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July 8, 2019
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Dynamic Frequency Analysis - use modes from previous design study error

  • July 8, 2019
  • 1 reply
  • 1989 views

Two issues here, hope someone can help:

 

When I Run Dynamic Frequency Analysis (DFA), 

 

  • there is an option to use Modes from previous design study. In this case, Creo uses a previously ran Modal and starts with DFA load set. Pre-req is that previously ran modal should be stress output for this option to be used. The issue I am having with this option (most times) is that during meshing, I get an meshing error due to different number of elements even though I don't change anything between running modal and FRA. Also, I have tried changing run setting to use elements from existing study but I get same error. There is an article CS117018 from 5 years ago that I can see in the knowledge base and it says its been resolved. Anyone knows a resolution to this issue ?

FRA3.jpg

  • If I don't check previous design study, I still have to select a previous modal to run the FRA. My understanding is that it for some reason needs the ConstrainSet of the selected modal analysis and then reruns modal analysis and then computes DFA. I am under the impression that as long as I don't change my constraints in the ConstrainSet, I can make changes to my design and run DFA directly and let the analysis run modal first and then DFA. But under this option Simulate does not run the DFA if the selected modal analysis wasn't ran with stress output. Does anyone know how is this options used ? Why does it need stress output if it is rerunning the modal anyways ?

 

 

Thanks in advance !

Best answer by SweetPeasHub

Issue1: Still sometimes without changing the model, during a run it can decide to re-mesh.  This is due to an issue with the data that the mesher worked around but the mesh was "off" a little.  Try running a first modal analysis, then a run a second with "use elements from existing mesh", and selecting the first modal analysis to get the mesh from.Use elements from existing meshUse elements from existing mesh

Then look at the status output for this...elements successfully copiedelements successfully copied

If that message does not appear, then you need to work on the geometry to fix the problems.  Use the same methods that are used to get a successful mesh on complex models, to correct this issue.  (start with simulation diagnostics).

Once you have this working you will no longer have it re-run the modal analysis.

 

Issue2:  To clarify this... the dynamic study must have a complete modal analysis with full stress results to move the the dynamic step.  If you do not check "use modes from previous design study"  you are telling Creo to newly run the modal analysis study selected.  The modal analysis will be newly run as defined and if it is not defined with stress output you receive this warning.WarningWarning

The newly run analysis will be stored down within the dynamic study.  So the directory structure with my example will be top level name "D" next level will have two directories "D" with dynamic data and "nmodes" with the re-run modal analysis.  When viewing dynamic results you will be able to get to both of these areas.

Now if you do check "use modes from previous design study" you must first have run the modal analysis (with stress output)  Your model cannot have changed in any way from the way it was when you ran the modal analysis.  Furthermore if the "A complete set of elements already exist" message is not obtained you will get errors. (I am being obscure because I do not have this exact information at my fingertips).

 

ultimate answer:

If you want to change your model and rerun dynamic, then you must have Creo run a new modal analysis as part of the study.  If you have several dynamics that you run on the same model, make a standard design study.  Creo is smart enough to realize that the nmodes needs to run first.  For my example the directory will be named "study1" and it will have subfolders "nmodes", "C", and "D".  (be sure to highlight the analysis to be run by the study)

Standard Design StudyStandard Design Study

 

Thus if you run "study1" and "study2" they will each have their own unique "nmodes" sub-study.  Also if you use descriptive naming instead of "study1" like "ribs_1mm_thicker" you can track the results without changing the name of the nmodes and the dynamic studies.

 

Thanks for asking the community!

1 reply

S
SweetPeasHub17-PeridotAnswer
17-Peridot
July 11, 2019

Issue1: Still sometimes without changing the model, during a run it can decide to re-mesh.  This is due to an issue with the data that the mesher worked around but the mesh was "off" a little.  Try running a first modal analysis, then a run a second with "use elements from existing mesh", and selecting the first modal analysis to get the mesh from.Use elements from existing meshUse elements from existing mesh

Then look at the status output for this...elements successfully copiedelements successfully copied

If that message does not appear, then you need to work on the geometry to fix the problems.  Use the same methods that are used to get a successful mesh on complex models, to correct this issue.  (start with simulation diagnostics).

Once you have this working you will no longer have it re-run the modal analysis.

 

Issue2:  To clarify this... the dynamic study must have a complete modal analysis with full stress results to move the the dynamic step.  If you do not check "use modes from previous design study"  you are telling Creo to newly run the modal analysis study selected.  The modal analysis will be newly run as defined and if it is not defined with stress output you receive this warning.WarningWarning

The newly run analysis will be stored down within the dynamic study.  So the directory structure with my example will be top level name "D" next level will have two directories "D" with dynamic data and "nmodes" with the re-run modal analysis.  When viewing dynamic results you will be able to get to both of these areas.

Now if you do check "use modes from previous design study" you must first have run the modal analysis (with stress output)  Your model cannot have changed in any way from the way it was when you ran the modal analysis.  Furthermore if the "A complete set of elements already exist" message is not obtained you will get errors. (I am being obscure because I do not have this exact information at my fingertips).

 

ultimate answer:

If you want to change your model and rerun dynamic, then you must have Creo run a new modal analysis as part of the study.  If you have several dynamics that you run on the same model, make a standard design study.  Creo is smart enough to realize that the nmodes needs to run first.  For my example the directory will be named "study1" and it will have subfolders "nmodes", "C", and "D".  (be sure to highlight the analysis to be run by the study)

Standard Design StudyStandard Design Study

 

Thus if you run "study1" and "study2" they will each have their own unique "nmodes" sub-study.  Also if you use descriptive naming instead of "study1" like "ribs_1mm_thicker" you can track the results without changing the name of the nmodes and the dynamic studies.

 

Thanks for asking the community!

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