Preprocessing

Preprocessing

Inlet and Outlet Geometry on CT Data

    • aCVP
      Subscriber

      Hi all. 


      I created an .STL file by segmenting a CT dataset in 3D Slicer. I imported it into SpaceClaim and used shrinkwrap. Using tetrahedron meshing, I was successfully able to generate a mesh. 


      However, when trying to select the inlet and outlet, it just selects the whole body. How do I define an inlet and outlet once I have used shrink wrap? For some reason it won't let me and when I try to separate it in SpaceClaim, I am not successful.


      Thanks in advance. 


      (I can provide the .STL file if needed)

    • Sandeep Medikonda
      Ansys Employee

      aginn,


      Please post some snapshots to explain your problem?


      It sounds like you are missing features. 


      You can always create features using the skin-surface tool right or is that what you are coming from?


      Check out the following tutorials on how to reverse engineer:


      Resource 1


      Resource 2


      ~Sandeep

    • peteroznewman
      Subscriber

      aginn,


      If you Attach the SpaceClaim .scdoc file, I will take a look. Please reply with a sketch of where you want the inlet and outlet and say which version of ANSYS you are using.


      Regards,


      Peter

    • aCVP
      Subscriber

      Hi - I've attached a link to the .sdoc file as well as the original .stl file. Please let me know if you have any trouble accessing it. I am currently using ANSYS 19 (Student Edition). 


      A picture defining the inlet/outlets is also included.


      Thank you so much!


      https://drive.google.com/drive/folders/1ZQipiu5kEBuaBJtO4qM1ADMmZ6swQ9eQ?usp=sharing


      Inlet_Outlet Definition

    • aCVP
      Subscriber

      Hi - I've attached a few screenshots. I was actually using the "shrink wrap" function rather than the "skin-surface tool" - perhaps this is my problem? Thank you for including additional resources; I plan to look into the skin-surface tool.


      Thanks again!




    • Sandeep Medikonda
      Ansys Employee

      aginn, 


        You just have a bunch of facets (small triangles enclosing the body) when you have both an STL or a Shrinkwrap. From what I understand you need a Solid or Surface body with some thickness?


        Right click on the STL/ShrinkWrap and convert it to a Solid body or use the 'Fill' tool, you might also find this thread useful. Once you have a solid body, using the 'Shell' tool in the Design tab make it hollow as needed. Create Named Selections in Mechanical for the Inlets and Outlets in mechanical to apply your boundary conditions.


        Check out these videos to see if they help: 




       


      Regards,


      Sandeep

    • peteroznewman
      Subscriber

      aginn, 


      Note that 19.0 can't open files created by 19.1. I have both available so I needed to know exactly which one and it looks like you have 19.0


      Sandeep has provided lots of great resources, but the key is that you want a solid model, maybe hollowed out, and not the STL facets that you have shown. I am learning how to handle STL files so I am going to try to make that solid model, but don't wait for me if you learn what you need to from Sandeep's resources.


      Regards,


      Peter

    • aCVP
      Subscriber
      I have version 19.0. Yes, I prefer to have a hollow model. I am going to attempt - let me know if you have any luck on your end.

      Thanks.
    • peteroznewman
      Subscriber

      This looks like a heart, since it has an aorta. What is your simulation goal. What wall thickess would you use to hollow out. If it is a CT image, the wall thickness would be visible in the image and a surface of the interior wall could have been made.



      There is a warning message about increasing the size of the model by orders of magnitude. I'm still waiting for that to finish.


      The problem you will face is that the resulting solid will have many more than the 300 faces that the Student license limit allows. I am fortunate to have two computers, one with a full license and another with the Student license.


      You need to bring the STL file into another CAD system, not SpaceClaim, and convert it to a solid using shrinkwrap-like methods in that CAD system to replace hundreds of facets with a single b-rep curved surface, and a collection of those surfaces, but < 150, will define the outside surface. When you hollow out the interior, the number of surfaces will double.  Each surface counts as a face.


      Regards,


      Peter


       

    • aCVP
      Subscriber

      Do you have a free software that you recommend for creating a surface? Definitely having issues coming in under the 300 faces that the student license allows.


      I'm planning to segment another geometry that might be less complicated, so it might help. Regardless, any free software that can do something similar would be fantastic.


      Thanks.

    • aCVP
      Subscriber

      Thank you for your reply! I was able to gain access to the full version of ANSYS through our IT department on the university server, so the face limit is no longer a problem.


      For anyone with the student version subject to the limitation:


      -Rhino Resurf can automatically generate a surface from a mesh


      -ANSYS Reverse Engineering "Skin Surface" tool works but is VERY time-consuming to complete

    • Diabq
      Subscriber
      I have a similar problem with an stl scanned file of blood vessel I have hundreds of thousands of facets. I tried to merge them but I could only merge small patches of them many patches give an error when I try to merge them. nSkin surface results in a small but unacceptable deviation and I need the exact geometry is there any other way I can use?n
    • Keyur Kanade
      Ansys Employee
      Hello, nYou can do this very quickly in Fluent Meshing. nSelect face filter at the bottom. nSelect any traingular face.nIt will highlight more options at the bottom. nClick on separate option. nHere it will separate your face zone. nArray you can also use this option. nYou can also search on forum for more resource. n you can also use this option. nYou can also search on forum for more resource. nRegards,nKeyurnGuidelines for Posting on Ansys Learning ForumnHow to access ANSYS help linksnn
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