ENGINEERING FEASIBILITY OF INDUCED STRAIN ACTUATORS FOR ROTOR BLADE ACTIVE VIBRATION CONTROL

Rotor blade vibration reduction based on Higher Harmonic Control-Individual Blade Control (HHC-IBC) principles is presented as a possible area of application of Induced Strain Actuation (ISA). Recent theoretical and experimental work on achieving HHC-IBC through conventional and ISA means is reviewed. Though the force-displacement and power-energy estimates vary significantly, some common-base values are identified. Hence, a bench-mark specification for a tentative HHC-IBC device based on the aerodynamic servo-flap principle operated through ISA means is developed. Values for the invariant quantities of energy, power and force-displacement product are identified, along with actual displacement and force values of practical interest. The implementation feasibility of this specification into an actual ISA device is then discussed. It is shown that direct actuation is not feasible due to the large required length of the ISA device, resulting in excessive compressibility effects (displacement loss and parasitic strain energy). Indirect actuation through a displacement amplifier was found to be more feasible, since it allows for matching of internal and external stiffness. A closed form formula was developed for finding the optimal amplification gain for each required value of the closed-loop amplification ratio. Preliminary studies based on force, stroke, energy and output power requirements show that available ISA stacks coupled with an optimally designed displacement amplifier might meet the bench-mark specifications.