Prevention of Torsional Vibration in Fan Motor Shaft Systems with Multiblade Fans : 2nd Report, Effect of Making the Shaft System Symmetrical on Vibration Reduction

Abstract

A thyristor-controlled multiblade fan motor generates noise from fans when torsional vibrations in its shaft system resonate with the pulsation torque of the fan motor. The autors analyzed the conditions that are necessary for avoiding torsional resonance in a shaft system with multiblade fans at both ends of the shaft, and examined the effect of making a shaft system symmetrical on vibration reduction. It was found that the number of resonant frequencies of a shaft system could be reduced from six to two by this method. The applicability of this method of making a shaft system symmetrical was also investigated with respect to practical shaft systems.