Solid Meshing of thin parts

[Anonymous]

Hello 

I have a pretty complex W Panel with stiffeners spaced at 24" on center. The panel is 4' x 9' (approx). I have tried all possible techniques of meshing the model. I need to put bolts in it, so I have to do a solid mesh (thin parts). The thickness of both the panel and stiffener is 0.125 inches. I have tried all possible techniques of meshing and nothing worked. We created 2 models in inventor, 1. With 16 parts and the other with just 4. parts. I am sending you a archive of both the models as well as the STEP and DWG files of both.

Please take a look at the meshing errors and let me know if there is any way I can resolve the errors. 

[John_Holtz]

Hi @Anonymous

1. What problem are you having?
2. I tried to mesh your model with the 16 parts and received an "ecrt_MeshEngineDriver_ResultsInitialization" error. Is that what you are getting?

A more important question is how are these parts supposed to be connected together? There are locations where the face of one part lies on another (locations 1, 2, 3 in the image below), and locations where the edge of the plate makes contact with the face of another plate (locations 4, 5, 6). How the parts need to be connected at these areas may dictate how you create the model.

• Can these edges and faces be free contact? And only the bolts hold it together?
• Is there contact (either bonded or surface contact) at one or both of those types of contact?

[Anonymous]

Face 1, 2 and 3 are in surface contact, while the other three (4,5 and 6) are just in free contact. The entire model was modeled in Inventor. Do you have any suggestions as to the best way of modelling such scenarios?

1. When i used the dwg file to mesh, only one of the stiffener (There are total of 5) got meshed. The stiffener is part 2 if you import the dwg file. I had no idea why that happened.

2.  When i meshed the file with 16 parts, It initially meshed, but some parts had "Cad mesh Options" in the tree, highlighted in red. If I tried to part mesh those parts alone, I would get the same error as the one that you got. 

3. One instance, The whole model got meshed, but when I checked the model, I got the "node number <1" error in one of the parts. I frequently get the "node number < 1" error whenever I use the thin solid mesh. It usually goes, after I refine the mesh a little and follow the following guidelines

https://knowledge.autodesk.com/support/simulation-mechanical/troubleshooting/caas/sfdcarticles/sfdca...

[Anonymous]

I tried meshing the model today, but this time, the model was created as separate parts in an Inventor assembly. The parts are held together by constraints (bolts). I just defined surface contact as the default. As you can see, the meshing looks fine, but the "Cad Mesh Options" is highlighted in red. But I am not able to figure out what the issue is. I have attached the plan and section of the model, so that you can get a better understanding of whats going on here. 

I have always been defining contacts between parts so far, Is that a wrong approach? Should the contact be defined with respect to the surface and not part? 

Thank you so much for the help.

Rahul Kannan

Structural Engineer in Training

SMA Engineering

[marwan_azzam]

Hello rkannan,

The best way to mesh thin parts is generate Plate or Shell elements.  This means performing a plate/shell or midplane mesh.  Your model is not suitable for a midplane mesh so a plate/shell is the way to go.  This means you will be meshing surfaces, not solids, and using plate or shell element type.

There are two ways to achieve that:

1- Convert your CAD model from a solid to a surface model.  This is to say parts will not have a thickness, they will be just surfaces.

2- Use a solid model but only mesh certain surfaces on each part with a plate/shell mesh.  I've done that to your simple model as shown in this image:

This, of course, means that you have to hand pick the surfaces you want to mesh (or exclude from meshing) and move some parts so that the surfaces selected for meshing coincide hence achieving mesh matching.  See image below:

As the model gains more parts and/or geometrical complexity, method 2 becomes nonviable for obvious reasons.

As such, method 1 (converting solid CAD model to a surface CAD model) is the recommended way.

Regards,

Marwan Azzam

[Anonymous]

Hello,

When you said "Convert Solid CAD model to Surface model", what did you actually mean? Is there a method of surface modeling in inventor? Or you meant to just plate/shell mesh the model?

If it is just plate or shell meshing, then it would not have any thickness. Will my analysis then be an accurate representation of real-time scenario? Also, if I plate mesh the model, will I be able to add bolts? 

Thanks

Rahul Kannan

[marwan_azzam · Accepted solution]

Hello rkannan,

By "Convert Solid CAD model to Surface model" I did mean doing it in Inventor.  There is a way to create surface models in Inventor.  I don't know how but I'm sure the folks in the Inventor forum would be happy to assist.

When using a plate or shell model you specify the thickness in element definition.  Please see this section of the documentation.

Also, if I plate mesh the model, will I be able to add bolts? 

You can but you will have to separate that parts and create contact elements between them in addition to the bolts.  This may or may not be feasible depending on the geometry of the parts.  This will definitely require time and some expertise with using the software.

In the end, depending on the complexity of the model and the amount of time and effort you are willing to put into the project It could just be easier to use brick elements.  Midside nodes will produce more accurate results at the expense of analysis time.

Regards,

Marwan Azzam