For the performance analysis of vibration isolation system, the concept of vibration power flow can be employed especially when the structure borne noise from the supporting structure is of interest. Although the formulas for estimation of the power flow are rather easy to derive, it is customary to simplify the process of experimentation under certain assumptions due to instrumental limitations. For example, the rotational degree of freedom is not well treated in bending vibrations of beam or plate-like structures. Several recent studies showed that the moments and rotations play an important role in power transmission and should generally be considered in vibration isolation analyses as the frequency range of interest goes to high. Therefore, it is readily believed that reduction of the noise radiation over high frequency range can be effectively accomplished by decrease of the rotational vibration power transmission.
In this paper, by modifying rotational stiffness of isolators, it is made an attempt to reduce vibration power transmitted through connecting points between source and receiver. The vibration power flow approach is applied to an A.C motor installed on a finite plate in order to illustrate the contributions of the rotational vibration power to the total vibration power transmission practically. In addition, the effects of rotational stiffness of the isolator to the rotational vibration power transmission are investigated by inserting the various isolators with different rotational stiffness between the motor and the plate. Furthermore, it is shown that it needs to design isolator shape considering the effects of rotational stiffness to improve vibration isolation and reduction of noise radiation as the frequency range of interest increases.
