  To understand the dynamo driven by time-dependent flow, e.g. turbulence, we
investigate numerically the dynamo induced by time-periodic force in rotating
magnetohydrodynamic flow and focus on the effect of force frequency on the
dynamo action. It is found that the dynamo action depends on the force
frequency. When the force frequency is near resonance the force can drive
dynamo but when it is far away from resonance dynamo fails. In the frequency
range near resonance to support dynamo, the force frequency at resonance
induces a weak magnetic field and magnetic energy increases as the force
frequency deviates from the resonant frequency. This is opposite to the
intuition that a strong flow at resonance will induce a strong field. It is
because magnetic field nonlinearly couples with fluid flow in the
self-sustained dynamo and changes the resonance of driving force and inertial
wave.
