The generalized dynamic equations of motion have been obtained by the direct stiffness method for multimass flexible rotor-bearing systems including the effects of unbalance, shaft bow, disk skew, rotor acceler¬ation, gyroscopic moments, and nonlinear bearing forces. The direct solution of the equations of motion is illustrated on a simple 3-mass system. However, for complex rotor-bearing systems, the direct solution of the equations becomes very difficult due to the large number of equations necessary to describe the dynamics of the system. The trans-formation of the equations of motion into modal coordinates can greatly simplify the computation for the solution. The uses of undamped and damped system mode shapes in the transformation are discussed.
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