Planar whole-body vibratory response of a nonlinear multi-body model of a seat-occupant system with polyurethane foam
Abstract
Vehicle occupants are exposed to low frequency vibrations, which can have harmful health effects such as mild discomfort, lower back pain, and even injury to the spine. The transmission of vibration to seated occupants can be minimized by appropriately designed automotive seats. Thus, the modeling and prediction of dynamic response of seated humans to these low frequency vibrations is important for understanding the dynamics of the seat-occupant system, and also because a reliable model can serve as a tool for optimization of seat design. Since the properties of the seating foam affect the response of the occupant, there is a need for good models of foam and seat-occupant systems through which the effects of foam properties on the dynamic response can be directly evaluated. In this research, a nonlinear multi-body seat-occupant model which incorporates the nonlinear viscoelastic behavior of flexible polyurethane foam, has been developed for planar motions. This model is a comprehensive model as it includes the profiles of the seat and occupant, a simple model for the interfacial forces and a model for foot-rail friction. This model is used to study the dynamic response of the occupant to harmonic excitation applied at the base of the seat, in terms of the frequency response in the vertical and fore-and-aft directions, the deflection shapes of the occupants, the seat-to-head transmissibility and the apparent mass. The model is further refined and a flexible seat back is introduced to study the effect of this on the response of the seat-occupant system. To better understand the role of nonlinear viscoelastic properties of seating foam in characterizing the system behavior, the response of a single-degree-of-freedom foam-mass system to harmonic and random base excitation is also examined. By varying the masses supported by the foam block in the foam-mass system, the nonlinear properties of foam can be exercised. Dynamic response near resonance in such a foam-mass system, when subjected to vertical acceleration at different acceleration levels, is also investigated. The dynamic response of the foam-mass system as well as that of the seat-occupant system is evaluated for two different foam blocks representing distinct nonlinear characteristics.
Degree
M.S.M.E.
Advisors
Davies, Purdue University.
Subject Area
Mechanical engineering
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