When a mechanical system having vibratory source is placed to a structure, vibrating force is transmitted and generating structure borne noise and vibration. Vibrational power transmission is an important concept to deal with this structure borne noise and vibration problem. The concept of vibrational power transmission is related with both the force and velocity of exciter and receiver. That means energy, transmitted through the coupling points, depends on the properties of exciter, receiver and isolator.
To reduce structure borne noise and vibration, its vibrational power inflow from exciter to receiver should be reduced. In this thesis, using the concept of structural dynamic modification, vibrational power transmitting through connecting points of exciter and receiver is attempted to reduce. Two kinds of indexes are introduced to find a optimal point of structural dynamic modification. Those are Power Reduction Index which is the ratio of vibrational input power between pre- and post-modified receiver and Band Power Reduction Index which is the ratio of average of vibratonal input power within the interesting frequency band between pre- and post-modified receiver. The former index is used to find frequency band in which vibrational input power is reduced and the later is applied to find optimal structural dynamic modified point where the average vibrational input power becomes a minimum value. The properties of the two indexes are examined by simulation works. Using a practical experimental setup which has a d.c.motor and a plate structure, the predicted vibrational power variations are verified according to the structural dynamic modification of receiving structure. Finally in order to certify how much modification is effective in the receiving structure, its vibration level is measured and compared.
