Optimal Occupant Protection Using Vertically Stroking Seat Suspensions with Magnetorheological Energy Absorbers

The study addresses optimal biodynamic response mitigation of a seated occupant exposed to a shock caused by an impact of a helicopter with the ground. The vertically stroking seat suspension employing an adaptive magnetorheological energy absorber (MREA) with a controllable load-stroke profile was analyzed for the minimization of biodynamic loads transferred to the occupant. The mathematical model of MREA was based on Bingham-plastic model with quadratic pressure losses characterized by Reynolds number. The controllability envelope of the MREA was optimized using design optimization based techniques to mitigate shocks corresponding to sink rates ranging from 5 to 12.8 m/s. The design variables involved with the optimization formulation defined the MREA geometry. Constraints were determined on the basis of permissible viscous force threshold and magnetic properties of fluid. A multiple degree-of-freedom nonlinear biodynamic lumped parameter model (BLPM) was considered for occupants varying from 5th percentile female to 95th percentile male. MREA with an optimized controllability envelope was integrated with the BLPM and the governing equations of motion were investigated theoretically. The variation of controllable MREA yield force with respect to the energy absorber stroke was optimized with the goal of minimizing biodynamic decelerations. Limited MREA stroke, yield force and total MREA stroking load established the constraints involved in the biodynamic response optimization. The MREA yield force and energy absorber stroke were the most crucial parameters for improved biodynamic response mitigation to shock loads. An assessment of potential of injury based on established injury criteria reflected that desired level of occupant protection was maintained by optimally controlling the MREA. In addition, the injury criteria was not violated for different body parts even for minor injury levels subjected to range of shocks under consideration.