Active Vibration Control of Aerospace Structural Systems for Specified Damping

Active vibration control is essential in several aerospace structural systems, such as large space structures, twin tailed high performance aircraft operating at high angles of attack and helicopters. Goh and Caughey did show that vibration controller designs can significantly benefit from the use of second order systems, in the controller design. In this paper, the subject of the design of active vibration control of buffet induced vibrations in high performance twin tailed aircraft is discussed using a combination of acceleration feedback and positive position feedback in second order systems. The goal is to design controllers to increase the closed loop damping ratio of the structural dynamic system to a specified level that would reduce the vibrations to the required level within a time frame of interest. The approach of Fanson and Caughey needed an iterative approach to design the controller parameters. They had more unknowns and fewer equations. In this paper, the problem is now formulated differently to obtain closed form solutions. This is accomplished by developing a procedure to design second order controllers to obtain the desired closed loop damping while maintaining the stability of the closed loop structural dynamic system. The design procedure starts with an objective to design control parameters that result in coincident closed loop frequencies for each mode. This is followed by a perturbation procedure to seek optimum solutions. The design procedure also yields the needed control authority that should be provided by actuators on the structure. An option to obtain the needed control authority by using offset piezoceramic stack actuator assemblies are discussed. The designed controllers are applied to control buffet induced vibrations of a high-performance aircraft at high angles of attack. This example also illustrates the control authority of the offset piezoceramic stack structural assembly.