| Rotor dynamics is a subset of vibration analysis that deals with the dynamic characteristics of spinning machines. The problem is characterized by generally nonsymmetric system matrices whose elements depend upon the rotor speed.; An approach to complex analysis of rotating systems is described which results in improved physical understanding of solutions to the eigenvalue problem and stresses commonality with conventional modal analysis. In the approach, a natural mode of the rotor is represented as the sum of two sub-modes which are rotating to the forward (i.e., with rotor rotation) and backward (i.e., against rotor rotation) directions. This definition of the natural mode allows complex analysis of free and forced vibration of anisotropic systems, which had not been reported previously. The complex mode representation enables clear definition of the forward mode and the backward mode, and more importantly enables one to complete the complex rotor analysis procedure.; Concepts are illustrated with a general rigid rotor model and a reduced form which is a two degree of freedom anisotropic model including gyroscopic effects. In order to verify the approach, a pendulum-mounted multi-axis force sensor was used as an impact device to excite the spinning rotor. This enabled measurement of the normal impact as well as the tangential force component induced by friction. Complex modal analysis was then applied to clearly distinguish forward and backward modes and separate them in the frequency domain. |
