The flapping model of rotor blade can be expressed as the model of Duffing′ oscillator with periodic exciting force in the dynamic balance test of helicopter rotor. To control the chaotic vibration in flapping, a method of changing exciting signals in Duffing′ model was proposed to restrain the chaos state in Duffing′ system. To couple a triple-period exciting signal in Duffing′ model, with the analytic method of Melnikov′ function based on chaos analysis, the chaos threshold of Duffing′ function were analyzed in the states of periodic exciting signal only, triple-period exciting signal only or combined action of the two signals respectively. Simulation experiments were also conducted according to the three kinds of exciting signals. The results indicate that the chaos range is reduced more evidently by coupling the triple-period exciting signal than that by period exciting signal only.
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