examine the effect of the backrest inclination angles on the biodynamic response in fore-aft, lateral and vertical directions when the human body was sitting in the rigid seat. It was found that, at different excitation magnitudes, the apparent masses in the three translational directions were affected by the increased backrest inclination angle up to 20°. Such an inclination angle also affected the degree of the nonlinearity caused by changing excitation magnitude. The experimental study on the human body seated in the rigid seat also investigated under triaxial excitations the effect of the excitation magnitude in fore-aft, lateral and vertical directions (up to 1.0 ms-2 r.m.s. in each axis) and the backrest inclination angle on the biodynamic response. The increased excitation magnitude in one (named as “primary-axis”) of three translational axes and that in the other two (named as “secondary-axes”) axes both led to the decrease of the resonance frequency of the apparent mass in the “primary-axis” under the conditions tested. Interactive effects were found between the excitation magnitudes in different directions: the reduction of the resonance frequency of the apparent mass with the increased excitation magnitude in the “primary-axis” became smaller when the excitation magnitude in the “secondary-axes” was increased, and vice versa. Furthermore, the effect of backrest inclination angle under tri-axial vibration on the apparent mass was found to be comparable with that under single-axial vibration. Results showed that the backrest inclination and the excitation magnitude had combined effect on the degree of nonlinearity of the apparent mass. The effect of the excitation magnitude and the backrest inclination angle on the transmissibility of the suspension seat with the seated subject was further studied with tri-axial excitation. Under the conditions tested, the suspension seat with loaded inert mass exhibited nonlinear behaviour in all three translational directions subject to the change of the excitation magnitude in the “primary axis”. The interaction between the excitation magnitude in the “primary-axis” and that in the “secondary-axes” were observed in the transmissibilities of the suspension seat with seated occupant. The backrest inclination angle also affected the moduli of the seat transmissibilities at the backrest. Based on the experimental studies, a linear multi-body biodynamic model of the seated human body exposed to tri-axial vibration was developed. With a rigorous calibration procedure, the model was shown to be capable of representing the tri-axial biodynamic responses of human body supported by either upright or inclined backrest. Four vibration modes of the human body, which contributed to the resonances of the lateral, fore-aft and vertical apparent masses respectively, were identified through a modal analysis with the calibrated biodynamic model. Finally, linear multi-body models of the suspension mechanism with inert mass, the suspension seat with inert mass, and suspension seat with occupant under tri-axial excitation were developed. Results showed that the suspension-seat-occupant model was capable of predicting the fore-aft and vertical seat transmissibilities at the seat pan and backrest under tri-axial excitation when the subject was seated. The parameters of the seat model (e.g., the contact stiffness at the sea to occupant interface) to which the seat transmissibilities were most sensitive were identified, providing useful information for the seat design to improve ride comfort.

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ORCID for Weitan Yin: orcid.org/0000-0002-1598-5514

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