Vibration reduction method using passive control of wave propagation by a neutralizer

On recent machine structures, the size of subsystems is far smaller than the whole structure. Therefore, the compliance of a subsystem is dominated by a rigid body mode at the frequency of interest. In case like this, even if degrees of freedom at the connection are multiple, few degrees of freedom of transmission forces dominate the resonance of a whole structure. Therefore, countermeasure based on existence of one or two dominant degrees of freedom of transmission forces is effective. Then, in this study, a design method in case that a single degree of freedom transmission force is dominant, is organized. A countermeasure method for vibration and noise of a whole structure using FRF based sub-structuring and a neutralizer is proposed. As an original viewpoint of this study, with a restriction that only subsystems can be structurally modified, it is an approach at subsystems only, for reducing vibration of a whole structure at a single target frequency. FRF based sub-structuring is adopted to identify coupling characteristics of two rigidly coupled systems. Neutralizer is adopted to set up virtual fixing end at a transmission path on subsystems, to realize perfect reflection of wave motion at the path. As a result, vibration transmission and wave propagation from an exciting degree of freedom on a subsystem to an evaluating degree of freedom on a whole structure at a target frequency is theoretically zero. There were some worries to occur resonance on the whole system as abuses of the proposed method, but assuming that there is some damping at whole structure, the method proved to be effective on any whole structure.