Frequency Analysis of a rotating shaft

Aim: To perform a frequency analysis on a rotating shaft and obtain 5 modes of shape and their frequency respectively.

Software Used: Simulation and modeling of the shaft have been done in Solidworks.

Theory: Before obtaining the different modes of shapes and performing a frequency analysis. Let us understand the frequency first.

Natural frequency: When a body oscillates under the absence of any continuous or repeated load. This frequency of oscillation is natural frequency.

Now when a body is subjected to any external load conditions it will start vibrating at various frequency and when this frequency matches with the natural frequency that the condition is called resonance and that frequency is called resonating frequency. Generally, the condition of resonance is not preferred as it may tend to the failure of the component. Hence we perform the frequency analysis to determine the critical conditions avoid those situations.

Now we will observe that we will be getting the different shapes of the body at different frequencies. Why it is so?

The reason is the mode shape i.e. It represents the pattern of the vibration w.r.t time at a particular frequency. As the frequency changes the mode shape will be different but it also depends on the system.

1. Dependent on the material of the body

2. Dependent on mechanical properties of the body

3. The type of load is applied.

4. Boundary conditions applied.

Sketching and Modeling: This is the sketch of the shaft, the dimensions are in mm and after making this sketch to convert this 2d object into 3d we'll rotate this sketch around the center axis using the Revolve feature and here is the shaft ready for the analysis.

Sketch

Model

Material Used: Material used for the shaft is Alloy steel.

Mesh: Mesh was set to fine quality which helps us to get more accurate results.

Boundary Conditions: We've applied the bearing fixture to the stepped part as shown in fig. via blue arrow.

Now all the conditions have been defined and after running the study we will get the plots like this:

Result:-

Mode 1

Mode 2

Mode 3

Mode 4

Mode 5

A combined plot can be seen below in which help us to observe somethings which are discussed below in observation and conclusion.

List of the resonant frequencies:-

Observation & Conclusion: As we observe the result plots which was performed on a rotating shaft we got the different frequencies shown above.

This helps us to know that we need to avoid the body to be in the situation which causes the vibration of the frequency of this range (as shown in the above table) to occur. The main reason is explained above that at the resonating frequency the body can lead to failure or severe damage that may occur which can be hindered the system.