Challenge

Frequency Analysis of a rotating shaft

FREQUENCY ANALYSIS OF ROTATING SHAFT

OBJECTIVE:

INTRODUCTION:

Frequency analysis is performed to find out the natural frequency and corresponding mode shapes of the component.
The natural frequency is the frequency with which component will vibrate if disturbed and allowed to vibrate on its own without any external force acting on it.
Mode shapes of the component give the direction in which component is vibrating at that corresponding natural frequency.
Damping effects are neglected in frequency analysis when finding the 'Natural frequency' of the component.
Components will have an infinite number of natural frequencies but the lowest natural frequency is known as the fundamental frequency.
Natural frequency is determined to avoid the resonance of the component.
Resonance occurs when the external frequency is equal to the natural frequency, in this state resonance amplitude causes the failure of the component.

MODELING:

The 3D model of the shaft is part modeled in Solidworks, according to the proportionate dimensions so as to fit the looks of the shaft in the problem definition.
The first sketch is created and the sketch is rotated about an axis to create a shaft.
All dimensions are in 'mm' only.

FREQUENCY ANALYSIS:

Frequency analysis is selected for simulation.
Alloy steel is the material applied to the shaft.
Bearing fixture is applied on the stepped surface of the shaft on both sides, it indicates that fixtures support the shaft to rotate about its own axis.
Default Mesh is applied, and simulation is solved for the results.

RESULTS:

In simulation results,5 natural frequency corresponding 5 mode shapes are obtained.

1st & 2nd mode

Both modes have the almost same natural frequency of 255 Hertz but the only difference is mode 1 oscillates in 'z' direction and mode 2 oscillates in 'y' direction.
It can be seen when you animate the results.

3rd mode

This mode is mechanism mode, this component has one rotational degree of freedom about its axis, hence the 3rd mode of natural frequency analysis is shown as a rigid mode.
Hence, this first mode has a natural frequency of 401.71 hertz.

4th and 5th mode

Both modes have the same natural frequency of almost 935 hertz but the only difference is mode 4 oscillates about 'y' axis and mode 5 oscillates about 'z' axis.
It can be seen when you animate the results.

Frequency table for different modes:

Conclusion:

In conclusion, mode shapes and natural frequency values give the direction in which external excitation frequency should be applied and the allowable excitation frequency can be applied.
But, generally, external excitation frequency cannot be controlled, So we need to alter the natural frequency of the component itself by varying its mass and stiffness.

Ship work like this
in your own course.