Vibration control of a local zone without changing the current vibration state of the other zones

In the active control of structural vibration, the vibration amplitude of a designated zone or the transmitted force amplitude through a joint is usually suppressed. The condition of the uninterested zone in the end result is often neglected or only checked with a criterion whether the control result satisfies the constraint specifying a maximum allowed amplitude or not. However, when the purpose of vibration control is to reduce the radiated sound field effectively, in particular for the structure-borne interior noise, the change of the whole vibration field due to the control action of the augmented actuators does not always assure an effective achievement of the desired sound field. In this work, the control strategy is that the vibration at a specific localized zone is to be nullified, while the vibration magnitude and phase at the other outside zone are kept unchanged as before. A thin beam with a large amplitude of vibration at a local zone is adopted as a simple test example. Two different actuator layouts are separately used for realizing the control purpose. First, the single array composed of two actuators is located just outside the interested zone to nullify the vibration. Second, four actuators are employed in using the double array system: two actuators encompass the target zone as like the single array, and the other two are slightly separated from the inner actuators toward the uninterested zone. The function of the outer actuator set is devised to cancel the propagating energy, which is generated from the inner actuator array, toward the uninterested zone. Experimental result at 200 Hz with a given spatial distribution of vibration characteristics shows that the reduction of vibration in the interested zone is about 14 dB in both array layouts. However, the velocity amplitude outside the target range controlled by single and double array is 118% and 13% of the original amplitude, respectively. The change of average phase is found to be 0.23 rad and 0.1 rad, respectively.