During vertical or fore-and-aft vibrations of a seated human body, the motion of the head is influenced by backrest forces transmitted to the lumbar region of the spine. Thus, it is essential to consider backrest support while developing a human body model to capture direct and cross-axis seat to head transmissibility. For this purpose, twelve degrees of freedom seated human body model of the appropriate level of complexity with inclined backrest support has been developed in this work. The interconnection of masses is modelled using rotational and translational springs-dampers and the contact with an inclined backrest gives a better simulation of forces transmitted to the lower torso in the x-z direction. The model parameters were identified and optimized using a multi-objective genetic algorithm by minimizing the least square difference between experimental head motion and analytical results. Subsequently, a sensitivity study was carried out to find the effect of model parameters on the peak transmissibility modulus and resonant frequency. This will help in refining the design of the seat and backrest for improving comfort. Modal analysis was carried out for an improved understanding of the relative motion of different sections. Power absorbed at different locations of the human body was studied to identify regions susceptible to long term damage. Internal forces in the neck region were also determined and these can be used to characterize the neck pain due to prolonged exposure to such vibrations. The research work reported in this work offers an in-depth understanding of biodynamic responses of backrest supported human body subjected to vertical/horizontal vibrations. We expect it to offer vehicle designers some insights to control human body parameters (acceleration/forces /moments/power absorbed/modal displacements/lower back pain) and design appropriate restraints-supports for improved comfort.

No abstract

No abstract

No abstract

Long duration exposure to vehicle induced vibration causes various ailments to humans. Amongst the various components of the human-vehicle system, the seat suspension plays a major role in determining the level of vibration transferred to humans. However, optimising the suspension for maximising human comfort leads to poor vehicle handling characteristics. Thus, predicting human comfort through various seat suspension models is a widely researched topic. However, the appropriate seat suspension model to be used has not been identified so far. Neither has any prior work reported integrating models of all the components necessary for this analysis, namely human body, cushion, seat suspension and vehicle chassis, each with the appropriate level of complexity. This work uses a two-dimensional 12 DoF seated human body model with inclined backrest support, a nonlinear cushion model, a seat suspension model and a full vehicle model. Two kinds of road profiles – one with random roughness and one with a bump – have been used. It then compares the performance of five different seat suspension models based on a number of human comfort related parameters (seat to head transmissibility, suspension travel, seat acceleration, cushion contact force and head acceleration in both vertical and fore-aft directions) and vehicle handling parameters (vertical, rolling and pitching acceleration of chassis). The results clearly show the superiority of the configuration which involves a spring parallel to an inclined multi-stage damper. A separate analysis was also done to judge whether the integration of the vehicle model (with its associated complication) was necessary for this analysis. A comparison of the human body’s internal forces, moments, acceleration, and absorbed power with and without the vehicle model clearly indicates the need of using the former.