Rotor Vibration Reduction

This example inspects a vibrating rotor and shows how to reduce vibrations with additional external damping.

The Jeffcott rotor introduced in the Internal Damping example is used, but the shaft in this example is put in motion by a motor. The motor accelerates from 0 rpm to 244 rpm in 250 seconds. 

The extDamping in Figure 1 must be disabled before simulating the model to see how the system behaves without additional damping.

Figure 1: Jeffcott rotor with additional external damping

Upon plotting the disk deflection against the rotational speed, it is observed in Figure 2 that the machinery becomes unstable due to the resonance.

Figure 2: Disc frequency response without additional damping.

It is obvious that the machinery should not be run at 10 rad/s or higher speeds. Fortunately, the problem can be solved through the addition of external damping. 

If the extDamping component is enabled and the simulation is run again, a noticable decrease of disc deflection is observed; see Figure 3.

Figure 3: Disc frequency response.

The effect of doubling the damping is illustrated in Figure 4.

Figure 4: Frequency response comparison of external damping.

The resonance frequency can be shifted slightly by changing the internal damping value (phase lag). Increasing the external damping can solve the problem if the deflection magnitude is the problem. Note that higher damping means higher energy dissipation. 

More information on damping of a system can be seen in this blog.