Excitations of oscillations in loaded systems with internal degrees of freedom

We show that oscillations are excited in a complex system under the influence of the external force, if the parameters of the system experience rapid change due to the changes in its internal structure. This excitation is collision-like and does not require any phase coherence or periodicity. The change of the internal structure may be achieved by other means which may require much lower energy expenses. The mechanism suggests control over switching oscillations on and off and may be of practical use.