|Title:||A new design of rotational hybrid vibration absorber for global structural vibration control|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Damping (Mechanics) -- Testing
|Department:||Department of Mechanical Engineering|
|Pages:||xii, 137 p. : ill. ; 30 cm.|
|Abstract:||In this project, an analytical model of rotational hybrid vibration absorber (RHVA), which is coupled with a flexible structure, is derived for controller design and vibration suppression. Unlike the case of translational HVA, it is easier to tune the passive absorption frequency of the rotational HVA. A novel controller, which is applicable to either rotational HVA or translational HVA, is developed on the basis of the pole placement method. The proposed controller introduces active damping to a flexible structure and attenuates vibration of the entire structure. This controller, hereinafter, is called a global structural vibration controller. The proposed rotational HVA and the global structural vibration controller was coupled to the end position of a cantilever beam for global structural vibration control in simulation tests, when random disturbance was applied at either a single point or a portion of the beam structure. Two indices, which are used to quantify the structural vibration motion, were calculated from the numerical test results. They include mean square motion which can be used to observe vibration motion at a single point, and spatial average mean square motion which can be used to observe average vibration motion of the beam structure. Simulation results demonstrate that the rotational HVA can mitigate more than 85% of mean square motion at the coupling point and more than 85% of spatial average mean square motion along the entire beam structure. This indicates that a rotational HVA can significantly suppress both point and entire beam structural vibration simultaneously. Groundhook damper and translational HVA, which are conventional devices used for structural vibration control, were also coupled with the same cantilever beam at the end position for global structural vibration control in separated simulation tests. Numerical results show that a groundhook damper and a translational HVA can alleviate more than 83% and more than 79% of mean square motions at their respective coupling points, and can alleviate more than 85% and more than 80% of spatial average mean square motions along the entire beam structure respectively. This signifies that a rotational HVA could provide better vibration attenuation ability than a translational HVA in global structural vibration control and similar vibration attenuation performance as a groundhook damper. Experimental rotational HVA and beam structure were fabricated to verify the proposed controller. The proposed analytical model of the rotational HVA and the global structural vibration controller were validated by the experimental results. Mean square motions and spatial average mean square motions were calculated from the experimental results and compared with those values calculated from the numerical results. It was found that experimental results are reasonably close to the numerical results. This investigation provides better understanding on the performance and design of a rotational HVA and its active controller. Numerical results clearly demonstrate that a rotational HVA itself can be an effective device and is feasible as a better alternative device to a groundhook damper or a translational HVA for global structural vibration control of a cantilever structure.|
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