Lack of the biodynamic data of lightweight and heavyweight human bodies in seating posture becomes an impediment to developing dynamic dummies and relevant standards for improving vehicle ride comfort and reducing health risks caused by vibration. To acquire missing data and gain an understanding of relevant biodynamic responses, the vertical apparent masses of seated subjects in lightweight and heavyweight groups as well as the mediumweight group (targeted mass 55 kg, 98–115 kg, and 75 kg) were experimentally measured and studied under 9 vibration magnitudes (0.25, 0.315, 0.4, 0.5, 0.63, 0.8, 1.0, 1.25 and 1.6 ms⁻² r.m.s. with a common ratio of ca. 1.25) without and with the support of an upright backrest. Each group had twelve subjects. With an increase in the vibration magnitude from 0.25 to 1.6 ms⁻² r.m.s., the resonance frequency of the vertical apparent mass showed a decreasing trend. This was observed with all three bodyweight groups and two backrest conditions. Results of pairwise Wilcoxon signed-rank tests showed that, when the vibration magnitude increased by a factor of ca. 1.25, its effect on the resonance frequency was statistically insignificant in most cases. The results provided data on the vertical apparent mass for the heavyweight subjects that have not been reported and augmented the database of those for the lightweight subjects.

Suspension seats are widely used in heavy vehicles to reduce vibration transmitted to human body and promote ride comfort. Previous studies have shown that the dynamics of the suspension seat exhibits nonlinear behaviour with changed vibration magnitudes. Despite various linear seat models developed in the past, a nonlinear model of the suspension seat capturing the nonlinear dynamic behaviour of the seat suspension and cushion has not been developed for the prediction of the seat transmissibility. This paper proposes a nonlinear lumped parameter model of the suspension seat to predict the nonlinear dynamic response of the seat. The suspension seat model comprises of a nonlinear suspension submodel integrated with a nonlinear cushion submodel. The parameters of the submodels are determined by minimizing the error between the simulated and the measured transmissibility of the suspension mechanism and the force-deflection curve of the seat cushion, respectively. The model of the complete seat is then validated using the seat transmissibility measured with inert mass under vertical vibration excitation. The results show that the proposed suspension seat model can be used to predict the seat transmissibility with various excitation magnitudes.

Vibration magnitudes and backrest inclination affect apparent masses of the seated human body, yet their interaction remains unexplored. In this study, the in-line fore-aft, lateral, and vertical apparent masses were studied experimentally with a series of vibration magnitudes (0.25, 0.5, and 1.0 ms^-2 r.m.s. in three translational directions, respectively) and backrest inclination angles (0°, 10°, and 20°). The peak modulus of the fore-aft apparent mass at the seat pan first decreased from 0° to 10° and then rose from 10° to 20°. Significant interaction between the two factors was found for fore-aft resonance parameters, which may be attributed to pelvic motion modulated by muscle activities. In contrast, lateral and vertical resonance parameters varied monotonically with backrest inclination and no significant interaction was detected. These findings reveal that the interaction between vibration magnitude and backrest inclination should be considered for accurate fore-aft ride comfort assessment.

Large-reclined seating has emerged as a favored configuration in the luxury transport sector. While the static advantages are evident, the effect of this posture on dynamic comfort is not clear. This study investigated the objective biodynamics and subjective discomfort of the human body sitting in a large-reclined posture (58° from the vertical) under single axis vertical and lateral vibration excitations. The transmissibility of the human–seat system and apparent mass of the human body were measured respectively. The results revealed a critical transition between static and dynamic comfort: while the 58° posture offers superior static relaxation, dynamic discomfort dominates the overall perception when the excitation intensity exceeds a threshold of 0.249 m/s² r.m.s. Objective measurements indicated that dynamic comfort degradation in large-reclined postures is primarily driven by altered inherent biodynamic characteristics. These findings highlight that future luxury vehicle seating must incorporate targeted dynamic isolation to compensate for posture-induced comfort degradation and ensure premium ride quality.

Despite the presence of multi-axis vibration in many vehicles, biodynamic responses of the human body are mostly studied under single-axis conditions. In this study, the fore-aft, lateral, and vertical apparent masses were measured under tri-axis translational excitation with various in-line (“primary-axis”) and cross-axis (“secondary-axes”) magnitudes and backrest inclinations (0°, 10°, and 20°). The softening effect of increasing the primary-axis magnitude was reduced by higher secondary-axes magnitudes, and the effect of secondary-axes magnitudes was similarly attenuated by higher primary-axis magnitudes. With tri-axis vibration, the fore-aft peak modulus at the seat pan first fell, then rose with the increasing backrest inclination as under single-axis conditions, whereas the resonance frequency lost the non-monotonic pattern. Backrest effects on fore-aft and lateral apparent masses were insignificant with single-axis vibration but became significant with tri-axis vibration. These findings suggest that incorporating multi-axis vibration and backrest inclination may improve the accuracy of ride comfort evaluation for realistic driving conditions.

Overall sitting comfort is related to both static pressure distribution and dynamic human–seat interaction during vibration. This study proposes a simplified finite-element model of the seated human body that could potentially be used to assess overall sitting comfort. The static pressures of the seated human body measured on a rigid seat with different footrest layouts, together with the overall and localised apparent masses of the human body measured in a previous study, were used for model validation. The proposed model contained homogeneous soft tissues of the buttocks and thighs and rigid bodies connected to represent the torso. The tissue geometry was adjusted to match the measured anthropometry. Viscoelastic material was assigned to the tissues, and the properties were identified by fitting the modelled pressures and apparent masses to the measurement results. The proposed model was capable of reproducing static pressures and dynamic forces over the seat for the three sitting postures.