Forced Response of SDOF

When there is a driving force acting on SDOF system, the system's vibrating frequency is determined by the driving force frequency and damping ratio. We are mostly interested in the magnitude and phase shift of the response. These characteristics are indicated in the system's Frequency Response Function. When driving frequency is close to the system's natural frequency, forced vibration magnitude is large. When driving frequency is equal to natural frequency, forced vibration reaches its maximum magnitude, this is called resonance. Under resonance, the response's phase shift is 90 degree. The damping ratio also has an effect on FRF. The greater the damping ratio, the less the forced vibration magnitude.

DANIEL J. INMAN, Engineering Vibration, Prentice Hall, Englewood Cliffs, New Jersey,1994