Some Type of Forced Oscillation

Abstract

An analysis was made on the character of a forced oscillation of a linear vibration system excited by force with periodically altering amplitude and frequency. The results are as follows. (1) The frequency of this type of forced oscillation is always equal to the natural frequency of the vibration system, even if the mean frequency of the exciting force is not equal to it. (2) In the ordinary linear vibration, the maximum value of magnification factor exists on the resonant frequency, but in this type of forced oscillation it is situated at an frequency lower than resonance. (3) The maximum value of magnification factor of this forced oscillation is equal to 50∼60 per cent of the linear vibration. This theory was applied to the vibration of steel stack induced by the wind, and the results were shown in the paper.