An optimal actuator placement methodology for active control of helicopterairframe vibrations

Active control of helicopter vibrations, with actuators in the airframe str ucture,, is appealing in terms of simplicity, airworthiness, and effectiven ess. The actuator locations of current active control systems are centrally located in the cabin or near the main rotor. A new actuator placement meth odology is proposed and explored in this research. The approach uses an opt imization process to distribute a set of actuators at optimal locations thr oughout the airframe. A reduced-order airframe dynamic model is utilized fo r the design methodology synthesis and system analysis. Oscillatory loads a t the main rotor hub and at the horizontal tail surface excite the airframe model. Actuation loads are integrated with the airframe dynamic model. A h ybrid optimization methodology is formulated to simultaneously determine op timal actuator placement and control actions. The optimization process coup les an optimal control formulation with a Simulated Annealing optimization routine. An analytical study is performed comparing optimally distributed a ctuator configurations to a representative state-of-the-art centralized act uator configuration. It is shown that actuators in the airframe can more ef fectively control some of the dominant airframe modes, rather than actuator s centralized near the main rotor support assembly. When compared to a repr esentative state-of-the-art centralized control configuration, the distribu ted actuator configuration can achieve significantly greater vibration redu ction with less control effort. One of the case studies shows that the cent ralized actuator configuration reduces vibration by 49% (below 0.07 g); how ever, the optimally distributed actuator configuration reduces vibration by 90% (below 0.03 g) and requires 50% less control effort The proposed desig n methodology that simultaneously determines actuator placement and the ass ociated control action is extremely beneficial to reduce vibration and cont rol effort.