Mesh trouble - inconsistent mesh across symmetrical geometry

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rmknox posted this 4 weeks ago

Hello everyone,

I'm having trouble refining the mesh for my model in ANSYS 18.0.

The model is bilaterally symmetric, but the mesh is behaving differently on the left and right sides. Two faces on the left side of my model won't remesh with the settings I've tried; however, the issue is that the corresponding faces on the right side (which are identical) have meshed easily with the same settings. I've included some screenshots below highlighting the issue.

The first image shows the faces in question and highlights their identical nature. The second image shows the result of attempting to re-mesh my model. As you can (hopefully) see, the faces are exactly the same, but for whatever reason, the faces on the left side don't like the mesh settings. I am able to individually refine the problematic faces at any relevance level but cannot refine the model as a whole.

Has anyone run across this problem before? I am happy to provide any additional information.

Thank you!

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peteroznewman posted this 4 weeks ago

Hello rmknox,

1. If the model is symmetric, why don't you cut it in half and only mesh the right side?

2. What do you care if the mesh is symmetric, as long as it is valid. You are going to perform a Mesh Refinement Study anyway, right?

3. There are times when you absolutely must have matching meshes, such as when using periodic symmetry, and for those special times, there is a mesh control to assure the meshes match perfectly. This does not seem to be one of those times.

Regards,

Peter

rmknox posted this 3 weeks ago

Thank you for your reply!

- I could absolutely cut the model in half for this simulation. However, down the line I'll be running additional simulations on the same model that involve asymmetric loading. Since the model itself won't have a symmetric response in those cases, I can't just use half of it and apply the same results to the other half. I'm more interested in understanding what's causing the mesh to fail so I can solve the issue in the future, rather than getting this specific simulation to solve.

- You're absolutely right, I don't care if the mesh is symmetric. The issue is that it simply doesn't exist on several faces. Like I said above, I'm more interested in fixing the underlying problem so I can actually refine the original mesh.

- I'm fairly new to ANSYS and am still learning a lot of the terminology. Is a Mesh Refinement Study different from the Refinement I can add from the Mesh Control menu in the Mechanical window?

To provide some more detail, I'm trying to perform a Contact Sizing refinement at the contact regions on the top and bottom of my model. You can't see them in the images I posted, but there are platons contacting the top and bottom of my model. There is some fairly fine geometry in these regions, so I am trying to specifically refine these areas.

Please let me know if you have any ideas! I'm happy to provide more information as necessary.

peteroznewman posted this 3 weeks ago

Here is a discussion on Mesh Refinement.

I didn't see that the issue was a failed mesh on one side. It was not that it didn't match the the right side, but that there was no mesh at all. If you reduce the maximum element size under Mesh Details, then do you get a successful mesh?

How was the geometry brought into the model for meshing?  Import a neutral file, through DesignModeler or through SpaceClaim?  

Check the geometry in DesignModeler with Tools --> Analysis Tools --> Fault Detection. Geometry should not have any errors before going to meshing.

Regards,

Peter

rmknox posted this 3 weeks ago

Hi Peter,

You are correct, the mesh is not present on the two faces in question. You can see the gap in the second picture I posted above. Like I previously mentioned, I don't care if the mesh itself is symmetric, I'm trying to figure out why, in my symmetric model, one side successfully meshes while the other does not.

I imported the geometry through SpaceClaim as a .step file using the Insert > File command. I've been trying to use Fault Detection but am not quite sure if I'm using it correctly. Once I select the body in question under "Entity Set" and press Apply, do I have to do anything else, or will errors show up automatically? No errors show up in the Details View, so I guess either nothing is wrong or I'm missing a step.

To clarify the issue further, the model successfully meshes when I first open the Mechanical window. I am able to refine the two problematic faces specifically, but am unable to refine the mesh for the body as a whole. However, I am trying to perform a local Contact Sizing refinement at the contact areas at the top and bottom of the body, since these areas have particularly fine geometries that have given me problems in the past.

Please let me know if I can provide more information. Thank you for your help thus far.

peteroznewman posted this 3 weeks ago

Do a File, Save As so you can check the geometry in DesignModeler with Tools --> Analysis Tools --> Fault Detection without breaking the model you built in SpaceClaim.

rmknox posted this 2 weeks ago

Hi Peter,

I was able to solve this issue by using the Repair Faces command in the DesignModeler window. As it turns out, there weren't any errors in geometry, but there were several tiny faces (on the order of ~10^-11 m^2) that wouldn't mesh, simply as a result of their size. I merged these faces with two larger coplanar faces and the meshing errors went away (as an aside, I'm not sure why the tiny faces existed in the first place, as they were literally overlapping the larger ones). Once I was able to successfully mesh the model, the rest of the simulation went off without a hitch.

Thank you very much for your time and help.

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