A comparison study is conducted to evaluate the performance of shear and flow mode magnetorheological energy absorbers (MREAs) for a semi-active seat suspension system. The design methodologies for both flow mode and shear mode MREAs are presented. To validate the analytical results, both flow-mode and shear-mode MREAs are developed and their performance such as yield force and viscous damping as a function of the velocity, is experimentally evaluated. It is shown that the off-state force (viscous force) of the shear mode MREA is only a linear function of the damper velocity and, in comparison, the viscous force of typical flow mode damper increases sharply as the damper velocity increases. Using the validated design methodologies, flow-mode and shear-mode MREAs are designed for a crashworthy helicopter crew seat, and resulting metrics such as the size and weight of the flow- and shear-mode MREAs are developed as a function of damper performance requirements, i.e. maximum yield force, viscous damping and maximum stroke.
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