Vibration on a Helicopter and Design of Magnetostrictive Electric Generators
The study toward the design of a magnetostrictive generator for vibration-to-electrical energy conversion in helicopter is presented in this report. Terfenol-D, a giant magnetostrictive material is used. A brief overview of magnetostriction including Terfenol-D properties is given. The generator uses vibrations as input. These vibrations are studied for different possible locations in helicopter. The main and tail rotors are the principal origins of vibrations in a helicopter. Currently, lead-lag dampers are used between the rotor and the rotor blades to damp vibrations. The proposal is to replace these dampers by a magnetostrictive generator to damp and produce electrical power simultaneously. The third location studied is between the pylon and the airframe. The generator could be put between the gearbox and the airframe instead of the existing rigid struts. Forces, amplitudes, vibration frequencies and mechanical power have been evaluated at each location. This study reveals that a damping system is always necessary in order to preserve the active material (Terfenol-D rod) of the transducer. The damping system adapts the input vibration level to the Terfenol-D rod properties. In all three locations the force and strain amplitude have to be adjusted. Thereafter an energy analysis is utilized to select the best location. Maximizing the mechanical power absorbed by the Terfenol-D, the magnetostrictive generator will produce the highest electrical power. It was demonstrated that the location between the pylon and the airframe is the best with respect to available mechanical power to be transformed to the electrical power.
Finally, the Terfenol-D is considered as a tunable passive vibration absorber. In this case, the priority is to absorb all the vibration and not maximize the electrical power.