Frequency Analysis of a rotating shaft

FREQUENCY ANALYSIS OF ROTATING SHAFT

AIM – To conduct a frequency analysis while applying bearing fixture on the stepped face of the rod at the two ends.

OBJECTIVES-

1. Create design of rotating shaft.
2. Run frequency analysis while applying bearing fixture on the stepped face of the rod at the two ends.
3. Show all mode shapes and resonant frequencies.

INTRODUCTION-

All stable, unforced, mechanical systems vibrate harmonically at certain discrete frequencies, known as natural frequencies of the system. The special initial displacements of a system that cause it to vibrate harmonically are called `mode shapes’ for the system.

If a system has several natural frequencies, there is a corresponding mode of vibration for each natural frequency.

The natural frequencies and mode shapes are arguably the single most important property of any mechanical system. This is because, as we shall see, the natural frequencies coincide (almost) with the system’s resonant frequencies. That is to say, if you apply a time varying force to the system, and choose the frequency of the force to be equal to one of the natural frequencies, you will observe very large amplitude vibrations.

When designing a mechanical system, you want to make sure that the natural frequencies of vibration are much larger than any excitation frequency that the system is likely to see.

PROCEDURE-

Draw sketch of rotating shaft according to following sketch.

1. Right click on Part> Apply/Edit material. Select Alloy steel.
2. Applying bearing fixture on the stepped face of the rod at the two ends.
3. Click on mesh and set parameter to 18 mm to generate fine mesh.
4. Click on run.
5. Right click on results. Select list of resonant frequencies.

RESULTS –

List of resonant frequencies-

Mode No.	Frequency(Rad/sec)	Frequency(Hertz)	Period(Seconds)
1	0.12557	0.019985	50.038
2	140.41	22.347	0.044748
3	140.43	22.35	0.044744
4	583.55	92.875	0.010767
5	583.67	92.894	0.010765

Mode 1:

Mode 2:

Mode 3:

Mode 4:

Mode 5:

CONCLUSIONS & EXPLANATIONS-

1. The displacement shown by solidworks frequency analysis is highly exaggerated but it does help to analyze the wave in better way.
2. Frequency range in operating conditions should not be near these natural frequencies. Else, the machine might undergo phenomenon of resonance increasing the amplitude and might cause damage to it.