Modeling and experiments of Force-Frequency Shifting with stationary active components

Force Frequency Shifting (FFS) has been developed for low frequency (less that 1 Hz) vibration excitation of large structures (i.e., buildings, bridges, stadiums, ballroom floors, etc.). Initial implementation of the method applied a time variant force to the test structure in a spatially varying fashion. More recent work has demonstrated that low frequency excitation performance gains may be realized through the use of carefully placed stationary components with controllable time variant damping and/or stiffness. This work will present the modeling and experimental results from a subscale laboratory test bed for one such implementation configuration. The FFS design uses a hinged beam supported by an active magneto-rheological damper. A system model is developed and numerically solved in Matlab-Simulink. A subscale hardware prototype of the configuration was designed and constructed. The prototype was instrumented to capture the important component forces, motions and operational parameters. A comprehensive set of experiments was performed and the results compared to the model. The comparison demonstrated that the model was capable of accurately capturing the Force Frequency Shifting phenomena. Further evaluation of the correlated model provides insight into the hardware requirements for a FFS shaker design with active elements that would be suitable for the target structures.