Harmonic analysis without stress results


#1

Hi everybody,

Lately I have been struggling with harmonic analysis for the first time. Some of you already know my project since I have ben facing some problems and hesitations. I still have a problem with the case itself, it is something I already stated in one of the threads I opened with no answer so far. As I think it is an important problem that need to be solved, or at least explained, I finally decided to open a new thread. The fact is that after I run the analysis I don’t get the stress field as a result, only displacements, although I tried to get both Cauchy and von Misses stress.

Is there a reason why I can’t get the stress field as a result? Am I doing anything wrong or is it a bug?

Thanks in advance

Alex


#2

Hi Alex!

Can you please share the corresponding project you have issues with? You have 4/5 projects that might fall into this category and several sub-simulations within the projects which makes it hard to test each one. Once that is clear I will have a closer look at this.

Best,

Jousef


#3

Hi Jousef!

You are right, I have been doing several test…:stuck_out_tongue:
Here you are! The last of the projects I have been working in. All the simulations are supposed to give both displacements and stress fields as a result, but only displacements are given.

Thanks for the support!

Alex


#4

Hi Alex and sorry for the delay.

I just saw and remember that you used the Harmonic analysis…that’s as far as I know included inside this module but you could use the displacements as an input for a static analysis if you like. A CSV upload is also possible. @ggiraldo, please add your ideas here as well if you like.

Cheers,

Jousef


#5

Hi @alex_roque, looks like a bug on our side.
I will investigate tomorrow and will let you know as soon as we have found a fix.
Best,
Richard


#6

Hi Jousef!

I know the benefits of CSV upload, actually that’s what I use in the definition of my loads. However, it seems not to be availabe in the case of displacements, look at the picture, it’s the definition of my zy constraint for the base of my geometry.

I am allowed to constrain or unconstrain the displacements in any direction but, in case of a prescribed value, this MUST be 0, no chance to give another value nor even a button for CSV uploading. Actually, that’s why I defined the load in the way shown in the previous link I provided.

Anyway, it would be a very interesting point to have the change to define the amplitude directly in a harmonic analysis.

Cheers,

Alex


#7

Hi @rszoeke,

It would be very nice to get it solved since I have wasted a lot of simulation time trying, I have been analysing the displacements in order to get an idea of what to do in order to enhance the behaviour of my structure, but I didn’t even know if it was necessary to improve it since I didn’t have any access to the stress generated by the vibrations. Would it be possible to get some of this time back?

Thanks for the help.

Cheers,

Alex


#8

Hi @alex_roque,
the problem was identified. Until it is fixed, all the tests have passed and we can release to the production system you can work around the issue by explicitly also adding the Cauchy Stress (real+imaginary representation) to your solution fields and it should work: cauchy_stress

Here is a view of your model with the von Mises stress (at 5Hz):

I will let you know once the fix has been released.

Best,
Richard


#9

So can I restart my simulations with the possibility to obtain the Cauchy stress (Re+Im) as a result now? Why only Cauchy and not von Misses?

By the way, I don’t know much about the interpretation of a stress field of complex nature because this is my first harmonic analysis. Could you give me some link or documentation where I can find information about the interpretation of complex stresses?

Thanks for everything

Alex


#10

No, you can also have the Von Mises stress (real/imag) results, but they require to also explicitly add the Cauchy Stress (until the bug is fixed).

The complex nature of the results is only relevant if you have damping in your model (or you have load inputs with a phase shift). If you don’t have this, the imaginary part of your results is always zero or talking in terms of module/phase representation, the response of the system is in phase with the loads (0° or 180° phase angle).

I currently do not have any material at hand that explains the complex nature of harmonic response analysis very well (other than a simple google search). Maybe @jousefm has some?

Best,
Richard


#11

Thanks for tagging me Richard,

good SimWiki material - let’s see if I can put something together to share it with @alex_roque.

Best,

Jousef