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Removing a Pole from a Structured Domain

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You may need to remove poles from time to time since not all structured solvers support them. What is the best way to do that? Let us look at an example.

We have a structured domain with a pole (a singularity) at its center. The circular connector and the pole connector have 41 grid points each. The branch connector has 11 points. The easiest way to get rid of the pole is to start by splitting the domain.

  1. Select the remaining domain.
  2. Edit, Split
  3. In the Split Direction frame, select J.
  4. In Split Location frame, check the Advanced frame and enter 1 7 for IJK.

  5. OK
  6. Select the inner domain.
  7. Edit, Delete Special (or hold Ctrl key down when you press Delete).

  8. The domain with a singularity has been removed. We will now mesh this empty space.

  9. Select the domain.
  10. Edit, Split
  11. In the Split Direction frame, select I.
  12. In the Split Location frame, create cuts one by one at IJK = 31, 21 and 11.

  13. Note that when you are picking out split locations for your own domain, you should try to split your domain into 4 equal parts.

  14. OK.
  15. Select the four inner connectors and create a structured domain by clicking on Assemble Domains in the toolbar.

  16. The grid on the interior no longer has a pole, however the four elements in the corner have really high included angles and the quality of the grid is not that great.

    To improve the quality of the domain, we are going to use the grid solver to float the connectors shared between the five domains. This will allow us to reduce the included angles in those problematic corner cells as well as achieve a more desirable inner domain shape. However, before we do that, we need to ensure that there is a smooth transition across the inner circular connector.

  17. Select the highlighted spacing constraints and set them equal to 0.1.

  18. Select all the domains.
  19. Grid, Solve
  20. In the Edge Attributes tab, set Boundary Conditions Type to Floating.
  21. Go to the Solve tab.
  22. Enter 10 for Iterations.
  23. Run
  24. OK

This is referred to as an O-H grid or a butterfly topology.

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