Development of a human body FE model for occupied seat vibration and comfort

Developing a vehicle seat with a minimum transmission of vibration to the occupant has been one of main focuses for seat manufacturers to deliver an optimum level of ride comfort to vehicle occupants. Predicting vibration transmissibility of the occupant-seat system involves investigating vibration characteristics of the dynamically coupled seated-occupant and the seat in which both individual systems are complex with nonlinear behaviours. To develop a vehicle seat with optimum vibration comfort in the early stage of seat design, it is required to have a reliable biodynamic model which can assess the vibration transmissibility of the occupant-seat system. This thesis investigates the coupled characteristics of the occupant-seat system to develop a human body FE (Finite Element) model for improved prediction of vibration transmissibility. The two most important contribution made in this thesis are: Firstly, vibration characteristics of the coupled occupant-seat system are verified in the frequency range up to 80 Hz, and secondly based on the characteristics observed, a seated human body FE model representing an occupant in a vehicle seat was developed. Major coupling of combined occupant and vehicle seat structure was observed in the frequency range of 10-60 Hz mainly due to dominant seat structural resonances. The low-order (simplified) human body FE model was developed implementing techniques of both Finite Element modelling and multi-body dynamics modelling methods. Additionally, the low-order human model provided an improved computational efficiency with a reliable accuracy. The developed human body model was validated with two different vehicle seats in which individually combined occupant-seat models were compared with the experimental results in terms of FRF (Frequency Response Function) and major vibration mode shapes. The validation of the model with the measured data demonstrates the feasibility of implementing the developed human body model on developing a vehicle seat with optimized occupied-seat vibration in the early stage of seat design