Multi-body modelling and ride comfort analysis of a seated occupant under whole-body vibration

Seated occupants of any on/off-road vehicle are continuously exposed to undue low-frequency mechanical whole-body vibration (WBV) owing to the vibration conveyed from seat and backrest because occupants need to compromise with comfort and safety, leading to several musculoskeletal disorders and injuries in the body. Pain in the lumbar region is one of the most common problems that develop because of force transmitted from the backrest. Thus, consideration of backrest is highly essential while developing a biomechanical model for ride comfort analysis. For this purpose, a 20 degrees-of-freedom (dofs) biomechanical model has been proposed with a backrest to analyse cross-coupled segmental transmissibility. The interconnection between different segments of mass and backrest are modelled using eight linearized (direct as well as cross-coupled) stiffness and damping parameters. Biomechanical model parameters are estimated and optimized through a multi-objective firefly algorithm by minimizing the sum of squares error difference between analytical results and experimental segmental transmissibility published in the literature. Subsequently, ride comfort analysis is performed by integrating the proposed model with 7-dofs passenger car model. For different body segments, simulated results are obtained in terms of vertical accelerations and compared with ride comfort standards as per ISO 2631-1:1997. Additionally, a sensitivity analysis (+/- 20% variation in mass, stiffness and damping) is performed to enhance the ride comfort of the occupant. The findings suggest that designers must focus on the pelvis, lower and upper back regions to improve the ride comfort of the occupants. The concepts and ideas outlined in this article are directly applicable in making human dummies, car suspension and seat design in the industry.