Getting Started with Free Modal Analysis in ANSYS

In summary: Sir, you are rirht but how can we find modes in ANSYS without holding. As a rigid body we have 6-modes fequency almost null, is that right?Yes, that's right. In ANSYS, there are six modes with frequencies that are equal to zero. They are located at the six vertices of a unit sphere.Where can we see these modes (rigid modes)?You can see these modes by opening ANSYS and selecting "Models" from the menu bar, then selecting "Rigid Body" from the menu bar. The "Rigid Body" model will have six "Modes" listed in the "View" panel. Each
  • #1
shankar127
2
0
Hi all,

If we do free free modal analysis in ANSYS shall we need constrain the model or not? Where can I see the first 6 modes which have frequency equal to zero. I am confused can anybody please help?


Regards
Shankar
 
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  • #2
What does free-free mean? Means nothings holding it right?

Also, by this terminology I assume that you're trying some sort of rotordynamic analysis? If so, I have a rather long post somewhere on here about how to do it. It's not quite as easy for complex geometries as you might think (i.e. you cannot use axisymmetric elements).
 
  • #3
Sir, you are rirht but how can we find modes in ANSYS without holding. As a rigid body we have 6-modes fequency almost null, is that right?

where can we see these modes (rigid modes)?
 
  • #4
Hi,
I am not sure about the performance of free-free modal analysis in ANSYS.
If I wanted to get the natural frequencies of a box-like structure with four wheels (at each corner of the bottom surface) by means of FE-analysis, should it be performed as constrained or unconstrained ?
Indeed, the wheels are not bounded to the ground, so please, could you help me?
Thank you very much
 
  • #5
minger said:
What does free-free mean? Means nothings holding it right?
Right.
Also, by this terminology I assume that you're trying some sort of rotordynamic analysis?
"Free-free" is used to describe any type of dynamic analysis, not just rotordynamics. It is often useful to correlate a free-free vibration model with test data (for example supporting the structure on very flexible springs or bungee ropes) to get the mass and striffness properties of the model correct, independent of figuring out how to model the constraints.

There are also some mathematical techniques for using free-free models constructed entirely from measured data, to combine them with models of other components (either measured or FE) models, constrain them in different ways, etc.
 

1. What is modal analysis in ANSYS?

Modal analysis in ANSYS is a technique used to predict the natural frequencies and mode shapes of a structure. It is commonly used in engineering and scientific fields to understand the dynamic behavior of a system.

2. How do I perform modal analysis in ANSYS?

To perform modal analysis in ANSYS, you first need to create a finite element model of your structure. Then, you need to apply appropriate boundary conditions and loads. Finally, you can use the modal analysis tool in ANSYS to calculate the natural frequencies and mode shapes.

3. What are the benefits of using modal analysis in ANSYS?

Modal analysis in ANSYS allows you to understand the dynamic behavior of a structure, which is essential in designing and optimizing engineering systems. It also helps in identifying potential design flaws and predicting failure modes.

4. Can ANSYS perform modal analysis on any type of structure?

Yes, ANSYS can perform modal analysis on a wide range of structures, including simple beams and complex assemblies. However, the accuracy of the results may depend on the complexity and accuracy of the finite element model.

5. Are there any limitations to modal analysis in ANSYS?

One limitation of modal analysis in ANSYS is that it assumes linear behavior of the structure. This means that it may not accurately predict the response of a non-linear structure. Additionally, it may not consider the effects of damping, which can be significant in some systems.

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