Learning Forum

[dwayne.provo]

When I run a modal analysis I'm looking for two pieces of information.

I want to see the modal frequencies and also the min and max deformation values.

I'm able to see the frequencies, but the results do not show the min/max values.

Instead it only shows the location with a blue and red circle. I need to see the actual value expressed in mm.

 

[Brian Bueno]

dwayne.provo

If you're using a fixed support, the minimum deformation in the body will always be 0.

The legend displays a range from the minimum to the maximum value.  That is the fastest way to see what the min/max deformation is.

You can also create a calculator to display the maximum deformation in the body.

[dwayne.provo]

Thanks Brian for the feedback. I removed the fix constraint from the bottom of this detail and re-ran the analysis. I still don't see the deformation values. I don't see how the values in the legend could represent deformation. This detail is approx. 600mm wide x 300mm tall. Are you saying this mode is showing a deformation of 293mm? Those values must represent something else.

Additionally,  I really need the bottom of this detail to be fixed as it will be bolted down. So with the bottom fixed, the same mode looks like this:

This is what I would expect to see; excitation at the top. Notice the legend now shows 794mm. Again, it's not possible to have that much deformation. There should only be approx. 0.8mm at this frequency(I ran this in another software.) It seems to me there should be value at the blue and red circles.

[Brian Bueno]

dwayne.provo 

Something strange is going on with the Modal analysis results in my release as well, even for simple models.  I need to look into that with the development team. 

There needs to be at least one support on the model, so there was nothing wrong with that.  A modal analysis with no supports is basically free to move around in any direction, so your results will be totally wrong.  My comment was just to point out that if you're looking for the minimum deformation over the entire model it's always going to report a minimum value of 0 at the location of the fixed support.

It would be best to create a calculator on a specific location of interest to see the deformation behavior there.

I'm going to contact the development team to find out if there's something we need to be doing differently.  I'll be out of the office until next Thursday, so one of my colleagues will provide an update.

[Naresh Patre]

Hello dwayne.provo

Modal analysis computes the frequency shape of modes and displays a magnitude of displacement that has no meaning for the displacement of a real structure because there is no load applied to the structure in a Modal analysis. Though the deformation values are not real, its the shape of the structure (mode shape) that is important in Modal Analysis. You may want to run a structural analysis with some loading to analyze the resulting deformation under that loading.