| Damping enhancement and disturbance force isolation are two important issues of structural vibration control. When a lightly damped structure has some closely spaced very low frequency modes and is also subject to some persistent periodic disturbance forces, especially when required vibration suppressions are very stringent, the related vibration control will be a very challenging task. Traditionally, robust stability and robust performance always need certain trade-off if there are large model uncertainties. In this dissertation, an active dynamic absorber (ADA) approach was proposed to deal with above problems. Three different ADA controller models were developed in which velocity measurements are not required. The connections between ADA and passive dynamic absorber were established and three basic properties of ADA (Band Modal Control, Arbitrary Assignable Transmission Zeros, and Multi-ADA Control Effort) were proved. To increase structural damping, the absorber behaviors of ADA internal parameters were studied in detail and an effective multivariable optimal design algorithm of ADA parameters was established. To control rigid body modes, it was showed that certain ADA with zero frequency and zero damping can turn all rigid body modes into oscillating modes and this is equivalent to the direct displacement output feedback control. To isolate periodic disturbance forces at the regulated locations, multivariable transmission zero theory was used to develop general nonlinear programming formulations for determining ADA internal parameters towards maximal isolation. Some relating problems, including ADA gain effect, ADA damping effect, and ADA frequency sensitivity, were also investigated. For some practical considerations, several important ADA synthesis issues were addressed and the effects of sensor noise and sensor bias were also discussed. Finally the numerical simulation was performed about NASA CSI testbed structure which successfully demonstrated the effectiveness of ADA approach in achieving both robust stability and robust performance. |
