In a modal analysis with multiple load steps corresponding to different angular velocities, you can generate a Campbell diagram showing the evolution of the natural frequencies. ANSYS also prints out the critical speeds for a rotating synchronous (unbalanced) or asynchronous force. As eigenfrequencies split with increasing spin velocity, ANSYS identifies forward (FW) and backward (BW) whirls, and unstable frequencies.

Dynamics of rotating structures analyzed using 3-D/1-D model representation in ANSYS.

Middle Step Residual Criterion for Structural Transient Analyses

In a transient analysis, the accuracy of the solution depends on the size of the time step. Usually, a smaller time step will yield a more accurate solution, but the total analysis time increases as the time step decreases. You can now request the computation of the middle step residual as a measurement of the accuracy of the solution within a time step.