Ansys modal analysis: extract nodal displacements over a period

[nsalva3]

Hi,

I am new to this forum and was wondering if you could help me out.

I am running a modal analysis of a cyclic symmetric structure (only one sector is meshed and the analysis is ran using CYCLIC option of /PREP7). Once the analysis is done, you can recompose double harmonics or nodal diameters into a single rotating mode and animate it (ANCYC in /POST1).

Up until this, all works fine. What I cannot manage to do is, for a given mode, to extract the nodal displacements of a chosen node (NSOL) over a period. In the end, what I would like to have, is the displacements of this node as a function of time for a given mode.

Do you know if there is any way of doing this through /POST26 ?

Thanks in advance,

Nicolas

 

[Drej]

If I understand you correctly you are carrying out a modal analysis on a cyclic symmetric basis. Nodal displacements from a modal anaysis do not represent 'actual' displacements, these are only relative. The modal analysis simply gives you the dynamic properties of the structure (ie mode shapes and natural frequencies). To obtain displacements over time based on your input loading you will need to carry out some form of transient dynamic analysis, but I'm inclined to believe it is unlikely you will be able to extact the information you need (disp vs time for a given mode).


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[nsalva3]

Thank you for the response Drej.

You are correct in the sens that modal displacements are only relative. Which is why their actual value is not of interest but their variation during the period studied. There is not a particular forcing involved, it would be just a way to better characterize each modeshape over its corresponding period other than just have the animations obtained with ANCYC and PLNSOL.

Do you think there is a way to extract this information ?

Nicolas

 

[0rel]

Can't a harmonic analysis do that ?

 

[nsalva3]

@Orel,

I believe that a harmonic analysis is somewhat of a forced response. You apply a cyclic load to the structure, sweep through a given excitation frequency range and obtain the displacements as a function of time for each load step. It's a nice way to obtain a frequency response curve.

In my case, I only want the displacements of a node, for a given modeshape during a period of animation (without any external forcing). It is only a way to better characterize the modeshape itself and not intended to describe how the structure would respond to a periodic excitation.

Nicolas