A simple method of reduction is presented for finite element model of non-axisymmetric rotors on non-isotropic spring support in a rotating frame. The frame is rotating about the undeformed centreline of the bearings with a speed equal to the shaft spin speed. In this frame the stiffness matrix, mass matrix and Coriolis matrix for the non-axisymmetric rotor (rotor with rectangular cross-section, cracked rotor, etc.) is independent of time but the support forces become periodic function of time. Therefore, in a rotating frame, it becomes necessary to deal with a large set of linear ordinary differential equations with periodic coefficients at support degrees of freedom, which requires substantial computational effort. To effectively handle this large system it needs to be reduced keeping the essential information almost intact.
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