Analyze Slowing-down Clamped Rotor

The vibrations of a running down motor with clearance are studied. When the rotor is running down from a high vibration (decreasing angular velocity), the behavior will be different compared to when it runs up. The reason for the lower vibration is that when contact occurs, the rotational speed is already lower than the "stiffer" resonance. In this case, all resonances are avoided. See the example RunningUpRotorClearance for a "running up" model.

Figure 1 shows all scenarios in the same plot:

Figure 1: Comparison of disk deflections.

There are main differences between the running up (green curve) and running down (red curve) that need to be noted, even though the system is identical. The responses of the system vary significantly depending on whether it is running up or down. Therefore, the designer must make a wise choice regarding how much clearance to maintain between the housing and the rotor, based on the machinery's running speed.