MODELING THE CONTACT PROBLEMS OF THE HUMAN BODY/SEAT INTERFACE IN A VIBRATION AREA

The Contact pressure distribution throughout the contact interface has a vital role on biological aspects of the contact systems. Generally, contact of deformable bodies is a nonlinear problem. Viscoelastic materials have a time-dependent response, since both viscous and elastic characteristics depend on time. Such types of materials have the capability of storing and dissipating energy. When at least one of the contacting bodies is made of a viscoelastic material, the contact problems become more difficult, and a nonlinear time-dependent contact problem is obtained. The vibration area is a common artificial surrounding with which humans have a limited tolerance to deal effectively with due to their body dynamics. This research numerically studied dynamic contact characteristics of a seated human body/seat system in a vibration area. The main result is a multi degrees of freedom lumped parameter model that synthesizes two basic dynamics: (I) global human dynamics, apparent mass phenomenon, including a systematic set of model parameters simulating various conditions like body posture, backrest, footrest, muscle tension, and vibration directions, and (II) local human dynamics, represented by the human pelvis/vibrating seat contact, using a cushioning interface. The model provided a numerical tool for human body dynamics research. It also enabled a primary tool for the seat and cushioning design. The model was further used to develop the design guidelines for a composite cushion using the principle of quasi-uniform body/seat contact force distribution.