Learning Forum

[Johanna_L]

Hi!

We have a .stl-file with a fairly large and organically shaped structure (topology optimization result from NX) and we are using ANSYS 2019 R2 Workbench for FEA (Static Structural analysis). This structure needs to be verified with some forces and pressures (simulating underwater use). We're not quite sure what requirements are in Mechanical for these kinds of geometry, and we have only limited experience working in Mechanical and SpaceClaim. The problem we've encountered in how to define the areas these will be applied to. The first thing we did was to clean up the .stl and make a shrinkwrap in SpaceClaim.

The shape is complex and if we just try to mesh it and select nodes to apply nodal forces/pressure, the number of nodes makes it very hard to select them properly. The selection tools seem to select the nodes "behind" the closest surface as well it they are facing the same direction. We can not find any way to deselect multiple nodes at once and the manual work of deselecting individual nodes would be way too much. The areas for the forces are small enough that this works, but the pressure areas are of varying sizes and "organic" (e.g. can't find any common xyz-coordinates).

Our next attempt was to use SpaceClaim to try to define faces of some sort. We found the Auto Skin tool for the R3-version online which we think would have been very useful, but we don't have access to that (is it possible to get it free in some student package?). Creating individual patches of surfaces would take a lot of time (there are many smaller, complex surfaces). Since the model is so organic it would also be very time consuming to try to reverse engineer it. If we try to convert it to a solid it becomes very slow, has many tiny faces (from the facets) and doesn't load into Mechanical.

Any suggestions on how we could proceed would be greatly appreciated. What is the best practice of dealing with complex facet bodies in Mechanical?

Thank you in advance.

/ Johanna and Eliza

[Gary_S]

Hi Johanna and Eliza
The STL format seems to be intended for visualization, and often will not easily convert to an editable or meshable 3D solid.
There are 3rd party programs that are specifically geared towards this sort of reverse engineering, a popular one is "cadfix".
Once the STL is processed, the Ansys tools have a better chance of success.
Gary

[peteroznewman]

Hello Johanna and Eliza I have spent some time learning how to use SpaceClaim to clean up STL files to make them useful for meshing in Mechanical.
https://www.youtube.com/watch?v=Y8uFzkQxmaA
https://www.youtube.com/watch?v=ZF8-kwYyavM
You can download the free ANSYS Student License to access the latest version and SpaceClaim with those tools are included. You can open STL files with that version, but as you convert them to geometry, you cannot end up with more than 300 faces, or you will not be able to save your work! I have a full license for ANSYS 2020 R1 so can work with an unlimited number of faces. I would be interested to see your STL file if you are willing to share it. Archive it in a .rar file and you can attach it to your reply.
If you would like to discuss this further, I will be checking this site over the weekend.

[peteroznewman]

Don't install the latest version of the free ANSYS Student license. They stripped out all the Save As functionality. See this post:
/forum/discussion/26117/export-geometry-to-step
I recommend you click on the Prior Releases link under the ANSYS Student license and choose ANSYS 2020 R1 to get the ability to save files in a format that will enable you to open the geometry in ANSYS 2019 R2.