This paper investigates the nonsynchronous motion of a rigid rotor in squeeze film damped systems without spring support subjected to both unbalance and unidirectional loading. Both harmonic balance and 4th order Runge–Kutta integration are used to obtain the unbalance response, the asymptotic stability of the harmonic balance equilibrium solutions being determined by Floquet theory. Depending on the system parameters stable subharmonic orbits with fundamental frequencies of half, one third and one quarter of excitation frequency were obtained. Also, bistable, tristable and quadristable solution possibilities were found. The effect of these subharmonic orbits on maximum transmissibilities is included.

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