FEA: Modal Analysis of a Rotating Shaft
Modal Analysis of a Rotating Shaft
Objective: To discern the natural frequencies of five modes using modal analysis.
Figure 1: Flywheel Shaft
Dimensions:
Figure 2: Dimensions of the Flywheel Shaft (mm)
Background: All objects have a characteristic natural frequency of vibration. When a loading or applications causes the object to experience vibrations in the vicinity of these natural frequencies, the object undergoes large deformations and, in many cases, total failure. Thus whenever, a mechanical or for that matter part for any application is designed, it is important to discern the natural frequencies which must be avoided in loading and in application to preserve the integrity of the component or part and avoid resonance or vibrations in the natural range. Every object has infinite modes of vibration, corresponding to the number of half waves present in the waveform and is thus classified into modal shapes. Each modal shape is made up of nodes and antinodes. Nodes correspond to zero deformation or amplitude of oscillation and antinodes correspond to maximum deformation and amplitude of resonance.
Method:
The flywheel-shaft was designed in SolidWorks as per the dimensions in figure 2. Frequency simulation was selected, and Alloy steel material was applied to the part. A bearing fixture was applied to the two stepped faces of the rod. A frequency analysis for five modes was performed using automatic FFEPlus/Direct Sparse Solver setting. The resonance plots were generated for the modes and the natural frequency data was extracted.
Figure 3: Bearing Fixture on Shaft
Data:
Mode 1
Mode 2
Mode 3
Mode 4
Mode 5
Conclusion:
Table 1: Summary of Results
|
Mode No. |
Frequency ‘f’ (Rad/sec) |
Frequency ‘f’ (Hz) |
Period (s) |
|
1 |
0 |
0 |
1e+32 |
|
2 |
527.18 |
83.903 |
0.011919 |
|
3 |
527.27 |
83.918 |
0.011916 |
|
4 |
2657.9 |
423.01 |
0.002364 |
|
5 |
2658.1 |
423.06 |
0.0023638 |
Shown in table 1, are the natural frequencies for the first five modal shapes. Loading operation resulting in frequencies within the vicinity of these frequencies must be avoided to preserve the integrity of the flywheel-shaft in its application. Any loading or operating condition resulting in vibrations of said frequencies will result in resonance and could be potentially hazardous to the structural integrity of the component.