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The vibration characteristics of car seats directly influence the ride comfort. Polyurethane foam is the key part of a seat, and its physical parameters have an important impact on the seat. In this study, the influence of the foam thickness and foam hardness on the vibration characteristics of seat cushion with different excitation magnitudes was investigated by using transmissibility and seat effective amplitude transmissibility (SEAT) value. First, vibration tests were carried out at a vertical vibration simulator with width-limited white noise vibration frequencies from 0.5 to 20 Hz with root-mean-square (r.m.s.) values of 0.4, 0.8, and 1.2 m/s2, the acceleration at the platform and the body-foam interfaces were measured to calculate the transmissibility, and the influence of the foam physical properties on the transmissibility was analyzed. Then, the SEAT value was introduced to assess the vibration isolation efficiency of the foam cushion, and the influence of the foam physical properties of the foam cushion on the vibration isolation efficiency was analyzed. With increasing thickness of the foam and decreasing hardness of the foam at the seat pan, the peak transmissibility increased and the resonance frequency decreased. The SEAT values show that increasing the foam thickness is beneficial to the improvement of the vibration isolation efficiency of the seat, but there is a diminishing return; the combination of physical parameters of low hardness and high thickness could make the vibration isolation performance of the seat better. In addition, the nonlinearity of human-seat system during different vibration magnitude was found. [ABSTRACT FROM AUTHOR]

Biodynamic modelling of seat-occupant systems can assist in seat comfort design. A finite element (FE) model of the seated human body, including detailed modelling of the lumbar spine, was established to reflect the human response to vibration and biodynamic response of the lumbar spine under whole-body vibration (WBV). The lumbar spine model was established and validated against the in-vitro results and calculated data. The posture of the lumbar spine was adjusted according to the radiological research results, and the adjusted model was combined to establish a FE model of the seated human body. The present seated human model with backrest inclination angles of 10, 20, and 30°, validated by comparing the measured apparent mass and seat-to-lumbar spine transmissibility, was used to calculate the biodynamic response of the lumbar spine with three inclined backrests under WBV. The results showed that the model could characterise the apparent mass, seat-to-lumbar spine transmissibility, and the biodynamic response of the lumbar spine. Practitioner summary: Biodynamic models can represent dynamic characteristics of the human body exposed to vibration and assist in seat comfort design. The three-dimensional FE model of the human body can be used to explore the human response to vibration and the biodynamic response of the lumbar spine under WBV. [ABSTRACT FROM AUTHOR]

Pressure distribution has been regarded as a crucial parameter for static comfort evaluation of the seated human body. However, the association between the pressure distribution and subjective rating, exposed to vertical vibration, is still unclear. This study devotes to characterizing the vibration discomfort of the seated human body on a foam seat using dynamic body pressure distribution and investigating the associations between them. First, the dynamic body pressure of twelve subjects seated on a foam seat exposed to vertical random excitation was measured at frequencies from 0.5 to 20 Hz with six magnitudes (0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 m/s2 r.m.s.). Meanwhile, the subjective discomfort rating of the foam seat was evaluated with the relative magnitude estimation method. Then, the influence of vibration magnitude on subjective discomfort ratings and dynamic body pressure indicators was investigated. The results show that with the increase of vibration magnitude, the mean average dynamic pressure, the mean peak dynamic pressure, the mean dynamic contact area, and the normal dynamic force had no significant change. On the contrary, the subjective discomfort ratings, normal dynamic force change rate root-mean-square, and the indicators related to pressure change rate root-mean-square increased significantly. Finally, the relation between the subjective discomfort ratings and dynamic body pressure indicators was analyzed using Stevens' power law. The linear regression fitting accuracy of the average dynamic pressure change rate root-mean-square, peak dynamic pressure change rate root-mean-square, area pressure change rate root-mean-square, and normal dynamic force change rate root-mean-square with discomfort ratings were above 95%. The four dynamic body pressure indicators are highly correlated with the subjective discomfort ratings, which can be used as objective indicators for vibration discomfort evaluation. Graphical Abstract [ABSTRACT FROM AUTHOR]