Frequency Analysis of a rotating shaft

Aim: Find out the critical frequencies of a rotating shaft in Solidworks. create the model in Solidworks.

Introduction :

First of all , create the required model in solidworks using required dimensions:

Explain the basic theory on the simulation:

Simulation modeling solves real-world problems safely and efficiently. It provides an important method of analysis which is easily verified, communicated, and understood.

The ability to analyze the model as it runs sets simulation modeling apart from other methods, such as those using Excel or linear programming.

Lets talk about some fundamentals theory,

Frequency Analysis

Every structure has the tendency to vibrate at certain frequencies, called natural or resonant frequencies. Each natural frequency is associated with a certain shape, called mode shape, that the model tends to assume when vibrating at that frequency.

When a structure is properly excited by a dynamic load with a frequency that coincides with one of its natural frequencies, the structure undergoes large displacements and stresses. This phenomenon is known as resonance. For undamped systems, resonance theoretically causes infinite motion. Damping, however, puts a limit on the response of the structures due to resonant loads.

If your design is subjected to dynamic environments, static studies cannot be used to evaluate the response. Frequency studies can help you avoid resonance and design vibration isolation systems. They also form the basis for evaluating the response of linear dynamic systems where the response of a system to a dynamic environment is assumed to be equal to the summation of the contributions of the modes considered in the analysis.

A real model has an infinite number of natural frequencies. However, a finite element model has a finite number of natural frequencies that is equal to the number of degrees of freedom considered in the model. Only the first few modes are needed for most purposes.

The natural frequencies and corresponding mode shapes depend on the geometry, material properties, and support conditions. The computation of natural frequencies and mode shapes is known as modal, frequency, and normal mode analysis.

Entire case setup :

To perform frequency analysis:

• Create a frequency study. Right-click the top icon in the Simulation study tree and select Properties. Choose default properties.
• Define material for parts.
• Define appropriate restraints.in our case as shaft is rotating we have to apply bearing support at each end.
• Define loads if desired. We didn’t apply it.
• Mesh the model and run the study.
• View the results.

Let's Go through it,

Create a frequency study :

keep all properties defaults,

Define material for parts:

I have applied alloy steel material

apply a bearing fixture on the stepped face of the rod at the two ends:

Mesh the model and run the study:

View the results:

Mode 1 :

Mode 2:

Mode 3:

Mode 4:

Mode 5:

List the resonant frequencies:

Observation and Conclusion :

It is clearly seen that, as the mode number changes the frequency of the system changes.

so,this means that the system will have different mode shapes for different frequency. And we should prevent our componant to vibrate at this frequency while working to prevent from resonance.

So,Frequency studies can help you avoid resonance and design vibration isolation systems.