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Virtual Assessment of Occupied Seat Vibration Transmissibility
Abstract:
This paper presents an integrated simulation process which has been performed in order to assess the riding comfort performance of a vehicle seat system virtually.
Present methods of seat comfort design rely on the extensive testing of numerous hardware prototypes. In order to overcome the limitations of this expensive and time-consuming process, and to fasten innovation, simulation-based design has to be used to predict the seat comfort performance very early in the seat design process, leading to a drastic reduction in the number of physical prototypes.
The accurate prediction of the seat transfer function by numerical simulation requires a complete simulation chain, which takes into account the successive stages determining the final seat behaviour when submitted to vibrations.
First the manufacturing stresses inside the cushion, resulting from the trimming process, are computed. Due to the highly non-linear behaviour of the foam material, these stresses modify the behaviour of the foam blocks, when further loaded by the occupant weight.
The pre-stressed seat model is thus used as a starting point to simulate the static seating of a 50th percentile human occupant. This human model includes all body segments, with anatomically precise features such as bones, full spine, ligaments, organs, muscle effects, deformable soft tissues around thighs, hips and trunk. The contact pressure distribution, and the resulting strain and stress distribution throughout the seat, are computed. As the foam dynamic behaviour is highly strain-dependant, the exact strain distribution at the end of the static stage has to be taken into account, to predict a correct behaviour of the foam blocks when further submitted to vibrations.
The resulting, static equilibrium between the seat and the occupant is then used as a starting point to simulate the vibration transmission to the occupant through the seat. A vertical acceleration signal is applied at the basis of the seat. The seat transfer function is computed and compares well with the experimental one.
This integrated simulation process takes into account the detailed seat characteristics and is predictive enough to consider a virtual seat design process for occupied seat vibration transmissibility. This predictiveness will have to be confirmed with other seats analysis.
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