In the last case the main effect is connected with the energy dissipation in the additional friction element occurring as soon as the vibrations' amplitude exceeds the threshold of the sticking. Thus the damping effect can be used selectively. The sequential friction-spring element remains locked up as long as the vibrations are sufficiently small. Hence no energy is dissipated under these circumstances. The additional spring can be chosen much stiffer than the main one in order to minimize the influence of the sequential element on the global system's dynamics.
The main effect is totally different in case of the force excitation. The vibrations’ amplitude is mainly limited due to the regular switching between two “natural” frequencies during each oscillation period. The first one corresponds to the frequency of the system with the sticking friction element; the second one is determined by the series connection of the main and the additional springs which are both active while the friction element slides. Thus the resonance amplitudes cannot grow up and remain limited in the whole range of excitation frequencies. The performed analysis enables the optimal parameter choice of the sequential friction-spring element. The additional spring has to be of the same order of magnitude as the main one and the additional friction is twice as much as the minimal value necessary for limiting the vibrations' amplitude. These values determined by the approximate analytic predictions are confirmed by the direct numeric simulations.