“…Recent studies [2] have shown that the NNM approach is effective in the case of weak energy exchange, while the concept of the limiting phase trajectories (LPT) can be used to describe intense energy exchange between weakly coupled oscillators or oscillatory chains, or targeted energy transfer from a source of energy to an oscillator. Recently, the LPT concept has been applied to study resonance energy transfer from a source of harmonic excitation to the Duffing oscillator, and the precise solution of the LPT problem have been obtained [3,4]. However, the precise solution expressed in terms of elliptic functions is * Corresponding author.…”