How does Simulation handle mid-plane meshes between parallel plates?

[gauravsuri]

I am meshing a large cabinet and running into issues with mesh density and elements becoming too fine at corners. I am considering switching to a plate mesh instead of the solid elements I have used so far. The only concern I have is how Simulation would detect contact between two parallel plates in contact (which would be separated by the sheetmetal thickness in the midplane model.

Any suggestions will be highly appreciated.

Sincerely

-Gaurav

[John_Holtz]

Hi Gaurav,

Let me make sure I understand the arrangement. Is this correct? In real life, you have two parallel plates, and one plate sits, rests, or is glued on top of the other plate. To reduce the model size, you want to use plate elements which naturally places the elements at the midplane of the real plates. Therefore, the plate elements are separated by a distance equal to 0.5*Plate A's thickness + 0.5*Plate B's thickness.

The next questions are:

(1) What type of analysis are you performing?

(2) How are the two plates connected in real life? Are they unconnected (other than touching each other)? Are they glued/welded/bonded together?

[gauravsuri]

John

Thanks for the quick response.

Yes you are correct in your description of the situation.

For now, I am running a linear static stress analysis, but as I develop the method, I might use it for seismic response too.

The two are bolted together at discrete locations, but for the purpose of this analysis, I am willing to consider them as bonded together, if that simplifies the solution process.

-Gaurav

[John_Holtz]

It would be a lot easier to assume that the bolts are strong enough and tightened enough to cause the two plates to behave as one. That is, there is no sliding. In that situation, update the CAD model to replace the two items with one.

[klnkai]

I had a similar problem and at first I wanted to use a mixed-dimensional analysis using solids for the two connected parts but there you run into further problems Autodesk Wiki.

Therefore I substituted the plates by elastic boundary conditions. If your lower plate is directly connected to the support of your system you could also think about that.

[gauravsuri]

John- I have been able to generate a midplane model in CAD, took some surfaces out and made them common. One question though - will Simulation be able to generate contact between two surfaces that are touching each other in the model?

Is it okay to have a mixture of solid & plate elements in the same model?

Thanks

-Gaurav

[gauravsuri]

John

Is there any other way to handle this? Combining surfaces in CAD is not simple in my situation either. Can I specify the two surfaces to be in bonded contact? Is there a setting I would need to change for it to detect contact over the gap?

Thanks

-Gaurav

[John_Holtz]

Hi Gaurav,

MES is the only analysis type that supports contact between objects that are not drawn in contact. You mentioned seismic response previously. I do not know how you were planning on simulating that, so you should determine that before deciding to go with MES. If you do use MES, I suggest setting the Element Definition > General > Analysis Type to Small Displacement.

The only other option that I can think of is to use beam elements to connect the two separate plates together. If the beam elements are stiff, they make a rigid connection between the two plates, and the displacements are related to the stiffness of the plate elements. But with an automatic mesh, the nodes on one plate will not be "directly above" the nodes on the other plate. Hence the connecting beam elements would not be perpendicular to the plates. I do not know what affect this would have on the results, so a simple simulation is suggested.

Are there any other ideas out there?

Going back to your original posting, you said the number of elements in the corners was getting too large (long runtime I presume), and that is why you were changing to plates. Is there some feature in the model that is causing the smaller elements at that location? Are there changes that can be made to the model or to the mesh settings to help minimize the number of elements at the corners?