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How to group elements from UNV mesh?

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  • How to group elements from UNV mesh?

    Posted by Pei-Ying Hsieh at August 20. 2007
    Dear Salome Experts:

    I imported a mesh in UNV format into Salome.  This mesh contains only nodes and elements - NO geometry associated with the mesh.

    To use this mesh for OpenFOAM calculation, I need to create groups for boundary conditions.  Unfortunately, some of the elements lie on curved surfaces (not simple geometries), is there any way to group the elements for each boundary conditions?  Is it possible to use mouse to select face elements and then, put them into groups?

    Thanks!

    phsieh
    • Re: How to group elements from UNV mesh?

      Posted by Grigory Zhivotovsky at August 20. 2007


      Hi,

      You can easily create groups for a mesh after import UNV file into Salome. 

      1. Mesh- Create group 

      2. Select "Face" radio-button

      3. Input group name "Boundary_1"

      4. Select relevant face elements in the viewer

      5. Click "Add" and then "Apply" buttons

      The other way is to create surfaces (plane, cylinder, etc) coinciding with your boundary an to use filter "Belong to plane",  "Belong to cylinder",  etc for selection of elements into group.

      Best Regards,
      Grigory

      • Re: How to group elements from UNV mesh?

        Posted by Pei-Ying Hsieh at August 20. 2007

        Dear Grigory:

        Thanks for the reply!

        I am still confuse.  When I clicked "create group", a "create group" windows comes up.  I then select the mesh, select Face, enter Name. Under group type, I selected "Standalone group".  I think that the difficulty I am having is "Conten".  If I select "set filter", then, I do not know what which one to chose for Criterion.  The mesh does not have geometry associated with it, then, I cannot select "Belong to Geom" nor "Belong to Plane" ...etc.

        Is it possible to use the mouse to click the face elements to select and then, put into the groups?

        phsieh

        • Re: How to group elements from UNV mesh?

          Posted by Pei-Ying Hsieh at August 21. 2007
          Hi, Grigory,

          I just did a simple test.  Could you advise what I did wrong?

          1. I created a simple box in SolidWorks.
          2. mesh the box using COSMOS. 
          3. Exported the mesh to UNV format.
          4. Exported the CAD geometry in step format.
          5. In Salome 3.2.2, imported the UNV mesh.
          6. In Salome, imported the step format CAD geometry.
          7. Exploded the geomtry to get 6 faces.
          8. Went to MESH module, tried to create groups (tried standalone group)
          9. No matter what I did in the "filter", I am not able to select the face elements associated with the faces.  In this case, the geometry and the mesh should match perfectly, BUT, not associated with each other.

          What are the steps/methods to get the mesh and geometry associated?

          phsieh2005
          • Re: How to group elements from UNV mesh?

            Posted by Grigory Zhivotovsky at August 21. 2007

            Hi,

            Please not that,

            1. Even if you create groups in Salome you will have to renumber all elements to satisfy OpenFOAM requirements to mesh. Otherwise you will have OpenFOAM errors.

            2. I don't understand your problem with creation of Standalone group using selection of mesh elements -faces with mouse in the viewer. Your scenario is right . Selected elements are colored by yellow (if you use default options). You click Add button - selected elements IDs appear in the dialog box and you click Apply or OK button. Group appears in the object browser. It is not very easy if you have large mesh, it has to be made by scratch if you remesh your model, but it must work.

            3. To use filters "Belong to Geom" or "Belong to Plane" ...etc you have to create corresponding geom , plane etc. It can be done in Salome directly. I know that you have no geom only mesh. You have to create corresponding geom entities coinciding with your boundaries with some tolerance. Some filters require that these geom must be meshed by Salome and geom and mesh must be associated. But filters that I name to you in previous message have no such requirement.

            To summarize
            1. import the UNV mesh.

            2. Create group by mouse picking in the viwer.

            3. Or create geometry in salome.

            4. create groups using filters "Belong to Plane", "Belong to cylinder"

            5. Renumber elements according to Openfoam (you can write python script)


            Best Regards,

            Grigory

            • Re: How to group elements from UNV mesh?

              Posted by Pei-Ying Hsieh at August 21. 2007

              Hi, Grigory,

              When I clicked on an face element to select, it did not turn into yellow or any color change.  In the create group window, when I clicked Add, nothing was added into the Id Elements window.  -- So, nothing was selected in my case. 

              Same problem with the "Set Filter" approach using Belong to Plane - nothing was added.

              Is the standalone group function supported in version 3.2.2?  I simply do not know how to select indivisual face element?

              phsieh

              • Re: How to group elements from UNV mesh?

                Posted by Pei-Ying Hsieh at August 22. 2007
                Hi, Grigory,

                Last night, I installed Salome 3.2.6 on a Ubuntu system.

                I created a simple box in Salome, then, mesh it.  in MESH module, I am able to select elements using a mouse, and then, add the elements into groups (standalone group) - no problem.  However, I am NOT able to do the same thing if I import an UNV mesh (no geometry) into Salome.  Is this a bug?

                Later today, I will try to create geometry in Salome, mesh it, export to UNV.  Read the UNV mesh back into Salome, and see if I can create standalone groups.

                phsieh
                • Re: How to group elements from UNV mesh?

                  Posted by Grigory Zhivotovsky at August 22. 2007


                  Hi,

                  I have a few unv files containing only mesh without geometry. After import an UNV mesh into Salome I can create groups and perform mesh editing (remove elements, change orientation etc) as for mesh computed inside Salome (excluding some filters  with associated geometry).

                  May be a problem is in format of your unv file. Try to get mesh advanced info to check what elements are in mesh, to select element in other dialog boxes not only in group creation, or send me your unv file if it is not to big.


                  Best Regards,

                  Grigory

                  • Re: How to group elements from UNV mesh?

                    Posted by Joël Cugnoni at August 22. 2007
                    If the imported mesh does not contain 2D "face" elements, you will not be able to select or create groups for "faces".. Salome will not automatically generate faces from an imported mesh containing only 3D elements.
                    So check if the mesh contains face elements first.

                    If not, the simplest option would be tu use OpenFOAM patchTool to create the patches or to use Salome directly for the mesh generation.

                    • Re: How to group elements from UNV mesh?

                      Posted by Pei-Ying Hsieh at August 22. 2007

                      Hi,

                      You are correct!  The original mesh does not have face elements defined - only nodes and volume elements.  Is there a quick way to get all external face elements into one group?  Then, it can be splitted into smaller group for specifying BCs?

                      phsieh

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