# Dynamic Simulation of a 5 Degrees of Freedom Rotor Dropping on a Protective Bearing
## 3 Characteristic Analysis of Dynamic Simulation Model of 5-Dof Rotor-Protective Bearing System
### Simulation Analysis of Rotor Speed Fluctuation during Rotor Dropping  
To study the rotor speed fluctuation and the change in the inner ring speed of the protective bearing, an ADAMS simulation is carried out on the rotor-protective bearing system by changing the contact friction coefficient between the rotor and the protective bearing and the initial speed of the rotor. When the rotating speed is 6000 r/min, the results are as follows. It can be seen from Figure 4 that the rotating speed of the rotor decreases in fluctuation under the action of the protective bearing, and it can be seen from Figure 5 that the rotating speed of the inner ring of the left and right protective bearings at this time is opposite to that of the rotor and increases in fluctuation. It can be found from the figure that the rotating speeds of the left and right protective bearings are not the same, which may be caused by the conical phenomenon when the rotor falls on the right and left protective bearings. But also related is that fact that the mass center of the rotor is not positioned at the midpoint of the left protective bearing and the right protective bearing, and so the system is not symmetrically distributed; by taking the mass center of the rotor as a center, the stress conditions of the left protective bearing and the right protective bearing are not symmetrical. Therefore, the rotor contact force on the left protective bearing is greater than that on the right protective bearing during the dropping process. According to Coulomb's law, with the increase in the normal contact force, the tangential friction force also increases, so the increase in speed of the left protective bearing is greater than that of the right protective bearing. Figure 3: Load change in protection bearing inner ring. It can be seen from the results that, compared with the previous results, there is not much difference between the rotor speed and the speed at the end of the simulation, but it can be found that the decline speed increases, while the speed of the inner ring of the protective bearing changes significantly. With the increase in the friction coefficient of the rolling elements in the protective bearing, because all the rolling elements act on the inner ring of the rolling bearing together, the friction force on the inner ring is very large. The inner ring keeps static most of the time, and the inner ring of the protective bearing will rotate only when the rotor falls on the protective bearing. At the same time, the rotating speeds of the left and right protective bearings are relatively consistent at the beginning, which indicates that the rotor does cylindrical motion in the inner ring of the protective bearing at the beginning, and the rotating speeds of the left and right inner rings are inconsistent at the later stage. It could be coning. Therefore, it can be found that the friction state of the inner rolling body of the protective bearing has a great influence on the motion state of the rotor in the falling process. In practical work, the damage to the system after the rotor falls can be improved by adding paint and other engineering methods to the inner rolling body of the protective bearing. To study the influence of the initial speed of the rotor on the falling process of the rotor-protective bearing system, the initial speed of the rotor is set from 6000 r/min to 8000 r/min and ADAMS simulation is carried out. The simulation time is 0.1 s, and the results are shown in Figures 10 and 11. Figure 10: Simulation of rotor speed fluctuation when the initial rotor speed is 8000 RPM. Figure 9: Simulation of bearing inner ring speed fluctuation with friction coefficient of 0.5.