Learning Forum

[Samuele Luigetti]

Hello, can anyone say why the peak on the frequency response of harmonic analysis does not match the natural frequencies of the structure found in the modal analysis? I don not know if it's not right, maybe is correct like this

thanks

[Erik Kostson]

Hi

 

Can you post some more info (post images).

Assume aslo you use FULL method and nor mode super position since that uses the actual modes from modal analysis.

All the best

Erik

[Samuele Luigetti]

I can't post images, simply the frequency at the peak of response is not one of the natural frequency of the structure, also if is similar. Anyway no, i'm using MSUP analysis, do you think that it's for this, since that is less accurate than full method? 

[Erik Kostson]

 

Hi

I would recommend using MSUP since that uses the actual modes found in the upstream modal analysis (include enough modes so to make sure mode participation factor is above 90% – see the below course for details) .

Below is our course in harmonic analysis (including msup and full method):

https://www.youtube.com/playlist?list=PLtt6-ZgUFmMJVMZViguORYLBdO0L9ikG4

https://courses.ansys.com/index.php/courses/harmonic-response-analysis-in-ansys-mechanical/

All the best

Erik

 

[Samuele Luigetti]

Already seen, anyway thank you for the support

[peteroznewman]

Samuele,

What is the frequency of the peak and what are the modal frequencies above and below that?

Here is an article that does a good job explaining experimental modal analysis. Figure 20 give you a hint on how Harmonic Response (FRF) of the structure could have peaks that are shifted from the modal frequencies.

https://www.uml.edu/docs/s-v-jan2001_modal_analysis_tcm18-189939.pdf

I just realized I gave you this paper before in your other discussion.