Compact Magnetorheological Energy Absorbers for Adaptive Crew Seat Suspensions
Becnel, Andrew C.
Hiemenz, Gregory J.
Wereley, Norman M.
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With an eye toward the broad range of operational dynamic environments required for manned spacecraft, the research in this work presents a novel shock and vibration isolation system incorporating semi-active magnetorheological fluid (MRF) energy absorbers for crew protection. MRFs are suspensions of magnetizable particles in a carrier fluid that exhibit a magnetic field-controllable apparent viscosity and change from a liquid to a solid along a continuous profile. By incorporating MRFs in energy absorbing devices, the effective damping of a crew seat system can be automatically tuned to account for different occupant weights or g levels. This allows the system to attenuate whole body vibration across a wider frequency range than passive dampers, which are only designed for a single operating condition. However, like passive energy absorbers, being fluid-based means that the MR energy absorbers are inherently fail-safe, and unlike alternative active energy absorbing devices they maintain a baseline damping ability even in the event of a power system failure. Additionally, when combined with a simple closed-loop feedback control system, the MR energy absorber can instantaneously generate the optimal load-stroke profile for an applied impact shock load, dissipating the maximum amount of energy between the vehicle and the crew seat, minimizing injury to the occupant. Weight and size constraints have made the application of MR energy absorbers to aerospace vehicles challenging, but by utilizing a hybrid mode of operation the specific energy absorption density (or the amount of energy absorbed per MRF volume) can be increased significantly. This research details the development of such a device, and highlights the potential application to acceleration, vibration, and impact attenuation systems designed to mitigate the dynamic flight event effects on crew members.