Learning Forum

[ansysuser]

Hello,

 

I was following the discussion here: LINK where there were some instructions to generate a 3D surface from a points file.  I managed to import the points, but now I do not know how to generate a surface based on the points.

Below are a couple of views of what I have.  There are several circles that make up surface.  How do I make the next step happen to have the surface drawn over the points?

 

Thanks

 

 

[peteroznewman]

Hello,

Are the points in the text file arranged so that you know which point is on which slice?  That should be easy to see because it looks like each slice has a constant X coordinate.

Are the points in the text file arranged so that they are sequentially chained in order around the loop on each slice?

That would be ideal, because then you can edit the text file to draw a closed curve for each loop upon import instead of just points.

If the points are not like that in the file, then you have to manually create a closed curve by picking each point individually, which would be tedious.

Once you have all the loops, there is a solid/surface body creation method in SpaceClaim called Blend where you pick the loops in sequence and it skins a surface over them.  In DesignModeler, that feature is called Skin/Loft.

If you attach the text file, I will see what it looks like.

 

[ansysuser]

Hello peteroznewman,

Thanks for the response.  The trouble with doing it manually is that I have shown a very coarse example.  The actual model is made of of slices as you point out, but thousands of them.  I did manage to find away to export the surface data to an stl file, so it seems I am closer.  But now I have surfaces which DM is calling bodies, but I need DM to recognize them as the boundaries for Fluent, not as bodies.  In other words, I want DM to generate a body based on these surfaces being the boundaries to use with Fluent.

How can I do that?  Would SpaceClaim be able to do it?

I tried to attach my simple workbench which only has one Fluent case and only the geometry as shown in the image, but this extension is not allowed and neither are my STL files?  How can I get something to you that you can use to help??

Thanks.

 

[peteroznewman]

The site allows .zip file attachments as long as the file size is < 120 MB.

SpaceClaim can convert an STL file to a body. There are tools to smooth the STL facets and skin them with a set of surfaces.

[ansysuser]

O.k.,

I have uploaded the STL files and created a video of myself getting them ready to use.  You can see the process I go through.  The video ends where I am merging faces but the problem is that it only lets me do that until there are 3 faces left on the larger boundary.  On the circular boundary I can merge all the faces just fine, so that one is not a problem.  I need all faces merged on the larger boundary, and it will only let me go down to 3. 

 

In DesignModeler the process is smoother, in that the importing of the STL files creates two surfaces without all the triangles (see earlier images) but I am unable to make it fill the volume in between the two bounding surfaces.

 

Here is a link to the video, so you can see what I mean.

 https://www.youtube.com/watch?v=UjNbJ1tvhD8&feature=youtu.be

VIDEO

[peteroznewman]

I'm not sure what you mean when you say you want to use this geometry for a boundary in FLUENT.  The video might have some useful information for you.

 

https://youtu.be/_sIMaid9tQ4

[ansysuser]

Hello peteroznewman,

 

Thank you for taking the time to make that response.  I appreciate it.

However, what I mean is this:  There are 2 STL files.  Each one is supposed to be a single surface and the volume inside of them is where the fluid flows around.  The circular surface is an outlet.  So in your video, when you first open in mesher you can see that there are hundreds of individual triangular surfaces that form the boundary to the interior fluid body.  I need there to be only two bounding surfaces, one corresponding to each STL file.  That is the reason why at the end of my video you see me merging the faces.  As I explained, I need there two be exactly and only 2 bounding surfaces, one corresponding to each surface that is initially triangulated in the STL files.  That is the entire reason why I am merging the facets on each of the 2 triangulated surfaces from the STL files.

So, each STL file contains a single triangulated surface, but when imported into SC, each triangle is treated as if it were an individual surface so instead of 2 surfaces that bound the interior region, I get hundreds unless I Merge Faces for each individual STL surface.  Thus you see me merging the faces at the end of my video.  The problem is that SC will only allow the facets of the larger of the STL surfaces to be merged down to 3 faces, so that I end up with a total of 4 bounding surfaces: 3 from the larger STL file and 1 from the circular STL file.   I need 2, not 4.

Hopefully that is clearer about my needs.

Thanks!

 

[peteroznewman]

I think I understand. You want the flat circular region to be an INLET, and the other surface to be a WALL and the volume inside to be a FLUID_VOL.

In the Mesh module, it is very easy to create Named Selections.  If I create a Named Selection of the flat circular region and called it INLET, it wouldn't matter if that was one face or one hundred faces. Fluent would use the Named Selection and assign an inlet boundary condition to all the faces in the Named Selection, no matter how many faces there were.  The same goes for the WALL.  If I can show you how to create those named selections, I think that will solve your problem. Do you agree?

[ansysuser]

Hello,

Yes, you understand what I need to do.  Thanks so much!

I also agree that we can group the facets into a unit by named selection, but the problem with keeping the individual facets as individual walls is that the movement of the walls on the large body will be determined by UDF during Fluent simulation, and so that would mean writing a UDF for each of those hundreds of facets instead of just one combined, untriangulated boundary wall.  Is there no way to do this?  It seems so basic!

Perhaps not through STL files, but by another means?  I have all the data that creates the surfaces in MATLAB stored as points, and that is what I used to write the STL surfaces.  If another format would get this done, just tell me what format would work and if I can write that with MATLAB I will do so!  I can write UDFs for a subset if that makes it easier, say 10 or so subsurfaces that are regular.  I have attached a file that has the larger surface broken into 10 pieces, but something is still not working.  I thought it would be easier to "Merge Faces" for these smaller ones but apparently not.  If I have the larger surface broken into 10 like in that file, then it should be ok because 10 UDFs of regularly shaped surfaces acting as one should be fine.

 

Thanks

 

Thanks again

[ansysuser]

Here is what happens when I import just 2 of the 10 in order to see if I can make individual surfaces out of each of these triangulated surfaces.  Before and After.  As you can see, SC lets me get the first surface reduced to 5 facets by "Merge Facets" but then when I try to merge them all into one, it for some unknown reason turns the result into a strange shape that has nothing to do with my geometry.  What happened? 

 

My plan and hope was that I could merge them all into one for each of the 10 pieces and then write UDFs for the 10 so that the movement will make them act as one surface.

 

 

 

[ansysuser]

Here I managed to do it for the first piece by importing the second STL file before the final merge of facets, but the second piece will just NOT let me merge it all the way whether I import the third STL file first or not.  Please help me get this working. I am able to get the second part of the surface into 2 pieces but not 1.  I could accomplish what I need to do if I could get all 10 STL files into individual surfaces for a total of 10 surfaces that can act together as one wall with 10 UDFs, but I am stuck on the second STL surface.

Is there some systematic reason it won't let me join the final 2 facets of the second STL file together?

https://youtu.be/l9UQCNy4Jn8

[ansysuser]

Here is an attempt to get the second STL file merged into one surface as I try to do this for each of the 10 STL files that make up this surface.  I thought perhaps if I got it as symmetric as possible SC could merge the final two.  Nope.  SC still says "Unable to merge" these final two facets even though they are as simple as I can make them!
There has got to be a way to do this!!

 

 

 

 

[peteroznewman]

Have you noticed some CAD systems break a cylindrical face of a hole into two halves?  That is because some formulations of surface geometry equations can't go much past 180 degrees of wrap without losing precision. 

Here is a simple way to get 4 faces for the walls and two faces for the inlet.

https://youtu.be/ZF8-kwYyavM

[ansysuser]

Thank you! I will look into this and see if I can make it work for my situation. If so I will come back and mark your response that's the solution.

[ansysuser]

Hello peteroznewman,

This solution will seem to work.  Two final questions.

1.  I have not found how to define a plane in SC.  For example, I have a point and a normal and I want to define the plane by those.  How do I do that?

2.  Is there a way to cut only the surfaces bounding the body, or merge the bodies but keep the surfaces separate at the end of your video?  I really need one body inside and several surfaces bounding the body. Your solution generates several bodies.

[peteroznewman]

1. Create a plane on the global triad then use the Move tool to move it by a specific distance on any axis or rotate it about any axis. 

2. At the end of the last video, there were four solid bodies.  Select the six external faces, Ctrl-C to copy and Ctrl-V to paste to create six surfaces. Delete the four solids. On the Repair tab, Stitch tool, pick the six surfaces and it will create one solid body with six faces.