Frequency Analysis of a rotating shaft
Frequency analysis on a rotating shaft using Solidworks
Aim: To perform frequency analysis on the rotating shaft.
Objective:
- Create a rotating shaft.
- Perform frequency analysis on it.
- To find out 5 mode shapes and list of resultant frequency.
- Explain the results.
Theory:
Natural frequency, is the frequency at which a system tends to oscillate in the absence of any driving or damping force. The motion pattern of a system oscillating at its natural frequency is called the normal mode (if all parts of the system move sinusoidally with that same frequency). If the oscillating system is driven by an external force at the frequency at which the amplitude of its motion is greatest (close to a natural frequency of the system), this frequency is called resonant frequency.
Free vibrations of an elastic body are called natural vibrations and occur at a frequency called the natural frequency. Natural vibrations are different from forced vibrations which happen at the frequency of an applied force (forced frequency). If the forced frequency is equal to the natural frequency, the vibrations' amplitude increases manyfold. This phenomenon is known as resonance.
In this project, frequency analysis is done on a rotating shaft subjected to the centrifugal force. To perform the analysis, first of all a rotating shaft is created by using solidworks. Geometry and model of the shaft is shown below
Sketch
Model
After creating the model, a frequency study is created by clicking on new study option in simulation. Next, material is specified as alloys steel for the whole model. In fixtures, both the sides of rotating shaft is subjected to bearing support.
A centrifugal load of 52 rad/sec which is approx. 500 rpm is applied on the disk.
After all these mesh refinement is set to fine and ran the simulation.
Results:
|
Mode No. |
Frequency(Rad/sec) |
Frequency(Hertz) |
Period(Seconds) |
|
1 |
51.955 |
8.2689 |
0.12094 |
|
2 |
1106.4 |
176.09 |
0.0056789 |
|
3 |
1106.4 |
176.09 |
0.0056788 |
|
4 |
5251.8 |
835.85 |
0.0011964 |
|
5 |
5251.9 |
835.87 |
0.0011964 |
Directions in which the model tends to vibrate at natural frequencies are shown below
Mode 1
Amplitude
In this mode, contraction and expansion of model takes place.
Mode 2
Amplitude
Model vibrates along x axis
Mode 3
Amplitude
Model vibrates along y axis
Mode 4
Amplitude
It is seen that, model vibrates along y axis having a node at the center.
Mode 5
Amplitude
Model vibrates along x axis having a node at the center of the rotating shaft.
Conclusion:
By doing the frequency analysis, all the possible ways in which the model can vibrate are studied. Also, the behavior of model at various frequencies is observed.
Reference: