An adaptive tuned vibration absorber (ATVA) can be used to suppress unwanted vibrations. If the excitation frequency is time harmonic but the frequency changes with time, it is desirable to retune the ATVA so that the natural frequency of the ATVA always coincides with the excitation frequency. One way of achieving this is to adjust the stiffness of the ATVA. The key challenge is to change the stiffness in real-time. Tunable fluids such as Magneto-Rheological (MR) fluids, whose properties can be controlled by a magnetic field, may be used to address this challenge. The subject of this thesis is an ATVA exploiting the changeable properties of MR fluids in the pre-yield state. The ATVA is designed as a three-layer beam with elastic face plates and MR fluuid in the core. Electromagnets are attached to the top and the bottom layers to generate a magnetic field. By varying the current supplied to the electromagnets, the shear stiffness of the MR fluid and hence the stiffness of the ATVA can be varied. The vibration characteristics of the ATVA as a function of the magnetic field strength are predicted by a finite element model together with an empirical model for the shear modulus of the MR fluid and a model for the magnetic field applied to the fluid. An MR fluid-filled ATVA was manufactured and tested to validate the predictions. This ATVA design allows the natural frequency to be changed by 40.6%. The self-tuning of the MR fluid-filled ATVA can be achieved by integrating an adaptive-passive controller with the ATVA so that its stiffness can be continuously adjusted in real-time. The control aims to drive the cosine of phase angle between the velocities of the host structure and the ATVA to zero. Various control algorithms, i.e. non-linear proportional, derivative, and proportional-plus-derivative controls, are investigated. Computer simulations and experimental results demonstrate that the MR fluid-filled ATVA is able to retune itself in the order of 0.2 seconds. The ATVA can also maintain the tuned condition within a reasonably wide frequency range between 110 and 146 Hz in the face of changes in the forcing frequency. The MR fluid-filled ATVA has the potential to substantially reduce vibration of a host structure. The proportional-plus-derivative control was found to be the best control approach for the ATVA.
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