Optimization of circular force generator placement for rotorcraft hub force and moment cancellation

High-speed forward flight in helicopters causes high vibratory loads at the rotor hub, which are transmitted into the fuselage. This results in pilot fatigue and highmaintenance requirements. Antivibration devices or vibration absorbers may be placed near the hub to reduce vibration transmission, whereas active vibration control systems may typically sense and reduce forces in specific areas of the fuselage. This paper focuses on developing strategies for optimal deployment (sizing, placement, and control) of circular force generators (CFGs) for vibration cancellation. Particle swarm optimization was used to carry out the optimization for two different load cases corresponding to different flight conditions. Converged solutions for CFG placement were obtained for different individual load cases, multiple-load cases, constrained and unconstrained actuator locations, and different numbers of actuators. Two CFGs were found to be sufficient to cancel hub loads for a single-load case. When two load cases are considered in multiobjective optimization, three actuators can substantially cancel the hub loads (to within 1%). Using four actuators can cancel the hub loads to within 0.1%. Finally, performance under actuator failure was considered as a way to distinguish among otherwise similarly performing placement solutions.