Contact Mesh Matching Issues

[Anonymous]

I have been having issues with mesh matching between parts for an analysis. (this is using 2012)

My Current Process is...

1.) export a step file from inventor

2.) import in autodesk simulation (automatically generate surface contact pairs is on)

3.) Define mesh for 63 part assembly (approx, 20 plate/shell parts, 20 brick and wedge parts, 23 brick & tet parts)

4.) mesh and solve

In order to get the solver to work I have Vcad turned off, and automatically refine surface mesh off. (I have tried turning on the auto surface redine and it does not change the results)

This results in a few places that have unmatched meshes between parts, as shown in the attached image (this is a plate/shell element part onto a brick & wedge element part) . These parts have a surface contact, that is set to the default bonded, so it should be matching. I have tried adding refinement point around this area, but that does not seem to help the matching. (the unmatched warning does come up in the mesh log).

There are multiple areas that have this issue, included plate/shell element parts to other plate/shell element parts.

A strange anomoly is that the surfaces will mesh correctly if I change the brick & wedge element part to a brick & tet part.

Any advice would be appreciated.

Thank you

-Dave

[Anonymous]

static or mes?

[Anonymous]

Static

[Anonymous]

i m not sure how surface contact works in static analysis......with a combination of plates and brick parts ...in a 60 part assembly...

[John_Holtz]

Hi Dave,

The "Brick and wedges (layered mesh of thin parts)" is not programmed to maintain mesh matching between parts.

The first thing to try is to have the overlap of the solid and plate parts to have surfaces of the same dimension. So you will split the plate along the edge of the brick part, and split the "top" and "bottom" face of the brick and wedge part along the edge of the plate part. (see attached image.) You will need to do this in the CAD model. With any luck, the meshes will match.

If the mesh still does not match, then you can try copying the surface from the brick and change the copy to the plate part. That is,

1. Delete the overlapping surface of plate (S2 in image)
2. Select the overlapping surface on the brick (S12 in the image)
3. Duplicate it to the same part number as the plate ("Draw > Pattern > Duplicate")
4. Adjust the nodes on the original plate surface (S1 in image) if needed to match up with the copied section. (Either "Draw > Modify > Point Move" or "Draw > Modify > Global Snap", but you need to be sure that no other parts of the model will acidentally get snapped when the "Set Search Tolerance" is large enough to get the nodes you want.)

[Anonymous]

John, Thank you, I can get it to match fine if I change the Brick & Wedge back to Brick & Tetrahedral(which I can work with by adding some refinement point). However, I still am having an issue elsewhere in this assembly between plate/shell element parts. If you take a look at the attached images you can the mesh not matching between parts in contact("NOSE ISO" shows the overview of the assembly, with a plate/shell element surface section highlighted yellow, "UNMATCHED SURFACE MESH ZOOM" shows the unmatced surfaces). I have the warning message"WARNING: 14 unmatched surfaces" when the mesh completes. Here is what I have done to try to address this: -Add refinement points -Refine the entire surface mesh None of these worked, so then I tried isolating the parts that were giving me trouble("ISOLATED COMPONENTS" shows this). Initially, the meshes had the same issue, but I figured out that by turning VCAD on and turning on Virtual Imprinting in 3D Mesh Settings>Options>Model, the parts would mesh exactly how I want them too ("SECTION OF GOOD MESH" shows a well matched mesh between 2 contact surfaces highlighted in yellow). This works fine, until I start to bring back the other components. If I bring back only 5 brick element parts (shown in "ISOLATED COMPONENTS + 5 ADDITIONAL PARTS") then the same issue comes back seen in "ISOLATED COMPONENTS + 5 ADDITIONAL PARTS UNMATCHED". So, I guess what I really need is a way to force surface contacts to match mesh?

[Anonymous]

Here are the additional Pics.

[John_Holtz]

Sorry Dave, you mentioned this before but I forgot to address it.

The messages "14 unmatched edges" has no significance in your situation. The message is really intended for solid parts where each edge of a surface must matchup with one and only one edge of another surface; otherwise, the surfaces do not form a valid solid.

For plate surfaces, it is expected that there are unmatched edges. Since the edge of the plate does not need to match up with another plate, these warnings are of no consequence.

It's hard to tell what surfaces are in the foreground and which are in the background, but it looks like your model does have a matched mesh between the selected surface (unmatched surface mesh.jpg) and the blue surface to its right and the blue-green surface below it.

[Anonymous]

John,

     That is good to know that UNMATCHED warning is only refering to the edges. However, I still am trying to get these parts to have matching meshes to get the load path correct. I am confident they are in contact due to the fact a surface contact was created when I imported the file, and that they are both model from the same surface in Inventor. There are some areas where it does mesh correctly accross the parts, but many more places where is does not match as specified above. I also attached a cross section of a typical problem area, note that both parts are surfaces to be meshed as Plate/Shell elements.

Thank you,

-Dave