FEA issues on Large assembly from a mix of frame generator parts, plates and rods in Inventor Natran environment

[benboubaker]

Hi,

i have a large assembly made of square tubing and angles from frame generator, extruded plates and rods, i try to work in the Nastran environment but i have lots of issues , some parts are turned off, the correct meshing is difficult to obtain due to small  parts and features according to large parts, corner radiuses on the tubes and angles from the frame generators are also a problem, some of the parts are used as additional weight for modal and vibration analyses i try to change from realistic models to concentrated mass

partially simplified assembly

in Nastran environment some of the parts are turned off even if the tree show them visible

i use Nastran for smaller assemblies with simplified models and i have no issues, i used before simulation mechanical that convert large models and get a good automatic mesh ratio,

is there a better way maybe to go from more realistic models to simplified assembly models and get good meshing?

i tested the Stress Analysis from inventor and i have got a direct meshing and result, i have also a modal done and got a decent results.

Thanks

[autodesk428JLG]

Hello!

What do u want to obtain from your analysis, sir?

[benboubaker]

Natural frequencies, i will have to apply some random vibrations, Response Spectrum , all inputs related to vibration analyses, obtain Max displacement and  von Mises stress, mode shapes etc.

[John_Holtz]

Hi @benboubaker 

About the part visibility, what happens if you "hide" the part from the Nastran Model Tree and then display it again? Is the part then visible in the graphics window?

About the meshing, can you elaborate on what problem you are facing? It would be helpful to see some images or provide the model.

Also, what version of Inventor Nastran are you using? (In the Nastran environment, click the "i" button in the "Nastran Support > About" ribbon.)

John

[benboubaker]

Hi John,

1- my department is currently using inventor 2022, Natran 2022, Vault 2022,

2- when i turn again the visibility in the Nastran InCAD environment, and save, then the tree shows the part as visible but the graphic window does not show them visible, i have to work back and forth in the tree to see them and select the parts for idealizations 

3- i have a lots of issues getting a good meshing ratio especially due to the discrepancy between the large parts and the small parts, at the Tube and angle radiuses from frame generator structural members, i am showing also an external mass of the structure that can be replaced by a a simplied FEA model for the modal and vibration analyses

i attached a STEP file of the model, 

Thank you

[John_Holtz]

Hi @benboubaker 

Thanks for the STEP file, but it does not help too much because:

1 - It does not include the frame generator details, only the solids that are a result of the frame generator parts.

2 - It does not indicate which parts are hidden/displayed, and as far as I can tell, all parts are visible in the graphics windows. (Most likely the parts that are not visible in the graphics is because of some issue with reading the frame generator parts, and that information is not transferred to the STEP file.)

3 - It does not indicate what mesh size you are using, whether you have added mesh controls or used the Mesh > Table to specify a different mesh size on different parts, and so on. In other words, show us the mesh that you do not like (and clarify why you do not like it if it is not obvious).

The better way to send an Inventor model with the Nastran setup is to create a pack-and-go file following the video by Roelof Feijen.

This is the mesh that was created with a mesh size of 1 inch and the "Mesh > Mesh Settings > Settings > Refinement Ratio" set to 0.1. It puts a smaller mesh on the curved pieces that sounds like a step in the right direction for what you want. 

John

[benboubaker]

Thank you John,

i will try that refinement mesh setting first, and see how it worked

[benboubaker]

Hi John,

please find attached a pack and go zipped version of the inventor model, it includes the parts created with the frame generator , Inventor 2022, in mean time i will try your recommendation to refine the mesh ratio

Best regards,

[John_Holtz]

Hi @benboubaker 

Thanks for the files. Here are a few strange things that I see happening in this model.

• The behavior on my computer is different than yours.
  • On my computer, the part visibility is in synch between the graphics window and model tree. Parts that are not shown in the graphics window are indicates as not visible in the Model Tree.
  • On your computer, the part visibility is not in synch between the graphics window and model tree. Parts that are not shown in the graphics window are shown as being visible in the Model Tree. (I have marked up one of your original images to show the obvious parts that are out-of-synch. I didn't check all the parts listed the in the image.)
• My experience has been that Nastran does not remember what parts are hidden. Every time I enter Nastran, all the parts are visible (and I need to re-hide the ones I want to be invisible). Your model does not follow that behavior! Some of the parts are hidden every time I enter the Nastran environment, and I need to find them in the model tree and make them visible.

If either of us find out something, we should update this thread. 🙂

John